Modified Benesi-Hildebrand Equation Research Articles

Performance of 4,5-diphenyl-1H-imidazole derived highly selective 'Turn-Off' fluorescent chemosensor for iron(III) ions detection and biological applications.

Two fluorescent chemosensors, denoted as chemosensor 1 and chemosensor 2, were synthesized and subjected to comprehensive characterization using various techniques. The characterization techniques employed were Fourier-transform infrared (FTIR), proton (1 H)- and carbon-13 (13 C)-nuclear magnetic resonance (NMR) spectroscopy, electrospray ionization (ESI) mass spectrometry, and single crystal X-ray diffraction analysis. Chemosensor 1 is composed of a 1H-imidazole core with specific substituents, including a 4-(2-(4,5-c-2-yl)naphthalene-3-yloxy)butoxy)naphthalene-1-yl moiety. However, chemosensor 2 features a 1H-imidazole core with distinct substituents, such as 4-methyl-2-(4,5-diphenyl-1H-imidazole-2-yl)phenoxy)butoxy)-5-methylphenyl. Chemosensor 1 crystallizes in the monoclinic space group C2/c. Both chemosensors 1 and 2 exhibit a discernible fluorescence quenching response selectively toward iron(III) ion (Fe3+ ) at 435 and 390 nm, respectively, in dimethylformamide (DMF) solutions, distinguishing them from other tested cations. This fluorescence quenching is attributed to the established mechanism of chelation quenched fluorescence (CHQF). The binding constants for the formation of the 1 + Fe3+ and 2 + Fe3+ complexes were determined using the modified Benesi-Hildebrand equation, yielding values of approximately 2.2 × 103 and 1.3 × 104 M-1 , respectively. The calculated average fluorescence lifetimes for 1 and 1 + Fe3+ were 2.51 and 1.17 ns, respectively, while for 2 and 2 + Fe3+ , the lifetimes were 1.13 and 0.63 ns, respectively. Additionally, the applicability of chemosensors 1 and 2 in detecting Fe3+ in live cells was demonstrated, with negligible observed cell toxicity.

A novel fluorescence sensor for uranyl ion detection based on a dansyl-modified peptide

It is of great significance to sensitively and selectively detect uranyl ion (UO22+) in environmental and biological samples due to the high risks of UO22+ to human health. However, such suitable sensors are still scarce. A novel fluorescence sensor based on a dansyl-modified peptide, Dansyl-Glu-Glu-Pro-Glu-Trp-COOH (D-P5), was efficiently synthesized by Fmoc solid phase peptide synthesis. As the first linear peptide-based fluorescence sensor for UO22+, D-P5 exhibited high selectivity and sensitivity to UO22+ over 27 metal ions (UO22+, Cr3+, Cu2+, Ba2+, Hg2+, Pb2+, Co2+, Ag+, Fe3+, Ca2+, K+, Mg2+, Mn2+, Na+, Ni2+, Cd2+, Zn2+, Al3+, Dy3+, Er3+, Gd2+, Ho3+, La3+, Lu3+, Pr3+, Sm3+, Tm3+) by a turn-off fluorescence response in 10 mM HEPES buffer (pH 6.3). The effects of anions such as S2−, NO3–, SO42− CO32–, HCOO–, antioxidant ascorbic acid and 4-nitrophenyl acetate on the selectivity for UO22+ detection were also studies. D-P5 sensor could be used for detecting UO22+ in a good linear relationship with concentration in the range of 0–8.0 μM with a low limit of detection of 83.2 nM. Furthermore, the interaction of the sensor with UO22+ was characterized by ESI-MS, IR, XPS and ITC measurements. The 1:1 binding stoichiometry between the sensor and UO22+ was measured by the job’s plot and further verified by ESI-MS. The binding constant of the sensor with UO22+ was calculated to be 9.8 × 104 M−1 by modified Benesi-Hildebrand equation. ITC results showed that theΔHθ andΔSθ for the interaction of D-P5 with UO22+ were −(7.167 ± 1.25) kJ·mol−1 and 66.5 J·mol−1·K−1, respectively. Time-resolved fluorescence spectroscopy indicated that the mechanism of fluorescence quenching of D-P5 by UO22+ ion was static quenching process. In addition, this sensor displayed a good practicality for UO22+ detection in lake water sample without tedious sample pretreatment.

