The direct electrochemical synthesis of neutral and anionic halogen complexes of uranium(IV) and uranium(VI)

The electrochemical oxidation of anodic uranium into acetonitrile solutions of X₂ (X = Cl, Br) under nitrogen gives rise to UCl₄·4CH₃CN or UBr₄·2CH₃CN in good yield. These compounds are easily converted to other UX₄ adducts. In the presence of oxygen, solutions of UO₂X₂ are produced by the electrolysis, and the parent halide, or neutral addition compounds, are readily obtained from these. Addition of R₄NX to the cell results in the direct synthesis of (R₄N)₂UX₆ under nitrogen, or (R₄N)₂UO₂X₄ under oxygen. The only iodo compound which could be formed by electrolysis into N,N- dimethylformamide (=dmf) was UI₄·4dmf.     

N,N-diisopropylcarboxylic acid amide complexes of thorium(IV) and uranium(IV) N-thiocyanates; the crystal structure of tetraisothiocyanato tetrakis(N,N-diisopropylacetamide-O)uranium(IV)

The complexes M(NCS)₄·xL (x = 2, M = U, L = Me₃CCON(Prⁱ)₂(dippva); x = 3, M = Th, L = Me₂CHCON(Prⁱ)₂(dipiba) and dippva, M = U, L = EtCON(Pr¹)₂(dippa), dipiba and dippva; x = 4, M = Th, L = MeCON(Prⁱ)₂(dipa), dippa and dipiba, M = U, L = dipa, dippa) and the solvates M(NCS)₄·4dipa·CH₂Cl₂ (M = Th, U) have been prepared. Their i.r. and u.v.-visible (M = U only) spectra are reported. The crystal and molecular structure of U(NCS)₄(dipa)₄· CH₂Cl₂ has been determined by the heavy-atom method from X-ray diffractometer data and refined by least squares to R 0.029 for 1135 independent reflections. The crystal is tetragonal, space group P$\text{4}$2₁c, with Z = 2, a = 15.663(4) and c = 10.512(3) Å. The coordination geometry about the 8-coordinate uranium atom is dodecahedral with the N atoms of the NCS groups occupying the dodecahedral A sites and the ‘dipa’ O atoms the B sites. The bonding distances of UO and UN are 2.363(8), and 2.444(11) Å respectively.     

Crystal structure of the low-dimensional uranium pentatelluride: UTe5

The crystal structure of UTe₅ (a = 17.915(5), b = 10.407(3), c = 4.220(2) Å, Pnma, Pn2₁a, Z =4) was refined from 822 intensities with I>3σ(I) to a conventional R factor of 0.060. The uranium coordination polyhedron is a three capped tellurium trigonal prism, and all the Te atoms are involved in TeTe bonds. The structure is built up with infinite chains of prisms stacked in the $\text{c}$ direction. The chains are linked into (b, c) layers by a single Te atom which exhibits some positional disorder.     

The geometry of the thioester group and its implications for the chemistry of acyl coenzyme A

L-929 cell surface membranes were incubated with S-adenosyl-l-[methyl-³H]-methionine and found to contain phosphatidylethanolamine: S-adenosylmethionine N-methyltransferase (phosphatidylethanolamine N-methyltransferase) activity. The enzyme or combination of enzymes responsible for this activity methylated endogenous phosphatidylethanolamine and its methylated derivatives to yield phosphatidyl-N-monomethylethanolamine, phosphatidyl-N,N-dimethylethanolamine, and phosphatidylcholine. Maximum enzyme activity was expressed at pH 6.9, the reaction was not dependent on the presence of divalent cations, and exogenously added phospholipids did not stimulate the rate of reaction. Phospholipid methylation was inhibited by S-adenosyl-l-homocysteine and by local anaesthetic drugs such as chlorpromazine and tetracaine which partition into the lipid bilayer. Control experiments demonstrated that the surface membrane-associated methyltransferase activity was not due to contamination of surface membrane preparations with intracellular membranes. Surface membranes were found to have higher specific methyltransferase activities than whole L-cell homogenates or endoplasmic reticulum-enriched microsomes. The low rate of methyltransferase function expressed in vitro (approximately 1 pmol/min · mg protein) suggests that phospholipid methylation is not a major metabolic source of surface membrane phosphatidylcholine.     

