Local electronic structure of the peptide bond probed by resonant inelastic soft X-ray scattering.

The local valence orbital structure of solid glycine, diglycine, and triglycine is studied using soft X-ray emission spectroscopy (XES), resonant inelastic soft X-ray scattering (RIXS) maps, and spectra calculations based on density-functional theory. Using a building block approach, the contributions of the different functional groups of the peptides are separated. Cuts through the RIXS maps furthermore allow monitoring selective excitations of the amino and peptide functional units, leading to a modification of the currently established assignment of spectral contributions. The results thus paint a new-and-improved picture of the peptide bond, enhance the understanding of larger molecules with peptide bonds, and simplify the investigation of such molecules in aqueous environment.

Site-specific electronic structure of imidazole and imidazolium in aqueous solutions.

The occupied and unoccupied electronic structure of imidazole (C3N2H4) and imidazolium (C3N2H5+) in aqueous solutions is studied by X-ray emission spectroscopy (XES) and resonant inelastic soft X-ray scattering (RIXS). Both systems show distinct RIXS fingerprints with strong resonant effects. A comparison with calculated X-ray emission spectra of isolated imidazole and imidazolium suggests only a small influence of hydrogen bonding in the aqueous solution on the electronic structure of imidazole and imidazolium, and allows the attribution of specific spectral features to the non-equivalent nitrogen and carbon atoms in the molecules. In the case of nitrogen, this can also be achieved by site-selective resonant excitation. Furthermore, we find spectator shifts and symmetry selectivity in the RIXS spectra, as well as indications for rapid proton dynamics on the femtosecond timescale of the RIXS process, and derive the HOMO-LUMO gaps for the two molecules in aqueous solution.

Isotope Effects in the Resonant Inelastic Soft X-ray Scattering Maps of Gas-Phase Methanol.

The electronic structure of gas-phase methanol molecules (H3COH, H3COD, and D3COD) at atmospheric pressure was investigated using resonant inelastic soft X-ray scattering (RIXS) at the O K and C K edges. We observe strong changes of the relative emission intensities of all valence orbitals as a function of excitation energy, which can be related to the symmetries of the involved orbitals causing an angularly anisotropic RIXS intensity. Furthermore, all observed emission lines are subject to strong spectator shifts of up to -0.9 eV at the O K edge and up to -0.3 eV at the C K edge. At the lowest O K resonance, we find clear evidence for dissociation of the methanol molecule on the time scale of the RIXS process, which is illustrated by comparing X-ray emission spectra of regular and deuterated methanol.

Probing hydrogen bonding orbitals: resonant inelastic soft X-ray scattering of aqueous NH3.

To probe the influence of hydrogen bonding on the electronic structure of ammonia, gas phase and aqueous NH3 have been investigated using soft X-ray absorption (XAS), resonant inelastic soft X-ray scattering (RIXS), and electronic structure calculations including dynamical effects. Strong spectral differences in the XAS scans as well as in the RIXS spectra between gas phase and aqueous NH3 are attributed to orbital mixing with the water orbitals, dipole-dipole interactions, differences in vibronic coupling, and nuclear dynamics on the time-scale of the RIXS process. All of these effects are consequences of hydrogen bonding and the impact of the associated orbitals, demonstrating the power of XAS and RIXS as unique tools to study hydrogen bonding in liquids.

Non-equivalent carbon atoms in the resonant inelastic soft X-ray scattering map of cysteine.

Resonant inelastic soft x-ray scattering (RIXS) was used to study the electronic structure of solid cysteine films. A RIXS map approach, i.e., plotting the x-ray emission intensity as a function of excitation and emission energy, allows us to separate the contributions of the three chemically non-equivalent carbon atoms in cysteine. In particular, we can identify orbitals localized near the photoexcited atoms, as well as orbitals that are delocalized over the entire molecule.

Electron-hole correlation effects in core-level spectroscopy probed by the resonant inelastic soft x-ray scattering map of C60.

We have employed a unique spectroscopic approach, a resonant inelastic soft x-ray scattering (RIXS) map, to identify and separate electron-hole correlation effects in core-level spectroscopy. With this approach, we are able to derive a comprehensive picture of the electronic structure, separating ground state properties (such as the HOMO-LUMO separation) from excited state properties (such as the C 1s core-exciton binding energy of C(60)). In particular, our approach allows us to determine the difference between core- and valence exciton binding energies in C(60) [0.5 (±0.2) eV]. Furthermore, the RIXS map gives detailed insight into the symmetries of the intermediate and final states of the RIXS process.