UV–VIS investigation of methyl red in presence of sodium dodecyl sulfate/methanol/ethanol/water system

This paper reports room temperature UV–VIS study of interaction of methyl red (MR) dye with sodium dodecyl sulfate (SDS)/methanol/ethanol/water systems in different ratios of the solvent components (R = 0, 10, 20, 30, and 40); where the concentration of water is represented by a R parameter. The concentration of SDS was varied from 1.4 × 10-4 to 2.8 × 10-3molL-1 for the SDS/methanol/water system and 2.2 × 10-4 to 4.4 × 10-3molL-1 for SDS/ethanol/water system. In all experiments, MR concentration was fixed to 7.4 × 10-6molL-1. The MR spectrum was very similar at lower R values. The solution appeared cloudy at R = 30. For R = 40, MR absorption maximum (λmax) strongly red-shifted from 412 nm to 493–495 nm on increasing the concentration of SDS in the methanol system but no such shift was observed in ethanol. The transparency of the solution again vanished at R = 50 and the experiment was not carried above. These observations suggested that MR exists in hydrazone and azo form in SDS/methanol and SDS/ethanol system; respectively. On increasing concentration of SDS, the MR absorbance increased in the methanol system (hyperchromic shift) and decreased in ethanol system (hypochromic shift). The distribution constant (K) and binding constant (K’) were evaluated through the NLREG procedure and the modified Benesi-Hildebrand equation was also introduced to calculate the binding constant (Kb) and Gibbs free energy of binding (ΔG0). With increasing R, the ΔG0 value became more negative in methanol system; whereas it became less negative in the ethanol system. The negative value of ΔG0 indicated the spontaneity of SDS binding with MR.

Octa‐substituted Zinc(II), Cu(II), and Co(II) phthalocyanines with 1‐(4‐hydroxyphenyl)propane‐1‐one: Synthesis, sensitive protonation behaviors, Ag(I) induced H‐type aggregation properties, antibacterial–antioxidant activity, and molecular docking studies

AbstractThis study shows the synthesis and characterization of 4,5‐bis(4‐propionylphenoxy)phthalonitrile (2) and its octa‐substituted phthalocyanine derivatives [ZnPc(3), CuPc(4), and CoPc(5)]. A combination of standard spectroscopic techniques has characterized the newly synthesized phthalonitrile derivative and phthalocyanines. The aggregation behaviors of new octa‐substituted phthalocyanines have been evaluated by ultraviolet–visible (UV‐vis) spectroscopy. The metal ion‐sensitive behaviors of new octa‐substituted phthalocyanines in the presence of soft metal ions have been performed by UV‐vis and fluorescence spectrophotometer. The quenching efficiency (Ksv) of Ag+ ions against ZnPc(3) was found using the Stern–Volmer equation. The binding constant (Ka) and binding stoichiometry (n) of ZnPc(3) with Ag+ ions were calculated using the modified Benesi–Hildebrand equation. Sensitive protonation behaviors of octa‐substituted phthalocyanines have been investigated by titration experiments as well as computational calculations. The ZnPc(3) and CuPc(4) were exhibited H‐type aggregation behaviors toward Ag+ ions. However, the protonation of octa‐substituted zinc and copper phthalocyanine during the titration with HCl caused J‐type self‐aggregation properties. In vitro antioxidant properties of the new compounds were investigated by the radical scavenging ability of 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH), chelating ability to ferrous ions, and reducing power methods. Additionally, in vitro antibacterial activities of the octa‐substituted phthalocyanines were determined. Finally, optimized structures of novel compounds [(2), ZnPc(3), CuPc(4), and CoPc(5)] were obtained on the HF (Hartree–Fock), B3LYP (Becke, 3‐parameter, Lee‐Yang‐Parr), M06–2X methods with 3–21 g, 6–31 g and SDD basis set. Then, biological activities of novel phthalonitrile and its phthalocyanine derivatives toward breast, liver, and lung cancer proteins were compared with molecular docking studies.

