Mechanistic insight into protonolysis and cis-trans isomerization of benzylplatinum(II) complexes assisted by weak ligand-to-metal interactions. A combined kinetic and DFT study

Low-temperature NMR measurements showed that protonolysis and deuterolysis by H(D)X acids on meta- and para-substituted dibenzylplatinum(II) complexes cis-[Pt(CH(2)Ar)(2)(PEt(3))(2)] (Ar = C(6)H(4)Y(-); Y = 4-Me, 1a; 3-Me, 1b; H, 1c; 4-F, 1d; 3-F, 1e; 4-Cl, 1f; 3-Cl, 1g; 3-CF(3), 1h) in CD(3)OD leads directly to the formation of trans-[Pt(CH(2)Ar)(PEt(3))(2)(CD(3)OD)]X (4a-4h) and toluene derivatives. The reaction obeys the rate law k(obsd) = k(H)[H(+)]. For CH(2)Ar = CH(2)C(6)H(5)(-), k(H) = 176 ± 3 M(-1) s(-1) and k(D) = 185 ± 5 M(-1) s(-1) at 298.2 K, ΔH(double dagger) = 46 ± 1 kJ mol(-1) and ΔS(double dagger) = -47 ± 1 J K(-1) mol(-1). In contrast, in acetonitrile-d(3), three subsequent stages can be distinguished, at different temperature ranges: (i) instantaneous formation of new benzylhydridoplatinum(IV) complexes cis-[Pt(CH(2)Ar)(2)(H)(CD(3)CN)(PEt(3))(2)]X (2a-2h, at 230 K), (ii) reductive elimination of 2a-2h to yield cis-[Pt(CH(2)Ar)(CD(3)CN)(PEt(3))(2)]X (3a-3h) and toluene derivatives (in the range 230-255 K), and finally (iii) spontaneous isomerization of the cis cationic solvento species to the corresponding trans isomers (4a-4h, in the range 260-280 K). All compounds were detected and fully characterized through their (1)H and (31)P{(1)H} NMR spectra. Kinetics monitored by (1)H and (31)P{(1)H} NMR and isotopic scrambling experiments on cis-[Pt(CH(2)Ar)(2)(H)(CD(3)CN)(PEt(3))(2)]X gave some insight onto the mechanism of reductive elimination of 2a-2h. Systematic kinetics of isomerization of 3a-3h were followed in the temperature range 285-320 K by stopped-flow techniques. The process goes, as expected, through the relatively slow dissociative loss of the weakly bonded solvent molecule and interconversion of two geometrically distinct T-shaped three-coordinate intermediates. The dissociation energy depends upon the solvent-coordinating ability. DFT optimization reveals that along the energy profile the "cis-like" [Pt(CH(2)Ar)(PMe(3))(2)](+) intermediate is strongly stabilized by a Pt···η(2)-C1-C(ipso) bond between the unsaturated metal and benzyl carbons. The value of the ensuing stabilization energy was estimated by computational data to be greater than that found for similar β-agostic Pt···η(2)-CH interactions with alkyl groups containing β-hydrogens. An observed consequence of the strong stabilization of "cis"-[Pt(η(2)-CH(2)Ar)(PMe(3))(2)](+) is the remarkable acceleration of the rate of isomerization, greater than that produced by the so-called "β-hydrogen kinetic effect". Kinetic and DFT data concur to indicate that electron donation by substituents on the benzyl ring leads to further stabilization of the "cis"-[Pt(η(2)-CH(2)Ar)(PMe(3))(2)](+) cationic species.     

Development of new chromatographic tools based on A2A adenosine receptor subtype for ligand characterization and screening by FAC-MS

A liquid chromatographic stationary phase containing immobilized membranes from cells expressing A_2A adenosine receptor (A_2AAR) is firstly described. Cellular membranes from CHO cells stably transfected with human A_2AAR vector (A_2A(+)) and from the same cell line transfected with the corresponding empty vector (A_2A(?)) were entrapped on immobilized artificial membrane (IAM) support and packed into 6.6 mm I.D. glass columns to create A_2A(+)-IAM and A_2A(?)-IAM stationary phases. Frontal chromatography experiments on both A_2A(+)-IAM and A_2A(?)-IAM columns demonstrated the presence of a low specific interaction with the receptor. However, immobilized A_2A retained its ability to specifically bind known ligands as demonstrated by the agreement of the calculated K _d values with two different chromatographic protocols in comparison to previously reported data. In order to maximize the specific interaction, the same cellular membranes were immobilized on the inner surface of a silica capillary (40 cm?×?100 μm I.D.) by non-covalent interactions using the avidin–biotin coupling system to create two open tubular columns A_2A(+)-OT and A_2A(?)-OT. The open tubular system was characterized by ranking experiments for affinity studies in mixture useful for the selection of new potential candidates.

