A fluorescent combinatorial logic gate with Na+, H+-enabled or and H+-driven low-medium-high ternary logic functions

Article abstract of DOI:10.1039/c7ob01828b

A novel fluorescent molecular logic gate with a 'fluorophore-spacer₁-receptor₁-spacer₂-receptor₂' format is demonstrated in 1:1 (v/v) methanol/water. The molecule consists of an anthracene fluorophore, and terti

Full text of DOI:10.1039/c7ob01828b

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+
+
A fluorescent combinatorial logic gate with Na /H -
+
enabled OR and H -driven low-medium-high ternary
Ccite this: DOI: 10.1039/x0xx00000x
logic functions
Received 00th January 2012,
Accepted 00th January 2012
Jasmine M. A. Spiteri, Carl J. Mallia, Glenn J. Scerri and David C. Magri*
DOI: 10.1039/x0xx00000x
www.rsc.org/chemcomm
A novel fluorescent molecular logic gate with a ‘fluorophore–spacer –receptor –spacer –receptor2’
1
1
2
format is demonstrated in 1:1 (v/v) methanol/water. The molecule consists of an anthracene
fluorophore, and tertiary alkyl amine and ꢀ(2ꢀmethoxyphenyl)azaꢀ15ꢀcrownꢀ5 ether receptors. In
N
+
+
the presence of threshold concentrations of H and Na , the molecule switches ‘on’ as an AND
logic gate with a fluorescence quantum yield of 0.21 with proton and sodium binding constants of
log βH+ = 9.0 and log βNa+ = 3.2, respectively. At higher proton levels, protonation also occurs at
+
+
the azaꢀ15ꢀcrownꢀ5 ether with a log βH+ = 4.2, which allows for Na /H ꢀenabled OR (OR + AND
+
circuit) and H ꢀdriven ternary logic functions. The reported molecule is compared and contrasted to
+
+
classic anthraceneꢀbased Na and H logic gates. We propose that such logicꢀbased molecules could
+
+
be useful tools for probing the vicinity of Na /H antiporters in biological systems.
Dedicated to Anthony W. Czarnik and A. Prasanna de Silva for their pioneering work in the fields
of Fluorescent Chemosensors and Molecular Logic.
Introduction
Two decades later, the field of chemosensors and molecular
7
logic gates continues to blossom. A themed focus nowadays is on
1
8,9
The field of molecular logicꢀbased computation sprouted with the finding realꢀlife applications for this once curiosityꢀdriven field.
first report of a molecular AND logic gate by de Silva and coꢀ Notwithstanding much creativity and innovation within the
2
+
+
workers in 1993. The molecule was designed according to a discipline, molecular logic gates for Na and H continue to attract
3
10
‘fluorophore–spacer –receptor –spacer –receptor ’ format.
An attention. For instance, Ozlem and Akkaya proposed a BOPIDYꢀ
1
1
2
2
+
anthracene fluorophore was connected by a methylene spacer to a based AND logic gate for singlet oxygen generation with Na and
tertiary amine for binding H , which was connected by a second H inputs, as a selective way of targeting tumor cells, which have
methylene spacer to a benzoꢀ15ꢀcrownꢀ5 ether for binding Na . higher intracellular levels of Na and H than normal healthy cells.
Concurrently, another visionary, Tony Czarnik, was setting the Benzoꢀ15ꢀcrownꢀ5 ether once again featured as the Na receptor due
+
+
11
+
+
+
+
groundwork for the future development of fluorescent anthraceneꢀ to its commercial availability and synthetic convenience. The
4
based chemosensors for metal ions and polyanions in water,
authors were admirably humble in acknowledging the limitations of
5
envisioning the detection of analyte congregations, and rallying their proofꢀofꢀconcept: threshold acidity and ion concentrations too
6
chemists and biologists to work together.
high for biological application, poor selectivity of the benzoꢀ15ꢀ
+
+
crownꢀ5 ether for Na over K , and demonstration in acetonitrile
rather than in water due to solubility issues.