α-Substituted phthalocyanines based on metal-induced H- or J-type aggregation for silver and palladium ions: synthesis, fluorescence, and antimicrobial and antioxidant properties.

In this study, firstly, 3-(2,3-bis(hexadecylthio)propoxy)phthalonitrile (2) as a new phthalonitrile derivative was prepared. Then, new types of non-peripheral phthalocyanine derivatives [CuPc (3), ZnPc (4), and CoPc (5)] were synthesized by using this ligand. The synthesized new compounds were characterized by common spectroscopic methods such as FTIR, 1H-NMR, 13C-NMR, MALDI-TOF, UV-Vis and fluorescence spectroscopy. The H- or J-type aggregation behaviors of novel type metallophthalocyanines in the presence of valuable metal ions such as Ag(i) and Pd(ii) were investigated by UV-Vis and fluorescence spectroscopy. The quenching efficiency of the Ag(i) and Pd(ii) ions for ZnPc (4) was obtained using the Stern-Volmer equation and the quenching constant of ZnPc (4) towards Ag(i) and Pd(ii) ions was found to be 2.9 × 105 mol L-1 and 1.2 × 105 mol L-1, respectively. The binding constant (Ka) and binding stoichiometry (n) of Ag(i) and Pd(ii) ions for ZnPc (5) were calculated using a modified Benesi-Hildebrand equation, and were found to be 1.4 × 108 M-1 and 3.4 × 107 M-1, respectively. The binding ratio and free energy change of Ag(i) and Pd(ii) ions for ZnPc (4) were found to be 1.86, 1.54, -46.49 kJ mol-1 and -42.9 kJ mol-1, respectively. Also, the antioxidant properties of the synthesized novel type metallophthalocyanines and their Ag(i) and Pd(ii) ion doped aggregates were determined using three different methods: DPPH free radical scavenging activity, ferrous ion chelating activity and reducing power activity. Finally, the antibacterial and antifungal activities of phthalocyanine compounds synthesized within the scope of this study were determined by disc diffusion and macrobroth dilution methods and the effect of the doping of Ag(i) and Pd(ii) ions on the antibacterial activities of phthalocyanines was investigated.

Electron-transfer complexation of morpholine donor molecule with some π – acceptors: Synthesis and spectroscopic characterizations

Abstract Morpholine is an interesting moiety that used widely in several organic syntheses. The intermolecular charge-transfer (CT) complexity associated between morpholine (Morp) donor with (monoiodobromide “IBr”, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone “DDQ”, 2,6-dichloroquinone-4-chloroimide “DCQ” and 2,6-dibromoquinone-4-chloroimide “DBQ”) π–acceptors have been spectrophotometrically investigated in CHCl3 and/or MeOH solvents. The structures of the intermolecular charge-transfer (CT) were elucidated by spectroscopic methods like, infrared spectroscopy. Also, different analyses techniques such as UV-Vis and elemental analyses were performed to characterize the four morpholine [(Morp)(IBr)], [(Morp)(DDQ)], [(Morp)(DCQ)] and [(Morp)(DBQ)] CT-complexes which reveals that the stoichiometry of the reactions is 1:1. The modified Benesi-Hildebrand equation was utilized to determine the physical spectroscopic parameters such as association constant (K) and the molar extinction coefficient (ε).

