A nanosecond molecular dynamics study of antiparallel d(G)(7) quadruplex structures: Effect of the coordinated cations

Nanosecond scale molecular dynamics simulations have been performed on antiparallel Greek key type d(G(7)) quadruplex structures with different coordinated ions, namely Na+ and K+ ion, water and Na+ counter ions, using the AMBER force field and Particle Mesh Ewald technique for electrostatic interactions. Antiparallel structures are stable during the simulation, with root mean square deviation values of similar to1.5 Angstrom from the initial structures. Hydrogen bonding patterns within the G-tetrads depend on the nature of the coordinated ion, with the G-tetrad undergoing local structural variation to accommodate different cations. However, alternating syn-anti arrangement of bases along a chain as well as in a quartet is maintained through out the MD simulation. Coordinated Na+ ions, within the quadruplex cavity are quite mobile within the central channel and can even enter or exit from the quadruplex core, whereas coordinated K+ ions are quite immobile. MD studies at 400 K indicate that K+ ion cannot come out from the quadruplex core without breaking the terminal G-tetrads. Smaller grooves in antiparallel structures are better binding sites for hydrated counter ions, while a string of hydrogen bonded water molecules are observed within both the small and large grooves. The hydration free energy for the K+ ion coordinated structure is more favourable than that for the Na+ ion coordinated antiparallel quadruplex structure.

Synthesis and electrical properties of the (PVA)(0.7)(Kl)(0.3)center dot xH(2)SO(4) (0 <= x <= 5) polymer electrolytes and their performance in a primary Zn/MnO2 battery

Solid acid polymer electrolytes (SAPE) were synthesised using polyvinyl alcohol, potassium iodide and sulphuric acid in different molar ratios by solution cast technique. The temperature dependent nature of electrical conductivity and the impedance of the polymer electrolytes were determined along with the associated activation energy. The electrical conductivity at room temperature was found to be strongly depended on the amorphous nature of the polymers and H2SO4 concentration. The ac (100 Hz to 10 MHz) and dc conductivities of the polymer electrolytes with different H2SO4 concentrations were analyzed. A maximum dc conductivity of 1.05 x 10(-3) S cm(-1) has been achieved at ambient temperature for electrolytes containing 5 M H2SO4. The frequency and temperature dependent dielectric and electrical modulus properties of the SAPE were studied. The charge transport in the present polymer electrolyte was obtained using Wagner's polarization technique, which demonstrated the charge transport to be mainly due to ions. Using these solid acid polymer electrolytes novel Zn/SAPE/MnO2 solid state batteries were fabricated and their discharge capacity was calculated. An open circuit voltage of 1.758V was obtained for 5 M H2SO4 based Zn/SAPE/MnO2 battery. (C) 2010 Elsevier Ltd. All rights reserved.

4-Azidomethyl-7-methyl-2-oxo-2H-chromene-6-sulfonyl azide

In the title compound, C11H8N6O4S, the plane of the coumarin aromatic ring is twisted by 17.2 (2)degrees with respect to the plane of the azide group bound to the methylene substituent, whereas it is twisted by 83.2 (2)degrees to the plane of the azide attached to the sulfonyl group. The crystal structure is stabilized by weak C-H center dot center dot center dot O interactions, leading to the formation of dimers with R-2(2)(12) graph-set motifs. These dimers are further linked by weak S-O center dot center dot center dot pi and pi-pi contacts centroid-centroid distance = 3.765 (2) angstrom], leading to the formation of a layered structure.

(2R,3R,4aS,6S,7S,8aS)-4a-Fluoro-8a-hydroxyperhydronaphthalene-2,3,6,7-te trayl tetraacetate

The title compound, C18H25FO9, exhibits a similar unit cell and packing to the alpha polymorph of axial 4a,8a-dihydroxyperhydronaphthalene-2,3,6,7-tetrayl tetraacetate. The carbonyl O atoms of two of the four acetate groups in the molecule are disordered over two sites with occupancy ratios of 0.59 (4):0.41 (4) and 0.57 (6):0.43 (6). Crystal packing is effected via intermolecular O-H center dot center dot center dot O hydrogen bonds, which link the tetraacetate molecules into tapes along the c axis.

