Total stepwise solid-phase synthesis of oligonucleotide-(3'-->N)-peptide conjugates

[structure: see text] An efficient total stepwise solid-phase synthesis of oligonucleotide-(3'-->N)-peptide conjugates is described that makes use of either a controlled pore glass support or macroporous polystyrene beads. Extending our previous homoserine linker approach, we prepared a range of conjugates containing one of four different cell or nuclear penetration peptides together with oligonucleotides containing 2'-deoxynucleoside or 2'-O-methylribonucleoside phosphodiesters, or gapmers containing 2'-deoxyphosphorothioates. The route also allows incorporation of a fluorescent label within the conjugate for cell uptake studies.     

A convenient route to 1-(2-oxiranyl)-1,4-diketones and their application to the synthesis of endo-brevicomin, endo-isobrevicomin, frontalin and related compounds via alkylated 6,8-dioxabicyclo[3.2.1]octan-2-ones

1-(2-Oxiranyl)-1,4-alkanediones were prepared from the ethylene acetals of ethyl 4-oxoalkanoates via the oxidation of the intermediate 1,2-dialkylcyclopropanols having a protected carbonyl group in an aliphatic chain. Intramolecular acetalization of these epoxy dicarbonyl compounds gave alkylated 6,8-dioxabicyclo[3.2.1]octan-2-ones in good yields. The latter were found suitable to be precursors for (±)-endo-brevicomin and its 2-hydroxy derivative, as well as (±)-endo-isobrevicomin and (±)-frontalin.     

Dichloro[N,N‐dimethyl‐1‐(1‐methyl‐1H‐tetrazol‐5‐yl‐κN4)methanamine‐κN]copper(II)

The title compound, [CuCl₂(C₅H₁₁N₅)], is the first structurally characterized molecular chelate complex involving an α‐­amino­alkyl­tetrazole. There are two complex mol­ecules in the asymmetric unit. The ligand mol­ecules are bidentate. Both Cu atoms reveal rather distorted square‐planar coordinations. The complex mol­ecules are linked together by van der Waals interactions only.     

Iron(III) dihydrogenphosphate(I)

The structure of rhombohedral (R) iron(III) tris­[di­hydrogen­phosphate(I)] or iron(III) hypophosphite, Fe(H₂PO₂)₃, has been determined by single‐crystal X‐ray diffraction. The structure consists of [001] chains of Fe³⁺ cations in octa­hedral sites with symmetry bridged by bidentate hypophosphite anions.     

Interaction of chromophore, 11-<Emphasis Type="Italic">cis</Emphasis>-retinal,with amino acid residues of the visual pigment rhodopsin in the region of protonated Schiff base: A molecular dynamics study

A molecular dynamics study of the dark adapted visual pigment rhodopsin molecule was carried out. The interaction of the chromophore group, 11-cis-retinal, with the nearest amino acid residues in the chromophore center of the molecule, namely, in the region of the protonated Schiff base linkage, was analyzed. Most likely, the interaction of the CH=NH bond with the negatively charged amino acid residue Glu113 cannot be described as a simple electrostatic interaction of two oppositely charged groups. One can propose that not only Glu113 but also Glu181 and Ser186 are involved in stabilization of the protonated Schiff base linkage. Accord-ing to calculations, Glu181 interacts, as the counter-ion, with the Schiff base indirectly via Ser186. The intramolecular mechanisms of protonated Schiff base stabilization in rhodopsin are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 19–27, January, 2007.     

X-ray, Raman and FTIRS studies of the microstructural evolution of zirconia particles caused by the thermal treatment

Genesis of the structure of zirconia particles prepared by precipitation of amorphous hydrated zirconia by ammonia from the ZrO(NO₃)₂ solution followed by a mild hydrothermal treatment (HTT) of precipitate, washing and calcination under air up to 1000 °C has been studied by X-ray diffraction (XRD), Raman and FTIRS. As revealed by FTIRS of lattice modes, the local structure of amorphous zirconia subjected to HTT is close to that in m-ZrO₂. This helps to obtain nearly single-phase monoclinic nanozirconia (particle size 5-15 nm) already after a mild calcination at 500 °C. Stability of this phase with nanoparticles sizes below the critical value determined by thermodynamic constraints is due to its excessive hydroxylation demonstrated by FTIRS. Dehydroxilation and sintering of these nanoparticles at higher (600-650 °C) temperatures of calcination leads to reappearance of the (111) “cubic” reflection in XRD patterns. Modeling of XRD patterns revealed that this phenomenon could be explained by polysynthetic (001) twinning earlier observed by HRTEM.     

Activation entropy of electron transfer reactions

We report microscopic calculations of free energies and entropies for intramolecular electron transfer reactions. The calculation algorithm combines the atomistic geometry and charge distribution of a molecular solute obtained from quantum calculations with the microscopic polarization response of a polar solvent expressed in terms of its polarization structure factors. The procedure is tested on a donor–acceptor complex in which ruthenium donor and cobalt acceptor sites are linked by a four-proline polypeptide. The reorganization energies and reaction energy gaps are calculated as a function of temperature by using structure factors obtained from our analytical procedure and from computer simulations. Good agreement between two procedures and with direct computer simulations of the reorganization energy is achieved. The microscopic algorithm is compared to the dielectric continuum calculations. We found that the strong dependence of the reorganization energy on the solvent refractive index predicted by continuum models is not supported by the microscopic theory. Also, the reorganization and overall solvation entropies are substantially larger in the microscopic theory compared to continuum models.     