Synthesis, spectroscopic, theoretical and antimicrobial studies on molecular charge-transfer complex of 4-(2-thiazolylazo)resorcinol (TAR) with 3, 5-dinitrosalicylic acid, picric acid, and chloranilic acid

Charge-transfer complex of 4-(2-thiazolylazo) resorcinol (TAR) with 3, 5-dinitrosalicylic acid (3,5-DNSA), picric acid (PA), and chloranilic acid (CLA) were synthesized and characterized spectroscopically and investigated theoretically. Molecular composition of the prepared complexes was determined by mole ratio method. It was found that the stoichiometry of all prepared complexes is 1:2 (donor: acceptor) in methanol solvent. Stability constant of the prepared complexes were determined by using modified Benesi-Hildebrand equation. High values of formation constant of the complexes were signifying the high stability of the complexes. Different spectroscopic parameter as ionization potential (ID) of donor, oscillator strength (f), transition dipole moment (μEN), etc. were determined using UV–Vis spectroscopy in same solvent. The effect of solvent polarity on the charge-transfer spectra was also verified in four different solvents. The infrared spectrum studies of the solid complexes explore the presence of charge-transfer interaction through a hydrogen bonding interaction. TGA-DTA of the prepared complexes was also done to find out the thermal nature and stability of the complex. Synthesized complexes were checked for antibacterial and antifungal activities against different bacterial and fungal strains and complexes shows potent antibacterial and antifungal activity. DFT method was employed to view the molecular structure, electronic and spectroscopic nature of the studied complexes. MEP calculation, HOMO and LUMO energies, interaction energy, NBO analysis were performed on optimized structures of the complexes.

Photo-physical investigation of the binding interactions of alumina nanoparticles with calf thymus DNA

A mechanism-based spectrophotometric titration of nano-alumina powder with calf thymus ds-DNA was carried out at two temperature levels with a view to generating possible mode of interaction between this industrially useful nanopowder and DNA. Varying molar ratio combinations of DNA with the nano-alumina powder were studied at 37 °C and 45 °C after 30 min incubation period. The UV–Vis spectral data were acquired from 200 to 650 nm. The effect of the nanopowder on the most prominent wavelength maximum of DNA at 280 nm was studied. Stoichiometric ratio determination was determined using Job’s method of continuous variation. The formation constants between the ds-DNA and alumina nanopowder were calculated from a modified Benesi–Hildebrand equation for complex formation. In order to understand the spectral changes observed, thermodynamic parameters were evaluated such as the Gibbs free energy, enthalpy and entropy changes. The alumina nanopowder produced a pronounced hypochromic effects on the spectra of ds-DNA at all mole ratios relative to 100% DNA. There was enhanced effect at the elevated temperature of 45 °C with slight hypsochromic shift. These suggest some level of interaction with ds-DNA. The plot of absorbance of complexes at the respective λmax produced two points of inflection which suggest that the two atoms of aluminum in Al2O3 were interacting with DNA molecule. The formation constant varied directly with increase in temperature exhibiting an endothermic reaction. Evaluation of the thermodynamic parameters showed a large free energy change with positive enthalpy and small positive entropy. This confirms a dative covalent bonding interaction. The simple method presented in this research can be used to screen suspected genotoxins especially following occupational exposures.

Spectroscopic study and antioxidant activity of the inclusion complexes of cyclodextrins and amlodipine besylate drug

The aim of the study was to synthesize and characterization the inclusion complexes of amlodipine besylate (AML) drug with β-cyclodextrin (β-CD) and γ-cyclodextrin (γ-CD) which has antioxidating activity property. The guest/host interaction of AML with β-CD and γ-CD in order to complexation drug in β-CD and γ-CD were investigated. The interaction inclusion complexes was characterized by fourier transform infrared and ultraviolet–visible spectroscopies. The formation constant was calculated by using a modified Benesi–Hildebrand equation at 25 °C. The stoichiometry of inclusion complexes was found to be 1:1 for β-CD and γ-CD with AML drug. The antioxidant activity of AML drug and its inclusion complexes were determined by the scavenging of stable radical 2,2′-diphenyl-1-picrylhydrazyl (DPPH·). Kinetic studies of DPPH· with AML and CDs complexes were done. The experimental results confirmed the forming of AML complexes with CDs also these indicated that the AML/β-CD and AML/γ-CD inclusion complexes was the most reactive than its free form into antioxidant activity.

