Continuous Variation Method Research Articles

Inclusion Compound of Efavirenz and γ-Cyclodextrin: Solid State Studies and Effect on Solubility.

Efavirenz is an antiretroviral drug of widespread use in the management of infections with human immunodeficiency virus type 1 (HIV-1). Efavirenz is also used in paediatrics, but due to its very poor aqueous solubility the liquid formulations available resort to oil-based excipients. In this report we describe the interaction of γ-cyclodextrin with efavirenz in solution and in the solid state. In aqueous solution, the preferential host–guest stoichiometry was determined by the continuous variation method using 1H NMR, which indicated a 3:2 host-to-guest proportion. Following, the solid inclusion compound was prepared at different stoichiometries by co-dissolution and freeze-drying. Solid-state characterisation of the products using FT-IR, 13C{1H} CP-MAS NMR, thermogravimetry, and X-ray powder diffraction has confirmed that the 3:2 stoichiometry is the adequate starting condition to isolate a solid inclusion compound in the pure form. The effect of γ-cyclodextrin on the solubility of efavirenz is studied by the isotherm method.

Inclusion complexation of 4′,6-diamidino-2-phenylindole (DAPI) with cucurbit[7]uril and cyclodextrins (native β-, 2,6-di-O-methylated β-, and γ-cyclodextrin): characteristic inclusion behaviour and fluorescence enhancement

Herein, we investigated the inclusion complexation of a fluorescent probe [4′,6-diamidino-2-phenylindole (DAPI)] using various cyclodextrins (CDs) and cucurbit[7]uril (CB7). Using the continuous variation method, DAPI was found to form a 1:1 inclusion complex with CDs and CB7. 1H-NMR and 2D ROESY (1H-1H rotating frame nuclear Overhauser effect) spectroscopy indicated that the inclusion of DAPI by the CDs and CB7 occurs via the encapsulation of the phenyl group and indole moiety of DAPI. The stability of the CB7 inclusion complex was higher than that of the CDs: the stability was attributed to the extra interaction formed between the dicationic dye (DAPI) and polar carbonyl groups at the portals of CB7. Furthermore, we determined the fluorescence quantum yield (Φ) of the inclusion complexes. The Φ values of DAPI were significantly enhanced upon its inclusion by CB7 and increased as the empirical solvent polarity parameter (ET(30)) decreased. Based on these results, we concluded that the polarity of the microenvironment and protonation ability of the excited state of DAPI play important roles in emission efficiency.

Structural, conformational and therapeutic studies on new thiazole complexes: drug-likeness and MOE-simulation assessments

A series of new complexes derived from Pd(II), Cu(II) and Fe(III) ions reacted with thiazole derivative (HL, CPTP) was prepared. Structures of all new compounds were characterized and confirmed using analytical and spectroscopic (IR, UV–Vis and 13C&1H NMR) techniques. All complexes have non-electrolytic nature based on molar conductance measurements. TGA was executed to confirm the presence of water molecules inside or outside the coordination sphere as well as the mono-nuclear feature of isolated complexes. Accordingly, thermo kinetic parameters were calculated for all decomposition steps. The obtained analytical data regarding complexation in solution, molar ratio and continuous variation methods suggest 1 M:1 L molar ratio. The oriented structures using advanced program assert on best distribution for coordinating sites (NH& NH2). Moreover, electrostatic potential map as well as iso-surface with array plot of ligand reflects high nucleophilic feature with reduced outer contour on two coordinating sites. In vitro antimicrobial, anticancer and antioxidant activities of ligand and its complexes were checked. All complexes exhibited superiority on free ligand in successful treatment, specifically CPTPPd complex. Drug-likeness as well as MOE-docking simulation outcomes indicates promising inhibitory feature of CPTPPd and CPTPCu complexes, in agreement with in vitro results.