Efficient passivation of n-type and p-type silicon surface defects by hydrogen sulfide gas reaction.

An efficient surface defect passivation is observed by reacting clean Si in a dilute hydrogen sulfide-argon gas mixture (<5% H2S in Ar) for both n-type and p-type Si wafers with planar and textured surfaces. Surface recombination velocities of 1.5 and 8 cm s-1are achieved on n-type and p-type Si wafers, respectively, at an optimum reaction temperature of 550 °C that are comparable to the best surface passivation quality used in high efficiency Si solar cells. Surface chemical analysis using x-ray photoelectron spectroscopy shows that sulfur is primarily bonded in a sulfide environment, and synchrotron-based soft x-ray emission spectroscopy of the adsorbed sulfur atoms suggests the formation of S-Si bonds. The sulfur surface passivation layer is unstable in air, attributed to surface oxide formation and a simultaneous decrease of sulfide bonds. However, the passivation can be stabilized by a low-temperature (300 °C) deposited amorphous silicon nitride (a-Si:NX:H) capping layer.

X-ray Emission Spectroscopy of Proteinogenic Amino Acids at All Relevant Absorption Edges.

Nonresonant N K, O K, C K, and S L2,3 X-ray emission spectra of the 20 most common proteinogenic amino acids in their solid zwitterionic form are reported. They represent a comprehensive database that can serve as a reliable basis for the X-ray absorption spectroscopy (XES) studies of peptides and proteins. At the most important N and O K edges, clear similarities and differences between the spectra of certain amino acids are observed and associated with the specific chemical structure of these molecules and their functional groups. Analysis of these spectra allows the generation of spectral fingerprints of the protonated amino group, the deprotonated carboxylic group, and, using a building block approach, the specific nitrogen- and oxygen-containing functional groups in the side chains of the amino acids. Some of these fingerprints are compared to the spectra of reference compounds with the respective functional groups; they exhibit reasonable similarity, underlining the validity of the spectral fingerprint approach. The C K and S L2,3 XES spectra are found to be specific for each amino acid, in accordance with the different local environments of the involved C and S atoms, respectively.

Investigation of the Ionic Hydration in Aqueous Salt Solutions by Soft X-ray Emission Spectroscopy.

Understanding the molecular structure of the hydration shells and their impact on the hydrogen bond (HB) network of water in aqueous salt solutions is a fundamentally important and technically relevant question. In the present work, such hydration effects were studied for a series of representative salt solutions (NaCl, KCl, CaCl2, MgCl2, and KBr) by soft X-ray emission spectroscopy (XES) and resonant inelastic soft X-ray scattering (RIXS). The oxygen K-edge XES spectra could be described with three components, attributed to initial state HB configurations in pure water, water molecules that have undergone an ultrafast dissociation initiated by the X-ray excitation, and water molecules in contact with salt ions. The behavior of the individual components, as well as the spectral shape of the latter component, has been analyzed in detail. In view of the role of ions in such effects as protein denaturation (i.e., the Hofmeister series), we discuss the ion-specific nature of the hydration shells and find that the results point to a predominant role of anions as compared to cations. Furthermore, we observe a concentration-dependent suppression of ultrafast dissociation in all salt solutions, associated with a significant distortion of intact HB configurations of water molecules facilitating such a dissociation.

Generalization of training effects in schizophrenia.

The primary goal of this study was to investigate transfer of training (generalization) in patients with schizophrenia. We randomly assigned 33 schizophrenia subjects to one of three conditions: training on the Wisconsin Card Sort Test (WCST-T), training on the Halstead Category Test (CAT-T), or no training (No-T). The WCST and CAT were administered to all subjects at baseline. Subjects in the WCST-T and CAT-T groups then received training on the respective test, while the No-T group received additional untrained trials. All participants were subsequently retested on the WCST and CAT, and completed a brief neuropsychological battery. As hypothesized, the WCST-T and CAT-T groups exhibited large improvements on the trained test and moderate improvement on the untrained test, while the No-T group failed to show improvement on either test. These results suggest that the training paradigm did produce generalization, and that the changes were not due to practice effects. The extent of generalization across both training groups was strongly associated with neuropsychological test performance (Spearman's rho=0.56, P<0.05). The implications of these findings for rehabilitation programs were discussed, and recommendations were made for future research.

