Electric field-induced conformational transition of bovine serum albumin from alpha-helix to beta-sheet

The irreversible conformational transition of bovine serum albumin (BSA) from alpha-helix to beta-sheet, induced by electric field near the electrode surface, was monitored by circular dichroism (CD) with a long optical path thin layer cell (LOPTLC).

Fabrication of layer-by-layer deposited multilayer films containing DNA and its interaction with methyl green

Multilayer films were fabricated by layer-by-layer electrostatic deposition techniques between poly(diallyIdimethylammonium chloride) (PDDA) and calf thymus DNA (CT DNA) on glassy carbon and quartz substrates. Electrochemical impedance spectroscopy (EIS), Fourier transform infrared (FTIR) spectroscopy and UV-vis spectroscopy demonstrated the uniform assembly of PDDA/DNA multilayer films, and X-ray photoelectron spectroscopy confirmed the elemental composition of the films. Moreover, the interaction of DNA in PDDA/DNA films with methyl green was investigated by UV-vis spectroscopy and circular dichroism (CD). (C) 2001 Elsevier Science B.V. All rights reserved.

Electrochemistry and spectroscopy study on the interaction of microperoxidase-11 with lipid membrane

The interaction of microperoxidase-11 (MP11) with cationic lipid vesicles of didodecyldimethylammonium bromide (DDAB) induces an alpha -helical conformation from random coil conformations in solution and this change then makes heme macrocycle more distorted. DDAB-induced MP11 conformations were investigated by cyclic votammetry (CV), circular dichroism (CD) and UV-vis spectrometry. All results indicate that the binding of MP11 in solution to DDAB vesicles and the ordered structure formation are driven by mostly electrostatic interaction between negatively charged residues in the undecapeptide and positively charged lipid headgroups on the membrane surface. Upon binding to DDAB, its half-peak potential was also changed. The mechanism of the interaction between MP11 and DDAB was also discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

Characterization of the structural and functional changes of hemoglobin in dimethyl sulfoxide by spectroscopic techniques

Circular dichroism (CD), fourier transform infrared (FTIR), and fluorescence spectroscopy were used to explore the effect of dimethyl sulfoxide (DMSO) on the structure and function of hemoglobin (Hb). The native tertiary structure was disrupted completely when the concentration of DMSO reached 50% (v/v), which was determined by loss of the characteristic Soret CD spectrum. Loss of the native tertiary structure could be mainly caused by breaking the hydrogen bonds, between the heme propionate groups and nearby surface amino acid residues, and by disorganizing the hydrophobic interior of this protein. Upon exposure of Hb to 52% DMSO for ca. 12 h in a D2O medium no significant change in 1652 cm(-1) band of the FTIR spectrum was produced, which demonstrated that alpha-helical structure predominated. When the concentration of DMSO increased to 57%: (1) the band at 1652 cm(-1) disappeared with the appearance of two new bands located at 1661 and 1648 cm(-1); (2) another new band at 1623 cm(-1) was attributed to the formation of intermolecular beta-sheet or aggregation, which was the direct consequence of breaking of the polypeptide chain by the competition of S=O groups in DMSO with C=O groups in amide bonds. Further increasing the DMSO concentration to 80%, the intensity at 1623 cm(-1) increased, and the bands at 1684, 1661 and 1648 cm(-1) shifted to 1688, 1664 and 1644 cm(-1), respectively. These changes showed that the native secondary structure of Hb was last and led to further aggregation and increase of the content of 'free' amide C=O groups. In pure DMSO solvent, the major band at 1664 cm(-1) indicated that almost all of both the intermolecular beta-sheet and any residual secondary structure were completely disrupted. The red shift of the fluorescence emission maxima showed that the tryptophan residues were exposed to a greater hydrophilic environment as the DMSO content increased. GO-binding experiment suggested that the biological function of Hb was disrupted seriously even if the content of DMSO was 20%. (C) 1998 Elsevier Science B.V. All rights reserved.

