Benesi-Hildebrand Research Articles

Simultaneous measurement of hydrogen carbonate and acetate anions using biologically active receptor based on azo derivatives of naphthalene.

A novel receptor based on azo-derivatives of 1-naphthylamine (2-((E)-((4-chloro-3-(trifluoromethyl)phenyl)imino)methyl)-4-((E)-naphthalene-1-yldiazenyl)phenol(2) abbreviated CTNP was successfully designed and synthesized. Its sensing properties were studied deeply. Systematic studies of CTNP with HCO3- and AcO- anions in DMSO disclosed that there is hydrogen-bonding between CTNP and incoming anions. Significant changes in the visible region of the spectrum, as well as a drastic color change of CTNP from pale yellow to red, observed due to interaction as mentioned earlier. The stoichiometry of [CTNP: HCO3- or AcO-] complexes and association constants determined through Job's method and Benesi-Hildebrand (B-H) plot, respectively. Taking into account the analysis results, CTNP performs the selective recognition of sub-millimolar concentrations of HCO3- and AcO- efficiently. The antifungal activity of the receptor was tested against Aspergillus brasiliensis and Aspergillus niger. CTNP exhibited excellent antifungal activity against both strains. CTNP also represented antibacterial activity against Gram-positive bacteria: Staphylococcus epidermidis. It was cleared that designed receptor can be applied under physiological conditions for a long duration.

β-cyclodextrin-enhanced Spectrofluorometric Methods for the Determination of Substituted Benzamides (Itopride Hydrochloride, Alizapride, and Mosapride Citrate) in Pharmaceutical Preparations

Two spectrofluorometric methods are developed and optimized for the determination of substituted benz amides, namely itopride hydrochloride (ITO), alizapride (ALI), and mosapride citrate (MOS), in drug substances and pharmaceutical formulations. The first method is based on the measurement of the relative fluorescence intensity of the cited drugs in the absence of methyl-β-cyclodextrin at 380 ± 2 nm using an excitation wavelength of 310 nm in an aqueous solution. The linearity ranges were found to be 0.05–10, 0.1–10, and 0.1–10 μg/mL, with mean recoveries of 100.04% ± 0.21, 100.06% ± 0.65, and 100.08% ± 0.26 for ITO, ALI, and MOS, respectively. The second method is based on the significant enhancement of the fluorescence intensities of the drugs produced through complex formation with methyl-β-cyclodextrin in an aqueous solution at pH 6.6 in the case of ITO and pH 7.2 in the case of ALI and MOS. The fluorescence intensities of the formed complexes were measured at 420 ± 2 nm using an excitation wavelength of 310 nm. The linearity ranges were found to be 5–35, 3–15, and 2–30 ng/mL, with mean recoveries of 100.22 ± 30, 100.12 ± 0.24, and 100.30 ± 0.44, and limits of detection of 1.98, 1.32, and 0.66 ng/mL for ITO, ALI, and MOS, respectively. 1:1 stoichiometries for β -CD-drugs complexes were established. Association constants and Gibbs free energy were calculated by applying the Benesi–Hil de brand equation. The results were found to agree statistically with those obtained from the reference methods.

Development of highly selective chemosensor for thorium estimation

A rapid and sensitive spectrophotometric method has been developed for the determination of Th4+ ions using tetra butyl 2,2′-bipyridine-5,5′-diylbis(methylene) diphosphonate (L) as a chemosensor. The selective complexation of L was examined with various f-metal ions like Th4+, U6+ and Ln's(III) ions and other selected metal ions (from s, p, and d-block elements). The chemosensor L selectively portrayed a naked-eye detectable colour change from colourless to pink with an appearance of a new charge transfer band at 320nm and 525nm. No noticeable spectral and colour changes of L were observed with other tested metal ions. This confirms high selectivity of L towards Th4+ ions. The Job’s plot delineated the formation of a host–guest complex between L and Th4+ in 1:1 binding stoichiometry. The binding constant for the complexation of L-Th4+ was calculated from Benesi–Hildebrand (BH) plot and was found to be 6×103M−1. The complexing ability L with Th4+ was supported by 31P NMR, FT-IR, UV-DRS, vibrating sample magnetometery and mass spectral data. The limit of detection (LOD) and limit of quantification (LOQ) of L for the analysis of Th4+ was calculated to be 2.02μM and 6.1μM, respectively. Finally, the chemosensor L was successfully applied for the quantification of Th4+ contents present in monazite sand, gas mantels and different water samples.

