Evaluation of the effects of crude glycerol on the production and properties of novel polyhydroxyalkanoate copolymers containing high 11‐hydroxyoctadecanoate by Cupriavidus necator IPT 029 and Bacillus megaterium IPT 429

Crude glycerol (CG), a by‐product from biodiesel production, is a carbon source with potential as feedstock for polyhydroxyalkanoate (PHA) production. PHAs are biological macromolecules synthesized by microorganisms as intracellular carbon and energy storage granules. PHA production and its properties were investigated using Cupriavidus necator IPT 029 and Bacillus megaterium IPT 429 cultivated with CGs from different origins. The highest PHA extraction percentage (71.56% [w/v]) occurred when C. necator IPT 029 metabolized CG 3 (from the processing of biodiesel from castor bean oil). The gas chromatography–mass spectrometry analyses revealed novel PHA constituents as building blocks of medium (3‐hydroxytetradecanoate) and long (11‐hydroxyoctadecanoate) chains. Molar mass distribution revealed range of 121–6900 kDa. The initial degradation temperature ranged from 181.83 to 287.50°C and the crystallinity ranged from 35.30 to 66.70%. The results obtained indicate that C. necator IPT 029 from CG 3 could produce copolymers with industrially applicable thermophysical properties. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and characterization of a novel extracellular polysaccharide by Rhodotorula glutinis

The aim of this work was to characterize an exopolysaccharide by Rhodotorula glutinis KCTC 7989 and to investigate the effect of the culture conditions on the production of this polymer. The extracellular polysaccharide (EPS) produced from this strain was a novel acidic heteropolysaccharide composed of neutral sugars (85%) and uronic acid (15%). The neutral sugar composition was identified by gas chromatography as mannose, fucose, glucose, and galactose in a 6.7:0.2:0.1:0.1 ratio. The molecular weight of purified EPS was estimated to be 1.0−3.8×10⁵ Dalton, and the distribution of the molecular weight was very homogeneous (polydispersity index =1.32). The EPS solution showed a characteristic of pseudoplastic non-Newtonian fluid at a concentration >2.0% in distilled water. The maximum EPS production was obtained when the strain was grown on glucose (30 g/L). Ammonium sulfate was the best suitable nitrogen source for EPS production. The highest yield of EPS was obtained at a carbon to nitrogen ratio of 15. The EPS synthesis was activated at the acidic range of pH 3.0–5.0 and increased when the pH of the culture broth decreased naturally to <2.0 during the fermentation. When the yeast was grown on glucose (30 g/L) and ammonium sulfate (2 g/L) at 22°C at an initial pH of 4.0, EPS production was maximized (4.0 g/L), and the glucose-based production yield coefficient and carbon-based production yield coefficient were 0.30 g of EPS/g of glucose and 0.34 g (carbon of EPS)/g (carbon of glucose), respectively.     

Kinetics and mechanism of hydrolysis of N‐(2′‐hydroxyphenyl)phthalamic acid (1) and N‐(2′‐methoxyphenyl)phthalamic Acid (2) in a highly alkaline medium

A kinetic study on hydrolysis of N‐(2′‐hydroxyphenyl)phthalamic acid ( 1 ), N‐(2′‐methoxyphenyl)phthalamic acid ( 2 ), and N‐(2′‐methoxyphenyl)benzamide ( 3 ) under a highly alkaline medium gives second‐order rate constants, k_OH, for the reactions of HO^? with 1, 2 , and 3 as (4.73 ± 0.36) × 10^?8 at 35°C, (2.42 ± 0.28) × 10^?6 and (5.94 ± 0.23) × 10^?5 M^?1 s^?1 at 65°C, respectively. Similar values of k_OH for 3 , N‐methylbenzanilide, N‐methylbenzamide, and N,N‐dimethylbenzamide despite the difference between pK_a values of aniline and ammonia of ～10 pK units are qualitatively explained. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 1–11, 2009     

