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1.
The excited-state photophysical properties of curcumin in the presence of bovine serum albumin (BSA) have been studied. The absorption and fluorescence changes in curcumin on binding to BSA have been followed at varying concentrations of either curcumin or BSA to determine the binding constant, which has been found to be approximately 10(4) to 10(5) M(-1). Stopped-flow kinetics studies suggested at least two distinct kinetic steps for the binding of curcumin to BSA. The photophysical properties of the singlet-excited state of the curcumin-BSA complex have also been studied. Whereas the absorption spectrum of curcumin is redshifted, the fluorescence spectrum of curcumin was blueshifted in the presence of BSA. The fluorescence quantum yield of curcumin on complexing with BSA was approximately 0.05. Steady-state fluorescence anisotropy studies showed a significant increase in the anisotropy value of 0.37 in BSA-bound curcumin. The fluorescence decay of the curcumin-BSA complex followed a biexponential decay with fluorescence lifetimes of 413 ps (33%) and 120 ps (67%). On the basis of these complementary results, it has been concluded that curcumin shows very high binding to BSA, probably at the hydrophobic cavities inside the protein. 相似文献
2.
Samik Gupta Anil Kumar Barik Sachindranath Pal Arijit Hazra Somnath Roy Ray J. Butcher Susanta Kumar Kar 《Polyhedron》2007
Four cis-dioxomolybdenum complexes of general formula [MoO2(Ln)EtOH] (n = 1–4) and one oxomolybdenum(IV) complex [MoO(L4)EtOH], with potentially tridentate Schiff bases derived from 5-methyl pyrazole-3-carbohydrazide and salicylaldehyde/substituted salicylaldehyde/o-hydroxy acetophenone have been prepared. The Mo(IV) complex is derived from the Mo(VI) dioxo complex by oxotransfer reaction with PPh3. The complexes are characterized by elemental analysis, electronic spectra, IR, 1H NMR, and by cyclic voltammetry. All the Mo(VI) species are crystallographically characterized. The complexes have a distorted octahedral structure in which the ligand behaves as a binegative donor one, leaving the pyrazole –N uncoordinated towards the metal center. It is also revealed from the crystal structure that the Mo(VI) center enjoys an NO5 donor environment. 相似文献
3.
Dr. Subrat Kumar Barik Shou-Chih Huo Chun-Yen Wu Tzu-Hao Chiu Jian-Hong Liao Dr. Xiaoping Wang Dr. Samia Kahlal Prof. Jean-Yves Saillard Prof. C. W. Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(46):10471-10479
Although atomically precise polyhydrido copper nanoclusters are of prime interest for a variety of applications, they have so far remained scarce. Herein, this work describes the synthesis of a dithiophosphate-protected copper(I) hydride-rich nanocluster (NC), [Cu30H18{S2P(OnPr)2}12] ( 1H ), fully characterized by various spectroscopic methods and single-crystal X-ray diffraction. The X-ray structure of 1H reveals an unprecedented central Cu12 hollow icosahedron. Six faces of this icosahedron are capped by Cu3 triangles, the whole Cu30 core being wrapped by twelve dithiophosphate ligands and the whole cluster has ideal S6 symmetry. The locations of the 18 hydrides in 1H were ascertained by a single-crystal neutron diffraction study. They are composed of three types: capping μ3-H, interstitial μ4-H (seesaw) and μ5-H ligands (square pyramidal), in good agreement with the DFT simulations. The numbers of hydrides and ligand resonances in the 1H NMR spectrum of 1H are in line with their coordination environment in the solid state, retaining the S6 symmetry in solution. Furthermore, two new Se-protected polyhydrido copper nanoclusters, [Cu30H18{Se2P(OR)2}12] ( 2H : R=iPr 3H : R=iBu) were synthesized from their sulfur relative 1H via ligand displacement reaction and their X-ray structures feature the exceptional case where both the NC shape and size are fully conserved during the course of ligand exchange. DFT and TD-DFT calculations allow understanding the bonding and optical properties of clusters 1H – 3H . In addition, the reaction of 1H with [Pd(PPh3)2Cl2] in the presence of terminal alkynes led to the formation of new bimetallic Cu−Pd alloy clusters [PdCu14H2{S2P(OnPr)2}6(C≡CR)6] ( 4 : R=Ph; 5 : R = C6H4F). 相似文献
4.