Preparative Enantioseparation of β-Substituted-2-Phenylpropionic Acids by Countercurrent Chromatography With Substituted β-Cyclodextrin as Chiral Selectors.

Preparative enantioseparation of four β-substituted-2-phenylpropionic acids was performed by countercurrent chromatography with substituted β-cyclodextrin as chiral selectors. The two-phase solvent system was composed of n-hexane-ethyl acetate-0.10 mol L-1 of phosphate buffer solution at pH 2.67 containing 0.10 mol L(-1) of hydroxypropyl-β-cyclodextrin (HP-β-CD) or sulfobutylether-β-cyclodextrin (SBE-β-CD). The influence factors, including the type of substituted β-cyclodextrin, composition of organic phase, concentration of chiral selector, pH value of the aqueous phase, and equilibrium temperature were optimized by enantioselective liquid-liquid extraction. Under the optimum separation conditions, 100 mg of 2-phenylbutyric acid, 100 mg of tropic acid, and 50 mg of 2,3-diphenylpropionic acid were successfully enantioseparated by high-speed countercurrent chromatography, and the recovery of the (±)-enantiomers was in the range of 90-91% for (±)-2-phenylbutyric acid, 91-92% for (±)-tropic acid, 85-87% for (±)-2,3-diphenylpropionic acid with purity of over 97%, 96%, and 98%, respectively. The formation of 1:1 stoichiometric inclusion complex of β-substituted-2-phenylpropionic acids with HP-β-CD was determined by UV spectrophotometry and the inclusion constants were calculated by a modified Benesi-Hildebrand equation. The results showed that different enantioselectivities among different racemates were mainly caused by different enantiorecognition between each enantiomer and HP-β-CD, while it might be partially caused by different inclusion capacity between racemic solutes and HP-β-CD.

Physico-Chemical Investigation on the Interaction Between Ochratoxin A and Heptakis-2,6-di-O-Methyl-β-Cyclodextrin

The interaction of ochratoxin A (OTA) with heptakis-2,6-di-O-methyl-β-cyclodextrin (DIMEB) in aqueous solutions at two different pHs (3.5 and 9.5) was studied by means of spectroscopic, calorimetric and electrochemical techniques. DIMEB affected the physico-chemical properties of OTA. A stronger interaction was observed at pH = 3.5 where the neutral form of OTA prevails. The spectroscopic information indicated that the OTA/DIMEB inclusion process occurred through the insertion of the phenylalanine group into the cyclodextrin (CD) cavity; moreover, voltammetry experiments showed that the isocoumarinic phenolic group was also involved, probably by non-inclusion interactions. At pH = 3.5, binding constants and thermodynamic parameters of the OTA/DIMEB complex were determined by means of the modified Benesi-Hildebrand equation and van’t Hoff plot. A 1:1 stoichiometry for the OTA/DIMEB complex was observed with a binding constant equal to 530 ± 50 L·mol−1 at 25 °C. The calculated thermodynamic parameters indicate that the interaction is highly endothermic and that the complex formation is driven by entropy. The results provide useful information for potential applications of cyclodextrins in the analysis of mycotoxins and in the field of mycotoxin sequestering agents.

Spectrophotometric investigation of interaction between iodine and pentadentate Schiff base ligands

The interaction between iodine as an electron acceptor (A), and three pentadentate Schiff bases, 1,3-bis(salicylideneamino)-2-propanol (SB1), 1,3-bis(2-hydroxy-1-naphthylideneamino)-2-propanol (SB2), and 1,3-bis[1-(pyridine-2-yl)methylideneamino]-2-propanol (SB3), as electron donor systems (D), was studied spectrophotometrically in methanol at 28°C. Equilibrium constants KAD and molar extinction coefficients εAD of the donor–acceptor complexes (AD) were determined using the modified Benesi–Hildebrand equation in conjunction with the non linear fit analysis. The method shows the formation of 1:1 type complexes as major species in solution. The free energy changes ΔG° and the energy of the charge transfer band ECT were also calculated for all complexes. The iodine complex derived from SB2 seems to be more stable than those derived from SB3 and SB1. On the other hand, the ionization potential ID of each Schiff base was estimated from the corresponding complex band energy, using an empirical equation. An inverse relationship between ID and KAD values was found. Blue and red shift observed for the 445nm band of iodine were also discussed on the basis of theoretical considerations.

