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71.
A simple procedure for the synthesis of organo-chalcogenides has been developed by the reaction of aryl/heteroaryl amines with di-aryl/heteroaryl dichalcogenides in the presence of tBuONO and Fe(0) nanoparticles. The reaction proceeds via in situ diazotization followed by chalcogenation. A series of functionalized diaryl/aryl heteroaryl/diheteroaryl/aryl-alkyl selenides, sulfides and tellurides have been obtained by this procedure. Significantly, using this procedure 2,4-dinitroaniline is converted to (2,4-dinitrophenyl)(phenyl)selane which is known as thioredoxin reductase (TR) and glutathione reductase (GR) inhibitor. The reaction goes by a radical pathway and a plausible mechanism has been suggested. 相似文献
72.
Cholesterol-based Schiff base 1 has been designed and synthesised. The Schiff base 1 forms yellow coloured gel in DMF:H2O (2:1, v/v) and the gel is anion responsive. Among different anions, the gel phase of 1 is selectively transformed into sol in the presence of CN– ions and validates its visual sensing. 1H NMR, FTIR and HRMS spectroscopic techniques were adopted to study the gelation of 1 and its responsive behaviour towards anions. 相似文献
73.
Naphthalene and pyrrole substituted guanidine 1 has been designed and synthesised. Compound 1 efficiently distinguishes Cu2+, Hg2+ and Pb2+ ions by exhibiting different responses in fluorescence. While compound 1 exhibited turn-on emission selectively in the presence of Hg2+ and Pb2+ ions in CH3CN and CH3CN–H2O (1:1, v/v), respectively, it showed decrease in emission upon interaction with Cu2+ ion in CH3CN. Furthermore, the Cu-1 ensemble has been established as a potential probe for selective detection of CN? ion over a series of other anions involving colour change (in ordinary light: colourless to light yellow and under UV light: colourless to sky blue). Theoretical insight has been invoked to understand the mode of metal–ligand interaction. 相似文献
74.
Prof. Dr. Mohamed Mokhtar Dr. Ghalia Alzhrani Prof. Dr. Elham S. Aazam Prof. Dr. Tamer S. Saleh Dr. Sulaiman Al-Faifi Dr. Subir Panja Prof. Dr. Debabrata Maiti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(34):8875-8885
Herein, we report the synthesis of nickel-layered double hydroxide amalgamated Y-zeolite (NiLDH@YZ) hybrids and the evaluation of the synergistic effect of various NiLDH@YZ catalysts and mechanochemical agitation on Glaser homocoupling reactions. Nitrogen adsorption-desorption experiments were carried out to estimate the surface area and porosity of NiLDH@YZ hybrids. The basicity and acidity of these hybrids were determined by CO2-TPD and NH3-TPD experiments respectively and this portrayed good acid-base bifunctional feature of the catalysts. The NiLDH@YZ-catalyzed mechanochemical Glaser coupling reaction achieved best yield of 83 % for the 0.5NiLDH@0.5YZ hybrid after 60 min of agitation, which revealed the highest acid-base bifunctional feature compared to all the investigated catalysts. The developed catalyst has proven itself as a robust and effective candidate that can successfully be employed up to four catalytic cycles without significant loss in catalytic activity, under optimized reaction conditions. This work demonstrated a new strategy for C−C bond formation enabled by the synergy between mechanochemistry and heterogeneous catalysis. 相似文献
75.
Kinetic studies on the oxidation of 2‐mercaptosuccinic acid by dinuclear [Mn2III/IV(μ‐O)2(cyclam)2](ClO4)3] ( 1 ) (abbreviated as MnIII–MnIV) (cyclam = 1,4,8,11‐tetraaza‐cyclotetradecane) have been carried out in aqueous medium in the pH range of 4.0–6.0, in the presence of acetate buffer at 30°C by UV–vis spectrophotometry. In the pH region, two species of complex 1 (MnIII–MnIV and MnIII–MnIVH, the later being μ‐O protonated form) were found to be kinetically significant. The first‐order dependence of the rate of the reactions on [Thiol] both in presence and absence of externally added copper(II) ions, first‐order dependence on [Cu2+] and a decrease of rate of the reactions with increase in pH have been rationalized by suitable sequence of reactions. Protonation of μ‐O bridge of 1 is evidenced by the perchloric acid catalyzed decomposition of 1 to mononuclear Mn(III) and Mn(IV) complex observed by UV–vis and EPR spectroscopy. The kinetic features have been rationalized considering Cu(RSH) as the reactive intermediate. EPR spectroscopy lends support for this. The formation of a hydrogen bonded outer‐sphere adduct between the reductant and the complex in the lower pH range prior to electron transfer reactions is most likely to occur. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 170–177 2004 相似文献
76.
Panja S Nielsen SB Hvelplund P Turecek F 《Journal of the American Society for Mass Spectrometry》2008,19(12):1726-1742
Collisional electron transfer from gaseous Cs atoms was studied for singly and doubly protonated peptides Gly-Arg (GR) and
Ala-Arg (AR) at 50- and 100-keV kinetic energies. Singly protonated GR and AR were discharged to radicals that in part rearranged
by migration of a Cα hydrogen atom onto the guanidine group. The Cα-radical isomers formed were detected as stable anions following transfer of a second electron. In addition to the stabilizing
rearrangements, the radicals underwent side-chain and backbone dissociations. The latter formed z fragments that were detected
as the corresponding anions. Analysis of the (GR+H)· radical potential energy surface using electronic structure theory in combination with Rice-Ramsperger-Kassel-Marcus calculations
of rate constants indicated that the arginine Cα hydrogen atom was likely to be transferred to the arginine side-chain on the experimental timescale of ≤200 ns. Transfer
of the Gly Cα-H was calculated to have a higher transition-state energy and was not kinetically competitive. Collisional electron transfer
to doubly protonated GR and AR resulted in complete dissociation of (GR+2H)+· and (AR+2H)+· ions by loss of H, ammonia, and N-Cα bond cleavage. Electronic structure theory analysis of (GR+2H)+· indicated the presence of multiple conformers and electronic states that differed in reactivity and steered the dissociations
to distinct channels. Electron attachment to (GR+2H)2+ resulted in the formation of closely spaced electronic states of (GR+2H)+· in which the electron density was delocalized over the guanidinium, ammonium, amide, and carboxyl groups. The different behavior
of (GR+H)· and (GR+2H)+· is explained by the different timescales for dissociation and different internal energies acquired upon electron transfer. 相似文献
77.
