Low-temperature radical polymerization of acrylamide in ethanol and glycerol under the action of molecular chlorine

It is shown by means of calorimetry, IR and EPR spectroscopy, elemental analysis, chromatography, and viscosimetry that radicals formed during the low-temperature action of molecular chlorine on acrylamide or its solutions in ethanol or glycerol initiate the polymerization reaction of acrylamide. It is established that during the low-temperature chlorination of pure acrylamide, polymerization takes place in the temperature range of 180–210 K with a polymer yield of ∼10%. The low-temperature chlorination of 20% solutions of acrylamide in ethanol or glycerol was performed to increase the product yield. It is shown that the low-temperature chlorination of acrylamide solution in glycerol increases the polymer yield by a factor of approximately two, and the content of chlorine in it falls by a factor of around ten. The low-temperature chlorination of acrylamide solution in ethanol did not lead to an increase in the polymer yield. A small reduction was noted in the chlorine content of the polymer.     

Protein phosphatase 2a (PP2A) binds within the oligomerization domain of striatin and regulates the phosphorylation and activation of the mammalian Ste20-Like kinase Mst3

Background

The repertoire of the antigen-binding receptors originates from the rearrangement of immunoglobulin and T-cell receptor genetic loci in a process known as V(D)J recombination. The initial site-specific DNA cleavage steps of this process are catalyzed by the lymphoid specific proteins RAG1 and RAG2. The majority of studies on RAG1 and RAG2 have focused on the minimal, core regions required for catalytic activity. Though not absolutely required, non-core regions of RAG1 and RAG2 have been shown to influence the efficiency and fidelity of the recombination reaction.

Results

Using a partial proteolysis approach in combination with bioinformatics analyses, we identified the domain boundaries of a structural domain that is present in the 380-residue N-terminal non-core region of RAG1. We term this domain the Central Non-core Domain (CND; residues 87-217).

Conclusions

We show how the CND alone, and in combination with other regions of non-core RAG1, functions in nuclear localization, zinc coordination, and interactions with nucleic acid. Together, these results demonstrate the multiple roles that the non-core region can play in the function of the full length protein.     

Photoisomerization of stilbene: a spin-flip density functional theory approach

The photoisomerization process of 1,2-diphenylethylene (stilbene) is investigated using the spin-flip density functional theory (SFDFT), which has recently been shown to be a promising approach for locating conical intersection (CI) points (Minezawa, N.; Gordon, M. S. J. Phys. Chem. A2009, 113, 12749). The SFDFT method gives valuable insight into twisted stilbene to which the linear response time-dependent DFT approach cannot be applied. In contrast to the previous SFDFT study of ethylene, a distinct twisted minimum is found for stilbene. The optimized structure has a sizable pyramidalization angle and strong ionic character, indicating that a purely twisted geometry is not a true minimum. In addition, the SFDFT approach can successfully locate two CI points: the twisted-pyramidalized CI that is similar to the ethylene counterpart and another CI that possibly lies on the cyclization pathway of cis-stilbene. The mechanisms of the cis--trans isomerization reaction are discussed on the basis of the two-dimensional potential energy surface along the twisting and pyramidalization angles.     

Polarization and fluence dependence of the polarized emission in nanosecond laser-induced breakdown spectroscopy

Several studies have appeared in the past two years reporting that the continuum emission produced by the laser ablation of solid materials is strongly polarized. In a paper that appears to conflict with these findings, Asgill et al. report that they did not observe a significant amount of polarization produced by nanosecond laser excitation of nitrogen gas and laser ablation of copper and steel ( M.E. Asgill, H.Y. Moon, N. Omenetto, D.W. Hahn, Investigation of polarization effects for nanosecond laser-induced breakdown spectroscopy, Spectrochim. Acta Part B (2010) xxx-xxx [7]). Here we show that the apparent discrepancy is resolved when laser fluence and polarization are taken into account. Using a 532 nm Nd:YAG laser to ablate Al samples in air, we find that the degree of polarization, P, of the continuum is greater for s- vs. p-polarized excitation and that P decreases with increasing fluence. We show that P would be < 10% under the conditions of Asgill et al., whereas P > 60% is obtained at low fluences with s-polarized excitation. We also confirm that at high fluence the polarization of the discrete emission is much smaller than that of the continuum.     

Physicochemical study of spiropyran-terthiophene derivatives: photochemistry and thermodynamics