Negative affect and sexual risk behavior: comment on Crepaz and Marks (2001).

In this commentary, the authors highlight the findings of the meta-analysis by N. Crepaz and G. Marks (2001). The role of affect in sexual risk behavior, although intuitively obvious, is not well understood and has been largely ignored by HIV prevention researchers in favor of social-cognitive models of behavior. Crepaz and Marks synthesized the results from studies that have examined the relation of negative affect (e.g., depression, anxiety, anger) to sexual risk behavior and concluded that in the literature to date, these variables appear unrelated. The authors suggest that the Crepaz and Marks findings are not surprising given the methods used in the reviewed studies and suggest methodological approaches that will allow more sensitive analyses of the association between affect and sexual risk behavior.

The relation of alcohol use to HIV-risk sexual behavior among adults with a severe and persistent mental illness.

The authors examined the relationship between alcohol use and HIV-risk sexual behavior and tested whether alcohol use immediately prior to sex is related to decreased condom use. The participants were 159 adults living with a severe and persistent mental illness. Each participated in a structured interview to assess all sexual and drug-use behavior over a 3-month period. Analysis of 3,026 sexual behaviors reported by 123 sexually active participants indicated that at the global level, participants who drank more heavily were more likely to have engaged in sexual risk behavior. At the event level, however, alcohol use was not related to condom use during vaginal or anal intercourse; that is, participants who used condoms when sober tended to use them to the same extent when drinking.

Increasing assertiveness skills to reduce HIV risk among women living with a severe and persistent mental illness.

This study examined whether training women living with a severe mental illness to be assertive in sexual situations would decrease their risk for HIV infection. Twenty female outpatients were randomly assigned to either a 10-session assertiveness training intervention or a waiting-list control condition. All participants completed measures of HIV-related information, motivation, skills, and sexual risk behavior pre- and postintervention and at 2- and 4-month follow-ups. Compared with controls, women in the intervention group increased their assertiveness skill, HIV knowledge, and frequency of condom-protected intercourse. It is concluded that assertiveness training for women living with a severe mental illness can serve as 1 part of a comprehensive HIV-risk-reduction program for this vulnerable population.

Assessing sexual risk behaviour with the Timeline Followback (TLFB) approach: continued development and psychometric evaluation with psychiatric outpatients.

This paper describes a series of 4 studies, designed to provide evidence of the feasibility, reliability, and validity of the Timeline Followback (TLFB) method when used to assess sexual risk behaviour with psychiatric outpatients. This population was selected because patients often have difficulty completing assessments of sexual risk behaviours due to deficits in attention, memory, and communication skills. All 4 studies demonstrated the feasibility of the HIV-risk TLFB. Study 1 also demonstrated that it can be completed in 20 min, and scored in less than 10 min. Qualitative data revealed that both patients and assessors found the features of the TLFB helpful. Study 2 provided evidence that the HIV-risk TLFB can be reliably scored by interviewers whereas Study 3 demonstrated that this measure can be completed reliably by patients and that TLFB of sexual behaviour were consistent over time. Study 4 provided initial evidence for the validity of the HIV-risk TLFB but also suggested that the TLFB may yield frequency estimates that are slightly less than those obtained with single-item measures. We conclude that the TLFB is feasible, reliable, and valid, even in a population known to have difficulty with self-report measures.

HIV risk reduction for the seriously mentally ill: pilot investigation and call for research.

Research indicates that people with serious mental illnesses (SMI; e.g., schizophrenia, schizoaffective disorder, bipolar disorder) are at enhanced risk for infection with the human immunodeficiency virus (HIV). To decrease this risk, we piloted a six-session HIV-risk reduction intervention for two single-gender groups (nine women, eight men; M age = 39.8 years) of SMI outpatients. The intervention and assessment were based on the Information-Motivation-Behavioral Skills model of HIV-preventive behavior (Fisher & Fisher, 1992, Psychological Bulletin, 111, 455-474) and employed activities designed specifically for people with a SMI. Data were collected at pre- and post-interventions and at a one-month follow-up. Results indicated that this brief intervention resulted in enhanced HIV-related knowledge, and trends toward enhanced skill at condom use negotiation and condom use self-efficacy. Overall, a modest decrease in risk behavior among participants was observed. Thus, this pilot investigation revealed that HIV-related risk of the SMI can be reduced through traditional behavioral skills and education methods. Future research employing control groups, more intensive interventions, and baseline screening for high risk is encouraged.

