Spectroscopic studies of zinc(II)tetraphenylporphyrin molecular complex with 1,4-dioxane

The molecular complex of zinc(II)tetraphenylporphyrin with 1,4-dioxane has been obtained. The IR spectra of the [Zn(TPhP)(1,4-dioxane)2] stabile molecular complex between 4000 and 50cm(-1) have been studied. An interpretation is given on the base the "chair" conformation of 1,4-dioxane molecule.     

Spectroscopic studies on quantum dots of PbI2

We report the preparation of PbI₂ clusters of sizes less than 30 Å by colloidal routes and characterization by optical absorption spectra. We show that the blue-shifted absorption spectra are not due to the presence of I⁻₃ ions, as suggested previously, but are characteristic of the clusters present. We also show that similar sized clusters form, though sparingly, on dissolving bulk PbI₂ in the solvents. We establish that the stability of a large concentration of these clusters in the colloidal process is due to the presence of excess iodine ions attached to the microcrystallites.     

己基取代的1,4-二(2-噻吩基)苯并[c]哒嗪合成与光谱性质研究

本文设计并合成了一系列含氮原子的缺电子芳香片段,包括以苯并哒嗪作为核心、以富电子噻吩衍生物作为共轭延长链的有机共轭小分子1,4-二(2-噻吩基)苯并[c]哒嗪(5a)、1,4-二[2-(3-己基噻吩基)]苯并[c]哒嗪(5b)和1,4-二[2-(5-己基噻吩基)]苯并[c]哒嗪(5c).通过紫外光谱和荧光光谱研究,证明在共轭体系中的不同位置引入烷基链,可以有效影响化合物的能隙,调节化合物的光电性质.     

Spectroscopic studies of azabicyclospirohydantoins

The IR spectra of 3-alkyl-3-azabicyclo(3.2.1)octane-8-spiro-, 3-alkyl-3-azabicyclo(3.3.1) nonane-9-spiro-, and 8-alkyl-8-azabicyclo(4.3.1)decane-10-spiro-5'-hydantoins have been studied in the solid state and in solution and the existence of different types of hydrogen bonding deduced from the spectra.The presence of intermolecular N_3'-H?N bonds in the solid state depends mainly on the steric hindrance of the polymethylene chain and on the bulk and shape of the piperidine _N-substituent. The possibility of strong N_3'-H?N bond formation is smaller than for isomeric nortropane- and granatanine-spirohydantoins.Results are confirmed in some cases by Raman and X-ray measurements.     

Spectroscopic studies of photochemical reactions in organic solids: Photopolymerization of 1,4 bis[β-pyridyl(2)vinyl] benzene

The laser Raman phonon spectroscopic technique has been used to study the photopolymerization reaction of 1,4 bis[β-pyridyl(2)vinyl] benzene (P2VB). Raman and infrared spectroscopy have been used to study the intramolecular vibrations of the reactant and the product and to characterize them. Absence of any large Stokes' shift between absorption and emission bands of the monomer crystal shows that exciton–phonon coupling is weak, and the reaction is not likely to be phonon mediated. Phonon spectroscopy shows that the reaction proceeds by a heterogeneous mechanism. Sharp phonon bands of the product, however, suggests that the photopoly P2VB lattice is highly ordered.     

Spectroscopic studies of microwave-excited plasma

Manganese solution was sprayed into a microwave-excited plasma torch (2450 MHz and ca. 200 W), whose profile was examined; the electron temperature, the degree or ionization and the total number of atoms and ions were estimated. Effects of alkali and alkaline earth metals were found to depend on the ionisation potentials of both manganese and the added metal.     

Spectroscopic studies of conducting polymers

Electronic and vibrational spectra of poly(p-phenylenevinylene) doped with donors or acceptors have been studied, together with the spectra obtained for the radical ions and divalent ions of its oligomers. The electronic absorption spectra of doped poly(p-phenylenevinylene) in the region from visible to near-infrared show two bands for the H₂SO₄-doped species and one very broad band for the Na-doped species. On the basis of the analyses of resonance Raman spectra, the two electronic absorption bands of the H₂SO₄-doped species are attributed to a polaron-lattice structure, whereas the broad band of the Na-doped species is attributed to overlapping absorptions associated with localized electronic levels of polarons and bipolarons. A Pauli spin susceptibility of the H₂SO₄-doped species is explained by the polaron-lattice structure.     