Thermolysis of 3‐alkyl‐3‐methyl‐1,2‐dioxetanes: activation parameters and chemiexcitation yields

3‐Methyl‐3‐(3‐pentyl)‐1,2‐dioxetane 1 and 3‐methyl‐3‐(2,2‐dimethyl‐1‐propyl)‐1,2‐dioxetane 2 were synthesized in low yield by the α‐bromohydroperoxide method. The activation parameters were determined by the chemiluminescence method (for 1 ΔH‡ = 25.0 ± 0.3 kcal/mol, ΔS‡ = −1.0 entropy unit (e.u.), ΔG‡ = 25.3 kcal/mol, k₁ (60°C) = 4.6 × 10⁻⁴s⁻¹; for 2 ΔH‡ = 24.2 ± 0.2 kcal/mol, ΔS‡ = −2.0 e.u., ΔG‡ = 24.9 kcal/mol, k₁ (60°C) = 9.2 × 10⁻⁴s⁻¹. Thermolysis of 1–2 produced excited carbonyl fragments (direct production of high yields of triplets relative to excited singlets) (chemiexcitation yields for 1: ϕ^T = 0.02, ϕ^S ≤ 0.0005; for 2: ϕ^T = 0.02, ϕ^S ≤ 0.0004). The results are discussed in relation to a diradical‐like mechanism. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:176–179, 2001     

Kinetic Studies of the Ligand Substitution Reaction of Some New Uranyl Schiff Base Complexes with Tri‐n‐butylphosphine

Kinetics of the substitution reaction of solvent molecule in uranyl(VI) Schiff base complexes by tri‐n‐butylposphine as the entering nucleophile in acetonitrile at 10–40°C was studied spectrophotometrically. The second‐order rate constants for the substitution reaction of the solvent molecule were found to be (8.8 ± 0.5) × 10^?3, (5.3 ± 0.2) × 10^?3, (7.5 ± 0.3) × 10^?3, (6.1 ± 0.3) × 10^?3, (13.5 ± 1.6) × 10^?3, (13.2 ± 0.9) × 10^?3, (52.9 ± 0.2) × 10^?3, and (88.1 ± 0.6) × 10^?3 M^?1 s^?1 at 40°C for [UO₂(Schiff base)(CH₃CN)], where Schiff base = L1–L8, respectively. In a temperature dependence study, the activation parameters ΔH^# and ΔS^# for the reaction of uranyl complexes with PBu₃ were determined. From the linear rate dependence on the concentration of PBu₃, the span of k₂ values and the large negative values of the activation entropy, an associative (A) mechanism is deduced for the solvent substitution. By comparing the second‐order rate constants k_2, it was concluded that the steric and the electronic properties of the complexes were important for the rate of the reactions.     

Trans ligand influence in cobalt(III) Schiff base complexes: Electronic and steric effects on the kinetics of hydrolysis

Rate constants for the hydrolysis (k_h) of six different amines in trans‐[Co((BA)₂en)(amine)₂]ClO₄ complexes (amine = aniline 1a , para‐toluidine 1b , benzylamine 1c (primary amines), pyrrolidine 2a , piperidine 2b , morpholine 2c (secondary amines), and (BA)₂en = Bisbenzoylacetoneethylenediiminato) in mixed methanol/water (1:1) solvent have been determined between 30 and 55°C. The hydrolysis product of 2c , trans‐[Co((BA)₂en)(morpholine)(H₂O)]ClO₄, has been separately prepared and characterized by UV–vis and ¹H NMR spectroscopy. Depending on the nature of the axial amine ligand the limiting first‐order rate constants for the amine hydrolysis at 40°C range from (3.42 ± 0.10) × 10^?5 to (5.32 ± 0.13) × 10^?5 s^?1. At the first glance, a reasonable trend cannot be established between k_h and the basicity or the inductive trans effect of the amine ligands. However, when the complexes are classified into two groups, based on the type of the amine (primary and secondary), the values of k_h correlate well with the basicity or inductive effect of the amine in each group. The observed trend in k_h values for the complexes with primary amines is 1a (5.32 ± 0.13) × 10^?5 s^?1 > 1b (3.51 ± 0.14) × 10^?5 > 1c (1.72 ± 0.03) × 10^?5 (40°C), which is opposite to the amine basicity strength. In the case of the complexes with secondary amines, the observed trend in k_h values is in accord with amine basicity (or inductive trans effect), i.e. 2a (5.02 ± 0.22) × 10^?5 > 2b (4.18 ± 0.10) × 10^?5 > 2c (3.42 ± 0.10) × 10^?5 s^?1 (40°C). © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 387–393, 2002     

