Microwave-mediated synthesis and manipulation of a 2-substituted-5-aminooxazole-4-carbonitrile library

A 2-substituted-5-aminooxazole-4-carbonitrile library has been synthesised and modified via microwave-mediated and flow chemistries. One synthesised compound, 5-(1H-pyrrol-1-yl)-4-(1H-tetrazol-5-yl)-2-(thien-2-yl)oxazole, contains three distinct heterocycles attached to the central oxazole core, highlighting the structural diversity of this approach. Three oxazoles had micromolar k_i values against cannabinoid (CB1/CB2) receptors.     

Reactivity of divalent germanium alkoxide complexes is in sharp contrast to the heavier tin and lead analogues

The chemistry of β-diketiminate germanium alkoxide complexes has been examined and shown to be in sharp contrast to its heavier congeners. For instance, (BDI)GeOR (BDI = [{N(2,6-(i)Pr(2)C(6)H(3))C(Me)}(2)CH], R = (i)Pr, (s)Bu, (t)Bu) does not react with carbon dioxide to form a metal carbonate complex. Addition of aliphatic electrophiles, such as methyl iodide or methyl triflate, results in the net oxidative addition to the germanium, giving cationic tetravalent germanium complexes, [(BDI)Ge(Me)OR][X] (X = I, OTf). An examination of the contrasting reactivities of the alkoxide ligand and the germanium loan pair with Lewis acids yielded the unusual germanium(II)-copper(I) adduct, {μ(2)-Cu(2)I(2)}[(BDI)GeO(t)Bu](2). This complex not only displays a rare example of a divalent Ge-Cu bond, but is the first example in which a planar Cu(2)I(2) diamond core possesses a three-coordinate copper bound to another metal center.     

Complexes of lanthanide nitrates with tri tert butylphosphine oxide

Reaction of lanthanide nitrates with (t)Bu(3)PO (=L) lead to the isolation of complexes Ln(NO(3))(3)L(2)·H(2)O·nEtOH (Ln = La (1), Nd(2)), Ln(NO(3))(3)L(2)?·nEtOH (Sm(3), Eu(4)), and Ln(NO(3))(3)L(2) (Dy(5), Er(6), Lu(7)). These have been characterized by elemental analysis, infrared and NMR((1)H, (13)C and (31)P) spectroscopy and single-crystal X-ray diffraction. The structures show L to be positioned on opposite sides of the metal with the nitrates forming an equatorial band. When Ln = Dy, Er, and Lu two distinct molecules are present in the unit cell. A major isomer (70%) has a (P)O-Ln-O(P) angle of less than 180° with one of the nitrate ligands twisted out of the plane of the other nitrates while the lower abundance isomer is more symmetric with the (P)O-Ln-O(P) angle of 180° and the nitrate ligands coplanar giving a hexagonal bipyramidal geometry. These isomers cannot be observed by variable temperature solution (31)P NMR measurements but are clearly seen in the solid-state NMR spectrum of the Lu complex. Variable temperature solid-state NMR indicates that the isomers do not interconvert at temperatures up to 100 °C. Attempts to prepare cationic species [Ln(NO(3))(2)L(3)](+)[PF(6)](-) have not been totally successful and led to the isolation of crystals of Lu(NO(3))(3)L(2) and Tb(NO(3))(3)L(2).CH(3)CN (8).     

The Laser and Electrical Kerr Effect in Pentyloxy - Cyanobiphenyl

The optical and dc pulsed field Kerr effects have been measured in 5 OCB in the isotropic phase and in dilute solution. The pretransitional behaviour has been examined in terms of the Landau-de Gennes model. The constants of this formalism have been given and a possible optical shutter has been suggested.     

PHOTOISOMERISING EFFECTS IN NITROAZO FLEXOELECTRIC DIMERIC NEMATIC SYSTEMS

Abstract

The photoisomerisation of a flexoelectric chiral nematic bimesogen system dyed with an azo dye has been investigated. The host material has a pitch and field dependent tilt angle that are temperature independent. Upon illumination by ultra violet, the azo dye molecules undergo a shape change from their trans to cis isomer. The effect of the shape change of the dye on the mixture is to decrease the I-N* transition temperatures, to increase the response times and to decrease the transmitted optical intensity. For the same reduced temperatures, the tilt angles, pitch and threshold voltages for the transition from focal conic to homeotropic textures are unchanged. The macroscopic parameters observed suggest that the orientational order parameter of the system is reduced by UV illumination. The cis isomers do not appear to separate from the host material or significantly change the flexoelectric coefficient.     

