Synthesis and photochemical properties of a light-activated fluorophore to label His-tagged proteins

Rapid and efficient light-induced fluorescence enhancement is demonstrated on a DMNPB-"caged" coumarin derivative carrying a His-tag recognition motif.     

Electrochemical study of the thermodynamics and kinetics of hydrophilic ion transfers across water | <Emphasis Type="Italic">n</Emphasis>-octanol interface

Thermodynamics and kinetics of hydrophilic ion transfers across water|n-octanol (W|OCT) interface have been electrochemically studied by means of novel three-phase and thin-film electrodes. Three-phase electrodes used for thermodynamics measurements comprise edge plane pyrolytic graphite, the surface of which was partly modified with an ultrathin film of OCT, containing hydrophobic lutetium bis(tetra-tert-butylphthalocyaninato) (Lu[tBu₄Pc]₂) as a redox probe. The transfers of anions and cations from W to OCT were electrochemically driven by reversible redox transformations of Lu[tBu₄Pc]₂ to chemically stable lipophilic monovalent cation and anion , respectively. Upon reduction of Lu[tBu₄Pc]₂, the transfers of alkali metal cations from W to OCT have been studied for the first time, enabling estimation of their Gibbs transfer energies. For kinetic measurements, a thin-film electrode configuration has been used, consisting of the same electrode covered completely with a thin layer of OCT that contained the redox probe and a suitable electrolyte. Combining the fast and sensitive square-wave voltammetry with thin-film electrodes, the kinetics of , , and Cl⁻ transfers have been estimated. Dedicated to Professor Dr. Yakov I. Tur’yan on the occasion of his 85th birthday.     

Solid phases of cyclopentane: combined experimental and simulation study

The phase diagram of cyclopentane has been studied by powder neutron diffraction, providing diffraction patterns for phases I, II, and III, over a range of temperatures and pressures. The putative phase IV was not observed. The structure of the ordered phase III has been solved by single-crystal diffraction. Computational modeling reveals that there are many equienergetic ordered structures for cyclopentane within a small energy range. Molecular dynamics simulations reproduce the structures and diffraction patterns for phases I and III and also show an intermediate disordered phase, which is used to interpret phase II.     

Trifluoromethylated enaminones and their explorative coordination chemistry with Cu(II): synthesis, redox properties and structural characterization of the complexes

The syntheses of three original trifluoromethylated enaminones L1H-L3H, an unexplored type of ligand with possible multiple coordination centres, their redox properties and explorative coordination chemistry with copper(II) are presented. The ability of these ligands to coordinate copper(II) and then to form new mono- and dinuclear complexes is presented and discussed. The consequences of this metal coordination on redox properties are also explored.     

Salarins a and B and tulearin a: new cytotoxic sponge-derived macrolides

Three novel nitrogenous macrolides designated salarin A and B (1 and 2) and tulearin A (3) were isolated from the Madagascar Fascaplysinopsis sp. sponge. The structures of the compounds were elucidated by interpretation of MS and 1D and 2D NMR spectra. Both salarins carry an acetylcarbamate moiety, and in addition, 1 contains a triacylamine group and 2 a methoxymethylketone lactam. Tulearin A carries the naturally rare carbamate ester. The compounds were found to be toxic to brine shrimp larvae, and salarin A and tulearin A were also cytotoxic to leukemia cells.     

Taumycins A and B, two bioactive lipodepsipeptides from the Madagascar sponge Fascaplysinopsis sp

Two closely related lipodepsipeptides, taumycins A and B (1 and 2) have been isolated from the Madagascar sponge Fascaplysinopsis sp. The two compounds have the same 12-membered oxodepsipeptide ring system in common. Both were toxic to brine shrimp larvae, and taumycin A (1 microM), but not taumycin B, inhibited growth of the human UT-7 leukemic cell line. The structure of the two compounds, likely to be derived from microorganisms, was established by MS and 1D and 2D NMR data.     

Property tuning in charge-transfer chromophores by systematic modulation of the spacer between donor and acceptor

A series of donor-acceptor chromophores was prepared in which the spacer separating 4-dimethylanilino (DMA) donor and C(CN)(2) acceptor moieties is systematically varied. All of the new push-pull systems, except 4 b, are thermally stable molecules. In series a, the DMA rings are directly attached to the central spacer, whereas in series b additional acetylene moieties are inserted. X-ray crystal structures were obtained for seven of the new, intensely colored target compounds. In series a, the DMA rings are sterically forced out of the mean plane of the residual pi system, whereas the entire conjugated pi system in series b is nearly planar. Support for strong donor-acceptor interactions was obtained through evaluation of the quinoid character of the DMA ring and by NMR and IR spectroscopy. The UV/Vis spectra feature bathochromically shifted, intense charge-transfer bands, with the lowest energy transitions and the smallest optical gap being measured for the two-dimensionally extended chromophores 6 a and 6 b. The redox behavior of the push-pull molecules was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). In the series 1 b, 2 b, 4 b, 5 b, in which the spacer between donor and acceptor moieties is systematically enlarged, the electrochemical gap decreases steadily from 1.94 V (1 b) to 1.53 V (5 b). This decrease is shown to be a consequence of a reduction in the D-A conjugation with increasing spacer length. Degenerate four-wave mixing experiments reveal high third-order optical nonlinearities, pointing to potentially interesting applications of some of the new chromophores in optoelectronic devices.     

Stereochemical preference of yeast epoxide hydrolase for the O-axial C3 epimers of 1-oxaspiro[2.5]octanes

The 1-oxaspiro[2.5]octane moiety is a common motif in many biologically active spiroepoxide compounds. Stereochemistry plays an important role in the action of these spiroepoxides, since the O-axial C3 epimers are predominantly responsible for biological activity. In view of this, the reactivity of the yeast epoxide hydrolase (YEH) from Rhodotorula glutinis towards both O-axial and O-equatorial C3 epimers of various 1-oxaspiro[2.5]octanes was investigated. O-axial C3 Epimers were hydrolyzed faster than the O-equatorial C3 epimers. The stereochemical preference was greatly dependent on the type of substitution on the cyclohexane ring. The preference of YEH for O-axial C3 epimers, found throughout this study, illustrates the effectiveness of YEH in enzymatic detoxification of spiroepoxides.     

On the trapping of Bjerrum defects in ice Ih: the case of the molecular vacancy

We present a density-function theory (DFT) study of Bjerrum-defect trapping centers involving the molecular vacancy in ice Ih. As a first step, we compute the intrinsic migration barrier to D-defect motion using the nudged elastic band (NEB) method and find them to be of the same order of magnitude as the energy barriers involving intrinsic L-defect motion. This finding suggests that intrinsic mobility factors cannot explain the experimentally observed inactivity of D defects, supporting the idea that D defects are trapped at other lattice-defect sites. Next we study the defect complexes formed by the combination of isolated D and L defects with a molecular vacancy. The corresponding geometries show that the formation of these aggregates significantly reduces elastic distortions that are present in isolated Bjerrum defects. An analysis of the energetics involved in the formation of both defect complexes reveals a significant binding energy, indicating that the molecular vacancy represents a strong trapping center for Bjerrum defects. On the other hand, the fact that there is no difference between the absolute values of the binding energies for both D and L defects suggests that the vacancy affects both species of Bjerrum defects in a similar fashion, possibly ruling out the vacancy trapping centers as an explanation for the experimentally observed inactivity of D defects.