N(nPr)4[B5O6(OH)4][B(OH)3]2 and N(nBu)4[B5O6(OH)4][B(OH)3]2: Clathrates with a diamondoid arrangement of hydrogen-bonded pentaborate anions

Single-crystal X-ray structure analyses of N(nPr)₄[B₅O₆(OH)₄][B(OH)₃]₂,1, and N(nBu)₄ [B₅O₆(OH)₄][B(OH)₃]₂,2, reveal that these materials are novel clathrates, the isotypic host structures of which are three-dimensional assemblies of hydrogen-bonded [B₅O₆(OH)₄]^– ionsand B(OH)₃ molecules. The assembly of only the pentaborate anions is a distorted (i.e., along [102] elongated) fourconnected diamond-related network. The N(nPr) ₄ ⁺ and N(nBu) ₄ ⁺ ions are trapped within the complex three-dimensional channel systems of the host frameworks. Both1 and2 crystallize monoclinically with space groupP2₁/c andZ=4. The cell constants are:1:a=13.592(5),b=12.082(2),c=17.355(6) Å, =106.60(2)° (298K);2:a=13.874(3),b=12.585(1),c=17.588(4) Å, =107.04(1)° (238 K). The results obtained by both¹¹B and¹³C MAS NMR spectroscopy are discussed. Thermogravimetric studies under a flowing inert-gas atmosphere suggest that water, stemming from polycondensation of the hydrous borate species, is released from the clathrates at ca. 443 K (1) and 398 K (2) before the decomposition of the organic cations starts at ca. 603 K (1) and 603 K (2).Author for correspondence. Supplementary Data relating to this article are deposited with the British Library as supplementary publication No. SUP 82172 (82 pages).     

Molecular orbital studies on the conformation of GABA (γ-aminobutyric acid)

In distinction to Extended Hückel Theory which predicts as the most stable conformation of free zwitterionic GABA a totally extended form, PCILO and SCF ab initio studies show that the intrinsically preferred conformation of the isolated molecule is a highly folded one, resulting from strong interactions between the two charged ends. Computations are also carried out for hydrated GABA in the supermolecule approach allowing moreover for the flexibility of binding of some of the water molecules of the first hydration shell. They predict the coexistence in solution of a large number of conformations showing different degrees of folding (or extension), a result confirmed by recent NMR studies. This and a number of similar results show that we have to adapt our thinking on the role of conformations in pharmacological activity to this situation, which was frequently obscured by the more abundant results of X-ray crystallography yielding a single conformation.     

Intramolecular Diels—Alder reaction of 4-(N-furfuryl)aminobut-1-enes. New approach to the synthesis of 6,8a-epoxyoctahydroisoquinoline (3-aza-11-oxatricyclo[6.2.1.01,6]undec-9-ene) derivatives

The intramolecular Diels—Alder reaction of readily accessible 4-substituted 4-(N-furfuryl)aminobut-1-enes was studied and a new one-step method was developed for the synthesis of 6,8a-epoxy-1,2,3,4,4a,5,6,8a-octahydroisoquinoline (3-aza-11-oxatricyclo[6.2.1.0^1,6]undec-9-ene) derivatives. The [4+2]-cycloaddition proceeds stereoselectively to form exo-adducts. The influence of substituents at the nitrogen atom in 4-(N-furfuryl)aminobut-1-enes on the cycloaddition pathway was examined.     

A fluorimetric assay for cortisol

A simple, rapid and sensitive fluorimetric assay for the quantitative determination of cortisol is reported. The assay is based on the formation of a fluorescent dye when cortisol is incubated with a mixture of sulfuric acid and acetic acid. The fluorescence spectrum recorded for the resulting dye shows a maximum extinction at 475 nm and a maximum emission at 525 nm. The solvent 2-methyl-4-pentanone was used for extraction and was found to act as a fluorescence amplifier. A limit of detection of 2.7 μM was achieved, making it possible to forego solvent evaporation. The assay suffers minor interference from 11-deoxycortisol which exhibits low fluorescence at λ _ex: 460 nm; λ _em: 505 nm. Typical standard deviations were below 4%. We validated the assay using a biotransformation with recombinant Schizosaccharomyces pombe which regioselectively hydroxylates 11-deoxycortisol to cortisol. The method described herein is suitable for preliminary screening of microorganisms capable of steroid hydroxylation.     

SAPO—11分子筛用i—Pr2NH导向合成及其酸性研究

以ＡｌＰＯ４、Ｈ３ＰＯ４、ＳｉＯ２等为原料采用单一模板剂ｉＰｒ２ＮＨ合成了ＳＡＰＯ１１分子筛，利用Ａｖｒａｍｉ方程等对合成过程进行了定量描述。还利用红外（ＩＲ）、程序升温脱附（ＴＰＤ）、线性丁烯骨架异构反应催化活性测试等手段表征了ＳＡＰＯ１１的酸性。结果表明，合成过程随温度有明显变化，晶化阶段的活化能远高于核化阶段的值。可用Ａｖｒａｍｉ方程的参数来表征合成过程的难易程度。分子筛中存在Ｂ酸和Ｌ酸位，主要在中等强度范围，从而对线性丁烯骨架异构反应有较好的催化活性。提高分子筛中硅含量可明显增大酸位浓度，酸强度也有轻度增强。     

