Combination of sensor potential and antimicrobial activity of a new 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide

Article abstract of DOI:10.1016/j.molstruc.2014.04.070

A blue emitting 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide bearing a dimethylaminoethyloxy group as a receptor fragment for metal ions and protons has been designed and synthesized. The basic photophysical properties of the compound have been investigated in organic solvents of different polarity. The detection of different metal cations (Pb²⁺, Cu²⁺, Cd²⁺, Co²⁺, Zn²⁺and Mn²⁺) has been studied by fluorescence spectroscopy. Depending on pH, the new compound shows "off-on" switching from alkaline to acid media. A new complex of Cu(II) with the 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide has been synthesized and characterized. The antibiotic activity of the complex was evaluated against some bacterial and yeast cultures.

Full text of DOI:10.1016/j.molstruc.2014.04.070

Accepted Manuscript
Combination of sensor potential and antimicrobial activity of a new 4-(2-dime-
thylaminoethyloxy)-N-buthyl-1,8-naphthalimide
Desislava Staneva, Evgenia Vasileva-Tonkova, Mohamad S.I. Makki, Abdullah
M. Asiri, Ivo Grabchev
PII:
S0022-2860(14)00437-2
DOI:
http://dx.doi.org/10.1016/j.molstruc.2014.04.070
MOLSTR 20577
Reference:
Journal of Molecular Structure
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23 April 2014
23 April 2014
Please cite this article as: D. Staneva, E. Vasileva-Tonkova, M.S.I. Makki, A.M. Asiri, I. Grabchev, Combination
of sensor potential and antimicrobial activity of a new 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide,
Journal of Molecular Structure (2014), doi: http://dx.doi.org/10.1016/j.molstruc.2014.04.070
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Combination of sensor potential and antimicrobial activity of a new
4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide
Desislava Staneva1, Evgenia Vasileva-Tonkova2, Mohamad S. I. Makki3,
Abdullah M. Asiri3,4, Ivo Grabchev3,5,*
1University of Chemical Technology and Metallurgy, 1756 Sofia, Bulgaria
2Institute of Microbiology, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
3Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi
Arabia
4Center of Excellence for Advanced Materials Research (CEAMR), King Abdulaziz
University, Jeddah 21589, Saudi Arabia
5Sofia University “St. Kliment Ohridski”, Faculty of Medicine, 1407 Sofia, Bulgaria
ABSTRACT
A
blue emitting 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide bearing
a
dimethylaminoethyloxy group as a receptor fragment for metal ions and protons has been
designed and synthesized. The basic photophysical properties of the compound have been
investigated in organic solvents of different polarity. The detection of different metal cations
(Pb2+ Cu2+, Cd2+, Co2+, Zn2+and Mn2+) has been studied by fluorescence spectroscopy. Depending
on pH, the new compound shows “off-on” switching from alkaline to acid media. A new
complexe of Cu(II) with the 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide has been
synthesized and characterized. The antibiotic activity of the complex was evaluated against some
bacterial and yeast cultures.
Keywords: 1,8-naphthalimide, fluorescence, sensor, metal ions, metal complex, antibiotic
activity
Corresponding author: Ivo Grabchev; i.grabchev@chem.uni-sofia.bg
Tel: 359 2 8161319
1

