UV-vis Titration Data Research Articles

Design and synthesis of new water-soluble dinuclear manganese(II) complexes as monosaccharide binding models

The present article describes the design, synthesis, physicochemical characterization and monosaccharide binding events of two new water-soluble dinuclear manganese(II) complexes [Mn2(phpda)(µ-Cl)]·2H2O (1) and [Mn2(phpda)(µ-OAc)]·2H2O (2) of carboxylate and pyridyl-functionalized multidentate ligand, H3phpda (H3phpda = N,N′-bis[2-pyridylmethyl]-2-hydroxy-1,3-propanediamine-N,N′-dipropionic acid). FTIR, UV–Vis, ESI-MS, microanalysis, molar conductivity, cyclic voltammetry and room-temperature magnetic data establish their compositions. Structural features of 1 and 2 obtained from theoretical calculations indicate a self-assembled and well-packed array with average Mn···Mn separation of 2.952 Å. Both 1 and 2 have been studied towards 1:1 binding interactions with biologically important monosaccharides, such as d-glucose, d-xylose and d-glucosamine by employing UV–Vis spectroscopy and DFT computation. The binding constant values of monosaccharide-bound manganese(II) complexes evaluated from UV–Vis titration data are 2.145 x 103 M−1, 2.156 x 103 M−1, 2.652 x 103 M−1, 1.388 x 103 M−1, 1.793 x 103 M−1 and 2.146 x 103 M−1 for 1/d-glucose, 1/d-xylose, 1/d-glucosamine, 2/d-glucose, 2/d-xylose and 2/d-glucosamine assemblies, respectively. The possible metal centers engaged in the binding events have been ascertained by calculating the Fukui functions (fk+) on the manganese sites, including HOMOs and LUMOs. A comparative assessment of sugar-binding properties, in particular, suggests that the order of binding ability of monosaccharides with 1 and 2 is found to be d-glucosamine > d-xylose > d-glucose.

Exceptionally water-soluble [CuII2] complexes for investigating monosaccharide-metal ion interactions

The design, synthesis and characterization of two new dinuclear copper(II) complexes [Cu2(phpda)(µ-Cl)]·2H2O (1) and [Cu2(phpda)(µ-NO3)]·2H2O (2) (H3phpda = N,N′ -bis[2-pyridylmethyl]-2‑hydroxy-1,3-propanediamine-N,N′-dipropionic acid) as carbohydrate binding models have been reported. The FTIR, UV–Vis, ESI-MS, microanalysis and molar conductance data have been utilized to characterize the synthesized complexes. The structures of 1 and 2 have been established by density functional theory (DFT) calculations that exhibit a self-aggregated closely packed arrangement with average inter-metallic Cu···Cu separation of 3.2484 Å. In aqueous alkaline media, both complexes have been studied for their binding interactions with biologically important monosaccharides, d-glucose and d-glucosamine by employing UV–Vis spectroscopy and DFT calculations. The binding-assisted steady decrease of absorbances of 1 and 2 accompanied by a significant red/blue shift of absorption maxima of the complexes upon UV–Vis titration of 1 and 2 with d-glucose and d-glucosamine has been observed, suggesting 1:1 complex/monosaccharide interactions. Evaluation of binding constant values of monosaccharide-bound copper(II) complexes has been accomplished by utilizing UV–Vis titration data, and the values are found to be 2.145 × 103 M−1, 2.652 × 103 M−1, 1.388 × 103 M−1 and 1.793 × 103 M−1 for 1/D-glucose, 1/D-glucosamine, 2/D-glucose and 2/D-glucosamine assemblies, respectively. Fukui functions (fk+) on the copper sites, including HOMO and LUMO in both complexes have been obtained from DFT calculations to understand the likely copper sites involved in the binding events with monosaccharides. However, a comparative assessment of their binding constant values showed that d-glucosamine interacts with 1 and 2 more preferentially than d-glucose.

