Luminescent lanthanide(III) complexes of DTPA-bis(amido-phenyl-terpyridine) for bioimaging and phototherapeutic applications

Article abstract of DOI:10.1016/j.saa.2021.119709

We report here a series of coordinatively-saturated and thermodynamically stable luminescent [Ln(dtntp)(H₂O)] [Ln(III) = Eu (1), Tb (2), Gd (3), Sm (4) and Dy (5)] complexes using an aminophenyl-terpyridine appended-DTPA (dtntp) chelating ligand as cell imaging and photocytotoxic agents. The N,N″-bisamide derivative of H₅DTPA named as dtntp is based on 4′-(4-aminophenyl)-2,2′:6′,2″-terpyridine conjugated to diethylenetriamine-N,N′,N″-pentaacetic acid. The structure, physicochemical properties, detailed photophysical aspects, interaction with DNA and serum proteins, and photocytotoxicity were studied. The intrinsic luminescence of Eu(III) and Tb(III) complexes due to f → f transitions used to evaluate their cellular uptake and distribution in cancer cells. The solid-state structure of [Eu(dtntp)(DMF)] (1·DMF) shows a discrete mononuclear molecule with nine-coordinated {EuN₃O₆} distorted tricapped-trigonal prism (TTP) coordination geometry around the Eu(III). The {EuN₃O₆} core results from three nitrogen atoms and three carboxylate oxygen atoms, and two carbonyl oxygen atoms of the amide groups of dtntp ligand. The ninth coordination site is occupied by an oxygen atom of DMF as a solvent from crystallization. The designed probes have two aromatic pendant phenyl-terpyridine (Ph-tpy) moieties as photo-sensitizing antennae to impart the desirable optical properties for cellular imaging and photocytotoxicity. The photostability, coordinative saturation, and energetically rightly poised triplet states of dtntp ligand allow the efficient energy transfer (ET) from Ph-tpy to the emissive excited states of the Eu(III)/Tb(III), makes them luminescent cellular imaging probes. The Ln(III) complexes show significant binding tendency to DNA (K ~ 10⁴ M^?1), and serum proteins (BSA and HSA) (K ~ 10⁵ M^?1). The luminescent Eu(III) (1) and Tb(III) (2) complexes were utilized for cellular internalization and cytotoxicity studies due to their optimal photophysical properties. The cellular uptake studies using fluorescence imaging displayed intracellular (cytosolic and nuclear) localization in cancer cells. The complexes 1 and 2 displayed significant photocytotoxicity in HeLa cells. These results offer a modular design strategy with further scope to utilize appended N,N,N-donor tpy moiety for developing light-responsive luminescent Ln(III) bioprobes for theranostic applications.

Full text of DOI:10.1016/j.saa.2021.119709

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Luminescent lanthanide(III) complexes of DTPA-bis(amido-phenyl-
terpyridine) for bioimaging and phototherapeutic applications
a
b
a
b
a,
⇑
Srikanth Dasari , Swati Singh , Zafar Abbas , Sri Sivakumar , Ashis K. Patra
a
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, UP, India
Department of Chemical Engineering and Center for Environmental Science and Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, UP, India
b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
2
A series of coordinatively saturated and thermodynamically stable [Ln(dtntp)(H O)] (1–5) bioprobes
were synthesized utilizing strategically designed novel DTPA-bisamide ph-tpy (dtntp) ligand, to satisfy
and modulate the dual functional prerequisites as cellular imaging and phototherapeutic agents.
ꢀ
2
A series of [Ln(dtntp)(H O)] (1–5)
complexes were synthesized as cell
imaging and phototherapeutic agents.
The pendant phenyl-terpyridine
ꢀ
(Ph-tpy) moieties act as photo-
sensitizing antennae to impart the
desirable optical properties.
ꢀ
ꢀ
The luminescence of Eu(III) and Tb
(III) used for fluorescence imaging
studies.
Eu(III) and Tb(III) complexes show
photocytotoxicity in HeLa cells at
365 nm.
a r t i c l e i n f o
a b s t r a c t
Article history:
We report here a series of coordinatively-saturated and thermodynamically stable luminescent [Ln(dt-
Received 17 October 2020
Received in revised form 31 January 2021
Accepted 10 March 2021
ntp)(H
2
O)] [Ln(III) = Eu (1), Tb (2), Gd (3), Sm (4) and Dy (5)] complexes using an aminophenyl-
terpyridine appended-DTPA (dtntp) chelating ligand as cell imaging and photocytotoxic agents. The N,
00
0
0
0
00
N -bisamide derivative of
5
H DTPA named as dtntp is based on 4 -(4-aminophenyl)-2,2 :6 ,2 -
Available online 18 March 2021
0
00
terpyridine conjugated to diethylenetriamine-N,N ,N -pentaacetic acid. The structure, physicochemical
properties, detailed photophysical aspects, interaction with DNA and serum proteins, and photocytotox-
icity were studied. The intrinsic luminescence of Eu(III) and Tb(III) complexes due to f ? f transitions
used to evaluate their cellular uptake and distribution in cancer cells. The solid-state structure of [Eu(dt-
Keywords:
Lanthanide
Luminescence
Europium
ntp)(DMF)] (1ꢁDMF) shows a discrete mononuclear molecule with nine-coordinated {EuN
3 6
O } distorted
tricapped-trigonal prism (TTP) coordination geometry around the Eu(III). The {EuN } core results from
3 6
O
Terbium
DTPA
Bioimaging
Photocytotoxicity
three nitrogen atoms and three carboxylate oxygen atoms, and two carbonyl oxygen atoms of the amide
groups of dtntp ligand. The ninth coordination site is occupied by an oxygen atom of DMF as a solvent
from crystallization. The designed probes have two aromatic pendant phenyl-terpyridine (Ph-tpy) moi-
eties as photo-sensitizing antennae to impart the desirable optical properties for cellular imaging and
photocytotoxicity. The photostability, coordinative saturation, and energetically rightly poised triplet
states of dtntp ligand allow the efficient energy transfer (ET) from Ph-tpy to the emissive excited states
of the Eu(III)/Tb(III), makes them luminescent cellular imaging probes. The Ln(III) complexes show signif-
icant binding tendency to DNA (K ~ 10 M ), and serum proteins (BSA and HSA) (K ~ 10 M ). The lumi-
nescent Eu(III) (1) and Tb(III) (2) complexes were utilized for cellular internalization and cytotoxicity
studies due to their optimal photophysical properties. The cellular uptake studies using fluorescence
4
ꢂ1
5
ꢂ1
⇑
Corresponding author.
E-mail address: akpatra@iitk.ac.in (A.K. Patra).
https://doi.org/10.1016/j.saa.2021.119709
386-1425/Ó 2021 Published by Elsevier B.V.
1

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
imaging displayed intracellular (cytosolic and nuclear) localization in cancer cells. The complexes 1 and 2
displayed significant photocytotoxicity in HeLa cells. These results offer a modular design strategy with
further scope to utilize appended N,N,N-donor tpy moiety for developing light-responsive luminescent Ln
(III) bioprobes for theranostic applications.
Ó 2021 Published by Elsevier B.V.
1
. Introduction
Designing of lanthanide probes for biomedical applications
N,N-donor (e.g., dipyridoquinoxaline, dpq; dipyridophenazine,
dppz) or O,O-donor b-diketonates (e.g. (trifluoro-1-(2-naphthyl)-1
,3-butanedionate, tfnb; thenoyltrifluoroacetone, ttfa) ligands.
These complexes can acts as effective luminescent bioprobes for
cellular imaging and phototherapeutic agents in the visible to
NIR region [20]. However, these Ln(III) probes have some intrinsic
limitations like the necessity of secondary ligands to fulfill the
coordination sphere for desirable thermodynamic stability and
poor aqueous solubility. We attempt here to overcome some of
these limitations associated with these probes and to fulfill the
necessary criteria to develop efficient luminescent Ln(III) probes.
Herein, we have designed a new multidentate poly(aminocarboxy-
have been gaining great attention in recent decades, e.g. as MRI
contrast agents in medical diagnosis and therapy, biomarkers for
immunoassays, photodynamic therapy (PDT), bioimaging and mul-
timodal imaging agents [1–6]. Magnetic resonance imaging (MRI)
is a popular imaging technique in medical diagnostics and biomed-
ical imaging. In MRI, thermodynamically stable Gd(III)-based acyc-
2ꢂ
lic diethylenetriaminepentaacetic acid ([Gd(DTPA)(H
Magnevist ) and the cyclic 1,4,7,10-tetraazacyclododecane-1,4,7,
2
O)]
,
Ò
ꢂ
Ò
1
2
0-tetraacetic acid ([Gd(DOTA)(H O)] , Dotarem )[7] complexes
0
are the most widespread MRI contrast agents in clinical use. Lumi-
nescent Ln(III) probes coupled with MRI improves the diagnostic
ability in multimodal imaging [8–10].
Ln(III) complexes with multidentate ligands, viz. DTPA, DOTA,
cyclen derivative were well exploited as MRI contrast agents,
bioimaging, cellular staining, or theranostic applications [3–5,9–
late) chelator (dtntp) based on DTPA-functionalized with 4 -(4-ami
0
0
00
nophenyl)-2,2 :6 ,2 -terpyridine moiety as light-harvesting pen-
dant antenna, as well to form thermodynamically stable lan-
thanide complexes. We elegantly utilized dtntp ligand for
2
designing stable luminescent [Ln(dtntp)(H O)] (Ln(III) = Eu (1),
Tb (2), Gd (3), Sm (4) and Dy (5)) complexes to modulate the desir-
able optical properties for cellular imaging application (Scheme 1).
[Eu(dtntp)(DMF)] (1ꢁDMF) was structurally characterized and
1
3]. This is due to their excellent thermodynamic stability origi-
nated from multidentate chelating ligands. The unique optical
properties like large Stokes’ shifts, line-like emission bands, longer
3 6
reveals a nine-coordinate {EuN O } tricapped-trigonal prismatic
lifetime (ms–
l
s), higher quantum yields are highly suitable for
(TTP) coordination geometry around the Eu(III). The dtntp ligand
here serves multiple purposes: (i) it provides eight coordination
sites and forms strong complexation with the Ln(III) with high
thermodynamic stability; (ii) protects the Ln(III) ion from nonra-
diative vibrational or solvent quenching; (iii) the pendant ph-tpy
antenna facilitate efficient ET to the Ln(III) ions to generate the
emissive excited states which results in enhanced luminescence
interference-free invitro and invivo cellular imaging applications.
The time-resolved luminescence coupled microscopic techniques
with high S/N ratio allows possible real-time imaging using long-
lived Ln(III) probes, and eliminates the short-lived autofluores-
cence from indigenous biological fluorophores [11-14]. The
DTPA-bisamide based multidentate chelates with eight coordina-
tion sites forms coordinatively-saturated and thermodynamically
stable Ln(III) complexes. These scafoldes protect the emissive Ln
intensity; (iv) the pendant phenyl-terpyridine moieties on dtntp
3
*) and/or 3(n-
are capable to generate photo-induced
excited states to transfer their energy to
(
p
O
-
p
p
*)
3
(
III) from nonradiative vibrational energy dissipation for bioimag-
2
to form ROS that
ing and sensing applications [3–5]. Thus, design of Ln(III) probes
with multidentate ligands like DTPA or DOTA, appended with light
harvesting fluorophore in single platform is a strategic approach
for the design of highly luminescent lanthanide-based bioprobes
causes the cell death [20,21]. Ln(III) complexes are showing signif-
icant DNA and protein binding propensity due to planer ter-
pyridine moieties which can intercalate with DNA and serum
proteins. The intrinsic red and green luminescence of the Eu(III)
(1) and Tb(III) (2) were utilized for cellular imaging studies in HeLa,
MCF-7 and H460 cancer cells using confocal fluorescence micro-
scopy. The complexes 1 and 2 display significant photocytotoxicity
at 365 nm UV-A light. Overall, present study offer a modular strat-
egy to satisfy the essential criteria for designing Ln(III) probes for
multimodal imaging and phototherapeutic agents.
[
1–5,11–14].
One of the emerging applications of Ln(III) complexes is in pho-
todynamic therapy (PDT) and light-responsive theranostic agents
15,16]. Ln(III) probes with photosensitizing antenna act as multi-
[
modal phototherapeutic agents considering favorable intersystem
crossing (ISC) due to heavy-atom effect. This results in facile gen-
1
eration
2
O /ROS, which ultimately leads to apoptotic cell death
[
16,17]. Moreover, recently lanthanide-based upconversion
2
. Results and discussion
nanoparticles (UCNP) were elegantly used in imaging-guided pho-
totherapy [18]. The Yb,Er-UCNPs with excellent depth of penetra-
tion of NIR radiation, transparent biological window, and
biocompatibility are ideal choice for non-invasive PDT modality.
Ln(III) probes also avoid the drawbacks (prolonged skin sensitivity
and hepatotoxicity) of conventional porphyrin-based PDT agents
2.1. Synthesis and general aspects
The dtntp ligand was synthesized by reacting two equivalents
0
0
0
00
of
4 -(4-aminophenyl)-2,2 :6 ,2 -terpyridine
with
(DTPA)-bis-
0
00
diethylenetriamine-N,N ,N -pentaacetic
anhydride in dry DMF resulting in ~87% yield (Scheme 2). The free
ligand was characterized by ESI-MS and FT-IR (Fig. S1). The (+)-ion
mode ESI-MS spectra of the dtntp showed the molecular ion peak
acid
[
16a-b]. Recently, K.-L. Wong et al., strategically designed Ln(III)
probes as new-generation PDT agent, light-triggered delivery and
tracking of anticancer drugs and as imaging probes for the early
prognosis of disease biomarkers [17,19].
The present work emerges from our continuousinterest in
exploring and designing stable luminescent lanthanide complexes
for bioimaging and theranostic applications [20,21]. In the previ-
ous works, we reported several Ln(III) complexes with bidentate
+
[
M+H] at m/z 1006.40. The FT-IR spectra show strong absorption
ꢂ1
band at 1665 cm attributed to the
the bands at 1601 cm and 1585 cm correspond to (
amides. The broad band around 3414 cm corresponds to
or
mC=O of the free acid, while
ꢂ1
ꢂ1
m
CONH-) of
ꢂ1
m
N-H
2
mO-H of the dtntp ligand [22,23]. The [Ln(dtntp)((H O)] (Ln
2