Does alcohol lead to sexual risk behavior? Findings from event-level research.

The belief that alcohol use leads to sexual risk behavior is nearly ubiquitous. To determine if this belief is warranted, we identify theory and research regarding the alcohol, risky-sex link. We focus our review on studies that use the event-level methodology because this approach provides a particularly sensitive but stringent test of the situational alcohol, risky-sex connection. Overall, the data from available event-level studies indicate that people who use condoms when they are sober also tend to use them when drinking; people who fail to use condoms when drinking probably also fail to use them when sober. We recognize several empirical exceptions to this rule and provide suggestions for future research.

Setup for in situ investigation of gases and gas/solid interfaces by soft x-ray emission and absorption spectroscopy.

We present a novel gas cell designed to study the electronic structure of gases and gas/solid interfaces using soft x-ray emission and absorption spectroscopies. In this cell, the sample gas is separated from the vacuum of the analysis chamber by a thin window membrane, allowing in situ measurements under atmospheric pressure. The temperature of the gas can be regulated from room temperature up to approximately 600 °C. To avoid beam damage, a constant mass flow can be maintained to continuously refresh the gaseous sample. Furthermore, the gas cell provides space for solid-state samples, allowing to study the gas/solid interface for surface catalytic reactions at elevated temperatures. To demonstrate the capabilities of the cell, we have investigated a TiO2 sample behind a mixture of N2 and He gas at atmospheric pressure.

"Building block picture" of the electronic structure of aqueous cysteine derived from resonant inelastic soft X-ray scattering.

The electronic structure of the amino acid L-cysteine in an aqueous environment was studied using resonant inelastic soft X-ray scattering (RIXS) in a 2D map representation and analyzed in the framework of a "building block" approach. The element selectivity of RIXS allows a local investigation of the electronic structure of the three functional groups of cysteine, namely, the carboxyl, amino, and thiol groups, by measuring at the O K, N K, and S L2,3 edges, respectively. Variation of the pH value allows an investigation of molecules with protonated and deprotonated functional groups, which can then be compared with simple reference molecules that represent the isolated functional groups. We find that such building blocks can provide an excellent description of X-ray emission spectroscopy (XES) and RIXS spectra, but only if all nearest-neighbor atoms are included. This finding is analogous to the building block principle commonly used in X-ray absorption spectroscopy. The building blocks show a distinct spectral character (fingerprint) and allow a comprehensive interpretation of the cysteine spectra. This simple approach opens the path to investigate the electronic structure of more complex biological molecules in aqueous solutions using XES and RIXS.

The Be K-edge in beryllium oxide and chalcogenides: soft x-ray absorption spectra from first-principles theory and experiment.

We have carried out a theoretical and experimental investigation of the beryllium K-edge soft x-ray absorption fine structure of beryllium compounds in the oxygen group, considering BeO, BeS, BeSe, and BeTe. Theoretical spectra are obtained ab initio, through many-body perturbation theory, by solving the Bethe-Salpeter equation (BSE), and by supercell calculations using the core-hole approximation. All calculations are performed with the full-potential linearized augmented plane-wave method. It is found that the two different theoretical approaches produce a similar fine structure, in good agreement with the experimental data. Using the BSE results, we interpret the spectra, distinguishing between bound core-excitons and higher energy excitations.

Ultrafast proton dynamics in aqueous amino acid solutions studied by resonant inelastic soft X-ray scattering.

Resonant inelastic soft X-ray scattering (RIXS) has been used to study the electronic structure of glycine and lysine in aqueous solution. Upon variation of the pH value of the solution from acidic to basic, major changes of the nitrogen K edge RIXS data are observed for both amino acids, which are associated with the protonation and deprotonation of the amino groups. The experimental results are compared with simulations based on density functional theory, yielding a detailed understanding of the spectral changes, as well as insights into the ultrafast proton dynamics in the intermediate core-excited/ionized state of the RIXS process.