Three and four inputs combinational logic circuits based on a azo-azomethine chemosensor for the detection of Ni2+ and CN−/OAC− ions: Experimental and DFT studies

A novel Schiff base ligand HL2 was synthesized as a colorimetric sensor for Ni2+ and CN−/OAC− ions. The binding constants (Ka) calculated using the Benesi-Hildebrand analysis of the UV–vis titration data for Ni2+ and CN−/OAC− ions were determined to be 2.88 × 1010, 7.03 × 104 and 3.44 × 103 M−1, respectively. The stoichiometry ratio between receptor HL2 and Ni2+ was verified to be 2:1. The experimental results were confirmed by Density Functional Theory (DFT) studies using the B3LYP level and 6-31+g (d) basis set. The absorbance outputs signals were measured at 370 nm (Out1) and 500 nm (Out 2) based on three chemical inputs CN− (Inc), OAC− (InO) and HSO4− (InH) in eight different combinations. The combinatorial circuit was designed by three logic gates (OR, NOT and AND) using different output signals towards CN− (Inc), OAC− (InO) and HSO4− (InH). The absorbance output signals for four chemical inputs, Including Ni2+ (In Ni2+), CN− (Inc), OAC− (InO) and HSO4− (InH) in sixteen different combinations, were successfully recorded at 500 nm (out1) and 425 nm (out2). Furthermore, two chemical inputs (Ni2+ and CN− or Ni2+ and OAC−) and one output (absorbance at 420 nm) can be used to construct a molecular keypad lock.

Synthesis, characterization and arsenate binding events of new mononuclear copper(II) complexes

Two new mononuclear copper (II) complexes [Cu(L)(H2O)Cl] (1) and [Cu(L)(H2O)(SCN)] (2) (HL = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol) have been synthesized and characterized in order to investigate their binding interaction with arsenate ions. Complexes 1 and 2 were synthesized by performing reaction of CuCl2·2H2O or CuCl2·2H2O/NH4SCN, respectively, with HL using Et3N as mild base in MeOH solution at room temperature, and characterized by employing a number of analytical techniques, for example, elemental analysis, molar electrical conductivity, FTIR, UV–Vis and mass spectrometry. Their structures, optimized at DFT/B3LYP/6-311G level, show that the copper atom in 1 and 2 exhibits a distorted square pyramidal geometry. In H2O/MeOH (3:1; v/v) solution, complexes 1 and 2 were examined for their binding affinity towards arsenate ions. The UV–Vis spectroscopic results specify that the arsenate group binds with 1 and 2 in 1:1 M ratio. The UV–Vis titration data were successfully utilized to calculate the binding constants of arsenate-bound Cu(II) complexes, and the values are found to be 1.723 × 104 M−1 and 2.161 × 104 M−1, corresponding to 1/AsO43− and 2/AsO43− assemblies, respectively.

Exploring new water soluble bridged dicopper(II) assemblies: Synthesis, structure, spectroscopic characterization, properties, and their interactions with d-glucosamine

Three new water soluble dimetallic copper(II) complexes, [Cu(H2O)5][Cu2(cpdp)(µ-O2As(CH3)2)]2Br2·13.83H2O·0.67CH3OH (1), [Cu2(Hcpdp)(µ-SO4)]·5H2O (2) and [Cu2(cpdp)(µ-pz)]·16H2O (3) (H3cpdp = N,N′-Bis[2-carboxybenzomethyl]-N,N′-Bis[2-pyridylmethyl]-1,3-diaminopropan-2-ol; (CH3)2AsO2− = cacodylate; SO42− = sulfate; pz− = pyrazolate) have been successfully synthesized and characterized for the investigation of coordination/binding aspects with biologically significant monosaccharide, d-glucosamine. Preparation of 1, 2 and 3 has been achieved by carrying out reaction of H3cpdp with stoichiometric quantities of CuCl2·2H2O/NaO2As(CH3)2·3H2O, CuSO4·5H2O and CuCl2·2H2O/1H-pyrazole, respectively, in the presence of NaOH in MeOH/H2O at ambient temperature. Diverse analytical methods, for example, microanalysis, FTIR, UV–Vis and mass spectral techniques, including single crystal X-ray crystallography, have been utilized to characterize these complexes. Temperature dependant (2–300 K) magnetic susceptibility measurements reveal the presence of antiferromagnetic interactions between the copper(II) centers in 1 and 2. Thermogravimetric analysis of 1–3 indicates that they are stable on average up to ~ 214 °C. We have employed the UV–Vis spectroscopic technique to study the 1:1 interactions of the complexes with d-glucosamine in alkaline aqueous solution. The UV–Vis titration spectra clearly indicate the binding-induced steady decrease of the absorption intensities of 1–3, with a substantial blue shift of absorption maxima of the complexes upon addition of increasing amounts of d-glucosamine. The binding constant values between the complexes and d-glucosamine have been evaluated from the experimentally obtained UV–Vis titration data. Fukui functions at the metal sites, including HOMOs and LUMOs in 1–3 have been calculated by DFT method to forecast the possible metal centers engaged in the binding process with d-glucosamine. To the best of our knowledge, to date, neither the substrate interaction nor the mode of interaction with respect to d-glucosamine using any metal complex of any nuclearity has been documented in the literature.