František Tureček Jace W. Jones Anne I. S. Holm Subhasis Panja Steen Brøndsted Nielsen Preben Hvelplund 《Journal of mass spectrometry : JMS》2009,44(5):707-724
Electron‐induced dissociations of gas‐phase ternary copper‐2,2′‐bipyridine complexes of Gly‐Gly‐Gly and Gly‐Gly‐Leu were studied on a time scale ranging from 130 ns to several milliseconds using a combination of charge‐reversal (+CR?) and electron‐capture‐induced dissociation (ECID) measured on a beam instrument and electron capture dissociation (ECD) measured in a Penning trap. Charge‐reduced intermediates were observed on the short time scale in the +CR? and ECID experiments but not in ECD. Ion dissociations following electron transfer or capture mostly occurred by competitive bpy or peptide ligand loss, whereas peptide backbone fragmentations were suppressed in the presence of the ligated metal ion. Extensive electron structure theory calculations using density functional theory and large basis sets provided optimized structures and energies for the precursor ions, charge‐reduced intermediates, and dissociation products. The Cu complexes underwent substantial structure changes upon electron capture. Cu was calculated to be pentacoordinated in the most stable singly charged complexes of the [Cu(peptide ? H)bpy]+ ? type where it carried a ~+ 1 atomic charge. Cu coordination in charge‐reduced [Cu(peptide ? H)bpy] intermediates depended on the spin state. The themodynamically more stable singlet states had tricoordinated Cu, whereas triplet states had a tetracoordinated Cu. Cu was tricoordinated in stable [Cu(peptide ? H)bpy]? ? products of electron transfer. [Cu(peptide)bpy]2 + ? complexes contained the peptide ligand in a zwitterionic form while Cu was tetracoordinated. Upon electron capture, Cu was tri‐ or tetracoordinated in the [Cu(peptide)bpy]+ charge‐reduced analogs and the peptide ligands underwent prototropic isomerization to canonical forms. The role of excited singlet and triplet electronic states is assessed. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
78.
Nabamita Panja Tapan K. Ghanty Prasanta K. Nandi 《Theoretical chemistry accounts》2010,126(5-6):323-337
The static first and second hyperpolarizabilities of a number of spiromolecules with varying degree of polarity have been calculated at the HF and MP2 level using the 6-31+G* basis set and the B3LYP/6-31+G* optimized geometry. The variation of mean second hyperpolarizability in these molecular systems has been explained in terms of the ground state dipole moment, mean linear polarizability and second-order polarizability. A number of relationships among these quantities have been derived in the framework of the sum-over-state scheme and the generalized Thomas–Kuhn sum rule. The spiroconjugation results in the significant increase of the mean polarizability. The appreciable enhancement of first hyperpolarizability due to the spiroconjugation between two dipolar monomer units has been accounted for the rather significant increase of the mean polarizability tensor and the ground state dipole moment. The relatively larger value of the average second hyperpolarizability of the spiroconjugated molecules compared to that of the corresponding monomers arises from the rather significant increase of the nonaxial component γ xxyy . The replacement of spirocarbon by spirosilicon results in the enhancement of the cubic polarizability manifold. The donor–acceptor substituted spirocompounds are predicted to be the superior third-order nonlinear optical (NLO) phores. The nature of π-conjugation in the monomer units around the spirocenter shows a strong modulation of the NLO properties of spirocompounds. The influence of electron correlation on the NLO properties at the MP2 level has been found to be rather significant. 相似文献
79.
We consider the unwinding of two lattice polymer strands of length N that are initially wound around each other in a double-helical conformation and evolve through Rouse dynamics. The problem relates to quickly bringing a double-stranded polymer well above its melting temperature, i.e., the binding interactions between the strands are neglected, and the strands separate from each other as it is entropically favorable for them to do so. The strands unwind by rotating around each other until they separate. We find that the process proceeds from the ends inward; intermediate conformations can be characterized by a tightly wound inner part, from which loose strands are sticking out, with length l~t(0.39). The total time needed for the two strands to unwind scales as a power of N as τ(u)~N(2.57±0.03). We present a theoretical argument, which suggests that during this unwinding process, these loose strands are far out of equilibrium. 相似文献
80.
This work is our first step to get multiresolution approximation of eigenelements of Sturm-Liouville problems within bounded domain of varied nature. The formula for obtaining elements of representation of Sturm-Liouville operator involving polynomial coefficients in wavelet basis of Daubechies family have been derived in a form which can be readily used for their computations by a simple computer program. Estimates of errors for both the eigenvalues and eigenfunctions are also presented here. The proposed wavelet-Galerkin scheme based on scale functions and wavelets of Daubechies family having three or four vanishing moments of their wavelets has been applied to get approximate eigenelements of regular and singular Sturm-Liouville problems within bounded domain and compared with the exact or approximate results whenever available. From our study it appears that the proposed method is efficient and rapidly convergent in comparison to other approximation schemes based on variational method in Haar basis or finite difference methods studied by Bujurke et al. [39]. 相似文献