Spectroscopic View Research Articles

Conformational States of ADP Ribosylation Factor 1 Complexed with Different Guanosine Triphosphates As Studied by 31P NMR Spectroscopy

Guanine nucleotide binding proteins (GNB-proteins) play an essential role in cellular signaling, acting as molecular switches, cycling between the inactive, GDP-bound form and the active, GTP-bound form. It has been shown that conformational equilibria also exist within the active form of GNB-proteins between conformational states with different functional properties. Here we present (31)P NMR data on ADP ribosylation factor 1 (Arf1), a GNB-protein involved in Golgi traffic, promoting the coating of secretory vesicles. To investigate conformational equilibria in active Arf1, the wild type and switch I mutants complexed with GTP and a variety of commonly used GTP analogues, namely, GppCH(2)p, GppNHp, and GTPγS, were analyzed. To gain deeper insight into the conformational state of active Arf1, we titrated with Cu(2+)-cyclen and GdmCl and formed the complex with the Sec7 domain of nucleotide exchange factor ARNO and an effector GAT domain. In contrast to the related proteins Ras, Ral, Cdc42, and Ran, from (31)P NMR spectroscopic view, Arf1 exists predominantly in a single conformation independent of the GTP analogue used. This state seems to correspond to the so-called state 2(T) conformation, according to Ras nomenclature, which is interacting with the effector domain. The exchange of the highly conserved threonine in position 48 with alanine led to a shift of the equilibrium toward a conformational state with typical properties obtained for state 1(T) in Ras, such as interaction with guanine nucleotide exchange factors, a lower affinity for nucleoside triphosphates, and greater sensitivity to chaotropic agents. In active Arf1(wt), the effector interacting conformation is strongly favored. These intrinsic conformational equilibria of active GNB-proteins could be a fine-tuning mechanism of regulation and thereby an interesting target for the modulation of protein activity.

Light-Echo Spectrum Reveals the Type of Tycho Brahe's 1572 Supernova

AbstractWe successfully obtained the first optical spectra of the faint light echoes around Cassiopeia A and Tycho Brahe's supernova remnants (SNRs) with FOCAS and the Subaru Telescope. We conclude that Cas A and Tycho's SN 1572 belong to the Type IIb and normal Type Ia supernovae, respectively. Light echo spectra are important in order to obtain further insight into the supernova explosion mechanism of Tycho's SN 1572: how the Type Ia explosion actually proceeds, and whether accretion occurs from a companion or by the merging of two white dwarfs. The proximity of the SN 1572 remnant has allowed detailed studies, such as the possible identification of the binary companion, and provides a unique opportunity to test theories of the explosion mechanism and the nature of the progenitor. Future light-echo spectra, obtained in different spatial directions of SN 1572, will enable to construct a three-dimensional spectroscopic view of the explosion.

High-resolution spectroscopic view of planet formation sites

AbstractTheories of planet formation predict the birth of giant planets in the inner, dense, and gas-rich regions of the circumstellar disks around young stars. These are the regions from which strong CO emission is expected. Observations have so far been unable to confirm the presence of planets caught in formation. We have developed a novel method to detect a giant planet still embedded in a circumstellar disk by the distortions of the CO molecular line profiles emerging from the protoplanetary disk's surface. The method is based on the fact that a giant planet significantly perturbs the gas velocity flow in addition to distorting the disk surface density. We have calculated the emerging molecular line profiles by combining hydrodynamical models with semianalytic radiative transfer calculations. Our results have shown that a giant Jupiter-like planet can be detected using contemporary or future high-resolution near-IR spectrographs such as VLT/CRIRES or ELT/METIS. We have also studied the effects of binarity on disk perturbations. The most interesting results have been found for eccentric circumprimary disks in mid-separation binaries, for which the disk eccentricity - detectable from the asymmetric line profiles - arises from the gravitational effects of the companion star. Our detailed simulations shed new light on how to constrain the disk kinematical state as well as its eccentricity profile. Recent findings by independent groups have shown that core-accretion is severely affected by disk eccentricity, hence detection of an eccentric protoplanetary disk in a young binary system would further constrain planet formation theories.

