Regio- and stereoselective reactions between cyclic Baylis-Hillman type adducts and N-nucleophiles and P-nucleophile

New important organic compounds multifunctionalized cyclic 6-membered and 7-membered allylic amines, azide and phosphonates have been obtained via regio- and diastereoselective reactions of cyclic Baylis-Hillman type adducts 1 with N-nucleophiles and P-nucleophile. We have found that the reactions proceed by S_N2 or S_N2′ processes exclusively, or by both processes simultaneously. The S_N2′ process occurs with anti stereochemistry.     

Chromium(III)-isonicotinate Complexes. Kinetics and Mechanism of Isonicotinate Ligand Liberation in HClO4 Solutions

Chromium(III)-isonicotinate complexes, cis-[Cr(C₂O₄)₂(N-inic)(H₂O)]^- and [Cr(C₂O₄)(H₂O)₃-OH-Cr(C₂O₄)₂(O-inic)]^-(N-inic)(H₂ (N-inic = N-bonded and O-inic = O-bonded isonicotinic acid) were obtained and characterized in solution. Kinetics of acid-catalyzed isonicotinate ligand liberation were studied spectrophotometrically in the 0.1–1.0 m HClO₄ range, at I=1.0 m. The dependencies of the pseudo-first order rate constant on [H⁺] were established: k_obs = k₀+k_HQ_H[H⁺] and k_obs = k_HQ_H[H⁺] for the N-inic and O-inic complex, respectively, where k₀ and k_H are the rate constants of the spontaneous and the acid-catalyzed reaction paths, and Q_H is the protonation constant of the carboxylic group in isonicotinic ligand. The obtained results indicate that N-bonded isonicotinic acid liberation occurs mainly via a spontaneous reaction path and is much slower than O-bonded inic liberation. The mechanisms for these processes are proposed.     

Codeposition of zinc with nickel from gluconate solutions

Journal of Solid State Electrochemistry - The codeposition of zinc and nickel from slightly acidic chloride, sulfate, and chloride-sulfate solutions containing a gluconate complexing agent was...     

Asymmetric elastic properties of Dictyostelium discoideum in relation to chemotaxis

In this study we used an AFM to investigate the cytoskeletal properties of live Dictyostelium discoideum cells by measuring the local stiffness across individual living cells. We have examined differences in elastic properties of polarized and unpolarized AX3 wild type and the mutant DAip1- cells, as well as the differences in the front and rear of the cells in relation to organization of the actin cytoskeleton. We found that the average Young's modulus increases upon polarization for the thin regions of the cell and that in polarized cells, the cell front was stiffer than the cell back. We also found that AX3 cells were stiffer than DAip1- cells. This finding suggests that actin polymerization is one of the major determinants of cell motility in Dictyostelium. In addition, a thin agarose film was studied as a model system to examine the influence of the substrate of thin materials probed with the AFM.     

Enantiodifferentiation of N-benzyloxycarbonylaminophosphonic and phosphinic acids and their esters using cyclodextrins by means of capillary electrophoresis

Capillary electrophoresis was successfully applied for separation of the enantiomers of N-benzyloxycarbonyl-alpha-aminophosphonic and alpha-aminophosphinic acids as well as their ethyl and phenyl monoesters with the use of a range of commercially available cyclodextrins (alpha, beta and hydroxypropyl-gamma-cyclodextrins) as chiral selectors. The dependence of effectiveness of separation on type and concentration of these chiral selectors as well as on pH of background electrolyte was examined in some detail.     

