Reaction kinetics of the addition of atomic sulfur to nitric oxide

The reaction of S((3)P(J)) with NO ((2)Pi) in an Ar bath gas has been studied by the laser photolysis-resonance fluorescence technique over 300-810 K at pressures from 60 to 800 mbar. The observed second-order rate constants are close to the low-pressure limit. Fitting of Troe's formalism to experiment, with an estimated F(cent) = 0.78 exp(-T/7445) and k(infinity) given subsequently, yields k(0) = (6.2+/-0.6) x 10(-33) exp(+ (940+/-40)/T) cm(6) molecule(-2) s(-1). Error limits are +/-25%. A theoretical analysis of this value suggests that the average energy transferred during collisions between Ar and the excited intermediate is DeltaE = -360(-160) (+90) cm(-1). Over 300-800 K, the high-pressure limit is predicted to be k(infinity) = 2.2 x 10(-10) (T/300)(0.24) cm(3) molecule(-1) s(-1). Doublet and quartet adducts between S and NO were characterized via CBS-QB3 theory. The kinetic data can be rationalized with SNO ((2)A(')) as the major product, and an ab initio estimate of Delta(f)H(298) for SNO is 176+/-8 kJ mol(-1).     

Separation of cyanogen bromide peptides of collagen by means of high-performance liquid chromatography

Cyanogen bromide peptides of bovine collagen Types I, II and III were analyzed using high-performance liquid chromatography (HPLC). Elution patterns of each collagen type were unique and reproducible.Elution patters of the CNBr peptides of the a1 and a2 chains of Type I collagen were also unique and together accounted for the major components of Type I collagen.Analysis of the eluted peptides from HPLC of each collagen type by sodium dodecyl sulphate-polyacrylamide gel electrophoresis showed specific patterns for each collagen. Thus, unique and reproducible HPLC chromatograms were obtained, providing a new analytical method that is simple, sensitive and rapid.     

Interpenetrating inclusion lattices: Comparison of the Β-hydroquinone and ellipsoidal clathrate structures

Crystallization of 2,7-dimethyltricyclo[43.1.1^3,8]undecane-syn-2,syn-7-diol 2 from acetonitrile or dichloro-methane yields the compounds (2)₄-(guest) in space group 14₁/acd which are further examples of the ellipsoidal clathrate structure. Both enantiomers of 2 are linked through (O-H)₄ cycles of hydrogen bonds to form a three-dimensional sublattice. Two inversion related sublattices interpenetrate thereby generating a superlattice with guest-occupied voids situated between the two individual sublattices. The two X-ray structures are compared and contrasted with that of Powell’s (hydroquinone)₃ (SO₂) clathrate compound. Translated fromZhurnal Strukturnoi Khimii, Vol. 40, No. 5, pp. 822–831, September–October, 1999.     

Biodegradable Polycarbonate Synthesis by Copolymerization of Carbon Dioxide with Epoxides Using a Heterogeneous Zinc Complex

As a means for the chemical fixation of carbon dioxide and the synthesis of biodegradable polycarbonates, copolymerizations of carbon dioxide with various epoxides such as cyclohexene oxide (CHO), cyclopetene oxide, 4-vinyl-1-cyclohexene-1,2epoxide, phenyl glycidyl ether, allyl glycidyl ether, propylene oxide, butene oxide, hexene oxide, octene oxide, and 1-chloro-2,3-epoxypropane were investigated in the presence of a double metal cyanide catalyst (DMC). The DMC catalyst was prepared by reacting K₃Co(CN)₆ with ZnCl₂, together with tertiary butyl alcohol and poly(tetramethylene ether glycol) as complexing reagents and was characterized by various spectroscopic methods. The DMC catalyst showed high activity (526.2 g-polymer/g-Zn atom) for CHO/CO₂ (P_CO2 = 140 psi) copolymerization at 80 °C, to yield biodegradable aliphatic polycarbonates of narrow polydispersity (M_w/M_n = 1.67) and moderate molecular weight (M_n = 8900). The DMC catalyst also showed high activities with different CO₂ reactivities for other epoxides to yield various aliphatic polycarbonates with narrow polydispersity.     

Synthesis of gel type dispersion polymers via living dispersion polymerization (LDP)

A gel type disperse polystyrene/divinylbenzene (DVB) copolymer was successfully prepared in hydrocarbon via ‘living dispersion polymerization (LDP)’ method. Characterization of the dispersed polymers was performed by a combination of size-exclusion chromatographic and transmission electron microscopic analyses. Poly(t-butylstyryl)lithium with 3,5 × 10⁴ g/mol of molecular weight was used as a steric stabilizing moiety in the living dispersion polymerization. The particle size of the dispersed polymers was able to be controlled by both the mole ratio of the concentration of poly(t-butylstyryl)lithium to n-butyllithium and the amount of monomer to over 2 μm.     

A Survey of the Coupon Collector’s Problem with Random Sample Sizes

This paper surveys the coupon collector’s waiting time problem with random sample sizes and equally likely balls. Consider an urn containing m red balls. For each draw, a random number of balls are removed from the urn. The group of removed balls is painted white and returned to the urn. Several approaches to addressing this problem are discussed, including a Markov chain approach to compute the distribution and expected value of the number of draws required for the urn to contain j white balls given that it currently contains i white balls. As a special case, E[N], the expected number of draws until all the balls are white given that all are currently red is also obtained.