Electropolymeric generation of optically active polypyrrole

The facile synthesis of optically active polypyrrole has been achieved via the enantioselective electropolymerization of pyrrole on indium-tin-oxide-coated glass electrodes in aqueous solution containing D-(+) or L-(-) tartaric acid, (1S)-(+)-10-camphorsulfonic acid and L-lactic acid. The dark films of conducting polypyrroles salt formed under electrostatic conditions (+0.65V vs. Ag/AgCl) exhibited strong circular dichroism (CD) spectra typical of polymers possessing helical chirality. The quantitative reversal of the CD spectrum of the salt grown in (+)-tartaric acid as opposed to (-)-tartaric acid suggests that electropolymerization is highly enantioselective, with one helical screw of the polymer chain being preferentially produced depending on the hand of the tartaric anion incorporated. (C) 1997 Elsevier Science Ltd.

A NEW SIMPLE LONG-PATH-LENGTH THIN-LAYER SPECTROELECTROCHEMICAL CELL IN VARIOUS USES

This article describes the design of a new type of long-path-length thin-layer cell (LPTLC), which is constructed by inserting two Teflon cell bodies into a standard cuvette. This cuvette holder enables the LPTLC to combine with photometric instrumentation conveniently. Gold, platinum, glassy carbon, and other materials can be used for the working electrode. Since no soluble adhesive material is used, the cell can meet various needs (in situ conventional and derivative W-vis, in situ circular dichroism, etc.) in both aqueous and nonaqueous systems.

HELIX-INDUCED ASYMMETRIC POLYMERIZATION

Asymmetric polymerization could be induced by an already formed optically active living prepolymer with one-handed screw sense helix conformation. The usually formed anionic active centre on the prepolymer could be changed to cationic, radical and even of Ziegler-Natta type. These living prepolymers with various kinds of active centre were all effective to induce a consequent asymmetric polymerization of a monomer which may be other than that in the prepolymer, to afford an optically active helical chain with the same screw sense as that of the prepolymer. Eight monomers have been used in the work. Optical rotation, circular dichroism and gelpermeation chromatography have been taken to prove the helix-induced asymmetric polymerization.

Characterization of the main light-harvesting chlorophyll a/b-protein complex of green alga, Bryopsis corticulans

The main light-harvesting chlorophyll a/b -protein complex (LHC II) has been isolated directly from thylakoid membranes of shiphonous green alga, Bryopsis corticulans Setch. by using two consecutive runs of anion exchange and gel-filtration chromatography. Monomeric and trimeric subcomplexes of LHC 11 were obtained by using sucrose gradient ultracentrifugation. Pigment analysis by reversed-phase high performance liquid chromatography showed that chlorophyll a (Chl a), chlorophyll b (Chl b), neoxanthin, violaxanthin and siphonaxanthin were involved in LHC 11 from B. corticulans. The properties of electronic transition of monomeric LHC II showed similarities to those of trimeric LHC II. Circular dichroism spectroscopy showed that strong intramolecular interaction of excitonic dipoles between Chl a and between Chl b exist in one LHC II apoprotein, while the intermolecular interaction of these dipoles can be intensified in the trimeric structure. The monomer has high efficient energy transfer from Chl b and siphonaxanthin to Chl a similarly to that of the trimer. Our results suggest that in B. corticulans, LHC II monomer has high ordered pigment organization that play effective physiological function as the trimer, and thus it might be also a functional organization existing in thylakoid membrane of B. corticulans.

Capillary Effect on Vertically Excited Surface Wave in Circular Cylindrical Vessel

In a vertically oscillating circular cylindrical container, singular perturbation theory of two-time scale expansions was developed in inviscid fluids to investigate the motion of single free surface standing wave including the effect of surface tension.

Instability Analysis of Nonlinear Surface Waves in a Circular Cylindrical Container Subjected to a Vertical Excitation