Bacterial rRNA A-site recognition by DAPI: Signatures of intercalative binding

The bacterial A-site RNA is one of the key targets towards the development of new antibacterials including new treatment options for tuberculosis. Using DAPI as a prototype, we have explored the potential of bisamidines as a potential chemical motif for bacterial A-site recognition. We have demonstrated that the binding of DAPI shows a concentration-dependent thermal stabilization of the bacterial A-site RNA (ΔTm = 9.9 °C). The binding, however, does not show pH-dependent changes upon lowering of pH. Both UV–vis and CD experiments show that the DAPI binding involves base stacking with the RNA bases in a manner that is analogous to intercalation. Scatchard analysis of the UV–vis titration data revealed a micromolar affinity of the DAPI to the bacterial rRNA A-Site (Ka = 1.14 × 106 M−1) which was corroborated by the FID-based relative binding affinity comparison with aminoglycosides. The molecular docking studies showed binding poses consistent with polar and stacking interactions with the RNA. These studies highlight the role of amidines in bacterial A-site recognition and the need for the development of their structural analogs towards the making of aminoglycoside mimics.

Insights into the binding properties of calf thymus DNA with lopinavir from spectroscopic and computational studies

Lopinavir (LPV), an important antiviral drug, can inhibit effectively wild type and mutant HIV protease. In this work, molecular interaction mechanism between LPV and calf thymus deoxyribonucleic acid (ct-DNA) was characterized by spectroscopic, viscosity and molecular docking approaches to attain some important information about the LPV-ct-DNA interaction including binding affinity, binding mode, main driving-forces and structural change of ct-DNA. UV–vis titration data demonstrated that the LPV-ct-DNA complex was formed, and the binding affinity under the studied conditions was weak due to the binding constant at the level of 103 M−1. The negative values of ΔH0 (−26.63 kJ∙mol−1) and ΔS0 (−24.11 J∙mol−1∙K−1) revealed that hydrogen bonding and Van der Waals forces played an indispensable part in the LPV-ct-DNA complexation process. The outcomes from viscosity measurements excluded the possibility of intercalation mode between LPV and ct-DNA. The results from UV–vis titration experiments, displacement experiments and influence of ionic strength indicated that LPV bound to the minor groove of ct-DNA, which was further confirmed by docking studies. Besides, a minor change in the conformation of ct-DNA can be observed from CD spectral analysis. Our studies scientifically elucidated the binding behavior between LPV and ct-DNA for the first time and were beneficial to assessing the pharmacological properties of this antiviral drug.

General up-scaled model of ligand binding with C60 fullerene clusters in aqueous solution

In the present work we suggest the general model of C60 fullerene-ligand complexation, adapted for numerical description of UV–Vis titration data and for obtaining equilibrium complexation constants and some other complexation parameters. The principal novelty of the model is the account for two major processes governing the complexation process, and the account for broad dispersion of C60 fullerene clusters by dimension. It removes the existing barrier for the use of absorption spectroscopy for quantitation the C60 fullerene-ligand complexation.

The crystal structure of a valinomycin•2Ca2+ complex and the multi-step solution equilibria in acetonitrile characterised by 1H NMR, UV–Vis, and mass spectrometry

Valinomycin is a well-known potassium-selective ion carrier, but the nature of its direct interaction with calcium ion, another biologically important cation, is also of considerable interest. We have determined the first crystal structure of a valinomycin–calcium complex, which crystallises exclusively as a 1:2 valinomycin:Ca2+ complex, [VCa2(OTf)2(H2O)2]2+ in the solid state (V = valinomycin, OTf = triflate). Along with the 1:2 complex, the solution phase 1:1 and 2:1 complexes have been characterised in acetonitrile by 1H NMR and UV–Vis titration experiments. The molar absorptivity curves and binding equilibrium constants for these complexes have been determined by the global analysis of the UV–Vis titration data using the program SIVVU™.