Amide hydrolysis reactivity of a N4O-ligated zinc complex: comparison of kinetic and themodynamic parameters with those of the corresponding amide methanolysis reaction

Treatment of the mononuclear amide-appended zinc complex [(ppbpa)Zn](ClO4)2 (1(ClO4)2) with Me4NOH.5H2O in CD3CN/D2O (3:1) results in the formation of the deprotonated amide species [(ppbpa-)Zn]ClO4 (2). Upon heating in CD3CN/D2O, this complex undergoes amide hydrolysis to produce a zinc carboxylate product, [(ambpa)Zn(O2CC(CH3)3)]ClO4 (3). X-ray crystallography, 1H and 13C NMR, IR, and elemental analysis were used to characterize 3. The hydrolysis reaction of 1(ClO4)2 exhibits saturation kinetic behavior with respect to the concentration of D2O. Variable-temperature kinetic studies of the amide hydrolysis reaction yielded DeltaH++ = 18.0(5) kcal/mol and DeltaS++ = -22(2) eu. These activation parameters are compared to those of the corresponding amide methanolysis reaction of 1(ClO4)2.     

A concise synthesis of the Pennsylvania Green fluorophore and labeling of intracellular targets with O6-benzylguanine derivatives

We report improved syntheses of the Pennsylvania Green and 4-carboxy-Pennsylvania Green fluorophores; the latter compound was prepared from methyl 4-iodo-3-methylbenzoate in a three-pot process (32% overall yield). Chinese hamster ovary cells expressing O6-alkylguanine-DNA alkyltransferase fusion proteins were treated with Pennsylvania Green and Oregon Green linked to O6-benzylguanine (SNAP-Tag substrates). Analysis of living cells by confocal microscopy revealed that Pennsylvania Green derivatives exhibit substantially higher cell permeability than analogous Oregon Green-derived molecular probes.     

Determination of pathogenic bacteria by CZE with surface-modified capillaries

The importance of electromigration techniques in molecular biology and medicine is increasing rapidly, especially in systematic studies on proteomes and metabolomes. Staphylococcus aureus and Escherichia coli are bacterial species most frequently encountered in human infections, and many serious illnesses can be observed in the hospital environment. In this contribution we proposed a CE method with different modification of internal capillary surface and with monolithic beds as a selective material for determination of bacteria in clinical samples. The electrophoretic separation depends on the differential mobility of bacteria in the capillary and selective interactions between bacterial cells and stationary phases (modified surface, monolithic beads). Proposed procedures could become an effective tool for diagnosis of certain diseases caused by S. aureus and E. coli as well as Proteus vulgaris.     

Chromium(III)-isocinchomeronato and quinolinato complexes: kinetic studies in NaOH solutions and effect on 3T3 fibroblast proliferation

The aquation of chromium(III)-isocinchomeronato and quinolinato complexes, mer-[Cr(icaH)₃]⁰ and mer-[Cr(quinH)₃]⁰ (where icaH⁻ and quinH⁻ are N,O-bonded isocinchomeronic and quinolinic acid anion, respectively) was studied in NaOH solutions. The process leads to successive ligand liberation in the fully deprotonated species. The kinetics of the first ligand liberation were studied spectrophotometrically in the visible region. A mechanism is proposed in which the rate of the chelate-ring opening at the Cr–N bond is much faster than the rate of the Cr–O bond breaking. The rate-determining step is described by the rate law: k _obs1 = k _OH(1) + k _O Q ₂ [OH⁻], where k _OH(1) and k _O are rate constants of the first ligand liberation from the hydroxo- and oxo-forms of the intermediate, respectively, and Q ₂ is an equilibrium constant between these two protolytic forms. The first pseudo-first-order rate constants (k _obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. The results are compared with those determined in acidic medium. Kinetics of the second and third ligand liberation were also studied and values of successive pseudo-first-order rate constants (k _obs2, k _obs3) are [OH⁻] independent. Effect of chromium(III)-quinolinato and isocinchomeronato complexes on 3T3 fibroblast proliferation was evaluated. Cytotoxicity of these complexes is low, suggesting they may be promising candidates as novel dietary supplements.     

Verteprofin conjugated to gold nanoparticles for fluorescent cellular bioimaging and X-ray mediated photodynamic therapy

Microchimica Acta - Photodynamic therapy (PDT) uses photosensitizers, light and molecular oxygen to generate cytotoxic reactive oxygen species. Its effectiveness is limited to <1 cm...