Membrane-bound alpha-synuclein forms an extended helix: long-distance pulsed ESR measurements using vesicles, bicelles, and rodlike micelles

We apply pulsed dipolar ESR spectroscopy (Ku-band DEER) to elucidate the global conformation of the Parkinson's disease-associated protein, alpha-synuclein (alphaS) bound to small unilamellar phospholipid vesicles, rodlike SDS micelles, or lipid bicelles. By measuring distances as long as approximately 7 nm between introduced pairs of nitroxide spin labels, we show that distances are close to the expectations for a single continuous helix in all cases studied. In particular, we find distances of 7.5 nm between sites 24 and 72; 5.5 nm between sites 24 and 61; and 2 nm between sites 35 and 50. We conclude that alphaS does not retain a "hairpin" structure with two antiparallel helices, as is known to occur with spheroidal micelles, in agreement with our earlier finding that the protein's geometry is determined by the surface topology rather than being constrained by the interhelix linker. While the possibility of local helix discontinuities in the structure of membrane-bound alphaS remains, our data are more consistent with one intact helix. Importantly, we demonstrate that bicelles produce very similar results to liposomes, while offering a major improvement in experimentally accessible distance range and resolution, and thus are an excellent lipid membrane mimetic for the purpose of pulse dipolar ESR spectroscopy.     

Electrochemical, spectroelectrochemical, and molecular quadratic and cubic nonlinear optical properties of alkynylruthenium dendrimers

A combination of cyclic voltammetry (CV), UV-vis-NIR spectroscopy and spectroelectrochemistry, hyper-Rayleigh scattering (HRS) [including depolarization studies], Z-scan and degenerate four-wave mixing (DFWM) [including studies employing an optically transparent thin-layer electrochemical (OTTLE) cell to effect electrochemical switching of nonlinearity], pump-probe, and electroabsorption (EA) measurements have been used to comprehensively investigate the electronic, linear optical, and nonlinear optical (NLO) properties of nanoscopic pi-delocalizable electron-rich alkynylruthenium dendrimers, their precursor dendrons, and their linear analogues. CV, UV-vis-NIR spectroscopy, and UV-vis-NIR spectroelectrochemistry reveal that the reversible metal-centered oxidation processes in these complexes are accompanied by strong linear optical changes, "switching on" low-energy absorption bands, the frequency of which is tunable by ligand replacement. HRS studies at 1064 nm employing nanosecond pulses reveal large nonlinearities for these formally octupolar dendrimers; depolarization measurements are consistent with lack of coplanarity upon pi-framework extension through the metal. EA studies at 350-800 nm in a poly(methyl methacrylate) matrix are consistent with the important transitions having a charge-transfer exciton character that increases markedly on introduction of peripheral polarizing substituent. Time-resolved pump-probe studies employing 55 ps, 527 nm pulses reveal absorption saturation, the longest excited-state lifetime being observed for the dendrimer. Z-scan studies at 800 nm employing femtosecond pulses reveal strong two-photon absorption that increases significantly on progression from linear complex to zero- and then first-generation dendrimer with no loss of optical transparency. Both refractive and absorptive nonlinearity for selected alkynylruthenium dendrimers have been reversibly "switched" by employing the Z-scan technique at 800 and 1180 nm and 100-150 fs pulses, together with a specially modified OTTLE cell, complementary femtosecond time-resolved DFWM and transient absorption studies at 800 nm suggesting that the NLO effects originate in picosecond time scale processes.     

Laser-based detection of PAHs and BTXE-aromatics in oil polluted soil samples

Time-resolved laser-induced fluorescence spectroscopy and fiber optics are applied for the detection of aromatic hydrocarbons in oil contaminated water and soil samples. Time-integrated data accumulation of fluorescence intensities in an "early" and in a "late" time window with respect to the exciting laser pulse simplifies the method in such a way that it becomes very attractive for practical applications. For ultraviolet laser excitation at 337 nm and recording fluorescence signals at 400 nm, typical detection limits of the present set-up are 0.5 mg engine oil/L in water and 5 mg engine oil/kg in soil. A discrimination between BTXE-aromatics and PAHs in oil polluted soil or water samples is possible, when more than one laser wavelength in the ultraviolet is used for the excitation. The possibilities for a thermal discrimination between different aromatics are also discussed.     