Multi-signaling thiocarbohydrazide based colorimetric sensors for the selective recognition of heavy metal ions in an aqueous medium

A series of colorimetric chemosensors R1–R6 have been developed from thiocarbohydrazide derivatives, for the selective detection of heavy metal ions. The structures of the receptors R1–R6 were well characterized by standard spectroscopic techniques like FT-IR, 1H NMR, and ESI-MS. The solid structure of receptor R1 and R2 were derived by single crystal X-ray diffraction (SC-XRD). The cation reorganization abilities of receptors R1–R6 were studied by UV–Vis spectroscopy. The receptors R1, R3 and R4 acts as a tremendous sensitive probe for heavy metal ions (Hg2+, Cd2+ and Pb2+) with the μM detection (R1 for Hg2+, 2.72, R3 for Cd2+, 3.22, R4 for Hg2+, Cd2+ & Pb2+, 0.70, 0.20 & 0.30μM) and the receptors R2, R5 &R6 are sensitive towards Cu2+ ions with the μM detection (3.34, 0.90 & 1.20μM) in an aqueous medium among all other tested cations. The receptor R4 shows a multi-color response towards Hg2+, Cu2+, Cd2+ and Pb2+ ions. The recognition mechanism, stoichiometric binding ratio and detection limit (DL) have been examined by UV–Visible spectroscopic titration experiments and Benesi-Hildebrand (B-H) plot, receptor R1–R6 sowed 1:1 binding ratio with good binding constant range of 103 to 105M−1 with Hg2+, Cu2+, Cd2+ and Pb2+ ions metal ions.

Tuning the constrained photophysics of a pyrazoline dye 3-naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline inside the cyclodextrin nanocavities: A detailed insight via experimental and theoretical approach

The modulation in the photophysics of a pyrazoline dye 3-naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline (NPCP), when it drifts from bulk water into the nanocages of aqueous cyclodextrin solutions was investigated. The intramolecular charge transfer (ICT) fluorescence band intensity was found to increase with a blue shift in the presence of cyclodextrins. The results from 1H NMR and 1HH COSY NMR spectral analysis clearly points out the position of pyrazoline ring inside the cavity and its role in complexation process. A quantitative assessment of the emission intensity data on Benesi-Hildebrand (B-H) equation along with ESI-MS spectra reveals the probable stoichiometry of NPCP-CD complexes. Molecular docking and molecular dynamics studies were conducted for β/γ cyclodextrin associated inclusion complexes of NPCP. The results obtained by computational studies are in good relation with the data obtained through experimental methods and both ascertain the encapsulation of NPCP into cyclodextrins.

RETRACTED: Synthesis and studies of selective chemosensor for naked-eye detection of anions and cations based on a new Schiff-base derivative

A new chromogenic receptor, 4-((2,4-dichlorophenyl)diazenyl)-2-(3-hydroxypropylimino) methyl)phenol, has been designed and synthesized for quantitative and low-cost detection of various biological anions and cations. The dye was characterized by elemental analyses, infrared, UV-visible spectroscopy, and NMR spectroscopy. Upon the addition of F(-) and H2PO4(-) to the solution of chemosensor in DMSO, the dramatic naked eye detectable color changes were observed from yellow to red and orange with a limit of detection (LOD) of 1.66×10(-6)mol. L(-1) and 1.24×10(-6)mol. L(-1) at room temperature, respectively. The chemosensor showed visual changes towards cations, such as Al(3+), Cu(2+), Fe(3+), and Cr(3+), in DMSO/water (9:1). The detection limit of receptor L for the analysis of Al(3+) ion was calculated to be 3.02×10(-6)mol. L(-1). The anion recognition property of the receptor via proton transfer was monitored by UV-visible titration and (1)HNMR spectroscopy. The binding constant (Ka) and stoichiometry of the host-guest complexes formed were determined by the Benesi-Hildebrand (B-H) plot and Job's method, respectively.