Removal of Toxic heavy metal ions by the formation of complex with Theophylline (Therapy drug): Thermodynamic and kinetic study

Chelation therapy drug is an established treatment for heavy metal toxicity. Chelation therapy agents that remove toxic metal ions such as Lead, Nickel, Zinc, iron and copper from the body by removing them from intracellular or extracellular spaces. The present study create all the experiment were performed at different temperature (303, 308, 313, 318, 323)°K. The UV-Vis measurements were carried out for the metal-drug complex by Spectrophotometric method. The absorption Spectrum of the mixture of drug and Nickel ion shows a batho chromic (red) shift in λmax, the absorbance change caused by complex arrangement between the Nickel ion and drug. The stoichiometry of the formed complex was investigated by the method of continuous variation and it was found (1: 1), In the present work we investigate the stability constant of therapy drug with Ni(II) ion using water at (298K, 303, 308K, 313, 318)°K, We employed to determine (Ni(II)-ligand) complex stability constant (logK) values. It is observed that Ni (II) ion forms 1: 1 complex. The thermodynamic parameter ΔGo, ΔHo and ΔSo were calculated from values of stability constant at different temperatures. The formations of (Ni(II)-drug) complex were found to be spontaneous and indothermic in nature. Chemical kinetics show, the Complication of drug with Ni ion was found to follow the second order reaction.

Charge-transfer chemistry of azithromycin, the antibiotic used worldwide to treat the coronavirus disease (COVID-19). Part I: Complexation with iodine in different solvents

Around the world, the antibiotic azithromycin (AZM) is currently being used to treat the coronavirus disease (COVID-19) in conjunction with hydroxychloroquine or chloroquine. Investigating the chemical and physical properties of compounds used alone or in combination to combat the COVID-19 pandemic is of vital and pressing importance. The purpose of this study was to characterize the charge transfer (CT) complexation of AZM with iodine in four different solvents: CH2Cl2, CHCl3, CCl4, and C6H5Cl. AZM reacted with iodine at a 1:1 M ratio (AZM to I2) in the CHCl3 solvent and a 1:2 M ratio in the other three solvents, as evidenced by data obtained from an elemental analysis of the solid CT products and spectrophotometric titration and Job's continuous variation method for the soluble CT products. Data obtained from UV–visible and Raman spectroscopies indicated that AZM strongly interacted with iodine in the CH2Cl2, CCl4, and C6H5Cl solvents by a physically potent n→σ* interaction to produce a tri-iodide complex formulated as [AZM·I+]I3−. XRD and TEM analyses revealed that, in all solvents, the AZM-I2 complex possessed an amorphous structure composed of spherical particles ranging from 80 to 110 nm that tended to aggregate into clusters. The findings described in the present study will hopefully contribute to optimizing the treatment protocols for COVID-19.

High-temperature binding parameters and molecular dynamics of 4-hydroxybenzoic acid and β-casein complexes, determined via the method of continuous variation and fluorescence spectroscopy

Interactions between β-casein and 4-hydroxybenzoic acid (4HBA) were investigated following ultra-high temperature (UHT) treatment at 140 °C for 10 s. The aim of the work was to identify the binding strength, binding stoichiometry and type of molecular interactions between protein and bioactive compound. Molecular dynamics (MD) analysis shows that binding is stabilised by a wider variety of residues than is often indicated in simpler docking studies. Construction of Job plots via fluorescence quenching argues that β-casein can accommodate two 4HBA molecules. This is in agreement with MD analysis, which demonstrates the stability of ligand in two different binding sites of the receptor. FTIR results indicate a binding interaction between the two components and UV–vis measurements record an increase in the absorption of 4HBA following UHT treatment in the presence of β-casein. The latter observation argues that 4HBA may be bound covalently following heat treatment. This is further supported by MD simulations and quantum mechanics calculations that indicate one site has the potential for binding covalently to 4HBA via the lysine32 residue of the β-casein molecule. This work addresses often overlooked issues in the determination of binding parameters, through the use of the method of continuous variation for the accurate determination of binding stoichiometry, as well as making use of a nonlinear fluorescence binding equation to account for the residual fluorescence of formed complexes. The findings give a broader understanding of the fate of bioactive ingredients in UHT treated beverage systems, allowing industry to make informed decisions on the inclusion of insoluble fibres and the impact of heat treatment on their products.