Department of Chemistry, Faculty of Science, University of Malta, Msida,
We wish to propose that another realm of potential practicality
+
+
MSD 2080, Malta. Email: david.magri@um.edu.mt; Website: for Na /H logic gates could be as fluorescent probes for
+
+
https://www.um.edu.mt/profile/davidmagri
Electronic Supplementary Information (ESI) available: Synthetic and antiporters. Na /H antiporters are ubiquitous membrane proteins
experimental details, UVꢀvis absorption spectra, NMR, IR and mass spectra. found in living organisms. They are central to maintaining the
investigating biological membrane interfaces and Na /H
10b
+
+
†
1
2
See DOI: 10.1039/c000000x/
homeostasis of cells with respect to these two common ions.
NhaA, the key antiporter of the bacterium Escherichia coli, is
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DOI: 10.1039/C B0182
Jou7Ornal Na8Bme
+
13
believed to regulate the cytoplasmic pH and Na levels. For every dichloroethane (DCE) gave 1 as a yellow oil after column
+
+
Na exported into the cytoplasm, two H are imported into the chromatography in 40% yield.
periplasm of the cell. Interestingly, the current model of thinking Prior to carrying out the experimental wet chemistry, we
suggests that Na and H compete for the same binding site within performed some key calculations. The first set was regarding the
+
+
1
4
the transport protein. Furthermore, NhaA shows a bellꢀshaped solubility properties. The octanolꢀwater partition coefficient (log P)
19
acidicꢀalkaline pH profile, which is reminiscent of ternary offꢀonꢀoff was predicted to be 5.1 ± 0.6. Attempts at measuring log P
15
logic. Below pH 6.5 NhaA is inactive. At pH 8.5 a conformational experimentally by the shake flask method proved unsuccessful
20
change results in a dramatic increase in the sodium flux. Higher pH confirming 1 is indeed hydrophobic. A calculation considering
1
4
+
retards NhaA activity.
1+H at pH 5.0 based on an average literature pK of 7.7, from
a
19,21
Herein we report the synthesis and characterisation of a novel waterꢀsoluble anthracene models,
fluorescent combinatorial logic gate that functions as a Na /H ꢀ equation 1. Consequently, we settled on a compromise of studying 1
enabled OR logic gate and H ꢀdriven ternary logic system in in 1:1 (v/v) methanol/water.
predicted a log D of 2.4 by
+
+
+
aqueous methanol. Molecule 1 is designed with a ‘fluorophore–
(
pK − pH)
a
spacer –receptor –spacer –receptor ’ arrangement and consists of
log D = log P + log[1/(1 + 10
)]
(1)
1
1
2
2
an anthracene fluorophore, a tertiary alkyl amine and a Nꢀ(2ꢀ
methoxyphenyl)azaꢀ15ꢀcrownꢀ5 ether receptor, respectively
Scheme 1). Although synthetically more demanding, the more electron transfer (PET) thermodynamics by the Weller equation.
The second set of calculations was regarding the photoinduced
2
2
(
1
6
selective Nꢀ(2ꢀmethoxyphenyl)azaꢀ15ꢀcrownꢀ5 was chosen as the The estimated driving forces for PET from the tertiary amine and the
+
+
17
Na ionophore due to its reputation for selective Na sensing, most anilinic amine are −0.16 eV and −0.86 eV, respectively, suggesting
1
8
notably in blood serum analysis.
PET is readily feasible in both cases. The greater driving force for
Scheme 1 Synthesis of molecular logic gate 1.
the anilinic nitrogen atom is a definite advantage as the separation
distance between the azaꢀcrown receptor donor and the fluorophore
is two carbonꢀcarbon bonds greater compared to the distance from
the tertiary alkyl amine.
