A fast flow tube study of gas phase H/D exchange of multiply protonated ubiquitin

An electrospray ionization (ESI)/fast-flow technique has been applied to the study of gas phase hydrogen/deuterium (H/D) exchange kinetics. Multiply charged ubiquitin ions [ubiquitin + nH](n)(+), in charge states n = 7-13, were reacted with ND(3). The behavior of ND(3) as exchange reagent is different from that of the previously studied reagents, D(2)O and CH(3)OD. Contrary to those, the maximum number of exchanged hydrogen atoms and the overall exchange rate were observed to increase with increasing charge state of the ubiquitin ions. The results are reagent-dependent because the exchange mechanisms are different for the different reagents. This observation is in agreement with a recent conclusion by Beauchamp and co-workers that contrary to the assumption often expressed in earlier studies, H/D exchange kinetics may not directly reflect ion structures. The results for all three reagents are, however, consistent with observations of previous ion mobility experiments that with increasing charge state the conformers change from more compact, partially folded structures to elongated nearly linear ones. H/D exchange of (ubiquitin + 13H)(13+) with ND(3) leads to two separated ion populations reflecting the possible existence of two conformers with different exchange rates. The ions (ubiquitin + 8H)(8+) and (ubiquitin + 11H)(11+) represent a partially folded structure and an unfolded structure, respectively, and were studied in greater detail. The relative abundances of ions were measured in steps of 0.5 m/z (mass-to-charge ratio), as a function of the ND(3) flow rate. The experimental results were simulated by computer fitted curves based on a recently developed algorithm. The algorithm allows the extraction of sets of grouped rate constants. Eight rate constant groups were deduced for each of the two ions. These rate constants correspond to 32 and 44 H/D exchanges for the 8+ and 11+ charged ions, respectively. The results indicate higher individual rates for most of the exchanged atoms in the 11+ ion compared to the 8+ ion.     

A Scalable Information Security Technique: Joint Authentication-Coding Mechanism for Multimedia over Heterogeneous Wireless Networks

There have been increasing concerns about the security issues of wireless transmission of multimedia in recent years. Wireless networks, by their natures, are more vulnerable to external intrusions than wired ones. Therefore, many applications demand authenticating the integrity of multimedia content delivered wirelessly. In this work, we propose a framework for jointly authenticating and coding multimedia to be transmitted over heterogeneous wireless networks. We firstly provide a novel graph-based authentication scheme which can not only construct the authentication graph flexibly but also trade-off well among some practical requirements such as overhead, robustness and delay. And then, a rate-distortion optimized joint source-channel coding (JSCC) approach for error-resilient scalable encoded video is presented, in which the video is encoded into multiple independent streams and each stream is assigned forward error correction (FEC) codes to avoid error propagation. Furthermore, we consider integrating authentication with the specific JSCC scheme to achieve a satisfactory authentication results and end-to-end reconstruction quality by optimally applying the appropriate authentication and coding rate. Simulation results show the effectiveness of the proposed authentication-coding scheme for multimedia over wireless networks.     

Low-temperature phases of the solid electrolyte Ag26I18W4O16

Single crystal X-ray diffraction photographs taken with a Buerger precession camera, at temperatures 250, 214, and 122 K, corroborate the existence of three low-temperature phases of Ag₂₆I₁₈W₄O₁₆. These phases are labeled α′, β, and γ in order of decreasing temperature. The α′ phase is monoclinic, space group P2₁, Z = 2; the β phase is triclinic, space group $\text{P}\text{1}$ or P1, Z = 2; and the γ phase is triclinic, space group P1, Z = 1. Lattice constants at the aforementioned temperatures are given. Twins in the β and γ phases are related by the albite and pericline laws, as are twins in the feldspars. The highest symmetry known to be attained by the (W₄O₁₆)^8? entity is 2(C₂), which, strictly, it must lose at the transition to the α′ phase.     

New germanium- and tin-containing polysalicylideneazomethines derived from tetraamines

Polysalicylideneazomethines containing Ge and Sn atoms in the polymeric chain were prepared by polycondensation of N,N′,N″,N‴-tetrasalicylidene-3,3′,4,4′-tetraaminodiphenyl ether with germanium or tin tetrachloride or tetraethoxide. Spectroscopic examination showed that the polymers exhibit nonclassical polyconjugation and belong to a new class of semiconductor polytransannular-conjugated polymers.     

Directional Synthesis of Hybrid Polymers from 2- and 4-Vinylpyridines

Formation of hybrid three-dimensional structures by treatment of copolymers of 2- and 4-vinylpyridine with butyllithium, followed by grafting of tert-butyl acrylate molecules, was studied by mass-spectrometric thermal analysis and ¹³C NMR spectroscopy.