Selective recovery of platinum by combining a novel reusable ionic liquid with electrodeposition

In this study, five new imidazolium ionic liquids (ILs) were synthesized, and their efficiencies toward the precipitation of PtCl62− in HCl media were evaluated. The prepared compounds were identified as 1-alkyl-3-propylimidazolium bromide ([CnPIm]Br, n = 12, 14, and 16), 1-tetradecyl-2-aminoethylimidazolium bromide ([C14PImNH2]Br), and 1-tetradecyl-3-butylimidazolium bromide ([C14PIm]Br). FT-IR, 1H NMR, and continuous variation method analysis were used to establish the ion-exchange model of Pt(IV) precipitation. To extract Pt(IV) from mixed metal solutions, and a novel mixed-ILs system was obtained through the dissolution of 1-tetradecyl-3-propylimidazolium bromide ([C14PIm]Br) in hydrophobic ILs ([C8MIm][PF6]). The mixed-ILs ([C14PIm]Br/[C8MIm][PF6]) exhibited excellent extraction efficiency compared to single [C8MIm][PF6]. Also, Pt(IV) ions were selectively separated from mixed metal solutions containing Rh(III), Fe3+, Ni2+, Cu2+, and Zn2+ metal ions. The separation factor βPt/M (M: Fe, Ni, Cu, Zn, or Rh) was above 105 for all systems. The optimal potentiostatic deposition voltage of Pt was estimated to −1.75 V. Direct electrodeposition from ILs containing [C14PIm]Br/[C8MIm][PF6] with Pt(IV), more than 97% of Pt(IV) was reduced to Pt(0) on the copper cathode, while the system could also be regenerated for PtCl62− extraction. Surface characterization techniques like SEM, TEM, and XPS identified the deposited silver-grey films on cathode surfaces as Pt metal with metallic luster.

Structure investigation for nickel and cobalt complexes formed during solvent extraction with the extractants Cyanex 272, Versatic 10 and their mixtures

This work reports the structure investigation of organometallic complexes formation between nickel and cobalt and the extractants Cyanex 272, Versatic 10 and their mixtures. For a better understanding of nickel and cobalt purification from solvent extraction technique, the experiments were carried out with a synthetic leach solution similar to the nickel laterite leach liquor. The coordination number of the metal complexes was evaluated by the ultraviolet–visible (UV–vis) absorption spectra of the organic phases after extraction. The results indicated that the nickel complexes exhibited an octahedral coordination geometry in all investigated organic phases. The cobalt-Versatic 10 complex showed an octahedral geometry, while for Cyanex 272 and the extractants mixture of 15% (v/v) Cyanex 272 and 5% (v/v) Versatic 10 (C15V5), the cobalt complexes presented a tetrahedral structure. Attenuated total reflectance with Fourier transform infrared spectroscopy (ATR/FTIR) was used to identify the interactions between the functional groups of the extractant and the metal ions. Thermogravimetric analysis (TGA) was used to examine the hydration of the complexes. The continuous variation method (Job’s method) was applied to determine the number of molecules involved in the metal-extractant complexes. The Ni-Versatic 10 complex was formed by three molecules of the extractant. For Ni-C15V5 complex, one molecule of Cyanex 272, one of Versatic 10 and two molecules of water formed the complex. For Co-Cyanex 272 and Co-C15V5, the complex was formed with two molecules of Cyanex 272, indicating that in this experimental condition there was no interaction of the extractant Versatic 10 in the extraction. After the stoichiometry of all the organometallic complexes formed had been defined, a structure was proposed for each metal-extractant complex.