Results and discussion
The UVꢀvisible absorption spectra of 10− M 1 exhibits three
5
The synthesis of
1
was achieved using 4ꢀformylꢀ2ꢀ
1
8
methoxyphenylazaꢀ15ꢀcrownꢀ5 ether 5 (Scheme 1). Compound 5 characteristic anthracenic absorption bands at 346 nm, 365 nm and
was obtained starting from oꢀanisidine 2 and excess 2ꢀchloroethanol 387 nm with molar extinction coefficients of 19000 L mol cm ,
in a suspension of potassium carbonate yielding N,Nꢀbis(2ꢀ 19500 L mol cm , and 15000 L mol cm , respectively. The
hydroxylethyl)ꢀ2ꢀmethoxyaniline 3 as a green oil in 88% yield. The spectra are essentially unchanged with no new bands observed on
−1
−1
−1
−1
−1
−1
2
ꢀmethoxyphenylazaꢀ15ꢀcrownꢀ5 macrocycle 4 was obtained as a titration with methanesulfonic acid or sodium methanesulfonate (Fig.
yellow oil in 20% yield by reacting with 1,2ꢀbis(2ꢀ S1). This negative result was welcomed as it confirmed that 1
3
chloroethoxy)ethane in the presence of NaOH and NaClO , the latter behaves as an ideal PET chemosensor with the fluorophore and
4
as a template agent. A VilsmeierꢀHaack reaction with DMF and receptors electronically isolated from one another by the methylene
3
phosphorus oxychloride provided 5 as a brownishꢀorange oil in 30% spacers.
yield. Finally, reductive amination of
5
with (Nꢀ
Fig.1 illustrates the fluorescence response of solutions of 1 in 1:1
methyl)aminomethylanthracene using NaB(OAc) H in 1,2ꢀ (v/v) MeOH/H O according to four input conditions. On addition of
3
2
−7
+
+
1
0
M H and 0.10 M Na a blue fluorescence is observed (Fig. 1
2
| J. Name., 2012, 00, 1-3
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DOI: 10.1039/C7OB01828B
Fig. 2 Fluorescent emission spectra of 5.0 ꢀM 1 in 1:1 (v/v) methanol/water
upon titrating with methanesulfonic acid between pH 3ꢀ12 excited at 365 nm.
Fig. 1 Visual demonstration of the ‘off’ and ‘on’ states of 5.0 ꢀM 1 in 1:1
−
12
+
+
(
v/v) methanol/water according to AND logic (top): (A) 10 M H , no Na
−
12
+
+
−7
+
+
−7
added (B) 10 M H , 0.10 M Na (C) 10 M H , no Na added (D) 10
M
+
+
−12
+
+
H , 0.10 M Na ; Enabled OR logic (bottom): (A) 10 M H , no Na added
B) 10− M H , 0.10 M Na (C) 10 M H , no Na added (D) 0.10 M Na
12
+
+
−3
+
+
+
(
and 10− M H .
3
+
AND, vial D). At these conditions, protonation occurs at the tertiary
+
amine and complexation of Na occurs at the azaꢀcrown ether in
accordance to an AND logic function. The absence of threshold
+
+
+
+
concentrations of H or Na or both H and Na results in no
fluorescence (Fig. 1 AND, vials B, C and A, respectively). Low
−12
+
proton concentration was taken as 10 M H by addition of 0.10 M
Bu NOH solution, while low Na was taken as the absence of added
sodium ion. When the threshold concentration of H is increased to
M H independent of the Na levels a blue fluorescence was
also observed. Hence, with the threshold conditions set at 10 M H
and 0.10 M Na 1 behaves as an enabled OR logic gate (Fig. 1,
Enabled OR, vials C&D).
+
+
4
Fig. 3 Fluorescence intensity of 5.0 ꢀM 1 as a function of H (in the presence
+
+
of 0.10 M Na ) observed at 435 nm in 1:1 (v/v) methanol/water excited at 365
−3
+
+
1
0
nm.
