Spectroscopic studies on the effect of temperature on pH-induced folded states of human serum albumin

Human serum albumin (HSA) is a very important multi-domain transporter protein in the circulatory system responsible for carriage of various kinds of ligands within the physiological system. HSA is also known to undergo conformational transformation at different pH(s) and temperatures. In this report we have studied the binding interactions of a photosensitizing drug, protoporphyrin IX (PPIX) with various conformers of HSA at different temperatures using picosecond time-resolved fluorescence spectroscopy. Also, using dynamic light scattering (DLS) and circular dichroism (CD) spectroscopy we have followed the structural transition of various conformers of HSA at different temperatures. Ensuring the intact binding of PPIX to various conformers of HSA at different temperatures as revealed through time-resolved fluorescence anisotropy decay and significant spectral overlap of emission of Trp214 residue (donor) in domain-IIA and absorption of PPIX (acceptor) bound to domain-IB of HSA, we have applied F?rster's resonance energy transfer (FRET) technique to determine the interdomain separation under various environmental conditions. The alkali-induced conformer of HSA shows almost no change in donor-acceptor distance in contrast to the native and acid-induced conformers of HSA, which show a decrease in distance with increase in temperature. Through this study the non-covalently bound PPIX is shown to be an efficient FRET probe in reporting the different temperature-induced folded states of HSA in buffer solutions of widely differing pH values.     

Dioxomolybdenum(VI) and dioxotungsten(VI) complexes supported by an amido ligand

Stepwise addition of one equivalent of n-butyllithium and trimethylsilyl chloride to 2-tert-butylmercaptoaniline affords the new ligand 1-(Me3SiNH)-2-(t-BuS)C6H4 (LH), that reacts with one equivalent of butyllithium to its lithium salt LLi. Dioxodichloromolybdenum [MoO2Cl2] and dioxodichlorotungsten dimethoxyethane [WO2Cl2(dme)] react in tetrahydrofuran solution at low temperature with two equivalents LLi to monomeric dioxomolybdenum(VI) [MoO2L2] (1) and dioxotungsten(VI) complex [WO2L2] (2) employing two bidentate amido thioether ligands. The crystallographic determination of the molecular structures of 1 and 2 show evidence for M...S contacts. The reaction of [MoO2Cl2] with LLi in tetrahydrofuran solution at room temperature leads next to 1 to two compounds where silyl group migration from nitrogen to oxygen atoms occurs forming [Mo(=NL')2(OSiMe)2] (3) and [Mo(=NL')2(OSiMe3)L] (4, L' = N-2-t-BuSC6H4) as determined by NMR spectroscopy. Compound 4 was isolated in low yield and its molecular structure determined by X-ray crystallography. Higher yields of a bisimido complex can be obtained by the direct reaction of one equivalent of LLi with [Mo(NAr)2Cl2(dme)] (Ar = 2,6-Me2C6H4) forming [Mo(NAr)2LCl] (5).     

Solvent effects on the rate of thermolysis of lauroyl peroxide

Thermolysis of lauroyl peroxide in various organic solvents was studied. It was shown that the primary homolytic dissociation of the peroxide group is accompanied by secondary reactions of chain-induced decomposition. The reaction medium affects the rate of both the primary homolytic dissociation and secondary induced decomposition processes. Correlation equations between the rate constants of the reactions in study and the physicochemical parameters of the solvents were proposed.     

Synthesis of multifunctional metal- and metal oxide core@mesoporous silica shell structures by using a wet chemical approach

We demonstrate a facile wet chemical approach for fabricating spherical metal/metal-oxide core@mesoporous silica shell hybrid nanoparticles with different core and shell thicknesses. Vertically aligned mesoporous silica (mSiO(2) ) shells were fabricated over the pre-synthesized spherical SiO(2) nanoparticles through a three-step strategy: 1)?synthesis of core materials, 2)?covering the core with an organic-inorganic composite layer, and 3)?removing the organic template through calcinations in air. The mechanisms of hybrid structure formation are proposed. The multifunctional nature of the hybrid structures could be induced by incorporating guest ions/molecules, such as Ag, Mn, and TiO(2) , into the pores of an mSiO(2) shell. Mn and TiO(2) cluster- incorporated composite structures have been tested to be antioxidizing agents and effective photocatalysts through electron spin resonance, radical scavenging tests, and the photocatalytic degradation of rhodamine B. The possibility of incorporating several hetero-element guest clusters in these mesoporous composite particles makes them highly attractive for multifunctional applications.     