The chemistry of rhenium and technetium. Part III. The synthesis and characterisation of oxo-bis-(tetrathiomolybdenato)-technetium(V) and its reduction by triphenylphosphine

The Complexes (Bu₄N)[TcO(MoS₄)₂] and Tc- (PPh₃)₂(MoS₄)₂ were prepared. The former complex has a much lower Tc-O stretching frequency than is generally found gor the TcO³⁺. moiety. The latter technetium(IV) Complex was obtained by the reduction of Tc^(v) O(MoS₄)₂^? with triphenylphosphine and also by the substitution reaction of TcCl₄(PPh₃)2 with MoS₄^2-. Previous reductions of this nature have led to the isolation of species that differ by two formal oxidation state numbers from the oxidant.     

On the protein crystal chemistry of chloroplatinite ions: general principles and interactions with triose phosphate isomerase

K₂[PtCl₄] has been used to prepare isomorphous derivatives of the majority of proteins for which detailed structure determinations have been published. As the derivatives were prepared under a wide variety of solvent conditions they include a number of chemically different platinum-protein complexes.New observations on the binding of K₂[PtCl₄] to crystalline chicken muscle triose phosphate isomerase are reported which, together with a review of its binding to other proteins and chemical considerations, provide a rational framework for understanding the reactions of this complex salt with crystalline proteins in the presence of various mother liquors. Means by which the reaction may be controlled are also discussed.     

Preparation and properties of hydrated uranium(III) complex chlorides. Part I. Uranium trichloride heptahydrate

The synthesis of uranium trichloride heptahydrate together with some of its structural, spectroscopic and magnetic properties is reported. The compound possesses the triclinic lattice of LaCl₃·7H₂O (space group P$\text{1}$). Controlled vacuum thermal dehydration of the substance enabled the preparation of the anhydrous trichloride in gram quantities. Magnetic susceptibilities of polycrystalline samples were measured by the Faraday method in the 6.5–295 K range. The uranium trichloride heptahydrate follows in this region the Curie-Weiss law with C = 1.0839 emu K mol^?1 and θ = ?32.7 K.     

Coordination chemistry of higher oxidation states. Part 15. Cobalt(III) complexes of bi- and multi-dentate phenylphosphines

Six-coordinate cobalt(III) complex trans-[Co{o-C₆H₄(PPh₂)₂}₂X₂]ClO₄, fac-[Co{PhP(CH₂CH₂PPh₂)₂}X₃],cis-[Co{P(CH₂CH₂PPh₂)₃}X₂]ClO₄ and cis-β-[Co{-CH₂P(Ph)CH₂CH₂PPh₂}₂X₂]PF₆ (X = Cl, Br) have been prepared by halogen oxidation of the Co(II) analogues, and characterised by IR, electronic and ³¹P NMR spectroscopy. The failure to obtain complexes with X = I, and with some related ligands is discussed, and the rather low stability of the above complexes is rationalised in terms of steric crowding at the metal centre.     

Solution chemistry and Mössbauer study of iron(II) and iron(III) complexes from gallocyanine

The iron solution chemistry of the FeCl₃-gallocyanine system has been investigated by pH titration, UV visible spectroscopy and Mössbauer spectroscopy. Iron reduction was found in the pH range 2–5 and photo-reduction of the iron(III) present was also noted. Due to the instability of the species present in solution, the use of gallocyanine as a spectrophotometric indicator in iron systems is not encouraged. The iron-gallocyanine system was proposed as a potential model of the photosensitive anti-cancer drug, Bleomycin.     

The preparation,spectral studies,and the crystal structure of dimethylbis(O-ethylxanthato)tin(IV)

Tin-119 NMR data indicate that the tin atom in (CH₃)₂Sn(S₂COC₂H₅)₂ is four co-ordinated in dichloromethane solution. However, single crystal X-ray analysis shows the tin atom to be six co-ordinated in the solid state in which the bidentate xanthate ligands display gross asymmetry in their mode of co-ordination to the tin. The crystals are molecular and there is no association between neighbouring molecules. The unit cell of Me₂Sn(exa)₂ is orthorhombic, Pnma, a = 14.165(1), b = 7.675(9), c = 13.977(2) Å with Z = 4. The structure was refined by conventional least squares methods with final R 0.041 and R_w 0.043 for 1229 unique reflections with 1 ? 2σ(I).     