−3
+
+
23
lowꢀmediumꢀhigh with a 20ꢀfold fluorescence enhancement. The
truth tables and fluorescence quantum yields are given in Table 1.
Threeꢀinput enable OR logic arrays have precedence in the
literature including Balzani’s example using light or micelles as
Given that logic gate 1 is able to bind protons at two different
+
+
sites, the H binding constants (and the Na binding constant) were
determined by fluorimetric titration in 1:1 (v/v) methanol/water.
Fluorescent spectroscopic titrations were performed for each
chemical input in the presence of analyte concentrations that saturate
the other receptor. The ion binding constants were determined from
24,25
−
inputs.
Lehn’s bidentate 2ꢀpyridylꢀ4ꢀpyrimidine uses OH and
2+
2+
26
various metal cations including Zn or Pb as inputs. Martίnezꢀ
Máñez’s functionalised diazacrown ether with anthracene and
ferrocene would give an increased fluorescence on high H or Cu
+
2+
intensity I ꢀpM profiles according to equation 2
27
F
levels and oxidation of ferrocene.
+
+
a
log[(IFmax
−
IF)/ (IF
−
IFmin)] =
−
log[M ]
−
log βM
(2)
Table 1. Truth table for logic gate 1 in 1:1 (v/v) methanol/water.
+
+
+
+
where pM = −log[M ] and M is either H or Na . From the I ꢀpM
F
+
titrations, the binding constant βM was determined as the
concentration at which half the receptor population is occupied by
the specific analyte. A sigmoidalꢀshaped curve was observed on
+
titration with Na over two logarithm units with a pβNa+ of 3.2.
Fluorescent emission spectra of 1 in 1:1 (v/v) MeOH/H O as a
2
a
b
+
−7
−3
function of pH are shown in Fig. 2. Peak maxima are observed at
5.0 ꢀM 1 excited at 365 nm. High H level 10 M for AND logic and 10
−12 +
+
4
14 nm, 440 nm and 463 nm. Titrations with H exhibited a pH M for enabled OR logic with CH
3
SO
3
H. Low input level at 10 M H by
c +
additional 0.1 M Bu
4
NOH solution (25% wt. in H
2
O) High Na level 0.10
M. Low Na level is no sodium ions added. Quantum yields measured with
reference to anthracene in aerated ethanol ( = 0.27). High threshold level
concentration resulting from sequential protonation of the tertiary set at ΦF ≥ 0.10.
alkyl amine and the azaꢀcrown ether with p H+
of 9.0 and 4.2,
profile with three plateau regions reminiscent of a staircase pattern
+
d
+
(
Fig. 3). The fluorescence intensity increases with increasing H
Φ
F
β
respectively. This stepꢀlike pH profile fits ternary logic according to
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Jou7Ornal Na8Bme
Table 2 summarises the fluorescence quantum yields (Φf) and case of 1 and 7. The CH NMe moiety has a Hammett σ = 0.01
2
2
p
+
+
+
Na and H binding constants for the anthraceneꢀbased logic gates 6- whereas on protonation the CH NH Me group has a Hammett σ =
2
2
p
30
8
(Fig. 4). Each of these logic gates is endowed with a different 0.43. So in effect the combination of the dimethylamino and
logic function: 6 is a Na ꢀdriven YES gate, 7 is a Na /H ꢀdriven methylene groups act as 'receptor' and 'spacer' when unprotonated,
AND gate, and 8 is a Na /H ꢀdriven OR gate. Our novel logic gate 1 but on protonation the 'spacerꢀreceptor' relationship is no longer
is a hybrid of 7 and 8 integrating AND and OR functions within the ideal because of an electric field effect transmitted across the short
same molecule, which sums up to an enabled OR logic circuit. The distance. Hence, the Φf of 0.21 for 1 results from a cooperative
compiled data for 6-8 are from published literature sources in contribution of no PET quenching and enhanced inductive/field
+
+
+
+
+
3
1
2,16a, 28
32
methanol or aqueous alcoholic solution.