Kinetics and electron spin resonance study of the radical polymerization of n‐butyl acrylate mediated by a nitroxide precursor: C‐phenyl‐N‐tert‐butylnitrone

The C‐phenyl‐N‐tert‐butylnitrone/azobisisobutyronitrile pair is able to impart control to the radical polymerization of n‐butyl acrylate as long as a two‐step process is implemented, that is, the prereaction of the nitrone and the initiator in toluene at 85 °C for 4 h followed by the addition and polymerization of n‐butyl acrylate at 110 °C. The structure of the in situ formed nitroxide has been established from kinetic and electron spin resonance data. The key parameters (the dissociation rate constant, combination rate constant, and equilibrium constant) that govern the process have been evaluated. The equilibrium constant between the dormant and active species is close to 1.6 × 10^?12 mol L^?1 at 110 °C. The dissociation rate constant and the activation energy for the C? ON bond homolysis are 1.9 × 10^?3 s^?1 and 122 ± 15 kJ mol^?1, respectively. The rate constant of recombination between the propagating radical and the nitroxide is as high as 1.2 × 10⁹ L mol^?1 s^?1. Finally, well‐defined poly(n‐butyl acrylate)‐b‐polystyrene block copolymers have been successfully prepared. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6299–6311, 2006     

Synthesis and Functional Characterization of Antibiofilm Exopolysaccharide Produced by Enterococcus faecium MC13 Isolated from the Gut of Fish

The synthesis and functional characterization of an antibiofilm exopolysaccharide (EPS) from a probiotic Enterococcus faecium MC13 were investigated. The temperature of 35 °C, pH of 6.5, and salinity of 1–2 % were found to be optimum for EPS production. The sucrose (30 g?l^?1) and yeast extract (20 g?l^?1) acted as suitable carbon and nitrogen sources, respectively, which strongly influenced EPS production with yield of 11.33 and 11.91 g?l^?1. Based on the thin layer chromatography, EPS of E. faecium MC13 was found to be a heteropolysaccharide, composed of galactose and glucose sugar units with a molecular mass of 2.0?×?10⁵?Da. Fourier transform infrared spectrum analysis of the EPS revealed many predominant functional groups including hydroxyl, carboxyl, and amide groups. EPS exhibited better emulsifying and flocculating activities which is relatively similar to those of commercial polysaccharides. In vitro antioxidant inspect of EPS showed lesser antioxidant activity than that of the control ascorbic acid. Thermal behavior of EPS was different from the other EPS produced by other lactic acid bacteria. In vitro antibiofilm assay of EPS exhibited significant biofilm inhibition, especially with Listeria monocytogenes. To the best of our knowledge, this is the first report on EPS of E. faecium with strong emulsifying and flocculating activities.     

