TG–DTA, UV and FTIR spectroscopic studies of urea–thiourea mixed crystal

A mixed crystal of urea–thiourea was grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterized by thermogravimetric–differential thermal analysis (TG–DTA), UV and FTIR spectroscopic analyses. A fitting decomposition pattern for the title compound was formulated on the TG curve which shows a two stage weight loss between 200 and 750 °C. In this temperature range DTA curve shows exothermic peaks supporting the formulated decomposition pattern. The UV and FTIR spectra show the characteristic absorption, vibration frequencies due to urea–thiourea mixed crystals. Detailed structural analysis of the compound is under progress.     

IR, UV and NMR studies of ��-cyclodextrin inclusion complexes of kazcaine and prosidol bases

The interaction of the analgesic prosidol [1-(2-ethoxyethyl)-4-phenyl-4-propionyl-oxypiperidine] and the anaesthetic kazcaine [1-(2-ethoxyethyl)-4-ethynyl-4-benzoyloxypiperidine] with ??-cyclodextrin (??-CD) in aqueous solutions has been studied by nuclear magnetic resonance (NMR), ultraviolet (UV) and infrared (IR) spectroscopy. The composition and structure of the formed guest:??-CD inclusion complexes have been determined and were found to have a molar ratio of 1:2, with the guest molecule located in the cavity formed by two ??-CD molecules in head-to-head orientation, with the O(2), O(3) rims interacting. The phenyl and ethoxyethyl substituents of the guests are in contact with the ??-CD molecules. In contrast to prosidol?Cbase and kazcaine?Cbase the complexes with ??-CD show a higher analgesic and local anaesthetic activity.     

An optical and electrochemical anion sensor of F− investigated by UV–vis, 1H NMR and cyclic voltammetry

A new anion receptor: 1,1′-di-(2″,4″-di-nitrophenylhydrazino-β-carbonyl)-ferrocene (1) based on ferrocene has been designed and synthesized as a highly colorimetric and electrochemical sensitive sensor for F^?. The binding mode with F^? was further investigated by UV–vis titration and ¹H NMR titration experiments. In addition, the cyclic voltammetry (CV) was performed to discuss the electrochemical sensing for F^?.     

Resonance Raman and UV–vis characterization of charge transfer complexes of TCNQ and aromatic amines

Although the molecular charge transfer complexes formed by 7,7,8,8-tetracyanoquinodimethane (TCNQ) and several different donors have been widely investigated in the past, in this paper it is shown for the first time the vibrational spectroscopic characterization of the complexes formed by TCNQ and the simplest series of substituted anilines in solution. The UV–vis spectra indicate the formation of TCNQ complexes stabilized by two aromatic amines in a sandwich π type complex. It was observed that the charge transfer transition energies of the complexes follow a linear correlation with the ionization potential of the amines. The resonance Raman spectra revealed, by the analysis of the ν(CC) and ν(CN) stretching modes of TCNQ, that the complexes keep their neutral character in the ground electronic state, and not as a TCNQ²⁻ dianion species as reported before. The observed enhancement of the TCNQ bands as the amine donor capacity increases, confirmed the charge transfer nature of the electronic transitions. The DFT and TDDFT results were obtained and the theoretical Raman and electronic spectra data supported the experimental findings. The results of the model systems presented herein can contribute to a deep understanding of the photoinduced charge transfer process in complexes of TCNQ, which is a key step in the designing of organic molecular devices.     

Thermal, UV and FTIR spectral studies of urea–thiourea zinc chloride single crystal

A single crystal of urea–thiourea was grown by slow evaporation of aqueous solution at room temperature. The bright and transparent crystals obtained were characterised by TG–DTA, UV and FTIR spectral analyses. A fitting decomposition pattern for the title compound was formulated on the TG curve which shows a two stage mass loss between 200 and 750 °C. DTA curve shows exothermic peaks supporting the formulated decomposition pattern in this temperature range. The UV and FTIR spectra show the characteristic absorption, vibration frequencies due to urea–thiourea zinc chloride crystals. Detailed structural analysis of the compound is under progress.     

