DNA electrochemistry through the base pairs not the sugar-phosphate backbone

Using intercalated, covalently bound daunomycin as a redox probe, ground state charge transport in DNA films with a perturbation in base pair stacking was examined in comparison with breaks in the sugar-phosphate backbone. While the introduction of one or even two nicks in the sugar-phosphate backbone yields no detectable effect on electron transfer, a CA mismatch significantly attenuates the electron transfer yield. These results confirm that the base pair stack is the pathway for DNA-mediated charge transfer, not the sugar-phosphate backbone.     

The proper structure of cubic ice confined in mesopores

To examine the reason for the formation and the structure of cubic ice in a restricted space, we measured the powder x-ray diffraction patterns of cubic ice formed within the mesopores of porous silicas as a function of pore size (4-70 nm). The results strongly suggest that cubic ice formed in the mesopores does not take a cubic structure as envisaged by Konig. It may be actually composed of very small crystallites of hexagonal ice that contains a large amount of growth faults depending on the crystallite size, that is, ice with disordered stacking sequence. Suppression of crystal growth of ice in the mesopores seems to be a vital factor for the formation and the stability of cubic ice.     

Selective binding of the cyano group in acrylonitrile adsorption on Si(100)-2 x 1

The covalent binding of acrylonitrile (CH(2)=CH-C triple bond N) and the formation of a C=C-C=N structure on Si(100) have been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and density functional theory (DFT) calculations. For chemisorbed acrylonitrile, the absence of nu(C triple bond N) at 2245 cm(-1) and the appearance of nu(C=N) at 1669 cm(-1) demonstrate that the cyano group directly participates in the interaction with Si(100), which is further supported by XPS and UPS observations. Our experimental results and DFT calculations unambiguously demonstrate a [2 + 2] cycloaddition mechanism for acrylonitrile chemisorption on Si(100) through the binding of C triple bond N to Si dimers. The resulting chemisorbed monolayer with a C=C-C=N skeleton can serve as a precursor for further chemical syntheses of multilayer organic thin films in a vacuum and surface functionalization for in situ device fabrication.     

Furan derivatives. Part 8 On substituent effects in the synthesis of 4,5-dihydro-3H-naphtho[1,8-bc]furans

4,5-Dihydro-3H-naphtho[1,8-bc]furans 4 and 6 which have various substituents (R¹ and R²) have been synthesized from 8-oxo-5,6,7,8-tetrahydro-1-naphthyloxyacetic acids 1 and 3 or their ethyl esters 2 . The reaction of acids 1 and 3 with sodium acetate in acetic anhydride gave a mixture of furans 4 and 6 and lactones 5 and 7 . The ratios of the products were varied according to the types of substituents (R¹ and R²) in acids 1 and 3 . As the substituent R¹ (R² = hydrogen) in acids 1 was changed from hydrogen to a methyl, ethyl or isopropyl group, production of furans 4 became more difficult. However, when a phenyl group was used as the substituent, furan 4 was obtained in good yield. Similarly, as the substituent R² (R¹ = hydrogen) in acids 1 was changed from hydrogen to a methyl, ethyl or isopropyl group, furan formation was more difficult. In contrast, acids 3 which had electron-withdrawing substituents such as chlorine, bromine or a nitro group at the 4-position afforded furans 6 in good yield. 4,5-Dihydro-3H-naphtho[1,8-bc]furans 4 and 4,5-dihydro-3H-naphtho[1,8-bc]furan-2-carbocylic acids 8 were synthesized from the reaction of esters 2 and potassium hydroxide in dioxane. When the substituents R¹ or R² in esters 2 were varied from hydrogen to a methyl, ethyl or isopropyl group the total yields of furans 4 and furancarboxylic acids 8 were reduced.     

Binding of brucine to human serum albumin

The feature of brucine binding to human serum albumin (HSA) was investigated via fluorescence and UV/vis absorption spectroscopy. The results revealed that brucine caused the fluorescence quenching of HSA by the formation of brucine–HSA complex. The hydrophobic interaction plays a major role in stabilizing the complex; the binding site number n and apparent binding constant K_A, corresponding thermodynamic parameters the free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) at different temperatures were calculated. The distance r between donor (HSA) and acceptor (brucine) was obtained according to fluorescence resonance energy transfer. The effect of brucine on the conformation of HSA was analyzed using synchronous fluorescence spectroscopy and UV/vis absorption spectroscopy.     

