Application of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and hydrogen exchange combined with enzymatic digestion for the structural characterization of antimalaric Spf66 peptide

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used in hydrogen exchange studies, exchanging deuteron (H/D) or proton (D/H), to determine the structure and conformational changes of antimalarial Spf66 synthetic peptide in its monomeric and dimeric forms. The accuracy of both analytical methods was assessed along with their suitability to study structural aspects. The results via these two approaches were in agreement, indicating that the dimer presents segments of secondary structure. In this last case, the combination of both methods with enzymatic digestion with pepsin was used in their identification. Although 100% coverage of Spf66 dimer was not observed, the higher levels of deuteration were observed for fragments located in the chain terminal where the structure may be more flexible, while the fragments near the disulfide bonds, which is, in theory, the more rigid region of the molecule, were not detected. This strategy is significantly time saving and allows rapid screening and help to characterize a protein, especially, when no prior structural information is available. However, a single spectrum is not certainly sufficient to obtain structural data; it is just an experimental limitation.Also, changes in peptide structure after storage at different temperatures and time were observed, which lead to a loss in the secondary structure as determined by circular dicroism measurements and an increase in aggregation products, since the trimer and tetramer species were detected by mass spectrometry.     

Prenylated xanthone derivatives with antiplasmodial activity from Allanblackia monticola STANER L.C

Further study of the methanol extract of the stem bark of Allanblackia monticola STANER L.C. resulted in the isolation of a new prenylated xanthenedione, designated allanxanthone C, together with the five known xanthones, garciniafuran, tovophyllin A, rubraxanthone, norcowanin and mangostin and one saponin, stigmasterol-3-O-beta-D-glucopyranoside. The structure of the new compound was established by detailed spectroscopic analysis to be 1,2-dihydro-3,6,8-trihydroxy-1,1,7-tri(3-methylbut-2-enyl)xanthen-2,9-dione (3-hydroxyapetalinone C). The methanol extract and pure compounds were tested on two strains of Plasmodium falciparum, F32 (chloroquine sensitive) and FcM29 (chloroquine resistant). The IC50 values obtained ranged from 0.6 to 8.9 microg/ml. Their cytotoxicity was estimated on human melanoma cells (A375) and the cytotoxicity/antiplasmodial ratio was found to be between 15.45 and 30.46. The antimicrobial activities against a range of microorganisms of the crude extract and some of these compounds are also reported.     

Correction to: X-coordinates of Pell equations as sums of two Tribonacci numbers

Periodica Mathematica Hungarica - In this work, we correct an oversight from [1].     

Contractions of group representations via geometric quantization

Letters in Mathematical Physics - We propose a general framework to contract unitary dual of Lie groups via holomorphic quantization of their coadjoint orbits, using geometric quantization. The...     

Controlled growth of rutile TiO2 by atomic layer deposition on oxidized ruthenium

Crystalline rutile TiO₂ films were grown by atomic layer deposition on oxidized Ru electrodes using a titanium methoxide as the metal precursor and O₃ as the oxidant. A protective layer of ～0.3 nm TiO₂ grown with H₂O as the oxidant was first deposited in order to avoid etching of the Ru bottom electrode by the O₃ used for the growth of the TiO₂ (bulk) layer. Electrical evaluation of the capacitor stacks with TiO₂ as dielectric, RuO₂/Ru and Pt as the bottom and top electrodes respectively, resulted in superior characteristics of the rutile phase as compared to the anatase. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The probabilistic analysis of a greedy satisfiability algorithm

On input a random 3‐CNF formula of clauses‐to‐variables ratio r₃ applies repeatedly the following simple heuristic: Set to True a literal that appears in the maximum number of clauses, irrespective of their size and the number of occurrences of the negation of the literal (ties are broken randomly; 1‐clauses when they appear get priority). We prove that for r₃ < 3.42 this heuristic succeeds with probability asymptotically bounded away from zero. Previously, heuristics of increasing sophistication were shown to succeed for r₃ < 3.26. We improve up to r₃ < 3.52 by further exploiting the degree of the negation of the evaluated to True literal. © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2006     

Crystal and molecular structure of gochnatolide,a sesquiterpene lactone

The crystal and molecular structure of the gochnatolide, has been determined by X-ray crystallographic analysis. The compound, obtained from the leaves ofGochnatia hypoleuca subsp.obtusata, is a germacr-8,12-olide. The two molecules in the asymmetric unit are linked together by hydrogen bonding which results in differences in the conformation of the ester side chains at C(14).Contribution No. 1097 of the Institute de Química, UNAM.     

Indium(I) trifluoromethanesulfonate and other soluble salts for univalent indium chemistry

Herein we report the synthesis, structure and preliminary reactivity studies of a series of unusually soluble indium(i) salts that are improved alternatives to indium(i) halide reagents.     

Atomic level control over surface species via a molecular precursor approach: isolated Cu(I) sites and Cu nanoparticles supported on mesoporous silica

A nonaqueous molecular precursor grafting approach was employed for the generation of well-defined surface structures featuring Cu on a mesoporous silica support. X-ray absorption measurements (XANES and EXAFS) were used to determine that [CuOSi(OtBu)3]4 provided 100% isolated Cu(I) sites upon grafting (without thermal treatment), whereas [CuOtBu]4 gave isolated species with most of the original Cu-O-Cu linkages intact, but in a more relaxed straight chain form. Upon heating under inert conditions, the vast majority of Cu in the materials from [CuOSi(OtBu)3]4 remained as isolated Cu(I) sites (up to 88% isolation), with significant stabilization provided from the -OSi(OtBu)3 ligands. In stark contrast, approximately 100% of the Cu in the materials generated from [CuOtBu]4 was readily reduced upon heating, forming isolated Cu metal particles with an average diameter of 0.7 nm.