Shape-controlled synthesis of polyhedral CdS flowerlike architectures and their optical properties

Fabrication of polyhedral CdS flower-like architectures have been achieved on a large scale through a mixed solvothermal method. The obtained CdS are characterized by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy, and the results indicate that the CdS flower-like architectures with diameters of 1.5–2.0 µm are hexagonal wurtzite phase and are assembled by some pyramids with the bottom side length of about 440 nm, which have some crystallographic faces. A series of relevant experiments through altering experimental parameters, indicate that the temperature, starting materials and solvent play key roles for the shape evolution of CdS flower-like architectures. The studies of optical properties for polyhedral CdS flower-like architectures indicate that the UV-vis spectroscopy shows a blue-shift absorption peak at 500 nm compared to that of bulk CdS, the photoluminescence spectroscopy shows an emission peak at 640 nm and another strong emission peak at 695 nm, which are believed to be attributed to excitonic emission and deep levels.      

X-ray spectroscopy study of lithiated graphite obtained by thermal deposition of lithium

X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy are used for in situ studies of the electronic structure of lithiated natural graphite produced by thermal deposition of lithium upon graphite in a vacuum. By XPS and NEXAFS spectroscopy it is found that lithium vapor thermal deposition results in the formation of a lithiated graphite surface layer and a change in its electronic structure. Based on the quantum chemical simulation of the experimental СK_α XES spectrum of lithiated graphite, it is found that lithium atoms are located mostly on the edges of graphite crystallites. Atomic force microscopy reveals that the size of natural graphite flakes varies from 50 nm to 200 nm.     

X-Shaped electro-optic chromophore with remarkably blue-shifted optical absorption. Synthesis, characterization, linear/nonlinear optical properties, self-assembly, and thin film microstructural characteristics

A novel type of "X-shaped" two-dimensional electro-optic (EO) chromophore with extended conjugation has been synthesized and characterized. This chromophore is found to exhibit a remarkably blue-shifted optical maximum (357 nm in CH(2)Cl(2)) while maintaining a very large first hyperpolarizability (beta). Hyper-Rayleigh Scattering (HRS) measurements at 800 nm provide a beta(zzz) value of 1840 x 10(-30) esu. Self-assembled thin films of this chromophore were fabricated via a layer-by-layer chemisorptive siloxane-based approach. The chromophoric multilayers have been characterized by transmission optical spectroscopy, advancing contact angle measurements, synchrotron X-ray reflectivity, atomic force microscopy, and angle-dependent polarized second harmonic generation spectroscopy. The self-assembled chromophoric films exhibit a dramatically blue-shifted optical maximum (325 nm) while maintaining a large EO response (chi(2)(333) approximately 232 pm/V at 1064 nm; r(33) approximately 45 pm/V at 1310 nm). This work demonstrates an attractive approach to developing EO materials offering improved nonlinearity-transparency trade-offs.     

Trace analysis of pollutants in water using the photothermal interferometry as HPLC detector

A new procedure including high performance liquid chromatography in combination with photothermal interference spectroscopy as detection device (HPLC/PIS) has been proposed, optimized and its figures of merit for pesticide residue analysis are shown. The flowing sample under study is set in one arm of a Mach-Zehnder interferometer, and its refractive index is modulated by a periodically chopped continuous wave argon ion laser. As chopper, an acousto optical modulator has been introduced to switch the excitation laser beam between different lines (457 nm, 488 nm, 514 nm) simultaneously. Thus a multi component analysis can be realized either by using an HPLC-system in front of the PIS device or by a multi line Ar⁺-laser, directly. The limit of detection of the HPLC/PIS system reached 71 g/l of the pesticide di-nitro-ortho-cresol (DNOC).     