Determination of Stability Constants of Iron(II) Complexes of as-Triazines Containing Ferroin-Yielding Chromogens

With the aim of determining stability constants of iron(II) complexes of 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT), 3-(2-pyridyl)-5,6-bis(p-methoxyphenyl)-1,2,4-triazine (PBMPT) and 3-(2-pyridyl)-5,6-bis(4-biphenyl)-1,2,4-triazine (PBBT), these organic reagents were prepared from commercially available relatively cheaper reactants. The absorptiometric characteristics of iron(II) complexes of these organic compounds; λmax and molar absorptivity (€max) were determined. The composition and stability constants of these iron(II) complexes were determined by both molar ratio and Job’s continuous variation methods. The mean logK values for iron(II) complexes of PDT, PBMPT and PBBT were found 16.48, 17.48 and 15.54 respectively reflecting the formation of very stable complexes. These are well comparable with the reported values for the iron(II) complexes of 2,2’-bipyridine, 1,10- phenanthroline, Ferrozine and Ferene. Higher sensitivity and stability constant values reflects the possibility of application of these compounds as promising chromogenic reagents for iron determination.
 Dhaka Univ. J. Sci. 68(2): 137-142, 2020 (July)

The Charge Transfer Complex Formed between the Components of Photopolymer Material as an Internal Sensitizer of Spectral Sensitivity

AbstractA photosensitive charge transfer complex (CTC) is formed between the components of the photopolymer material: the tetra–acrylate monomer synthesized from dihydroxydiphenyl sulfide (TADDS) and a photoinitiator, a cationic sulfonium salt synthesized from diethylthioxanthen‐9‐one (SSDETX). It allows one to perform laser recording of the microstructures in the hybrid photopolymer material using absorption of CTC at λ=473 nm. The 1 : 1 molecular composition of CTC was confirmed by applying the Job's method of continuous variation to determine the stoichiometry. The association constant (KAS(278°K)=17 L mol−1) was calculated using the modified Benesi‐Hildebrand equation. The thermodynamic parameters, such as enthalpy (ΔH=−15.63 kJ mol), entropy (ΔS°=−32.6 J mol−1 K−1), and the Gibbs free energy (ΔG=−6.63 kJ mol−1) were calculated using the Van't Hoff equation. These results indicate that CTC formation is an exothermic reaction. The experimental findings were supplemented by density functional theory (DFT) study of CTCs at the UB3LYP/6‐311G level as implemented in the Gaussian 09 software package. Charge transfer excitations were simulated by means of the time‐dependent density functional theory (TDDFT) approach. The DFT‐calculated spectra agree with the experimental data of spectral and photochemical properties of the [SSDETX‐TADDS] CTC.

Synergistic Interaction of Natural Snail Mucin and Lincomycin for Immuno-chemotherapy against Streptopneumococcal Infection: Checkerboard Evaluations

Introduction: Pneumonia is an acute infection of lung majorly caused by Streptoneumococcal bacteria or other microbes which present cough with phlegm (mucus), fever and other clinical symptoms. This mucus produced are easily polymerize with other similar natural product like snail mucin when taken which serves as a natural antimicrobial immune booster for enhanced or synergistic response against causative agent in the presence of antibiotics. This work was carried out to determine the combined effect of snail mucin as animal sourced natural product antimicrobial agent with lincomycin against different strains of Streptococcus pneumoniae as alternative treatment option for this respiratory tract infection “pneumonia” which has been a global challenge especially in the tropical Africa. Methods: Separate solution each of the two agent was prepared in sterile normal saline to get a different concentration of the agents, each solution contained twice the MIC of the agent. The agents were then combined in different ratios for interaction effect by adopting the standard continuous variation method and further diluted using two-fold serially dilutions and evaluated against the test organisms using both agar diffusion and dilution method respectively. Results: The result of FIC index was calculated showed greater synergy in the equal ratio (50:50) combination against all the strains of tested organisms. Also, better performance at the combinations ratios of 60:40 and 40:60 of mucin and lincomycin respectively emerged. Conclusion: This synergistic effect has shown an improved natural product immuno-antimicrobial chemotherapy for alternative treatment option of such acute infection in the absent orthodox medicine.

