Laser-induced periodic surface structures (LIPSS; ripples) with different spatial characteristics have been observed after irradiation of single-crystalline indium phosphide ͑c-InP͒ with multiple linearly polarized femtosecond pulses (130 fs, 800 nm) in air. With an increasing number of pulses per spot, N, up to 100, a characteristic evolution of two different types of ripples has been observed, i.e., (i) the growth of a grating perpendicular to the polarization vector consisting of nearly wavelength-sized periodic lines and (ii), in a specific pulse number regime ͑N =5-30͒, the additional formation of equally oriented ripples with a spatial period close to half of the laser wavelength. For pulse numbers higher than 50, the formation of micrometer-spaced grooves has been found, which are oriented perpendicular to the ripples. These topographical surface alterations are discussed in the frame of existing LIPSS theories.
Force−displacement curves have been obtained with a commercial atomic force microscope
(AFM) at different temperatures and probe rates on a thick film of poly(n-butyl methacrylate) (PnBMA).
The analysis of the force−displacement curves has been focused on the contact portion of the curves,
giving information about the stiffness of the sample and its Young's modulus. A novel model of sample
deformations that extends the basic equations of the elastic continuum contact theories to the plastic
deformations is presented. This model gives several insights into the processes of deformation of soft
samples and permits to calculate not only the parameters of the Williams−Landel−Ferry equation but
also the Young's modulus and the yielding force of the polymer as a function of temperature and/or probe
rate. These quantities have been measured in a wide range of temperatures (70 K) and probe rates (6
decades) for the first time with the AFM, and the results are in very good agreement with measurements
performed with customary techniques, such as broadband spectroscopy and dynamic mechanical analysis.
Microorganisms accumulate molar concentrations of compatible solutes like ectoine to prevent proteins from denaturation. Direct structural or spectroscopic information on the mechanism and about the hydration shell around ectoine are scarce. We combined surface plasmon resonance (SPR), confocal Raman spectroscopy, molecular dynamics simulations, and density functional theory (DFT) calculations to study the local hydration shell around ectoine and its influence on the binding of a gene-5-protein (G5P) to a single-stranded DNA (dT25). Due to the very high hygroscopicity of ectoine, it was possible to analyze the highly stable hydration shell by confocal Raman spectroscopy. Corresponding molecular dynamics simulation results revealed a significant change of the water dielectric constant in the presence of a high molar ectoine concentration as compared to pure water. The SPR data showed that the amount of protein bound to DNA decreases in the presence of ectoine, and hence, the protein-DNA dissociation constant increases in a concentration-dependent manner. Concomitantly, the Raman spectra in terms of the amide I region revealed large changes in the protein secondary structure. Our results indicate that ectoine strongly affects the molecular recognition between the protein and the oligonucleotide, which has important consequences for osmotic regulation mechanisms.
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