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The characteristic collision energy (CCE) to obtain 50% fragmentation of positively and negatively single charged noncovalent clusters has been measured. CCE was found to increase linearly with the degrees of freedom (DoF) of the precursor ion, analogously to that observed for synthetic polymers. This suggests that fragmentation behavior (e.g. energy randomization) in covalent molecules and clusters are similar. Analysis of the slope of CCE with molecular size (DoF) indicates that activation energy of fragmentation of these clusters (loss of a monomer unit) is similar to that of the lowest energy fragmentation of protonated leucine–enkephalin. Positively and negatively charged aggregates behave similarly, but the slope of the CCE versus DoF plot is steeper for positive ions, suggesting that these are more stable than their negative counterparts. Copyright © 2013 John Wiley & Sons, Ltd.

The main aim of th is paper pivote d ar ound th e influence of some parameters relev ant to biomass pyrolys is on the numerical solutions of the nth order distributed activation energy model (DAEM) using the Gamma distribution. The upper limit of ‘dE’ integral, frequency factor, reaction order, and the shape and rate parameters of the Gamma distribution are investigated. Analys is of the mathematical model is done with the help of asymptotic expansion.

The temperature-dependences of the 1H n.m.r. spectra of 6H,12H,18H-tribenzo[b,f,j][1,5,9]trithiacyclodode (7) and its 5,5,11,11,17,17-hexaoxide (8) have been interpreted in terms of ring inversions between enantiomeric helical conformations. The free energy of activation for conformational inversion in the cyclic trisulphide (7) is compared with that previously obtained for the ring inversion of the enantiomeric C2 conformations of the parent hydrocarbon 5,6,11,12,17,18-hexahydrotribenzo[a,e,i]cyclododecene (1).

The interpretation of the results of thermal measurements followed over decades the Arrhenius law. In recent years an apparently different interpretation (Eyring's equation) has been emerging in the literature on polymers. As the main reason for this, a direct connection to material properties has been claimed. The paper shows some weak points in the Eyring theory and in its application as well. Firstly, the parameters of the two equations are mathematically convertible to each other. Thus Eyring's conceptual quantities (entropy and enthalpy of activation) give no new physical information. Secondly, the Eyring theory postulates an equilibrium for the activated state. In the case of processes, however, in which change is an inherent characteristic, this assumption seems to be unjustified.

The reactions of CF3 with benzotrifluoride (BTF) were studied at 1029, 1070 and 1132 K. The RCF3H/R½C2F6[BTF] ratio was found to decrease with increasing benzotrifluoride pressure, which was interpreted as simultaneous formation of C2F6 by CF3 recombination and an inversion reaction between CF3 and C6H5CF3.From experiments in the absence and presence of hydrogen, we obtained log(k2/l. mol–1 s–1)=(9.1 ± 0.3)–(9.4 ± 1.2)/θ and log(k7/l. mol–1 s–1)=(8.7 ± 0.1)–(9.3 ± 0.1)/θ, (θ= 2.303 RT/kcal mol–1) for the rate coefficients of H-abstraction by CF3 from C6H5CF3 and H2, respectively. Hence we obtained, with an assumed value for the activation energy of step (–2), D°(CF3C6H4—H)= 109.0 ± 2.5 kcal mol–1. CF3H + C6H4CF3→ CF3+ C6H5CF3(–2)

Abstract This paper deals with the influence of some parameters relevant to biomass pyrolysis on the numerical solutions of the nonisothermal n th order distributed activation energy model using the Rayleigh distribution. Investigated parameters are the integral upper limit, the frequency factor, the heating rate, the reaction order and the scale parameters of the Rayleigh distribution. The influence of these parameters has been considered for the determination of the kinetic parameters of the non-isothermal n th order Rayleigh distribution from the experimentally derived thermoanalytical data of biomass pyrolysis.

Abstract This paper describes the influence of some parameters significant to biomass pyrolysis on the numerical solutions of the non-isothermal nth order distributed activation energy model (DAEM) using the Gamma distribution and discusses the special case for the positive integer value of the scale parameter (λ), i.e. the Erlang distribution. Investigated parameters are the integral upper limit, the frequency factor, the heating rate, the reaction order, and the shape and rate parameters of the Gamma distribution. Influence of these parameters has been considered for the determination of the kinetic parameters of the non-isothermal nth order Gamma distribution from the experimentally derived thermoanalytical data of biomass pyrolysis. Mathematically, the effect of parameters on numerical solution is also used for predicting the behaviour of the unpyrolysized fraction of biomass with respect to temperature. Analysis of the mathematical model is based upon asymptotic expansions, which leads to the systematic methods for efficient way to determine the accurate approximations. The proposed method, therefore, provides a rapid and highly effective way for estimating the kinetic parameters and the distribution of activation energies.

The rates of protein conformational changes are usually not only limited by external but also internal friction, however, the origin and significance of this latter phenomenon is poorly understood. It is often found experimentally that a linear fit to the reciprocal of the reaction rate as a function of the viscosity of the external medium has a non-zero value at zero viscosity, signifying the presence of internal friction. Furthermore, for a few proteins (including trypsin) the temperature dependence of the internal friction was also determined, which shows an Arrhenius-like behavior, with an activation energy in the range of tens of kJ/mol. This indicates that the internal structural rearrangement of proteins occurs in a rugged energy landscape. To better understand this phenomenon, we performed molecular dynamics simulations of the conformational changes of trypsin. The simulations allowed us to control the external viscosity over a wide range, well exceeding the experimentally accessible values. The results confirm not only the existence of internal friction, but also its Arrhenius-like temperature dependence, and that the activation energy of the internal friction is indeed several tens of kJ/mol, in good agreement with the experimentally obtained values.