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181.
Nikhil Guchhait 《Journal of Chemical Sciences》2002,114(1):61-74
The nature of methyl internal rotational barrier in thioacetaldehyde has been investigated by relaxation effect, natural bond
orbital (NBO) analysis and Pauling exchange interactions. The true experimental barrier can be obtained by considering fully
relaxed rotation. Nuclear-electron attraction term is a barrier forming term in the fully relaxed rotation, but it appears
as an antibarrier for rigid rotation. It is seen that during methyl rotation, the torsional mode is coupled with the aldehydic
hydrogen out-of-plane wagging motion. Natural bond orbital analysis shows that the principal barrier forming term originates
from the C-C bond. The lengthening of the C-C bond is explained by considering charge transfer interaction between several
bonding and antibonding orbitals in the C-C bond region, which leads to higher bonding overlap for the eclipsed conformer
compared to the staggered conformer. S-C(σ)/Cme-Hp and C-Hald/Cme-Hop interactions appear to be the main barrier-forming Pauling exchange terms but have less contribution to make to the barrier
compared to the C-C bond interaction. 相似文献
182.
Nikhil A. Kolhatkar Amber M. Monfette Shuo Lin Massoud J. Miri 《Journal of polymer science. Part A, Polymer chemistry》2012,50(5):986-995
Two neutral salicylaldiminato methyl pyridine nickel(II) complexes were synthesized and evaluated for ethylene polymerization. Each catalyst bears a methoxy group in the 3‐position and a halogen atom in the 5‐position of the salicyl ligand, chlorine in case of catalyst 3a and bromine in 3b . Molecular structures of the catalysts were obtained by X‐ray crystallography. The resulting polymerization activities, for example, indicated by a maximum turnover frequency of 4,870 mol ethylene/(mol Ni × h) for 1‐h runs obtained with 3a , were higher than those of similar catalysts at comparable conditions reported in the literature. Catalyst 3a was slightly more active than catalyst 3b . The polymers are branched as measured by 1H NMR and 13C NMR. This was also reflected in the melting temperatures between 76 and 113 °C obtained by differential scanning calorimetry. By using gel permeation chromatography measurements, it was determined that the Mw of the polymers ranges between about 5,400 and 21,600 g/mol. In particular, the effect of the polymerization temperature on the catalyst activity, degree of branching, and molecular weight properties has been described. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
183.
Shivpal Singh Jeetendra Singh Negi Rohit Bisht Vandana Negi Nikhil Kasliwal Vinay Thakur Aadesh Upadhyay 《Journal of inclusion phenomena and macrocyclic chemistry》2014,78(1-4):239-247
Amisulpride (AMI) is an atypical antipsychotic having poor aqueous solubility and poor oral bioavailability. Inclusion complex between AMI and gamma cyclodextrin (γ-CD) was prepared by kneading method using 1:1 stoichiometry. Solubility of AMI was enhanced by 3.74 times after inclusion complex formation. Amisulpride–γ-cyclodextrin inclusion complex was characterized by FTIR, DSC and XRD techniques. Further sustained release granules of Amisulpride–γ-cyclodextrin inclusion complex (CDSR) were prepared by treating complex with molten stearic acid. Drug release from CDSR granules was sustained up to 12 h with 100 % stearic acid proportion. The integrity of AMI–γ-CD inclusion complex in lipid phase was assessed by XRD study. Finally orodispersible tablets of CDSR granules (OD-CDSR) were prepared using Ac-Di-Sol and microcrystalline cellulose. Disintegration time was assessed by both pharmacopoeial and modified method. Optimized formulation was rapidly disintegrated within 25 s. Thus solubility enhancement and sustained release of AMI was achieved by orodispersion of CDSR granules for improvement of patient compliance. 相似文献
184.
Le Barbu-Debus K Lahmani F Zehnacker-Rentien A Guchhait N Panja SS Chakraborty T 《The Journal of chemical physics》2006,125(17):174305
The laser-induced fluorescence excitation, dispersed fluorescence, and IR-UV double resonance spectra of chiral (+/-)-indan-1-ol have been measured in a supersonic expansion. Three low energy conformers of the molecule have been identified, and the ground state vibrational modes of each conformer are tentatively assigned with the aid of quantum chemistry calculations. The frequencies of the nu(OH) and nu(CH) stretch modes of the two most abundant conformers have been measured by fluorescence dip IR spectroscopy and have been used for their assignment. The dispersed fluorescence spectra clearly indicate the coupling of low-frequency modes, as was seen in other substituted indanes such as 1-aminoindan and 1-amino-2-indanol. (R)- and (S)-indan-1-ol distinctly form different types of clusters with (R)- and (S)- methyl- and ethyl-lactate. Both hetero- and homochiral clusters are characterized by complex spectra which exhibit a progression built on low-frequency intermolecular modes. 相似文献
185.