一种基于壳聚糖固定葡萄糖氧化酶的葡萄糖生物传感器的研究

本文选用生物相容性好的壳聚糖作为基体材料，使其与戊二醛交联成网状结构包埋葡萄糖氧化酶制成电化学传感器。这种壳聚糖膜不仅可以减小葡萄糖氧化酶的流失，而且能为酶提供了适宜的微环境。用红外光谱、紫外光谱及透射电镜对膜的形态和性质进行了表征。实验结果表明该传感器具有很快的响应速度，很好的稳定性和重现性，能选择性地催化葡萄糖并测定其浓度。该传感器的制备方法简单，成本低，于冰箱中放置两周信号保持在90％以上，对葡萄糖测量的线性范围为1×10^-5 - 3.4×10^-3mol•L^-1，当信噪比为3:1时检测限为5×10^-6mol•L^-1。     

A Lactulose Bienzyme Biosensor Based on Self‐Assembled Monolayer Modified Electrodes

A bienzyme biosensor in which the enzymes β‐galactosidase (β‐Gal), fructose dehydrogenase (FDH), and the mediator tetrathiafulvalene (TTF) were coimmobilized by cross‐linking with glutaraldehyde atop a 3‐mercaptopropionic acid (MPA) self‐assembled monolayer on a gold disk electrode, is reported. The working conditions selected were E_app=+0.10 V and (25±1) °C. The useful lifetime of one single TTF‐β‐Gal‐FDH‐MPA‐AuE was surprisingly long, 81 days. A linear calibration plot was obtained for lactulose over the 3.0×10^?5–1.0×10^?3 mol L^?1 concentration range, with a limit of detection of 9.6×10^?6 mol L^?1. The effect of potential interferents (lactose, glucose, galactose, sucrose, and ascorbic acid) on the biosensor response was evaluated. The behavior of the SAM‐based biosensor in flow‐injection systems in connection with amperometric detection was tested. The analytical usefulness of the biosensor was evaluated by determining lactulose in a pharmaceutical preparation containing a high lactulose concentration, and in different types of milk. Finally, the analytical characteristics of the TTF‐β‐Gal‐FDH‐MPA‐AuE are critically compared with those reported for other recent enzymatic determinations of lactulose.     

Polar,functionalized diene‐based materials. V. Free‐radical polymerization of 2‐[(N‐benzyl‐n‐methylamino)methyl]‐1,3‐butadiene and copolymerization with styrene

2‐[(N‐Benzyl‐N‐methylamino)methyl]‐1,3‐butadiene (BMAMBD), the first asymmetric tertiary amino‐containing diene‐based monomer, was synthesized by sulfone chemistry and a nickel‐catalyzed Grignard coupling reaction in high purity and good yield. The bulk and solution free‐radical polymerizations of this monomer were studied. Traditional bulk free‐radical polymerization kinetics were observed, giving polymers with 〈M_n〉 values of 21 × 10³ to 48 × 10³ g/mol (where M_n is the number‐average molecular weight) and polydispersity indices near 1.5. In solution polymerization, polymers with higher molecular weights were obtained in cyclohexane than in tetrahydrofuran (THF) because of the higher chain transfer to the solvent. The chain‐transfer constants calculated for cyclohexane and THF were 1.97 × 10^?3 and 5.77 × 10^?3, respectively. To further tailor polymer properties, we also completed copolymerization studies with styrene. Kinetic studies showed that BMAMBD incorporated into the polymer chain at a faster rate than styrene. With the Mayo–Lewis equation, the monomer reactivity ratios of BMAMBD and styrene at 75 °C were determined to be 2.6 ± 0.3 and 0.28 ± 0.02, respectively. Altering the composition of BMAMBD in the copolymer from 17 to 93% caused the glass‐transition temperature of the resulting copolymer to decrease from 64 to ?7 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3227–3238, 2001     

Kinetic study of some reactions related to the Mn(II)-catalyzed bromate-saccharide oscillating reactions