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
Scheme 1. The design strategy for [Ln(dtntp)(H
2
O)] (1–5) bioprobes containing photosensitizing dtntp pendant antenna moiety for bioimaging and phototherapeutic
applications.
(
III) = Eu (1), Tb (2), Gd (3), Sm (4), Dy (5)) complexes were synthe-
sized following a generalized synthetic route (Scheme 2), with
84% yield by reacting Eu/Tb(CF SO 3, Gd(NO O, Dy(NO
ꢁ6H
hydrate and SmCl O with 1:1 mol ratio of dtntp deproto-
DTPA–bisamide derivatives with lanthanides. Here Ln(III) ion is
coordinated to dtntp via three oxygen atoms of the carboxylate
groups and three nitrogen atoms and two carbonyl oxygen atoms
of the amide groups, and the ninth coordination site is occupied
~
ꢁ
3
3
)
3
)
3
2
3 3
) -
3
ꢂ
3
ꢁ6H
2
nated by NaOH in 1:3 mol ratio with the free ligand, in boiling
by a water molecule [21–25]. The solid-state structure of
methanol. The ESI-MS spectra of the complexes 1–4 showed
[Eu(dtntp)(DMF)] (1) also confirms this bonding connectivity in a
nine-coordinated TTP geometry.
+
respective molecular ion peaks as [MꢂH
2
O + H] . The complex 5
2
O] with predicted isotopic distribution
+
shows m/z peak for [MꢂH
(Figs. S2-S6). The presence of molecular ion peaks in ESI-MS dis-
2.2. X-ray crystal structure
playing incorporation of respective Ln(III) in the dtntp core and
their structural integrity in solution. However, in aqueous-DMF
solution, presumably, there will be fast ligand-exchange reactions
between DMF and water as determined by inner-sphere hydration
number (q) values of the compounds due to fast ligand-exchange
The single crystals of complex 1 were obtained from the layer-
ing of Et O into a DMF/methanol solution of complex 1 at RT. The
2
X-ray structure shows discrete mononuclear nine coordination
{EuN O } polyhedra around the Eu(III) center. It crystallized in
3 6
kinetics of Ln(III). Upon complexation, the FT-IR spectra of the
the triclinic space group P-1 with eight molecules in the unit cell.
The asymmetric unit contains one MeOH as a solvent of crystalliza-
tion. The Eu(III) complex has one bound DMF on the ninth coordi-
nation site as a solvent of crystallization.
ꢂ1
complexes showed lower
m
C=O stretching (~60 cm ) compared to
free dtntp ligand, which suggests oxygen coordination to the Ln
III) ions. The overlapping FT-IR spectra of the complexes suggest
(
their structural resemblances (Figure S7). These results are consis-
tent with the previously reported analogous nine-coordinated
The selected crystallographic data and bonding parameters for
complex 1 were shown in Table S1. The ORTEP diagram of complex
Scheme 2. Synthesis of the dtntp ligand and [Ln(dpntp)(H
2
O)] complexes (Ln(III) = Eu (1), Tb (2), Gd (3), Sm (4), Dy (5).
3

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
1
is given in Fig. 1a. The unit cell packing diagram is shown in Fig-
traces for the complexes 1–5 in aqueous-DMF and in Tris buffer
at 298 K do not show any noticeable changes. This suggests the
complexes’ excellent thermodynamic stability in solution as dtntp
chelate forms coordinatively saturated stable lanthanide
complexes.
ure S8, and selected bond lengths and bond angles reported in
Table S2. The Eu(III) is coordinated through the three carboxylate
oxygens, two amide oxygens, and three amine nitrogens of the
eight-coordinated dtntp chelator. The ninth coordination site is
occupied by the oxygen atom of the DMF solvent used for crystal-
The efficient energy transfer (ET) requires a suitable energy dif-
3
lization. Such coordination results in a nine-coordinated {EuN
O
3 6
}
ference between the triplet state ( T) of the sensitizing antenna
distorted tricapped-trigonal prism (TTP) geometry around the Eu
and the emissive excited states of the Ln(III) ions. An optimal
L ? Ln(III) ET-process depends on ligands, which is capable of
effective energy transfer to its triplet state via intersystem crossing
(
(
III) center (Fig. 1b) [24,26–29]. The terminal amine nitrogens
N1, N2) together with the O9 oxygen of the coordinated DMF,
are forming the three rectangular face caps. The two triangular
faces of the trigonal prism are constituted by a pair of [O1, O2,
O5] and [N3, O3, O4] set of planes, respectively. The Eu(III) is sitting
in the middle of the trigonal prism, and Eu–O(9)DMF bond is almost
protruding out perpendicularly to the rectangular mean plane to
which it’s capped. Eu–Oamide bond distances range from 2.480(3)
Å to 2.452(4) Å and Eu–Ocarboxylate bond length ranges from 2.386
(ISC). The desirable energy gap (
D
E) between the lowest triplet
3
3
states of ligands (e.g., n-p*, p-p*) to the emissive excited states
ꢂ1
of Ln(III) ideally ꢃ 2500 cm according to the Latva’a empirical
rule [20,30,31].
To gain more insights into the energy gap of Ln(III) and ligand
triplet states, we measured the photophysical properties of the
dtntp ligand and Gd(III) complex (3) in aqueous-DMF at 298 K
shown in the Figs. S9-S10. The steady-state luminescence spectra
of Gd(III) complex at kex = 284 nm results in ligand-centered broad
emission that arises mainly from singlet states (
(
3) Å to 2.352(3) Å. Eu-Nterminal bonds range from 2.740(4) Å to
.641(3) Å, whereas Eu-Ncentral bond length is 2.643(3) Å and Ln-
DMF bond distance is 2.417(3) Å respectively, which are compara-
2
O
1
p–p*) (Fig. S10).
ble with the literature reported values [24,26–29]. On average, Eu–
N bond distances are ~0.3 Å longer than the Eu–O distances reveal-
ing the higher bond strength of the Eu–O ionic bonds, as compared
to the less polar Ln–N bonds [24,26–29]. We presume analogous
isostructures for other [Ln(dtntp)(Solv)] compounds, as observed
earlier with related DTPA-bisamide-quinoline derivatives, consid-
ering similar binding modes for Ln(III) [24a].
The phosphorescence mode spectra of Gd(III) complex showing
3
the lower energy triplet states (
p–p*) emission, which is indepen-
dent of the ligand to Gd(III) energy transfer. The Gd(III) emissive
6
excited state ( P7/2) situated much higher in energy than the dtntp,
thus arrest any ligand-to-metal energy transfer. As a result, the
detected luminescence is exclusively due to the dtntp chro-
mophore, which further allows us to determine the triplet state
1
(T ) energy of the dtntp ligand [22,31]. To estimate the approxi-
mate energy transfers pathways (due to only available room tem-
perature data) in the Ln(III) complexes, the approximate singlet
2.3. Photophysical properties
(
3
S
1
) and triplet (T
1
) energy levels of the dtntp ligand (324 nm,
UV–visible absorption spectra of the ligand and the Ln(III) com-
ꢂ1
ꢂ1
0864 cm , and 410 nm, 24400 cm ) were obtained by referenc-
plexes 1–5 in aqueous-DMF (99: 1 v/v) shows broad bands in the
range of ~270 to 350 nm with absorption maxima at 284 nm and
a broad shoulder at 324 nm can be attributed to the ligand-
ing their higher absorption edges and lower emission edge wave-
lengths of the corresponding phosphorescence spectra of dtntp
ligand and [Gd(dtntp)(H
5
2
O)] (3) at 298 K [20–23]. The D
0
emissive
centered
p
-p
* and n-
p* electronic transition of DTPA-bis-amide-
ꢂ1
5
ꢂ1
excited states of Eu(III) (17500 cm ), D
4
of Tb(III) (20400 cm ),
F15/2 state of Dy(III)
phenyl-terpyridine based dtntp ligand (Fig. 2a) [22–24]. The
significant resemblance of the UV–visible spectra of the Ln(III)
complexes 1–5 suggests electronic states are quite independent
of the nature of Ln(III) and very minimal ligand-field effect. The
excitation spectra for the complexes 1–5 were recorded using their
most intense Ln(III) emission bands. The excitation spectra in
Fig. 2b show broad bands ranging from ~270 to 350 nm, which
resembles their absorption spectra, which indicates, the Ln(III)
emission is sensitized through the photosensitizing pendant
ph-tpy antenna [22,23]. The time-dependent absorption spectral
4
ꢂ1
4
G
5/2 of Sm(III) (17800 cm
)
and
ꢂ1
(
[
(
21000 cm ) are well-known and obtained from the literature
32,33]. We determined the approximate qualitative energy gap
D
E = ET1-ELn*) between the T
1
state of dtntp ligand and excited-
ꢂ1
state energy levels of the Eu(III) (
D
E ~ 6900 cm ), Tb(III)
ꢂ1
ꢂ1
ꢂ1
(D
E
~
4000 cm ), Sm(III)
(
D
E
~
6600 cm
)
and Dy(III)
(D
E ~ 3400 cm ) respectively at RT from photoluminescence
and phosphorescence measurements. The determined room-
temperature T state energy level of the dtntp ligand is at higher
1
Fig. 1. (a) ORTEP view of [Eu(dtntp)(DMF)] (1ꢁDMF) at 50% probability thermal ellipsoid with the heteroatom numbering scheme. The hydrogen atoms were omitted for
clarity. (b) Coordination polyhedra of (1) showing the nine-coordinate {EuN
3
O
6
} Eu(III) core with distorted tricapped-trigonal prism (TTP) coordination geometry.
4