Mn(II) complexes of some acylhydrazones with NNO donor sites: Syntheses, a spectroscopic view on their coordination possibilities and crystal structures

Mn(II) complexes derived from a set of acylhydrazones were synthesised and characterized by elemental analyzes, IR, UV–vis and X-band EPR spectral studies as well as conductivity and magnetic susceptibility measurements. In the reported complexes, the hydrazones exist either in the keto or enolate form, as evidenced by IR spectral data. Crystal structures of two complexes are well established using single crystal X-ray diffraction studies. In both of these complexes two equivalent monoanionic ligands are coordinated in a meridional fashion using cis pyridyl, trans azomethine nitrogen and cis enolate oxygen atoms positioned very nearly perpendicular to each other. EPR spectra in DMF solutions at 77 K show hyperfine sextets and in some of the complexes the low intensity forbidden lines lying between each of the two hyperfine lines are also observed.

Eyes to the Needle

Eyes to the Needle

Relationship between oxygen defects and the photoluminescence property of ZnO nanoparticles: A spectroscopic view

The present paper deals with the synthesis and characterization of ZnO nanoparticles obtained by coprecipitation method at three different pH conditions. Samples characterizations aimed at understanding their spectroscopic properties are carried out using a variety of experimental techniques. X-ray diffraction and transmission electron microscopic studies show significant increase in the particle size of the synthesized ZnO nanoparticles ranging from 3–40 nm with increasing pH values. Absorption spectra show particle size dependent blueshift in the energy band, which may be ascribed to quantum confinement effect. Fourier transform infrared (FTIR) spectroscopy reveals enhancement in the surface defects of the synthesized ZnO nanoparticles with increasing pH values. Electron paramagnetic resonance studies at room temperature (300 K) and several liquid helium temperatures (including the lowest temperature 13 K for all samples) indicate the presence of singly ionized oxygen vacancy defects (VO+) and O2− superoxide ions in the ZnO nanoparticles. These results are well supported by FTIR and photoluminescence spectroscopy. The emissions from these nanoparticles are also found to be size dependent, whereas the ratio of UV emission to oxygen vacancy related green emission is found to increase with increasing pH values. Furthermore, a plausible mechanism of the observed defect mediated green emission is proposed.

A molecular spectroscopic view of surface plasmon enhanced resonance Raman scattering

The enhancement of resonance Raman scattering by coupling to the plasmon resonance of a metal nanoparticle is developed by treating the molecule-metal interaction as transition dipole coupling between the molecular electronic transition and the much stronger optical transition of the nanoparticle. A density matrix treatment accounts for coupling of both transitions to the electromagnetic field, near-resonant energy transfer between the molecule-excited and nanoparticle-excited states, and dephasing processes. This fully quantum mechanical approach reproduces the interference effects observed in extinction spectra of J-aggregated dyes adsorbed to metal nanoparticles and makes testable predictions for surface-enhanced resonance Raman excitation profiles.

Spectroscopic View of Life and Work of the Nobel Laureate Sir C.V. Raman

Raman spectroscopic and microscopic techniques have been used for nondestructive characterization of tissues and to differentiate benign and malignant tissues. The discovery of the principles of spectroscopy is credited to Sir C.V. Raman of India, who in 1930 brought the Nobel Prize in Physics to the East side of Suez. We present the life and work of Sir C.V. Raman with brief review of the uses of Raman spectroscopy in urology.

