Similar appearance, different mechanisms: xerosis in HIV, atopic dermatitis and ageing.

Xerosis is one of the most common dermatologic disorders occurring in the elderly and in patients with atopic dermatitis (AD) and human immunodeficiency virus (HIV) infection. Xerosis has been linked to an impaired skin barrier function of the stratum corneum. Using Raman microspectroscopy, we concentrated on deeper skin layers, viable epidermis and dermis of 47 volunteers and associated molecular alterations to the evolution of xerosis and the skin barrier, for example, lipid, water and antioxidant content. A decrease in lipids within the viable epidermis is found for elderly and HIV-patients. Lipid and water values of AD patients and their healthy reference group are similar. Decreases in lipids and simultaneous increases in water are found in the dermis for HIV and AD patients in comparison to their healthy reference groups. Excessive levels of epidermal carotenoids, mainly lycopene, in HIV-patients were found potentially leading to adverse effects such as premature skin ageing.

Watching the low-frequency motions in aqueous salt solutions: the terahertz vibrational signatures of hydrated ions.

The details of ion hydration still raise fundamental questions relevant to a large variety of problems in chemistry and biology. The concept of water "structure breaking" and "structure making" by ions in aqueous solutions has been invoked to explain the Hofmeister series introduced over 100 years ago, which still provides the basis for the interpretation of experimental observations, in particular the stabilization/destabilization of biomolecules. Recent studies, using state-of-the-art experiments and molecular dynamics simulations, either challenge or support some key points of the structure maker/breaker concept, specifically regarding long-ranged ordering/disordering effects. Here, we report a systematic terahertz absorption spectroscopy and molecular dynamics simulation study of a series of aqueous solutions of divalent salts, which adds a new piece to the puzzle. The picture that emerges from the concentration dependence and assignment of the observed absorption features is one of a limited range of ion effects that is confined to the first solvation shell.

Exploring hydrophobicity by THz absorption spectroscopy of solvated amino acids.

Although hydrophobicity is a commonly used concept, its microscopic nature, particularly in the context of hydration, is not well understood. Here, we present a study of hydrophobic and hydrophilic solutes using terahertz (THz) spectroscopy and molecular dynamics (MD) simulations. We measured the concentration dependent THz absorption (2.1-2.7 THz) of several amino acids and peptides in aqueous solution. Experimentally, we find a correlation between the change in THz absorption of solvating water and specific properties of the solute such as polarity and hydrophobicity. In addition, we studied the effect of hydrophobic and hydrophilic model particles on water dynamics by MD simulations. We are able to link the vibrational density of states (VDOS) in hydration water around the model particles to the experimentally observed change in THz absorption of solvated amino acids. We find a stronger increase in THz absorption and in the oxygen VDOS of solvating water molecules for the hydrophilic versus hydrophobic solutes. The simulations provide us with a microscopic insight into the change of the hydration dynamics as induced by hydrophobic and hydrophilic solutes. For hydrophobic and hydrophilic model particles a retardation of dynamical processes on the picosecond timescale is found, which is more pronounced for hydrophilic compared to hydrophobic solutes.

Interfacial Cu/ZnO contact by selective photodeposition of copper onto the surface of small ZnO nanoparticles in non-aqueous colloidal solution.

Nanoscale copper was selectively photodeposited onto the surface of hexadecylamine (HDA) stabilized (monodispersed not agglomerated) ZnO nanoparticles (NPs) of a diameter of 2-5 nm, which leads to HDA-stabilized Cu/ZnO NPs of varied Cu loading. The particles are soluble in non-polar organic solvents. The line broadening and the red shift of the surface plasmon band of Cu/ZnO NPs relative to HDA-stabilized Cu NPs, the profound decrease of the Cu/ZnO NPs visible photoluminescence at 525 nm, the increase of the UV emission intensity at 365 nm and the enhancement of the Raman scattering (RS) intensity in comparison to the parent ZnO NPs confirmed the interfacial contact between the Cu and ZnO phase.

The formation of nitrogen-containing functional groups on carbon nanotube surfaces: a quantitative XPS and TPD study.

Nitrogen-containing functional groups were generated on the surface of partially oxidized multi-walled carbon nanotubes (CNTs) via post-treatment in ammonia. The treatment temperature was varied in order to tune the amount and type of nitrogen- and oxygen-containing functional groups, which were studied using high-resolution X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). The surface defects on CNTs due to the incorporation of nitrogen were investigated by Raman spectroscopy. Deconvoluted XP N1s spectra were used for the quantification of different nitrogen-containing functional groups, and TPD studies were performed in inert and ammonia atmosphere to investigate the surface reactions occurring on the oxidized CNT surfaces quantitatively. Nitrile, lactam, imide and amine-type functional groups were formed in the presence of ammonia below 300 degrees C. When the OCNTs were treated in the medium temperature range between 300 degrees C to 500 degrees C, mainly pyridine-type nitrogen groups were generated, whereas pyridinic, pyrrolic and quaternary-type nitrogen groups were the dominating species present on the CNT surface when treated above 500 degrees C. It was found that about 38% of the oxygen functional groups react with ammonia below 500 degrees C.

Confocal Raman microspectroscopy as an analytical tool to assess the mitochondrial status in human spermatozoa.