Introduction
Metal ions are important part of the development of medical chemistry from many years.
Some of them have been used in the drugs and diagnostic agents to treat a variety of diseases
[1,2]. Biological important metal ions as Zn(II), Cu(II), Co(II), Fe(II) and Fe(III), play key roles
in the structural organization and activation of enzymes and biologically important compounds
[3] . The antibacterial activity of the metal complexes is highly dependent on the nature of the
metal ions and the ligands because different ligands exhibit different biological properties.
Currently there is a real need for the discovery of new compounds with antimicrobial activities.
These compounds must be more effective and possibly to act through a distinct mechanism from
those of well-known classes of antimicrobial agents to which many clinically relevant pathogens
are now resistant. Several biologically active compounds used as antimicrobial agents possess
high antibacterial activity when administered in the form of metal complexes [4-9].
1,8-Naphthalimides and their 4-substituted derivatives are well known as typical
intramolecular charge transfer chromophore which have been investigated in a large variety of
areas due to their strong absorption and emission in the visible region, high photostability and
large Stokes shift [10-19]. Recently, special attention was devoted to the photoinduced electron
transfer (PET) occurring in tailored 1,8-naphthalimide systems and the potential use of these
fluorophores as sensors for metal cations and protons [20-22]. The design of the multi-component
PET fluorescence sensors has been chosen so that the electron transfer between the fluorophore
signaling unit and the receptor results into a “switching off” of the fluorescence intensity. Due to
the presence of guests in the system (protons or alkaline, alkaline-earth, transition or heavy metal
ions capable to form a bond with the lone pair electrons of the receptor) leads to cutting-off PET
interaction and to “switching on” the fluorescence of the system [20]. On the other hand, some
1,8-naphthalimides derivatives exhibit very interesting biological and antibacterial activity [23-
29]. To our knowledge 1,8-naphthalimide metal complexes have not investigated as antimicrobial
agents.
In this paper we present the synthesis and functional properties of a new 4-(2-
dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide (NI) designed to act as a fluorescent PET
sensor. The influence of some transition metal cations on the fluorescence intensity in N,N-
2

dimethylformamide solution has been discussed. The antibiotic activity of its complex with
cuprum cations has been also investigated.
Experimental part
Material and methods
UV-Vis spectrophotometric investigations were performed using “Thermo Spectronic Unicam
UV 500” spectrophotometer. Emission spectra were taken on a “Cary Eclipse”
spectrofluorometer. All spectra were recorded using 1 cm path length synthetic quartz glass cells
(Hellma, Germany). Fluorescence quantum yield was determined on the basis of the absorption
and fluorescence spectra. All absorption and fluorescence measurements of the NI were carried
out at 10−5 mol l−1 concentration. Anthracene was used as a reference (Φst = 0.26) [30]. The effect
of the metal cations and protons upon the fluorescence intensity was examined by adding a few
µl of stock solution (c = 10−2 mol l−1) of the metal cations to a known volume of the ligand
solution (3 ml). The addition was limited to 0.08 ml, so that dilution remained insignificant [31].
CuCl2·2H2O, Pb(NO3)2·6H2O, Co(NO3)2·6H2O and Zn(NO3)2·4H2O, Cd(NO3)2·4H2O
Mn(NO3)2·4H2O were investigated as sources for metal cations. The NMR spectra were obtained
1
13
on an Oxford AS400 operating at 400 MHz and 100 MHz, for H and C, respectively. The
measurements were carried out in a CDCl3 solution at ambient temperature. The chemical shifts
were referenced to a tetramethylsilane (TMS) standard. Thin layer chromatographic (TLC)
analysis of the dyes was followed on silica gel (Fluka F60 254 20x20; 0.2 mm) using the solvent
system n-heptane/acetone (1:1) as an eluent.
In vitro antimicrobial activity assay
The synthesized complex was investigated for antibiotic activity in vitro against nine
pathogenic indicator cultures using conventional well/disc diffusion assay. The following
indicator microorganisms were used: Gram-positive bacteria Bacillus subtilis, Bacillus cereus,
Sarcina lutea and Micrococcus luteus, Gram-negative bacteria Pseudomonas aeruginosa,
Escherichia coli, Acinetobacter johnsonii and Xanthomonas oryzae, and yeast strain Candida
lipolytica. Tetracycline (30 µg/disc, 6 mm in diameter) was used as positive control for
comparison. The synthesized complex was dissolved in 5% DMSO to obtain a 0.5% stock
solution. Exponentially grown cultures were smeared onto sterile nutrient agar medium in each
3