In the stirred batch experiment, the Mn(II)-catalyzed bromate-saccharide reaction in aqueous H₂SO₄ or HClO₄ solution exhibits damped oscillations in the concentrations of bromide and Mn(II) ions. Peculiar multiple oscillations are observed in the system with arabinose or ribose. The apparent second-order rate constants of the Mn(III)-saccharide reactions at 25°C are (0.659, 1.03, 1.76, 2.32, and 6.95) M⁻¹ s⁻¹ in 1.00 M H₂SO₄ and (4.69, 7.51, 10.2, 13.5, and 36.2) M⁻¹ s⁻¹ in (2.00–4.00) M HClO₄ for (glucose, galactose, xylose, arabinose, and ribose), respectively. At 25°C, the observed pseudo-first-order rate constant of the Mn(III)-Br⁻ reaction is k_obs = (0.2 ± 0.1) [Br⁻] + (130 ± 5)[Br⁻]² + (2.6 ± 0.1) × 10³[Br⁻]³ + (1.2 ± 0.2) × 10⁴[Br⁻]⁴ s⁻¹ and the rate constant of the Br₂ Mn(II) reaction is less than 1 × 10⁻⁴ M⁻¹ s⁻¹. The second-order rate constants of the Br₂-saccharide reactions are (3.65 ± 0.15, 11.0 ± 0.5, 4.05, 12.5 ± 0.7, and 2.62) × 10⁻⁴ M⁻¹ s⁻¹ at 25°C for glucose, galactose, xylose, arabinose, and ribose, respectively.     

Ester Hydrolysis by a Cyclodextrin Dimer Catalyst with a Tridentate N,N′,N′′‐Zinc Linking Group

A new β‐cyclodextrin dimer, 2,6‐dimethylpyridine‐bridged‐bis(6‐monoammonio‐β‐cyclodextrin) (pyridyl BisCD, L), is synthesized. Its zinc complex (ZnL) is prepared, characterized, and applied as a catalyst for diester hydrolysis. The formation constant (log K_ML=7.31±0.04) of the complex and deprotonation constant (pK_a1=8.14±0.03, pK_a2=9.24±0.01) of the coordinated water molecule were determined by a potentiometric pH titration at (25±0.1)°C, indicating a tridentate N,N′,N′′‐zinc coordination. Hydrolysis kinetics of carboxylic acid esters were determined with bis(4‐nitrophenyl)carbonate (BNPC) and 4‐nitrophenyl acetate (NA) as the substrates. The resulting hydrolysis rate constants show that ZnL has a very high rate of catalysis for BNPC hydrolysis, yielding an 8.98×10³‐fold rate enhancement over uncatalyzed hydrolysis at pH 7.00, compared to only a 71.76‐fold rate enhancement for NA hydrolysis. Hydrolysis kinetics of phosphate esters catalyzed by ZnL are also investigated using bis(4‐nitrophenyl)phosphate (BNPP) and disodium 4‐nitrophenyl phosphate (NPP) as the substrates. The initial first‐order rate constant of catalytic hydrolysis for BNPP was 1.29×10^?7 s^?1 at pH 8.5, 35 °C and 0.1 mM catalyst concentration, about 1600‐fold acceleration over uncatalyzed hydrolysis. The pH dependence of the BNPP cleavage in aqueous buffer was shown as a sigmoidal curve with an inflection point around pH 8.25, which is nearly identical to the pK_a value of the catalyst from the potentiometric titration. The k_BNPP of BNPP hydrolysis promoted by ZnL is found to be 1.68×10^?3 M ^?1 s^?1, higher than that of NPP, and comparatively higher than those promoted by its other tridentate N,N′,N′′‐zinc analogues.     

Negative thermal expansion of a polydiacetylene single crystal

Macroscopic thermal expansion in the chain direction has been measured for the first time on organic polymeric single crystals. Negative linear thermal expansion coefficients αM are reported and related to chain torsional motion and equilibrium point-defect formation for a solid-state polymerized phase of 2,4-hexadiyne-1,6-diol bisphenylurethane (HDU) which contains crystallographically located interstitial dioxane and for a dioxanefree phase obtained by thermal annealing. Data for as-polymerized single crystals (which are probably of extended chain morphology) between ?50 and 100°C give αM = ?(1.686 ± 0.039) × 10^?5 ? (1.35 ± 0.18) × 10^?7 t with t in °C. During volatilization of 11.7 ± 1.0 wt-% interstitial dioxane and a resulting crystal structure change, the as-polymerized fibers fibrillate and shrink irreversibly by 0.16 ± 0.04%. Although dichroism and diffraction measurements indicate both a high degree of crystallinity and chain alignment for the dioxane-free phase, the average thermal expansion coefficient, (?3.0 ± 1.0) × 10^?6 °C^?1 between ?50 and 150°C, is about an order of magnitude less than for the as-polymerized single crystals.     

