Structure of the mitochondrial URFA6L gene and tRNA(Lys) gene from CARP.

The carp mitochondrial URFA6L gene consists of 165 base pairs. The overall structural organization of the gene is very similar to that of the Xenopus URFA6L gene. Their nucleotide sequences exhibit 68% homology. The carp URFA6L gene encodes a protein of 54 amino acids. The amino acid composition of the protein is unusual because almost half of the residues consist of 5 hydrophobic amino acids (proline, tryptophan, leucine, isoleucine and tyrosine). A comparison between the amino acid sequences of 5 vertebrate URFA6L proteins and the yeast ATPase 8 showed that they have weak but very important common structural features, suggesting that the vertebrate URFA6L proteins may function as ATPase8. The nucleotide sequence of the lysine tRNA gene from carp has been determined and represented in clover-leaf secondary structure. Similar to amphibian and mammalian mitochondrial tRNA(Lys) genes, the carp mitochondrial tRNA(Lys) gene also has some unusual structural features as compared with its cytoplasmic counterpart. A comparison between the nucleotide sequences of the tRNA(Lys) gene from 7 vertebrates showed that the most conservative portions are the anticodon loop, nucleotides 8 and 9, the variable loop, the anticodon stem and the aminoacyl stem. The least conservative portions are the D-loop and the T-loop. These structural features may show that the mitochondrial tRNA(Lys) has a different interaction with mitochondrial ribosome.     

Effect of replacing a hydroxyl group with a methyl group on arsenic (V) species adsorption on goethite (alpha-FeOOH)

Arsenate and methylated arsenicals, such as dimethylarsinate (DMA) and monomethylarsonate (MMA), are being found with increasing frequency in natural water systems. The mobility and bioavailability of these arsenic species in the environment are strongly influenced by their interactions with mineral surface, especially iron and aluminum oxides. Goethite (alpha-FeOOH), one of the most abundant ferric (hydr)oxides in natural systems, has a high retention capacity for arsenic species. Unfortunately, the sorption mechanism for the species is not completely understood, which limits our ability to model their behavior in natural systems. The purpose of this study is to investigate the effect of replacing a hydroxyl group with a methyl group on the adsorption behaviors of arsenic (V) species using adsorption edges, the influence of the background electrolyte on arsenic adsorption, and their effect on the zeta potential of goethite. The affinity of the three species to the goethite surface decreases in the order of AsO4=MMA>DMA. The uptake of DMA and MMA is independent of the concentration of background electrolyte, indicating that both species form inner-sphere complexes on the goethite surface and the most charge of adsorbed DMA and MMA locates at the surface plane. Arsenate uptake increases with increasing concentrations of background electrolyte at pH above 4, possibly due to that the charge of adsorbed arsenate is distributed between the surface plane and another electrostatic plane. DMA and lower concentrations of MMA have small effect on the zeta potential, whereas the zeta potential of goethite decreases in the presence of arsenate. The small effect on zeta potential of DMA or MMA adsorption suggests that the sorption sites for the anions is not important in controlling the surface charge. This observation is inconsistent with most adsorption models that postulate a singly coordinated hydroxyls contributing to both the adsorption and the surface charge, but supports the thesis that the charge on the goethite surface comes primarily from protonation of the triply bound oxygen atoms on the surface.     

Synthesis and biophysical characterization of tRNA(Lys,3) anticodon stem-loop RNAs containing the mcm(5)s(2)U nucleoside

[reaction: see text] Phosphoramidite reagents of the naturally occurring modified nucleosides mcm(5)s(2)U and mcm(5)U were synthesized and along with pseudouridine were incorporated into 17-nucleotide lysine tRNA anticodon stem-loop domains. Standard RNA phosphoramidite coupling chemistry allowed us to systematically investigate the thermodynamic effects of nucleoside modification and to correlate thermodynamic trends with qualitative structure effects seen by NMR spectroscopy.     

Reactions of the ketone group in σ-ferrocenoyl methyl(π-cyclopentadienyl)dicarbonyliron

Russian Chemical Bulletin -     

Tacticity effects on the barriers to rotation of the ester methyl group in poly (methyl methacrylate): a deuteron magnetic resonance study

In isotactic poly(methyl methacrylate) (PMMA), we investigate the dynamics of the ester methyl groups by means of deuteron magnetic resonance (DMR) in a deuterated sample. We find that the motion of the CD(3)-group affects the deuteron spin-lattice relaxation as well as the DMR line shape in a characteristic way. Quadrupolar order spin lattice relaxation measurements between T=291 K and T=70 K reveal a broad temperature dependent probability distribution of autocorrelation times tau(c) for the 2pi/3 reorientation. This broad distribution corresponds to a temperature independent Gaussian distribution of activation energies rho(E(a)) with variance sigma(E(a) )=13.8+/-0.5 meV (1.33 kJ/mol). The line shape transition between T=70 K and T=23 K is explained with the freezing in of the methyl group reorientation. By comparing our results in an 88% isotactic sample with results obtained from a 50% syndiotactic, 30% atactic, and 20% isotactic sample of a previous investigation, we demonstrate the higher local order of the 88% isotactic sample, which corresponds to a ratio of 1.6 in the relative width sigma(E(a) )/E(a) of the E(a) distribution. We show that different stereospecific forms of PMMA can be easily distinguished by the characteristics of their line shape transition between T=70 K and T=23 K.     