Spectroscopic studies of mixed halogenotetraphosphazenes

Cyclotetraphosphazenes substituted non-geminally by fluorine and either chlorine or bromine have been prepared. The compounds with the general formula     

Spectroscopic and spectrofluorimetric studies on the interaction of irbesartan with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and iodine

Raman, UV-vis, 1H NMR, FT-IR, mass and fluorescence spectral techniques were employed to investigate the mechanism of interaction of irbesartan (IRB) drug with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and iodine. Interaction of IRB with iodine yields triiodide ion and its formation was confirmed by electronic and Raman spectra. The peaks appeared in Raman spectrum of the isolated product at 143, 113 and 76 cm(-1) are assigned to νas(I-I), νs(I-I) and δ(I3-) respectively, confirmed the presence of I3- ion. The interaction of DDQ with irbesartan was found to proceed through the formation of outer complex and its conversion to the CT complex. Formation constant (K), molar extinction coefficient (?) and thermodynamic properties ΔH#, ΔS# and ΔG# were determined and discussed. Fluorescence quenching studies indicated that the interaction between the IRB and the acceptors are spontaneous and the IRB-DDQ interaction is found to be stronger than that the other system. Solvent variation studies indicated that the binding constant increased with an increase in polarity of the medium.     

Spectroscopic studies on modified wood

The FTIR spectra of solid resin-free samples of chemically modified Norway spruce wood were recorded. Correlations were noted between spectral and hydrogen bond structure, chemical modification, fibre crystallinity and macroscopic softening point.     

Spectroscopic and computational studies of the intramolecular hydrogen bonding of 2-indanol

2-Indanol in its most stable form is stabilized by internal hydrogen bonding, which exists between the hydroxyl hydrogen atom and the pi-cloud of the benzene ring. A comprehensive ab initio calculation using the MP2/cc-pVTZ level of theory showed that 2-indanol can exist in four possible conformations, which can interchange through the ring-puckering vibration and the internal rotation of the OH group on the five-membered ring. A potential energy surface in terms of these two vibrational coordinates was calculated. Density functional theory calculations were used to predict the vibrational frequencies and to help in normal mode assignments. Fluorescence excitation spectra of 2-indanol confirm the presence of the four conformers in the electronic ground and excited states. The spectral intensities indicate that, at 90 degrees C, 82% of the molecules exist in its most stable form with the intramolecular hydrogen bonding. The other isomers are present at approximately 11, 5, and 3%. The MP2/6-311++G(d,p) calculation predicts a distribution of 70, 13, 9, and 8% at 90 degrees C, the experimental sample temperature.     

Spectroscopic studies of some antidiabetic drugs

The infrared absorption spectrum of antidiabetic drugs Pioglitazone and Pioglitazone.HCl has been recorded at high resolution in the spectral region 200-4000 cm(-1). Most of the frequencies in the latter compound are slightly lower in magnitude than corresponding value in the former. The absorption intensities are however slightly larger. In order to confirm the vibrational assignment of the bands obtained from experimental observation, a normal co-ordinate analysis has been carried out using semi empirical AM1 method through MOPAC 5.1 computer program. In addition to these compounds, the vibrational frequencies for some of the intermediate metabolite of Pioglitazone have also been calculated.     

Spectroscopic studies of fluorescent perylene dyes

The lowest electronic transition of the fluorescent perylene dye bis-(3,5-di-tertbutylphenyl)-perylene-3, 4:9,10-biscarboximide has been investigated b     

Structure and Spectroscopic Studies of 4,8-bis(2-Hydroxybenzyl)-cis-octahydro[1,4]-oxazino [3,2-b]-1,4-oxazine

The title compound 4,8-bis(2-Hydroxybenzyl)-cis-octahydro [1,4]-oxazino [3,2-b]-1,4-oxazine (1) has been synthesized by the reaction of N-(2-hydroxybenzyl)-2-amino-1-ethanol with glyoxal. This novel compound was characterized by elemental analysis, IR, and ¹H NMR. The structure was also confirmed by a single crystal X-ray study. The compound crystallizes in monoclinic C2/C space group with unit cell dimensions: a = 18.318(4), b = 8.6110(17), c = 13.267(3) Å, = 119.90(3), V = 1814.1(6) ų, Z = 4. The two fused six-membered rings in 1 adopt chairlike conformations slightly flattened around the nitrogen atoms. In the central fusion bond, the geometry is a staggered conformation, with the two angular hydrogen atoms in the cis positions with respect to the rings, the nitrogen atoms antiperiplanar to each other, while the oxygen atoms remain gauche to each other and antiperiplanar to the hydrogen atoms. The ring conformations in 1 have been discussed on the basis of the anomeric effects and the presence of two strong intramolecular hydrogen bonds between the phenolic hydrogens and the amino groups.     

