The Journal of Organic Chemistry
Article
7.68 Hz); 13C NMR (CDCl3, δ ppm) 168.8, 156.4, 135.5, 128.5, 127.1,
124.7, 123.8, 119.2, 115.5 (Nap-C); 66.9, 61.1 (−CH2−CH3); 14.1
(−CH3); ESI-MS m/z (%), 491 (80, [M + H]+); 261 (100). Anal. (%)
Calcd for C28H26O6S: C, 68.55; H, 5.34; S, 6.54. Found: C, 68.42; H,
5.34; S, 6.21.
gaussview from the single-crystal XRD structure of a similar
methylene-bisnaphthalene-amidomethyl benzimidazole di-derivative.12
The structure was then optimized by semiemprical methods followed
by HF and then by DFT in a cascade fashion. In order to generate the
metal complex, silver ion has been placed randomly at a distance that
is far away from the benzimidazole region. The corresponding complex
of L with Ag+ was then optimized in a cascade fashion by going
through AM1 → HF/3-21G → B3LYP/3-21G level of computation.
Fluorescence Titrations. All of the fluorescence titrations were
carried out on a Perkin-Elmer LS55 at 280 nm excitation wavelength
in 1 cm quartz cell. Bulk solutions (6 × 10−4 M) of L were freshly
made before each set of experiments by dissolving the ligand in
DMSO (50 μL) and then making up with the 2:3 methanol−water
1,1′-Thiobis(2-naphthoxy acetic acid) (L3). Into a 250 mL
single-neck flask containing ethanol (100 mL) and L2 (19 g, 38.76
mmol) was added 15% aqueous sodium hydroxide (42 mL, 158
mmol), and the mixture was heated to reflux for 24 h. After the
reaction, the mixture was evaporated under reduced pressure to yield a
white solid. The residue was diluted (suspension) with cold water, and
hydrochloric acid (3 N) was added with vigorous mixing until pH 1
was reached. A white precipitate obtained was collected, washed with
water, and dried. Pure L3 was obtained after recrystallization from
ethanol: yield (15.98 g, 95%); FTIR (KBr, cm−1) 3210−2420 (br),
mixture. The metal perchlorate salts were made at 6 × 10−4
M
concentration in 2:3 methanol−water mixture. The fluorescence
titrations were carried by exciting the solution at 280 nm wavelength
after adding an appropriate volume of metal salt solution to result in
requisite mole ratios of [Mn+]/[L], yet maintaining the final [L] as 10
μM in a total solution volume of 3 mL achieved by diluting with
solvent.
1
1720, 1710, 1620, 1430, 1275; H NMR (400 MHz, DMSO-d6, δ
ppm) 4.83 (s, 4H, O−CH2), 7.23 (t, 4H, Ar−H, J = 7.75 Hz), 7.37 (t,
2H, Ar−H, J = 8.20 Hz), 7.75 (d, 2H, Ar−H, J = 9.1 Hz), 7.85 (d, Ar−
H, 2H, J = 7.76 Hz), 8.50 (d, 2H, J = 8.52 Hz), 13.15 (br, 2H,
−COOH); 13C NMR (DMSO-d6, δ ppm) 170.8, 156.6, 135.3, 130.1,
129.6, 128.3, 127.1, 125.9, 124.3, 119.1, 115.1, 66.6; ESI-MS m/z (%),
457 (67, [M + Na]+); 435 (46, [M + H]+); 232 (100). Anal. (%)
Calcd for C24H18O6S: C, 66.35; H, 4.18; S, 7.38. Found: C, 66.28; H,
4.08; S, 7.14.
Absorption Titrations. Bulk solutions were made by similar
procedure as in fluorescence studies. Titrations were performed by
varying equivalents of [Mn+] from 0.2 to 10 and fixing the
concentration of L at 35 μM.
1H NMR Titration. L (0.01 M) was taken in NMR tube in DMSO-
d6 (400 μL) followed by addition of a varying quantity of Ag+
(dissolved in DMSO-d6).
Synthesis of L. To a solution of L3 (0.3 g, 0.690 mmol) in DMF
(50 mL) were added Et3N (0.5 mL, 3.46 mmol), 1-ethyl-(3-
dimethylaminopropyl)-3-carbodiimide hydrochloride (0.40 g, 2.07
mmol), and catalytic amount of 1-hydroxybenzotriazole (HOBT),
and the solution was stirred at 0 °C for 30 min under N2 atmosphere.
