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31.
The syntheses and the fluorescence properties of 7H‐3,6‐dihydro‐1,2,3‐triazolo[4,5‐d]pyrimidin‐7‐one 2′‐deoxy‐β‐D ‐ribonucleosides (=2′‐deoxy‐8‐azainosine) 3 (N3), 15 (N2), and 16 (N1) as well as of 1,2,3‐benzotriazole 2′‐O‐methyl‐β‐ or ‐α‐D ‐ribofuranosides 6 (N1) and 24 (N1) are described. Also the fluorescence properties of 1,2,3‐benzotriazole 2′‐deoxy‐β‐D ‐ribofuranosides 4 (N1) and 5 (N2) are evaluated. From the nucleosides 3 – 6 , the phosphoramidites 19, 26a, 26b , and 28 are prepared and employed in solid‐phase oligonucleotide synthesis. In 12‐mer DNA duplexes, compound 3 shows similar ambiguous base‐pairing properties as 2′‐deoxyinosine ( 1 ), while the nucleosides 4 – 6 show strong pairing with each other and discriminate very little the four canonical DNA constituents. 相似文献
32.
Amitava Choudhury Larisa A. Polyakova Ingo Hartenbach Thomas Schleid Peter K. Dorhout 《无机化学与普通化学杂志》2006,632(15):2395-2401
Four related quaternary compounds containing rare‐earth metals have been synthesized employing the molten flux method and metathesis. The reactions of Eu and Rb2S5 with Si and Ge in evacuated fused silica ampoules at 725 °C for 150 h yielded RbEuSiS4 ( I ) and RbEuGeS4 ( II ), respectively. On the other hand, a reaction between CeCl3 and K4Ge4Se10 at 650 °C for 148 h has yielded KCeGeSe4 ( III ) and KPrSiSe4( IV ) was obtained by the reaction of elemental Pr, Si and Se in KCl flux at 850 °C for 168 h. Crystal data for these compounds are as follows: I , orthorhombic, space group P212121 (#19), a = 6.392(1), b = 6.634(2), c = 17.001(3) Å, α = β = γ = 90°, Z = 4; II , monoclinic, space group P21/m (#11), a = 6.498(2), b = 6.689(3), c = 8.964(3) Å, β = 108.647(6)°, Z = 2; III , monoclinic, space group P21 (#4), a = 6.852(2), b = 7.025(2), c = 9.017(3) Å, β = 108.116(2)°, Z = 2; IV , monoclinic, space group P21 (#4), a = 6.736(2), b = 6.943(2), c = 8.990(1) Å, β = 108.262(2)°, Z = 2. The crystal structures of I ‐ IV contain two‐dimensional corrugated anionic layers of the general formula, [LnEQ4]? (Ln = Ce, Pr, Eu; E = Si, Ge and Q = S, Se) alternately piled upon layers of alkali cations. In addition to structural elucidation, Raman and UV‐visible spectroscopy, and magnetic measurements for compound III (KCeGeSe4) are also discussed. 相似文献
33.
By reaction of KC(2)H and K(2)Zn(CN)(4) in liquid ammonia, the diammoniate K(2)Zn(C(2)H)(4).2NH(3) was obtained. K(2)Cd(C(2)H)(4).2NH(3) was synthesized by reacting KC(2)H, Cd(NH(2))(2), and acetylene in liquid ammonia. The crystal structures of the air and temperature sensitive compounds were determined by X-ray single crystal diffraction at low temperatures (T = 170 K). Both compounds crystallize in the monoclinic space group I2/a (No. 15) with Z = 4. K(2)Zn(C(2)H)(4).2NH(3): a = 7.289(1) A, b = 12.765(2) A, c = 14.066(2) A, beta = 98.11(2) degrees. K(2)Cd(C(2)H)(4).2NH(3): a = 7.444(1) A, b = 12.619(3) A, c = 14.304(2) A, beta = 98.94(1) degrees. Characteristic structural motifs are tetrahedral [M(C(2)H)(4)](2-) fragments (M = Zn, Cd) and zigzag chains of edge sharing distorted (C(2)H)(6) octahedra centered by potassium ions. These zigzag chains are connected by a second type of crystallographically distinct potassium ions that also bind to two ammonia molecules. 相似文献
34.
Muegge I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(9):1976-1981
Drug discovery efforts rely increasingly on the identification of quality lead compounds through high-throughput synthesis and screening. However, large-scale random libraries have yielded only a low number of quality lead molecules. To address this shortcoming researchers have paid more attention to the concept of "drug-likeness" of molecules in combinatorial and screening libraries. Database profiling and analysis methods have been employed to identify the structural features of known drug molecules. Neural networks and machine learning methods help to distinguish between drugs and nondrugs. More recently, database-independent pharmacophore filters have been introduced that provide simple intuitive rules to classify potential drugs. 相似文献
35.