1H NMR and UV spectroscopic study of inclusion complex formation between pyridoxine and β- and γ-cyclodextrins

Inclusion complex formation between pyridoxine and - and -cyclodextrins in aqueous solution has been investigated by¹H NMR and UV spectroscopy. Both complexes exhibited a 1:1 stoichiometry and the inclusion process has been shown to perturb the equilibrium between the lactim and the lactam tautomer of pyridoxine, with a preferential inclusion of the former, less polar tautomer.     

Quantitative control and identification of copper species in Cu–SAPO-34: a combined UV–vis spectroscopic and H2-TPR analysis

Research on Chemical Intermediates - A series of Cu–SAPO-34 catalysts with different copper contents were prepared using a modified ion-exchange method, i.e., impregnation–activation....     

Synthesis,characterization and spectroscopic study of riboflavin–molybdenum complex

A riboflavin–molybdenum [(RF)–Mo(V)] complex in powder form was synthesized and characterized by elemental analysis, UV–Vis, IR, NMR spectroscopy and X-ray diffraction. During the synthesis of this metal complex, another metal complex [Mo₂O₄(H₂O)₆]²⁺ was also synthesized and characterized. The results of X-ray diffraction study have revealed an orthorhombic cubic system for the RF–Mo complex. The steady state absorption and emission studies of RF and RF–Mo in hydrochloric acid (HCl) of varying pH were investigated. The steady state absorption with RF–Mo showed distinct changes in the absorption spectra of RF after complexation. The steady state emission results, consistent with prior reports showed fluorescence quenching in the aqueous solution of both RF and RF–Mo in HCl with the proton acting as a quencher. The Stern–Volmer constant observed was 108.79 and 98.68 for RF and RF–Mo, respectively. The binding constant for RF–Mo complex was found to be 1.201 × 10³ M⁻¹ at 298 K.     

Complexation studies of pioglitazone hydrochloride and β-cyclodextrin: NMR (1H, ROESY) spectroscopic study in solution

Pioglitazone hydrochloride (PIO) is an agonist of the peroxisome proliferator-activated receptor γ (PPARγ), used to treat diabetes. ¹H-NMR spectroscopic analysis of varying ratios of β-cyclodextrin (β-CyD) and PIO in D₂O confirmed the formation of β-CyD–PIO inclusion complex in aqueous solution. The 1:1 stoichiometry of β-CyD–PIO inclusion complex was determined by Scott’s plot method and binding constant (K _a ) was calculated to be 155 M^?1. 2D ROESY experiments confirmed that the phenyl ring of PIO act as a guest and deeply penetrate in β-CyD cavity from wider as well as narrower rim side and form two 1:1 stable inclusion complexes. Some of the PIO protons exhibited splitting, in the presence of β-CyD, indicating chiral differentiation of PIO by β-CyD.     

Reproduction and interpretation of the UV–vis spectra of some flavonoids

The UV–vis spectra of 15 naturally occurring flavonoids, including flavones, flavonols, and isoflavones, were simulated and compared to literature experimental results. For this purpose, the TDDFT method in conjunction with the B3LYP-D3 and B3LYP functionals was applied. In spite of some discrepancy between the structural predictions, the differences between the TDDFT/B3LYP and TDDFT/B3LYP-D3 results are negligible. The performance of both functionals in reproducing the UV–vis spectra of the selected flavonoids is satisfactory. The NLMO clusters, i.e. molecular moieties characterised with distinguished electron density, were created. The combined results from the TDDFT and NLMO approaches were employed to perform deep analysis of the spectra. It was found that the transitions from the bonding NLMO clusters to the LUMO cluster are favoured at longer wavelengths, whereas the transitions from the HOMO and HOMO?1 clusters to the antibonding NLMO clusters are favoured at shorter wavelengths. All flavonoids show the HOMO → LUMO and HOMO?1 → LUMO transitions at long wavelengths, and majority of them show the HOMO → LUMO+1 transition at moderate wavelengths. This investigation confirms our earlier finding that the TDDFT and NBO approaches are complementary, implying that the results from the two theories can be combined to better understand the redistribution of electron density upon excitation.     