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
2 2
Fig. 2. (a) UV–vis absorption spectra of dtntp and [Ln(dtntp)(H O)] complexes 1–5 (28 mM) in aqueous-DMF (1:99, %DMF: %H O) at 298 K. (b) Excitation spectra of complexes
2
1–5 (10 mM) in aqueous-DMF (1:99, %DMF: %H O) at 298 K, (kem = 615 nm (1), kem = 545 nm (2), kem = 410 nm (3), kem = 598 nm (4), kem = 570 nm (5), Exc. and Em. slit
width = 5 nm.
energy than the emissive excited states of the Ln(III) ions. The
approximate schematic energy level diagram with possible
intramolecular ET process from dtntp antenna to the emissive
excited state of Ln(III) was shown in Fig. 3. In complexes 1 and 2,
this energy difference is sufficiently higher, which facilitates the
efficient ET from the pendant dtntp antenna triplet state to the
qEu = 1.2 (1) and qTb = 1.1 (2) confirms the presence of one
coordinated water molecule. This is in good agreement with the
solid-state structure of [Eu(dtntp)(DMF)] (1ꢁDMF), which contains
only one labile and exchangeable coordinated DMF molecule.
These
q values are consistent with the literature reported
nine-coordinated lanthanide complexes with DTPA-bisamide
derivatives; those generally provide eight coordination sites to
the Ln(III), and the ninth coordination site is occupied by one water
molecule in aqueous media [21a,23,28,29].
5
5
emissive excited states ( D
0 4
) of Eu(III) and ( D ) of Tb(III). However,
4
such indirect energy transfer to the excited states of Sm(III) ( G5/2
)
4
and of Dy(III) ( F15/2) was found less effective as observed from
their weak luminescence properties. A more precise quantitative
understanding of energy-levels requires low-temperature (e.g.,
The Sm(III) (4) and Dy(III) (5) complexes at kex = 284 nm
showed characteristic visible emission bands for Sm(III) and Dy
4
6
4
4
Liquid N
2
, 77 K) phosphorescence measurements along with theo-
(III) ions, attributed to G5/2 ? H
J
(J = 5/2 ? 13/2) and F15/2/ F9/2
6
retical calculation of the associated energy levels.
? H (J = 15/2 ? 9/2) f–f transitions (Fig. 5) [32c-32f]. The presence
J
The time-resolved luminescence spectra of the complexes 1 and
of ligand-based fluorescence observed at ~410 nm in complexes 4
and 5 implies that the energy transfer from dtntp to Sm(III) and Dy
(III) is not optimal with poor quantum yields [22–23,32]. The
monoexponential decay curves presumably indicating the pres-
ence of a single chemical environment (i.e. exchange of one labile
ligand-exchange site) around each luminescent Ln(III) ion in the
solution (Fig. S14, Table 1) [21–24].
2
upon excitation at 284 nm, display intrinsic red and green lumi-
5
7
5
7
nescence of Eu(III) and Tb(III) due to D
J = 6–3) transitions respectively (Fig. 4). The excited-state lumi-
nescent lifetimes of Eu(III) (1) and Tb(III) (2) was measured in
the H O and D O at room temperature to determine the number
0 J 4 J
? F (J = 0–4) and D ? F
(
2
2
of Ln(III)-coordinated water molecules in aqueous media (Table 1).
The emission decay profiles were fitted by using a single-
exponential fitting (Fig. S13). The hydration number (q) for com-
plexes 1 and 2 was calculated using the modified Horrocks’ equa-
tion [34]. The determined q values for the Ln(III) complexes
The overall quantum yield (
Uoverall) of the complexes 1–5 were
measured in the H O, and D O reported in the Table 1 are compa-
2
2
rable or higher than the existing Ln(III) complexes with DTPA-bis
amide derivatives [31–35]. As compared to complexes 1 and 2,
Fig. 3. Schematic approximate energy level diagram showing the possible intramolecular energy transfer processes from dtntp antenna to the emissive excited states of Ln
(
1 1
III) in complexes 1–5 based on photophysical data at 298 K. S , first excited singlet state; T , first excited triplet state, ISC, intersystem crossing.
5

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
Fig. 4. Time-resolved luminescence spectra of complexes 1 (red) and 2 (green) in
Fig. 5. Luminescence spectra of complexes 4 (magenta) and 5 (olive) in aqueous-
5
5
7
aqueous-DMF (1:99, %DMF: %H
2
O) showing their corresponding
D
0
/ D
4
? F
J
O) showing their corresponding 4
5/2 and 4
4
6
DMF (1:99, %DMF: %H
2
G
F15/2/ F9/2 ? H
J
transitions. ([complex] = 12 mM, kex = 284 nm, Exc./Em. slit width = 5 nm).
transitions. (20 mM, kex = 284 nm, Exc./Em. slit width = 10 nm).
the lower
s and U of the complexes 4 and 5 are mainly due to the
transfer agents to nucleic acid, and serum proteins, photothera-
peutic agents [20,21,39,40]. The Ln(III) complexes 1–5 containing
dtntp ligand with two pendant planer phenyl-terpyridine anten-
nae have allowed us to study their binding interaction with
duplex DNA. Upon gradual addition of CT-DNA to the dtntp
Sm(III) and Dy(III) excited states are more susceptible towards
additional non-radiative deactivation pathways. Their excited
states are possibly quenched by non-radiative vibrational relax-
ation by O–H and N–H oscillators present in the surrounding sol-
vent and ligand [22a, 35]. The stuided Ln(III) complexes follow
ligand and [Ln(dtntp)(H
chromic shift in absorption spectra due to binding between Ln
III) complexes and the base pairs of DNA (Fig. 6a and
Figs. S15-S18). The intrinsic equilibrium binding constant (K
2
O)] complexes 1–5 results in a hypo-
similar trend in excited state lifetimes (
yield ( ) with analogous Ln(III)- DTPA-bis amide derivatives. For
example, for Ln(III)- DTPA-bis-6-aminoquinoline (LnL) ( and
for EuL = 0.6 ms and 4%; SmL = 0.01 ms, 0.1%) [22a]. Similar
trend in overall observed in a series of Ln(III) complexes with
DTPA-bis-p-thiophenyl derivatives (LnL ) (
s) and overall quantum
U
(
s
U
b
)
4
ꢂ1
for the complexes 1–5 were calculated are K
reported in Table 2 [24]. These results suggesting their moderate
binding propensity with CT-DNA possibly via partial intercala-
b
ꢄ10
M
and
U
x
x
x
x
U
= EuL , TbL , DyL
and SmL are 0.32%, 0.04%, 0.03% and 0.02% respectively) [35a].
The longer and higher of the complexes in D O as compared
to H O is the results of less nonradiative deactivation induced by
x
tion binding mode or
p-p interaction through two pendant pla-
s
U
2
nar phenyl-terpyridine antennae moieties of dtntp with DNA
base pairs [41].
2
O–D vibrations than by O–H [36]. Overall, the present series of
Ln(III) complexes show higher thermodynamic stability, coordina-
tive saturation (q = 1), desirable optical parameters, photostability.
These properties underscore their suitability towards satisfying
necessary criteria for designing effective Ln(III) bioprobes for cellu-
lar imaging applications.
Ethidium bromide (EthB), a planer cationic fluorescent dye, acts
as an effective spectral probe to determine the relative binding
affinity of the complexes to CT-DNA. The apparent binding con-
stant (Kapp) of the complexes 1–5 to CT-DNA was monitored by
successive changes observed in the emission band of EthB bound
DNA [42]. The emission intensity of the EthB was significantly
quenched upon titration with complexes ensuring the displace-
ment of ethidium bromide (EthB) and possible partial intercalation
with DNA (Fig. 6b and Figs. S19-S22). The calculated Kapp values are
2.4. DNA binding studies
6
ꢂ1
(K
app) ~ 10 M (Table 2), which suggests complexes have an effi-
cient binding affinity with CT-DNA. The higher values of K and
app of the complexes 1–5 reveals significant binding affinity to
DNA is one of the most important pharmacological targets for
several metal-based therapeutic drugs (cisplatin, carboplatin,
oxaliplatin, Ru-drugs) [37,38]. Numerous transition metal and
lanthanide complexes containing planer phenanthroline and
polypyridyl ligands were utilized in DNA recognition, charge-
b
K
CT-DNA, possibly through partial intercalation with planar
Ph-tpy moieties.
Table 1
Photophysical properties of the complexes 1–5.
exa(nm)/(
e
/M cm
ꢂ1
ꢂ1
)
s
H
2
b(ms)
s
D
c
(ms)
qd
/
overalle(H
/
fo verall(D
O)
2
Complex
k
O
2
2
O)
1
2
4
5
284(61780)
284(60900)
284(64400)
284(63600)
0.45
0.65
0.27
0.20
1.08
0.80
0.39
0.29
1.2
1.1
–
0.231
0.178
0.078
0.048
0.378
0.297
0.128
0.086
–
a
b, c
d
UV/visible absorption spectra.
Luminescence lifetimes ( ) in H
Hydration number (q) calculated using modified Horrocks’ equation ignoring any alternative deactivation pathways.
s
2 2
O and D O.
e,
f
Overall quantum yield (/overall) of the Ln(III) complexes in H
2
O and D
2
O (contains 1% DMF). The experimental errors
s,±10%; q, ±10%; /Overall,±10%.
6