Investigation of the Interaction of Gadolinium with Several Organic Ligands and Humic Acid by Ligand Competition Using 4-(2-Pyridylazo)-Resorcinol (PAR)

Gd3+ forms a strongly colored complex with 4-(2-pyridylazo)-resorcinol (PAR) in aqueous solutions. We characterized the Gd3+-PAR complex in order to use it as a probe of Gd3+ speciation in the presence of environmentally relevant ligands. The formation of the Gd3+-PAR complex was investigated from pH 5 to 8 in the presence of excess PAR. The absorbance of the Gd3+-PAR complex dramatically increased from pH 5 to 8 and application of the method of continuous variation indicates that the complex was primarily 1:2 Gd(PAR)2 at pH 8. Stability constants for Gd3+ with other ligands can be quantified by competitive displacement of the PAR ligand. To establish the viability of this approach, we measured the stability constants between Gd3+ and several organic acids and carbonate. Our measurements show reasonable agreement with the literature values. We used the competitive displacement approach to establish that humic acids can competitively displace PAR from the Gd(PAR)2 complex.

Studies on the supramolecular complex of a guanosine with beta-cyclodextrin and evaluation of its anti-proliferative activity

The behavior of the inclusion behavior of guanosine (GU) with beta-cyclodextrin (β-CD) in the liquid, solid and virtual state were investigated. The absorption and fluorescence spectral were used to determine the inclusion behavior in liquid state. FT-IR, NMR, TGA, DSC, PXRD and FESEM techniques were used to investigate the inclusion behavior in solid-state, meanwhile the virtual state studies are done by molecular docking. The solid inclusion complex (GU: β-CD) was prepared by using the co-precipitation method. The binding constant (K) of (GU: β-CD) was calculated by using Benesi-Hildebrand. Besides that, the 1:1 stoichiometric ratio of inclusion complex was confirmed by using the Benesi-Hildebrand plot and Job's plot of continuous variation method. The most preferable model of GU: β-CD that suggested via molecular docking studies was in good agreement with experimental results. The inclusion complex of GU: β-CD exerted its toxicity effects towards HepG2 cell lines based on the reduced number of cell viability and lowest IC50 value compared to the GU and β-CD viability.

Highly reproducible, simple and selective analytical method for extractive UV-visible spectrophotometric determination of ruthenium(III): Analysis of catalyst, fissium alloy and sequential separation.

An easy and selective method has been developed for the extractive spectrophotometric determination of ruthenium(III) with 4-(4'-flurobenzylideneimino)-3-methyl-5-mercapto-1,2,4-triazole (FBIMMT) as a chelating reagent. The basis of the method is the formation of stable complex of 'soft base' FBIMMT with 'soft acid' ruthenium(III). The reagent FBIMMT in n-butanol easily forms extractable yellow coloured complex with ruthenium(III) in acetate buffer of pH4.8. The absorbance of [Ru(III)-FBIMMT] complex is measured at 394nm against the reagent blank. Good linearity range of concentration up to 27.0μgmL-1 of ruthenium(III) is attained with correlation coefficient R2=0.998. The optimum concentration range is 6 to 27.0μgmL-1 which is deduced by Ringbom's plot. The apparent molar absorptivity found to be 2.75×103Lmol-1cm-1. Some additional characteristics such as limit of detection (LOD=0.48μgmL-1), limit of quantification (LOQ=1.19μgmL-1), and Sandell's sensitivity (SS=of 0.0367μgcm-2) are also estimated. The composition of [Ru(III)-FBIMMT] complex has been established from Job's continuous variation method, mole ratio method, and log-log plot method. The specificity towards ruthenium(III) is well studied and appropriate masking agents are applied wherever required to boost it. The intra-day and inter-day precision values are found to be brilliant with % relative standard deviation of 0.52 and 0.68 respectively with % accuracy within the range of 99.00-100. The method is effectively used for determination of ruthenium(III) from water samples, binary and ternary synthetic mixtures, fissium alloy samples and catalyst materials. A scheme for sequential group separation of ruthenium(III), palladium(II) and osmium(VIII) has also been developed. The reproducible results of the present method confirm that the method has a good potential for quantitative determination of ruthenium(III) from various matrices.