Petri plate. Wells (6 mm in diameter) were punched in the agar medium, to which 10, 30 and 50
µl of the stock solution were added. Three replicates were maintained for each treatment. The
plates were incubated 24 h at 28 2°C, and the size of the resulting zone of inhibition, if any,
was determined.
Synthesis of 4-bromo-N-buthyl-1,8-naphthalimide
A ethanol solution (10 ml) of buthylamine (0.8 ml, 0.01 mol) was added drop wise over 3
hours to 4-bromo-naphthalic anhydride ethanol solution at vigorously stirring (50 ml solution of
2.88 g, 0.01 mol) at 75 ºC. After cooling the precipitate was filtered, washed with water, and then
dried in vacuum at 400C. Yield: 89 %
FT-IR, cm-1: 2951, 2823, 2770, 1692, 1651, 1595, 1350, 1261, 1232, 1085, 1029, 781.
1H NMR (CDCl3, δ, ppm): 8.63 (d, J=7.07 Hz, 1H-Ar), 8.53 (d, J=8.47 Hz, 1H-Ar), 8.39 (d,
J=7.55 Hz, 1H-Ar), 8.01 (d, J=7.36, 6.1 Hz, 1H-Ar), 7.82 (t, J=7.18 Hz, 1H-Ar), 4.15 (t, J=7.18
Hz, 2H), 1.69 (m, 2H) 1.43 (q, 2H), 0.98 (t, J=6.48, Hz, 3H)
13C NMR (CDCl3, δ, ppm):164.3, 133.9, 132.7, 131.9, 131.7, 130.8, 129.6, 128.7, 123.7, 123.0, 41.0,
30.8, 21.0, 14.5.
Analysis: C16H14NO2Br (332.1 g mol-1) Calculated (%): C 57.83, H 4.21, N 4.21; Found (%): C
57.79, H 4.27, N 4.18
Synthesis of 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide (NI)
A solution of (3.32 g, 0.01 mol) of 4-bromo-N-buthyl-1,8-naphthalimide and 2-(N,N’-
dimethylamino)ethanol (1.0, 0.01 mol) in 20 ml N,N-dimethylformamide was stirred at 500C in
the presence of 0.01 mol KOH for 3 hours. The process was controlled by thin-layer
chromatography and the final product was filtered off with very high yield and purity after
pouring the liquor into water. The resulting precipitate was washed with water, and then dried in
vacuum at 400C. Yield: 82 %
FT-IR, cm-1: 3071, 2958, 1692, 1650, 1595, 1457, 1350, 1159, 1030, 781.
4

1H NMR (CDCl3, δ, ppm): 8.53 (m, 3H-Ar), 7.61 (dd, J=7.5, 6.1 Hz, 1H-Ar), 6.94 (d, J=7.99 Hz,
1H-Ar), 4.34 (t, 2H,), 4.16 (t, J=6.8 Hz, 2H), 2.93 (t, 2H), 2.43 (s, 6H), 1.71 (m, 2H) 1.45 (q, 2H),
0.99 (t, J=6.83 Hz, 3H).
13C NMR (CDCl3, δ, ppm): 164.8, 164.2, 160.3, 133.6, 131.8, 129.6, 129.,126.2, 113.8, 122.7, 115.4,
106.2, 68.0,58.5, 46.6, 40.5, 30.7, 20.9, 14.4.
Analysis: C20H24N2O3 (340.05 g mol-1) Calculated (%): C 70.58, H 7.06, N 8.23; Found (%): C
70.39, H 7.10, N 8.16
Scheme 1. Chemical structure of 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide (NI)
Synthesis of [Cu(NI)(Cl)2] complex
Coper complexes of NI were prepared by mixing of NI and CuCl2•2H2O in a molar ratio of 1:2
in ethanol solution and the reaction mixture was refluxed for 3h.The completion of the reaction
was monitored by thin layer chromatography. After cooling to room temperature the solid
complexes formed were filtered, washed with ethanol (10 ml, 3 times) and finally dried under
vacuum.
FT-IR, cm-1: 3076, 2957, 1695, 1649, 1593, 1352, 1155, 1234, 777, 752,
1H NMR (CDCl3, δ, ppm): 8.71 (brs, 1H-Ar), 8.46 (bs, 2H-Ar), 7.81 (brs, 1H-Ar), 7.40 (brs, 1H-Ar),
4.64 (bs, 2H,), 4.00 (t, J=7.1 Hz, 2H), 2.93 (t, J=7.6 2H), 2.50 (s, 6H), 1.57 (t, 2H) 1.31 (q, 2H), 0.89
(t, J=6.9 Hz, 3H).
13C NMR (CDCl3, δ, ppm): 164.0, 163.3, 146.3, 133.6, 131.6, 129.4, 129.0,126.5, 123.3, 122.3,
115.0, 107.8, 63.5, 58.3, 46.8, 40.3, 30.2, 20.7, 14.4.
Analysis: C20H24N2O3CuCl2 (469.08 g mol-1) Calculated (%): C 51.17, H 5.12, N 5.97; Found
(%): C 51.26, H 5.04, N 5.89
Results and discussion
Photophysical characteristics of NI
Table 1 presents the spectral characteristics of 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-
naphthalimide (NI) under study in DMF, ethanol and acetonitrile solution: absorption (λA) and
5

