Degradative chain transfer in vinyl acetate polymerizations using toluene as solvent

In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (C_trs) determined using the Mayo method is equal to 3.8 × 10^?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10^?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the M_n data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007     

Statistical Analysis of the Effect of Mineral Admixtures on the Strength of the Interfacial Transition Zone

Microscopic evidence indicates that the thickness of the interfacial transition zone (ITZ) between the aggregate and the cement paste is modified when mineral admixtures partially replace portland cement. Unfortunately, there is limited information on the significance of these microscopic modifications to the mechanical properties of the ITZ. This research reports experimental results on the shear and tensile strength of the ITZ as affected by the addition of the following mineral admixtures: silica fume, fly ash, and natural pozzolan. Statistical analysis was used to identify the significant parameters affecting the tensile and shear strength of the ITZ. Experimental results indicate that not only does the incorporation of silica fume and fly ash increase the strength of the ITZ, these mineral admixtures have a greater influence on the strength increase of the ITZ than in the strength increase of the cement paste.     

Surface characterization of recycled tire rubber to be used in cement paste matrix

The surface modification of tire rubber after treatment with saturated NaOH aqueous solution was investigated by HATR infrared analysis, potentiometric titration, and contact angle measurements. Infrared analysis of the powdered treated rubber showed a decrease in absorption at 1540, 1450, and 1395 cm(-1). This decrease is attributed to the removal of zinc stearate, an additive present in tire formulations that often migrates and diffuses to the surface, resulting in poor adhesion between the rubber and other materials. The potentiometric titration of the suspension of powdered rubber in 0.1 M NaCl showed that more hydrochloric acid was consumed by the untreated rubber, most likely a result of the hyrdrolysis of the zinc stearate to the organic acid. Contact angles of flat tire pieces showed an homogeneity enhancement of the treated rubber surface. The decrease of the zinc stearate on the treated rubber surface explains the improvement in the adhesion of this material to the cement matrix, observed in a previous research. The promising results of this study are a starting point for future research on incorporating rubber particles into cementitious materials as a means of successfully utilizing the vast amounts of tire waste currently in landfills.     

Phase separation of p53 precedes aggregation and is affected by oncogenic mutations and ligands

Mutant p53 tends to form aggregates with amyloid properties, especially amyloid oligomers inside the nucleus, which are believed to cause oncogenic gain-of-function (GoF). The mechanism of the formation of the aggregates in the nucleus remains uncertain. The present study demonstrated that the DNA-binding domain of p53 (p53C) underwent phase separation (PS) on the pathway to aggregation under various conditions. p53C phase separated in the presence of the crowding agent polyethylene glycol (PEG). Similarly, mutant p53C (M237I and R249S) underwent PS; however, the process evolved to a solid-like phase transition faster than that in the case of wild-type p53C. The data obtained by microscopy of live cells indicated that transfection of mutant full-length p53 into the cells tended to result in PS and phase transition (PT) in the nuclear compartments, which are likely the cause of the GoF effects. Fluorescence recovery after photobleaching (FRAP) experiments revealed liquid characteristics of the condensates in the nucleus. Mutant p53 tended to undergo gel- and solid-like phase transitions in the nucleus and in nuclear bodies demonstrated by slow and incomplete recovery of fluorescence after photobleaching. Polyanions, such as heparin and RNA, were able to modulate PS and PT in vitro. Heparin apparently stabilized the condensates in a gel-like state, and RNA apparently induced a solid-like state of the protein even in the absence of PEG. Conditions that destabilize p53C into a molten globule conformation also produced liquid droplets in the absence of crowding. The disordered transactivation domain (TAD) modulated both phase separation and amyloid aggregation. In summary, our data provide mechanistic insight into the formation of p53 condensates and conditions that may result in the formation of aggregated structures, such as mutant amyloid oligomers, in cancer. The pathway of mutant p53 from liquid droplets to gel-like and solid-like (amyloid) species may be a suitable target for anticancer therapy.

Mutant p53 tends to form aggregates with amyloid properties, especially amyloid oligomers inside the nucleus, which are believed to cause oncogenic gain-of-function (GoF).     

Preparative Droplet Counter-Current Chromatography for the Separation of the New Nor-Seco-Triterpene and Pentacyclic Triterpenoids from Qualea Parviflora

The methanolic extract of the bark of the medicinal plant Qualea parviflora (Vochysiaceae) contains new nor-seco-triterpene and pentacyclic triterpenoids. They were separated in a preparative scale using droplet counter-current chromatography. The optimum solvent used was composed of a mixture of CHCl₃/MeOH/H₂O (43:37:20, v/v) in the descending mode and led to a successful separation of the new compound 28-nor-17, 22-seco-2α, 3β, 19, 22, 23-pentahydroxy-Δ¹²-oleanane, besides the known triterpenoids bellericagenin B, bellericaside B and arjunglucoside I . Identification was performed by ESI-MS, ¹H NMR and ¹³C NMR analyses.     

Spin-Projected EHF equations

Extended Hartree-Fock (EHF ) equations are developed for the general open-shell case using a modified pair-orthogonality-constrained variation (POCV ) method. The EHF energy is expressed in terms of corresponding orbitals that are required to remain orthogonal and paired for all arbitrary infinitesimal variations. The Euler equations for each set of orbitals are reduced to unique pseudosecular equations, the LCAO form of which may easily be derived. The Euler equations and the expressions obtained for the off-diagonal elements of the ?^γδ (γ, δ = a or b) matrices for the closed-shell case are identical to those obtained by Mayer, who used the generalized Brillouin theorem method. However, the present method yields equations for both closed- and open-shell cases and for any spin state.     

Genericity and existence of a minimum for scalar integral functionals

This paper is concerned with the existence of a minimum in a Sobolev space for the functional $$F_g (x): = \int_0^T {g(x(t)){\text{ }}dt + \int_0^T {h(x'(t)){\text{ }}dt,{\text{ }}x(0) = a,{\text{ }}x(T) = b,} }$$ wherea,b are real numbers,g is a continuous map, andh is lower semicontinuous, satisfying adequate growth conditions. As shown by Cellina and Mariconda, there exists a dense subset of the space of continuous functions bounded below such that, forg in this subset, the above functional attains its minimum no matter whichh is used. This subset contains in particular the monotone maps, as shown by Marcellini, and the concave maps, as shown by Cellina and Colombo. Our aim is twofold: first to show that this subset, although dense, is meager in the sense of the Baire category; and second to show that it contains a class of functions which we call concave-monotone, because it generalizes both the classes of concave and of monotone functions.