The photochemistry and thermodynamics of two terthiophene (TTh) derivatives bearing benzospiropyran (BSP) moieties, 1-(3,3″-dimethylindoline-6'-nitrobenzospiropyranyl)-2-ethyl 4,4″-didecyloxy-2,2':5',2″-terthiophene-3'-acetate (BSP-2) and 1-(3,3″-dimethylindoline-6'-nitrobenzospiropyranyl)-2-ethyl 4,4″-didecyloxy-2,2':5',2″-terthiophene-3'-carboxylate (BSP-3), differing only by a single methylene spacer unit, have been studied. The kinetics of photogeneration of the equivalent merocyanine (MC) isomers (MC-2 and MC-3, respectively), the isomerisation properties of MC-2 and MC-3, and the thermodynamic parameters have been studied in acetonitrile, and compared to the parent, non-TTh-functionalised, benzospiropyran derivative, BSP-1. Despite the close structural similarity of BSP-2 and BSP-3, their physicochemical properties were found to differ significantly; examples include activation energies (E(a(MC-2)) = 75.05 kJ mol(-1), E(a(MC-3)) = 100.39 kJ mol(-1)) and entropies of activation (ΔS = 43.38 J K(-1) mol(-1), ΔS = 37.78 J K(-1) mol(-1)) for the thermal relaxation from MC to BSP, with the MC-3 value much closer to the unmodified MC-1 value (46.48 J K(-1) mol(-1)) for this latter quantity. The thermal relaxation kinetics and solvatochromic behaviour of the derivatives in a range of solvents of differing polarity (ethanol, dichloromethane, acetone, toluene and diethyl ether) are also presented. Differences in the estimated values of these thermodynamic and kinetic parameters are discussed with reference to the molecular structure of the derivatives.     

Architectures, mechanisms and molecular evolution of natural product methyltransferases

Covering: up to January 2012The addition of a methyl moiety to a small chemical is a common transformation in the biosynthesis of natural products across all three domains of life. These methylation reactions are most often catalysed by S-adenosyl-l-methionine (SAM)-dependent methyltransferases (MTs). MTs are categorized based on the electron-rich, methyl accepting atom, usually O, N, C, or S. SAM-dependent natural product MTs (NPMTs) are responsible for the modification of a wide array of structurally distinct substrates, including signalling and host defense compounds, pigments, prosthetic groups, cofactors, cell membrane and cell wall components, and xenobiotics. Most notably, methylation modulates the bioavailability, bioactivity, and reactivity of acceptor molecules, and thus exerts a central role on the functional output of many metabolic pathways. Our current understanding of the structural enzymology of NPMTs groups these phylogenetically diverse enzymes into two MT-superfamily fold classes (class I and class III). Structural biology has also shed light on the catalytic mechanisms and molecular bases for substrate specificity for over fifty NPMTs. These biophysical-based approaches have contributed to our understanding of NPMT evolution, demonstrating how a widespread protein fold evolved to accommodate chemically diverse methyl acceptors and to catalyse disparate mechanisms suited to the physiochemical properties of the target substrates. This evolutionary diversity suggests that NPMTs may serve as starting points for generating new biocatalysts.     

Vibrational spectroscopy as a probe of molecule-based devices

This critical review discusses the applicability of vibrational spectroscopic techniques, specifically Raman and mid-infrared, to the study of molecule-based electronics through a series of examples. We focus on a number of devices currently of interest, such as solar cells, organic light emitting diodes, molecular junctions, switches and transistors. Infrared and Raman spectroscopic techniques and their variations, the main focus of this article, can be used to investigate properties such as crystallinity, multiphasic distributions in three dimensions, as well as lifetimes, structures and energetics of excited-states on ultrashort to very long timescales (210 references).     

Four polyanionic compounds in the K–Au–Ga system: a case study in exploratory synthesis and of the art of structural analysis

The K-Au-Ga system has been investigated at 350 °C for <50 at. % K. The potassium gold gallides K(0.55)Au(2)Ga(2), KAu(3)Ga(2), KAu(2)Ga(4) and the solid solution KAu(x)Ga(3-x) (x = 0-0.33) were synthesized directly from the elements via typical high-temperature reactions, and their crystal structures were determined by single crystal X-ray diffraction: K(0.55)Au(2)Ga(2) (I, I4/mcm, a = 8.860(3) ?, c = 4.834(2) ?, Z = 4), KAu(3)Ga(2) (II, Cmcm, a = 11.078(2) ?, b = 8.486(2) ?, c = 5.569(1) ?, Z = 4), KAu(2)Ga(4) (III, Immm, a = 4.4070(9) ?, b = 7.339(1) ?, c = 8.664(2) ?, Z = 2), KAu(0.33)Ga(2.67) (IV, I-4m2, a = 6.0900(9) ?, c = 15.450(3) ?, Z = 6). The first two compounds contain different kinds of tunnels built of puckered six- (II) or eight-membered (I) ordered Au/Ga rings with completely different cation placements: uniaxial in I and III but in novel 2D-zigzag chains in II. III contains only infinite chains of a potassium-centered 20-vertex polyhedron (K@Au(8)Ga(12)) built of ordered 6-8-6 planar Au/Ga rings. The main structural feature of IV is dodecahedral (Au/Ga)(8) clusters. Tight-binding electronic structure calculations by linear muffin-tin-orbital methods were performed for idealized models of I, II, and III to gain insights into their structure-bonding relationships. Density of states curves reveal metallic character for all compounds, and the overall crystal orbital Hamilton populations are dominated by polar covalent Au-Ga bonds. The relativistic effects of gold lead to formation of bonds of greater population with most post-transition elements or to itself, and these appear to be responsible for a variety of compounds, as in the K-Au-Ga system.