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
2 af
Fig. 6. (a) UV–vis spectral traces of [Eu(dtntp)(H O)] (1, 34 mM) in 5 mM Tris-buffer (pH 7.2) with increasing concentration of CT-DNA at 298 K. The inset shows De /Debf vs.
[
CT-DNA] plot for complex 1. (b) Emission spectral traces of EthB bound CT-DNA with increasing amount of 1 in 5 mM Tris-buffer (pH 7.2) at 298 K, kex = 546 nm,
k
em = 603 nm, [CT-DNA] = 313
lM, [EthB] = 12
lM. The inset shows plots of fluorescence intensity I/I
0
vs. [complex] for 1–5.
Table 2
Binding interaction parameters for the complexes 1–5 with biomolecules.
DNA BSA
HSA
ꢅ 10 [M ]a
4
ꢂ1
K
app ꢅ 10 [M ]b
6
ꢂ1
K
BSA ꢅ 10 [M ]c
5
ꢂ1
k
q
ꢅ 10 [M ]d
13
ꢂ1
K ꢅ 10 [M ]e
5
ꢂ1
K
HSA ꢅ 10 [M ]c
4
ꢂ1
k
q
ꢅ 10 [M
12
ꢂ1
]
K ꢅ 10 [M
3
ꢂ1
]
K
b
1
2
3
4
5
1.29(±0.03)
2.61 ± 0.02)
1.25(±0.04)
2.85(±0.03)
1.53(±0.02)
2.95
2.05
2.15
1.93
2.18
3.74(±0.02)
4.57(±0.03)
–
3.40(±0.02)
5.39(±0.04)
3.74
4.57
–
3.40
5.39
5.27
1.52
–
1.96
3.37
1.84(±0.01)
3.02(±0.04)
–
6.57(±0.12)
4.53(±0.02)
2.84
3.02
–
6.57
4.53
6.44
3.14
–
8.81
1.86
a
b
c
K
K
b
, equilibrium DNA binding constant.
app, apparent DNA binding constant. For dtntp ligand: K
4
ꢂ1
6
ꢂ1
b
= 3.33(±0.03) ꢅ 10
M
and Kapp = 2.03(±0.04) ꢅ 10
M .
K
BSA/HSA, Stern-Volmer quenching constant for BSA and HSA fluorescence.
d
kq, quenching rate constant.
e
K, binding constant with BSA and HSA. Number of binding sites (n) are 1.49 (1), 1.03 (2), 1.47 (4) and 0.92 (5) for BSA and 0.42 (1), 0.55 (2), 0.80 (4) and 0.66 (5) for HSA
respectively.
2
.5. Serum protein binding studies
Synchronous emission spectroscopy study can provide critical
information about the molecular microenvironment in the vicinity
of fluorophores (Tyr or Trp residues) in the HSA protein [46]. In
synchronous fluorescence spectra, tryptophan residues give typical
Serum albumin is the most abundant blood protein, constitutes
~
55% of total blood plasma. Serum protein has been the most
extensively studied proteins and plays a vital role in drug transport
and metabolism [43,44]. Structurally homologous bovine serum
albumin (BSA) and human serum albumin (HSA) were used to
study the binding interaction with present Ln(III) complexes. The
intrinsic tryptophan and tyrosine residues in serum proteins are
responsible for the fluorescence properties in BSA and HSA. The
binding affinity of the Ln(III) complexes 1–5 with BSA and HSA
were investigated using characteristic tryptophan emission
quenching of BSA (Trp 135 and Trp 214) and HSA (Trp 214) in
the presence of complexes 1–5. The gradual increase of concentra-
tion of the complexes 1–5 results in significant quenching of emis-
sion intensity of BSA and HSA at k = 345 nm (Fig. 7a-b and
Figs. S23-S33). The changes observed in spectral intensity and shift
in emission wavelengths upon binding with complexes attributed
to various changes in the secondary structure of the proteins, sub-
strate binding, or structural changes of proteins [44].
emission at
emission at
D
D
k = 60 nm and tyrosine residues give characteristic
k = 15 nm. Synchronous emission spectra of HSA
were monitored with the gradual addition of increasing concentra-
tion of complexes 1–5 both at k = 15 nm and k = 60 nm (Fig. 7 c-
d). The synchronous emission of HSA ( k = 15 nm) with varying
complex concentration results in decrease in emission intensity
at 284 nm with a minor shift in the band position, indicating the
effect of complexes depends less likely upon the microenviron-
ment of the tyrosine residues in HSA. However, synchronous emis-
D
D
D
sion of HSA at
Dk = 60 nm with the addition of 1–5 leads to a
much-pronounced quenching of emission intensity at 280 nm with
minor red-shift of peak maxima. We also observed an isosbestic
point at 295 nm and a concomitant formation of a new band at
315 nm. The significant changes in synchronous fluorescence
intensity indicates the altered polarity in the protein microenvi-
ronment [60].
The Stern-Volmer equation has been utilized and calculated the
Stern-Volmer quenching constant KBSA and KHSA for complexes 1–5
are in the range of KBSA ~ 10 M and KHSA ~ 10 M reported in
Table 2 [45]. The values of binding constant (K), the number of the
2
.6. Cellular imaging studies
5
ꢂ1
4
ꢂ1
2
The cellular uptake and distribution of the [Eu/Tb(dtntp)(H O)]
q
binding site (n) and quenching rate constant (k ) for complexes to
(1, 2) complexes were studied by confocal fluorescence microscopy
BSA and HSA were determined by using Scatchard equation: log
via examining the red and green emission originating from Eu(III)
and Tb(III) ions. The cytotoxicity of dtntp ligand and complexes 1, 2
were assessed using well-known MTT assay in various cancer cells
(
I
0
ꢂ I)/ I = log K + n log[Q] (Fig. S26 and Fig. S33). The higher values
of KBSA and KHSA suggest a significant binding affinity of the com-
plexes to serum proteins, which may facilitate the transporting
of such Ln(III) bioprobes to the pathological site [44d].
(
HeLa, MCF-7, and H460) are depicted in Figs. S34-S35. The IC50
values for 1 and 2 were reported in Table S4 and found to be mod-
7

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
Fig. 7. (a) The effect of the addition of complex 1 on the emission spectral quenching of BSA in 5 mM Tris-buffer (pH 7.2) at 298 K. Inset: Stern–Volmer plots of the
fluorescence titrations of complexes 1–2 and 4–5 with BSA. (b) Fluorescence spectral quenching of the HSA emission with the addition of an increasing amount of complex 1.
Inset: Stern–Volmer plots of 1–2 and 4–5. kex = 295 nm, kem = 345 nm, [BSA] = 5
the presence of an increasing concentration of complex 1 with ex. and em. wavelength difference of
l
M, [HSA] = 2
l
M. (c) Uncorrected synchronous fluorescence spectra of HSA protein (2
k = 15 nm, and (d) k = 60 nm.
lM), in
D
D
erately cytotoxic in the dark and remain significantly viable within
the concentration ranges (20 M) used for cellular imaging studies.
from the Eu(III)/Tb(III) bioprobes were stable and consistent
throughout experiments suggesting their photostability and resis-
tance towards possible photobleaching. These desirable features
were essential for their utility as potential cellular imaging agents.
The pendant terpyridine moieties in these complexes could be
potentially exploited for their metal-binding capability or rich
electronic effects.
l
The cellular imaging studies of the Eu(III) and Tb(III) complexes
were carried out in HeLa, MCF-7, and H460 cancer cells to probe
the potential uses of these luminescent Ln(III) complexes as lumi-
nescent cellular stains. The cancer cells were incubated with the
solution of Eu(III) (1) and Tb(III) (2) (20 mM) complexes in DMEM
for 4 h, and the nucleus was stained with Hoechst 33258 dye to
determine the subcellular localization of the compounds. The fluo-
rescence cell images of the cancer cells were captured with an exci-
tation wavelength (kex) of 405 nm for Eu(ΙΙΙ) and 488 nm for the Tb
2.7. Photocytotoxicity
(
ΙΙΙ) are shown in (Figs. 8-10 and Figs. S36-37) respectively. The
Photo-responsive therapeutic agents play a critical role in can-
cer chemotherapy. Metal complexes are gaining increasing inter-
est as photosensitizers in PDT and photo-activated chemotherapy
(PACT) [49]. A Ru(II)-based photosensitizer (TLD1433) recently
entered in clinical trials [49a]. The Ln(III) complexes with a wide
window of excited-state energy levels (Vis-NIR), upconversion
ability, and high degree of modularity in their design have excel-
lent potential in photochemotherapy. The photocytotoxicity of
complexes 1 and 2 were examined in the HeLa cells upon pho-
toirradiation at 365 nm (6 W) for 1 h from the MTT assay
cellular internalization of these Ln(III) probes was evaluated from
their characteristic intense red and green emission from the
excited states ( D
multiphoton confocal laser scanning fluorescence microscopy
(
5
5
0 4
) of Eu(ΙΙΙ) and ( D ) of Tb(ΙΙΙ) respectively using
MCLSFM).
Confocal fluorescence images of both the complexes are con-
firming their significant uptake within the cells (panel-Ι in Figs. 8
and 9). These Ln(III) bioprobes seem most likely accumulate into
the cytoplasm and nucleus. The results demonstrate that tested
complexes possibly permeate through the cytoplasm, then traverse
through the nuclear membrane, and ultimately enter the nuclei.
Acquired confocal images of HeLa, MCF-7, and H460 cells are show-
ing bright red, and green spots within the nuclei assigned with
arrows (Fig. 10) were suggesting their sufficient localization inside
the nuclei or specifically in protein-rich nucleoli [47–48,11,20].
The thermodynamically stable Eu(III)/Tb(III) complexes with
(Fig. 11). The IC50 values for complexes 1 and 2 are 32.5 ± 0.8
l
M and 28.6 ± 1.0 M respectively and were found to be signifi-
l
cantly toxic than in the dark makes them suitable for potential
photo-responsive therapeutic agents [20,49b–c]. The complexes
remain moderately less toxic in the dark as evidenced by cell via-
bility assay in the dark (Figs. S34-S35) and cell imaging studies.
Thus, these complexes can serve the dual purpose as a cellular
imaging tool and phototherapeutic agents or light-responsive
theranostic probes.
longer
s and U values have elegantly reduced the autofluorescence
and scattering from the background. The luminescence originated
8

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
ꢂ1
Fig. 8. MCLSFM images of the HeLa, MCF-7, H460 cells incubated with complex 1 at 20
l
M for 4 h and nucleus staining Hoechst 33258 dye (5
l
gmL ) showing the
intracellular distribution profile of the Eu(III) complex (1). Panel-I: Red emission from Eu(III); Panel-II: blue emission from nucleus staining Hoechst 33258 dye; panel III:
merged images showing subcellular (nuclear and cytosolic) localization of the complex; Scale bar = 10 m and kex = 405 nm.
l
3
. Conclusions
4. Experimental section
We strategically designed a DTPA-bisamide derivative of eight
4.1. Material and methods
coordinate dtntp chelator containing two phenyl-terpyridine (Ph-
tpy) pendant antenna moieties to sensitize the Ln(III) ions. The
ligand yields a series of structurally identical thermodynamically
Ln(III) salts (Eu(CF
ꢁ6H O (99.9%), Dy(NO
3
SO
3
)
3
(98%), Tb(CF
3
SO
3
)
3
(97%), Gd(NO
3 3
) -
2
3
)
3
ꢁhydrate (99.9%), SmCl
3
ꢁ6H O (99.98%)),
2
stable lanthanide complexes: [Ln(dtntp)(H
2
O)] [Ln(III) = Eu, Tb,
Diethylenetriaminepentaacetic dianhydride from Sigma-Aldrich.
All other reagents and solvents were purchased from commercial
sources (Sigma-Aldrich, Alfa Aesar, Fisher Scientific) and used
Gd, Sm, Dy (1–5)]. The modular design principle satisfies the dual
functional prerequisites as cell imaging and photocytotoxic
agents. The solid-state structure of the [Eu(dtntp)(DMF)] shows
0
without further purification unless otherwise mentioned. 4 -(4-a
0
0
00
discrete nine-coordinated {EuN
3
O
6
}
cores with distorted
minophenyl)-2,2 :6 ,2 -terpyridine was synthesized according to
the literature procedure [24b,50]. HeLa, MCF-7 and H460 cancer
cells were obtained from National Center for Cell Sciences, Pune,
India. FT-IR spectral data were recorded using KBr pellets on a
Perkin-Elmer model 1320 FT-IR spectrometer. Electrospray
Ionization Mass spectrometry (ESI-MS) spectra were acquired by
using Waters Q-TOF Premier mass spectrometer.
tricapped-trigonal prism (TTP) coordination geometry around
the Eu(III). Photophysical studies reveal triplet state of dtntp
and the Ln(III) emissive excited states are having suitable energy
gap that allows efficient energy transfer from the dtntp pendant
antenna to the Ln(III). This results in desirable optical properties
2
and photostability of [Eu/Tb(dtntp)(H O)] complexes required
for cellular imaging. The complexes 1–5 showed significant CT-
DNA binding propensity possibly through partial intercalation
via planer ph-tpy moieties of dtntp and DNA base pairs. The com-
plexes 1–5 revealed efficient binding to serum proteins possibly
due to various molecular interactions. The cellular imaging stud-
ies of Eu and Tb-complexes in different cancer cells reveals their
cytosolic and nuclear localization ensures their potential use as
cellular imaging agents. The Eu(III) and Tb(III) complexes showed
enhanced photocytotoxicity in HeLa cells at 365 nm for their
therapeutic utility. Thus, collectively these results are promising
and offer an improved modular strategy for the development of
multimodal Ln(III) bioprobes for light-responsive theranostic
application.
4.2. Photophysical measurements
Absorption spectral data were recorded at 298 K using Perkin-
Elmer Lambda 25 spectrophotometer. All the steady state fluores-
cence emission and time-delayed luminescence spectral data were
monitored on Agilent Cary Eclipse fluorescence spectrophotometer
at 298 K. Excitation spectra of complexes 1–5 in aqueous-DMF at
298 K were measured by fixing their corresponding major Ln(III)
ions emission wavelength (kem = 615 nm (1), kem = 545 nm (2),
k
em = 410 nm (3), kem = 598 nm (4), kem = 570 nm (5) respectively.
Luminescence lifetime ( ) measurements were recorded under
ambient conditions in H O and D O (contains 1% DMF) using a
s
2
2
9

