p-Benzoquinone-tin polycondensates as stabilisers for polybutadiene rubber against photo-degradation

p-Benzoquinone-tin derivatives, obtained by polycondensation of the quinone and SnCl₄ in the absence of solvent, have been investigated as uv stabilisers for polybutadiene rubber. Intrinsic viscosity measurements have shown the greater efficiency of these products relative to phenyl salicylate which is commonly used in industry. The stabilising efficiency increases as the tin content of the stabiliser increases. A mechanism based on the involvement of both the quinone part of the stabiliser and the SnSn bonds in scavenging the radical species formed, as well as blocking the radical sites on the polymeric chains, has been developed. Moreover, it has been shown that prior oxidation of the stabilisers of higher tin content can afford complete protection of rubber from degradation by uv irradiation.     

Selective nitrosation of guanazine: preparation of azidoaminotriazole and nitrosoguanazine anion-Cu(II) complexes

Guanazine (3,4,5-triamino-1,2,4-triazole) is selectively nitrosated on C-NH₂ to produce nitrosoguanazine (3-nitrosamino-4,5-diamino-1,2,4-triazole). The nitrosoguanazine is used to prepare 5-azido-3-amino-1,2,4-triazole and nitrosoguanazine anion-Cu(II) complexes.     

Polymerization products of p-benzoquinone as thermal stabilizers for rigid poly(vinyl chloride). Part II—Evaluation of the stabilizing efficiency

Quinone-tin polymers prepared by the cationic polymerization of p-benzoquinone with tin(II)chloride in the absence of solvent have been investigated as thermal stabilizers for rigid PVC at 180°C in air by measuring the rate of dehydrochlorination. The results reveal the higher stabilizing efficiency of these products relative to dibutyltin maleate, basic lead carbonate and barium-cadmium stearate stabilizers commonly used in industry. The induction period in the early stages of the dehydrochlorination process increases as a function of the metal content in the stabilizer molecule. The evidence indicates that the quinone and the metal part (

) of the stabilizer participate in the stabilization process by trapping the radical intermediates, as well as blocking the odd electron sites formed on the PVC chains. The mechanism of stabilization suggested to account for the results obtained supports a radical mechanism for the dehydrochlorination reaction.     

Anthraquinone derivatives as organic stabilizers for rigid poly(vinyl chloride) against photo-degradation

Anthraquinone derivatives have been prepared and investigated as photo-stabilizers for rigid PVC by measuring the extent of weight loss (%), the amount of gel formation as well as the intrinsic viscosity of the soluble fractions of the degraded polymer. The results indicated a reasonable stabilizing effect of these derivatives compared with UV-commercially used stabilizers. A synergistic effect is achieved when the anthraquinone derivatives are mixed with UV-absorbers in a weight ratio of 75% of investigated organic stabilizer and 25% of reference stabilizer.A probable radical mechanism is proposed to account for the stabilizing action of the organic investigated materials.     

Enhancing the Anticancer Potential of Targeting Tumor-Associated Metalloenzymes via VEGFR Inhibition by New Triazolo[4,3-a]pyrimidinone Acyclo C-Nucleosides Multitarget Agents

The role of metalloenzymes in tumor progression had broadened their application in cancer therapy. Of these, MMPs and CAs are validated druggable targets that share some pivotal signaling pathways. The majority of MMPs or CAs inhibitors are designed as single-target agents. Despite their transient efficacy, these agents are often susceptible to resistance. This set the stage to introduce dual inhibitors of correlated MMPs and CAs. The next step is expected to target the common vital signaling nodes as well. In this regard, VEGFR-2 is central to various tumorigenesis events involving both families, especially MMP-2 and CA II. Herein, we report simultaneous inhibition of MMP-2, CA II, and VEGFR-2 via rationally designed hybrid 1,2,4-triazolo[4,3-a]pyrimidinone acyclo C-nucleosides. The promising derivatives were nanomolar inhibitors of VEGFR-2 (8; IC₅₀ = 5.89 nM, 9; IC₅₀ = 10.52 nM) and MMP-2 (8; IC₅₀ = 17.44 nM, 9; IC₅₀ = 30.93 nM) and submicromolar inhibitors of CA II (8; IC₅₀ = 0.21 µM, 9; IC₅₀ = 0.36 µM). Docking studies predicted their binding modes into the enzyme active sites and the structural determinants of activity regarding substitution and regioselectivity. MTT assay demonstrated that both compounds were 12 folds safer than doxorubicin with superior anticancer activities against three human cancers recording single-digit nanomolar IC₅₀, thus echoing their enzymatic activities. Up to our knowledge, this study introduces the first in class triazolopyrimidinone acyclo C-nucleosides VEGFR-2/MMP-2/CA II inhibitors that deserve further investigation.     

