Near-Ultraviolet Circular Dichroism and Two-Dimensional Spectroscopy of Polypeptides

A fully quantitative theory of the relationship between protein conformation and optical spectroscopy would facilitate deeper insights into biophysical and simulation studies of protein dynamics and folding. In contrast to intense bands in the far-ultraviolet, near-UV bands are much weaker and have been challenging to compute theoretically. We report some advances in the accuracy of calculations in the near-UV, which were realised through the consideration of the vibrational structure of the electronic transitions of aromatic side chains.     

Investigating microcrystalline cellulose crystallinity using Raman spectroscopy

Cellulose - Microcrystalline cellulose (MCC) is a semi-crystalline material with inherent variable crystallinity due to raw material source and variable manufacturing conditions. MCC crystallinity...     

Assessment of dual plane PIV measurements in wall turbulence using DNS data

Experimental dual plane particle image velocimetry (PIV) data are assessed using direct numerical simulation (DNS) data of a similar flow with the aim of studying the effect of averaging within the interrogation window. The primary reason for the use of dual plane PIV is that the entire velocity gradient tensor and hence the full vorticity vector can be obtained. One limitation of PIV is the limit on dynamic range, while DNS is typically limited by the Reynolds number of the flow. In this study, the DNS data are resolved more finely than the PIV data, and an averaging scheme is implemented on the DNS data of similar Reynolds number to compare the effects of averaging inherent to the present PIV technique. The effects of averaging on the RMS values of the velocity and vorticity are analyzed in order to estimate the percentage of turbulence intensity and enstrophy captured for a given PIV resolution in turbulent boundary layers. The focus is also to identify vortex core angle distributions, for which the two-dimensional and three-dimensional swirl strengths are used. The studies are performed in the logarithmic region of a turbulent boundary layer at z ⁺ = 110 from the wall. The dual plane PIV data are measured in a zero pressure gradient flow over a flat plate at Re _τ = 1,160, while the DNS data are extracted from a channel flow at Re _τ = 934. Representative plots at various wall-normal locations for the RMS values of velocity and vorticity indicate the attenuation of the variance with increasing filter size. Further, the effect of averaging on the vortex core angle statistics is negligible when compared with the raw DNS data. These results indicate that the present PIV technique is an accurate and reliable method for the purposes of statistical analysis and identification of vortex structures.     

Numerical methods for the simulation of a coalescence-driven droplet size distribution

The droplet size distribution in a turbulent flow field is considered and modeled by means of a population balance system. This paper studies different numerical methods for the 4D population balance equation and their impact on an output of interest, the time-space-averaged droplet size distribution at the outlet, which is known from experiments. These methods include different interpolations of the experimental data at the inlet, various discretizations in time and space, and different schemes for computing the coalescence integrals. It will be shown that noticeable changes in the output of interest might occur. In addition, the computational efficiency of the studied methods is discussed.     

Isosteres of Natural Phosphates. Methylene and Hydroxyrnethylene Analogues of Tyrosine O-Phosphate

Abstract

The ability of phosphonic acid analogues isosteric with natural phosphate esters to Serve as inhibitors of enzymatic phosphate hydrolysis has been documented in a wide variety of systems.¹ The use of such an analogue in place of the natural phosphate ester provides a functionality which the enzyme may not be able to distinguish from the natural ester, but which is incapable of being hydrolyzed. In some instances the use of hydroxymethylene analogues has resulted in a greater degree of recognition, and resultant inhibition of hydrolytic activity, than the simple methylene analogues.² On this basis, the methylene and hydroxymethylene analogues of tyrosine O-phosphate appear to be reasonable candidates to Serve as inhibitors for phosphoprotein phosphatases and alkaline phosphatase, and as probes for biological mechanisms.     

Engineered-membranes: A novel concept for clustering of native lipid bilayers

A strategy for clustering of native lipid membranes is presented. It relies on the formation of complexes between hydrophobic chelators embedded within the lipid bilayer and metal cations in the aqueous phase, capable of binding two (or more) chelators simultaneously Fig. 1. We used this approach with purple membranes containing the light driven proton pump protein bacteriorhodopsin (bR) and showed that patches of purple membranes cluster into mm sized aggregates and that these are stable for months when incubated at 19 °C in the dark. The strategy may be general since four different hydrophobic chelators (1,10-phenanthroline, bathophenanthroline, Phen-C10, and 8-hydroxyquinoline) and various divalent cations (Ni²⁺, Zn²⁺, Cd²⁺, Mn²⁺, and Cu²⁺) induced formation of membrane clusters. Moreover, the absolute requirement for a hydrophobic chelator and the appropriate metal cations was demonstrated with light and atomic force microscopy (AFM); the presence of the metal does not appear to affect the functional state of the protein. The potential utility of the approach as an alternative to assembled lipid bilayers is suggested.