Structures of Bis(trifluoromethyl)halogeno and thiocyanato Mercurates, [Hg(CF3)2X]— (X = Br, I, SCN), and a Comparison of the Structural Parameters of the CF3 Groups [(18‐C‐6)K]2[Hg(CF3)2SCN]2 (1) and [P(CH3)(C6H5)3]2[Hg(CF3)2X]2 (X = Br (2) , I (3) ) are prepared and their crystal structures are determined. [(18‐C‐6)K]2[Hg(CF3)2SCN]2 (1) crystallizes in the monoclinic space group P21/c with Z = 2, [P(CH3)(C6H5)3]2[Hg(CF3)2Br]2 (2) in the monoclinic space group P21/n with Z = 2 and [P(CH3)(C6H5)3]2[Hg(CF3)2I]2 (3) in the triclinic space group P1¯ with Z = 1. In the solid state the three compounds form dimeric anions with planar Hg2X2 rings. The structural parameters of the Hg(CF3)2 units in the till now known bis(trifluoromethyl)halogeno mercurates are compared. In all compounds one nearly symmetric and one distorted CF3 group exist. The largest differences of the C—F bond lengths is found for [(18‐C‐6)K][Hg(CF3)2I]. This can be regarded as the experimental evidence for the properties of trifluoromethyl mercury compounds to act as excellent difluorocarbene sources in the presence of alkali iodides. 相似文献
36.
A reversed-phase LC–MS method with quadrupole-time of flight (QTOF) detection has been developed for the determination of four dinitro-toluenesulfonic acids and two amino-nitro-toluenesulfonic acids in groundwater. The analytes were separated by HPLC with 0.1% (v/v) formic acid as mobile phase modifier compatible with mass spectrometric detection. QTOF-MS analysis with negative ion electrospray ionization afforded good selectivity and sensitivity for analysis of the dinitro- and amino-nitro-toluenesulfonic acids. Structure elucidation and confirmation were accomplished by tandem mass spectrometry. Characteristic ions resulting from the loss of NO, NO2, and SO2 from the [M–H]– ions were detected. An intense fragment ion at m/z 80 representing the [SO3]– ion was detected for all dinitro- and amino-nitro-toluenesulfonic acids. Solid-phase extraction using a co-polymer cartridge was developed for preconcentration of the analytes from water. Good recovery (>85%) was achieved when 0.1% formic acid was added into the water samples before extraction. Method detection limits ranged from 10 to 76 ng L–1 for the targeted compounds when 10 mL water was analyzed. Groundwater samples collected from wells close to a former ammunition plant in Stadtallendorf, Germany, were analyzed for the dinitro- and amino-nitro-toluenesulfonic acids. 相似文献
37.
Alicia Reyes-Arellano Roland Boese Ingo Steller Reiner Sustmann 《Structural chemistry》1995,6(6):391-396
The crystal structures of molecular complexes betweenmeso- 1,2-diphenyl-1,2-ethanediol and two bisimines (N,N-(dibenzylidene)-ethylenediamine and glyoxylidene-bis(2,4-dimethyl-3-pentyl-amine) are reported at different temperatures. The structure-determining motif of the cocrystalline arrangement is one single O-H . N hydrogen bond resulting in infinite ladderlike polymers. The supramolecular structure is formed by recognition of fitting species: Thed- orl-isomers do not arrange in such structures.1H NMR experiments show that no prearrangements take place by forming complexes in solution. 相似文献
38.
Albrecht M Mirtschin S de Groot M Janser I Runsink J Raabe G Kogej M Schalley CA Fröhlich R 《Journal of the American Chemical Society》2005,127(29):10371-10387
The ligands 4-7-H(2) were used in coordination studies with titanium(IV) and gallium(III) ions to obtain dimeric complexes Li(4)[(4-7)(6)Ti(2)] and Li(6)[(4/5a)(6)Ga(2)]. The X-ray crystal structures of Li(4)[(4)(6)Ti(2)], Li(4)[(5b)(6)Ti(2)], and Li(4)[(7a)(6)Ti(2)] could be obtained. While these complexes are triply lithium-bridged dimers in the solid state, a monomer/dimer equilibrium is observed in solution by NMR spectroscopy and ESI FT-ICR MS. The stability of the dimer is enhanced by high negative charges (Ti(IV) versus Ga(III)) of the monomers, when the carbonyl units are good donors (aldehydes versus ketones and esters), when the solvent does not efficiently solvate the bridging lithium ions (DMSO versus acetone), and when sterical hindrance is minimized (methyl versus primary and secondary carbon substituents). The dimer is thermodynamically favored by enthalpy as well as entropy. ESI FT-ICR mass spectrometry provides detailed insight into the mechanisms with which monomeric triscatecholate complexes as well as single catechol ligands exchange in the dimers. Tandem mass spectrometric experiments in the gas phase show the dimers to decompose either in a symmetric (Ti) or in an unsymmetric (Ga) fashion when collisionally activated. The differences between the Ti and Ga complexes can be attributed to different electronic properties and a charge-controlled reactivity of the ions in the gas phase. The complexes represent an excellent example for hierarchical self-assembly, in which two different noncovalent interactions of well balanced strengths bring together eleven individual components into one well-defined aggregate. 相似文献
39.