fluorescence (λF) maxima, the extinction coefficient (ε), Stokes shift (νA - νF), and quantum
fluorescence yield (ΦF).
Table 1
As seen from the data in Table 1, the NI absorb in the near UV region with maxima at
λA=365-367 nm. The respective fluorescence maxima are at 427-433 nm. The molar extinction
coefficient (ε) is at 14900-16200 l mol-1 cm-1, corresponding to a S0→S1 transition.
The polarity of the organic solvents is of great importance for the photophysical properties of
NI under study and especially for the quantum fluorescence yield and Stokes shift. The Stokes
shift is a parameter, which indicates the difference in the properties and structure of the
fluorophore between the ground state S0, and the first exited state S1. The Stokes shift has been
calculated by the equation 1.
(νA - νF) = (1/λA -1/λF) x 107 cm-1,
(1)
The obtained Stokes shift values are in the 4155-4439 cm−1 region. It is seen that the
polarity of the environment do not influence on the Stokes shift values (Table 1) which is in a
good accordance with other our investigations on 1,8-naphthalimide derivatives [32,33]. The
ability of the NI molecules to emit absorbed light energy is characterized quantitatively by the
quantum yield of fluorescence ΦF. The fluorescence quantum yield has been calculated on the
basis of the absorption and fluorescence spectra using antracene as reference (Φst = 0.26)
according to equation 2.
2
Su Ast nDu
(2)
ΦF = Φst
2
Sst Au
nDst
where the ΦF is the emission quantum yield of the sample, Φst is the emission quantum yield of
the standard, Ast and Au represent the absorbance of the standard and sample at the excited
wavelength, respectively, while Sst and Su are the integrated emission band areas of the standard
6

and sample, respectively, and nst and nu is the solvent refractive index of the standard and sample,
subscripts u and s refer to the unknown and standard, respectively. As seen from Table 1, in
acetonitrile and DMF solutions the quantum yield is low, ΦF = 0.007-0.009, while in ethanol
solutions the respective quantum yield is two times higher, but retains the low value. This fact
can be explained by the photoinduced electron transfer (PET) process which is favored in polar
solvents and the fluorescence emission is lower [34].
Influence of metal cations on the fluorescence intensity of NI
The fluorescent intensity of NI as a ligand in the presence of different metal cations (Pb2+ Cu2+ ,
Cd2+, Co2+, Zn2+and Mn2+) has been investigated in acetonitrile solution. This particular solvent
has been chosen for all the spectral measurements since it has a low quantum florescent yield and
favours the PET fluorescence switch. On the other hand, acetonitrile guaranties a good solubility
of the used metal salts, ligand and the respective complexes.
The presence of metal cations in the solution the NI acts as a ligand during the interaction
between the components which is signalled by the changes in the fluorescence intensity. These
changes depend on the electronic configuration of the metal cation used.
The influence of the metal cations on the fluorescence enhancement (FE) as a qualitative
parameter is presented in Figure 1. The FE = I/Io has been determined from the ratio of
maximum fluorescence intensity I (after addition of metal cations) and minimum fluorescence
intensity Io (before metal cations addition).
Some of the metal cations (Cd2+, Co3+and Mn2+) induce a negligible enhancement of the
fluorescence intensity. Probably in the case the complex formed is instable. On the other hand,
metal cations as Pb2+, Cu3+and Zn2+ enhance the fluorescence intensity. The highest values have
been observed in the presence of Cu2+ cations (FE = 51.5).
Figure 1
Figure 2 plots as an example the changes in the fluorescent intensity of the NI (c = 1x10-
5mol l-1) in acetonitrile solutions as a function of the concentration of Cu2+ cations. Free of metal
cations NI has a very weak fluorescence emission. A pronounced increase in the fluorescence
7