Radical polymerization of vinyl thiocyanatoacetate: Participation of group‐transfer mechanism

Vinyl thiocyanatoacetate (VTCA) was synthesized, and its radical polymerization behavior was studied in acetone with dimethyl 2,2′‐azobisisobutyrate (MAIB) as an initiator. The initial polymerization rate (R_p) at 60 °C was expressed by R_p = k[MAIB]^0.6±0.1 [VTCA]^1.0±0.1 where k is a rate constant. The overall activation energy of the polymerization was 112 kJ/mol. The number‐average molecular weights of the resulting poly (VTCA)s (1.4–1.6 × 10⁴) were almost independent of the concentrations of the initiator and monomer, indicating chain transfer to the monomer. The chain‐transfer constant to the monomer was estimated to be 9.6 × 10^?3 at 60 °C. According to the ¹H and ¹³C NMR spectra of poly (VTCA), the radical polymerization of VTCA proceeded through normal vinyl addition and intramolecular transfer of the cyano group. The cyano group transfer became progressively more important with decreasing monomer concentration. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 573–582, 2002; DOI 10.1002/pola.10137     

Controlled radical polymerization of styrene mediated by the C‐phenyl‐N‐tert‐butylnitrone/AIBN pair: Kinetics and electron spin resonance analysis

Kinetics of the free radical polymerization of styrene at 110 °C has been investigated in the presence of C‐phenyl‐N‐tert‐butylnitrone (PBN) and 2,2′‐azobis(isobutyronitrile) (AIBN) after prereaction in toluene at 85 °C. The effect of the prereaction time and the PBN/AIBN molar ratio on the in situ formation of nitroxides and alkoxyamines (at 85 °C), and ultimately on the control of the styrene polymerization at 110 °C, has been investigated. As a rule, the styrene radical polymerization is controlled, and the mechanism is one of the classical nitroxide‐mediated polymerization. Only one type of nitroxide (low‐molecular‐mass nitroxide) is formed whatever the prereaction conditions at 85 °C, and the equilibrium constant (K) between active and dormant species is 8.7 × 10^?10 mol L^?1 at 110 °C. At this temperature, the dissociation rate constant (k_d) is 3.7 × 10^?3 s^?1, the recombination rate constant (k_c) is 4.3 × 10⁶ L mol^?1 s^?1, whereas the activation energy (E_a,diss.), for the dissociation of the alkoxyamine at the chain‐end is ～125 kJ mol^?1. Importantly, the propagation rate at 110 °C, which does not change significantly with the prereaction time and the PBN/AIBN molar ratio at 85 °C, is higher than that for the thermal polymerization at 110 °C. This propagation rate directly depends on the equilibrium constant K and on the alkoxyamine and nitroxide concentrations, as well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1219–1235, 2007     

