Nuclear surface waves in alpha-particle and ion-ion collisions

Our earlier methods of interpretation of the resonances in ion-ion scattering (such as ¹²C + ¹²C, ¹²C + ¹⁶O, or ¹⁶O + ¹⁶O where they appear both experimentally and via optical-model calculations) in terms of nuclear surface waves are applied to the case of α-⁴⁰Ca scattering. The optical-model resonance results of Brink et al. are here extended in order to render them suitable for a surface-wave picture as well. Recent experimental results on ¹²C + ¹²C scattering are used to demonstrate the existence of surface waves of both Rayleigh and whispering gallery type in this system.     

Direct Photocontrol of Peptidomimetics: An Alternative to Oxygen‐Dependent Photodynamic Cancer Therapy

Conventional photodynamic treatment strategies are based on the principle of activating molecular oxygen in situ by light, mediated by a photosensitizer, which leads to the generation of reactive oxygen species and thereby causes cell death. A diarylethene‐derived peptidomimetic is presented that is suitable for photodynamic cancer therapy without any involvement of oxygen. This light‐sensitive molecule is not a mediator but is itself the cytotoxic agent. As a derivative of the cyclic amphiphilic peptide gramicidin S, the peptidomimetic exists in two thermally stable photoforms that are interconvertible by light of different wavelengths. The isomer generated by visible light shows much stronger toxicity against tumor cells than the UV‐generated isomer. First in vivo applications are demonstrated on a tumor animal model to illustrate how the peptidomimetic can be administered in the less toxic form and then activated locally in a solid tumor by visible light.     

The choice of appropriate density functional for the calculation of static first hyperpolarizability of azochromophores and stacking dimers

The effect of the stacked azo‐chromophore dimer formation on the values of static first hyperpolarizability is studied in the framework of the DFT‐based approach; calculations were also performed at the MP2 level. A number of dispersion‐corrected density functionals—В97D, ωВ97X‐D, and M06‐2X—is tested to calculate the structure of the dimer, the value of binding energy, and molecular nonlinear optical characteristics. According to the QTAIM analysis, the presence of bond critical points is revealed in the intermolecular region, the signs and values of topological characteristics giving evidence for the noncovalent van der Waals interaction between the chromophores. The formation of stacks results in moderate increase of dimer static first hyperpolarizability as compared to that of a single chromophore, the effect depending on the relative shift of the chromophores in dimer. In a special case of greatly shifted chromophores, this enhancement of the first hyperpolarizability becomes appreciable and achieves 72%. © 2015 Wiley Periodicals, Inc.     

Preparation of Pd/C catalysts via deposition of palladium hydroxide onto Sibunit carbon and their application to partial hydrogenation of rapeseed oil

Pd/Sibunit catalysts were prepared by deposition of palladium hydroxide onto the support surface in an alkaline medium. It was found that the palladium distribution throughout the catalyst grain, and the dispersion of Pd particles depend on (i) the order of the addition of H₂PdCl₄ and Na₂CO₃ to carbon suspension, (ii) Na₂CO₃ to H₂PdCl₄ ratio, and (iii) aging time of the mixture H₂PdCl₄ + Na₂CO₃ before its addition to the carbon. The catalysts were tested in the hydrogenation of cyclohexene and rapeseed oil under static conditions. The yield of trans-isomers as products of partial hydrogenation of rapeseed oil was found to decrease with decreasing the Pd particle size in the catalysts, as well as with increasing the Pd concentration on the periphery of the support grains.     