Strong and symmetric halogen bonding in coordination compounds of carboxylic acid derivatives; the crystal structure of (3,6-dithiaoctanedioato-S,S′-(3,6-dithiaoctanedioic acid-S,S′)-copper(I) redetermined at 173 K

3,6-dithianoctanedioic acid forms a Cu(I) compound in which electrical neutrality is achieved by elaborate hydrogen bonding and sharing on protons. The title compund crystallizes in the monoclinic space group P2/n with Z = 2. Unit-cell parameters are a = 11.625(2), b = 7.664(1), c = 9.874(2) Å, β = 95.16°, D_m = 1.80(2), D_c = 1.83 g cm^?3. The structure was solved by means of standard direct methods and refined with full-matrix least-squares techniques to an R-value of 0.026 (R_w = 0.042). The Cu(I) ion is tetrahedrally coordinated by four thioether S-atoms (CuS = 2.29–2.33 Å). The molecules are linked by very strong hydrogen bonds between non-coordinating carboxylate groups in such a way that the average number of acidic hydrogens per molecule is three. One of these hydrogens lies on a twofold axis and forms a short symmetrical hydrogen bond, with a OO distance of 2.441(2) Å. Unusual features in the infrared spectrum of this compund can be interpreted on the basis of the observed crystal structure.     

Fatty acid synthetase, malic enzyme and other NADP+ binding dehydrogenases have similar antigenic determinant(s) at the NADPH binding domain

The sequence of tryptic and chymotryptic peptides from cytosolic and mitochondrial rabbit liver serine hydroxymethyltransferase are compared to the proposed sequence of a protein coded for by the glyA gene of Escherichia coli. The E. coli glyA gene is believed to code for serine hydroxymethyltransferase. Extensive sequence homology between these peptides were found for the proposed E. coli enzyme in the aminoterminal two-thirds of the molecule. All three proteins have identical sequences from residue 222-231. This sequence is known to contain the lysyl residue which forms a Schiff's base with pyridoxal-P in the two rabbit liver enzymes. These results support the interpretation that the proposed sequence of E. coli serine hydroxymethyltransferase is correct. The data also show that cytosolic and mitochondrial serine hydroxymethyltransferase are homologous proteins.     

The A protomer of islet-activating protein,pertussis toxin,as an active peptide catalyzing ADP-ribosylation of a membrane protein

Islet-activating protein (IAP), pertussis toxin, is an oligomeric protein composed of an A protomer and a B oligomer. IAP and its A protomer were equipotent, on a molar basis, in enhancing GTP-dependent adenylate cyclase activity and in causing ADP-ribosylation of the 41,000 M_r protein when directly added to the cell-free membrane preparation from rat C6 glioma cells. Similar actions of IAP observed upon its addition to intact C6 cells were not mimicked by its A protomer, indicating that the A protomer had to be associated with the B oligomer to become accessible to its site of action on the inner surface of the membrane of intact cells. The A protomer, but not IAP, exhibited NAD-glycohydrolase activity in the reaction mixture lacking cellular components but containing dithiothreitol. Their actions on membranes were not accelerated by dithiothreitol, but markedly suppressed by oxidized glutathione. Thus, C6 cell membranes may possess certain “processing” enzyme(s) responsible for releasing the A protomer from the IAP molecule and for reductive cleavage of an intrachain disulfide bond in the released protomer, thereby producing an active peptide which functions to cause ADP-ribosylation of one of the subunits of guanine nucleotide regulatory protein in the receptor-adenylate cyclase system.     