Barbu-Debus KL Lahmani F Zehnacker-Rentien A Guchhait N 《Physical chemistry chemical physics : PCCP》2006,8(8):1001-1006
Two low energy conformers of the chiral (R)-1-aminoindan molecule are identified in supersonic jet and their ground and excited states vibrational spectroscopy has been investigated by laser-induced fluorescence (LIF) excitation and single vibronic level (SVL) emission spectroscopy. Ab initio calculations confirm the existence of two lowest-energy structures, where the amino group is in equatorial position with its lone pair directed opposite to the aromatic electron cloud. Harmonic frequencies have been calculated for these two conformers at the DFT level with B3LYP functional. A low-frequency progression of 118 cm(-1) and 114 cm(-1), respectively, appears in the fluorescence excitation spectrum of the two conformers, with its ground state counterpart at approximately 147 cm(-1). It has been assigned to the puckering motion coupled with the ring flapping mode. The other calculated low-frequency mode corresponds to the puckering motion coupled with the ring twisting mode and its ground state frequency has been observed at 119 cm(-1) and 111 cm(-1) from SVL spectra. Both conformers form similar 1 : 1 water clusters, whose 0-0 transitions are shifted to the blue by 41 cm(-1) and 44 cm(-1), respectively, and whose SVL spectra are similar. Interestingly, one of the conformers seems to preferentially make complexes with (S)-methyllactate, while the other one shows selective complexation to (R)-methyllactate. 相似文献
186.
The poly(o-anisidine)–sulfuric acid–glucose oxidase (POA–H2SO4–GOx) electrode has been investigated in the present work. Platinum electrode was used for the synthesis of poly (o-anisidine)–sulfuric acid (POA–H2SO4) film using galvanostatic method with 0.2 M o-anisidine, 1.0 M H2SO4 solution, 1.0 pH and 2 mA/cm2 applied current density. The synthesized film was characterized using electrochemical technique, conductivity measurement,
UV–visible spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. GOX was immobilized on synthesized POA–H2SO4 film by cross-linking via glutaraldehyde in phosphate and acetate buffer. The Michaelis–Menten constant (
K\textm¢K_{\text{m}}^\prime ) was determined for the immobilized enzyme. The glucose oxidase electrode shows the maximum current response at pH 5.5 and
potential 0.6 V. The sensitivity of POA–H2SO4–GOX electrode in phosphate and acetate buffer has been recorded. The results of this study reveal that the phosphate buffer gives
fast response as compared to acetate buffer in amperometric measurements. 相似文献
187.
The phenomenon of excited state twisted intramolecular charge transfer (TICT) process in N,N-dimethylaminonaphthyl-(acrylo)-nitrile (DMANAN) has been reported on the basis of steady-state absorption and fluorescence spectroscopy in combination with quantum chemical calculations. The absorption and fluorescence characteristics of DMANAN in solvents of different polarity reveal the presence of a single species in the ground state which forms the intramolecular charge transfer state upon photoexcitation. The observed dual fluorescence is assigned to a high-energy emission from the locally excited or the Franck-Condon state and the red-shifted emission from the charge transfer (CT) state. In polar protic solvents, hydrogen-bonding interaction on CT emission has been established from the linear dependency of the position of the low-energy emission maxima on hydrogen-bonding parameter (α). The experimental findings have been correlated with the theoretical results based on TICT model obtained at density functional theory (DFT) level. The theoretical potential energy surface for the first excited state along both the donor and acceptor twist coordinates in the gas phase obtained by time dependent density functional theory (TDDFT) method and in polar solvent by time dependent density functional theory-polarized continuum model (TDDFT-PCM) method predicts well the experimental spectral properties. 相似文献
188.
Raj M. Venkata Nikhil Bhar Kishalay Jain Surbhi Rana Monika Khan Tanveer A. Sharma Anuj K. 《Transition Metal Chemistry》2019,44(7):615-626
Transition Metal Chemistry - The present work reports the synthesis, spectroscopic and structural characterizations of Fe(III) complexes of types [Fe(L)(H2O)(NCS)] (1),... 相似文献
189.
Mandal Madhuri Ranjan Jana Nikhil Kundu Subrata Kumar Ghosh Sujit Panigrahi Mruganka Pal Tarasankar 《Journal of nanoparticle research》2004,6(1):53-61
This paper reports the evolution of a new class of core–shell type, that is, Aucore–Agshell bimetallic nanoparticles by seed mediated technique for surface enhanced Raman scattering (SERS) study. Here it is demonstrated how to control the thickness of Ag-shell with the variation of gold seed (15 nm) to Ag ion concentration which in turn control the particle size in the range from 50 to 100 nm with increase of shell thickness. For 50 nm core–shell particles the thickness of the shell was 17 nm, for 70 nm particles the thickness was 27 nm and for 100 nm the thickness was 42 nm. SERS study was performed on those particles using the analyte crystal violet (CV) to examine the impact of the size and field effects of the bimetallics on SERS spectra. A surprising finding is that a small particle as low as 50 nm have been found to be highly efficient for SERS, even it enables the detection of a selected dye molecule down to single molecular level. The sensitivity of the SERS detection limit has been improved further with an activating reagent like NaCl. The newly modeled bimetallic system establishes a relationship between the local electromagnetic (EM) field effect and chemical effect (CE) on the enhancement of SERS spectra, which provides further insight into the enhancement mechanism of SERS. 相似文献
190.