Stereocontrolled alkylative construction of quaternary carbon centers

Protocols for the stereodefined formation of alpha,alpha-disubstituted enolates of pseudoephedrine amides are presented followed by the implementation of these in diastereoselective alkylation reactions. Direct alkylation of alpha,alpha-disubstituted pseudoephedrine amide substrates is demonstrated to be both efficient and diastereoselective across a range of substrates, as exemplified by alkylation of the diastereomeric pseudoephedrine alpha-methylbutyramides, where both substrates are found to undergo stereospecific replacement of the alpha-C-H bond with alpha-C-alkyl, with retention of stereochemistry. This is shown to arise by sequential stereospecific enolization and alkylation reactions, with the alkyl halide attacking a common pi-face of the E- and Z-enolates, proposed to be opposite the pseudoephedrine alkoxide side chain. Pseudoephedrine alpha-phenylbutyramides are found to undergo highly stereoselective but not stereospecific alpha-alkylation reactions, which evidence suggests is due to facile enolate isomerization. Also, we show that alpha,alpha-disubstituted pseudoephedrine amide enolates can be generated in a highly stereocontrolled fashion by conjugate addition of an alkyllithium reagent to the s-cis-conformer of an alpha-alkyl-alpha,beta-unsaturated pseudoephedrine amide, providing alpha,alpha-disubstituted enolate substrates that undergo alkylation in the same sense as those formed by direct deprotonation. Methods are presented to transform the alpha-quaternary pseudoephedrine amide products into optically active carboxylic acids, ketones, primary alcohols, and aldehydes.     

Study of the slow electrolyte-induced changes in the TiO<Subscript>2</Subscript> hydrosol structure

Slow changes in the TiO₂ hydrosol structure induced by a small KCl additive were studied using the small-angle X-ray scattering. The initial sol of anisometric anatase nanocrystals stabilized by HCl was prepared. After addition of KCl scattering curves were measured regularly for 2 years. It was established the formation and the accumulation of small dense aggregates. A model of the slow structural changes in the TiO₂ sols with electrolyte additives comprising the two steps of aggregation was proposed. At first the larger anatase nanocrystals combine slowly forming the small dense aggregates through the oriented attachment mechanism. Then, at the critical size of such aggregates, they coagulate quickly forming the looser particles.     

The N-domain of angiotensin-converting enzyme specifically hydrolyzes the Arg-5-His-6 bond of Alzheimer's Abeta-(1-16) peptide and its isoAsp-7 analogue with different efficiency as evidenced by quantitative matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Chronic imbalance between production and degradation of the human amyloid-beta peptide (Abeta) is assumed to play an important role in pathogenesis of Alzheimer's disease (AD). Post-translational modifications of Abeta could influence its interactions with specifically cleaving proteases and, therefore, perturb the Abeta homeostasis. The angiotensin-converting enzyme (ACE) was previously shown to degrade non-modified Abeta in vitro and in cells. In the presented work, we investigated the effect of isomerization of Asp-7, a common non-enzymatic age-related modification found in AD-associated Abeta species, on hydrolysis of Abeta by ACE. Two synthetic peptides corresponding to the Abeta region 1-16 with either Asp or isoAsp residues in position 7 were examined as monomeric soluble substrates for the N- as well as for the C-domain of ACE. The use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) coupled with the (18)O-labeled internal standard approach has allowed us to show that (i) the N-domain of ACE (N-ACE), but not the C-domain, selectively cleaves the Arg-5-His-6 bond in both peptides, and that (ii) N-ACE hydrolyzes the isoAsp-7 analogue more efficiently than the non-modified one. Our results demonstrate a new endopeptidase activity of N-ACE as well as high preference of the domain to recognize and hydrolyze the isomerized Abeta species that were earlier suggested to promote AD pathogenesis. The results suggest the need for further analysis of biological effects of isomerized Abeta and its interaction with ACE in AD pathogenesis.     

First examples of the cocrystallization of diastereomers of chiral phosphorus compounds

The first three examples of the cocrystallization of covalent diastereomers of phosphorus compounds containing different chiral elements (centres of chirality on carbon and phosphorus, and an axis of chirality) are reported. The phenomenon can be attributed to the complementarity of the molecular shapes of the diastereomers. The X-ray data of all the crystals exhibit centrosymmetric statistics regardless of their very different natures. Dedicated to the memory of Professor Viktor Naumov (1932–2007).