Positional Effects of Hydroxy Groups on Catalytic Activity of Proton-Responsive Half-Sandwich Cp*Iridium(III) Complexes

Proton-responsive half-sandwich Cp*Ir(III) complexes possessing a bipyridine ligand with two hydroxy groups at the 3,3′-, 4,4′-, 5,5′-, or 6,6′-positions (3DHBP, 4DHBP, 5DHBP, or 6DHBP) were systematically investigated. UV–vis titration data provided average pKa values of the hydroxy groups on the ligands. Both hydroxy groups were found to deprotonate in the pH 4.6–5.6 range for the 4–6DHBP complexes. One of the hydroxy groups of the 3DHBP complex exhibited a low pKa value of <0.4 because the deprotonation is facilitated by the strong intramolecular hydrogen bond formed between the generated oxyanion and the remaining hydroxy group, which in turn leads to an elevated pKa value of ∼13.6 for the second deprotonation step. The crystal structures of the 4- and 6DHBP complexes obtained from basic aqueous solutions revealed their deprotonated forms. The intramolecular hydrogen bond in the 3DHBP complex was also observed in the crystal structures. The catalytic activities of these complexes in aqueous phase reactions, at appropriate pH, for hydrogenation of carbon dioxide (pH 8.5), dehydrogenation of formic acid (pH 1.8), and transfer hydrogenation reactions using formic acid/formate as a hydrogen source (pH 2.6 and 7.2) were investigated to compare the positional effects of the hydroxy groups. The 4- and 6DHBP complexes exhibited remarkably enhanced catalytic activities under basic conditions because of the resonance effect of the strong electron-donating oxyanions, whereas the 5DHBP complex exhibited negligible activity despite the presence of electron-donating groups. The 3DHBP complex exhibited relatively high catalytic activity at low pH owing to the one strong electron-donating oxyanion group stabilized by the intramolecular hydrogen bond. DFT calculations were employed to study the mechanism of CO2 hydrogenation by the 4DHBP and 6DHBP complexes, and comparison of the activation free energies of the H2 heterolysis and CO2 insertion steps indicated that H2 heterolysis is the rate-determining step for both complexes. The presence of a pendent base in the 6DHBP complex was found to facilitate the rate-determining step and renders 6DHBP a more effective catalyst for formate production.

Merging catalysis and supramolecular aggregation features of triptycene based Zn(salphen)s

A series of trinuclear, triptycene-based metallosalphen complexes (M = Zn, Ni) have been prepared incorporating various peripheral substituents. The introduction of Zn metal centres into these triptycene based salphen ligands gives rise to cross-linking between different triptycene molecules through μ-phenoxo bridges between the Zn metal centres, and variation in the peripheral groups allows the control of the self-assembling properties as shown by UV-Vis titration data. The strong association of these trinuclear Zn3 complexes under relatively apolar conditions has been exploited to recover the complex after its application as a catalyst in the cycloaddition of carbon dioxide to 1,2-epoxyhexane. The catalysis results and recycling studies show that the co-catalyst structure is important for efficient recovery of the binary system, demonstrating that reversible supramolecular aggregation may become a useful tool for recycling homogeneous catalysts.

Spectroscopic study on the interaction of ct-DNA with manganese Salen complex containing triphenyl phosphonium groups

The DNA binding properties of a bulky and hydrophobic Schiff base complex of manganese(III) [N,N′-bis(5-(triphenyl phosphonium methyl)salicylidene)-1,2-ethylene diamine chloride Mn(III) acetate] was examined by spectroscopic techniques. UV–vis titration data indicate both hypo and hyperchromic effect with addition of DNA to complex. A competitive binding study showed that the enhanced emission intensity of ethidium bromide (EB) in the presence of DNA was quenched by adding Mn Salen complex. This finding indicates that Mn Salen complex displaces EB from its binding site in DNA. Helix melting studies indicate improvement in the helix stability, and an increase in the melting temperature. The analysis of CD spectra represents the structural changes in DNA due to the binding of Mn Salen complex. The binding constant has been calculated using absorbance and fluorescence data. The results also represent that the binding process proceeds by strong electrostatic and hydrophobic interactions.

