A FeCl3-promoted highly atropodiastereoselective cascade reaction: synthetic utility of radical cations in indolostilbene construction

The FeCl₃-promoted oxidative cyclization/coupling of acetamidostilbenes possessing 3-methoxy, 4-methoxy and 3,5-methoxy substitutions (21), (22) and (23) is described. Only 3,5-substitution gave rise to novel indolostilbenes, each possessing two stereogenic axes (axially chiral but racemic dimers (39) and (40)). The 4-methoxy substituted acetamidostilbenes, by contrast, yielded the bisindoline dimer (36).     

Distinct dynamic behaviors of water molecules in hydrated pores

Water molecules confined inside narrow pores are of great importance in understanding the structure, stability, and function of water channels. Here we report that besides the H-bonding water that structures the pore, the permanent presence of a significant, fast-moving fraction of incompletely H-bonded water molecules inside the pore should control the free entry and exit of water. This is achieved by means of complementary DSC and solid-state NMR studies. We also present compelling evidence from X-ray diffraction data that the cluster formed by six water molecules in the most stable cage-like structure is sufficiently hydrophobic to be stably adsorbed in a nonpolar environment.     

Free aluminium extraction from various reference materials and acid soils with relation to plant availability

The single extractions with 15 extractants (agents) (H₂O, KCl, NH₄Cl, NH₄F, CaCl₂, BaCl₂, CuCl₂, LaCl₃, Na₂S₂O₄, (NH₄)₂C₂O₄, Na₄P₂O₇, NTA, EDTA, DTPA, HCl), the optimised BCR (Community Bureau of Reference) three-step sequential extraction procedure (SEP) and the solid phase extraction (SPE) by the chelating ion-exchanger Iontosorb Salicyl (cellulose resin containing covalently bound salicylic acid functional groups) were used for the partitioning of Al in very acid soil samples taken from an area influenced by acid mine solutions. The precision, accuracy and repeatibility for all steps of the optimised BCR SEP were checked on the various reference materials (CRM 483 sewage sludge amended soil, CRM BCR 701 freshwater sediment, SRM 2710 and SRM 2711 Montana soils). Also the new indicative values of the optimised BCR SEP fractional Al concentrations were obtained for these reference materials. The aluminium amounts obtained by the used extraction procedures were valuated and discussed from the aspect of the Al concentration in the plants (grass) growing on the same studied soils. The aluminium toxicity indexes (ATI) calculated for the studied soils, the BaCl₂ and acetic acid soil extracts and the grass stems and roots were used for the assessment of the Al toxicity to the plants. The ATI value was defined as the ratio of the nutrient cations (Ca, Mg, K, Na) concentration sum to the Al concentration. The flame atomic absorption spectrometry (LOQ = 0.2 mg l⁻¹) and the inductively coupled plasma optical emission spectrometry (LOQ = 0.03 mg l⁻¹) were used for the aluminium quantification.     

Hybrid GR-SVM for prediction of surface roughness in abrasive water jet machining

This paper presents a hybridization model of support vector machine (SVM) and grey relational analysis (GRA) in predicting surface roughness value of abrasive water jet (AWJ) machining process. The influential factors of five process parameters in AWJ, namely traverse speed, water jet pressure, standoff distance, abrasive grit size and abrasive flow rate, need to be analyzed using GRA approach. Then, the irrelevance factors of process parameters are eliminated. There is a need of determining the influential factors of process parameters to the surface roughness as to develop a robust prediction model. GRA acts as feature selection method in preprocessing process of hybrid grey relational-support vector machine (GR-SVM) prediction model. Efficiency of the proposed model is demonstrated. GR-SVM presents more accurate result than conventional SVM as it removes the redundant features and irrelevant element from the experimental datasets.     

pH-Dependent Behavior of Hydrophobically Modified Polyelectrolyte Shells of Polymeric Nanoparticles

Summary: The self-assembled core-shell nanoparticles based on fluorescently double-tagged high-molar-mass polystyrene-block-poly(methacrylic acid), PS-PMA, were prepared in aqueous buffers by dialysis from 1,4-dioxane – water mixtures. The conformations of shell-forming PMA chains were studied using nonradiative excitation energy transfer measurements. The study shows that two populations of distinctly different conformations (collapsed and stretched) coexist in the shell and their ratio depends on pH.     

Crystallization kinetics study of cerium titanate CeTi2O6

Cerium titanate CeTi₂O₆ has been investigated recently for its photocatalytic activity and as a safe analogue to actinide-containing brannerite-like titanates (UTi₂O₆, PuTi₂O₆, e.g.) which are intensively studied because of their use for storing nuclear waste. In this paper we report on the monoclinic phase CeTi₂O₆ obtained from the Ti–Ce oxide mixture prepared by a reverse micelles directed sol–gel method and subsequently annealed. The kinetics of the isothermal crystallization process is investigated by means of Johnson–Mehl–Avrami–Kolmogorov equation. The effective activation energy of the formation of CeTi₂O₆ particles, which is an important parameter for its synthesis, is estimated.     

