Encapsulated guest molecules in the dimer of octahydroxypyridine[4]arene

Recently a new type of calix[4]arenes has been synthesized via condensation of 2,6-dihydroxypyridine and a number of aldehydes. This type of pyridine[4]arenes forms capsules consisting of two single pyridine[4]arenes. These capsules can incorporate different guest molecules, like carboxylic acids and amides in this case. We proved that the guest acids really are incorporated inside the cavity of the capsules by electrospray mass spectrometry, NMR spectroscopy, and theoretical calculations.     

Influence of protein concentration and order of addition on thermal stability of beta-lactoglobulin stabilized n-hexadecane oil-in-water emulsions at neutral pH

The influence of protein concentration and order of addition relative to homogenization (before or after) on the extent of droplet flocculation in heat-treated oil-in-water emulsions stabilized by a globular protein were examined using laser diffraction. n-Hexadecane (10 wt%) oil-in-water emulsions (pH 7, 150 mM NaCl) stabilized by beta-lactoglobulin (beta-Lg) were prepared by three methods: (1) 4 mg/mL beta-Lg added before homogenization; (2) 4 mg/mL beta-Lg added before homogenization and 6 mg/mL beta-Lg added after homogenization; (3) 10 mg/mL beta-Lg added before homogenization. The emulsions were then subjected to various isothermal heat treatments (30-95 degrees C for 20 min), with the 150 mM NaCl being added either before or after heating. Emulsion 1 contained little nonadsorbed protein and exhibited extensive droplet aggregation at all temperatures, which was attributed to the fact that the droplets had a high surface hydrophobicity, e.g., due to exposed oil or extensive protein surface denaturation. Emulsions 2 and 3 contained a significant fraction of nonadsorbed beta-Lg. When the NaCl was added before heating, these emulsions were relatively stable to droplet flocculation below a critical holding temperature (75 and 60 degrees C, respectively) but showed extensive flocculation above this temperature. The stability at low temperatures was attributed to the droplets having a relatively low surface hydrophobicity, e.g., due to complete saturation of the droplet surface with protein or due to more limited surface denaturation. The instability at high temperatures was attributed to thermal denaturation of the adsorbed and nonadsorbed proteins leading to increased hydrophobic interactions between droplets. When the salt was added to Emulsions 2 and 3 after heating, little droplet flocculation was observed at high temperatures, which was attributed to the dominance of intra-membrane over inter-membrane protein-protein interactions. Our data suggests that protein concentration and order of addition have a strong influence on the flocculation stability of protein-stabilized emulsions, which has important implications for the formulation and production of many emulsion-based products.     

Photodegradation of UV-cured coatings II. Polyurethane–acrylate networks

Highly crosslinked aliphatic and aromatic polyurethane-acrylate (PUA) coatings have been obtained by photopolymerization of multifunctional monomers. The discoloration and chemical modifications occurring upon accelerated QUV aging were monitored by UV and IR spectroscopy. The polymers were found to undergo photooxidation and loss of carbamate and phenyl groups, with lower quantum yields (10^?3 mol photon^?1) than in related linear polymers. Hydroxy-phenyl benzotriazole UV-absorbers have a limited effect on the degradation rate, at the concentration used (0.5%). Hindered amines (HALS) are substantially more effective, especially in aliphatic PUA. A 20-fold increase in the stabilization efficiency was found with the UVA + HALS combination. Aromatic PUA are more difficult to stabilize, because of the strong absorption and photolysis of the phenyl group which yields colored products. Radical-induced oxidation is predominant in aliphatic PUA and develops with long kinetic chains, while in aromatic PUA it competes with direct photolysis.     

Degradation of poly(vinyl chloride) by u.v. radiation—II: Mechanism

The mechanism of the light-induced degradation of solid poly(vinyl chloride) (PVC) has been investigated, and an overall reaction scheme has been developed, based on values of the quantum yields for the primary photoproducts. Only a very small fraction (0.2%) of the excited polyenes induces the degradation of PVC, primarily by photocleavage of the allylic CCl bond. The high instability of β-chloroalkyl radicals is responsible for the chain dehydrochlorination that leads to formation of polyenes. In the absence of O₂, chain scissions and crosslinking are postulated to originate mainly from α-chloroalkyl radicals through β-cleavage of CC bonds and radical coupling, respectively. In the presence of O₂, the chain dehydrochlorination still proceeds, together with an oxidative chain process which yields, via peroxy and alkoxy radicals, hydroperoxides, ketones and peroxide crosslinks. Cleavage of the polymer backbone results most probably from the decomposition of tertiary alkoxy radicals by a carbon-carbon β-scission process.