Catalytic, asymmetric synthesis of α,α-disubstituted amino acids

Copper(salen) complex 1 has been found to catalyse the asymmetric alkylation of enolates derived from a variety of amino acids. There is a clear relationship between the size of the side chain in the substrate and the enantioselectivity of the process, so that the enantioselectivity decreases in the order alanine>aminobutyric acid>allylglycine>leucine>phenylalanine>valine. A transition state model which accounts for the influence of the size of the side chain on the enantioselectivity of the reactions is presented.     

Adhesion of polyelectrolyte multilayers: sealing and transfer of microchamber arrays

Polyelectrolyte multilayer (PEM) films with array of responsive microchambers are promising candidates for site-specific release of chemicals in small and precisely defined quantities on demand. It requires effective sealing of the microchambers toward a support to prevent leakage of a cargo. In this paper, we study the pressure-induced adhesion of poly(allylammonium)-poly(4-styrenesulfonate) (PAH-PSS) multilayers assembled on different templates toward the poly(4-styrenesulfonate)-poly(diallyldimethylammonium) multilayer. The tensile bond strength increases from 0.4 to 3.5 MPa upon the increase of PAH-PSS bilayers from 10 to 40, if assembled on a silicon template. Weaker tensile bond strength of 0.35 MPa between the PAH-PSS multilayer and a poly(methylmethacrylate) (PMMA) template results in adhesive break at this interface and allows mechanical removal of the template. The successful PEM transfer is demonstrated for templates of various geometrical patterns, while the tensile break of a multilayer film happens for the others.     

Equations of motion and boundary conditions of physical meaning of micropolar theory of thin bodies with two small cuts

Nowadays, microcontinuous mechanics (mechanics of media with microstructure) is being developed very intensively, which is testified by recently published papers [1–14] and by many others, as well as by the symposiumdedicated to the hundredth anniversary of the brothers Cosserat monograph [15], held inParis in 2009. A survey of foreign papers is given in [16], and a special place is occupied by earlier publications of Soviet scientists on micropolar theory of elasticity [17–24]. A brief survey of Cosserat theory of elasticity and an analysis and prospects of such theories in mechanics of rigid deformable bodies is given in [21]. It should be noted that, in a majority of cases, the structure strength calculations are based on the classical theory of elasticity. But there are materials such as animal bones, graphite, several polymers, polyurethane films, porous materials (pumice), various synthetic materials, and materials with inclusions which, under certain conditions, exhibit micropolar properties. There are effects which cannot be prescribed by the classical theory. In statics, nonclassical behavior can be observed in bending of thin films and cantilevers, in torsion of thin and thin-walled rods, and in the case of stress concentration near holes, corner points, cracks, and inclusions. For example, thin specimens are more rigid in bending and torsion as is prescribed by the classical theory [25–27]. The stress concentration near holes decreases, and the concentration factor depends on the radius [28]. The stress concentration near cracks also becomes lower. Conversely, the stress concentration near inclusions is higher than predicted by the classical theory [29–31]. If the material has no center of symmetry of elastic properties, then calculations according to the micropolar theory shows that the specimen is twisted in tension [32]. In dynamical problems, several phenomena also differ from the classical concepts. For example, shear waves propagate with dispersion, microrotation waves arise, and the vibration natural modes differ from the classical ones [2, 7, 11–13, 33]. All these phenomena are used to determine material constants of the micropolar theory of elasticity. There are many methods for determining such constants [2, 34]. Since thin bodies (one-, two-, three-, and multilayer structures) are widely used, it is necessary to create new refined microcontinual theories of thin bodies and advanced methods for their computations. In the present paper, various representations of the system of equations of motion are obtained in the micropolar theory of thin bodies with two small parameters in momenta with respect to a system of Legendre polynomials in the case where an arbitrary line is taken for the base. In this connection, a vector parametric equation of the region of a thin body is given for the parametrization under study, different families of bases (frames) are introduced, and expressions for components of the unit tensor of rank two (UTRT) are obtained. Representations of gradient, tensor divergence, equations of motion, and boundary conditions for the considered parametrization are given. Definitions of (m, n)th-order moment of a variable with respect to an arbitrary system of orthogonal polynomials and a system of Legendre polynomials is given. Expressions for themoments of partial derivatives and several expressions with respect to a system of Legendre polynomials and boundary conditions in moments are obtained.     

Dynamic equations of the theory of thin prismatic bodies with expansion in the system of Legendre polynomials

For a thin anisotropic body that is inhomogeneous with respect to curvilinear coordinates x ¹ and x ² and for an arbitrary homogeneous prismatic anisotropic elastic body of variable thickness with one small dimension in the case of the classical parametrization of its domain, we obtain the equations of motion of the Cosserat theory of elasticity in terms of moments with the kinematic boundary conditions of kinematic meaning and with boundary conditions of physical meaning taken into account.     

Representation of solutions to equations of hyperbolic type

The general solutions to hyperbolic equations of fourth and sixth order are obtained using Vekua’s method for the representation of the general solutions to elliptic equations of order 2n with the aid of n analytic functions. It is assumed that the right-hand sides of the hyperbolic equations can be expanded in time series of sines. The systems of equations of various approximations for a prismatic thin body in terms of moments with respect to the system of Legendre polynomials can be reduced to these equations and to some hyperbolic-type equations of higher order.     