PHOTOISOMERISING EFFECTS IN NITROAZO FERROELECTRIC DYE GUEST HOST SYSTEMS

Abstract

The effect of a photoisomerising dye in a ferroelectric liquid crystal host has been investigated. A nitroazo dye incorporating the same three-siloxane unit as an organosiloxane ferroelectric host has been used to insure good miscibility and high dye concentrations. The effect of photoisomerisation by 300–400 nm UV of up to 430 mW. cm^?2 has been investigated in two mixtures with 25% and 50% molar weight of dye. The 25% mixture has an I-SmC*-crystal phase sequence, while the 50% mixture has I-SmA*-SmC*-crystal. Transition temperatures of both the mixtures are reduced by increased UV illumination. For the first mixture at a constant temperature, the spontaneous polarisation in the ferroelectric phase is reduced by UV illumination. For the second mixture both the spontaneous polarisation and tilt angle of the SmC* phase are reduced by UV illumination and the phase is changed from SmC* to SmA* at temperatures close to the transition. The change of tilt angle and observations of micrograph textures indicate that this is a macroscopic change of the material rather than any phase separation of the dye and host materials.     

Semipinacol rearrangement of cis-fused β-lactam diols into keto-bridged bicyclic lactams

The 6-azabicyclo[3.2.1]octane ring system, prevalent in a range of biologically active molecules, is prepared through a novel semipinacol rearrangement utilizing a cyclic phosphorane or sulfite intermediate. The rearrangement proceeds with exclusive N-acyl group migration of a β-lactam ring and results in carbonyl functionality at the 7- and bridging 8-position of the bicycle. Precursor ring-fused β-lactam diols are prepared through a sequence of 4-exo trig carbamoyl radical cyclization, regioselective dithiocarbamate group elimination, and dihydroxylation.     

A new methodology for precise cadmium isotope analyses of seawater

Previous studies have revealed considerable Cd isotope fractionations in seawater, which can be used to study the marine cycling of this micronutrient element. The low Cd concentrations that are commonly encountered in nutrient-depleted surface seawater, however, pose a particular challenge for precise Cd stable isotope analyses. In this study, we have developed a new procedure for Cd isotope analyses of seawater, which is suitable for samples as large as 20 L and Cd concentrations as low as 1 pmol/L. The procedure involves the use of a ¹¹¹Cd–¹¹³Cd double spike, co-precipitation of Cd from seawater using Al(OH)₃, and subsequent Cd purification by column chromatography. To save time, seawater samples with higher Cd contents can be processed without co-precipitation. The Cd isotope analyses are carried out by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The performance of this technique was verified by analyzing multiple aliquots of a large seawater sample that was collected from the English Channel, the SAFe D1 seawater reference material, and several samples from the GEOTRACES Atlantic intercalibration exercise. The overall Cd yield of the procedure is consistently better than 85% and the methodology can routinely provide ε ^114/110Cd data with a precision of about ±0.5 ε (2sd, standard deviation) when at least 20–30 ng of natural Cd is available for analysis. However, even seawater samples with Cd contents of only 1–3 ng can be analyzed with a reproducibility of about ±3 to ±5 ε. A number of experiments were furthermore conducted to verify that the isotopic results are accurate to within the quoted uncertainty.     

Af+AB星型聚合体系的统计热力学

应用统计力学和热力学原理研究了 A_f+AB星型聚合体系的性质. 首先从两种不同的角度给出了与聚合反应相应的配分函数, 并据此得到反应体系的平衡自由能、质量作用定律及数量分布函数, 进而得到了体系的平衡状态方程和比热. 在此基础上, 以反应体系的回转半径为例研究了溶剂效应对星型高分子空间尺度的影响.     

硫铝酸盐水泥复合调凝剂的制备及其性能研究

为了有效地控制硫铝酸盐水泥的凝结时间, 研究了不同掺量葡萄糖酸钠、柠檬酸钠、硫酸铝及氢氧化锂在复掺和混掺条件下对硫铝酸盐水泥凝结时间和工作性能的影响. 结果表明: 在以一定比例复合的柠檬酸钠和葡萄糖酸钠二相体系中, 再加入水泥质量1%～3%的硫酸铝或0.4%～1.5%氢氧化锂制成的三相调凝体系, 可以更灵活有效地控制快硬硫铝酸盐水泥的初凝结时间, 并可以更好地改善硫铝酸盐水泥的工作性能及常温体积安定性.