Confocal Raman microspectroscopy was used to investigate human sperm cells. Raman mapping with a 532 nm excitation laser allowed to unambiguously characterize the nucleus, the neck, and, in particular, the mitochondria-rich middle piece of a human sperm cell. The effect of ultraviolet radiation on different organelles of the sperm was quantified by localized spectral Raman signatures obtained within milliseconds. Chemical changes within the sub-cellular structure of the sperm cells were recorded as a function of ultraviolet light exposure time, showing the proof-of-principle that Raman microspectroscopy can be a fast diagnostic method for detecting the mitochondrial and motility status of human spermatozoa.

Rattling in the cage: ions as probes of sub-picosecond water network dynamics.

We present terahertz (THz) measurements of salt solutions that shed new light on the controversy over whether salts act as kosmotropes (structure makers) or chaotropes (structure breakers), which enhance or reduce the solvent order, respectively. We have carried out precise measurements of the concentration-dependent THz absorption coefficient of 15 solvated alkali halide salts around 85 cm(-1) (2.5 THz). In addition, we recorded overview spectra between 30 and 300 cm(-1) using a THz Fourier transform spectrometer for six alkali halides. For all solutions we found a linear increase of THz absorption compared to pure water (THz excess) with increasing solute concentration. These results suggest that the ions may be treated as simple defects in an H-bond network. They therefore cannot be characterized as either kosmotropes or chaotropes. Below 200 cm(-1), the observed THz excess of all salts can be described by a linear superposition of the water absorption and an additional absorption that is attributed to a rattling motion of the ions within the water network. By providing a comprehensive set of data for different salt solutions, we find that the solutions can all be very well described by a model that includes damped harmonic oscillations of the anions and cations within the water network. We find this model predicts the main features of THz spectra for a variety of salt solutions. The assumption of the existence of these ion rattling motions on sub-picosecond time scales is supported by THz Fourier transform spectroscopy of six alkali halides. Above 200 cm(-1) the excess is interpreted in terms of a change in the wing of the water network librational mode. Accompanying molecular dynamics simulations using the TIP3P water model support our conclusion and show that the fast sub-picosecond motions of the ions and their surroundings are almost decoupled. These findings provide a complete description of the solute-induced changes in the THz solvation dynamics for the investigated salts. Our results show that THz spectroscopy is a powerful experimental tool to establish a new view on the contributions of anions and cations to the structuring of water.

Water solvation properties: an experimental and theoretical investigation of salt solutions at finite dilution.

Our combined analysis of first-principle simulations and experiments conducted on salt solutions at finite dilution shows that the high frequency range of the infrared spectrum of an aqueous solution of NaCl displays a shift toward higher frequencies of the stretching band with respect to pure water. We ascribe this effect to a lowering of the molecular dipole moments due to a decrease in the dipole moments of molecules belonging to the first and second solvation shells with respect to bulk water. An analysis of the dipole orientation correlations proves that the screening of solutes is dominated by short-range effects. These jointly experimental and theoretical results are corroborated by the good agreement between calculated and measured dielectric constants of our target solution.

A first principles investigation of water dipole moment in a defective continuous hydrogen bond network.

First principles molecular dynamics simulations of an aqueous solution salt system at finite concentration containing both Na(+) and Cl(-) ions show that a change in the distribution of the molecular dipole moment of H(2)O monomers appears when ions are present in solution. Simulations suggest a lowering of the dipole moments of the water molecules in the solvation shells of Na(+) and Cl(-) as compared to the pure water case, while the dipoles of the rest of the molecules are hardly affected. However, finer analysis in terms of the Wannier centers distribution suggests a change in the electronic structure of the water molecules even in the bulk. Also a change of the H-bond network arrangement was found and correlation between dipole and MOH parameter evidences such subtle effects, suggesting a lowering of tetrahedral order in salty solutions. All these changes can be related to observable quantities such as the infrared spectra thus allowing for a rationalization of the experimental outcome on neutral aqueous solutions.

Defective continuous hydrogen-bond networks: an alternative interpretation of IR spectroscopy.

We apply our previously developed deconvolution method and interpretation to analyze changes in the OH stretching band [nu(OH) band] of low-concentration (< or =0.2 m) aqueous solutions of NaCl and KCl. We treat these simple, monovalent ions as defects in the hydrogen-bond network of pure water and quantify the changes in the spectra at low defect concentration with an "order parameter". Order-parameter analysis of difference spectra of the two solutions leads to hydration numbers of 7.0+/-1.0 and 5.9+/-0.3 for K(+) and Na(+), respectively. Additionally, we find that changes in the nu(OH) band due to low concentrations of ions result from changes in the topology of the hydrogen-bond network.

Structural correlations in liquid water: a new interpretation of IR spectroscopy.

We present a new and alternative interpretation of the structure of the IR vibrational mode (nu(OH) band) of pure water. The re-interpretation is based on the influence of the cooperative hydrogen bonding arising from a network of hydrogen bonds in the liquid. The nu(OH) band has six components that are dominated by differences in their O-H bond lengths but deviate from thermodynamically average values due to interactions with the hydrogen bond network. The physical origin of the structure in the nu(OH) band is directly related to the O-H bond length, and variations in this bond length are caused by the influence of the surrounding hydrogen-bonded network of water molecules.