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
ꢂ1
Fig. 9. MCLSFM images of the HeLa, MCF-7, H460 cells incubated with complex 2 at 20
l
M for 4 h and nucleus staining Hoechst 33258 dye (5
l
gmL ) showing the
intracellular distribution profile from Tb(III) complex (2). Panel-I: Green emission from Tb(III); panel-II: blue emission from nucleus staining Hoechst 33258 dye; panel III:
merged images showing subcellular (nuclear and cytosolic) localization of the complex; Scale bar = 10 m and kex = 488 nm.
l
Fig. 10. MCLSFM imaging study of the complexes 1 (upper row), and 2 (lower row) in HeLa, MCF-7, and H460 cancer cells showing cellular behavior of Eu(III) and Tb(III)
respectively. Bright red and green spots are shown with arrows distinguishing localization of 1 and 2 into cell nuclei. Scale bar = 5 m.
l
pulsed Xenon lamp at excitation wavelength (kex) of 284 nm, and
emission wavelength (kem) at 615 nm and 545 nm for Eu(ΙΙΙ) and
Tb(ΙΙΙ) complexes (1, 2) and 598 nm and 570 nm for Sm(III) and
Dy(III) complexes (4, 5) respectively with a delay/gate time of
fitting using the non-linear least square method. Lifetime data
for complexes 1–5 in H O and D O contains 1% DMF was shown
in Figs. S13-S14 and Table 1. In complexes 1 and 2, the excited-
state lifetime measurements in H O and D O allowed us to deter-
mine the number of water molecules (q) directly coordinated to
2
2
2
2
0
.1 ms. Emission decay curves were fitted by a single exponential
10

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
were synthesized by following a generalized synthetic procedure
in which a hot methanolic solution of Eu(CF
.334 mmol) and Tb(CF SO (0.200 g, 0.330 mmol), Gd(NO
6H O, (0.200 g, 0.443 mmol), SmCl O (0.200 g, 0.548 mmol),
ꢁ6H
Dy(NO
3 3 3
SO ) (0.200 g,
0
3
3
)
3
3 3
) -
ꢁ
2
3
2
3
)
3
ꢁhydrate (0.200 g, 0.574 mmol), in 10 mL of boiling
methanol was added drop wise to 30 mL hot stirred methanolic
solution of dtntp (0.336 g, 0.334 mmol) (1), and (0.332 g,
0
.330 mmol) (2), (0.446 g, 0.443 mmol) (3), (0.552 g, 0.548 mmol)
(4), (0.577 g, 0.574 mmol) (5), pretreated with 3 equivalents of
NaOH for 30 min. The reaction mixture was refluxed for 12 h on
oil bath at 70 °C under nitrogen atmosphere. The solvent was evap-
orated in the reduced pressure and re-dissolved in the small
amount of MeOH and precipitated by the addition of Et
was then filtered and washed with 10 mL of hot MeOH, 10 mL of
Et O, and finally dried in vacuum over P 10. The complex 1 was
dissolved in DMF/MeOH and slow evaporation with addition of
Et O/MeCN at RT after couple of months yields a very small block
2
O. which
2
4
O
2
shaped yellowish single crystals were obtained suitable for X-ray
crystallography. The solid-state structure of complex 1 shows Eu
(
III) 9th coordination site is occupied by the DMF solvent due to
the solvent of crystallization.
[Eu(dtntp)(H O)] (1). Yield ~84% (0.463 g). ESI-MS (in DMF): m/
z (%) calcd. For [MꢂH
155.2958(50), 1157.2958(58), 1158.2958(20). Found: 1156.2974
Fig. 11. Cell viability plots of HeLa cells treated and incubated with complexes 1
and 2 for 4 h in the dark followed by irradiated to UV-A light at 365 nm (6 W) for 1 h
showing the photocytotoxicity activity.
2
+
2
O + H] , 1156.2958(100), 1154.2958(76),
1
the respective Ln(III) using the following modified Horrocks’ equa-
(
(
100), 1154.2844(74), 1155.2928(50), 1157.2986(57), 1158.3029
tions for Eu(ΙΙΙ) (1) and Tb(ΙΙΙ) (2), [34].
ꢂ1
21). FT-IR (KBr, cm ): 3405(w, br,
N-H ,
m ) 2923(m), 2850(m),
ꢀ
ꢁ
ꢀ
ꢁ
ꢂ
1
s 2
H
1
1
s 2
H
1
1602(vs,
(
1
m
asym (CO
2
)), 1517(s,
m
C=O(CONH) amide), 1469(s), 1442
qEu ¼ 1:2
ꢂ
ꢂ 0:25 ; q ¼ 5:0
ꢂ
ꢂ 0:06
O
ꢂ
Tb
vs), 1392(vs,
masym (CO
2
)) 1324(s), 1257(s), 1166(m), 1118(s),
O
s
D2
O
O
s
D2
092(vs), 1032(m), 993(m), 928(m), 838(vs), 792(vs), 516(m).
The overall emission quantum yields (
U
) of the complexes (1–2
ꢂ1
ꢂ1
UV–vis (aqueous-DMF) [kmax/nm (
e
/M cm )]: 284(61780), 294
/ms): 0.455 (H O), 1.087 (D O);
Hydration number (q) = 1.23 at 298 K.
and 4–5) were measured at 298 K using quinine sulfate as refer-
ence using the following equation:[45]
(
59500), 324(21800). Lifetimes (
s
2
2
2
[Tb(dtntp)(H O)] (2). Yield ~84% (0.328 g). ESI-MS (in DMF): m/
A
AIref
ref In
n
2
+
£overall ¼ £ref
z (%) calcd. For [MꢂH
O + H] , 1162.3013(100), 1163.3013(67),
2
ref
2
1
164.3013(23), 1165.3013(8). Found. 1162.3020(100), 1163.3035
ꢂ1
Where A, I and n denote the respective absorbance at kex, area under
the emission curve and refractive index of the solvent respectively.
The /ref represents the reference standard quinine sulfate solution
quantum yield.
(65), 1164.3029(23), 1165.3032(6). FT-IR (KBr, cm ): 3412(w, br,
ꢂ
m N-H), 2919(m), 2850(m), 1601(vs,
amide), 1470(s), 1441(vs), 1385(vs,
1185(m), 1118(s), 1097(vs), 1039(m), 993(m), 928(m), 838(vs),
92(vs), 518(m). UV–vis (aqueous-DMF) [kmax/nm (
284(60900), 294(58800) 324(21770). Lifetimes
O), 0.803 (D O); Hydration number (q) = 1.12 at 298 K.
[Gd(dtntp)(H O)] (3). Yield ~84% (0.328 g). ESI-MS (in DMF): m/
z (%) calcd. For [MꢂH
1159.2957(75), 1160.2957(80), 1162.2957(52), 1163.2957(70),
1164.2957(39), 1165.2975(13). Found: 1161.3004(100),
m
asym (CO )), 1518(s, mC=O(CONH)
2
m
sym (CO2 )) 1321(s), 1260(s),
ꢂ
ꢂ1
ꢂ1
7
e
/M cm )]:
4
.3. Synthesis and characterization
(s/ms): 0.654
(
H
2
2
0
0
0
00
Synthesis of Bis(4 -(4-aminophenyl)-2,2 :6 ,2 -terpyridine)
derivative of dtpa [dtpa(Aph-tpy)
minophenyl)-2,2 :6 ,2 -terpyridine (1.09 g, 3.36 mmol, 2 equiv)
and diethylenetriaminepentaacetic acid bisanhydride (600 mg,
2
0
+
2
(dtntp)]. A mixture of 4 -(4-a
2
O + H] , 1161.2957(100), 1158.2957(40),
0
0
00
1
7
.68 mmol, 1 equiv) in dry DMF (20 mL) was stirred overnight at
0 °C. Diethyl ether (100 mL) was added to the reaction mixture
1158.2976(35), 1159.3009(69), 1160.2975(80), 1162.2990(52),
ꢂ1
1163.3052(68), 1164.2996(38), 1165.3009(14). FT-IR (KBr, cm ):
ꢂ
at 0 °C, and the desired dtntp ligand precipitate formed were then
filtered and washed twice with 10 mL of Et O, and finally dried in
vacuum over P
3435(w, br,
m
(N-H), 2918(m), 2849(m), 1601(vs,
m
asym (CO
2
)),
2
1517(s,
m
C=O(CONH) amide), 1468(s), 1440(vs), 1384(vs,
m
sym
ꢂ
4
O
10 and to yields crystalline product.
(CO
2
)), 1321(s), 1259(s), 1184(m), 1118(s), 1092(vs), 1055(m),
ꢂ1
dtntp: Yield ~87% (1.478 g). FT-IR (KBr, cm ): 3418 (w, br,
m
N-
994(m), 929(m), 837(vs), 791(vs), 513(m). UV–vis (aqueous-DMF)
ꢂ1
ꢂ1
H
), 3264 (w), 3051(m), 2925(m), 2850(m), 1665 (vs,
acid), 1601 (s, C=O(CONH) amide I), 1584 (s,
521(s), 1467(s), 1441(vs), 1413(m), 1388(vs) 1318(m), 1254(s),
mC=O, CO free
[kmax/nm (
e
/M cm )]: 284(53800), 294(52500), 324(20950).
O)] (4). Yield ~85% (0.550 g). ESI-MS (in DMF):
m
mC=O(CONH) amide II),
[Sm(dtntp)(H
2
+
1
1
6
1
m/z (%) calcd. for [MꢂH
2
O + H] , 1155.2885(100), 1150.2885(52),
227(m), 1092(vs), 1039(m), 990(m), 893(m), 837(vs), 791(vs),
1151.2885(72), 1152.2885(84), 1153.2885(67), 1154.2885(30),
1156.2885(62), 1157.2885(98), 1158.2885(56), 1159.2885(18).
+
60(vs), 516(m). ESI-MS (in DMF): m/z (%) calcd. For [M+H] ,
006.4000(100), 1007.4000(66), 1008.4000(23), 1009.4000(6);
Found:
1155.2983(100),
1150.2997(48),
1151.2979(72),
found,
009.3909(6). Elemental analysis: Calcd. for C56
H, 5.11; N, 15.31. Found: C, 66.78; H, 5.07; N, 15.24. UV–vis (in
1006.4008(100),
1007.4078(63),
1008.4085(23),
1152.2916(79), 1153.2965(68), 1154.2937(32), 1156.3057(64),
ꢂ1
1
H
51
N
11
O
8
: 66.85;
1157.3070(96), 1158.2949(56), 1159.2423(21). FT-IR (KBr, cm ):
ꢂ
3435(w, br,
mN-H), 2924(m), 2852(m), 1603(vs,
masym (CO
2
)),
ꢂ1
ꢂ1
aqueous-DMF) [kmax/nm (
95(60600), 284(62500).
Synthesis and Characterization of [Ln(dtntp)(H
e
/M cm )]: 383(2040), 324(25300),
1518(s,
m
C=O(CONH) amide), 1468(s), 1441(vs), 1392(vs,
m
sym
ꢂ
2
(CO
2
)), 1325(s), 1263(s), 1187(m), 1118(s), 1092(vs), 1039(m),
2
O)] (Ln
993(m), 930(m), 837(vs), 791(vs), 517(m). UV–vis (aqueous-DMF)
ꢂ1
ꢂ1
(
(
III) = Eu(III), Tb(III), Gd(III), Sm(III), Dy(III)). Lanthanide(III) (Ln
III) = Eu(1), Tb(2), Gd(3), Sm(4), Dy(5), complexes of the dtntp
[kmax/nm (
e
/M
cm )]: 284(64400), 294(62200), 324(24500).
O), 0.387 (D O).
Lifetimes (
s
/ms): 0.268 (H
2
2
11