Synthesis of 6,13-Dihydroxyimino-5,12-Dimethyl- 7,14-Dioxo-1,4,8,11-Tetraazacyclotetradeca-4,11-Diene

6,13-Dihydroxyimino-5,12-dimethyl-7,14-dioxo-1,4,8,11-tetraazacyclotetradeca-4,11-diene 2 was prepared by condensation of ethyl α-oximinoacetoacetate with ethylenediamine in tetrahydrofuran at room temperature. Reduction of 2 gave the corresponding 6,13-dihydroxyimino-5,12-dimethyl-7,14-dioxo-1,4,8,11-tetraazacyclotetradecane 3 . Acylation of 2 afforded 6,13-bis(O-acetoxyimino)-5,12-dimethyl-7,14-dioxo-1,4,8,1 l-tetraazacyclotetradeca-4,11-diene 4 . The structures of 2 , 3 and 4 were determined by IR, NMR and mass spectroscopy.     

Synthesis, structure and physical properties of Ru ferrites: BaMRu5O11 (M=Li and Cu) and BaM′2Ru4O11 (M′=Mn, Fe and Co)

The synthesis, structure, and physical properties of five R-type Ru ferrites with chemical formula BaMRu₅O₁₁ (M=Li and Cu) and BaM′₂Ru₄O₁₁ (M′=Mn, Fe and Co) are reported. All the ferrites crystallize in space group P6₃/mmc and consist of layers of edge sharing octahedra interconnected by pairs of face sharing octahedra and isolated trigonal bipyramids. For M=Li and Cu, the ferrites are paramagnetic metals with the M atoms found on the trigonal bipyramid sites exclusively. For M′=Mn, Fe and Co, the ferrites are soft ferromagnetic metals. For M′=Mn, the Mn atoms are mixed randomly with Ru atoms on different sites. The magnetic structure for BaMn₂Ru₄O₁₁ is reported.     

Additions- und SubstitutionsReaktionen an Tetrafluor- und Tetrachlordiboran(4)

Addition and Substitution Reactions at Tetrafluoro- and Tetrachlorodiborane(4) From equimolar mixtures of B₂F₄ and Me_nN(SiMe₃)_3-n (n = 0–3) the mono-addition products 1–4 are formed at low temperatures. By elimination of Me₃SiF the adduct 2 gives the dimeric monosubstituted diborane 8 , which slowly decomposes at room temperature to the aminoborane 6 and (BF)_n. The course of the reactions was studied by means of ¹¹B and ¹⁹F NMR spectroscopy and by measuring the vapor pressures. According to the ¹¹B and ³¹P NMR spectra the reaction of B₂Cl₄ with PCl₅ or [Me₄N]Cl in liquid hydrogen chloride at 0°C does not yield [PCl₄]₂⁺[B₂Cl₆]^2? or [Me₄N]₂⁺[B₂Cl₆]^2? but gives [PCl₄]⁺[BCl₄]^?, PCl₃ and BCl₃ or [Me₄N]⁺[BCl₄]^? and BCl₃ besides (BCl)_n.     

Synthese und thermische Eigenschaften von molekularen Clusterverbindungen zusammengesetzt aus Elementen der Gruppen 11‐13‐16

Syntheses and Thermal Properties of Cluster Molecules, formed from Groups 11‐13‐16 Elements In the presence of PPh₃, CuX (X = Cl, CH₃COO) or AgOC(O)C₆H₅ and GaCl₃ react in THF with S(SiMe₃)₂ or Se(SiMe₃)₂ to yield [Cu₆Ga₈Cl₄S₁₃(PPh₃)₆] ( 1 ), [Cu₆Ga₈Cl₄Se₁₃(PPh₃)₆] ( 2 ), [Ag₆Ga₈Cl₄S₁₃(PPh₃)₆] ( 4 ) and [Ag₆Ga₈Cl₄Se₁₃(PPh₃)₆] ( 5 ). The use of PⁿPr₂Ph instead of PPh₃ and subsequent layering with n‐hexane leads to the formation of the cluster [Cu₆Ga₈Cl₄Se₁₃(PⁿPr₂Ph)₁₂] ( 3a , 3b ). Reaction of CuCl, GaCl₃ and PⁿPr₃ with Se(SiMe₃)₂ in THF results in the crystallisation of the ionic cluster (HPⁿPr₃)₂[Cu₂Ga₄Cl₄Se₆(PⁿPr₃)₄] ( 6 ). The structures of 1 — 6 were determined by X‐ray single crystal structure analysis. Thermogravimetric measurements of the cluster molecules and powder diffraction patterns of the remaining powders reveal the potential use of them as single source precursor compounds for the synthesis of the related ternary solid state materials.     

Comparison ofn-decane hydroconversion with Pt/SAPO-5 and Pt/SAPO-11 catalysts

The product distributions from bifunctional conversion ofn-decane over Pt/SAPO-5 and Pt/SAPO-11 catalysts are compared in detail. Selectivities in decane reaction vary largely with the catalyst employed: Pt/SAPO-11 produces high yields of feed isomers, whereas Pt/SAPO-5 gives high yields of cracked products and only under mild reaction conditions are isodecanes the main products obtained. These selectivities seem to be determined by the structure of the catalyst.