effects. In comparison, the Φf of 1 is in agreement with the value of
The physiochemical comparison of 6-8 and 1 starts with the 6. The presence of an aqueous environment tends to lower the
primary standards, anthracene, 9ꢀmethylanthracene and 9ꢀ binding constant of the crown ether and the emission quantum yield.
cyanoanthracene, as representative PASS 1 logic gates withΦf of The lower Φf of 7 is due to a residual PET from the benzoꢀ15ꢀ
+
0
.27, 0.33, 0.80 in aerated ethanol or methanol solution, crownꢀ5 to the excited anthracene as a consequence of the Na ion
29
respectively. Compound 6 has a maximum Φf of 0.22, which is not adequately lowering the HOMO level of the benzoꢀ15ꢀcrownꢀ5
33
comparable to anthracene, but less than 9ꢀcyanoanthracene. The ether receptor.
similarity in the Φf between 1 and 6 is rather fortuitous given that the
solvent conditions and crown ether are different. The reported value group
2ꢀMethoxyphenylazaꢀ15ꢀcrownꢀ5 is being used by other research
+
to
develop
selective
Na
chemosensors.
7ꢀ
of 0.38 for 8 is significantly higher. In the case of 6 and 7, the CN diethylaminocoumarin conjugates were reported with pK s of 4.9
a
3
0
16b
moiety with a Hammett σ = 0.66 is required to lower the LUMO and 4.6 and K s of 120 mM and 260 mM in water. No relative
p
d
+
energy of the anthracene fluorophore for PET to be feasible. By quantum yields were reported; however, the Na ꢀinduced fluorescent
contrast, the CN moiety is not required in 8 and 1 due to the more enhancement factors ranged from 2.5 to 5.0. Most recently, an
favourable electronꢀdonating properties of Nꢀ(2ꢀmethoxyphenyl)azaꢀ analogous fluorescent BODIPY chemosensor was tested in
34
1
eV).
5ꢀcrownꢀ5 (E = 0.45 eV) versus 15ꢀbenzoꢀ5ꢀcrown (EOX = 1.30 polyurethane hydrogels. In hydrogel D1 (70% water) the Φf in the
OX
10a
+
+
presence of either 1 M Na or 0.1 M H was 0.23 or 0.86,
+
respectively. Binding of Na occurred with an apparent pK of 3.03
a
and a fluorescent enhancement factor of 12. These latter values are
in good agreement with 1 taking into account the variation in the
molecular structure and microenvironment (refer to Table 2).
Conclusions
We have designed and synthesised
a novel fluorescent
combinatorial logic gate with the Boolean ‘sumꢀofꢀproducts’
algebraic expression A+B•C. The molecular device emulates
characteristics of multiꢀvalued logic and enabled OR logic. We
envision that fluorescent molecular logic gates with carefully
adapted properties could be useful tools for exploring the vicinity
and mechanism of action of various types of antiporters in biological
systems.
Fig 4. Anthraceneꢀbased logic gates 6-8 and 1.
Table 2 Fluorescence quantum yields and binding constants of logic
gates 6-8 and 1 in alcohol or aqueous methanol.
Experimental
a
b
c
A list of chemicals and instrumentation are provided in the electronic
Parameters
Solvent
6
7
8
1
supplementary information (ESI). The synthesis of
1 from
MeOH
0.22
3.0
MeOH/2ꢀPrOH
MeOH/H
0.38
2
O
MeOH/H
2
O
Φ
Fmax
0.068
2.6
0.21
3.2
commercially available oꢀanisidine is shown in Scheme 1.