Evaluation of Stoichiometry, Stability Constants and Gibbs Free Energies of Acetaminophen-Zn (II) complex at Different Temperatures

Acetaminophen also known as paracetamol, is a drug used in the treatment of pain and fever. It is essentially used for the relief of mild to moderate pain. The presence of phenol and carbonyl oxygen atom enables acetaminophen to behave as a bidentate ligand. The stoichiometry, stability constants and Gibbs free energies of acetaminophen-Zn (II) were determined colorimetrically at 25 and 40 oC using continuous variation and mole ratio methods. The formation of Zn (II) complex with acetaminophen was studied colorimetrically at an absorption maximum of 630 nm at different temperatures. The data showed that Zn (II) and acetaminophen combine in the molar ratio of 1:1 at pH 7.4 with ionic strength maintained using 0.1M KNO3. Calculated stability constants values were 2.70 x 103 and 2.20 x 103 using continuous variation method and 7.21 x 103 and 7.21 x 103 using mole ratio methods at 25 and 40 oC respectively. Calculated ΔGƟ for the complex were - 1.96 x 104 and -1.98 x 104 J using continuous variation method and -2.2 x 104 J and - 2.31 x 104 J using mole ratio method at 25 and 40 oC respectively. The stability constant and Gibbs free energy results suggested that acetaminophen used in the study is a good chelating agent and can be an efficient antidote in the therapy of Zn (II) overload or poisoning.
 Keywords: Acetaminophen, Zinc, complex, stability constant, Gibbs free energy.

Colorimetric Determination of Stability Constant of Sulfamethoxazole-Cu(II) Complex at Different Temperatures by Continuous Variation Method

Sulfamethoxazole is an antibiotic that is used for the treatment of bacterial infections such as prostatitis, bronchitis and urinary tract infections. It is effective against gram negative and gram positive bacteria. Classical equation has been used in the calculation of stability constant of SulfamethoxazoleCu(II) complex depending on the theoretical explanation of the stoichiometry. The formation of Cu(II) complex with sulfamethoxazole was studied colorimetrically at an absorption maximum of 430 nm at 25, 30, 35 and 40 oC. The data showed that Cu(II) and sulfamethoxazole combine in the molar ratio of 1:2 at pH 7.4 with ionic strength maintained using 0.1M KNO3. Calculated stability constants values were 4.02 x 106 , 2.93 x 106 , 1.37 x 106 and 9.21 x 105 using continuous variation method. Calculated ∆GƟ for the complex were -3.77 x 104 , -3.75 x 104 , -3.62 x 104 and - 3.57 x 104 . The stoichiometry, stability constant and Gibbs free energy results suggested that sulfamethoxazole used in the study is a good chelating agent and can be an efficient antidote in the therapy of Cu(II) overload or poisoning

Determination of Stability Constants and Thermodynamic parameters of Cefotaxime –Fe(III) Complex at Different Temperatures

Cefotaxime, a β-lactam antibiotic, has a structure which enables it to act as a chelating agent. The formation of Fe(III) complex with cefotaxime has been studied colorimetrically at an absorption maximum of 480 nm at different temperatures. The data showed that Fe(III) and cefotaxime combine in the molar ratio of 1:1 at pH 7.4 with ionic strength maintained using 0.1M KNO3. The stability constants of the complex were calculated to be 1.56 - 1.90 x 104 by continuous variation method and 1.34 - 1.71 x 104 by mole ratio method at 25 and 40 oC respectively. ∆HƟ values for the complex were calculated to be -1.02 x 104 and -1.05 x 104 J by continuous variation method and mole ratio method respectively. ∆GƟ of the complex were calculated to be -2.44 – (-2.51) x 104 J by continuous variation method and -2.41- (- 2.48) x 104 J by mole ratio method at 25 and 40 oC. ∆SƟ of the complex were calculated to be 2.44 - 2.51 x 104 J/K by continuous variation method and -2.41 -2.48) x 104 J/K by mole ratio method at 25 and 40 oC respectively. Cefotaxime is a good chelating agent and can be an efficient antidote in the therapy of copper overload or poisoning.

