A Safety Strategy for Producing Poly(Acrylic Acid) of Low Molar Mass

The synthesis of poly(acrylic acid) (PAA) of low molar mass under safe conditions is difficult due to the high polymerization rate of acrylic acid (AA) and the fast heat generation. The aqueous‐solution “semibatch” polymerization of non‐ionized AA in almost starved conditions involves high initiator loads when low molar masses are required. This article proposes the simultaneous feeding of AA and nonconventional chain transfer agents (CTA) as a strategy aimed at controlling both the molar masses and the generated heat rate. Three CTAs are investigated: 2‐mercaptoethanol, thioglycolic acid, and isopropyl alcohol. Even when PAA of relatively low molar mass can be produced by adequately selecting the flow rates and concentrations of both AA and CTA, it is found that the nature of CTA can have a significant effect on the polymerizations kinetics. The mechanisms responsible for these effects are discussed with the help of a representative mathematical model.

     

Continuous photochemical generation of catalytically active [CpRu]+ complexes from CpRu(η6-C6H6)PF6

Inter- and intramolecular ene-yne coupling reactions catalyzed by a species generated in situ via photolysis of CpRu(η(6)-C(6)H(6))PF(6)--an inexpensive, readily available, and shelf-stable complex--have been demonstrated under conditions of continuous flow. Importantly, the catalyst can be recovered quantitatively at the end of the reaction. Various functional groups are tolerated by the reaction, which affords skipped diene products in high yields.     

Structure-guided redesign of D-fructose-6-phosphate aldolase from E. coli: remarkable activity and selectivity towards acceptor substrates by two-point mutation

Structure-guided re-design of the acceptor binding site of D-fructose-6-phosphate aldolase from E. coli leads to the construction of FSA A129S/A165G double mutant with an activity between 5- to >900-fold higher than that of wild-type towards N-Cbz-aminoaldehyde derivatives.     

Solvatomorphism in (E)‐2‐(2,6‐dichloro‐4‐hydroxybenzylidene)hydrazinecarboximidamide

The structures of orthorhombic (E)‐4‐(2‐{[amino(iminio)methyl]amino}vinyl)‐3,5‐dichlorophenolate dihydrate, C₈H₈Cl₂N₄O·2H₂O, (I), triclinic (E)‐4‐(2‐{[amino(iminio)methyl]amino}vinyl)‐3,5‐dichlorophenolate methanol disolvate, C₈H₈Cl₂N₄O·2CH₄O, (II), and orthorhombic (E)‐amino[(2,6‐dichloro‐4‐hydroxystyryl)amino]methaniminium acetate, C₈H₉Cl₂N₄O⁺·C₂H₃O₂⁻, (III), all crystallize with one formula unit in the asymmetric unit, with the molecule in an E configuration and the phenol H atom transferred to the guanidine N atom. Although the molecules of the title compounds form extended chains via hydrogen bonding in all three forms, owing to the presence of different solvent molecules, those chains are connected differently in the individual forms. In (II), the molecules are all coplanar, while in (I) and (III), adjacent molecules are tilted relative to one another to varying degrees. Also, because of the variation in hydrogen‐bond‐formation ability of the solvents, the hydrogen‐bonding arrangements vary in the three forms.     

Pentagalloyl Glucose (PGG) Partially Prevents Arterial Mechanical Changes Due to Elastin Degradation

Experimental Mechanics - Elastic fibers are composed primarily of the protein elastin and they provide reversible elasticity to the large arteries. Degradation of elastic fibers is a common...     

The Kneser Property for the Second Order Functional Abstract Cauchy Problem

In this work we establish existence of mild solutions for a class of abstract semi-linear functional differential equations of second order and we prove that the set consisting of the mild solutions for these problems is connected.     

Almost periodic Schrödinger operators along interval exchange transformations

It is shown that Schrödinger operators, with potentials along the shift embedding of irreducible interval exchange transformations in a dense set, have pure singular continuous spectrum for Lebesgue almost all points of the interval. Such potentials are natural generalizations of the Sturmian case.     

Transverse vibrations of circular plates with stepped thickness

The study of the dynamic behaviour of circular plates with stepped thickness is of interest in view of their use in the construction of high frequency transducers. A simple analytical approach which allows for the prediction of their natural frequencies is proposed in the present Note.     

New semiconducting oxide photoanodes for water splitting in a photoelectrochemical cell Electrochemistry of n-type NiTiO3

The electrochemical behaviour of NiTiO₃ has been studied. The interest in this mixed-metal oxide lays in its possible use for solar-energy conversion. Anodic oxidation of NiTi0₃ was very irreversible. The electrode became aged, probably due to formation of a porous film of an irreducible higher oxide. The stirring-independent Cottrell behaviour of the anodic oxidation of NiTiO₃ should be due to current limitation by diffusion of a reaction product away from the NiTi0₃ surface through this irreducible higher oxide, which should be of a porous nature. The diffusion-limiting species could not be OH^?, as the Cottrell slopes only increased by about five times for a pH increase from 3 to 14. Five and two processes were involved in the anodic oxidation of NiTiO₃ at pH 14 and 3 respectively, as determined by chronopotentiometry. The same number of processes appeared upon inversion of the current.     

Mineralization procedure for use with the fluorometric determination of zinc in biological samples

Several minerelization procedures have been evaluated for use in conjunction with a method to determine zinc in milk, eggs, water and whole diets, based on the formation and extraction into diethyl ether, of Zn-5,7-dibromo-8-quinolinol. The results were compared with the known contents of standard samples or those obtained by flame atomic-absorption spectrometry. The most satisfactory procedure employed digestion with acid mixtures to destroy organic matter, and yielded a detection limit of 0.3 mg/kg for Zn.