intensity has been observed by increasing the concentration of Cu2+ cations up to 2.0x10-4 mol l-1
(Figure 2). Above this concentration the change in the fluorescence intensity is negligible. The
fluorescence titration profile shows that a linear curve appears (R=0.99865) in the 0.5x10-5 –
10x10-5 mol l-1 concentration range of Cu2+ cations (Inset to Figure 2). A detection limit of 0.05
x10-5 mol l-1 for Cu2+ has been determined. Such a linear curve and a detection limit are sufficient
enough to sense and determined Cu2+ ions.
Figure 2.
The fluorescence characteristics obtained for NI in acetonitrile solution in the presence of metal
cations under study are collected in Table 2. It is seen that during the complexation the position
of the fluorescence maximum does not change significantly. The Pb2+, Cu3+and Zn2+ metal
cations induce a small hypsochromic shift in the fluorescence maxima (∆λF = 3-4) indicating a
possible interaction between NI and the metal cations [32,33]. On the other hand, the
fluorescence quantum yield is improved from .F = 0.007 to .F = 0.347 when Cu2+ cations are
added. The respective increase in the fluorescence depends on the nature of the metal cations
used. We suppose the higher quantum yield in the case to be on account of the better coordination
ability of Cu2+ cations as well as because of the stabilized coplanar system of the complex
formed.
Table 2.
Effect of protons on the NI fluorescence intensity
Figure 3 presents the pH dependence of NI fluorescence intensity in an ethanol/water solution
(1:4). As seen, the fluorescence intensity depends strongly on pH values in the 3.5-11.0 pH
region. The results show that the protonation of the tertiary amino group from 2-
dimethylaminoethyloxy substituent at C-4 position increases the florescence intensity, which
demonstrates the high sensitivity to proton concentration. As Figure 3 reveals, the constant value
of the fluorescence intensity which is observed up to pH = 7.5 decreases strongly and at values
higher than pH 9.6 the curve forms again a plateau of a weak fluorescence. A 15 fold
fluorescence quenching is observed from the acidic and neutral medium to the basic pH = 10.2.
8

The pH dependence of the fluorescence intensity has been analyzed using equation (3).
pH-pKa =log(IFmax-IF)/(IF-IFmin
)
(3)
The calculated value pKa = 8.32. This value is similar to that of the other 1,8-naphthalimide with
the same receptor fragment in the fluorophores structure (pKa = 8.40) [32]. Both values are
higher, if compared to those of the bis-4-(2-dimethylaminoethyl oxy)-1,8-naphthalimide whose
pKa = 7.61 [35].
Figure 3.
The change in the fluorescent spectra of NI in the pH range of 5 ÷ 10.2 is shown in Figure 4.
Enhancement of the fluorescence emission was observed in an acidic environment when
compared with that at pH = 10.2. It is also seen a slightly hypochromic shift of the fluorescence
maximum with 6 nm during the transition from an alkaline to an acidic media.
Figure 4.
Preparation of [Cu(NI)(Cl)2] complex
A copper complex of NI is obtained by mixing with copper chloride in an ethanol solution and
the reaction system was refluxed for 3 hours. Thus obtained copper complex was studied by
NMR, FTIR, UV-Vis and fluorescent spectroscopy and elemental analysis. The results of
elemental analysis showed that the complex was prepared in a 1:1 stoichiometry. FTIR spectral
characteristics of NI as a ligand and its cuprum complex are presented in Table 3 and Figure 5.
The FT-IR stretching frequencies of free ligand were compared with that of [Cu(NI)Cl2].
Table 3.
Symmetrical and asymmetrical oscillations of C = O band are at 1649-1650 cm-1 and at 1692-
1695 cm-1, respectively, which values are common for other 1,8-naphtjhalimide derivatives with
an alkoxy substituent at C-4 position of the 1,8-naphthalimide structure [36]. The comparison of
those data with the data obtained for [Cu(NI)Cl2] show a slight change in the positions of the
characteristic bands though there is only a change in the intensity of the bands in this region,
9