High-throughput protein precipitation method with 96-well plate for determination of doxepin and nordoxepin in human plasma using LC–MS/MS

The aim of this study was to establish a high-throughput and sensitive LC–MS/MS method for the determination of doxepin and its major active metabolite nordoxepin in human plasma. It has been designed for bioequivalence study for formulations containing 25 mg of doxepin. Doxepin and nordoxepin were extracted from human plasma samples by protein precipitation with acetonitrile by using protein precipitation 96-well plates. The analyte was separated using a Phenomenex Kinetex Biphenyl column (100 × 2.1 mm, 2.6 μm) using isocratic elution with a mobile phase of 20 mM ammonium formate (30%) and acetonitrile:methanol 3:7 v:v (70%) at a flow rate of 0.5 mL/min and an injection volume of 10 μL. The detection was performed using a triple quadrupole mass spectrometer by multiple reaction monitoring mode to monitor the precursor-to-product ion transitions of m/z 280.4 → 107.0 and 283.4 → 235.0 for doxepin and doxepin-D3, respectively, and 266.3 → 106.9 and 269.3 → 235.0 for nordoxepin and nordoxepin-D3, respectively, in positive electrospray ionization mode. The total run time was 3.5 min. The method was validated over a concentration range of 50–10,000 pg/mL using a Triple Quad 4500 MS System (Sciex) for both analytes. The developed and validated method can be successfully used to study the bioequivalence/pharmacokinetics of doxepin and nordoxepin.     

Oxidation of guanine in double-stranded DNA by [Ru(bpy)2dppz]Cl2 in cationic reverse micelles

DNA oxidation has been investigated in the medium of cationic reverse micelles (RMs). The oxidative chemistry is photochemically initiated using the DNA intercalator bis(bipyridine)dipyridophenazine ruthenium(II) chloride ([Ru(bpy)2dppz]Cl2) bound to duplex DNA in the RMs. High-resolution polyacrylamide gel electrophoresis (PAGE) is used to reveal and quantify guanine (G) oxidation products, including 8-oxo-7,8-dihydroguanine (8OG). In buffer solution, the addition of the oxidative quenchers potassium ferricyanide or pentaamminechlorocobalt(III) dichloride leads to an increase in the amount of piperidine-labile G oxidation products generated via one-electron oxidation. In RMs, however, the yield of oxidatively generated damage is attenuated. With or without ferricyanide quencher in the RMs, the yield of oxidatively generated products is approximately the same. Inclusion of the cationic quencher [CoCl(NH3)5]2+ in the RMs increases the amount of oxidation products generated but not to the extent that it does in buffer solution. Under anaerobic conditions, all of the samples in RMs, with or without added oxidative quenchers, show decreased levels of piperidine-labile oxidation products, suggesting that the primary oxidant in RMs is singlet oxygen. G oxidation is enhanced in D2O and deuterated heptane and is diminished in the presence of sodium azide in RMs, also supporting 1O2 as the main G oxidant in RMs. Isotopic labeling experiments show that the oxygen atom in 8OG produced in RMs is not from water. The observed change in the G oxidation mechanism from a one-electron process in buffer to mostly 1O2 in RMs illustrates the importance of both DNA structure and DNA environment on the chemistry of G oxidation.     

Protein precipitation method for determination of clobazam and N-desmethylclobazam in human plasma by LC–MS/MS

A protein precipitation method for the determination of clobazam (CLB) and its major active metabolite N-desmethylclobazam (N-CLB) in human plasma by liquid chromatography tandem mass spectrometry (LC–MS/MS) was established. CLB and N-CLB were extracted from human plasma samples by protein precipitation with methanol. Analyte separation was done using a Phenomenex Kinetex™ Biphenyl (50 × 2.1 mm, 1.7 μm) column using isocratic elution with a mobile phase of 5 mm ammonium formate with 0.01% ammonium hydroxide (40%) and methanol (60%) at a flow rate of 0.4 mL/min and an injection volume of 10 μL. The detection was performed on a triple quadrupole mass spectrometer in multiple reaction monitoring mode to monitor the precursor-to-product ion transitions of m/z 301.1 → 259.0, 306.0 → 263.9 for CLB and CLB-D5 and 287.0 → 245.0, 292.0 → 250.0 for N-CLB and N-CLB-D5 in positive electrospray ionization mode, respectively. The method was validated over a concentration range of 2.0–750 ng/mL for CLB and 0.7–200 ng/mL for N-CLB on SCIEX Triple Quad 4500 MS System. Total run time was 5 min. This method has been designed for bioequivalence study for formulations containing 20 mg of CLB.     

Modeling of multilayer thin bodies

In this work, we considered the new parametrization of a multilayer thin domain. In particular, in contrast to classic approaches, we used several base surfaces and an analytic method with the application of orthogonal polynomial systems. We gave the vector parametric equation of each layer and the system of vector parametric equations of a multilayer thin domain and introduced the geometric characteristics for the proposed parametrization. We also derived the expressions for the transfer components of the second-rank identity tensor and the relations connecting the various families of bases and presented some differential operators, the system of equations of motion, the heat flow equation, the constitutive relations of the theory of the micropolar elasticity, and the Fourier heat conduction law under this parametrization of the thin-body domain. Finally, we gave the classification and statements of boundary value problems in the theory of thin bodies.