Solution combustion derived nanocrystalline Zn2SiO4:Mn phosphors: A spectroscopic view

Manganese doped nanocrystalline willemite powder phosphors Zn(2-x)Mn(x)SiO(4) (0.1<or=x<or=0.5) have been synthesized by a low-temperature initiated, self-propagating, gas producing solution combustion process. The phosphors have been characterized by using x-ray diffraction (XRD), energy dispersive spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR), and photo luminescence (PL) spectroscopic techniques. The lattice parameters calculated from XRD confirm that Zn(2-x)Mn(x)SiO(4) has a rhombohedral space group R3H. The XRD patterns confirm that Zn(2-x)Mn(x)SiO(4) phosphor samples undergo a phase transformation from beta-willemite to alpha-willemite phase at 950 degrees C. The EPR spectra of Mn(2+) ions exhibit resonance signals at g approximately = 3.24 and g approximately = 2.02, with a sextet hyperfine structure centered around g approximately = 2.02. The EPR signals of Mn(2+) give a clear indication of the presence of two different Mn(2+) sites. The magnitude of the hyperfine splitting (A) indicates that the Mn(2+) is in an ionic environment. The number of spins participating in resonance (N), the paramagnetic susceptibility (chi), and the zero-field splitting parameter (D) have been evaluated as function of x. It is interesting to observe that the variation of N with temperature obeys Boltzmann. The paramagnetic susceptibility is calculated from the EPR data at various temperatures and the Curie constant and Curie paramagnetic temperature was evaluated from the 1/chi versus T graph. The luminescence of Mn(2+) ion in Zn(2)SiO(4) shows a strong green emission peak around 520 nm from the synthesized phosphor particles under UV excitation (251 nm). The luminescence is assigned to a transition from the upper (4)T(1)-->(6)A(1) ground state. The mechanism involved in the generation of a green emission has been explained in detail. The effect of Mn content on luminescence has also been studied.

A spectroscopic view of electron–phonon coupling at metal surfaces

AbstractIt is now possible to extract from high‐resolution angle‐resolved photoemission data the Eliashberg function α2F(ω) for electron‐phonon coupling (EPC). At the same time, first‐principles calculations of the EPC for surface states are appearing in the literature presenting an exquisite picture of the origin of the Eliashberg function. The advances in this field will be illustrated with new data from surface states on two faces of berylium and a direct comparisin to theory for Be(0001). (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A Spectroscopic View of Some Recent Advances in the Study of Blue Light Photoreception*

Abstract:The blue to UV‐A region of the spectrum, spanning the region of about 320–520 nm, strongly influences the growth and development of plants and fungi. Photomorphogenesis in plants is, to a great extent, controlled by phytochrome, but there are unique contributions of the blue region, which cannot be duplicated by any amount of red light. Phototropism is, with few exceptions, a purely blue light response. In fungi, the blue region dominates the photocontrol of growth and development, though some red light effects have been reported. Many blue light action spectra fit the definition of cryptochrome, a pigment class defined by its UV‐A and blue peaks. The action spectrum, if measured to sufficient resolution, displays several minor maxima or shoulders in the blue region which call to mind the vibrational levels of carotenoids and flavins. Recent molecular genetic studies, as well as photobiological work, have shown that some cryptochromes are related to the DNA repair enzyme photolyase, while others appear genetically and spectroscopically distinct. In this review, we have applied established criteria from photobiology, in particular, comparison of action spectra with absorption spectra, to these recent results. It is apparent that photolyase homologs such as CRY1 can explain the blue light portion of the action spectrum for hypocotyl elongation, assuming participation of the oxidized flavin. In fungi, the photoreceptor question remains open. Identification of the nph1 gene in Arabidopsis may soon lead to a photoreceptor for higher plant phototropism. Also, we present a possible solution to the most recent version of the long‐standing flavin‐carotenoid controversy, the zeaxanthin hypothesis for higher plant phototropism. In conclusion, there appear to be at least three classes of cryptochromes.