Charge-transfer interactions of metoclopramide nausea drug against six kind of π-acceptors: Spectral and thermal discussions

The target of this paper is aimed to discuss the fast and newly techniques in order to assessment the metoclopramide (Mcp) nausea drug in pure form in solid and solution shape with different kind of π-acceptors upon charge transfer interactions. Charge-transfer complexes (CTC) of metoclopramide with picric acid (PA), 2,3-dichloro-5,6-dicyano-p-benzoquinon (DDQ), tetracyanoquinodimethane (TCNQ), m-dinitrobenzene (DNB), p-nitrobenzoic acid (p-NBA) and tetrachloro-p-quinon (p-CL) have been studied spectrophotometrically in absolute methanol at room temperature. The stoichiometries of the complexes were found to be 1:1 ratio by the spectrophotometric titration between metoclopramide and represented π-acceptors. The equilibrium constants, molar extinction coefficient (εCT) and spectroscopic-physical parameters (standard free energy (ΔG°), oscillator strength (ƒ), transition dipole moment (μ), resonance energy (RN) and ionization potential (ID)) of the complexes were determined upon the modified Benesi-Hildebrand equation. The results indicate that the formation constants for the complexes depend on the nature of electron acceptors and configuration of drug donor, and also the spectral studies of the complexes were determined by (infrared, Raman, and 1H NMR) spectra and X-ray powder diffraction (XRD). The charge-transfer complexes are formed during the interaction of electron-acceptors and electron-donors as result of partial or complete transfer of a negative charge from (D+−A−).

Synthesis and Characterization of the Inclusion Complex of β-cyclodextrin and Azomethine

A β-cyclodextrin (β-Cyd) inclusion complex containing azomethine as a guest was prepared by kneading method with aliquot addition of ethanol. The product was characterized by Fourier Transform Infrared (FTIR) spectrometer, 1H Nuclear Magnetic Resonance (1H NMR) and Thermogravimetric Analyzer (TGA), which proves the formation of the inclusion complex where the benzyl part of azomethine has been encapsulated by the hydrophobic cavity of β-Cyd. The interaction of β-Cyd and azomethine was also analyzed by means of spectrometry by UV-Vis spectrophotometer to determine the formation constant. The formation constant was calculated by using a modified Benesi-Hildebrand equation at 25 °C. The apparent formation constant obtained was 1.29 × 104 L/mol. Besides that, the stoichiometry ratio was also determined to be 1:1 for the inclusion complex of β-Cyd with azomethine.

A proof-of-concept fluorescent strategy for highly selective detection of Cr(vi) based on inner filter effect using a hydrophilic ionic chemosensor

In this article, a facile and versatile strategy for highly selective detection of Cr(VI) in 100% aqueous solution was developed based on fluorescence inner filter effect (IFE) using a hydrophilic ionic chemosensor. In the presence of Cr(VI), remarkable fluorescence quenching of the chemosensor could be observed because of the strong absorption of Cr(VI) to both the excitation and emission light of the fluorophore (in this work, acridine was chosen as the model fluorophore). By utilizing the modified Benesi–Hildebrand equation, not only was the efficiency of IFE quantitatively calculated, but also the calibration curve used for Cr(VI) determination was vastly broadened. A linear range of 5.0 × 10−6 to 1.4 × 10−3 M for Cr(VI), along with a detection limit of 8.9 × 10−7 M and a RSD of 3.6% at 2.5 × 10−5 M in 100% aqueous solution were obtained. In addition, the detection limit could be as low as 9.2 × 10−8 M in MeCN aqueous solution. Meanwhile, the present method possesses an excellent selectivity for Cr(VI) detection. It was also successfully applied in Cr(VI)-spiked tap water samples and wastewater samples.

