Synthesis of 4-Alkyl-4-alkoxybutenolides Having Unsaturated Side Chains via Chromium Carbene Complex Photochemistry: (+)-Cerulenin

The photochemical reaction between optically active ene carbamates and chromium alkoxycarbene complexes containing unsaturated aliphatic side chains was further developed. Although remote olefinic groups, including conjugated dienes, were tolerated, a homoallylic side chain underwent intramolecular reaction to give a strained cyclobutanone. (+)-Cerulenin was synthesized utilizing the photochemical reaction of an alkynylcarbene complex with an optically active ene carbamate and the bis(pi-crotyl)nickel halide alkylation of a vinyl bromide as key steps.     

Electrophilic fluorinating reagent mediated synthesis of fluorinated alpha-keto Ethers,benzil, and 6,6'-dialkoxy-2,2'-bipyridines

Interactions of various fluorinated and nonfluorinated alcohols with trans-stilbene in the presence of electrophilic reagents were studied. Under neat conditions, reactions of trans-stilbene (1) with fluorinated alcohols, R(f)OH (R(f) = CF3CH2-, CFH2CH2-, CF3CF2CH2-, CF2H(CF2)3CH2-, (CF3)2CH-, (CF3)3C- (2a-f) in the presence of an electrophilic reagent, 1-(chloromethyl)-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor) or N,N-difluoro-2,2'-bipyridinium bis(tetrafluoroborate) (MEC-31), gave alpha-keto ethers (3a-f) and benzil (4) in good to moderate yields. alpha-Keto ether and benzil formation was very much dependent on the reaction time, the degree of fluorination of the alcohols, and whether a solvent such as CH3CN, DMF or DMA was utilized. In solution, alpha-keto ethers and benzil did not form. Interestingly, under neat conditions, nonfluorinated alcohols, ROH (R = CH3-, CH3CH2-, CH3CH2CH2-, CH3CH2CH2CH2-, CH3CH2CH2CH2CH2CH2-) (5g-k) did not react with trans-stilbene in the presence of MEC-31 but gave 6,6'-dialkoxy-2,2'-bipyridines (6g-k), regioselectively, in excellent isolated yields. On the other hand, fluorinated alcohols did not react with MEC-31. Reaction of MEC-31 with an excess of diethylene glycol (7) gave the bipyridine derivative (8) in 88% isolated yield. Reaction of 8 either with diethylaminosulfur trifluoride (DAST) or bis(2-methoxyethyl)aminosulfur trifluoride (Deoxofluor) readily produced the corresponding difluoro derivative (9) in 85% isolated yield. All new compounds have been characterized by spectroscopic and elemental analysis.     

Quantification of β-Sitosterol in Hairy Root Cultures and Natural Plant Parts of Butterfly Pea (Clitoria ternatea L.)

JPC – Journal of Planar Chromatography – Modern TLC - A simple normal-phase high-performance thin-layer chromatography (HPTLC) method has been developed for the quantification of...     

Simultaneous high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) analysis of cyanide and thiocyanate from swine plasma

An analytical procedure for the simultaneous determination of cyanide and thiocyanate in swine plasma was developed and validated. Cyanide and thiocyanate were simultaneously analyzed by high-performance liquid chromatography tandem mass spectrometry in negative ionization mode after rapid and simple sample preparation. Isotopically labeled internal standards, Na¹³C¹⁵N and NaS¹³C¹⁵N, were mixed with swine plasma (spiked and nonspiked), proteins were precipitated with acetone, the samples were centrifuged, and the supernatant was removed and dried. The dried samples were reconstituted in 10 mM ammonium formate. Cyanide was reacted with naphthalene-2,3-dicarboxaldehyde and taurine to form N-substituted 1-cyano[f]benzoisoindole, while thiocyanate was chemically modified with monobromobimane to form an SCN-bimane product. The method produced dynamic ranges of 0.1–50 and 0.2–50 μM for cyanide and thiocyanate, respectively, with limits of detection of 10 nM for cyanide and 50 nM for thiocyanate. For quality control standards, the precision, as measured by percent relative standard deviation, was below 8 %, and the accuracy was within ±10 % of the nominal concentration. Following validation, the analytical procedure successfully detected cyanide and thiocyanate simultaneously from the plasma of cyanide-exposed swine.     

Permutation-symmetric multicritical points in random antiferromagnetic spin chains

We present a general theory of a class of multicritical points in the phase diagrams of random antiferromagnetic spin chains. We show that low-energy properties of these points are almost completely determined by a permutation symmetry of the effective theory not shared by the microscopic Hamiltonian. One case provides an analytic theory of the quantum critical point in the random spin-3/2 chain, studied in a recent work by Refael, Kehrein, and Fisher.     

Fractional spin textures in the frustrated magnet SrCr(9p)Ga(12-9p)O₁₉

We consider the archetypal frustrated antiferromagnet SrCr(9p)Ga(12-9p)O?? in its well-known spin-liquid state, and demonstrate that a Cr(3+) spin S=3/2 ion in direct proximity to a pair of vacancies (in disordered p<1 samples) is cloaked by a spatially extended spin texture that encodes the correlations of the parent spin liquid. In this spin-liquid regime, our analytic theory predicts that the combined object has a magnetic response identical to a classical spin of length S/2=3/4, which dominates over the small intrinsic susceptibility of the pure system. This fractional-spin texture leaves an unmistakable imprint on the measured ?1Ga nuclear magnetic resonance line shapes, which we compute using Monte Carlo simulations and compare with experimental data.     

A pyrene-based fluorescent sensor for Zn2+ ions: a molecular 'butterfly'

A simple pyrene-based triazole receptor has been synthesised and shown to self-assemble in the presence of ZnCl(2) in an exclusively 2:1 ratio, whereas a mixture of 2:1 and 1:1 ratios are observed for other Zn(2+) salts. The pyrene units are syn in orientation; this is supported by a strong excimer signal observed at 410 nm in the presence of ZnCl(2) in acetonitrile. DFT calculations and 2D NMR support the proposed structure.     

Effect of gadolinium substitution on the linear thermal expansion of barium sodium niobate

Ba₂NaNb₅O₁₅ (BSN) exhibits a large thermal contraction in its c-axis between 350° and 750°C. This behaviour contributes to a serious cracking problem during its crystal growth. The substitutions of Gd for Ba and/or Na in BSN can be made with either anion or cation compensation. The former, namely, type A, compositions were found to eliminate the thermal contraction behaviors, and had small variations in their linear thermal expansion coefficients, α, between 50° and 650°C. With good ferroelectric and dielectric properties, they showed potentials to replace the BSN crystal in electro-optic devices.     

Application of thermogravimetric equations in the thermal decomposition of manganese(II) soaps

Summary Thermal decomposition of manganese(II) soaps of general composition, Mn(O₂CR)₂ (where R = C₁₇H₃₃, C₁₁H₂₃, C₉H₁₉, C₇H₁₅) has been studied by t.g.a. and a probable mechanism of decomposition is proposed. The activation energies have been determined using the different equations of Horowitz and Metzger and of Coats and Redfern. The results obtained are consistent.