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
[
Dy(dtntp)(H
(%) calcd. For [MꢂH
165.2939(89), 1167.2939(50), 1168.2939(15), 1169.2939(4),
2
O)] (5). Yield ~84% (0.576 g). ESI-MS (in DMF): m/
4.6. Protein binding experiments
+
z
1
2
O] , 1166.2939(100), 1164.2939(74),
The fluorescence emission quenching of tryptophan at 345 nm
(kex = 280 nm) of serum protein namely BSA/HSA in Tris-HCl/
NaCl buffer (pH = 7.2) were performed to study the binding inter-
action of complexes. The addition of quencher (complexes 1–5) to
serum proteins lead to the gradual decrease of emission intensity,
found.
1166.2996(100),
1164.3040(69),
1165.3003(84),
ꢂ1
1
3
1
167.3015(50), 1168.3081(15), 1169.3069(4). FT-IR (KBr, cm ):
430(w, br,
ꢂ
2
)),
m
N-H), 2919(m), 2850(m), 1600(vs,
m
asym (CO
sym
516(s,
m
C=O(CONH) amide), 1469(s), 1441(vs), 1384(vs, m
ꢂ
(
CO
2
)), 1324(s), 1260(s), 1184(m), 1116(s), 1093(vs), 1039(m),
the quenching constant (KBSA/HSA) and quenching rate constant (K
q
)
9
95(m), 931(m), 837(vs), 792(vs), 517(m). UV–vis (aqueous-DMF)
were determined from a linear fit of Stern-Volmer equation:[45]
ꢂ1
ꢂ1
[
k
max/nm (e/M
cm )]: 284(63600), 294(61650) 324(23800).
O), 0.287 (D O).
I
0
=I ¼ 1 þ KBSA=HSA½QꢆI
0
=I ¼ 1 þ k
q
s
0
½Qꢆ
Lifetimes (
s
/ms): 0.198 (H
2
2
where the terms I
teins before and after the addition of complex concentration [Q] and
is the average lifetime of chromophore tryptophan residue of the
0
and I are the emission intensities of serum pro-
4.4. Single-Crystal X-ray structure determination
s
0
protein in free from the quencher, any possible inner-filter effect
was not considered. The equilibrium binding constant (K) of com-
plexes 1–5 with BSA and HSA proteins and the number of binding
sites available (n) per molecule of the proteins were calculated from
the intercept and slope of the linear fit of the Scatchard equation:
Suitable X-ray quality crystals were mounted and all geometric
and intensity data were collected on a Bruker SMART II diffrac-
tometer equipped with a graphite monochromator with Mo K
radiation at 100(2) K. The data integration and reduction were pro-
cessed with SAINT software,[51] and the data absorption correc-
tions were made by using Bruker SADABS program [52]. The
structures were solved by direct methods using the SHELXS pro-
gram package and refined by the full matrix least-squares method
based on F2 by using the SHELX-2017 program (Sheldrick 2017)
a
[
59] log(I
Synchronous fluorescence spectra of the complexes were
recorded using the k = 60 nm and k = 15 nm ( k = difference
0
-I)/I = log K + nlog[Q].
D
D
D
of excitation and emission wavelengths) respectively in 5 mM
Tris-HCl/NaCl between the range of 230 nm and 500 nm under
the similar condition of fluorescence quenching experiments.
[
53]. The structures were further refined and processed with the
SHELX-2017 incorporated into the Olex2 software package [54].
All non–hydrogen atoms were refined anisotropically till conver-
gence is reached. All hydrogen atoms were placed geometrically
and refined using the riding model. Some of the highly disordered
solvent molecules in 1 were removed using the solvent mask com-
mand of Olex2 software [54]. Perspective views of the complex
were obtained using ORTEP [55]. Selected crystallographic data
and structure refinement parameters for 1 was given in Table S1.
Selected bond distances and angles for all the complexes are given
in Table S2. The CCDC deposition numbers for complex 1 is
4
.7. Cellular uptake studies
HeLa, MCF-7 and H460 cancer cells were cultured in DMEM cell
culture media supplemented with 10% fetal bovine serum (FBS) in
5
% CO at 37 °C and 99% humidified incubator. The cancer cells
2
from the exponentially growing cultures were used for the cyto-
toxicity, photocytotoxicity and cellular internalization studies.
The cytotoxicity and photocytotoxicity of complexes 1 and 2 were
determined by MTT assay by employing the procedure described
earlier [20]. Ln(III) complexes 1 and 2 (20 mM) were dissolved in
the DMEM cell culture media containing 1% DMSO. The HeLa,
1
,991,342 containing supplementary crystallographic data.
4
MCF-7 and H460 cells were seeded (1 ꢅ 10 cells per well) in ster-
4.5. DNA and serum proteins binding experiments
ilized glass coverslip containing 24 well plates (13 mm, 0.2%
gelatin-coated) for 10 h. Complexes 1 and 2 were added for incuba-
tion of 4 h at 37 °C in a 5% CO -humidified incubator. Then, treated
2
cells were washed thrice with 1X PBS buffer in an interval of 5 min
to remove the debris and fixed with 4% formaldehyde solution for
DNA, BSA and HSA binding studies were carried out by employ-
ing procedure reported by us previously [20]. The DNA binding
experiments were carried out in 5 mM Tris-HCl-NaCl buffer
(
pH = 7.2) using calf thymus (CT)-DNA by absorption spectral mea-
2
0 min and subsequent removal of excess formaldehyde by 1X PBS
surement. The concentration of DNA was calculated from its
buffer. Subsequently, cell nuclei were stained with Hoechst 33258
dye for about 15 min, and the excess stain was removed by wash-
ing thrice with 1X PBS buffer. Coverslips were then mounted on
slides coated with buffered mounting medium to prevent fading
and drying. The slides were observed and fluorescence images of
the Ln(III) complexes were acquired with Carl Zeiss (LSM780NLO)
multiphoton confocal laser scanning microscopy (MCLSM) with the
inverted motorized stand (AxioObserver, Zeiss) at 40X magnifica-
tion. The emission in cellular images were collected by excitation
wavelength (kex) for Eu(ΙΙΙ) 405 nm and for Tb(ΙΙΙ) 488 nm respec-
tively. To avoid the scattering from samples and emission from the
staining dye we were applied appropriate bandpass filters for blue
ꢂ1
ꢂ1
known molar absorptivity at k260 nm (
the purity was confirmed from absorbance ratio A260/A280 (1.8–
.9) [56]. A stock solution was prepared freshly and the intrinsic
binding constant (K ) of the 1–5 were obtained from the slope to
intercept ratio of the following equation:
e260 = 6600 M cm ) and
1
b
½
DNAꢆ=ð
e
a
ꢂ
e
f
Þ ¼ ½DNAꢆ=ð
e
b
ꢂ
e
f
Þ þ 1=K
b
ðe
b
ꢂ
e
f
Þ
Where [DNA] is the concentration of DNA in the base pairs,
a, f,
e e
and where the molar extinction coefficient of the complexes cor-
e
b
responding to apparent, free and fully bound to DNA [57]. The
competitive DNA binding of complexes with ethidium bromide
EthB) was measured from the gradual addition of the complexes
to highly fluorescent CT-DNA and EthB adduct (kex = 546 nm and
em = 603 nm) in Tris-HCl/NaCl buffer (pH = 7.2). The apparent
(
(
(
blue ch1: 371–486 nm), red (red ch2: 563–739 nm) and green
green ch1: 490–544 nm) emission from Hoechst 33258, and Eu
III) and Tb(III) respectively.
(
k
binding constant of complexes with CT-DNA obtained from equa-
tion: Kapp ꢅ C50 = KEthB ꢅ [EthB], where, Kapp, the apparent binding
constant of the complex studied; C50, the [complex] at 50% quench-
ing of DNA-bound EthB emission intensity and KEthB, the binding
CRediT authorship contribution statement
Srikanth Dasari: Conceptualization, Methodology, Data cura-
tion, Validation, Writing - original draft. Swati Singh: Data cura-
tion. Zafar Abbas: Data curation, Investigation. Sri Sivakumar:
7
ꢂ1
constant of EthB (1 ꢅ 10 M ) itself and [EthB] is the concentra-
tion of EthB (12 M) used [58].
l
12