Selectivity of 2-mercaptobenzimidazole derivatives on metal ions studied by UV–vis spectromentry and DFT calculations

UV–vis absorption spectrometry and DFT calculations were used to study the selective binding of 2-mercaptobenzimidazole derivatives (MBI, EMBI, PMBI and BMBI) as chelating collectors with metal ions, including Fe3+, Cu2+, Pb2+, Zn2+ and Ag+. The results showed superior selectivity of these collectors towards Ag+ as compared with the other metal ions. The binding stoichiometry of MBI derivatives with Ag+ was found by Job-plot method to be 1:1. The binding constant determined using Benesi–Hildebrand (B-H) method showed the following order of BMBI-Ag > PMBI-Ag > EMBI-Ag > MBI-Ag. The binding energies of MBI derivatives with Ag+ calculated by DFT method followed the same order as the binding constant calculated by B-H method. All the calculation results were in good agreement with the results of UV–vis experiments which showed the highest selectivity and binding energies of BMBI towards Ag+. This study clearly shows that the BMBI is a good sensor for Ag+ ion. Therefore, the BMBI could be a highly selective and efficient collector to enhance the recovery of silver from silver-rich lead–zinc sulfide minerals.

Comparative Study on the Effect of Nitrogen-donor Groups Versus Macro-ring Size in O2Nx-Azacrowns on the Complexation with [60]Fullerene

The interaction of [60]fullerene with a newly synthesized series of 17- to 21-membered macrocyclic ligands containing an O2N3-donor set has been investigated. The formation constants (K) arising from their complexation with [60]fullerene macrocycles, having various ring size, were measured in CHCl3 media by UV-visible spectroscopy applying Benesi-Hildebrand (BH) equation and their stoichiometries were also determined by the Job method. The best K value was measured for 20-membered ring macrocycle in which a 1:1 complexation stoichiometry with [60]fullerene was dominant. Furthermore, 1H NMR spectroscopy data reveled that the macrocylic ligand coordinates [60]fullerene via the nitrogen-donor groups. Evaluation of the thermodynamic parameters, for example, formation enthalpies (ΔH O f) and entropies (ΔS O f) confirmed on these complexations as both enthalpy and entropy favorite processes. Comparing with our previous observation for similar [60]fullerene complexation with the O2N2-donor macrocylic ligands, we concluded that increasing the number of nitrogen-donor groups on the macrocycle had rather more pronounce effect on these complexation than the macro-ring size.

Determination of cyclodextrin inclusion constant for aromatic carbonyl compounds through spectrophotometric and electrochemical methods

α- and β-Cyclodextrins cavity inclusion constants ( K i) were determined for a series of benzaldehydes and acetophenones by using two different methods: Benesi–Hildebrand (BH) UV/vis spectroscopic method and electrochemical current (EC) method, determined by cyclic voltammetry. The values determined in the group of benzaldehydes varied from 322 ± 27 to 5688 ± 317 mol −1 dm 3 for UV/vis method, and 342 ± 19 to 7386 ± 142 mol −1 dm 3 for EC method. The values determined in the group of acetophenones varied from 2201 ± 88 to 9125 ± 251 mol −1 dm 3 for UV/vis method, and 1473 ± 33 to 7555 ± 187 mol −1 dm 3 for EC method. The equilibrium time estimated for UV/vis spectroscopic (BH) method was 240 min and for the cyclic voltammetry (EC) method was 310 min. Notably, despite their limitations, both methods were suitable and reliable for inclusion constant measurement, if the equilibrium time of the system is well established.

Spectrophotometric determination of some amino heterocyclic donors through charge transfer complex formation with chloranilic acid in acetonitrile

The present study is directed toward a development of simple, rapid and accurate spectrophotometric method for determination of some amino heterocyclic donors. The Charge transfer (CT) interactions between 3-aminopyrazole (AP), 3,5-dimethyl-pyrazole (DMP), 3-amino-5-methyl-pyrazole (AMP), 2-amino-4-methyl-thiazole (AMT), 2-amino-5-methyl-1,3,4-thiadiazole (AMTD) and 2-amino-5,6-dimethyl-1,2,4-triazine (ADMT) with chloranilic acid (CLA) as π-acceptor have been investigated spectrophotometrically in acetonitrile. Factors controlling the CT-reactions were also studied and optimized. Under the optimum conditions, linear relationships with good correlation coefficients were identified with high accuracy and precision. Job's method of continuous variation, spectrophotometric and conductometric titrations were used to identify the composition of the formed CT-complexes. Benesi-Hildebrand (BH) equation has been used to calculate the formation constants of the charge transfer reactions K CT and the molar extinction coefficients ε. Free energy change (Δ G o), oscillator strength ( f), transition dipole moment ( µ), ionization potential ( I P) and charge transfer energy of the formed CT-complexes ( E CT) were also determined and evaluated.