A Sensitive Spectrofluorometric Method for Determination of Ergosta-4,6,8(14),22-Tetraen-3-One in Rat Plasma, Feces, and Urine for Application to Pharmacokinetic Studies Using Cerium(III) as a Probe

Ergosta-4,6,8(14),22-tetraen-3-one (ergone) isolated from Polyporus umbellatus possesses a variety of pharmacological activities in vivo and in vitro, including cytotoxic, diuretic, and immunosuppressive effect. The interaction of cerium ions (Ce(3+)) with ergone was studied by fluorescence and absorption spectroscopy. Spectra data revealed that Ce(3+) ions exhibited emission maxima around 350 nm when the excitation wavelength was fixed at 255 or 290 nm, and the fluorescence of Ce(3+) ions was quenched by the addition of ergone, indicating that a Ce(3+)-ergone complex was formed. According to the modified Benesi-Hildebrand equation, the binding constant of interaction of Ce(3+) ions with ergone was obtained at room temperature. Based on this, a sensitive spectrofluorometric method using Ce(3+) ions as a probe was applied for the identification and quantification of ergone in rat plasma, feces, and urine. The linear ranges of the calibration curves were 1.31 to 4.50 μM for plasma, 1.12-9.87 μM for feces, and 1.28-3.42 μM for urine, and the ergone recoveries were found to be 97.1 ± 0.9%, 98.2 ± 0.7% and 96.5 ± 1.4% for plasma, feces, and urine, respectively. The intraday and inter-day relative standard deviations were less than 9.7%. The proposed spectrofluorometric method is simple and rapid for the quantitative determination of ergone in rat plasma, feces, and urine, and it is affordable for most laboratories because it has few requirements and uses low cost, easy to operate equipment.

Spectroscopic and thermal investigations on the charge transfer interaction between risperidone as a schizophrenia drug with some traditional π-acceptors: Part 2

The focus of present investigation was to assess the utility of non-expensive techniques in the evaluation of risperidone (Ris) in solid and solution states with different traditional π-acceptors and subsequent incorporation of the analytical determination into pharmaceutical formulation for a faster release of risperidone. Charge-transfer complexes (CTC) of risperidone with picric acid (PA), 2,3-dichloro-5,6-dicyano-p-benzoquinon (DDQ), tetracyanoquinodimethane (TCNQ), tetracyano ethylene (TCNE), tetrabromo-p-quinon (BL) and tetrachloro-p-quinon (CL) have been studied spectrophotometrically in absolute methanol at room temperature. The stoichiometries of the complexes were found to be 1:1 ratio by the photometric molar ratio between risperidone and the π-acceptors. The equilibrium constants, molar extinction coefficient (εCT) and spectroscopic-physical parameters (standard free energy (ΔGo), oscillator strength (f), transition dipole moment (μ), resonance energy (RN) and ionization potential (ID)) of the complexes were determined upon the modified Benesi–Hildebrand equation. Risperidone in pure form was applied in this study. The results indicate that the formation constants for the complexes depend on the nature of electron acceptors and donor, and also the spectral studies of the complexes were determined by (infrared, Raman, and 1H NMR) spectra and X-ray powder diffraction (XRD). The most stable mono-protonated form of Ris is characterized by the formation of +NH (pyrimidine ring) intramolecular hydrogen bonded. In the high-wavenumber spectral region ∼3400cm−1, the bands of the +NH stretching vibrations and of the pyrimidine nitrogen atom could be potentially useful to discriminate the investigated forms of Ris. The infrared spectra of both Ris complexes are confirming the participation of +NH pyrimidine ring in the donor–acceptor interaction.