Off-resonance correction using an estimated linear time map

Images acquired in the presence of magnetic field deviations and reconstructed without taking into account the off-resonance, are distorted and corrupted with artifacts. Several post-processing algorithms have been developed for correcting the distortion when it is not possible to fix the field inhomogeneities. These off-resonance correction methods are, in general, slow and computing intensive. To make them faster they are usually adapted to a particular situation or approximated. One of these approximations is to assume that the field map is linear. Although this assumption makes the algorithm fast and robust it is not well suited for arbitrary field maps. On the other hand, there are k-space trajectories with an almost linear time map (time at which each k-space value is acquired), such as 2DFT and EPI. This paper presents an algorithm for off-resonance correction based on a linear time map approximation. This approximation allows a fast algorithm that takes advantage of the almost linearity of the time map and uses the whole field map to correct the images. The proposed correction algorithm reduces the off-resonance induced artifacts while being fast. The linear approximation of the time map needs to be done only once for each trajectory because it does not depend on the acquired image or field map data. The method can also be extended to a multi-plane approximation for sequences with more complex time maps.     

The role of entropy in initializing the aggregation of peptides: a first principle study on oligopeptide oligomerization

The initiation and progression of Alzheimer's disease is coupled to the oligo- and polymerization of amyloid peptides in the brain. Amyloid like aggregates of protein domains were found practically independent of their primary sequences. Thus, the driving force of the transformation from the original to a disordered amyloid fold is expected to lie in the protein backbone common to all proteins. In order to investigate the thermodynamics of oligomerization, full geometry optimizations and frequency calculations were performed both on parallel and antiparallel β-pleated sheet model structures of [HCO-(Ala)(1-6)-NH(2)](2) and (For-Ala(1-2)-NH(2))(1-6) peptides, both at the B3LYP and M05-2X/6-311++G(d,p)//M05-2X/6-31G(d) levels of theory, both in vacuum and in water. Our results show that relative entropy and enthalpy both show a hyperbolic decrease with increasing residue number and with increasing number of strands as well. Thus, di- and oligomerization are always thermodynamically favored. Antiparallel arrangements were found to have greater stability than parallel arrangements of the polypeptide backbones. During our study the relative changes in thermodynamic functions are found to be constant for long enough peptides, indicating that stability and entropy terms are predictable. All thermodynamic functions of antiparallel di- and oligomers show a staggered nature along the increasing residue number. By identifying and analyzing the 6 newly emerging dimer vibrational modes of the 10- and 14-membered building units, the staggered nature of the entropy function can be rationalized. Thus, the vanishing rotational and translational modes with respect to single strands are converted into entropy terms "holding tight" the dimers and oligomers formed, rationalizing the intrinsic adherence of natural polypeptide backbones to aggregate.     

Morphology and crystallization kinetics of compact (HGW) and porous (ASW) amorphous water ice

An investigation of porosity and isothermal crystallization kinetics of amorphous ice produced either by background water vapour deposition (ASW) or by hyperquenching of liquid droplets (HGW) is presented. These two types of ice are relevant for astronomical ice research (Gálvez et al., Astrophys. J., 2010, 724, 539) and are studied here for the first time under comparable experimental conditions. From CH(4) isothermal adsorption experiments at 40 K, surface areas of 280 ± 30 m(2) g(-1) for the ASW deposits and of 40 ± 12 m(2) g(-1) for comparable HGW samples were obtained. The crystallization kinetics was studied at 150 K by following the evolution of the band shape of the OD stretching vibration in HDO doped ASW and HGW samples generated at 14 K, 40 K and 90 K. Comparable rate constants of ～7 × 10(-4) s(-1) were obtained in all cases. However a significant difference was found between the n Avrami parameter of the samples generated at 14 K (n～ 1) and that of the rest (n > 2). This result hints at the possible existence of a structurally different form of amorphous ice for very low generation temperatures, already suggested in previous literature works.     

Enantioselective synthesis of chiral sulfones by ir-catalyzed asymmetric hydrogenation: a facile approach to the preparation of chiral allylic and homoallylic compounds

A highly efficient and enantioselective Ir-catalyzed hydrogenation of unsaturated sulfones was developed. Chiral cyclic and acyclic sulfones were produced in excellent enantioselectivities (up to 98% ee). Coupled with the Ramberg-B?cklund rearrangement, this reaction offers a novel route to chiral allylic and homoallylic compounds in excellent enantioselectivities (up to 97% ee) and high yields (up to 94%).