Organometallic chemistry of diphosphazanes. Part 7. Platinum(II), palladium-(o), -(I) and -(II) complexes of RN[P(OPh)2]2(R = Me or Ph)

The reactions of [MCl2(cod)](M = Pd or Pt, cod = cycloocta-1,5-diene) with RN[P(OPh)2]2[R = Me (L1) or Ph (L2)] afford the chelate complexes [MCl2L1] and [MCl2L2]. The dinuclear palladium(O) complex, [Pd2L13] has been synthesized by starting from [Pd2(dba)3](dba = dibenzylideneacetone). Redox condensation of [Pd2(dba)3] and [PdCl2(PhCN)2] in the presence of the diphosphazane ligands gives the dinuclear palladium(I) complexes [Pd2Cl2L12] and [Pd2Cl2L22]. The structures of the complexes have been deduced from 1H and 31P NMR spectroscopic data. Single-crystal X-ray diffraction studies confirm the structures of [Pd2L13] and [Pd2Cl2L22].

Solvation and axial ligation properties of (2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrinato)zinc(II)

he solvation of (2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrinato)zinc(II)[Zn(obtpp)], in twelve different solvents results in large red shifts of the B and Q bands of the porphyrin accompanied by enhanced absorbance ratios of the Q bands. These observations are ascribed to the destabilisation of the highest occupied molecular orbital a2u of the porphyrin arising from a flow of charge from the axial ligand to the porphyrin ring through the zinc(II) ion. The binding constants of adducts of [Zn(obtpp)] with neutral bases have been found to be an order of magnitude greater than those observed for the corresponding adducts of (5,10,15,20-tetraphenylporphyrinato)-zinc and vary in the order piperidine > imidazole > pyridine > 3-methylpyridine > pyridine-3-carbaldehyde. The enhanced binding constants and large spectral shifts are interpreted in terms of the electrophilicity of [Zn(obtpp)] induced by the electron-withdrawing bromine substituents in the porphyrin core. The structure of [Zn(obtpp)(PrCN)2] has been determined; it reveals six-co-ordinated zinc(II) with two long Zn–N distance [2.51(4), 2.59(3)Å]. The porphyrin is non-planar and displays a saddle-shaped conformation.

Structure of pregna-4,16-diene-7[alpha],14[alpha]-diol-3,20-dione

7a,14a-Dihydroxypregna-4,16-diene-3,20- dione, C21H2804, M r = 344.45, orthorhombic, P212121, a = 7.136 (1), b = 12.342 (1), c = 20.049 (3)/k, V= 1765.7 (3)/k 3, Z = 4, Dx = 1.295 g cm -3, A(Cu Kte) = 1.5418/k, /z = 6.7 cm- a, F(000) = 744, T = 293 K, R = 0.048 for 1345 observations. The A ring may be described as in a l a,2flhalf- chair conformation or a l a-sofa conformation. The B and C rings adopt normal chair conformations and the D ring has a 14a-envelope conforma tion. The molecules are held together by a hydrogen bond [0(3)...0(7)= 2.767 A].