Cu/dioxidine hybrid nanocomposites: cryochemical synthesis and antibacterial activity

Hybrid nanocomposites consisting of an antibacterial drug, dioxidine, and copper nanoparticles are obtained by cryochemical synthesis. It is shown by UV spectroscopy, X-ray diffraction, PAM, and low temperature argon adsorption that the obtained hybrid systems represent dioxidine particles with a size of 100 to 400 nm, including copper particles with the size of 50 to 150 nm. The resulting composites possessed higher antibacterial activity against E. coli 52 than the initial dioxidine and copper nanoparticles.     

A spectroscopic study of mercury vapor adsorption on gold nanoparticle films

We have modified the surfaces of glass and Si(100) with 3-aminopropyltrimethoxy silane, a fourth generation amine-terminated poly(amidoamine) dendrimer, and poly(diallydimethyl ammonium chloride) to facilitate adsorption onto colloidal gold particles (average diameter 3, 5, 12, and 22 nm). UV-vis absorption spectroscopy and atomic force microscopy monitored the adsorption process, which is governed by particle diffusion to the surface. The differences in adsorption to the three adhesion layers as a function of pH are discussed. Mercury vapor was exposed to the gold particle films and quantified by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. The surface plasmon oscillation of 5-, 12-, and 22-nm particles blue-shifts after exposure to parts-per-million levels of mercury vapor in air. Particle films prepared from the 3-nm gold particles develop a broad peak centered near 530 nm after exposure to mercury vapor. The results demonstrate a novel "litmus" film for mercury vapor.     

Porous GaN as a template to produce surface-enhanced Raman scattering-active surfaces

Surface-enhanced Raman spectroscopy (SERS) substrates have been prepared by depositing Au or Ag on porous GaN (PGaN). The PGaN used as the template for the metal deposition in these studies was generated by a Pt-assisted electroless etching technique. PGaN was chosen as a potential SERS template due to its nanostructured surface and high surface area, two characteristics that are important for SERS substrates. Metal films were deposited either by solution-based electroless deposition or by thermal vacuum evaporation. SERS spectra were recorded at lambda = 752.5 nm for Au films and at lambda = 514.5 nm for Ag films deposited on PGaN. The SERS signal strength across the metal coated PGaN substrates was uniform and was not plagued by "hot" or "cold" spots on the surface, a common problem with other SERS surfaces. The Ag film deposited by electroless deposition had the highest overall SERS response, with an enhancement factor (EF) relative to normal Raman spectroscopy of 10(8). A portion of the increase in EF relative to typical SERS-active substrates can be assigned to the large surface area characteristic of the PGaN-Ag structures, but some of the enhancement is intrinsic and is likely related to the specific morphology of the metal-nanopore composite structure.     

Alumina-based nanoparticles obtained by anodic dissolution of Al in electrolytes with alcohol solvents

In the present work, alumina-based nanoparticles were produced by an electrochemical method. Alcohols (methanol, ethanol, and propanol) containing 5 % of water and LiCl were applied as electrolytes. Sizes of the micelles in the obtained solution ranged from 200 nm to over 1 μm depending on the used alcohol. Measurements performed by ultraviolet and visible light (UV-VIS) spectroscopy indicated a presence of aluminum oxides and hydroxides in the solution. Studies using transmission electron microscopy (TEM) revealed that the obtained nanoparticles are in a form of flakes and membranes and their size is ~200 nm for methanol and ~50 nm for propanol. The composition of the product was characterized by the Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD). It consists of amorphous Al oxides and hydroxides as well as poorly crystallized aluminates and metallic Al.     