Determining the stoichiometry and binding constants of inclusion complexes formed between aromatic compounds and β-cyclodextrin by solid-phase microextraction coupled to high-performance liquid chromatography

The complexation of native β-cyclodextrin (CD) and seven aromatic compounds, namely, phenetole, toluene, m-xylene, naphthalene, biphenyl, fluorene and phenanthrene, has been studied for first time utilizing a solid-phase microextraction (SPME)–high-performance liquid chromatography (HPLC) method. The stoichiometries of the analyte:β-CD complexes were found to be either 1:1 or 1:2. The formation of 1:2 complexes was confirmed for naphthalene, biphenyl, fluorene, and phenanthrene only when utilizing relatively high concentrations of β-CD (up to 6.6 mM). The 1:2 stoichiometries were confirmed using the classical modified Benesi–Hildebrand (BH) method. The calculated binding constants for 1:1 stoichiometries ( K 1) using the SPME method varied from 115.3 M −1 for toluene to 3510 M −1 for phenanthrene, whereas the corresponding values to the 1:2 stoichiometries ( K 3) varied from 7.30 × 10 5 M −2 for biphenyl to 9.03 × 10 6 M −2 for naphthalene.

Validity and Reliability of Benesi-Hildebrand Method

Benesi-Hildebrand (B-H) method is a widely used approach for determining the stoichiometry and equilibrium constants of nonbonded interactions, particularly 1:1 and 1:2 interactions. Using computer simulation, it was shown that, under certain conditions, the approach could generate inappropriate stoichiometric conclusions for 1:2 interactions. This problem could occur in the cases of both weak and strong interactions, where the 1:1 B-H plots showed a linear feature and the 1:2 B-H plots showed a nonlinear feature. In addition, effect of the initial concentrations on the accurate evaluation of equilibrium constants of 1:1 interactions was investigated. It was found that the minimum safe concentration ratio r 0 between ligand and central species was 100. However, for weak nonbonding interactions, for example K<25 L·mol –1 ( C P 0 =4×10 –4 mol·L –1), the ratio r 0 has no limitation. Two conditions proposed in literatures for the safe application of the B-H method were examined. It was found that the inequation, 1/( KC 0 P)≥10, was a condition to secure C B/ C 0 B >91%. The other inequation, KC 0 B>0.1, was not found to be the safe condition to validate the B-H method.

Graphical method for the determination of the complex NMR shift and equilibrium constant for a hetero-association accompanying self-associations

We describe a novel graphical method which, in conjunction with the previously proposed graphical determination of monomer shift, dimer shift, and dimerization constant for self-association, allows us to determine the complex shift and equilibrium constant for a hetero-association, A + B ⇌ AB, accompanying self-associations, A + A ⇌ A2, and B + B ⇌ B2. The merit of the new method includes the removal of the restrictions imposed on the conventional Benesi-Hildebrand (B-H) plot: (1) that the concentration of one component must be much less than that of the other; (2) that there be no accompanying self-association. The simultaneous equilibrium of the self-association of 2-pyrrolidone (A) and that of 4-methyl-α-pyrrolidone (B) and the hetero-association between A and B in acetonitrile-d3 at 25‡C is studied. The inappropriateness of the B-H plot in dealing with this case is also pointed out.

Graphic method for the determination of the complex NMR shift and equilibrium constant for a hetero-association accompanying a self-association

A novel graphic method to determine the complex shift and equilibrium constant for a hetero-association, A + B ⇌ AB, accompanying a self-association A + A ⇌ A2 has been described. The method is to be used in conjunction with a graphic determination of the monomer shift, dimer shift and dimerization constant proposed previously. Our new method is advantageous over the conventional Benesi–Hildebrand (BH) plot in that the limitations, (1) that the concentration of one component must be much less than that of the other and (2) that self-association of species is not allowed, are completely removed. The related parameters of the self-association of 2-isopropylphenol (A) and the hetero-association of 2-isopropylphenol with acetone (B) in the inert solvent [2H12] cyclohexane has been used to demonstrated the use of this new graphic method. Comparison with the results from a BH plot has also been made.