Self-bonding in an amorphous polymer below the glass transition: A T-peel test investigation

Films of amorphous polystyrene (PS) with a weight-average molecular weight (M_w) of 225 × 10³ g/mol were bonded in a T-peel test geometry, and the fracture energy (G) of a PS/PS interface was measured at the ambient temperature as a function of the healing time (t_h) and healing temperature (T_h). G was found to develop with (t_h)^1/2 at T_h = T_g-bulk − 33 °C (where T_g-bulk is the glass-transition temperature of the bulk sample), and log G was found to develop with 1/T_h at T_g-bulk − 43 °C ≤ T_h ≤ T_g-bulk − 23 °C. The smallest measured value of G = 1.4 J/m² was at least one order of magnitude larger than the work of adhesion required to reversibly separate the PS surfaces. These three observations indicated that the development of G at the PS/PS interface in the temperature range investigated (<T_g-bulk) was controlled by the diffusion of chain segments feasible above the glass-transition temperature of the interfacial layer, in agreement with our previous findings for fracture stress development at several polymer/polymer interfaces well below T_g-bulk. Close values of G = 8–9 J/m² were measured for the symmetric interfaces of polydisperse PS [M_w = 225 × 10³, weight-average molecular weight/number-average molecular weight (M_w/M_n) = 3] and monodisperse PS (M_w = 200 × 10³, M_w/M_n = 1.04) after healing at T_h = T_g-bulk − 33 °C for 24 h. This implies that the self-bonding of high-molecular-weight PS at such relatively low temperatures is not governed by polydispersity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1861–1867, 2004     

Alkaloids of far-eastern species ofThalictrum. IV

Summary The alkaloid composition of four far-eastern species ofThalictrum — Th. amurense, Th. contortum, Th. filamentosum, andTh. minus — have been studied, for the first time in the case of the first three species.Th. amurense contains -allocryptopine and thalictrisine, andTh. contortum contains -allocryptopine. Glaucine and thalicsimidine have been found inTh. filamentosum, and argemonine has been isolated fromTh. minus for the first time.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Pacific Ocean Institute of Bioorganic Chemistry, Far-Eastern Scientific Center of the Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 788–791, November–December, 1976.     

Hot-wire anemometer measurement of local skin friction coefficient

Based on fine measurement of time-averaged data of hot-wire anemometer we have developed the method determining local values of skin-friction coefficient in the vicinity of the wall on the planar porous surface at the flow past which the noncanonical turbulent boundary layer is formed. The method may be applied at investigation of the efficiency of various effects on the incompressible boundary layer, in particular, with microblowing of air where usage of direct methods of friction determination is complicated.     

On an integral equation of the problem for an elastic strip with a slit

A new singular integral equation is obtained that describes the elastic equilibrium of a strip with both an inner and an edge slit (crack) and has a considerable advantage over existing equations /1–9/, etc.) from the viewpoint of a numerical realization and clarification of the analytical relationship with an analogous equation for a half-plane. Numerical results are given of a computation of the stress intensity coefficients at the tips of the inner and edge cracks that refine data in the literature.     

Plane logarithmic spiral with peripheral excitation

Conclusion In a planar logarithmic spiral excited at its periphery there simultaneously exist surface, quasieffluent, and radiated waves; the phase velocities of surface and quasieffluent waves are identical and depend on the reduced radius k, which defines the regions of normal and anomalous dispersion; in the region kn the surface wave transforms to a radiated one by means of the quasieffluent; the directional pattern differs little from that for central excitation, with ellipticity coefficient of a spiral open at the center varying from 0.7 to 0.9 over a 1:2 frequency range; the input impedance depends weakly on the presence of reflection at the center of the spiral, is of an oscillating character, and changes more intensely than for central excitation.Khar'kov State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 1, pp. 78–84, January, 1990.     

Orientational optical torque in a nematic liquid crystal,caused by trans- and cis-isomers of low- and high-molecular compounds

The effect of light on the conformational composition of low- and high-molecular (fifth-generation dendrimer) azobenzene dyes in a nematic host is studied. The orientational optical response of the nematic liquid crystal (NLC), caused by the presence of these compounds in the nematic host, is measured. The contributions of isomers to the orientational optical torque affecting the NLC director are determined. The results obtained suggest that the increase in the optical orientation efficiency in NLCs when using high-molecular dopants instead of low-molecular ones is unrelated to the difference in their conformational composition in the light field, but is caused by deceleration of orientational motion of chromophores.     

Rational Design of Practically Important Enzymes

Majority of native enzymes are poorly applicable for practical usage: that is why different methods of enzyme modification are used to obtain the biocatalysts with appropriate characteristics. Development of genome sequencing and various modern approaches in protein engineering allow one to identify protein of interest and to improve the enzyme properties for a particular process. This review describes the results on development of novel biocatalysts based on bioinformatics and rational design. New genes encoding formate dehydrogenase (FDH) from bacterium Staphylococcus aureus, yeasts Ogataea parapolymorpha and Saccharomyces cerevisiae and moss Physcomitrella patens (SauFDH, OpaFDH, SceFDH and PpaFDH, respectively), have been cloned. New FDHs were produced in the active form and characterized. SauFDH was shown to have at least 2-fold higher catalytic constant than other known FDHs. OpaFDH has catalytic parameters as good as those for soy FDH mutant forms, and in addition, is more thermostable. Apo- and holo-forms of SauFDH have been crystallized. Mutation of two Cys residues in Pseudomonas sp.101 enzyme (PseFDH) yields enzyme preparations with improved kinetic parameters and enhanced thermal and chemical stability. New generation of PseFDH preparations with the coenzyme specificity changed from NAD⁺ to NADP⁺ have been obtained. The effect of ionic liquids on the catalytic properties and thermal stability of six wild-type recombinant FDHs, and a number of their mutants, have been studied. In case of D-amino acid oxidase (DAAO), single-point mutations have been combined to create multi-point mutants. The introduced amino acid replacements have been shown to exert an additive effect, improving both kinetic parameters and increasing thermal and chemical stability. DAAO genes from Hansenula polymorpha yeast have been cloned. α-Amino acid ester hydrolase (AEH) gene has been cloned and expressed in the active form in E. coli. Structural modeling has been performed and the effectiveness in amino beta-lactams synthesis studied. The structure of a single-chain penicillin acylase from Alcaligenes faecalis (scAfPA) has been modeled and two variants of scAfPA gene was generated by PCR. Both variants have been expressed in E. coli, isolated and characterized. Catalytic properties of scAfPA were slightly better than those of its natural heterodimer.     

Directed Aminomethylation of Pyrrole,Indole, and Carbazole with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N′</Emphasis>,<Emphasis Type="Italic">N′</Emphasis>-Tetramethylmethanediamine

Catalytic aminomethylation of pyrrole and indole with N,N,N′,N′-tetramethylmethanediamine in the presence of 5 mol % of ZrOCl₂·8H₂O proceeds selectively at the positions 2, 5 of pyrrole and 1, 3 of indole. Carbazole under the same conditions affords 3-formyl-9-aminomethyl derivative. The reaction in the presence of 5 mol % of K₂CO₃ occurs as monoaminomethylation: for pyrrole at the position 2, for indole at the position 3, and for carbazole at the nitrogen atom of the substrate. Water-soluble 1,1′-(1H-pyrrole-2,5-diyl)bis(N,N-dimethylmethanamine) exhibits a fungistatic activity with respect to phytopathogenic fungi Rhizoctonia solani.