Upon reacting P(4)S(3) with AgAl(hfip)(4) and AgAl(pftb)(4) [hfip = OC(H)(CF(3))(2); pftb = OC(CF(3))(3)], the compounds Ag(P(4)S(3))Al(hfip)(4) 1 and Ag(P(4)S(3))(2)(+)[Al(pftb)(4)](-) 2 formed in CS(2) (1) or CS(2)/CH(2)Cl(2) (2) solution. Compounds 1 and 2 were characterized by single-crystal X-ray structure determinations, Raman and solution NMR spectroscopy, and elemental analyses. One-dimensional chains of [Ag(P(4)S(3))(x)](infinity) (x = 1, 1; x = 2, 2) formed in the solid state with P(4)S(3) ligands that bridge through a 1,3-P,S, a 2,4-P,S, or a 3,4-P,P eta(1) coordination to the silver ions. Compound 2 with the least basic anion contains the first homoleptic metal(P(4)S(3)) complex. Compounds 1 and 2 also include the long sought sulfur coordination of P(4)S(3). Raman spectra of 1 and 2 were assigned on the basis of DFT calculations of related species. The influence of the silver coordination on the geometry of the P(4)S(3) cage is discussed, additionally aided by DFT calculations. Consequences for the frequently observed degradation of the cage are suggested. An experimental silver ion affinity scale based on the solid-state structures of several weak Lewis acid base adducts of type (L)AgAl(hfip)(4) is given. The affinity of the ligand L to the silver ion increases according to P(4) < CH(2)Cl(2) < P(4)S(3) < S(8) < 1,2-C(2)H(4)Cl(2) < toluene. 相似文献
40.
Bihlmeier A Gonsior M Raabe I Trapp N Krossing I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(20):5041-5051
The unexpected but facile preparation of the silver salt of the least coordinating [(RO)3Al‐F‐Al(OR)3]? anion (R=C(CF3)3) by reaction of Ag[Al(OR)4] with one equivalent of PCl3 is described. The mechanism of the formation of Ag[(RO)3Al‐F‐Al(OR)3] is explained based on the available experimental data as well as on quantum chemical calculations with the inclusion of entropy and COSMO solvation enthalpies. The crystal structures of (RO)3Al←OC4H8, Cs+[(RO)2(Me)Al‐F‐Al(Me)(OR)2]?, Ag(CH2Cl2)3+[(RO)3Al‐F‐Al(OR)3]? and Ag(η2‐P4)2+[(RO)3Al‐F‐Al(OR)3]? are described. From the collected data it will be shown that the [(RO)3Al‐F‐Al(OR)3]? anion is the least coordinating anion currently known. With respect to the fluoride ion affinity of two parent Lewis acids Al(OR)3 of 685 kJ mol?1, the ligand affinity (441 kJ mol?1), the proton and copper decomposition reactions (?983 and ?297 kJ mol?1) as well as HOMO level and HOMO–LUMO gap and in comparison with [Sb4F21]?, [Sb(OTeF5)6]?, [Al(OR)4]? as well as [B(RF)4]? (RF=CF3 or C6F5) the [(RO)3Al‐F‐Al(OR)3]? anion is among the best weakly coordinating anions (WCAs) according to each value. In contrast to most of the other cited anions, the [(RO)3Al‐F‐Al(OR)3] anion is available by a simple preparation in conventional inorganic laboratories. The least coordinating character of this anion was employed to clarify the question of the ground state geometry of the Ag(η2‐P4)2+ cation (D2h, D2 or D2d?). In agreement with computational data and NMR spectra it could be shown that the rotation along the Ag‐(P‐P‐centroid) vector has no barrier and that the structure adopted in the solid state depends on packing effects which lead to an almost D2h symmetric Ag(η2‐P4)2+ cation (0 to 10.6° torsion) for the more symmetrical [Al(OR)4]? anion, but to a D2 symmetric Ag(η2‐P4)2+ cation with a 44° twist angle of the two AgP2 planes for the less symmetrical [(RO)3Al‐F‐Al(OR)3]? anion. This implies that silver back bonding, suggested by quantum chemical population analyses to be of importance, is only weak. 相似文献