Crystallisation-induced asymmetric transformation (CIAT) for the synthesis of dipeptides containing homophenylalanine

A novel synthesis of highly enantioenriched dipeptides containing homophenylalanine is described. The process involves a crystallisation-induced asymmetric transformation (CIAT) in a Michael addition followed by exhaustive reduction. A unique example of a formally stereodivergent CIAT in conjugate addition of an achiral N-nucleophile to enantiomerically pure Michael acceptor has been discovered.     

氟胺氰菊酯的定性定量分析

氟胺氰菊酯是一种用于蜜峰的高效杀螨剂。从20%商品氟胺氰菊酯粉剂中通过硅胶柱层板分离得到了96.6%的纯品并用FTIR和GC/MC进行定性量测定。采用GC/MS定量分析的方法，氟胺氰菊酯的浓度在0.05-10mg/L范围为线性响应，最低检测极限为 0.01mg/L。采用R（-）N-3，5-二硝基苯甲酰-苯基甘氨酸和长链烃的硅胶微粒手性柱，可成功地分离氟胺氰菊酯的二种旋光异构体，它们在商品氟胺氰菊酯中的比例近似为1：1。     

Total synthesis and proof of structure of mycothiol bimane

Mycothiol is a low-molecular weight thiol produced by actinomycetes that serves to protect these organisms from oxidative stress and alkylating agents. We report the total synthesis of mycothiol bimane (1) which is a commonly isolated derivative of mycothiol. The synthesis confirms the original structure assignment and unambiguously establishes the absolute stereochemistry of mycothiol to be 1-d-myo-inosityl 2-deoxy-2-(N-acetamido-l-cysteinamido)-alpha-d-glucopyranoside.     

The inhibited photo-oxidation of polystyrene and styrene/HALS copolymers

The influence of molecular weight and the mode of binding of HALS stabilisers on their efficiency in the inhibited photo-oxidation of polystyrene and styrene/HALS copolymers was investigated. Photo-oxidation was performed with radiation of λ > 310 nm and 366 nm. The following functionalised HALS stabilisers were prepared: 4-methacryloylamino-2,2,6,6-tetramethylpiperidine, 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine, 4-methacryloyloxy-1,2,2,6,6-pentamethylpiperidine and 15-methacryloyl-7,15-diazadispiro [5.1,5.3] hexadecane-14,16-dione. Binding by copolymerisation is substantially less efficient than addition of low molecular weight stabiliser.     

Preparation and Photophysics of 2-(1-Pyrenyl)acrylic Acid and Its Methyl and 2′,2′,6′,6′-Tetramethyl-4′-Piperidyl Esters

Novel probes represented connection of pyrene as chromophore and sterically hindered amine stabilizers (HAS) in the form of esters of 2-(1-pyrenyl)acrylic acid were synthesized. HAS was in the form of parent amine (PAP) as well as stable nitroxyl radical form (PAP-NO^.). Photophysics of these probes were compared with their precursor as 2-(1-pyrenyl)acrylic acid (PAA) and its methyl ester (PAM). The fluorescence spectrum of PAA strongly depends on the acidity of the solution. The spectrum in neutral methanol indicates that it originates from the anionic form –COO⁻. Changes of acidity or basicity of methanol solution resulted in the changes of shape, position as well as the intensity of fluorescence band. This is due to the presence of protolytic equilibria, either in the ground state or in the singlet excited state, leading to the formation of molecular form –COOH and the cationic form –COOH₂⁺. The ester analogues did not show any changes in various pH conditions. Fluorescence of all probes depends on the polarity of solvents and the presence of oxygen. Intermolecular quenching was studied with external quenchers TEMPO and oxygen and the data were compared with the intramolecular quenching using 1′-oxo-2′,2′,6′,6′-tetramethyl-4′-piperidinyl-2-(1-pyrenyl)acrylate (PAP-NO^.).     

Effects of gemini surfactants on egg phosphatidylcholine bilayers in the fluid lamellar phase

The influence of 1,4-butanediamonium-N,N'-dialkyl-N,N,N',N'-tetramethyl dibromides (CmA, m = 7-16 is the number of alkyl carbons) on the egg yolk phosphatidylcholine (EYPC) bilayer thickness and lipid surface area at the bilayer-aqueous phase interface is studied using X-ray diffraction on fluid lamellar CmA + EYPC + H2O phases as a function of CmA:EYPC and H2O:EYPC molar ratios and the alkyl chain length m. At the constant CmA:EYPC = 0.4 and H2O:EYPC = 18 molar ratios, the CmA induced bilayer thickness decrease shows a minimum and the lipid surface area increase a maximum at the alkyl chain length m = 9. The obtained results are discussed in the context of a structural perturbation model of the cut-off effect in biological potencies of surfactants which occurs when increasing the alkyl substituent chain length above the critical value.     

Multiple equilibria,periodic solutions and a priori bounds for solutions in superlinear parabolic problems

Consider the Dirichlet problem for the parabolic equation in , where $\Omega$ is a bounded domain in and f has superlinear subcritical growth in u. If f is independent of t and satisfies some additional conditions then using a dynamical method we find multiple (three, six or infinitely many) nontrivial stationary solutions. If f has the form where m is periodic, positive and m,g satisfy some technical conditions then we prove the existence of a positive periodic solution and we provide a locally uniform bound for all global solutions.