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
Data curation, Investigation. Ashis K. Patra: Supervision, Concep-
tualization, Writing - review & editing, Funding acquisition.
(c) Z. Zhu, X. Wang, T. Li, S. Aime, P.J. Sadler, Z. Guo, Angew. Chem. Int. Ed. 53
(
2014) 13225–13228.
[
17] (a) T. Zhang, C.-F. Chan, R. Lan, H. Li, N.-K. Mak, W.-K. Wong, K.-L. Wong,
Chem. Commun. 49 (2013) 7252–7254;
Declaration of Competing Interest
(b) T. Zhang, R. Lan, C.-F. Chan, G.-L. Law, W.-K. Wong, K.-L. Wong, Proc. Natl.
Acad. Sci. U. S. A. 111 (2014) E5492–E5497;
(
c) H. Li, R. Lan, C.-F. Chan, L. Jiang, L. Dai, D.W.J.K. Wong, M.H.-W. Lam, K.-L.
The authors declare that they have no known competing finan-
cial and personal relationships that could influence the work
reported herein.
Wong, Chem. Commun. 51 (2015) 14022–14025;
(d) H. Li, C. Xie, R. Lan, S. Zha, C.-F. Chan, W.-Y. Wong, K.-L. Ho, B.D. Chan, Y.
Luo, J.-X. Zhang, G.-L. Law, W.C.S. Tai, J.-C.G. Bünzli, K.-L. Wong, J. Med. Chem.
6
0 (2017) 8923–8932.
[
18] (a) P. Zhang, W. Steelant, M. Kumar, M. Scholfield, J. Am. Chem. Soc. 129
(2007) 4526–4527;
Acknowledgments
(
1
(
b) S.S. Lucky, N.M. Idris, Z. Li, K. Huang, K.C. Soo, Y. Zhang, ACS Nano 9 (2015)
91–205;
c) N.M. Idris, M.K. Gnanasammandhan, J. Zhang, P.C. Ho, R. Mahendran, Y.
We thank Science and Engineering Research Board (SERB),
Government of India (Grant No. EMR/ 2016/000521) for financial
support. S.D thanks MHRD and ZA to U.G.C. for research fellow-
ships. Thanks to Priyaranjan Kumar for fruitful discussions and
Sharad Sachan for his help and discussion in the solving crystal
structure.
Zhang, Nat. Med. 18 (2012) 1580–1585.
[
19] (a) Z. Liang, T.-H. Tsoi, C.-F. Chan, L. Dai, Y. Wu, G. Du, L. Zhu, C.-S. Lee, W.-T.
Wong, G.-L. Law, K.-L. Wong, Chem. Sci. 7 (2016) 2151–2156;
(
b) H. Li, R. Lan, C.-F. Chan, G. Bao, C. Xie, P.-H. Chu, W.C.S. Tai, S. Zha, J.X.
Zhang, K.-L. Wong, Chem. Commun. 53 (2017) 7084–7087.
[
20] (a) S. Dasari, S. Singh, S. Sivakumar, A.K. Patra, Chem. Eur. J. 22 (2016) 17387–
1
(
1
(
7396;
b) S. Dasari, S. Singh, P. Kumar, S. Sivakumar, A.K. Patra, Eur. J. Med. Chem.
63 (2019) 546–559;
c) S. Dasari, A.K. Maparu, Z. Abbas, P. Kumar, H. Birla, S. Sivakumar, A.K. Patra,
Appendix A. Supplementary material
Eur. J. Inorg. Chem. 31 (2020) 2998–3009;
(d) Z. Abbas, P. Singh, S. Dasari, S. Sivakumar, A.K. Patra, New J. Chem. 44
Supplementary Information (SI) available: Spectral characteri-
zation, additional crystallographic figures, photophysical proper-
ties, binding interaction with biological targets, cell culture,
cytotoxicity, photocytotoxicity and cell imaging figures (PDF). For
SI and crystallographic data in CIF or other electronic format see
https://doi.org/10.1016/j.saa.2021.119709.
(
2020) 15685–15697.
21] (a) A. Chandra, K. Singh, S. Singh, S. Sivakumar, A.K. Patra, Dalton Trans. 45
2016) 494–497;
[
(
(b) K. Singh, S. Singh, P. Srivastava, S. Sivakumar, A.K. Patra, Chem. Commun.
53 (2017) 6144–6147.
[
22] (a) D.J. Lewis, F. Moretta, T. Hollooway, Z. Pikramenou, Dalton Trans. 41 (2012)
1
(
3138–13146;
b) E. Debroye, S.V. Eliseeva, S. Laurent, L.V. Elst, S. Petoud, R.N. Muller, T.N.
Parac-Vogt, Eur. J. Inorg. Chem. (2013) 2629–2639;
c) A. Sebastian, M.K. Mahato, E. Prasad, Soft Matter 15 (2019) 3407–3417.
References
(
[
23] (a) G. Dehaen, P. Verwilst, S.V. Eliseeva, S. Laurent, L.V. Elst, R.N. Muller, W.M.
De Borggraeve, K. Binnemans, T.N. Parac-Vogt, Inorg. Chem. 50 (2011) 10005–
[
1] (a) P. Caravan, J.J. Ellison, T.J. McMurry, R.B. Lauffer, Chem. Rev. 99 (1999)
293–2352;
2
1
(
0014;
b) G. Dehaen, S.V. Eliseeva, P. Verwilst, S. Laurent, L.V. Elst, R.N. Muller, W.D.
Borggraeve, K. Binnemans, T.N. Parac-Vogt, Inorg. Chem. 51 (2012) 8775–
783;
c) K. Kimpe, T.N. Parac-Vogt, S. Laurent, C. Piérart, L. Vander Elst, R.N. Muller,
(
(
(
b) P. Caravan, Chem. Soc. Rev. 35 (2006) 512–523;
b) E.J. Werner, A. Datta, C.J. Jocher, K.N. Raymond, Angew. Chem. Int. Ed. 47
2008) 8568–8580.
8
(
[
2] (a) J.-C.G. Bünzli, Chem. Rev. 110 (2010) 2729–2755;
(
(
b) J.-C.G. Bünzli, S.V. Eliseeva, Chem. Sci. 4 (2013) 1939–1949;
d) J.-C.G. Bünzli, Coord. Chem. Rev. 293–294 (2015) 19–47.
K. Binnemans, Eur. J. Inorg. Chem. (2003) 3021–3027.
[
[
24] (a) K. Singh, S. Banerjee, A.K. Patra, RSC Adv. 5 (2015) 107503–107513;
[
3] (a) C.P. Montgomery, B.S. Murray, E.J. New, R. Pal, D. Parker, Acc. Chem. Res. 42
(
(
b) S. Ghosh, Z. Abbas, S. Dasari, A.K. Patra, J. Lumin. 187 (2017) 46–52;
c) K. Singh, A. Goenka, S. Ganesh, Ashis K. Patra, Eur. J. Inorg. Chem. (2018)
(
(
(
2009) 925–937;
b) E.J. New, D. Parker, D.G. Smith, J.W. Walton, Curr. Opin. Chem. Biol. 14
2010) 238–246.
3942–3951.
25] F. Wan, L. Wang, W. Xu, C. Li, Y. Li, C. Zhang, L. Jiang, Polyhedron, 145 (2018)
[
4] (a) M.C. Hefferin, L.M. Matosziuk, T.J. Meade, Chem. Rev. 114 (2014) 4496–
539;
1
6
41–146; (b) FU-X. Wan, T-K. Zhang, Y. Li, C.-C. Li, L. Jiang, J. Chil. Chem. Soc.
1 (2016) 2.
4
(
(
b) T. Gunnlaugsson, J.P. Leonard, Chem. Commun. (2005) 3114–3131;
c) A.J. Amoroso, S.J.A. Pope, Chem. Soc. Rev. 44 (2015) 4723–4742.
[
[
[
26] (a) D. Parker, K. Pulukkody, F.C. Smith, A. Batsanov, J.A.K. Howard, J. Chem. Soc.
Dalton Trans. (1994) 689–693.
27] (a) D. Parker, R.S. Dickins, H. Puschmann, C. Crossl, J.A.K. Howard, Chem. Rev.
[
5] (a) E.G. Moore, A.P.S. Samuel, K.N. Raymond, Acc. Chem. Res. 42 (2009) 542–
52;
5
102 (2002) 1977–2010.
(
(
b) M. Sy, A. Nonat, N. Hildebrandt, L.J. Charbonnière, Chem. Commun. 52
2016) 5080–5095.
28] (a) M.S. Konings, W.C. Dow, D.B. Love, K.N. Reymond, S.C. Quay, S.M. Rocklage,
Inorg. Chem. 29 (1990) 1488–1491;
[
[
[
6] R.D. Teo, J. Termini, H.B. Gray, J. Med. Chem. 59 (2016) 6012–6024.
7] V.C. Pierre, M.J. Allen, P. Caravan, J. Biol. Inorg. Chem. 19 (2014) 127–131.
8] (a) F.G. Shellock, E. Kanal, J. Magn. Reson. Imaging 10 (1999) 477–484;
(
b) S.J. Franklin, K.N. Raymond, Inorg. Chem. 33 (1994) 5794–5804.
[
29] (a) S. Aime, F. Benetollo, G. Bombieri, S. Colla, M. Fasano, S. Paoletti, Inorg.
Chim. Acta 254 (1997) 63–70;
(
b) M.E. Bartolini, J. Pekar, D.R. Chettle, F. McNeill, A. Scott, J. Sykes, F.S. Prato,
(
b) Y.-M. Wang, Y.-J. Wang, R.-S. Sheu, G.-C. Liu, W.-C. Lin, J.-H. Liao,
Polyhedron 18 (1999) 1147–1152;
c) P. Hermann, J. Kotek, V. Kubí cˇ ek, I. Lukeš, Dalton Trans. (2008) 3027–3047.
G.R. Moran, Magn. Reson. Imaging 21 (2003) 541–544;
(
(
c) M. Ceulemans, K. Nuyts, W.M. De Borggraeve, T.N. Parac-Vogt, Inorganics 3
2015) 516–533.
(
[
30] (a) M. Latva, H. Takalo, V.M. Mukkala, C. Matachescu, J.C. Rodriguez Ubis, J.
Kanakare, J. Lumin. 75 (1997) 149–169;
[
9] E. Debroye, T.N. Parac-Vogt, Chem. Soc. Rev. 43 (2014) 8178–8192.
[
10] (a) A. Louie, Chem. Rev. 110 (2010) 3146–3195;
b) L. Frullano, T.J. Meade, J. Biol. Inorg. Chem. 12 (2007) 939–949.
11] (a) S.J. Butler, L. Lamarque, R. Pal, D. Parker, Chem. Sci. 5 (2014) 1750–1756;
b) S.J. Butler, M. Delbianco, L. Lamarque, B.K. Mc Mahon, E.R. Neil, R. Pal, D.
Parker, J.W. Walton, J.M. Zwier, Dalton Trans. 44 (2015) 4791–4803.
12] (a) A. Thibon, V.C. Pierre, Anal. Bioanal. Chem. 394 (2009) 107–120.
13] (a) S. Faulkner, S.J.A. Pope, B.P. Burton-Pye, Appl. Spectrosc. Rev. 40 (2005) 1–
(
b) S.B. Meshkova, Z.M. Topilova, D.V. Bolshoy, S.V. Beltyukova, Acta. Phy. Pol.
A. 95 (1999) 983–990;
c) R. Devi, R. Boddula, J. Tagare, A.B. Kajjam, K. Singh, S. Vaidyanathan, J.
Mater. Chem. C 8 (2020) 11715–11726;
(
[
(
(
(
(
(
(
d) R. Devi, K. Singh, S. Vaidyanathan, J. Mater. Chem. C 8 (2020) 8643–8653;
e) R. Boddula, S. Vaidyanathan, Inorg. Chem. Acta 494 (2019) 141–153;
f) R. Devi, S. Vaidyanathan, Dalton Trans. 49 (2020) 6205–6219;
[
[
3
1.
g) B. Rajamouli, P. Sood, S. Giri, V. Krishnan, V. Sivakumar, Eur. J. Inorg. Chem.
[
14] (a) M. Delbianco, V. Sadovnikova, E. Bourrier, G. Mathis, L. Lamarque, J.M.
Zwier, D. Parker, Angew. Chem. Int. Ed. 53 (2014) 10718–10722;
24 (2016) 3900–3911.
[
[
31] (a) J. Andres, A.-S. Chauvin, In The rare earth elements: fundamentals and
applications; D. A. Atwood, Ed.; Wiley: New York, 2012; pp. 606 (b) J. D.
Routledge, M. W. Jones, S. Faulkner, M. Tropiano, Inorg. Chem. 54 (2015)
(
(
b) E.J. New, A. Congreve, D. Parker, Chem. Sci. 1 (2010) 111–118;
b) S. Shuvaev, M. Starck, D. Parker, Chem. Eur. J. 23 (2017) 9974–9989.
[
15] (a) S.S. Kelkar, T.M. Reineke, Bioconjugate Chem. 22 (2011) 1879–1903;
b) P. Rai, S. Mallidi, X. Zheng, R. Rahmanzadeh, Y. Mir, S. Elrington, A.
Khurshid, T. Hasan, Adv. Drug Deliv. Rev. 62 (2010) 1094–1124;
c) S. Wilhelm, A.J. Tavares, Q. Dai, S. Ohta, J. Audet, H.F. Dvorak, W.C.W. Chan,
3
337–334; (c) T. C. de Oliveira, H. P. Santos, M. G. Lahoud, D. F. Franco, R. O.
Freire, J. D. L. Dutra, A. Cuin, J. F. de Lima, L. F. Marques, J. Lumin. 181 (2017)
96–210; (d) E. M. Gomes, D. F. Franco, S. L Scarpari, M. V. Colaço, M. S.
(
1
(
Ferreira, R. O. Freire, L. F. Marques, J. Lumin. 210 (2019) 104-118.
Nat. Rev. Mater. (2016) 16014.
32] (a) G. Bobba, Y. Bretonnière, J.-C. Frias and D. Parker, Org. Biomol. Chem. 1
[
16] (a) J.L. Sessler, R.A. Miller, Biochem. Pharmacol. 59 (2000) 733–739;
(
2003) 1870–1872; (b) F. J. Steemers, W. Verboom, D. N. Reinhoudt, E. B. van
(
b) G. Thiabaud, R. McCall, G. He, J.F. Arambula, Z.H. Siddik, J.L. Sessler, Angew.
der Tol, J. W. Verhoeven, J. Am. Chem. Soc. 117 (1995) 9408–9414; (c) C. Kachi-
Chem. Int. Ed. 55 (2016) 12626–12631;
13