indicating non-participation of the coordination of C=O with cuprum ions (Figure 5A). The
results show that the polarity of both 1,8-naphthalimide chromophoric systems are different. The
absorption bands in the 1350-1352 cm-1 region are characteristic for the imide (C-N-C) bonds in
the 1,8-naphthalimide structure. The infrared frequencies at 1159-1232cm-1 are assigned to C-N
bonds. The characteristic vibrations of C-O-C bond for the free NI are at 1030 cm-1 and 1233 cm-
1. In the spectrum of the [Cu(NI)Cl2], a decrease of the band intensity at 1233 has been observed
as well as a disappearance of the band at 1030 cm-1 (Figure 5B). This result indicates that the
ether oxygen atom participates in the formation of a complex with the copper ions. The suggested
structure of [Cu(NI)Cl2] complex is presented in Scheme 2.
Figure 5.
Scheme 2.
Absorption and fluorescence spectra of NI and its [Cu(NI)Cl2] complex was recorded in
acetonitrile solution with concentration c = 10-5 mol l-1 at room temperature. As seen from Figure
6A plotting both spectra, the absorption maximum of the cuprum complex is shifted
hypsochromicaly with 8 nm. But more interesting fact has been observed in the visible spectral
region, where it occurs with a small peak with maximum at 464 nm. Probably this insignificant
absorption in the visible region is due to the complex formed and the change the polarization of
the 1,8-naphthalimide chromophoric system. The formation of the complex causes the
enhancement of the fluorescence intensity, without any change of the position of fluorescence
peak (Figure 6B).
Figure 6.
Antibiotic activity
The synthesized [Cu(NI)Cl2] complex has been investigated in vitro for its antibiotic
activity against eight bacterial and one yeast culture. The complex inhibited the growth of all
tested indicator cultures; applied in 30 and 50 µl, it showed good or better zones of inhibition
against most indicator cultures compared with standard (Figure 7). The highest inhibition activity
was observed against X. oryzae and A. johnsonii (zones 40 and 38 mm in diameter, respectively),
followed by P. aeruginosa, B. subtilis, B. cereus and S. lutea (zones in the range 29 - 30 mm)
(Figure 8). The lowest inhibitory activity of the compound has been observed against E. coli
10

(inhibition zone 17 mm). The complex showed good inhibition zone against yeasts C. lipolytica
(inhibition zone 25 mm). Therefore, the newly synthesized complex could be used in designing
new effective antimicrobial preparations. The antibiotic activity of the complex against
phytopathogenic X. oryzae opens a perspective for future application in the agriculture for plant
protection.
Figure 7.
Figure 8.
Conclusions
In this paper we described the synthesis and characterization of a new 4-(2-
dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide. Its photophysical properties have been
investigated in three organic solvents. The dependence of the fluorescence intensity on the
presence of different metal cations (Pb2+, Cu2+, Cd2+, Co2+, Zn2+and Mn2+) and protons has been
investigated in an acetonitrile solution. The results showed that the new 1,8-naphthahlimide can
detect metal cations in the concentration range from 0.5x10-5 – 10x10-5 mol l-1. The detection is
realized via the quenching of photoinduced electron transfer processes occurring in the
chromiphore system. A cuprum complex of 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-
naphthalimide has been synthesized and characterized. The synthesized [Cu(NI)Cl2] complex has
been investigated in vitro for antibiotic activity against eight bacterial and one yeast cultures. The
complex demonstrated inhibitory activity against all indicator cultures producing the best effect
against X. oryzae and A. johnsonii.
Acknowledgement
This paper was funded by the Deanship of Scientific Research (DSR), King Abdulaziz
University, under grant No. 17-130-35-HiCi. The authors, therefore, acknowledge with thanks
DSR technical and financial support.
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13

60
50
40
30
20
10
0
Mn2+
Pb2+
Co2+
Zn2+
Cu2+
Cd2+
none
Figure 1. Fluorescence enhancement factor (FE) of NI (c = 1x10−5 mol l−1) in the presence of
different metal cations (c = 1 x 10−4 mol l−1) in acetonitrile solutions.
14