Facile fabrication of aggregation-induced emission based red fluorescent organic nanoparticles for cell imaging

A cyano-substituted diarylethlene derivative aggregation-induced emission （ALE） dye with two amino end-groups and 4,4＇-（hexafluoroisopropylidene）diphthalic anhydride were facilely incorporated into red fluorescent organic nanoparticles （FONs） via room temperature anhydride ring-opening polymerization under an air atmosphere. These obtained RO-HFDA FONs were characterized by a series of techniques including gel permeation chromatography, Fourier transform infrared spectroscopy, size distribution and zeta potential measurements, UV-Vis absorption spectrum, fluorescent spectroscopy and transmission electron microscopy. Biocompatibility evaluation and cell uptake behavior of RO-HFDA FONs were further investigated to explore their potential biomedical application. We demonstrated that such FONs showed high water dispersibility, stable uniform spherical morphology （150-200 nm）, broad excitation band （350-605 nm）, intense red fluorescence （627 nm） and excellent biocompatibility, making them promising for cell imaging applications.     

Characterization of iron promoter in tungstated zirconia catalysts by Mössbauer spectroscopy at very low temperatures

A tungstated zirconia (WZ) catalyst with iron promoter used for the conversion of n-pentane into isopentane has been characterized by M?ssbauer spectroscopy. The M?ssbauer spectra have been recorded in zero magnetic field in the temperature range 0.05-295 K and with a magnetic field up to 7 T between 4.2 and 50 K. Both the recording of M?ssbauer spectra with an applied magnetic field and at extremely low temperature allowed for the demonstration that iron is present in the catalysts as (i) hematite (alpha-Fe2O3) particles a few 10 nm in size, (ii) very small oligomeric Fe(III) species, probably in solid solution in zirconia, and (iii) Fe(III) oxide clusters showing magnetic ordering, probably embedded in the first surface layer and thus forming "rafts". These latter clusters form two ensembles with quite different sizes: one with diameters of about 3 nm, the other with diameters larger than 30 nm. These results are in agreement with those recently obtained by X-ray absorption spectroscopy and electron paramagnetic resonance.     

Glass transition of polymers confined to nanoporous glasses

The glassy dynamics of poly(propylene glycol) (PPG) and poly(methyl phenyl siloxane) (PMPS) confined to nanoporous glasses (pore sizes 2.5–20 nm) investigated by dielectric spectroscopy, temperature modulated DSC and neutron scattering is compared. For both systems the relaxation rates estimated from dielectric spectroscopy and temperature modulated DSC agree quantitatively indicating that both experiments sense the glass transition.For PPG the glassy dynamics in nanopores is determined by a counterbalance of an adsorption and a confinement effect where the temperature dependence of the relaxation times obeys the Vogel/Fulcher/Tammann (VFT-) equation. The former effect results from an interaction of the confined macromolecules with the internal surfaces which in general slows down the molecular dynamics. A confinement effect leads to an acceleration of the segmental dynamics compared to the bulk state and points to an inherent length scale on which the glassy dynamics takes place. The step of the specific heat capacity c_p at the glass transition vanishes at a finite length scale of 1.8 nm. This result supports further the conception that a characteristic length scale is relevant for glassy dynamics.For PMPS down to a pore size of 7.5 nm the temperature dependence of the relaxation times follows the VFT-dependence and a confinement effect is observed like for PPG. At a pore size of 5 nm this changes to an Arrhenius-like behavior with a low activation energy. At the same pore size c_p vanishes for PMPS. This points to a dramatic change in the character of molecular motions responsible for glassy dynamics and supports further the relevance of a characteristic length scale on which it takes place.Quasielastic neutron scattering experiments on PMPS reveal that the microscopic dynamics characterized by the mean square displacement depends on confinement above the glass transition. The diffusive character of the relevant molecular motions seems to disappear at a length scale of about 1.6 nm.     

Application of vibronic spectroscopy to conformational analysis. Investigations of molecules of carbonyl compounds

Application of vibronic spectroscopy to the conformational analysis of molecules in the ground and excited electronic states is reviewed. The basic concepts of the method as well as its methodological and technical aspects are discussed. The abilities of vibronic spectroscopy are exemplified by the results obtained for molecules of carbonyl compounds.The review is based on a report at the Vibrational Spectroscopy Conference dedicated to the 80th birthday of B. I. Stepanov (Minsk, Belarus', October 3–5, 1993).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 783–791, May, 1994.This work was performed with the partial financial support of the Russian.Universities State Program.     