Infrared spectra of human central nervous system tissue: Diagnosis of alzheimer's disease by multivariate analyses

AbstractWe present an infrared (IR) spectroscopic view of the pathological features of Alzheimer's disease (AD), along with a means of classifying the spectroscopic data nonsubjectively using several multivariate methods. The results demonstrate that IR spectroscopy can potentially be used in the diagnosis of AD from autopsy tissue. Although several spectral features that appear to be related to the disease process can be detected by a visual inspection of the IR spectra of AD grey matter, the appearance of these features was inconsistent. A more successful (consistent) diagnosis is achieved using multivariate analysis of the spectroscopic data. It is shown that correct classification of white and grey matter from brains identified by standard pathological methods as heavily, moderately, and minimally involved can be achieved with success rates of greater than 90% using appropriate methods. Classification of tissue as either control or AD was achieved with a success rate of 100%. © 1995 John Wiley &amp; Sons, Inc.

Thermally desactivated resonant current in high peak to valley current ratio (69:1) GaAs/GaAlAs resonant tunneling structures: A spectroscopic view of the emitter density of state

We describe the realization of very high peak to valley current ratio double barrier resonant tunneling structures by molecular beam epitaxy. We find that the resonant current through the ground state resonance decreases as the temperature is raised. This unique behavior is explained within the Esaki-Tsu formalism and originates in the Fermi-Dirac statistics.

An FTIR spectroscopic view of the initiation of ethylene polymerization on Cr/SiO 2 catalyst

The onset of polymerization of ethylene on Cr/SiO 2 catalyst activated by high-temperature treatment was studied at room temperature using fast-scanning FTIR spectral measurements. Initial rapid adsorption of molecular ethylene on the pre-activated catalyst preceded the onset of polymerization. A time-delay between adsorption and polymerization was observed. The experimental evidence suggests that initiation of polymerization follows dissociation of ethylene, presumably on two Cr sites. Propagation and other mechanistic steps then follow as suggested earlier.

A spectroscopic view of internal conversion in a small polyatomic molecule: Sub-Doppler intracavity dye laser spectroscopy of thioformaldehyde

Intracavity dye laser spectroscopy has been used to obtain sub-Doppler spectra of selected rotational lines in the à 1A2–X̃ 1A1 410 band of thioformaldehyde with very high resolution and sensitivity. Many of the spectra show extra lines due to perturbations involving high vibrational levels of the ground state. Most of the perturbations observed for K′a = 0 and 4 are found to correlate well with previous observations of anomalously long single rotational level fluorescence lifetimes and reduced quantum yields [J. Dunlop and D. J. Clouthier, J. Chem. Phys. 93, 6371 (1990)]. S1–S0 interaction matrix elements of 0.001–0.006 cm−1 are found for levels involved in simple two level perturbations. The large number of small random perturbations by levels of the ground state is indicative of the first stages of the onset of quantum chaos in a small molecule. Some larger perturbations in the rotational structure are also observed; these are caused by additional local interactions with levels of the nearby triplet state.

Pervaporation of ethanol-water mixture by plasma films prepared from hexamethyldisiloxane

The plasma polymerization process was investigated to obtain plasma films like poly(dimethylsiloxane), and the formed films were applied as membranes for pervaporation of ethanol-water solution. A reaction chamber which had the triode electrode structure for initiation of a glow discharge was provided for preparation of films like poly(dimethylsiloxane) by plasma polymerization. Films plasma-polymerized from hexamethyldisiloxane (HMDSO) resembled poly(dimethylsiloxane) in spectroscopic view and were composed of dimethylsiloxane chains with branches of trimethylsilyl groups. The surface energy for the films was 19.6 mN/m. The films deposited from HMDSO on Nuclepore membrane showed good ethanol-selectivity in pervaporation of ethanol-water solution. The separation factor depended on the film thickness as well as the feed composition. The film-thickness effect was maximized at 34 nm thick, and the separation factor reached 4.5. A model for the separation process using our composite membrane was discussed.

Solute-solute interactions in liquid ammonia solutions: a vibrational spectroscopic view

Abstract