Singular perturbation theory of two-time scale expansions was developed both in inviscid and weak viscous fluids to investigate the motion of single surface standing wave in a liquid-filled circular cylindrical vessel, which is subject to a vertical periodical oscillation. Firstly, it is assumed that the fluid in the circular cylindrical vessel is inviscid, incompressible and the motion is irrotational, a nonlinear evolution equation of slowly varying complex amplitude, which incorporates cubic nonlinear term, external excitation and the influence of surface tension, was derived from solvability condition of high-order approximation. It shows that when forced frequency is low, the effect of surface tension on mode selection of surface wave is not important. However, when forced frequency is high, the influence of surface tension is significant, and can not be neglected. This proved that the surface tension has the function, which causes free surface returning to equilibrium location. Theoretical results much close to experimental results when the surface tension is considered. In fact, the damping will appear in actual physical system due to dissipation of viscosity of fluid. Based upon weakly viscous fluids assumption, the fluid field was divided into an outer potential flow region and an inner boundary layer region. A linear amplitude equation of slowly varying complex amplitude, which incorporates damping term and external excitation, was derived from linearized Navier-Stokes equation. The analytical expression of damping coefficient was determined and the relation between damping and other related parameters (such as viscosity, forced amplitude and depth of fluid) was presented. The nonlinear amplitude equation and a dispersion, which had been derived from the inviscid fluid approximation, were modified by adding linear damping. It was found that the modified results much reasonably close to experimental results. Moreover, the influence both of the surface tension and the weak viscosity on the mode formation was described by comparing theoretical and experimental results. The results show that when the forcing frequency is low, the viscosity of the fluid is prominent for the mode selection. However, when the forcing frequency is high, the surface tension of the fluid is prominent. Finally, instability of the surface wave is analyzed and properties of the solutions of the modified amplitude equation are determined together with phase-plane trajectories. A necessary condition of forming stable surface wave is obtained and unstable regions are illustrated. (c) 2005 Elsevier SAS. All rights reserved.

A thermal-elastic analysis on laser-induced reverse bulging and plugging in circular brass foil

A new failure mode is observed in circular brass foils induced by laser beam. The new failure is based on the following experimental facts : (1) the peripheries of the circular brass foils are fixed and the surfaces of the foils are radiated by laser beam ; (2) the laser beam used is considered to be non-Gaussian spatially, actually an approximately uniform distribution limited in a certain size spot ; (3) the pulse on time of laser beam should be 250 μs, i.e. so called long duration pulse laser. The failure process consists of three stages ; i.e. thermal bulging, localized shear deformation and perforation by plugging. The word reverse in reverse bulging and plugging mode means that bulging and plugging occur in the direction of incident laser beam. To study the newly-discovered type of failure quantitatively, analytical solutions for the axisymmetric temperature field and deflection curve are derived. The calculated results show that the newly discovered failure mode is attributed to the spatial structure effect of laser beam indeed.

Three-dimensional instability of an oscillating viscous flow past a circular cylinder

A systematically numerical study of the sinusoidally oscillating viscous flow around a circular cylinder was performed to investigate vortical instability by solving the three-dimensional incompressible Navier-Stokes equations. The transition from two- to three-dimensional flow structures along the axial direction due to the vortical instability appears, and the three-dimensional structures lie alternatively on the two sides of the cylinder. Numerical study has been taken for the Keulegan-Carpenter( KC) numbers from 1 to 3.2 and frequency parameters from 100 to 600. The force behaviors are also studied by solving the Morison equation. Calculated results agree well with experimental data and theoretical prediction.

A Lagrangian for von Karman Equations of Large Deflection Problem of Thin Circular Plate

By the semi-inverse method proposed by He, a Lagrangian is established for the large deflection problem of thin circular plate. Ritz method is used to obtain an approximate analytical solution of the problem. First order approximate solution is obtained, which is similar to those in open literature. By Mathematica a more accurate solution can be deduced.

Nonlinear Faraday Waves in a Parametrically Excited Circular Cylindrical Container

In the cylindrical coordinate system, a singular perturbation theory of multiple-scale asymptotic expansions was developed to study single standing water wave mode by solving potential equations of water waves in a rigid circular cylinder, which is subjec

Control of Mean and Fluctuating Forces on a Circular Cylinder at High Reynolds Numbers

A narrow strip is used to control mean and fluctuating forces on a circular cylinder at Reynolds numbers from 2.0 x 10(4) to 1.0 x 10(5). The axes of the strip and cylinder are parallel. The control parameters are strip width ratio and strip position characterized by angle of attack and distance from the cylinder. Wind tunnel tests show that the vortex shedding from both sides of the cylinder can be suppressed, and mean drag and fluctuating lift on the cylinder can be reduced if the strip is installed in an effective zone downstream of the cylinder. A phenomenon of mono-side vortex shedding is found. The strip-induced local changes of velocity profiles in the near wake of the cylinder are measured, and the relation between base suction and peak value in the power spectrum of fluctuating lift is studied. The control mechanism is then discussed from different points of view.