A hydrochloride salt of 2-aminomethyl benzimidazole (0.32 g, 1.4
mmol) was added to this reaction mixture and stirred at room
temperature overnight. The resulting mixture was added with water
(50 mL) and extracted in dichloromethane (100 mL × 2). The
dichloromethane extract was washed with water followed by saturated
NaHCO3 and brine. The organic phase was evaporated to give white
solid, L. The product was recrystallized from dichloromethane/
Sample Preparations for AFM and TEM. For AFM studies, the
stock solution of (L) and Ag+ were taken as 6 × 10−5 M. The L was
dissolved in methanol/water (2:3) system. The ligand to Ag+ ratio was
1:2, and the system was sonicated for 10 min, after which 50−70 μL of
aliquot was taken and spread over a mica sheet using the drop-cast
method. The sample was then dried and subjected to AFM studies.
For TEM studies, the sample preparation procedure followed for AFM
was adopted except that the stock solution of L and Ag+ used was 6 ×
10−3 M. The samples were dispersed on a carbon-coated grid by drop-
cast method.
1
methanol: yield (0.35 g, 73%); FTIR (KBr, cm−1) 1686 (νCO); H
NMR (400 MHz, DMSO-d6, δ ppm) 4.51 (s, 4H, NCH2), 4.67 (s, 4H,
OCH2), 7.12 (br, 4H, Benz-H), 7.4 (m, 12H, Ar−H), 7.82 (t, 2H,
CONH, J = 8.2 Hz), 8.44 (br, 4H, Ar−H), 12.71 (s, 2H, Benz-NH);
13C NMR: (DMSO-d6, δ ppm) 36.1, 68.6, 115.7, 117.5, 121.4, 124.2,
124.8, 127.3, 129.6, 130.1, 134.2, 151.8, 156.2, 168.1; ESI-MS m/z
(%), 692 (100, [M]+); HRMS (EI) calcd for C40H33N6O4S m/z
693.2284, found m/z 693.2311.
ASSOCIATED CONTENT
■
S
* Supporting Information
Synthesis and characterization including spectral data of L and
its precursors, fluorescence and absorption data, minimum
detection limit, and computational data. This material is
Synthesis of Control Molecule L4. To a solution of phenoxy-
acetic acid (1 g, 6.5 mmol) in dry CH2Cl2 (60 mL) were added Et3N
(2.28 mL, 16.45 mmol), 1-ethyl-(3-dimethylaminopropyl)-3-carbodii-
mide hydrochloride (2.50 g, 13 mmol), and a catalytic amount of 1-
hydroxybenzotriazole (HOBT), and then the solution was stirred at 0
°C for 30 min under N2 atmosphere. A hydrochloride salt of 2-
aminomethyl benzimidazole (1.5 g, 6.8 mmol) was added to this
reaction mixture and stirred at room temperature overnight. The
reaction mixture was concentrated by rotary evaporation, and solid
crude product obtained was redissolved in CH2Cl2. The dichloro-
methane portion was washed with water (50 mL × 3) followed by
brine and dried over anhydrous sodium sulfate, filtered, and solvent
was removed by rotary evaporation. The solid crude product, L4, was
purified by silica gel column chromatography using ethyl acetate/
petroleum ether (4:6 v/v) as eluent: yield (1.29 g, 71%); FTIR (KBr,
AUTHOR INFORMATION
■
Corresponding Author
*Phone: +91-22-2576-7162. Fax: +91-22-2572-3480. E-mail:
ACKNOWLEDGMENTS
■
C.P.R. acknowledges the financial support from DST, CSIR,
and DAE BRNS. Both A.M. and G.S.B. acknowledge CSIR, and
K.T. acknowledges UGC for their fellowships. J.D. acknowl-
edges DRDL for allowing to register for the Ph.D. program at
IIT Bombay. We also acknowledge FIST (Physics)-IRCC
central SPM facility of IIT Bombay for AFM studies.
1
cm−1) 1667 (νCO), 1068; H NMR (400 MHz, DMSO-d6, δ ppm)
4.57−4.59 (2s, 4H, NCH2 and OCH2), 6.97 (t, 1H, Ar−H J = 7.36
Hz,), 7.02 (d, 2H, Ar−H, J = 7.84 Hz), 7.15 (m, 2H, Ar−H), 7.32 (t,
2H, Ar−H, J = 8.03 Hz,), 7.50 (br, 2H, Benz-H), 8.79 (t, 1H, CONH,
J = 5.86 Hz), 12.25 (s, 1H, Benz-NH); 13C NMR (DMSO-d6, δ ppm)
37.6, 67.5, 115.4, 115.4, 121.9, 122.1, 130.2, 152.7, 158.3, 168.9;
HRMS (EI) calcd for C16H16N3O2 m/z 281.1252, found m/z
281.1243.
REFERENCES
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Computational Studies. Computational studies were carried out
using Gaussian 03 package.11 Prior to assuming the initial guess model
for computational calculations, structure of L was generated using
(2) Mcdonnell, G.; Russell, D. A. Clin. Microbiol. Rev. 1999, 12, 147.
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dx.doi.org/10.1021/jo201926q | J. Org. Chem. 2012, 77, 371−378