Photocrosslinking of poly(methyl acrylate)s containing the 1,3-dioxolane structure as a pendant group

(2-Ethyl-2-methyl-1,3-dioxolan-4-yl)methyl- and (2-methyl-2-phenyl-1,3-dioxolan-4-yl) methyl acrylates were synthesized and polymerized. The photochemical behavior of the resulting polymers was investigated to determine whether the polymers pending on the 1,3-dioxolane structure were readily crosslinked with ultraviolet (UV) irradiation. The degree of crosslinking was estimated by the weight-loss method by immersion in acetone, with the result that the polymer with an aromatic substituent was more photocrosslinkable than the polymer that bore the aliphatic substituent. The catalytic effect on photocrosslinking of polymers was also studied by using benzoin and cobalt naphthenate. The infrared (IR) spectra of polymers irradiated in air that showed the new band at 3450 cm^?1 were attributed to a hydroxyl group; however, the spectra of polymers irradiated in vacuum displayed little absorption at 3450 cm^?1. To explain the mechanism of crosslinking model compounds were prepared and irradiated with UV light. It was concluded that crosslinking proceeds mainly from the fission of the 1,3-dioxolane ring and the coupling of the yielding radicals, together with autooxidation by atmospheric oxygen.     

Oxidation of peptides by methyl(trifluoromethyl)dioxirane: the protecting group matters

Representative Boc-protected and acetyl-protected peptide methyl esters bearing alkyl side chains undergo effective oxidation using methyl(trifluoromethyl)dioxirane (1b) under mild conditions. We observe a protecting group dependency in the chemoselectivity displayed by the dioxirane 1b. N-Hydroxylation occurs in the case of the Boc-protected peptides, and side chain hydroxylation takes place in the case of acetyl-protected peptides. Both are attractive transformations since they yield derivatized peptides that serve as valuable synthons.     

The effect of sidearm heteroatoms and a quaternary methyl group at the pivot position in lariat ethers

A methyl group geminal to the “pivot” carbon in hydroxy-methyl-derived lariat ethers dramatically enhances the binding afforded a complexed cation by the sidearm.     

The degradation of poly(methyl methacrylate) in the effect of negative thixotropy

An investigation of the degradation of poly(methyl methacrylate) in the case of negative thixotropy of its solutions in tricresyl phosphate showed that the number of polymer bonds broken by flow as expressed through the decrease of molecular weight in the course of the effect is determined by shear energy imposed on the system, irrespective of the velocity gradient and temperature used.     

The bis(trimethylsilyl)methyl group as an effective N-protecting group and site-selective control element in rhodium(II)-catalyzed reaction of diazoamides

The intramolecular rhodium(II)-carbenoid-mediated C-H insertion reaction of structurally varied N-bis(trimethylsilyl)methyl,N-substituted diazoamides is studied. It has been found that in tertiary diazoamides the N-bis(trimethylsilyl)methyl (N-BTMSM) group is effective for conformational control about the amide N-C(O) bond; C-H insertion occurs at the other N-substituent. In C(alpha)-branched diazoamides, the N-BTMSM is found also to exert its influence on the conformational preference about the N-C(alpha) bond, which affects the regioselectivity of the C-H insertion in these systems. In unbranched diazoamides, inherent electronic effects of the N-substituent affect the regio- and chemoselectivity of the reaction; however, in branched diazoamides, electronic effects of the N-substituent and the alpha-substituent at the carbenoid carbon are subtle, but important in the deciding the eventual outcome of the reaction.     

Decomposition of silver carbonate; the crystal structure of two high-temperature modifications of Ag(2)CO(3)

High-resolution powder diffraction was used to study the thermal transformation of silver carbonate. A sample of Ag(2)CO(3) was heated in a capillary under 4.5 atm CO(2) pressure. The decomposition temperature of silver carbonate to silver oxide is thereby increased, allowing high-resolution synchrotron X-ray powder diffraction patterns of the two high-temperature phases of Ag(2)CO(3) to be collected. The structure of the low-temperature (lt) phase was confirmed, and the structures of the two high-temperature phases were determined by direct methods and refined using the Rietveld method: lt-Ag(2)CO(3) (295 K) P2(1)/m, z = 2, a = 4.8521(2) A, b = 9.5489(4) A, c = 3.2536(1) A, beta = 91.9713(3) degrees; beta-Ag(2)CO(3) (453 K) P31c, z = 6, a = 9.1716(4) A, c = 6.5176(3) A; alpha-Ag(2)CO(3) (476 K) P6 macro 2m, z = 3, a = 9.0924(4) A, c = 3.3249(1) A. In addition, thermal expansion properties, anisotropic microstrain distributions, and thermal transformations of the three silver carbonate phases and silver oxide are described.     

Oxidative addition with methyl group transfer in Diplatinum complexes: Crystal structure of a bridged platinum(IV)-platinum(II) complex

Reactions of [Me₂Pt(μ-dmpm)₂PtMe₂], (dmpm = Me₂PCH₂PMe₂) with halogens, (X₂) or methyl iodide give the platinum(IV)-platinum(II) complexes [Me₃Pt(μ-X)(μ-dmpm)₂PtMe]X or [Me₃IPt(μ-dmpm)₂PtMe₂] respectively, and the former reactions involve methyl group transfer between the platinum atoms of the binuclear complex; one of the derivatives ([Me₃Pt(μ-I)(μ-dmpm)₂PtL]I₃, L = 1/2I + 1/2 Me) is characterized by an X-ray crystal structure determination.