Spectroscopic studies of tautomeric systems—III : 2-arylhydrazones of 1,2,3-triketones

The IR and NMR spectra of a range of 2-arylhydrazones of 1,2,3-tricarbonyl compounds have been recorded. Compounds containing different end groups in the 1,2,3-tricarbonyl system can exist in two different tautomeric forms. The influence of electronic and steric factors on the structure of the preferred tautomer is discussed.     

Spectroscopic studies of the conformations of n-decamethyltetrasilane

The conformational properties of n-decamethyltetrasilane, n-Si₄(CH₃)₁₀, have been studied by variable temperature NMR (¹H and ¹³C) and vibrational (IR and Raman) spectroscopy. As in related alkane systems, the anti conformer ismore stable than the gauche conformer. Values of △H⁰ and △S⁰ for the anti → gauche reaction are 2.26 ± 0.15 kJ mol^-1 and △S⁰ = 7.82± 0.86 J K^-1mol^-1, respectively. Thus, the two conformers are present in comparable quantities at room temperature. At very low temperatures, broadening of the two proton resonances (SiMe₂, SiMe₃) occurs, but phase changes precluded the observation of decoalescence. By approximate lineshape anaylysis, the free energy of activation, △G3, for rotation about the central SiSi bond is estimated to be ～25 kJ mol^-1.     

Spectroscopic studies on caffeine and isocaffeine

UV and NMR spectra of caffeine and Isocaffeine were measured in three solvents of different polarity. The Information so obtained revealed unique differences in the electronic structure of 7- and 9- alkyl substituted xanthines. 9-Methyl derivatives bear a “soft” nitrogen at position 3; in 7-methylxanthines this nitrogen is rather “hard”. This characteristic distinction is explained on the basis of orbital interactions, which are also responsible for self-association. In the process of self-association. isocaffeine and caffeine share a hydrophobic effect, but in caffeine water bridges play a decisive rote in molecular aggregation. In contrast, in isocaffeine high polarisability makes the most important contribution to self-association. Steric interference between 3- and 9-alkyl substituents or between a 9-methy1 and a 3-NH group, proposed earlier, does not explain satisfactorily the properties of these xanthines.     

Spectroscopic studies on the formation of charge transfer complexes of l-phenylalanine with 2,3,5-trichloro-6-alkoxy-1,4-benzoquinones in aqueous medium

UV–Vis, FT-IR, LC–MS and fluorescence spectral techniques were employed to investigate the mechanism of interaction of l-phenylalanine with new π-acceptors, 6-alkoxy-2,3,5-trichloro-1,4-benzoquinones. The interaction of these quinones with l-phenylalanine (LPA) yielding radical ion pair was found to proceed through the formation of donor–acceptor complex. The stoichiometry of the complexes was determined by Job’s continuous variation method and was found to be 1:1 in all the cases. Kinetic and thermodynamic properties of the complexes were determined in aqueous medium at physiological conditions (pH = 7). Fluorescence quenching studies indicated that the interaction between the donors and the acceptor is spontaneous. Correlation of association constants of the CT complexes with Taft’s polar and steric constants indicated that the electronic effects of the substitutions play a significant role in governing the reactivity of the quinones when compared to steric factors.     

Spectroscopic studies on the inclusion complex of 2-naphthol-6-sulfonate with beta-cyclodextrin

The photophysical properties of 2-naphthol-6-sulfonate (2-NOH-6-S) in various solvents and in aqueous beta-cyclodextrin solution have been investigated. The fluorescence quantum yields in non-aqueous solvents are approximately 0.20+/-0.02, while in water the yield is higher. The fluorescence quantum yield in water was found to depend on the pH value of the medium and increases as the pH increase up to a pH value of 4.0 where it comes to be constant. Absorption and fluorescence measurements show 1:1 inclusion of 2-NOH-6-S in the beta-cyclodextrin cavity. The association constant of 2-NOH-6-S-beta-cyclodextrin complex based on fluorescence measurements was calculated using Benesi-Hildbrand relationship and found to be 330+/-30M(-1). (1)H NMR studies are used to confirm the inclusion and to provide information on the geometry of 2-NOH-6-S inside the cavity of beta-cyclodextrin.     

Spectroscopic and quantum chemical studies of isocytosine

The methods of electronic and vibrational (IR) spectroscopy were used to study the spectral properties of isocytosine in H₂O, D₂O, chloroform, and hexane in a wide concentration interval. Quantum chemical calculations of tautomeric forms and dimers of isocytosine were carried out. The bands of the calculated and experimental spectra were assigned. The results of the quantum calculations were compared with the experimental data. The spectral bands were classified according to the type of tautomer or dimer to which they belong.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 29–36, January–February, 1988.The authors are grateful to I. M. Ginzberg and L. F. Strelkova for their participation in the discussion of the infrared spectroscopy results.