Synthesis of (±)-thaps-7(15)-ene and (±)-thaps-6-enes

The synthesis of (±)-3a,4,4,7a-tetramethylhydrindan-2-one 8, containing three contiguous quaternary carbons as present in thapsanes, and the total synthesis of thaps-7(15)-ene 6 and thaps-6-ene 7, probable biogenetic precursors of thapsanes, have been achieved. Thus, orthoester Claisen rearrangement of cyclogeraniol 14, followed by hydrolysis of the resultant ester 16 furnished the eneacid 13. Copper sulfate-catalysed intramolecular cyclopropanation of the diazo ketone 18, derived from the acid 13, generated the cyclopropyl ketone 12. Regiospecific reductive cleavage of cyclopropyl ketone 12 furnished the hydrindanone 8, whereas the diazo ketone 26 furnished the hydrindanone 28avia the cyclopropyl ketone 27. Wittig methylenation of the hydrindanone 28a furnished thaps-7(15)-ene 6, which on isomerisation gave thaps-6-ene 7. Allylic oxidation of thaps-6-ene furnished the thapsenone 31, a degradation product of the natural thapsane 1b.

Ground state geometric distortions Image distal substituent effects in determining the β-facial selectivity in 7-norbornenones

The X-ray structure of Image and MNDO optimized geometries of related 7-norbornenone derivatives show a clear tilt of the carbonyl bridge away from the C=C double bond. The preferred reduction from the more hindered face of the diester reveals the electron/electrostatic origin of π - facial selectivity in these systems. X-ray structure and MNDO calculations reveal the dominance of electronic effects in determining the π-facial selectivity in 4a.

The Zintl ion As-7](2-): an example of an electron-deficient As-x radical anion

K(2,2,2-crypt)](2)As-7]center dot THF, 1 (2,2,2-crypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo8.8.8]hexacosane) is the first well characterized seven-atom radical anion of group 15. UV-Vis spectroscopy confirms the presence and electronic structure of As-7](2-). Cyclic voltammetry in DMF solution shows the As-7(3) /As-7(2) redox couple as a one-electron reversible process. Theoretical investigations explore the bonding and properties of compound 1.

Bi2W1–xCuxO6–x(0.7[less-than-or-eq]x[less-than-or-eq]0.8): a new oxide-ion conductor

Anion-deficient Aurivillius phases of the general formula, Bi2Wi-xCuxO6-2x, possessing orthorhombic/tetragonal Bi2WO6-like structures, have been synthesized by quenching the oxide melts. The tetragonal phase stabilized for the compositions 0.7 less-than-or-equal-to x less-than-or-equal-to 0.8 is a good oxide-ion conductor in the temperature range 500-900 K, the x = 0.7 composition exhibiting the highest conductivity in the series.

Chiral Synthons from Carvone. Part 10. Synthesis of (+)-(1S,3S,4S,7S, 8R)-5,7-Dimethyl-10-oxatetracyclo-(5.3.0.03,5,04,8)decan-9-one.

Degradation of the tolyl group in the tricyclic ketone 1b followed by stereospecific reduction of the resultant ketoester (6) furnishes the title compound (4) containing a new tetracyclic framework, establishing the stereochemistry of the aryl group in 1.

Electrophilic additions to 7-methylenenorbornenes and 7- isopropylidenenorbornenes:can remote substituents swamp electrostatic control of π-face selectivity

pi-Face selectivities in electrophilic additiions (typically CCl2) to 7-methylenenorbornenes and 7-isopropylidenenorbornenes are modulated by endo-substituents.

Synthesis based on cyclohexadienes: Part 10 synthesis of 5,5-dimethyl-7-methoxy-4-oxatricyclo[4.3.1.0]decan-2-ones

Synthesis of 5, 5-dimethyl- 7-methoxy-4 -oxatricyclo[4,3,1,0(3,7)]- decan-2-one 3a, a novel heterocyclic ring system present in morellin 1, and its 3-substituted derivatives 3b-e, is described from the Diels-Alder adducts 7, available from 1-methoxycyclohexa-1,4-dienes 4. Two routes, which involved the halocyclisation and the oxidative addition, were investigated for the conversion of the adducts 7 into 3. While the halocyclisation method resulted in mixtures, excellent yields of the target molecule were obtained by the second method. Solvolysis of the bromoether 9 resulted in a mixture of rearranged products 10, 13, 15 and 16.