S. Dasari, S. Singh, Z. Abbas et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 256 (2021) 119709
Terajima, K. Yanagi, T. Kaziki, T. Kitazawaa, M. Hasegawa, Dalton Trans. 40
[46] (a) J.N. Miller, Proc. Anal. Div. Chem. Soc. 16 (1979) 203–208;
(b) Y.J. Hu, Y. Liu, Z.B. Pi, S.S. Qu, Bioorg. Med. Chem. 13 (2005) 6609–6614;
(c) J.H. Tang, F. Luan, X.G. Chen, Bioorg. Med. Chem. 49 (2006) 3210–3217.
[47] (a) J. Yu, D. Parker, R. Pal, R.A. Poole, M.J. Cann, J. Am. Chem. Soc. 128 (2006)
2294–2299;
(
2011) 2249–2256; (d) G. L. Law, T. A. Pham, J. D. Xu, K. N. Raymond, Angew.
Chem., Int. Ed. 51 (2012) 2371–2374; (e) M. D. Regulacio, M. H. Pablico, J. A.
Vasquez, P. N. Myers, S. Gentry, M. Prushan, S.-W. Tam-Chang, S. L. Stoll, Inorg.
Chem. 47 (2008) 1512ꢂ1523; (f) Z. Ahmed, K. Iftikhar, J. Phys. Chem. A, 117
(
2013) 11183ꢂ11201; (g) S. Shuvaev, V. Utochnikova, Ł. Marciniak, A.
(b) S.J. Butler, B.K. McMahon, R. Pal, D. Parker, J.W. Walton, Chem. Eur. J. 19
(2013) 9511–9517;
(c) E. Deiters, B. Song, A.-S. Chauvin, C.D.B. Vandevyver, F. Gumy, J.-C.G. Bünzli,
Chem. Eur. J. 15 (2009) 885–900.
Freidzon, I. Sinev, R. V. Deun, R. O. Freire, Y. Zubavichus, W. Grünert, N.
Kuzmina, Dalton Trans. 43 (2014) 3121–3136; (f) N. Kofod, R. Arppe-Tabbara,
T. J. Sørensen, DOI: 10.1021/acs.jpca.8b12034.
[
33] (a) J.C.G. Bünzli, A.S. Chauvin, H.K. Kim, E. Deiters, S.V. Eliseeva, Coord. Chem.
Rev. 254 (2010) 2623–2633;
[48] (a) V. Divya, M.L.P. Reddy, R. Pavithran, Dalton Trans. 42 (2013) 15249–15262;
(b) V. Divya, V. Sankar, K.G. Raghu, M.L.P. Reddy, Dalton Trans. 42 (2013)
12317–12323;
(
(
(
b) D. Parker, Coord. Chem. Rev. 205 (2000) 109–130;
c) T. Gunnlaugsson, J.P. Leonard, Chem. Commun. (2005) 3114–3131;
d) K. Sénéchal-David, A. Hemeryck, N. Tancrez, L. Toupet, J.A.G. Williams, I.
(c) T.M. George, M.S. Krishna, M.L.P. Reddy, Dalton Trans. 45 (2016) 18719–
18729.
Ledoux, J. Zyss, A. Boucekkine, J.-P. Guégan, H.L. Bozec, O. Maury, J. Am. Chem.
Soc. 128 (37) (2006) 12243–12255.
34] (a) W.D.W. Horrocks Jr., D.R. Sudnick, J. Am. Chem. Soc. 101 (1979) 334–340;
[49] (a) S. Monro, K.L. Colón, H. Yin, J. Roque, P. Konda, S. Gujar, R.P. Thummel, L.
Lilge, C.G. Cameron, S.A. McFarland, Chem. Rev. 119 (2019) 797–828;
(b) G.-L. Law, R. Pal, L.O. Palsson, D. Parker, K.-L. Wong, Chem. Commun.
(2009) 7321–7323;
[
(
b) A. Beeby, I.M. Clarkson, R.S. Dickins, S. Faulkner, D. Parker, L. Royle, A.S. de
Sousa, J.A.G. Williams, M. Woods, J. Chem. Soc. Perkin Trans. 1 (1999) 493–504.
35] (a) D.J. Lewis, P.B. Glover, M.C. Solomons, Z. Pikramenou, J. Am. Chem. Soc. 133
(c) J.-X. Zhang, H. Li, C.-F. Chan, R. Lan, W.-L. Chan, G.-L. Law, W.-K. Wong, K.-L.
Wong, Chem. Commun. 48 (2012) 9646–9648;
[
(
(
2011) 1033–1043;
(d) A. de Bettencourt-Dias, K.R. Johnson, S.B. Vittardi, M.A. Gracia-Nava, J. J.
Rack 26 (2020) 7274–7280.
b) P.B. Glover, A.P. Bassett, P. Nockemann, B.M. Kariuki, R. Van Deun, Z.
Pikramenou, Chem. Eur. J. 13 (2007) 6308–6320;
c) Y. Haas, G. Stein, E.J. Wurzburg, Chem. Phys. 60 (1974) 258–263.
36] G. Stein, E. Würzberg, J. Chem. Phys. 62 (1975) 208–213.
[50] (a) W.Y. Ng, X. Gong, W.K. Chan, Chem. Mater. 11 (1999) 1165–1170;
(b) C. Zhang, Z.-M. Huo, T.-T. Wang, H.-P. Zeng, J. Phys. Org. Chem. 25 (2012)
754–759.
(
[
[
[
37] A.C. Komor, J.K. Barton, Chem. Commun. 49 (2013) 3617–3630.
38] T.M. Kelly, A.B. Tossi, D.J. McConnell, T.C. Strekas, Nucleic Acid Res. 13 (1985)
[51] APEX2 v2012.4, Bruker AXS: Madison, WI, 1999.
[52] (a) G. M. Sheldrick, SADABS 2.0; University of Göttingen: Göttingen, Germany,
2000; (b) G. M. Sheldrick, SADABS, Area Detector Absorption Correction,
University of Göttingen, Göttingen, Germany, 2001.
[53] (a) G.M. Sheldrick, SHELXL-2014: Program for Crystal Structure Refinement,
University of Göttingen, Göttingen, Germany, 2014;
(b) G.M. Sheldrick, Acta Crystallogr. C 71 (2015) 3–8.
[54] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, OLEX2:
A complete structure solution, refinement and analysis program, J. Appl. Cryst.
42 (2009) 339–341.
[55] M.N. Burnett, C.K. Johnson, ORTEP-III, Report ORNL - 6895, Oak Ridge, TN, Oak
Ridge National Laboratory, 1996.
6
017–6034.
[
39] (a) A. Hussain, S. Gadadhar, T.K. Goswami, A.A. Karande, A.R. Chakravarty,
Dalton Trans. 41 (2012) 885–895;
(
b) A. Hussain, K. Somyajit, B. Banik, S. Banerjee, G. Nagaraju, A.R. Chakravarty,
Dalton Trans. 42 (2013) 182–195;
c) X. Liu, J. Xu, Y. Lv, W. Wu, W. Liu, Y. Tang, Dalton Trans. 42 (2013) 9840–
846;
d) X. Wang, X. Wang, S. Cui, Y. Wang, G. Chen, Z. Guo, Chem. Sci. 4 (2013)
748–3752.
(
9
(
3
[
40] (a) R. Jastrza, M. Nowak, M. Skroba n´ ska, A. Toli n´ ska, M. Zabiszak, M. Gabryel,
Ł. Marciniak, M.T. Kaczmarek, Coord. Chem. Rev. 382 (2019) 145–159;
[56] (a) J. Marmur, J. Mol. Biol. 3 (1961) 208–218;
(
b) S. Shuvaev, M. Starck, D. Parker, Chem. Eur. J. 23 (2017) 9974–9989.
(b) M.E. Reichmann, C.A. Rice, C.A. Thomas, P. Doty, J. Am. Chem. Soc. 76
(1954) 3047–3053.
[57] (a) A. Wolfe, G.H. Shimer Jr., T. Meehan, Biochemistry 26 (1987) 6392–6396;
(b) D.E.V. Schmechel, D.M. Crothers, Biopolymers 10 (1971) 465–480.
[58] (a) M. Lee, A.L. Rhodes, M.D. Wyatt, S. Forrow, J.A. Hartley, Biochemistry 32
(1993) 4237–4245;
[
41] (a) P.B. Glover, P.R. Ashton, L.J. Childs, A. Rodger, M. Kercher, R.M. Williams, L.
D. Cola, Z. Pikramenou, J. Am. Chem. Soc. 125 (2003) 9918–9919;
(
b) E.L. Crossley, J.B. Aitken, S. Vogt, H.H. Harris, L.M. Rendina, Angew. Chem.
Int. Ed. 49 (2010) 1231–1233.
[
42] (a) M.J. Waring, J. Mol. Biol. 13 (1965) 269–282;
(
b) D.L. Boger, B.E. Fink, S.R. Brunnette, W.C. Tse, M.P. Hedrick, J. Am. Chem.
(b) A.R. Morgan, J.S. Lee, D.E. Pulleyblank, N.L. Murray, D.H. Evans, Nucleic
Acids Res. 7 (1979) 547–569;
Soc. 123 (2001) 5878–5891.
[
[
43] N.S. Quiming, R.B. Vergel, M.G. Nicolas, J.A. Villanueva, J. Health Sci. 51 (2005)
(c) F.J. Meyer-Almes, D. Porschke, Biochemistry 32 (1993) 4246–4253;
(d) F.D. Abreu, T.F. Paulo, M.H. Gehlen, R.A. Ando, L.G.F. Lopes, A.C.S. Gondim,
M.A. Vasconcelos, E.H. Teixeria, E.H.S. Sousa, I.M.M. de Carvalho, Inorg. Chem.
56 (2017) 9084–9096.
8
–15.
44] (a) A. Sulkowska, J. Mol. Struct. 616 (2002) 227–232;
(b) D. Voet, Biochemistry, John Wiley & Sons, Inc, 3rd edn, 1995;
(c) J.R. Lakowicz, G. Webber, Biochemistry 12 (1973) 4161–4170;
(d) J. Ghuman, P.A. Zunszain, I. Petitpas, A.A. Bhattacharya, M. Otagiri, S. Curry,
[59] G. Scatchard, Ann. N. Y. Acad. Sci. 51 (1949) 660–672.
[60] (a) P. Qu, H. Lu, X. Ding, Y. Tao, Z. Lu, J. Mol. Struct. 920 (2009) 172–177;
(b) Y.-Q. Wang, H.-M. Zhang, Q.-H. Zhou, J. Mol. Struct. 932 (2009) 31–37;
(c) R.G. Machicote, M.E. Pacheco, L. Bruzzone, Spectrochim. Acta A 78 (2011)
1535–1539.
J. Mol. Biol. 353 (2005) 38–52.
[
45] J.R. Lakowicz, Principles of Fluorescence Spectroscopy, third ed., Springer, New
York, 2006.
14