Global behavior and asymptotic reduction of a chemical kinetics system with continua of equilibria

We consider a model chemical kinetics system describing the dynamics of species concentrations taking part is consecutive-competitive reaction in a continuopusly stirred tank reactor. Corresponding dynamical system has a continua of equilibria. Particular equilibrium to which the solution of the system tends depends on the initial conditions. The global behavior of the system and its reductions via the invariant manifold and the boundary function methods are studied.AMS Subject Classification: 34D15, 34D35, 37C10     

Stability of mycophenolate mofetil in polypropylene 5% dextrose infusion bags and chemical compatibility associated with the use of the Equashield® closed‐system transfer device

Stability studies are necessary in healthcare settings as they facilitate fast, cost‐effective and efficient work related to batch manufacturing and availability of supplies. We studied the stability of 1–10 mg/mL mycophenolate mofetil (MMF) in polypropylene 5% dextrose infusion bags prepared from Cellcept^® and with a generic brand name (Micofenolato de Mofetilo Accord) at different storage temperatures. To ensure chemical compatibility during preparation, we also tested MMF sorption to the Equashield^® closed‐system drug transfer device used in this step. For this, a validated stability‐indicating high‐performance liquid chromatography method was developed for the quantification and identification of MMF in the infusion bags. The analytical selectivity of the assay was determined by subjecting an MMF sample to extreme values of pH, oxidative stress and heat conditions to force degradation. Protected from light, 1–10 mg/mL MMF in infusion polypropylene bags prepared from reconstituted Cellcept^® 500 mg or Accord 500 mg in 5% dextrose was stable for at least 35 days when stored at 2–8°C or between ?15 and ?25°C, and for 14 days when stored at 25°C. MMF loss owing to chemical sorption to the Equashield^® closed‐system drug transfer device set was negligible.     

Dynamic NMR spectroscopy in studies of the kinetics of photoinduced chemical exchange in solutions

Modern NMR-based methods of studying the kinetics and mechanisms of reversible photochemical reactions in solutions are surveyed. Detailed consideration of peculiar features of the experimental techniques based on NMR lineshape analysis and double resonance NMR and used for the determination of the effective rate constants for and quantum yields of photoinduced chemical exchange processes is presented. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1631–1641, October, 2006.     

The bonding picture in hypervalent XF3 (X = Cl,Br, I,At) fluorides revisited with quantum chemical topology

Hypervalent XF₃ (X = Cl, Br, I, At) fluorides exhibit T‐shaped C_2V equilibrium structures with the heavier of them, AtF₃, also revealing an almost isoenergetic planar D_3h structure. Factors explaining this behavior based on simple “chemical intuition” are currently missing. In this work, we combine non‐relativistic (ClF₃), scalar‐relativistic and two‐component (X = Br − At) density functional theory calculations, and bonding analyses based on the electron localization function and the quantum theory of atoms in molecules. Typical signatures of charge‐shift bonding have been identified at the bent T‐shaped structures of ClF₃ and BrF₃, while the bonds of the other structures exhibit a dominant ionic character. With the aim of explaining the D_3h structure of AtF₃, we extend the multipole expansion analysis to the framework of two‐component single‐reference calculations. This methodological advance enables us to rationalize the relative stability of the T‐shaped C_2v and the planar D_3h structures: the Coulomb repulsions between the two lone‐pairs of the central atom and between each lone‐pair and each fluorine ligand are found significantly larger at the D_3h structures than at the C_2v ones for X = Cl − I, but not with X = At. This comes with the increasing stabilization, along the XF₃ series, of the planar D_3h structure with respect to the global T‐shaped C_2v minima. Hence, we show that the careful use of principles that are at the heart of the valence shell electron pair repulsion model provides reasonable justifications for stable planar D_3h structures in AX₃E₂ systems. © 2017 Wiley Periodicals, Inc.