Kinetics of OH and Cl reactions with a series of aldehydes

The rate constants for the reactions of the OH radicals with a series of aldehydes have been measured in the temperature range 243–372 K, using the pulsed laser photolysis‐pulsed laser induced fluorescence method. The obtained data for propanaldehyde, iso‐butyraldehyde, tert‐butyraldehyde, and n‐pentaldehyde were as follows (in cm³ molecule⁻¹ s⁻¹): (a) in the Arrhenius form: (5.3 ± 0.5) × 10⁻¹² exp[(405 ± 30)/T], (7.3 ± 1.9) × 10⁻¹² exp[(390 ± 78)/T], (4.7 ± 0.8) × 10⁻¹² exp[(564 ± 52)/T], and (9.9 ± 1.9) × 10⁻¹² exp[(306 ± 56)/T]; (b) at 298 K: (2.0 ± 0.3) × 10⁻¹¹, (2.6 ± 0.4) × 10⁻¹¹, (2.7 ± 0.4) × 10⁻¹¹, and (2.8 ± 0.2) × 10⁻¹¹, respectively. In addition, using the relative rate method and alkanes as the reference compounds, the room‐temperature rate constants have been measured for the reactions of chlorine atoms with propanaldehyde, iso‐butyraldehyde, tert‐butyraldehyde, n‐pentaldehyde, acrolein, and crotonaldehyde. The obtained values were (in cm³ molecule⁻¹ s⁻¹): (1.4 ± 0.3) × 10⁻¹⁰, (1.7 ± 0.3)10⁻¹⁰, (1.6 ± 0.3) × 10⁻¹⁰, (2.6 ± 0.3) × 10⁻¹⁰, (2.2 ± 0.3) × 10⁻¹⁰, and (2.6 ± 0.3) × 10⁻¹⁰, respectively. The results are presented and discussed in terms of structure‐reactivity relationships and atmospheric importance. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 676–685, 2000     

Mechanism and kinetics of the imidazolidinone nitroxide‐mediated free‐radical polymerization of styrene

Styrene radical polymerizations mediated by the imidazolidinone nitroxides 2,5‐bis(spirocyclohexyl)‐3‐methylimidazolidin‐4‐one‐1‐oxyl (NO88Me) and 2,5‐bis(spirocyclohexyl)‐3‐benzylimidazolidin‐4‐one‐1‐oxyl (NO88Bn) were investigated. Polymeric alkoxyamine (PS‐NO88Bn)‐initiated systems exhibited controlled/living characteristics at 100–120 °C but not at 80 °C. All systems exhibited rates of polymerization similar to those of thermal polymerization, with the exception of the PS‐NO88Bn system at 80 °C, which polymerized twice as quickly. The dissociation rate constants (k_d) for the PS‐NO88Me and PS‐NO88Bn coupling products were determined by electron spin resonance at 50–100 °C. The equilibrium constants were estimated to be 9.01 × 10^?11 and 6.47 × 10^?11 mol L^?1 at 120 °C for NO88Me and NO88Bn, respectively, resulting in the combination rate constants (k_c) 2.77 × 10⁶ (NO88Me) and 2.07 × 10⁶ L mol^?1 s^?1 (NO88Bn). The similar polymerization results and kinetic parameters for NO88Me and NO88Bn indicated the absence of any 3‐N‐transannular effect by the benzyl substituent relative to the methyl substituent. The values of k_d and k_c were 4–8 and 25–33 times lower, respectively, than the reported values for PS‐TEMPO at 120 °C, indicating that the 2,5‐spirodicyclohexyl rings have a more profound effect on the combination reaction rather than the dissociation reaction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 327–334, 2003     

ab initio calculations and thermochemical analysis on C1 atom abstractions of chlorine from chlorocarbons and the reverse alkyl abstractions: Cl2 + R· ↔ Cl· + RCl