Synthesis and structure of 1-benzyl-5-amino-1H-tetrazole in the solid state and in solution: Combining X-ray diffraction, 1H NMR,FT–IR,and UV–Vis spectra and DFT calculations

Compound 1-benzyl-5-amino-1H-tetrazole (BAT) was synthesized and characterized by ¹H NMR, FT–IR, and UV–Vis spectroscopies and elemental (CHNS) analysis. The crystal structure was further elucidated by single-crystal X-ray diffraction. Density functional theory (DFT) calculations with B3LYP and PBE1PBE functionals of the BAT were performed to provide structural and spectroscopic information and guide spectral assignments. The compound crystallizes in monoclinic primitive system space group P2(1)/c with a = 14.91 Å, b = 5.12 Å, c = 11.19 Å, V = 852 Å³, Z = 4, R₁ = 0.0428 at 298 K. The structure exhibits intermolecular hydrogen bonds of the type N–H(amino)···N(tetrazole). Simultaneous hydrogen bonds between amino···tetrazole and tetrazole···amino establish a dimeric intermolecular structure, whereas another hydrogen bond between the remaining H atom of the amino group and the other N atoms of the tetrazole ring extends the structure into another dimension. The crystal structure of BAT is properly reproduced by DFT calculations only when a dimeric or tetrameric model is employed in the modeling. Comparisons between experimental and calculated spectral properties suggest that the monomeric form of BAT is dominant in aprotic, polar, hydrogen-bonding solvents, such as DMSO and DMF.     

UV–vis spectroscopic study directly detecting inorganic phosphorus in urine and our reagent kit

The determination of inorganic phosphorus in human urine is very important, since it has diagnostic value in some clinical cases. Here we apply a simple, sensitive and direct method to determine inorganic phosphorus in urine. This new ensemble is prepared by adding ytterbium chloride and pyrocatechol violet in a 2:1 molar ratio in an aqueous solution of 10 mM 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid buffer at pH 7.0. The addition of the urine sample turned the blue ensemble yellow and altered the UV–vis absorption spectra. The ensemble exhibits excellent selectivity for inorganic phosphorus over other constituents of urine. We validate the accuracy of our method by the standard procedure (molybdenum blue assay for phosphate). The detection results are basically consistent with normal excretion of phosphate. Furthermore, we fabricated a new kind of inorganic phosphorus reagent kit, which enables us to inspect phosphate concentrations of urine with the naked eye. Fit for all kinds of various clinic uses, our reagent kit is a hopeful substitute for the molybdenum reagent kit.      

Orientational order of guest molecules in aligned liquid crystal as measured by EPR and UV–vis techniques

Orientational order of guest molecules in aligned liquid crystal 4-cyano-4′-pentylbiphenyl (5CB) is studied via optical dichroism and electron paramagnetic resonance (EPR) spectra measurements. The guest molecules used are bifunctional molecules bearing paramagnetic nitroxide group and photochromic azobenzene moiety. The bifunctional probe with rigidly bonded nitroxide and azobenzene moieties was found to align as a whole, while flexible long spacer between the moieties provides independent alignment for the nitroxide and azobenzene parts. Intermolecular interactions responsible for the alignment of azobenzene and nitroxide moieties of the probe molecules are discussed. The molecules with cis-configuration of azobenzene moiety are able to align in the liquid-crystalline medium, but to a lesser extent than the molecules with trans-configuration. Directions of orientational axes and characteristics of rotational mobility of spin probes are determined. Second, fourth and, in some cases, sixth rank order parameter values are found.     