Interlocked catenane-like structure predicted in Au24(SR)20: implication to structural evolution of thiolated gold clusters from homoleptic gold(I) thiolates to core-stacked nanoparticles

Atomic structure of a recently synthesized ligand-covered cluster Au(24)(SR)(20) [J. Phys. Chem. Lett., 2010, 1, 1003] is resolved based on the developed classical force-field based divide-and-protect approach. The computed UV-vis absorption spectrum and powder X-ray diffraction (XRD) curve for the lowest-energy isomer are in good agreement with experimental measurements. Unique catenane-like staple motifs are predicted for the first time in core-stacked thiolate-group (RS-) covered gold nanoparticles (RS-AuNPs), suggesting the onset of structural transformation in RS-AuNPs at relatively low Au/SR ratio. Since the lowest-energy structure of Au(24)(SR)(20) entails interlocked Au(5)(SR)(4) and Au(7)(SR)(6) oligomers, it supports a recently proposed growth model of RS-AuNPs [J. Phys. Chem. Lett., 2011, 2, 990], that is, Au(n)(SR)(n-1) oligomers are formed during the initial growth of RS-AuNPs. By comparing the Au-core structure of Au(24)(SR)(20) with other structurally resolved RS-AuNPs, we conclude that the tetrahedral Au(4) motif is a prevalent structural unit for small-sized RS-AuNPs with relatively low Au/SR ratio. The structural prediction of Au(24)(SR)(20) offers additional insights into the structural evolution of thiolated gold clusters from homoleptic gold(I) thiolate to core-stacked RS-AuNPs. Specifically, with the increase of interfacial bond length of Au(core)-S in RS-AuNPs, increasingly larger "metallic" Au-core is formed, which results in smaller HOMO-LUMO (or optical) gap. Calculations of electronic structures and UV-vis absorption spectra of Au(24)(SR)(20) and larger RS-AuNPs (up to ~2 nm in size) show that the ligand layer can strongly affect optical absorption behavior of RS-AuNPs.     

An efficient ‘on-water’ synthesis of 1,4-dihydropyridines using Fe3O4@SiO2 nanoparticles as a reusable catalyst

An ‘on-water’, efficient, high yielding, expeditious method has been developed for the synthesis of 1,4-dihydropyridine (1,4-DHP) derivatives via an one-pot multi-component condensation of dimedone or 4-hydroxycoumarine, aldehydes, and ammonium acetate using Fe₃O₄@SiO₂ nanoparticles as a recyclable heterogeneous catalyst. This method takes advantage of the fact that water, a green solvent is used in combination with Fe₃O₄@SiO₂ nanoparticles as catalyst which can be easily recovered magnetically and reused for further runs.     

Reactions of titanium(IV) isopropoxide with aliphatic and aromatic hydroxy esters,part I. 5-, 6-, 7- and 8-coordinate titanium(IV) complexes

Summary Reactions of titanium(IV) isopropoxide with ethyl 1-hydroxycyclohexylacetate, ethyl 2-hydroxy-2-arylpropionate, ethyl 2-hydroxy-2-arylbutyrate and ethyl 2-hydroxy-2-arylhydrocinnamate have been studied in dry benzene in different molar ratios under strictly anhydrous conditions. The Ti(OPr-i)₄-_nL_n type compounds, where L = hydroxy ester and n = 1 to 4, have been isolated and characterised by elemental analysis, molecular weight, i.r. and n.m.r. spectral studies. These products may be distilled unchanged under reduced pressure.Reprints of this are not available.     

Synthesis and characterization of a novel polymeric hydrogel based on hydroxypropyl methyl cellulose grafted with polyacrylamide

A novel hydrogel has synthesized by grafting polyacrylamide chains onto hydroxypropyl methylcellulose in presence of potassium persulphate as initiator using solution polymerization technique. The reaction was carried out in homogeneous aqueous medium. The effect of reaction parameters on percentage of grafting (% G) and grafting efficiency (% GE) were discussed. The parameters were varied systematically to achieve the best hydrogel. Developed hydrogels were characterized by various materials characterization techniques. The dynamic and equilibrium swelling properties of hydrogels were investigated as a function of pH and time in various buffer solutions similar to that of gastric and intestinal fluid. Results showed that with increase in % G and % GE, the rate of swelling decreases, which can opens the door for further study of their utilization as matrices for controlled/sustained/targeted drug delivery.     

Composition and reactivity of aminolysis products of phenyl glycidyl ether with benzylamine

Composition of aminolysis products of phenyl glycidyl ether with benzylamine in various conditions was studied. The ratio of 1-(benzylamino)-3-phenoxypropan-2-ol and 1,1'-(benzylazanediyl)bis(3-phenoxypropan-2-ol) does not considerably depend on the nature of the solvent and is basically determined by ratio of initial reagents. 2,6-Bis(phenoxymethyl)morpholine was obtained by dehydration of aminodiol in conditions of Mitsunobu reaction with subsequent reductive debenzylation.