Intermolecular hydrogen bond complexes by in situ charge transfer complexation of o-tolidine with picric and chloranilic acids

A two new charge transfer complexes formed from the interactions between o-tolidine (o-TOL) and picric (PA) or chloranilic (CA) acids, with the compositions, [(o-TOL)(PA) 2] and [(o-TOL)(CA) 2] have been prepared. The 13C NMR, 1H NMR, 1H-Cosy, and IR show that the charge-transfer chelation occurs via the formation of chain structures O–H⋯N intermolecular hydrogen bond between 2NH 2 groups of o-TOL molecule and OH group in each PA or CA units. Photometric titration measurements concerning the two reactions in methanol were performed and the measurements show that the donor–acceptor molar ratio was found to be 1:2 using the modified Benesi–Hildebrand equation. The spectroscopic data were discussed in terms of formation constant, molar extinction coefficient, oscillator strength, dipole moment, standard free energy, and ionization potential. Thermal behavior of both charge transfer complexes showed that the complexes were more stable than their parents. The thermodynamic parameters were estimated from the differential thermogravimetric curves. The results indicated that the formation of molecular charge transfer complexes is spontaneous and endothermic.

Determination of Individual Proton Affinities of Reserpine from Its UV−Vis and Charge-Transfer Spectra

Proton affinities of the two N atoms of reserpine (methyl-11,17alpha-dimethoxy-18beta-[(3,4,5-trimethoxybenzoyl)oxy]-3beta,20alpha-yohimban-16beta-carboxylate) have been determined in two ways from the pH-dependent variation of the UV-vis absorption spectra (i) of reserpine itself and (ii) of the charge-transfer (CT) spectra of its complexes with o-chloranil, p-chloranil, and DDQ in aqueous medium (containing 0.1% ethanol v/v). For the second method, the CT absorption bands of the complexes were determined, their formation constants were estimated by a modified Benesi-Hildebrand equation, and variation of CT absorption spectra with a change in pH was noted. A necessary working formula for the second method was derived and utilized with the experimental data. The pKa values obtained by the two methods are well in agreement with each other within the limits of experimental error. To our knowledge, so far, this is the first report on determination of pKa from charge-transfer complex formation in aqueous solution using simple absorption spectroscopy in the UV-vis region. The results obtained were further checked by noting the variation of fluorescence intensity of reserpine upon addition of o-chloranil, acid, and base, and almost complete agreement with the absorption spectrometric result was observed.

Nanoscale Thin Film Ordering Produced by Channel Formation in the Inclusion Complex of α-Cyclodextrin with a Polyurethane Composed of Polyethylene Oxide and Hexamethylene

A polyurethane consisting of six blocks of polyethylene glycol and five blocks of hexamethylene diisocyanate was synthesized. The influence of the addition of a-cyclodextrin (a-CyD) on the lower critical solution temperature behavior of the polyurethane was investigated by “cloud point” measurements, and the dependence of the phase state (solution, suspension, and gel) of a-CyD/polyurethane mixtures on the concentration of the two components was determined. The results suggest that the polyurethane forms inclusion complexes with a-CyD and that close to the maximum number of a-CyDs was included. The associative constant of the a-CyD/polyurethane inclusion complex was determined by 1H NMR shift titration using a modified Benesi-Hildebrand equation, and the complex was characterized in the solid state by 13C cross polarization/magic angle spinning NMR and X-ray diffraction. These studies showed that the complexes adopted a channel-like structure. Finally, the morphology of a-CyD/polyurethane complexes in the solid state was visualized by scanning electron microscopy and atomic force microscopy (AFM). AFM images of the inclusion complexes spun-cast on to silicon reveal the existence of ordered domains with heights commensurate with the existence of tetra- and higher-order a-CyD channels. The height quanta of these well-ordered, discrete plateaus point to the dominating influence of the size of the polyethylene glycol blocks within the polyurethane and suggest a route to the production of controlled subnanometer structured surfaces.