Imidazole‐initiated polymerizations of α‐amino acid N‐carboxyanhydrides – simultaneous chain‐growth and step‐growth polymerization

The N‐carboxyanhydrides (NCAs) of sarcosine (Sar), D ,L ‐leucine (D ,L ‐Leu), D ,L ‐phenylalanine (D ,L ‐Phe), and L ‐alanine (L ‐Ala) were polymerized in dioxane. Imidazole served as initiator and the NCA/initiator ratio was varied from 1/1 to 40/1. The isolated polypeptides were characterized by ¹H NMR spectroscopy, by MALDI‐TOF mass spectrometry, by viscosity measurements, and by SEC measurements in the case of poly(sarcosine). Cyclic oligopeptides were found in all reaction products and in the case of polySar, poly(D ,L ‐Leu), and poly(D ,L ‐Phe) the cycles were the main products. In the case of poly(L ‐Ala), rapid precipitation of β‐sheet lamellaes prevented efficient cyclizations and stabilized imidazolide endgroups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5690–5698, 2005     

H‐atom abstraction from selected C?H bonds in 2,3‐dimethylpentanal, 1,4‐cyclohexadiene,and 1,3,5‐cycloheptatriene

The gas‐phase reactions of OH radicals with 1,4‐cyclohexadiene, 1,3,5‐cycloheptatriene, and 2,3‐dimethylpentanal have been investigated to determine the importance of H‐atom abstraction at specific positions in these molecules. Benzene was observed as a product of the reaction of OH radicals with 1,4‐cyclohexadiene in 12.5 ± 1.2% yield, in good agreement with a previous study and indicating that this is the fraction of the reaction proceeding by H‐atom abstraction from the allylic C? H bonds. In contrast, no formation of tropone from 1,3,5‐cycloheptatriene was observed, suggesting that in this case H‐atom abstraction is not important. For the reaction of OH radicals with 2,3‐dimethylpentanal, formation of 3‐methyl‐2‐pentanone was observed in 5.4 ± 1.0% yield (after correction for reaction of 3‐methyl‐2‐pentanone with OH radicals), and this product is predicted to be formed after initial H‐atom abstraction from the 2‐position CH group. Acetaldehyde and 2‐butanone were also observed as products, with initial yields of ～90% and ～26%, respectively, and their formation appeared to involve, at least in part, an intermediary acyl peroxy radical. Using a relative rate method, the measured rate constants for the reactions of OH radicals with 2,3‐dimethylpentanal, 3‐methyl‐2‐pentanone, and tropone are (in units of 10^?12 cm³ molecule^?1 s^?1) 2,3‐dimethylpentanal, 42 ± 7; 3‐methyl‐2‐pentanone, 6.87 ± 0.08; and tropone, 42 ± 6. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 415–426, 2003     

Rate constants for the gas-phase reactions of O3 with a series of Terpenes and OH radical formation from the O3 reactions with Sesquiterpenes at 296 ± 2 K

Rate constants for the gas-phase reactions of O₃ with the sesquiterpenes α-cedrene, α-copaene, β-caryophyllene, α-humulene, and longifolene, and with the monoterpenes limonene, terpinolene, α-phellandrene, and α-terpinene, have been measured using a relative rate technique at 296 ± 2 K and atmospheric pressure of air. The rate constants obtained (in units of 10^?17 cm³ molecule^?1 s^?1) are: limonene, 20.1 ± 5.1; terpinolene, 188 ± 67; α-phellandrene, 298 ± 105; α-terpinene, 2110 ± 770; α-cedrene, 2.78 ± 0.71; α-copaene, 15.8 ± 5.6; β-caryophyllene, 1160 ± 430; α-humulene, 1170 ± 450; and longifolene, <0.07, where the indicated errors include the estimated overall uncertainties in the rate constants for the reference organics. Hydroxyl radical formation yields were also determined for the O₃ reactions with the sesquiterpenes, of 0.67 for α-cedrene, 0.35 for α-copaene, 0.06 for β-caryophyllene, and 0.22 for α-humulene, all with estimated overall uncertainties of a factor of ca. 1.5. The tropospheric lifetimes of the sesquiterpenes due to reaction with O₃ are calculated. © 1994 John Wiley & Sons, Inc.     

Vapor—liquid equilibria for the binary system 2-methylbutene-2 and 2-methyl-1,3-butadiene at 310.93, 316.48 and 322.04 K

Total pressure, vapor—liquid equilibrium data for the binary system 2-methyl-1,3-butadiene and 2-methylbutene-2 are reported at 310.93, 316.48 and 322.04 K. The experimental uncertainties in measured variables, expressed as standard deviations, are 0.0005 mole fraction, 0.01 K and 0.2% of measured pressure. The coefficients for a modified Wilson solution model are also reported. These coefficients were determined from the experimental data using a general non-linear least-squares technique which accounts for experimental uncertainties in independent and dependent variables. The standard deviations of prediction for temperature-independent coefficients are 0.17% for pressure, 0.001 K for temperature and 0.00001 for mole fraction.     

Vibrational and luminescence spectra of a new binuclear uranyl complex [(C2H5)4N]2[UO2F(NO3)2]2

The preparation, vibrational and luminescence spectra of the title compound are described. The complex has bidentate nitrate groups and bridging fluoride ions. The spectra are assigned in detail and interpreted as showing couplings between the uranyl antisymmetric stretching modes and between the nitrate modes within the dimer, the coupling energy being 17 cm^? in the former case. There is no clear evidence for electronic coupling involving the uranyl groups.     

Simulation of flourine migration in NiF2

The point defect and transport properties of nickel fluoride have been predicted using atomistic simulation. Results suggest that the dominant intrinsic defect reaction is anion Frenkel, however, formation energies are sufficiently high to suggest that intrinsic defect concentrations are low. Migration activation energies are consistent with flourine, as the most highly mobile species, being transported in the ab plane via the formation of a split interstitial configuration. Transport of both flourine and nickel will be considerably anisotropic.