Absolute rates of hole transfer in DNA

Absolute rates of hole transfer between guanine nucleobases separated by one or two A:T base pairs in stilbenedicarboxamide-linked DNA hairpins were obtained by improved kinetic analysis of experimental data. The charge-transfer rates in four different DNA sequences were calculated using a density-functional-based tight-binding model and a semiclassical superexchange model. Site energies and charge-transfer integrals were calculated directly as the diagonal and off-diagonal matrix elements of the Kohn-Sham Hamiltonian, respectively, for all possible combinations of nucleobases. Taking into account the Coulomb interaction between the negative charge on the stilbenedicarboxamide linker and the hole on the DNA strand as well as effects of base pair twisting, the relative order of the experimental rates for hole transfer in different hairpins could be reproduced by tight-binding calculations. To reproduce quantitatively the absolute values of the measured rate constants, the effect of the reorganization energy was taken into account within the semiclassical superexchange model for charge transfer. The experimental rates could be reproduced with reorganization energies near 1 eV. The quantum chemical data obtained were used to discuss charge carrier mobility and hole-transport equilibria in DNA.     

Synthesis and Structure of [Fe(TPA)Cl2](ClO4) and [{Fe(TPA)Cl}2O](ClO4)2 Where TPA = Tris-(2-pyridylmethyl)amine

Journal of Chemical Crystallography - [Fe(TPA)Cl2](ClO4), where TPA is tris-(2-pyridylmethyl)amine, crystallizes in the orthorhombic space group P212121 with Z?=?4,...     

Combined Alkali‐Organoammonium Structure Direction of High‐Charge‐Density Heteroatom‐Containing Aluminophosphate Molecular Sieves

The charge density mismatch concept was applied to the synthesis of high‐charge‐density silicoaluminophosphate SAPO‐69 (OFF) and SAPO‐79 (ERI) and zincoaluminophosphate PST‐16 (CGS), PST‐17 (BPH), PST‐19 (SBS), and ZnAPO‐88 (MER) molecular sieves. Combined alkali‐organoammonium structure direction in these systems is thus enabled. Structure direction is treated from the perspective of stabilizing an ionic framework, the relationships between reaction charge density (OH^?/H₃PO₄), alkali and organoammonium content, and ionicity of tetrahedral framework atoms in successful structure direction are presented.     

Crosslinker Copolymerization for Property Control in Inverse Vulcanization

Sulfur is an underused by-product of the petrochemicals industry. Recent research into inverse vulcanization has shown how this excess sulfur can be transformed into functional polymers, by stabilization with organic crosslinkers. For these interesting new materials to realize their potential for applications, more understanding and control of their physical properties is needed. Here we report four new terpolymers prepared from sulfur and two distinct alkene monomers that can be predictively tuned in glass transition, molecular weight, solubility, mechanical properties, and color.     

Synthesis of Functional Monosilanes by Disilane Cleavage with Phosphonium Chlorides

The Müller–Rochow direct process (DP) for the large-scale production of methylchlorosilanes Me_nSiCl_4−n (n=1–3) generates a disilane residue (Me_nSi₂Cl_6−n, n=1–6, DPR) in thousands of tons annually. This report is on methylchlorodisilane cleavage reactions with use of phosphonium chlorides as the cleavage catalysts and reaction partners to preferably obtain bifunctional monosilanes Me_xSiH_yCl_z (x=2, y=z=1; x,y=1, z=2; x=z=1, y=2). Product formation is controlled by the reaction temperature, the amount of phosphonium chloride employed, the choice of substituents at the phosphorus atom, and optionally by the presence of hydrogen chloride, dissolved in ethers, in the reaction mixture. Replacement of chloro by hydrido substituents at the disilane backbone strongly increases the overall efficiency of disilane cleavage, which allows nearly quantitative silane monomer formation under comparably moderate conditions. This efficient workup of the DPR thus not only increases the economic value of the DP, but also minimizes environmental pollution.