Effect of molecule-substrate interaction on thin-film structures and molecular orientation of pentacene on silver and gold

Evaporated pentacene thin films with thicknesses from several nm to 150 nm on gold and silver substrates have been studied by ultraviolet photoelectron spectroscopy (UPS), near-edge X-ray absorption fine structure (NEXAFS), scanning tunneling microscopy (STM), and atomic force microscopy (AFM). It was found that pentacene thin-film structures, particularly their molecular orientations, are strongly influenced by the metal substrates. UPS measurements revealed a distinct change in the valence band structures of pentacene on Au compared to those on Ag, which is attributed to the different packing between adjacent molecules. Using NEXAFS, we observed 74+/-5 degrees and 46+/-5 degrees molecular tilt angles on Ag and Au, respectively, for all measured thicknesses. We propose that pentacene molecules stand up on the surface and form the "thin-film phase" structure on Ag. On Au, pentacene films grow in domains with molecules either lying flat or standing up on the substrate. Such a mixture of two crystalline phases leads to an average tilt angle of 46 degrees for the whole film and the change in valence band structures. STM and distance-voltage (z-V) spectroscopy studies confirm the existence of two crystalline phases on Au with different conducting properties. z-V spectra on the low conducting phase clearly indicate its nature as "thin-film phase".     

FEMTOSECOND STUDIES OF PRIMARY PHOTOPROCESSES IN OCTOPUS RHODOPSIN

Abstract— Femtosecond spectroscopy of octopus rhodopsin in H₂O and D₂O was performed over a very wide spectral region of 400–1000 nm. Transient gain and absorption from the excited state were observed for the first time around 650 and 700 nm, respectively, just after 300 fs pulse excitation. Bathorhodopsin was formed within 400 fs from the excited state; therefore, the cis-trans isomerization completes within 400 fs. The first intermediate "primerhodopsin" found in our previous paper is most likely "quasi-thermal" bathorhodopsin, in which the local thermalization of the chromophore is achieved. Then cooling down of the chromophore to the surrounding protein temperature takes place with 20 ± 10 ps along with blue-shifting of a spectrum of 10 ± 5 nm. In addition to these observations, a prominent gain in the region of > 850 nm was observed and decayed with 2–3 ps in H₂O. A similar time constant was estimated for a partial decay of an induced absorption around 600 nm. This process may be related with two forms of bathorhodopsin reported previously. In this scheme, two forms of bathorhodopsin are formed with time constants of about 400 fs and 2 ps. In the sample in D₂O, time constant of 3–4 ps was obtained for the slower process.     

Oxygen reactivity of the biferrous site in the de novo designed four helix bundle peptide DFsc: nature of the "intermediate" and reaction mechanism

The DFsc and DFscE11D de novo designed protein scaffolds support biomimetic diiron cofactor sites that react with dioxygen forming a 520 nm "intermediate" species with an apparent pseudo-first-order formation rate constant of 2.2 and 4.8 s-1, respectively. Resonance Raman spectroscopy shows that this absorption feature is due to a phenolate-to-ferric charge transfer transition arising from a single tyrosine residue coordinating terminally to one of the ferric ions in the site. Phenol coordination could provide a proton to promote rapid loss of a putative peroxo species.     

Distribution and thickness of the surface contaminations on STM tungsten tips,studied by AES/SEM and ARXPS

The combination of Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and angle resolved X-ray photoelectron spectroscopy (ARXPS) has been applied to the analysis of the distribution of elements at the surface region of electrochemically etched tungsten tips and the determination of the thickness of a layer with oxygen and carbon contamination. Auger line profiling revealed a homogeneous distribution of oxygen and significant enrichment of carbon on the W tip between 0 and 1.5 m from the top. The thickness of the contamination layer on various W materials, electrochemically etched, was found to be 1.35±0.15 nm as measured using ARXPS, and was estimated to be about 1–3 nm as measured by AES.