Enzyme-catalyzed kinetic resolution of N-Boc-trans-3-hydroxy-4-phenylpyrrolidine

The first enzyme-catalyzed kinetic resolution of tert-butyl-3-hydroxy-4-phenylpyrrolidine-1-carboxylate is presented. Enzyme, solvent and temperature optimization resulted in a new resolution method with E = 40 enantioselectivity. The acetate derivative of the (+)-(3S,4R) enantiomer formed while the (?)-(3R,4S) isomer remained intact. Very good enantioselectivities (E > 200) were achieved in the enzyme-catalyzed alcoholysis of the racemic acetate in i-propanol and t-butanol where the (+)-(3S,4R) enantiomer was prepared in pure form (ee > 99.7%). Absolute configuration of the (?)-(3R,4S)-enantiomer was determined by single crystal X-ray diffraction method.      

How does a hydrocarbon staple affect peptide hydrophobicity?

Water is essential for the proper folding of proteins and the assembly of protein–protein/ligand complexes. How water regulates complex formation depends on the chemical and topological details of the interface. The dynamics of water in the interdomain region between an E3 ubiquitin ligase (MDM2) and three different peptides derived from the tumor suppressor protein p53 are studied using molecular dynamics. The peptides show bimodal distributions of interdomain water densities across a range of distances. The addition of a hydrocarbon chain to rigidify the peptides (in a process known as stapling) results in an increase in average hydrophobicity of the peptide–protein interface. Additionally, the hydrophobic staple shields a network of water molecules, kinetically stabilizing a water chain hydrogen‐bonded between the peptide and MDM2. These properties could result in a decrease in the energy barrier associated with dehydrating the peptide–protein interface, thereby regulating the kinetics of peptide binding. © 2015 Wiley Periodicals, Inc.     

Potential of prodendronic polyamines with modulated segmental charge density as novel coating for fast and efficient analysis of peptides and basic proteins by CE and CE‐MS

In this work, the suitability of a new polymer family has been investigated as capillary coatings for the analysis of peptides and basic proteins by CE. This polymer family has been designed to minimize or completely prevent protein–capillary wall interactions and to modify the EOF. These coating materials are linear polymeric chains bearing as side cationizable moiety a dentronic triamine derived from N,N,N’,N’‐tetraethyldiethylenetriamine (TEDETA), which is linked to the backbone through a spacer (unit labeled as TEDETAMA). Four different polymers have been prepared and evaluated: a homopolymer which comprised only of those cationizable repetitive units of TEDETAMA, and three copolymers that randomly incorporate TEDETAMA together with neutral hydrosoluble units of N‐(2‐hydroxypropyl) methacrylamide (HPMA) at different molar percentages (25:75, 50:50 and 75:25). It has been demonstrated that the composition of the copolymers influences the EOF and therefore the separation of the investigated biopolymers. Among the novel polymers studied, poly‐(TEDETAMA‐co‐HPMA) 50:50 copolymer was successfully applied as coating material of the inner capillary surface in CE‐UV and CE‐MS, providing EOF reversing together with fast and efficient baseline separation of peptides and basic proteins. Finally, the feasibility of the polymer‐coated capillary was shown through the analysis of lysozyme in a cheese sample.     

Enhanced Photocatalytic Activity of MIL‐125 by Post‐Synthetic Modification with CrIII and Ag Nanoparticles

NH₂‐MIL‐125, [Ti₈O₈(OH)₄(bdc‐NH₂)₆] (bdc^2?=1,4‐benzene dicarboxylate) is a highly porous metal–organic framework (MOF) that has a band gap lying within the ultraviolet region at about 2.6 eV. The band gap may be reduced by a suitable post‐synthetic modification of the nanochannels using conventional organic chemistry methods. Here, it is shown that the photocatalytic activity of NH₂‐MIL‐125 in the degradation of methylene blue under visible light is remarkably augmented by post‐synthetic modification with acetylacetone followed by Cr^III complexation. The latter metal ion extends the absorption from the ultraviolet to the visible light region (band gap 2.21 eV). The photogenerated holes migrate from the MOF’s valence band to the Cr^III valence band, promoting the separation of holes and electrons and increasing the recombination time. Moreover, it is shown that the MOF’s photocatalytic activity is also much improved by doping with Ag nanoparticles, formed in situ by the reduction of Ag⁺ with the acetylacetonate pendant groups (the resulting MOF band gap is 2.09 eV). Presumably, the Ag nanoparticles are able to accept the MOF’s photogenerated electrons, thus avoiding electron–hole recombination. Both, the Cr‐ and Ag‐bearing materials are stable under photocatalytic conditions. These findings open new avenues for improving the photocatalytic activity of MOFs.     