An alternate synthesis of 6-substituted-5-deazapteridines

A procedure for synthesis of 2,4-diamino-6-substituted-5-deazapteridines (pyrido[2,3-d]pyrimidines) is described. Condensation of 1-piperidino-1-propene with ethoxymethylenemalononitrile afforded an enamino malononitrile adduct, which when treated with ammonia yielded 2-amino-3-cyano-5-methylpyridine. Cyclization to 2,4-diamino-6-methyl-5-deazapteridine could be effected with guanidine. Similar condensation of piperidinopropene with ethyl methoxymethylenecyanoacetate followed by cyclization with hydroxylamine gave 2-amino-3-carbethoxy-6-methylpyridine 1-oxide. Reduction with phosphorus trichloride afforded the pyridine base, however, attempts to cyclize the amino ester to 2-amino-4-hydroxy-6-methyl-5-deazapteridine were unusccessful.     

Synthesis and Crystal Structure of a Novel Compound of （C2N2H8O2） H6V10O28

A novel vanadate decamer, involving all vanadium atoms present in +5 oxidation and one formhydroxamic acid dimer cation readical, has been synthesized. The single-crystal X-ray diffraction shows that the orange crystal is formed in the triclinic system, space group Pi, a = 8. 4960 (17), b = 10.447 (2), c = 11.299 (2) A, α= 68. 82 (3)°,β= 87.35 (3)°, γ = 66.97(3)°. V = 855. 3(3) A3, Z = 8, R1 = 0. 0857, wR2=0. 2551. X-ray crystallographic and packing in superlattice studies showed that the crystal structure was constructed by electrostatic attraction of O-H…O hydrogen bonds between formhydroxamic acid dimer cation and decavanadate polyanion. Formhydroxamic acid dimer is got through controlling the condition of the reaction using formhydroxamic acid.     

甲烷在Mo/HZSM-5催化剂上的脱氢聚合反应

对不同Mo含量的Mo／HZSM－5催化剂的结构进行了表征，并对这些催化剂的甲烷非氧气氛下的转化反应进行了考察．催化剂的BET比表面积及酸性随Mo含量的增加而降低，当Mo含量大于5％时，Mo对ZSM－5分子筛的晶型有影响，并出现MoO3物相．甲烷在700℃时可高选择性地生成苯和乙烯，最佳Mo含量大约为2％．纯的MoO3或HZSM－5上该反应几乎不进行，因此，可能是分散的钼氧离子和分子筛的酸中心是甲烷转化的活性中心，只有二者的协同作用才能促进甲烷的转化．反应后催化剂中的钼物种被还原了．催化剂上的积炭可能是催化剂失活的主要原因之一，烧炭后催化剂活性基本恢复．     

Dynamic structural change of a twisted hexaporphyrin complex by highly specific molecular recognition

The highly specific molecular recognition of a twisted hexaporphyrin complex, tris[5,5'-bis[5,10,15-tris[methoxy(ethoxy)(2)carbonylethyl]porphyrinatozinc(II)]-2,2'-bipyridine]ruthenium(II) chloride (2), is described. Complex 2 has two trisporphyrin binding sites and can bind two triamines, tris(2-aminoethyl)amine (3) (K(1) = 3.0 x 10(8) M(-1), K(2) = 3.0 x 10(7) M(-1)), 1,1,1-tris(aminomethyl)ethane (4) (K(1) = 2.0 x 10(7) M(-1), K(2) = 1.4 x 10(6) M(-1)), tris(3-aminopropyl)amine (5) (K(1) = 3.5 x 10(6) M(-1), K(2) = 6.0 x 10(6) M(-1)), and 1,3,5-tris(aminomethyl)benzene (6) (K(1) = 2.9 x 10(6) M(-1), K(2) = 1.2 x 10(6) M(-1)), strongly with its torsional motion. The 1:2 complex between 2 and the best fit triamine 3 showed the nature of the specific rigid structure in the UV-vis, fluorescence, and (1)H NMR spectra and isothermal titration calorimetry (ITC) measurements.