Compounds 3-5 were synthesised using a literature procedure at
+
2.5
−
log
log
β
Na
d
+
−
4.5
5.3
4.2, 9.0
18,34
−
β
H
reduced quantities and gave correct spectral and analytical data.
The synthesis and characterisation data of 1 are given below.
Quantum yields correspond to maximum values in the presence of excess
+
protons and/or sodium cations. (a) Ref. 28. (b) Ref. 2. (c) Ref. 16a. (d) p
of 4.2 and 9.0 are for the anilinic and tertiary alkyl amine, respectively.
β
H
1
-(anthracen-9-yl)-N-(3-methoxy-4-(1,4,7,10-tetraoxa-13-aza
cyclopentadecan-13-yl)benzyl)-N-methylmethanamine (1)
In a 100 mL roundꢀbottom flask (Nꢀmethyl)aminomethyl anthracene
1.1 g, 5.0 mmol), 5 (1.6 g, 4.5 mmol), sodium triacetoxy
(
Furthermore, an inductive effect contributes to enhance the PET
rate from the azaꢀcrown on protonation of the tertiary amine in the
borohydride (1.7 g, 7.6 mmol) and three drops of glacial acetic acid
were dissolved in 14 mL of dried 1,2ꢀdichloroethane in the presence
4
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P. de Silva, J. Am. Chem. Soc., 2005, 127, 8920; (c) D. C. Magri, G. D.
Coen, R. L. Boyd and A. P. de Silva, Anal. Chim. Acta., 2006, 568, 156;
of cylindrical 4Å molecular sieves. The solution was stirred at room
temperature for 96 hours, filtered and diluted with CH Cl . The
2
2
(d) S. Uchiyama, G. D. McClean, K. Iwai, and A. P. de Silva, J. Am.
organic layer was dried over anhydrous MgSO , filtered and the
Chem. Soc., 2005, 127, 8920; (e) D. C. Magri, M. Camilleri Fava and C.
J. Mallia, Chem. Commun., 2014, 50, 1009.
S. Ozlem and E. U. Akkaya, J. Am. Chem. Soc., 2009, 131, 48.
C. Hunte, E. Screpanti, M. Venturi, A. Rimon, E. Padan and H. Michel,
Nature, 2005, 435, 1197.
4
solvent removed by rotary evaporator. Purification by column
chromatography on alumina (gradient eluent hexanes to 1:3
hexanes/ethyl acetate) gave a yellow gum 1 (0.81 g, 40% yield): Rf
1
1
1
2
(
alumina, hexanes)
=
0.10, Rf (silica, hexanes)
=
0.30. 13 E. Padan, M. Venturi, Y. Gerchman and N. Dover, Biochim. Biophys.
Acta., 2001, 1505, 144.
Recrystallisation from methanol gave a yellow powder: m.p. 172ꢀ
74 °C; H NMR (500 MHz, CDCl , ppm): δ 2.26 (s, 3H, ꢀNCH ),
3 3
1
4
Y. Huang, W. Chen. D. L. Dotson, O. Beckstein and J. Stein, Nature
Commun., 2016, 7, 1.
1
1
3
.57ꢀ3.69 (m, 20H, ꢀOCH CH Oꢀ; 2H, CH , spacer ), 3.72 (s, 3H, ꢀ 15 (a) A. P. de Silva, H. Q. N. Gunaratne and C. P. McCoy, Chem.
2
2
2
2
Commun., 1996, 2399; (b) J. F. Callan, A. P. de Silva and N. D.
McClenaghan, Chem Commum., 2004, 2048; (c) S. A. de Silva, B.
Amorelli, D. C. Isidor, K. C. Loo, K. E. Crooker and Y. E. Pena, Chem.
Commun., 2002, 1360; (d) S. A. de Silva, K. C. Loo, B. Amorelli, S. L.