70
60
50
40
30
20
10
0
60
40
20
0
R = 0.99867
0
2
4
6
8
10
[Cu2+] x10-5 mol l-1
0
4
8
12
16
20
[Cu2+] x10-5 mol l-1
Figure 2. Variation of the fluorescence intensity of NI (c = 1x10-5 mol l-1) as a function of
cuprum cation concentrations. The insert shows the linear curve fluorescence intensity and Cu2+
cation concentrations.
15

160
120
80
40
0
pKa = 8.32
4
6
8
10
pH
Figure 3. The influence of pH upon the fluorescence intensity of NI in ethanol-water solution
(1:4, v/v)
16

160
120
80
40
0
pH = 5.0
pH = 10.2
400
450
500
550
600
Wavelength / nm
Figure 4. Fluorescence spectra of NI in ethanol-water solution (1:4, v/v) at different pH values
17

100
95
90
85
80
75
70
65
60
AS
ν
C=O
νSC=O
NI
A
[Cu(NI)Cl ]
2
1800
1750
1700
1650
1600
1550
1500
-1
Wavenumber / cm
100
95
90
85
80
75
70
B
νC-N-C
as
νsC-O-C
ν
C-O-C
NI
[Cu(NI)Cl ]
2
1250
1200
1150
1100
1050
1000
-1
Wavenumber / cm
Figure 5. Infrared spectra of solid NI and [Cu(NI)Cl2]
18

0.25
0.20
0.15
0.10
0.05
0.00
NI
A
Cu(NI)Cl
2
300
350
400
450
500
550
Wavelength / nm
300
250
200
150
100
50
NI
B
Cu(NI)Cl
2
0
400
450
500
550
600
Wavelength / nm
Figure 6. Absorption (A) and Fluorescence (B) spectra of NI and [Cu(NI)Cl2] in acetonitrile
solution.
19

Figure 7. Growth inhibition of some of the tested indicator cultures by the synthesized complex
(10 and 30 µL). T, Tetracycline (30 µg/disc)
20

50
45
40
35
30
25
20
15
10
5
10 µL
30 µL
50 µL
Tetracycline
0
Figure 8. Zones of inhibition of the tested indicator cultures caused by the [Cu(NI)Cl2] complex
21

Graphical abstract
70
60
50
40
30
20
10
0
Cl
Cu
Cl
O
O
N
N
O
400
450
500
550
600
Wavelength / nm
22

Highlights
• The synthesis and functional properties of a blue fluorescent 4-(2-
dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide as sensor for metal ions and
protons have been described.
• A cuprum complex of 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide has
been synthesized and characterized.
• The antibacterial activity of [Cu(NI)Cl2] complex demonstrated inhibitory activity
against all indicator cultures producing the best effect against X. oryzae and A.
johnsonii.
23

Scheme 1. Chemical structure of 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide (NI)
24

Scheme 2. Suggested structure of [Cu(NI)Cl2] complex
25

Table 1. Photophysical characteristics of NI in organic solvents with different polarity
λA
nm
λF
l mol -1 cm-1 nm
νA - νF
cm-1
ΦF
ε
Organic solution
Acetonitrile
DMF
Ethanol
364
367
366
15300
16200
14900
434
433
437
4355
4153
4439
0.007
0.009
0.018
26

Table 2. Fluorescence characteristics of NI in acetonitrile in the presence of metal cations
Metal cations
free
λF / nm ∆λF / nm
ΦF
434
432
431
430
433
434
434
432
-
0.007
0.133
0.189
0.347
0.035
0.008
0.008
0.035
Zn2+
2
3
4
3
0
0
2
Pb2+
Cu2+
Mn3+
Ni2
Co2+
Cd2+
27

Table 3. Infrared spectra of 4-(2-dimethylaminoethyloxy)-N-buthyl-1,8-naphthalimide and its
complex [Cu(NI)Cl2]
NI
3071
[Cu(NI)Cl2]
3076
νC-H
arom
νCH2
aliph
νAS
2958
2874
1692
1650
1624
1595
1457
1233
1030
2957
2733
1695
1649
1593
C=O
νS
C=O
νC=C
arom
1458
1234
1029
νCH2 aliph
νCOC
1350
1159
874
1352
1155
840
777
752
νCNC
δC-H
arom
781
28