Rapid determination of sterols in vegetable oils by CEC using methacrylate ester‐based monolithic columns

A method for the determination of sterols in vegetable oils by CEC with UV–Vis detection, using methacrylate ester‐based monolithic columns, has been developed. To prepare the columns, polymerization mixtures containing monomers of different hydrophobicities were tried. The influence of composition of polymerization mixture was optimized in terms of porogenic solvent, monomers/porogens and monomer/crosslinker ratios. The composition of the mobile phase was also studied. The optimum monolith was obtained with lauryl methacrylate monomer at 60:40% (wt:wt) lauryl methacrylate/ethylene dimethacrylate ratio and 60 wt% porogens with 20 wt% of 1,4‐butanediol (12 wt% 1,4‐butanediol in the polymerization mixture). Excellent resolution between sterols was achieved in less than 7 min with an 85:10:5 v/v/v ACN–2‐propanol–water buffer containing 5 mM Tris at pH 8.0. The limits of detection were lower than 0.04 mM, and inter‐day and column‐to‐column reproducibilities at 0.75 mM were better than 6.2%. The method was applied to the determination of sterols in vegetable oils with different botanical origins and to detect olive oil adulteration with sunflower and soybean oils.     

Application of X-ray fluorescence analytical techniques in phytoremediation and plant biology studies

Phytoremediation is an emerging technology that employs the use of higher plants for the clean-up of contaminated environments. Progress in the field is however handicapped by limited knowledge of the biological processes involved in plant metal uptake, translocation, tolerance and plant–microbe–soil interactions; therefore a better understanding of the basic biological mechanisms involved in plant/microbe/soil/contaminant interactions would allow further optimization of phytoremediation technologies. In view of the needs of global environmental protection, it is important that in phytoremediation and plant biology studies the analytical procedures for elemental determination in plant tissues and soil should be fast and cheap, with simple sample preparation, and of adequate accuracy and reproducibility. The aim of this study was therefore to present the main characteristics, sample preparation protocols and applications of X-ray fluorescence-based analytical techniques (energy dispersive X-ray fluorescence spectrometry—EDXRF, total reflection X-ray fluorescence spectrometry—TXRF and micro-proton induced X-ray emission—micro-PIXE). Element concentrations in plant leaves from metal polluted and non-polluted sites, as well as standard reference materials, were analyzed by the mentioned techniques, and additionally by instrumental neutron activation analysis (INAA) and atomic absorption spectrometry (AAS). The results were compared and critically evaluated in order to assess the performance and capability of X-ray fluorescence-based techniques in phytoremediation and plant biology studies. It is the EDXRF, which is recommended as suitable to be used in the analyses of a large number of samples, because it is multi-elemental, requires only simple preparation of sample material, and it is analytically comparable to the most frequently used instrumental chemical techniques. The TXRF is compatible to FAAS in sample preparation, but relative to AAS it is fast, sensitive and multi-elemental. The micro-PIXE technique requires rather expensive instrumentation, but offers multi-elemental analysis on the tissue and cellular level.     

Temperature-dependent 3-D CuI coordination polymers of calix[4]-bis-dithiacrown: crystal-to-crystal transformation and photoluminescence change on coordinated solvent removal

The temperature-dependent assembly of two 3-D CuI coordination polymers containing calix[4]-bis-thiacrown with different networking motifs are reported. Upon removal of the coordinated solvent molecules the initial solvent-coordinated polymer undergoes a unique single-crystal-to-single-crystal transformation to the desolvated polymer. Structural characteristics observed in the solvent-coordinated and the desolvated polymers also reveal related solvato-photolunimescence "off-on" behavior.