Pathirana, M. Nyakirang'ani, M. Dharmasena, S. Demarais, B. Dorcley,
P. Pullay and Y. A. Salih, J. Mater. Chem., 2005, 15, 2791; (e) R.
Zammit, M. Pappova, E. Zammit, J. Gabarretta and D. C. Magri, Can. J.
Chem., 2015, 93, 199.
OCH ), 4.46 (s, 2H, CH , spacer ), 6.77ꢀ6.84 (m, 2H, phenyl crown),
3
2
1
7
7
.00 (d, 1H, J = 8.0 Hz, phenyl crown), 7.42ꢀ7.49 (m, 4H, AntH),
.97 (dd, 2H, J = 8.1 Hz, J = 1.4 Hz, AntH), 8.39 (s, 1H, AntH), 8.45
1
3
(
d, 2H, J = 8.9 Hz, AntH); C NMR (125 MHz, CDCl , ppm): δc
3
1
3
(
C
DEPT) 42.56(↑), 53.00(↓), 53.24(↓), 55.25(↑), 62.16(↓),
7
1
1
0.10(↓), 70.34(↓), 70.56(↓), 70.91(↓), 112.50(↑), 120.32(↑),
21.19(↑), 124.76(↑), 125.15(↑), 125.43(↑), 127.36(↑), 128.96(↑), 16 (a) T. Gunnlaugsson, M. Nieuwenhuyzen, L. Richard and V. Thoss, J.
Chem. Soc., Perkin Trans.2, 2002, 141; (b) T. Schwarze, H. Müller, S.
30.63(–), 131.31(–), 131.44(–), 133.63(–), 138.79(–), 152.68(–); IR
Ast, D. Steinbrück, S. Eidner, F. GeiBler, M. U. Kumke and H.ꢀJ. Holdt,
ꢀ
1
(NaCl, thin film, cm ): 3049, 2936, 2860, 2787, 1506, 1446, 1413,
Chem. Commun., 2014, 50, 14167.
352, 1292, 1251, 1120, 1035, 987, 785, 732; HRMS (ESIꢀTOF): 17 D. C. Magri, Metal Ion Sensing for Biomedical Uses, in Molecular and
1
Supramolecular Information Processing: From Molecular Switches to
Logic Systems, ed. E. Katz, WileyꢀVCH Verlag, Weinheim, 2012, p. 79.
(a) H. He, M.A. Mortellaro, M. J. P. Leiner, S. T. Young, R. J. Fraatz
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Mater. Chem., 2005, 15, 2640.
The log P was predicted using Chemsketch© product version 12.01. In
previous work we reported the log P of anthraceneꢀbased waterꢀsoluble
fluorescent pH indicators: M. A. Cardona, C. J. Mallia, U. Baisch and D.
C. Magri, RSC Adv., 2016, 6, 3783.
Calculated C H N O Na [M+Na] 581.2991, Found 581.2994; UVꢀ
34
42
2
5
ꢀ
1
ꢀ1
vis, 1:1 MeOH/H O, λmax/nm (ε/cm mol L): 346 (19000), 365
2
1
1
8
9
(19500), 385 (15000).
Acknowledgements
Financial support is gratefully acknowledged from the University of
Malta and the Strategic Educational Pathways Scholarship (Malta)
program partꢀfinanced by the European Social Fund (ESF) under
Operational Programme II – Cohesion Policy 2007ꢀ2013. We thank
Prof. Robert M. Borg for NMR assistance.
2
2
0
1
M. F. Harris and J. L. Logan, J. Chem. Ed. 2014, 91, 915.
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(
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2 A. Weller, Pure Appl. Chem., 1968, 16, 115. The driving forces for
2
2
electron transfer are calculated as
where OX is the oxidation potential of anilinic amine (0.45 eV),
tertiary amine (1.15 eV), ERED is the reduction potential of
methylanthracene ( 1.87 eV), is the excited state singlet energy of
ꢁ
G
PET
=
E
OX
RED S
− E – E – e /εr
E
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