Hydroxy-neo-Clerodanes and 5,10-seco-neo-Clerodanes from Salvia decora.

Preliminary analysis of the mass spectrometric (MS) and NMR spectroscopic data of the primary fractions from the biologically active extract of Salvia decora revealed spectra that are characteristic for neo-clerodane-type diterpenoids. MS-guided isolation of the bioactive fractions led to the isolation of three new chemical entities, including two hydroxy-neo-clerodanes (1 and 2) and one acylated 5,10-seco-neo-clerodane (3), along with three known diterpenoids (4-6), ursolic acid (7), and eupatorin (8). The structures of the new compounds were established by analysis of the 1D and 2D NMR and MS data, whereas their absolute configuration was deduced using a combination of experimental and theoretical ECD data and confirmed by X-ray crystallography (1 and 4). Furthermore, compounds 1, 3, 4, and 6-8 were evaluated as hPTP1B1-400 (human protein tyrosine phosphatase) inhibitors, where 7 showed the best activity, with an IC50 value in the lower μM range. Additionally, compound 7 was evaluated as an α-glucosidase inhibitor. The affinity constant of the 7-hPTP1B1-400 complex was determined by quenching fluorescence experiments (ka = 1.3 × 104 M-1), while the stoichiometry ratio (1:1 protein-ligand) was determined by a continuous variation method.

Interactions between glycyl-L-phenylalanine and β-cyclodextrin from diffusion, spectroscopic and computational studies

The transport and association of the dipeptide glycyl-L-phenylalanine (Gly-L-Phen) in solutions containing cyclodextrins are of prime importance given its relevance in different areas, from biochemistry to wastewater treatment. We have investigated the interaction between aqueous Gly-L-Phen and β-cyclodextrin (β-CD) by NMR, DFT calculations in parallel with UV/visible absorption, luminescence spectral measurements and diffusion experiments. Ternary mutual diffusion coefficients of aqueous {Gly-L-Phen + β-CD} solutions have been measured by using the Taylor dispersion technique. The results show that the association of Gly-L-Phen and β-CD has a significant effect on the diffusion coefficients, consistent with an association constant of about 50 to 100, assuming a 1:1 (Gly-L-Phen):(β-CD) stoichiometry. This stoichiometry has been assessed by the continuous variation (Job's plot) method and the association constant was determined by using the Hildebrand-Benesi equation modified for NMR applications. The association constant was estimated to be equal to 40. This association constant is in close agreement with that obtained by fluorescence measurements (K = 43). Additionally, from NMR, detailed structural information on the complex has been obtained. This has been complemented by DFT and TD-DFT studies.

DNA Binding, DFT and Spectroscopic Studies of a Charge Transfer Complex Consisting of a Bioactive Donor 1-(2-Methylbenzyl)piperazine

A bioactive donor, 1-(2-methylbenzyl)piperazine is used to synthesize a new charge transfer complex (CTC) with the π-acceptor p-chloranil (p-CHL), which is characterized spectrophotometrically. The quantitative estimation of electronic interaction of the acceptor with the donor has been examined in acetonitrile (AN). The 1:1 composition of the CTC is confirmed by Jobs’ method of continuous variation and spectrophotometric (at $$\lambda$$ max 554 nm) methods at 298 K. The Benesi–Hildebrand method gives the formation constant (KCT) and molar extinction coefficient (e) values of CTC. The spectral analysis was used to characterize CTC and its stability in solution and in the crystalline form. A DNA binding study of the CT-complex was carried out using UV–visible spectroscopy. A density functional theory (DFT) study of the CTC (gas phase/PCM) at using the B3LYP functional and 6-31G(d,p) basis set supports the experimental work. The optimization of the frontier molecular orbital surfaces was carried out by using the DFT-gasphase/PCM correlation methods. Mulliken atomic charges and reactive parameters of acceptor and donor recommend the MBPZ acts as a good electron donor and p-CHL acts as a good electron acceptor to form a highly stable electron transfer complex.