Processes associated with ionic current rectification at a 2D-titanate nanosheet deposit on a microhole poly(ethylene terephthalate) substrate

Films of titanate nanosheets (approx. 1.8-nm layer thickness and 200-nm size) having a lamellar structure can form electrolyte-filled semi-permeable channels containing tetrabutylammonium cations. By evaporation of a colloidal solution, persistent deposits are readily formed with approx. 10-μm thickness on a 6-μm-thick poly(ethylene-terephthalate) (PET) substrate with a 20-μm diameter microhole. When immersed in aqueous solution, the titanate nanosheets exhibit a p.z.c. of − 37 mV, consistent with the formation of a cation conducting (semi-permeable) deposit. With a sufficiently low ionic strength in the aqueous electrolyte, ionic current rectification is observed (cationic diode behaviour). Currents can be dissected into (i) electrolyte cation transport, (ii) electrolyte anion transport and (iii) water heterolysis causing additional proton transport. For all types of electrolyte cations, a water heterolysis mechanism is observed. For Ca²⁺ and Mg²⁺ions, water heterolysis causes ion current blocking, presumably due to localised hydroxide-induced precipitation processes. Aqueous NBu₄⁺ is shown to ‘invert’ the diode effect (from cationic to anionic diode). Potential for applications in desalination and/or ion sensing are discussed.

     

Molybdenum triamidoamine complexes that contain hexa-tert-butylterphenyl, hexamethylterphenyl, or p-bromohexaisopropylterphenyl substituents. An examination of some catalyst variations for the catalytic reduction of dinitrogen

Three new tetramines, (ArNHCH(2)CH(2))(3)N, have been synthesized in which Ar = 3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3) (H(3)[HTBTN(3)N]), 3,5-(2,4,6-Me(3)C(6)H(2))(2)C(6)H(3) (H(3)[HMTN(3)N]), or 4-Br-3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H(2) (H(3)[pBrHIPTN(3)N]). The diarylated tetramine, [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(2), has also been isolated, and the "hybrid" tetramine [3,5-(2,4,6-t-Bu(3)C(6)H(2))(2)C(6)H(3)NHCH(2)CH(2)](2)NCH(2)CH(2)NH(4-t-BuC(6)H(4)) has been prepared from it. Monochloride complexes, [(TerNCH(2)CH(2))(3)N]MoCl, have been prepared, as well as a selection of intermediates that would be expected in a catalytic dinitrogen reduction such as [(TerNCH(2)CH(2))(3)N]Mo[triple bond]N and [[(TerNCH(2)CH(2))(3)N]Mo(NH(3))][BAr'(4)] (Ter = HTBT, HMT, or pBrHIPT and Ar' = 3,5-(CF(3))(2)C(6)H(3))). Intermediates that contain the new terphenyl-substituted ligands are then evaluated for their efficiency for the catalytic reduction of dinitrogen under conditions where analogous [HIPTN(3)N]Mo species give four turnovers to ammonia under "standard" conditions with an efficiency of approximately 65%. Only [pBrHIPTN(3)N]Mo compounds are efficient catalysts for dinitrogen reduction. The reasons are explored and discussed.     

Synthesis and crystal structure of ionic multicomponent complex: ([Cr(I)(PhH)(2)].+))(2)[Co(II)TPP(C(60)(CN)(2))]-[C(60)(CN)(2)](.-).3(o-C(6)H(4)Cl(2)) containing C(60)(CN)(2).- radical anion and sigma-bonded diamagnetic Co(II)TPP(C(60)(CN)(2)) -anion

The ionic multicomponent complex complex: ([Cr(I)(PhH)(2)].+))(2)[Co(II)TPP(C(60)(CN)(2))]-[C(60)(CN)(2)](.-).3(o-C(6)H(4)Cl(2)) (Co(II)TPP: cobalt (II) tetraphenylporphyrin; Cr(PhH)(2): bis(benzene)chromium; o-C(6)H(4)Cl(2): o-dichlorobenzene) containing CoTPP(C(60)(CN)(2)- anion and C(60)(CN)(2).- radical anion was obtained. The complex has the cage structure with channels, which accommodate Cr(I)(PhH)(2)(.+) and o-C(6)H(4)Cl(2) molecules. For the first time the sigma-bonding of Co(II)TPP to the fullerene radical anion with the essentially shortened Co.C(C(60)(CN)(2)) contact of 2.282 A is observed. The sigma-bonding results in the diamagnetism of Co(II)TPP(C(60)(CN)(2))(-) anion. The nonbonded C(60)(CN)(2)(.-) radical anion retains both the C(2)(v)symmetry and the shape of the molecule. The length of the C(triple bond)N bonds is 1.141 and 1.152 A.