A liposome-based assay for quantitation of detergents

The amount of enzyme released from liposomes exposed to detergents varies with the amount of detergent present. This fact makes it possible to quantitate the detergent. Multilamellar liposomes containing entrapped peroxidase were adsorbed to paper discs and then exposed to solutions containing detergents. The assay procedure proved useful for assaying detergents down to their critical micelle concentration (CMC), and for an induced leakage of ionic detergents also below their CMCs.     

Recent developments in the line-by-line modeling of outgoing longwave radiation

High frequency resolution radiative transfer model calculations with the Atmospheric Radiative Transfer Simulator (ARTS) were used to simulate the clear-sky outgoing longwave radiative flux (OLR) at the top of the atmosphere. Compared to earlier calculations by Clough and coworkers the model used a spherical atmosphere instead of a plane parallel atmosphere, updated spectroscopic parameters from HITRAN, and updated continuum parameterizations from Mlawer and coworkers. These modifications lead to a reduction in simulated OLR by approximately 4.1%, the largest part, approximately 2.5%, being due to the absence of the plane parallel approximation. As a simple application of the new model, the sensitivity of OLR to changes in humidity, carbon dioxide concentration, and temperature were investigated for different cloud-free atmospheric scenarios. It was found that for the tropical scenario a 20% change in humidity has a larger impact than a doubling of the carbon dioxide concentration. The sensitive altitude region for temperature and humidity changes is the entire free troposphere, including the upper troposphere where humidity data quality is poor.     

The role of nucleobase carboradical and carbanion on DNA lesions: a theoretical study

DNA base release induced by H and OH radical addition to thymine and their corresponding electron adducts is studied at the DFT B3LYP/6-31+G(d,p) level in gas phase and in solution. H atom transfer after radical formation from C2' on the sugar to the C6 site on the base is shown to be prohibited for the radical species. Their corresponding electron adducts, albeit minor events in cellular systems, show excellent capabilities to proton transfer from C2' on the sugar to the C6 site on the base. The barriers for subsequent N-glycosidic bond dissociation range from 0.1 to 1.6 kcal mol(-1) at the B3LYP level and around 5 kcal mol(-1) using the BB1K functional, implying that these reactions can serve as a source to abasic sites. Analysis of bond dissociation energies show that all the reactions are exothermic, which is consistent with the changes in N-glycosidic bond lengths during the proton-transfer reactions. Bulk solvation plays a reverse influence on proton transfer and the bond rupture reactions. Molecular orbitals, NPA charges, and electron affinities are calculated to shed further light on the properties leading up to the intramolecular reactions.     

Theoretical study of the antioxidant properties of pyridoxine

Molecules acting as antioxidants capable of scavenging reactive oxygen species (ROS) are of utmost importance in the living cell. The antioxidative properties of pyridoxine (vitamin B6) have recently been discovered. In this study, we have analyzed the reactivity of pyridoxine toward the ROS (.-)OH, (.-)OOH, and (.-)O(2)- at the density functional theory level (functionals B3LYP and MPW1B95). Two reaction types have been studied as follows: addition to the aromatic ring atoms and hydrogen/proton abstraction. Our results show that (.-)OH is the most reactive species, while (.-)OOH displays low reactivity and (.-)O2(-) does not react at all with pyridoxine. The most exergonic reactions are those where (.-)H is removed from the CH(2)OH groups or the ring-bound OH group and range from -33 to -39 kcal/mol. The most exergonic addition reactions occur by attacking the carbon atoms bonded to nitrogen but with an energy gain of only 6 kcal/mol.     

Measuring energy differences by BEC interferometry on a chip

We investigate the use of a Bose-Einstein condensate trapped on an atom chip for making interferometric measurements of small energy differences. We measure and explain the noise in the energy difference of the split condensates, which derives from statistical noise in the number difference. We also consider systematic errors. A leading effect is the variation of the rf magnetic field in the trap with distance from the wires on the chip surface. This can produce energy differences that are comparable with those due to gravity.     

Megavariate Analysis of Environmental QSAR Data. Part II – Investigating Very Complex Problem Formulations Using Hierarchical, Non-Linear and Batch-Wise Extensions of PCA and PLS

Summary Three extensions of the basic PCA and PLS methodologies are described. These extensions are hierarchical, non-linear and batch-based in nature. The objectives of these methods are to assist in problem understanding and problem solving in very complex (QSAR) problem formulations. The method extensions are illustrated using two example QSAR data sets containing many X- and Y-variables.     

Entropy driven stabilization of energetically unstable crystal structures explained from first principles theory

Conventional methods to calculate the thermodynamics of crystals evaluate the harmonic phonon spectra and therefore do not work in frequent and important situations where the crystal structure is unstable in the harmonic approximation, such as the body-centered cubic (bcc) crystal structure when it appears as a high-temperature phase of many metals. A method for calculating temperature dependent phonon spectra self-consistently from first principles has been developed to address this issue. The method combines concepts from Born's interatomic self-consistent phonon approach with first principles calculations of accurate interatomic forces in a supercell. The method has been tested on the high-temperature bcc phase of Ti, Zr, and Hf, as representative examples, and is found to reproduce the observed high-temperature phonon frequencies with good accuracy.     

Increasing the equilibrium solubility of dopants in semiconductor multilayers and alloys

We have theoretically studied the possibility to control the equilibrium solubility of dopants in semiconductor alloys, by strategic tuning of the alloy concentration. From the modeled cases of C(0) in Si(x)Ge(1-x), Zn(-) and Cd(-) in Ga(x)In(1-x)P it is seen that under certain conditions the dopant solubility can be orders of magnitude higher in an alloy or multilayer than in either of the elements of the alloy. This is found to be due to the solubility's strong dependence on the lattice constant for size mismatched dopants. The equilibrium doping concentration in alloys or multilayers could therefore be increased significantly. More specifically, Zn- in a Ga(x)In(1-x)P multilayer is found to have a maximum solubility for x = 0.9, which is 5 orders of magnitude larger than that of pure InP.     

Solvent‐Dependent Structure of the I3− Ion Derived from Photoelectron Spectroscopy and Ab Initio Molecular Dynamics Simulations

Ab initio molecular dynamics (MD) simulations of the solvation of LiI₃ in four different solvents (water, methanol, ethanol, and acetonitrile) are employed to investigate the molecular and electronic structure of the I₃^? ion in relation to X‐ray photoelectron spectroscopy (XPS). Simulations show that hydrogen‐bond rearrangement in the solvation shell is coupled to intramolecular bond‐length asymmetry in the I₃^? ion. By a combination of charge analysis and I 4 d core‐level XPS measurements, the mechanism of the solvent‐induced distortions has been studied, and it has been concluded that charge localization mediates intermolecular interactions and intramolecular distortion. The approach involving a synergistic combination of theory and experiment probes the solvent‐dependent structure of the I₃^? ion, and the geometric structure has been correlated with the electronic structure.