Photodegradation of Brilliant Green Dye by a Zinc bioMOF and Crystallographic Visualization of Resulting CO2

We present a novel bio-friendly water-stable Zn-based MOF (1), derived from the natural amino acid L-serine, which was able to efficiently photodegrade water solutions of brilliant green dye in only 120 min. The total degradation was followed by UV-Vis spectroscopy and further confirmed by single-crystal X-ray crystallography, revealing the presence of CO₂ within its channels. Reusability studies further demonstrate the structural and performance robustness of 1.     

Disordered Nanoporous Crystalline Modifications of Syndiotactic Polystyrene

Disordered crystalline modifications formed by s(2/1)2 helices of syndiotactic polystyrene (s-PS) can be prepared by the removal of bulky guest molecules from intercalate as well as from triclinic δ clathrate forms. The X-ray diffraction pattern of the disordered crystalline modification is characterized from 2θ_CuKα < 12° by only a broad diffraction peak whose maximum is located in the 2θ_CuKα range between 8.7° and 9.8°. Films presenting disordered crystalline modifications have been used for the removal of an organic pollutant from dilute aqueous solutions. The sorption behavior of the disordered crystalline modifications are compared with that of the nanoporous-crystalline δ form as well as of the dense γ form. The disordered crystalline modifications of s-PS presents pollutant (1,2-dichloroethylene) uptake comparable to those of the nanoporous δ and ε forms and much higher than those obtained for the dense γ form. Moreover, FTIR data relative to sorption of 1,2-dichloroethane show that the guest sorption occurs essentially only in the crystalline phase. As a consequence, the obtained disordered crystalline modifications of s-PS can be fully considered disordered nanoporous-crystalline modifications.     

Stereoselective synthesis of 2,3-unsaturated 1,6-oligosaccharides by means of a glycal-derived allyl epoxide and N-nosyl aziridine

beta-D-threo- and 4-deoxy-4-amino-alpha-D-erythro-hex-2-enopyranosyl di- (n = 0) and trisaccharides (n = 1) of types A and B were synthetized by means of a reiterative, completely stereoselective glycosylation process which makes use of the D-galactal-derived allyl epoxide 1beta and D-allal-derived allyl N-nosyl aziridine 2alpha, respectively.     

Balanced and strongly balanced Pk-designs

Given a graph $G$, a G-decomposition of the complete graph $K_v$ is a set of graphs, all isomorphic to $G$, whose edge sets partition the edge set of $K_v$. A $G$-decomposition of $K_v$ is also called a G-design and the graphs of the partition are said to be the blocks. A $G$-design is said to be balanced if the number of blocks containing any given vertex of $K_v$ is a constant.In this paper the concept of strongly balanced G-design is introduced and strongly balanced path-designs are studied. Furthermore, we determine the spectrum of those path-designs which are balanced, but not strongly balanced.     

Designing of sequencing assay assisted by capillary electrophoresis based on DNA folding analysis: an application to the VCAM1 gene

In this work, we describe a fast standardized molecular method for DNA sequencing assisted by capillary electrophoresis with a particular emphasis on bioinformatic approaches to avoid sequencing errors due to complex DNA regions. In this case, the method was applied on the human vascular adhesion molecule 1 (VCAM1) gene. VCAM1 sequence, in fact, shows many thermodynamically critical parameters such as very low GC content (30-40%), many nucleotide stack areas, i.e. hairpins, self-complementary regions. With a traditional primer design approach it was difficult to design correct PCR oligonucleotides, thus sometimes, the chromatogram showed an illegible profile. By a strategy involving various bioinformatic tools (Mfold, Oligo, Highter), we investigated the role of the DNA-folding analysis in the assistance of primer design for the DNA sequencing of fragments with high -ΔG stem-loop regions. This new approach allowed us to sequence nine different VCAM1 regions each containing the respective exon. Our results, based on different DNA samples recruited from oral brushes taken from ten different subjects, identified four different SNPs (c.662-7C/T, c.1793-79A>G, c.2079C/T, c.2208A>G) with high reproducibility.     

Accidental exposure to UV radiation produced by germicidal lamp: case report and risk assessment

Ultraviolet radiation is known to cause both benefits and harmful effects on humans. The adverse effects mainly involve two target organs, skin and eye, and can be further divided into short- and long-term effects. The present case report describes an accidental exposure of two health-care workers to ultraviolet radiation produced by a germicidal lamp in a hospital pharmacy. The germicidal lamp presented a spectrum with an intense UV-C component as well as a modest UV-B contribution. Overexposure to UV-C radiation was over 100 times as large as the ICNIRP exposure limits. A few hours after the exposure, the two subjects reported symptoms of acute UV injury and both of them continued having significant clinical signs for over 2 years. In this study, we describe acute and potentially irreversible effects caused by high UV exposure. In addition, we present the results of risk assessment by occupational exposure to germicidal lamps.