A coumarin based ICT probe for fluoride in aqueous medium with its real application

A new coumarin based hydrazone (receptor 1) synthesized by modifying one of our earlier reported receptor detected fluoride ion selectively through naked eye in aq. DMSO (5:95, v/v). It was also able to detect fluoride through naked eye in a toothpaste sample. The addition of 1 equiv. of fluoride as its tetrabutylammonium salt to the 5 × 10 −5 M aq. DMSO solution of the receptor 1 produced red color while the similar addition of acetate produced faint pink color. The dihydrogenphosphate and a variety of other anions were not able to produce any significant color change with receptor 1 under similar experimental conditions. The corresponding UV–vis measurements showed a bathochromic shifting of 455 nm band of receptor 1 to 514 and 484 nm for fluoride and acetate, respectively. The non-linear fittings of corresponding UV–vis titration data in 1:1 binding equation yielded association constants in 10 5:1 ratio for fluoride and acetate, respectively. The 1H NMR titrations studies shade further light on their mode of binding with receptor 1. The quantum mechanical calculations through time dependant density functional theory (TD-DFT) using basis set b3lyp/6-311g** supported our experimental findings nicely.

Naked-eye recognition of CuII, ZnII and acetate ion by the first guanine-based difunctional chromoinophore

The first guanine-based difunctional colorimetric receptor 8-[(4-nitrophenyl)azo]guanine (receptor 1) was designed, synthesized and characterized by IR, UV-vis, (1)H NMR and mass spectrometric analysis. The synthesized receptor 1 was able to recognize Cu(II), Zn(II) and acetate ion through visible color changes in its DMSO and DMSO-H(2)O (95:5, v/v) solution. The binding affinity of the receptor 1 with the chosen analytes has been estimated in terms of binding constants through non-linear fittings of corresponding UV-vis titration data while the binding mode of the same was studied through (1)H NMR spectral studies.

Modelling triazolophane–halide binding equilibria using Sivvu analysis of UV–vis titration data recorded under medium binding conditions

Two different models that calculate association constants from UV–vis titration data have been evaluated for the 1:1 binding between triazolophane receptor ([Host] = 1–13 μM) and various halides F− , Cl− , Br− and I− in CH2Cl2 (K a ≈ 103–106 M− 1). The Drago model fits the ΔA values at a single wavelength as a function of the added guest concentration. The new computer program Sivvu performs equilibrium-restricted factor analysis using all the wavelengths of the dataset simultaneously. Both models generate comparable K a values, and both provide a means to assess the accuracy of the binding constant determination: K a [host] < 12. Analysis with Sivvu (1) allows the number of unique chemical absorbers to be identified in an unbiased manner. This analysis allowed for a 2:1, triazolophane:F− intermediate to be identified and included in the model. Sivvu also (2) allows alternate models to be quickly evaluated, (3) generates more accurate binding constants, and (4) generates the extinction profiles for each absorbing species in solution.

Solvent effects on complexation of thallium(I) with guanosine 5′‐monophosphate in methanol–water mixtures

AbstractThe interaction of guanosine 5′‐monophosphate, GMP, with the thallium(I) ion was studied by UV–vis and potentiometric titration methods and 31P NMR spectroscopy. Both NMR spectra and UV–vis titration data have shown that GMP coordinates via guanine to the thallium(I) ion in the pH range 1.5–10. Our study of the system Tl(I) + GMP was performed in water–methanol mixtures with different volume ratios of methanol. The complexation equilibrium in the pH range of study led to the following mononuclear species: TlH2(GMP)+, TlH(GMP) and Tl(GMP)−, where (GMP)2− represents the fully dissociated ligand. The formation constants of the species were calculated in the various media at constant temperature (25 °C) and constant ionic strength of sodium perchlorate (0.1 mol dm−3) using a suitable computer program. The formation constants were analyzed in terms of Kamlet and Taft's parameters. A single‐parameter correlation of the formation constants, β121, β111 and β101 vs α (hydrogen‐bond donor acidity), β (hydrogen‐bond acceptor basicity) and for π* (dipolarity/polarizability) are relatively poor in all solutions, but multi‐parameter correlations represent significant improvements with regard to the single‐parameter model. In this work, we have also used the normalized polarity parameter, ETN, alone and in combination with some of the Kamlet–Taft parameters to find a better correlation of the formation constants in different methanol–water mixtures. Copyright © 2007 John Wiley &amp; Sons, Ltd.