A clean, mild, and efficient catalytic deoximation procedure compatible with several common functional groups has been developed using 30% hydrogen peroxide activated by iodine catalyst in aqueous acetonitrile under essentially neutral conditions. The mechanistic features of an iodonium ion–driven nucleophilic cleavage of oximic C[dbnd]N have been revealed. 相似文献
5.
An empirical mass formula is tested for the basic fermion sequences of charged quarks and leptons. This relation is a generalization
of Barut’s mass formula for the lepton sequence (e, μ, τ......). It is found that successful mass extrapolation to the third and possibly to other higher generations (N>2) can be obtained with the first and second generation masses as inputs, which predicts the top quark massm
t to be around 20 GeV. This also leads to the mass ratios between members of two different sequences (i) and (i′) corresponding to the same higher generations (N>2). 相似文献
6.
Kinsuk Das Tarak Nath Mandal Somnath Roy Samik Gupta Anil Kumar Barik Partha Mitra Arnold L. Rheingold Susanta Kumar Kar 《Polyhedron》2010
The varying coordination modes of the title ligand, L [5-methyl-1-(pyridin-2-yl)-N′-[pyridin-2-ylmethylidene]pyrazole-3-carbohydrazide] towards the different metal centers is reported by preparation and characterization of Cu(II), Zn(II) and Cd(II) complexes, [Cu(L)NO3.H2O](NO3) (1) [Zn(L)2](ClO4)2·2DMF (2) and [Cd(L)(I)2] (3) respectively. In 1, the neutral ligand serves as tetradentate 4 N donor where both pyridine and pyrazole nitrogen atoms of pyridyl–pyrazole part are coordinatively active, leaving the carbonyl oxygen of the carbohydrazide part inactive. The same pyridine and pyrazole N atoms remain abstained from the coordination process towards the Zn(II) and Cd(II) metal centers. For 2 and 3 the ligand behaves as a tridentate NNO donor where the two nitrogen atoms come from azomethine, pyridine of pyridine-2-carbaldehyde parts and O from carbonyl oxygen atoms (carbohydrazide part). The complex 1 and 2 are distorted octahedral while complex 3 adopts distorted square pyramidal geometry. All the complexes are X-ray crystallographically characterized. 相似文献
7.
Of interest here is a characterization of the undirected graphs G such that the Laplacian matrix associated with G can be diagonalized by some Hadamard matrix. Many interesting and fundamental properties are presented for such graphs along with a partial characterization of the cographs that have this property. 相似文献
8.
Sufficient conditions are obtained so that every solution of the neutral functional difference equation
$
\Delta ^m (y_n - p_n y_{\tau (n)} ) + q_n G(y_{\sigma (n)} ) - u_n H(y_{\alpha (n)} ) = f_n ,
$
\Delta ^m (y_n - p_n y_{\tau (n)} ) + q_n G(y_{\sigma (n)} ) - u_n H(y_{\alpha (n)} ) = f_n ,
相似文献
9.
10.
Po‐Yu Lin Dai‐Ying Li Feng‐Hsien Ho Jian‐Hong Liao Subrat Kumar Barik C. W. Liu 《中国化学会会志》2019,66(9):988-995
A structural study of ligand exchange on chalcogen‐passivated copper nanoclusters is far less developed. Herein, we report the synthesis of polyhydrido copper nanoclusters [Cu20H11{Se2P(O iBu)2}9] ( 2 ) passivated by Se‐donor ligands via ligand replacement reaction on [Cu20H11{S2P(O iPr)2}9] ( 1 ) with NH4[Se2P(O iBu)2]. In parallel to the synthesis of 2 , cluster [Cu20H11{S2P(CH2CH2Ph)2}9] ( 4 ) was produced by the ligand exchange reaction on a new derivative of 1 , that is [Cu20H11{S2P(O nPr)2}9] ( 3 ). Solid state structures of both clusters 2 and 4 were unequivocally established by single‐crystal X‐ray diffraction studies and cluster 4 epitomizes exceptional case to preserve both the shape and size of the nanocluster during the course of ligand exchange. Structurally precise cluster 2 is the second example where the copper hydride nanocluster is stabilized by Se‐donor ligands. The anatomy of 2 can be visualized as a twisted cuboctahedral Cu13 core, two triangular faces of which are capped by a Cu6 cupola and a single Cu atom along the C3 rotational axis. 相似文献
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