Antigen presentation in the rat: role of a nonadherent, nonphagocytic, W3/13, OX-6 positive T cell in the presentation of antigen to primed T lymphocytes

The nature of accessory cells in rat lymph nodes which can present antigen to primed T cells was investigated. Removal of adherent, phagocytic cells from antigen-primed lymph node cells by passage over glass-bead and nylon wool columns followed by treatment with carbonyl iron did not abrogate the antigen-specific proliferative response to keyhole limpet hemocyanin (KLH) or to the synthetic polypeptide L-glutamic acid-L-alanine-L-tyrosine (GAT). This T cell-enriched population was free of contaminating macrophages as determined by latex bead ingestion and morphological criteria during a 4-day culture period. Treatment of the T cell preparation with rabbit anti-rat IgG and complement or rosetting with IgG-coated sheep erythrocytes to remove any remaining B cells or macrophages did not significantly affect the proliferative response to antigen. Analysis of the T cell preparation by panning techniques with monoclonal antibodies to T cell surface markers suggested that both the responding T cell and the antigen-presenting cell were positive for the rat T cell marker, W3/13. The KLH-primed LN T cell-enriched fraction contained two distinct cell populations that were separable on the basis of their reactivity to OX-6 antibody. Two populations, an OX-6+ and an OX-6-, interacted synergistically in a KLH-dependent in vitro proliferative response. The cells within the T cell-enriched fraction that were positive for the OX-6 marker functioned primarily as the APCs, while the OX-6- cell fraction contained cells that proliferated to antigen when OX-6+ cells from either the T cell fraction or the adherent fraction were present. The implications of these findings are discussed.     

Bacteriophage lambda DNA maturation. The functional relationships among the products of genes Nul, A and FI

The FI gene of bacteriophage λ functions in head assembly, but its exact role is not well understood. FI mutants are leaky, producing between 0.1 and 0.5 viable particles per infected cell. In order to investigate the function of the FI product (gpFI) in vivo, mutants of λ were isolated that are able to grow in the absence of gpFI. These mutants, called fin (for FI independence) map in the region of gene Nul and the beginning of gene A.Proteins made in cells infected with the fin mutants were labelled with [³⁵S]methionine and analysed by polyacrylamide gel electrophoresis. In addition, the levels of activity of the A product were measured in the in vitro DNA packaging assay. As a result of these experiments, the fin mutants can be classified in two groups. Upon infection, fin mutants of one group selectively produce three to fivefold more gpA than do wild-type phage fin mutants of the second group do not overproduce any λ late gene product detectable by the autoradiographic technique.gpA overproducers can also be isolated by selecting for λAam Wam phages that can plate on a weak suII cell strain. The mutation responsible for this pseudoreversion is called Aop and maps in the Nu1-A region. Aop is also a fin mutation, since its presence in λFI^? enables it to plate on non-permissive hosts.Therefore, it seems that one condition sufficient for normal growth of FI^? phage is the overproduction of gpA. The nature of the fin mutations that do not result in gpA overproduction is discussed.     

One-electron photooxidation of porphyrins at low temperature

The π-cation radicals of the metalloporphyrins magnesium octaethylporphyrin (MgOEP), magnesium tetraphenylporphyrin (MgTPP), and zinc tetraphenylporphyrin (ZnTPP), as well as the free base porphyrins of tetratolylporphyrin (H₂TTP) and tetraphenylporphyrin (H₂TPP) have been formed at liquid nitrogen temperatures in a rigid matrix of alkyl chloride glasses containing CCl₄ or 1,1,2,2-tetrachloroethane (TCE), following photolysis of the porphyrins with visible light. The reaction proceeds via electron transfer from the photoexcited porphyrin to the solvent molecules; the efficiency of thie electron transfer may be qualitatively evaluated in terms of electron tunneling in the solid matrices. This is the first report of the photochemical formation of a free base porphyrin π-cation radical species.     

The role of grafted skin in the regeneration of X-irradiated axolotl limbs

The primary aim of these experiments was to follow the cells descended from limb skin through the process of limb regeneration to determine what range of differentiations these cells may assume. Triploid hindlimb or forelimb skin was grafted to the denuded thighs of diploid host axolotls that had previously received 3000 R of X irradiation across both hindlimbs and the intervening pelvic area. The host limbs were then amputated through their grafts and permitted to regenerate. Cartilage, perichondrium, joint connective tissue, general connective tissue, dermis, and epidermis were present in all the regenerated limbs, but only 10% of the regenerates contained muscle. Tabulation of nucleolar numbers showed that the majority of cells in each regenerated tissue originated from the grafted skin. A strong correlation was demonstrated between the forelimb or hindlimb origin of the skin grafts and the number of digits regenerated.