Thermal,spectroscopic, and dissolution studies of ketoconazole–Pluronic F127 system

One strategy for improving the dissolution of poorly water soluble drugs is to prepare solid dispersions such as binary mixtures with hydrophilic carriers. These mixtures are generally characterized by better solubility than those of the individual components from which they are formed. In the present study, solid dispersions of ketoconazole (KET) with Pluronic F127 (PLU) were prepared by the grinding method. Solid–liquid equilibria in the system being studied were investigated by differential scanning calorimetry. A phase diagram for the whole range of compositions was constructed. The investigation revealed that ketoconazole and Pluronic F127 form a simple eutectic system containing 4.4 % w/w of ketoconazole at the eutectic point. The results of Fourier transform infrared spectroscopy and X-ray powder diffractometry studies of obtained mixtures suggest that there is no drug-carrier interaction and both components are crystalline in the solid dispersion with the whole range of composition. The prepared mixtures show an appreciable improvement of the dissolution rate of KET in 0.5 % w/v sodium lauryl sulfate. The improvement of the dissolution rate of drug is additionally increased by effective solubilization.     

Computational investigation of solvent effect on the structure,spectroscopic properties (13C, 1H NMR and IR,UV), NLO properties and HOMO–LUMO analysis of Ru(NHC)2Cl2(=CH-p-C6H5) complex

This paper presents, a theoretical study of the structural, ¹³C and ¹H NMR chemical shifts, electronic transitions, vibrational analysis, and first hyperpolarizability for Ru(NHC)₂Cl₂(=CH-p-C₆H₅) complex in gas phase and different solvents. The solvent effect on structural parameters, frontier orbital energies, Ru=C_carbene and C_carbene-H stretching frequencies, and chemical shifts of C_carbene, C_NHC and H_carbene of complex was explored based on Polarizable Continuum Model (PCM). The wavenumbers of υ(Ru=C_carbene) and υ(C_carbene-H) of complex in different solvents were correlated with the Kirkwood–Bauer–Magat equation (KBM). As well as, the polarizability and the first order hyperpolarizability values of the investigated compound were computed in various solvents.     

Thermal, spectroscopic, and dissolution studies of the simvastatin–acetylsalicylic acid mixtures

The objective of the present investigation was to study the effect of eutectic formation on in vitro dissolution of simvastatin (SIM) released from mixtures with acetylsalicylic acid (ASA) prepared by a grinding method. SIM–ASA mixtures were characterized by means of differential scanning calorimetry (DSC), infrared spectroscopy (IR), X-ray powder diffractometry (XRPD), and in vitro dissolution tests. IR spectroscopy and XRPD studies indicated no interaction between SIM and ASA in the solid state. The DSC investigation has revealed that SIM and ASA form a simple eutectic system containing 66.6 % w/w of SIM at the eutectic point. In vitro dissolution studies of SIM and its mixtures with ASA were carried out. The eutectic mixture shows an appreciable increase in the dissolution rate in comparison with other ratios and SIM in 0.5 % w/v sodium lauryl sulfate. The dissolution enhancement of SIM was related to the effective wetting of the drug particles with a significantly reduced size released from eutectic composition. In conclusion, dissolution of SIM can be enhanced through eutectic formation with ASA by means of simple mechanical activation (a grinding method).     

X-ray and IR spectroscopic studies of specific intermolecular interactions inN′-substituted isonicotinohydrazides

_N-Thenylidene- andN-(o-nitrobenzylidene)hydrazides of isonicotinic acid have been studied by X-ray structural analysis and IR spectroscopy. In the crystalline state, these molecules are linked through intermolecular N—H ... Np_y hydrogen bonds. Carbonyl groups are not involved in intermolecular hydrogen bonds. However, it was found that the C=O group participates in an attractive interaction with the sulfur atom of the thiophene group. The energy of this interaction is comparable with the energies of intermolecular C=O ... H—N hydrogen bonds in amides.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 896–900, April, 1996.