Thermodynamic properties (ΔH°_f(298), S°₍₂₉₈₎ and Cp(T) from 300 to 1500 K) for reactants, adducts, transition states, and products in reactions of CH₃ and C₂H₅ with Cl₂ are calculated using CBSQ//MP2/6‐311G(d,p). Molecular structures and vibration frequencies are determined at the MP2/6‐311G(d,p), with single‐point calculations for energy at QCISD(T)/6‐311 + G(d,p), MP4(SDQ)/CbsB4, and MP2/CBSB3 levels of calculation with scaled vibration frequencies. Contributions of rotational frequencies for S°₍₂₉₈₎ and Cp(T)'s are calculated based on rotational barrier heights and moments of inertia using the method of Pitzer and Gwinn [1]. Thermodynamic parameters, ΔH°_f(298), S°₍₂₉₈₎, and C_P(T), are evaluated for C₁ and C₂ chlorocarbon molecules and radicals. These thermodynamic properties are used in evaluation and comparison of Cl₂ + R· → Cl· + RCl (defined forward direction) reaction rate constants from the kinetics literature for comparison with the calculations. Data from some 20 reactions in the literature show linearity on a plot of Ea_fwd vs. ΔH_rxn,fwd, yielding a slope of (0.38 ± 0.04) and intercept of (10.12 ± 0.81) kcal/mole. A correlation of average Arrhenius preexponential factor for Cl· + RCl → Cl₂ + R· (reverse rxn) of (4.44 ± 1.58) × 10¹³ cm³/mol‐sec on a per‐chlorine basis is obtained with Ea_Rev = (0.64 ± 0.04) × ΔH_rxn,Rev + (9.72 ± 0.83) kcal/mole, where Ea_Rev is 0.0 if ΔH_rxn,Rev is more than 15.2 kcal/mole exothermic. Kinetic evaluations of literature data are also performed for classes of reactions. Ea_fwd = (0.39 ± 0.11) × ΔH_rxn,fwd + (10.49 ± 2.21) kcal/mole and average A_fwd = (5.89 ± 2.48) × 10¹² cm³/mole‐sec for hydrocarbons: Ea_fwd = (0.40 ± 0.07) × ΔH_rxn,fwd + (10.32 ± 1.31) kcal/mole and average A_fwd = (6.89 ± 2.15) × 10¹¹ cm³/mole‐sec for C₁ chlorocarbons: Ea_fwd = (0.33 ± 0.08) × ΔH_rxn,fwd + (9.46 ± 1.35) kcal/mole and average A_fwd = (4.64 ± 2.10) × 10¹¹ cm³/mole‐sec for C₂ chlorocarbons. Calculation results on the methyl and ethyl reactions with Cl₂ show agreement with the experimental data after an adjustment of +2.3 kcal/mole is made in the calculated negative Ea's. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 548–565, 2000     

A simplified mass isotopomer approach to estimate gluconeogenesis rate in vivo using deuterium oxide

We compare a new simplified ²H enrichment mass isotopomer analysis (MIA) against the laborious hexamethylentetramine (HMT) method to quantify the contribution of gluconeogenesis (GNG) to total glucose production (GP) in calves. Both methods are based on the ²H labeling of glucose after in vivo administration of deuterium oxide. The ²H enrichments of plasma glucose at different C‐H positions were measured as aldonitrile pentaacetate (AAc) and methyloxime‐trimethylsilyl (MoxTMS) derivatives or HMT by gas chromatography/mass spectrometry (GC/MS). Two pre‐ruminating fasted Holstein calves (51 kg body mass, BM, age 7 days) received two oral bolus doses of ²H₂O (10 g/kg BM, 70 atom% ²H) at 7:00 h and 11:00 h after overnight food withdrawal. Blood samples for fractional GNG determination were collected at ?24 and between 6 and 9 h after the first ²H₂O dose. The ratio of ²H enrichments C5/C2 represents the contribution of GNG to GP. The ²H enrichment at C2 was calculated based on the ion fragments at m/z 328 (C1‐C6) ‐ m/z 187 (C3‐C6) of glucose AAc. The ²H enrichment at C5 was approximated either by averaging the ²H enrichment at C5‐C6 using the ion fragment of glucose MoxTMS at m/z 205 or by conversion of the C5 of glucose into HMT. The fractional GNG calculated by the C5‐C6 average ²H enrichment method (41.4 ± 6.9%) compared to the HMT method (34.3 ± 11.4%) was not different (mean ± SD, n = 6 replicates). In conclusion, GNG can be estimated with less laborious sample preparation by means of our new C5‐C6 average ²H enrichment method using AAc and MoxTMS glucose derivatives. Copyright © 2010 John Wiley & Sons, Ltd.