Tilting up iterated tilted algebras

We show that, if is a representation-finite iterated tilted algebra of euclidean type , then there exist a sequence of algebras , and a sequence of modules , where , such that each is an APR-tilting -module, or an APR-cotilting -module, and is tilted representation-finite.

     

Nucleation of the Al6(Fe,Mn)-to-α-Al–(Fe,Mn)–Si transformation in 3XXX aluminium alloys. II. Transformation in cast aluminium alloys

The nucleation behaviour of the homogenization-induced Al₆(Fe,?Mn)-to-α-Al–(Fe,?Mn)–Si transformation is investigated in a companion paper to part I (a study with roll-bonded diffusion couples). Diffusion experiments using silicon-coated Al–0.53?wt%?Fe–1.02?wt%?Mn alloy blocks allow control of the thermodynamic driving force for transformation within a microstructure typical of a cast ingot. As expected, this microstructure appears to give ready and yet stochastic nucleation as silicon diffuses into the alloy sections. In addition, transmission electron microscopy is used to analyse partially transformed particles in heat-treated alloy samples of fixed silicon content. This confirms the suggestion made in part I that the transformation preferentially nucleates at matrix grain/cell boundaries. Nucleation theory suggests this results from the ability of the boundaries to relieve volume changes associated with the nucleation event.     

Contact mechanisms and design principles for alloyed Ohmic contacts to p-type GaN

Contact mechanisms and design principles of alloyed Ohmic contacts to p-type GaN (p-GaN) are studied. Illustrative studies include bilayer, trilayer and quadrilayer Ohmic contacts. Almost all contacts appear to follow the proposed design principles. The removal of the surface insulating layer, preferably by plasma etching, leads to metal/semiconductor barrier lowering. This, together with thermionic emission, plays a crucial role for yielding low-resistance metal/p-GaN contacts. Band-gap narrowing and/or image force lowering due to heavy doping also contribute to the low contact resistivity. A judicious choice of the layer thicknesses of appropriate metal combination, rapid thermal annealing (RTA) time, RTA temperature and RTA ambient can produce large-work-function alloy(s) in contact with the p-GaN epitaxial layer, creating a robust low-resistivity thermionic-emission-induced Ohmic contact. The fundamental physics of contact mechanisms and design principles proposed in the study is useful for making other contacts. These are general enough to be extended to other III–V nitride materials, at the least.     

On the dual-phase-lag thermoelasticity theory

The uniqueness and reciprocal theorems are proved without the use of Laplace Transforms for the Dual-Phase-Lag thermoelasticity theory. Variational principle is established for a linear anisotropic and inhomogeneous thermoelastic solid. The dissipative inequality is used to obtain a continuous dependence result for isotropic solid.     

Thermodynamics and molecular bases of the interaction of ampicillin and streptomycin at their binding sites of bovine serum albumin

Among the biological parameters of chemotherapeutics, serum albumin binding is a critical factor in determining drug distribution and bioavailability. In this study, the binding properties as well as the interaction of ampicillin and streptomycin at their binding sites of bovine serum albumin (BSA) were investigated. The binding constant varied from 3.2 × 10³ M^?1 at 298 K to 37.5 × 10³ M^?1 at 313 K for ampicillin, and from 10.7 × 10³ M^?1 at 298 K to 3.5 × 10³ M^?1 at 313 K for streptomycin. By increasing the temperature, from 298 to 313 K, the binding affinity decreased by about 11-fold for ampicillin. Conversely, streptomycin showed stronger binding at higher temperature, which is decreased by threefold at 298 K. Interestingly, the affinity of ampicillin with the free BSA was ~4-fold higher than the binding with BSA/streptomycin complex. In contrast, the affinity of streptomycin with the free BSA was ~6-fold lower than the binding with BSA/ampicillin complex. Mutual binding experiments indicate that ampicillin and streptomycin are sharing both of common and different binding sites on BSA. Dissection of the forces of interactions indicated that rigid-body binding was the mode of binding of ampicillin and streptomycin with BSA with minor degree of conformational changes. Both of ampicillin and streptomycin can bind with free BSA. Furthermore, the binding of ampicillin with BSA improves the binding of streptomycin, while the binding of streptomycin with BSA adversely affect the binding of ampicillin.