Methyl methacrylate as solvent for the thermal decomposition of the cyclic molecule pinacolone diperoxide: Toward the polymerization process

The decomposition rate constant (k_d) of pinacolone diperoxide (PDP, 3,6‐diterbutyl‐3,6‐dimethyl‐1,2,4,5‐tetraoxacyclohexane) in methyl methacrylate (MMA) is determined by the kinetic study of its thermal decomposition at temperatures from 110 °C to 140 °C. The calculated k_d values for PDP are higher than the corresponding values previously determined and reported for diethyl ketone triperoxide (DEKTP, 3,3,6,6,9,9‐hexaethyl‐1,2,4,5,7,8‐hexaoxacyclononane), for example, at 140 °C the k_d for PDP is 75.4 × 10^?5 s^?1, while for DEKTP, it is 50.6 × 10^?5 s^?1. The difference in the k_d between 130 °C and 140 °C indicates that the decomposition mechanism, sequential and/or concerted, is a function of temperature. The conformations of both initiators justify the higher k_d for PDP in MMA than DEKTP, where one single conformer is found for PDP, whereas 212 conformers are found for DEKTP. Bulk polymerization of MMA using PDP as the initiator reveals also the presence of an induction period, such as in DEKTP case. This work provides mechanistic insights into the interactions among the bifunctional cyclic peroxide PDP and the MMA monomer and their influence on the polymerization kinetics. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 997–1007     

Branched-chain organic compounds. Part 11: Validation of a new method for determination of the potential energy of cohesion of an organic crystal and deduction of the heat capacity of the vapour

Abstract  

The cohesion energy of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, as obtained from the change of kinetic and potential energies in the heat of sublimation of the crystal, E _p,coh = −46.7 kJ mol⁻¹ (78.6 °C), has been validated. A safe physicomathematic test based on the balance of entropy for the sublimation and Planck’s equation for changes of state, extended to entropy, was devised to ascertain the kinetic energies of the crystal and the gas molecule. Entropic equations were developed for the phase equilibrium to find precisely and with simplicity the vibrational energy of the crystal by using the vapour pressure exclusively and independently from the internal rotational and vibrational motion of the gas molecule. The heat capacity of the vapour was determined in this way, which in this case releases the solid allowing vibrational movement in the gas phase to meet the pressure of sublimation, C _p (T)/J K⁻¹ mol⁻¹ = 1.268 T/K + 58.62 (71.1–86.1 °C). An independent variational method of deducing the vibrational entropy, energy, or heat capacity of the gas molecule from each other was compared with the equations and was shown to yield the quantities with high accuracy. Values of the Nernst–Lindemann functions are tabulated.     

Stable Pyrrole-Linked Bioconjugates through Tetrazine-Triggered Azanorbornadiene Fragmentation

An azanorbornadiene bromovinyl sulfone reagent for cysteine-selective bioconjugation has been developed. Subsequent reaction with dipyridyl tetrazine leads to bond cleavage and formation of a pyrrole-linked conjugate. The latter involves ligation of the tetrazine to the azanorbornadiene-tagged protein through inverse electron demand Diels–Alder cycloaddition with subsequent double retro-Diels–Alder reactions to form a stable pyrrole linkage. The sequence of site-selective bioconjugation followed by bioorthogonal bond cleavage was efficiently employed for the labelling of three different proteins. This method benefits from easy preparation of these reagents, selectivity for cysteine, and stability after reaction with a commercial tetrazine, which has potential for the routine preparation of protein conjugates for chemical biology studies.     

Mathematical modeling of the immune system response to pathogens

The detection and elimination of pathogens in an organism are the main tasks of its immune system. The most important cells involved in these processes are neutrophils and macrophages. These processes might have two resolutions: The first is the possibility of pathogen elimination, and the other the possibility of the inflammation resolution. In this work, we present several mathematical models involving immune cell densities and inflammation levels. Our general goal is to exhibit the possible pathogen eradication or the inflammation resolution. We use bifurcation techniques in order to analyze how parameter variations may change the system evolution. Our results indicate that the elimination of apoptotic neutrophils by macrophages has a dichotomy effect: It contributes to the decrease of the inflammation level, but it may hinder the pathogen elimination. Also, an increment of the average neutrophil life can improve healthy outcomes. Moreover, we find scenarios when pathogens cannot be eliminated, as well as conditions for their successful eradication.     

Comment on “Diferential transform method for the solutions to some initial value problems in chemistry”

Journal of Mathematical Chemistry - We argue that the differential transform method is merely the well known Taylor series approach in disguise. We show that the examples chosen by Qin and Lou have...     

Nonmonotone inexact restoration approach for minimization with orthogonality constraints

Numerical Algorithms - Minimizing a differentiable function restricted to the set of matrices with orthonormal columns finds applications in several fields of science and engineering. In this...