Scanning Electron Microscopic Evidence of Spontaneous Heteropeptide Formation in Abiotic Solutions of Selected α-Amino Acid Pairs

Spontaneous nonlinear peptidization of the monomeric and enantiomerically pure α-amino acids in abiotic aqueous and nonaqueous solutions is still regarded by some as a somewhat puzzling phenomenon, and therefore it needs additional experimental authentication. In our earlier studies, we employed several analytical techniques to prove its occurrence. In this study, we present the scanning electron microscopic (SEM) evidence of spontaneous heteropeptide formation in the binary L-Cys−L-Phe, L-Cys−L-Phg, and L-Cys−L-Pro mixtures dissolved in 70 % aqueous methanol. With each α-amino acid pair, one amino acid (L-Cys) is equipped with three functionalities (−SH, −NH₂, and −COOH), enabling formation of the spherical homopeptide microstructures, while its counterpart (L-Phe, L-Phg, or L-Pro, respectively) is equipped with the two functionalities only (−NH₂ or =NH, and −COOH). The SEM micrographs of the peptidization products originating from the three investigated α-amino acid pairs show three different, yet spherical, structures, which seem suggestive of the heteropeptide formation involving both L-Cys and its counterpart α-amino acid. Additional confirmation of heteropeptide formation is furnished by high performance liquid chromatography (HPLC), the biuret test, and mass spectrometry (MS).     

Assessment of the N-nitrosopiperidine formation risk from piperine and piperidine contained in spices used as meat product additives

The N-nitrosopiperidine (NPIP) formation in blends of spices and nitrite curing salt was investigated in relation with the piperine and piperidine contents in spices. Firstly, two analytical methods were developed. Piperine was extracted with dichloromethane by means of accelerated solvent extraction (ASE) and determined by high-performance liquid chromatography (HPLC)–diode array detector (λ = 343 nm). A selective hydroextraction of piperidine using ASE and its quantification by HPLC–ELSD was applied. Both methods were sufficiently sensitive and accurate (limit of detection, limit of quantification, and recovery: 0.28, 0.84 μg, and 98.9 ± 2.6 % for piperine, and 5.76, 17.45 μg, and 95.9 ± 2.9 % for piperidine, respectively). Secondly, both compounds were quantified in commercial samples (black and white pepper, paprika, chili pepper, allspice, and nutmeg). The maximum amount of piperine (21.12 mg g^?1) was found in pepper, while the other spices contained only traces. Piperidine was detected mainly in the pepper samples, whereby the highest concentration was found in the white pepper extract (11.42 mg g^?1). Thirdly, during the storage of spices blended with nitrite curing salt, the NPIP content was determined, using a gas chromatograph coupled with a thermal energy analyzer. Against our expectations, no NPIP formation was observed in the curing mixture which contained white pepper extract. This result remains in contrast with the white pepper mixture, in which the NPIP content significantly increased from not detected to 9.80 ± 0.41 ng g^?1 after the 2 months storage period. In conclusion, high amounts of piperine or piperidine in spices do not systematically result in the formation of NPIP, when blended with nitrite curing salt .     

Kinetics of lithium evaporation from solid solutions of Li2O in NiO

Measurements of the kinetics of evaporation of Li₂O from polycrystalline solid solutions of Li₂O in NiO have been performed under varying temperatures (1340 to 1665 K) and solution concentrations (0.25 to 19.5 at.% Li). By taking into account the changes in specific surface area during annealing of the preparations, an equation has been derived describing the kinetics of the evaporation process.     

Salmonella spp. on chicken carcasses in processing plants in Poland

Chickens at selected points in the slaughter process and after slaughter on the dressing line in poultry plants were sampled and analyzed for Salmonella. These chickens came from the northeast part of Poland. The examinations were carried out in quarters I, II, III, and IV of 1999. All the birds were determined to be healthy by a veterinary inspection. Swab samples were taken from the cloaca after stunning and from the skin surface and body cavity of the whole bird after evisceration, after rinsing at the final rinse station but before chilling in the spin-chiller, and after cooling in the continuous cooling plant at the end of the production day. In 1999, 400 whole chickens were examined. The percentage of these 400 chickens from which Salmonella spp. were isolated was relatively high (23.75%; Salmonella-positive results were observed in 95 cases). Salmonella spp. were found after stunning in 6% of the chickens (6 of 100 samples), after evisceration in 24% (24 of 100), before cooling in 52% (52 of 100), and after cooling in 13% (13 of 100). These results show that Salmonella spp. were found more often at some processing points than at others. The lowest Salmonella spp. contamination rate (6%) for slaughter birds was found after stunning, and the highest contamination rate was found before chilling (52%). The serological types of Salmonella spp. isolated from whole chickens were Salmonella Enteritidis, Salmonella Typhimurium, Salmonella Saintpaul, Salmonella Agona, and Salmonella Infantis. The results of these investigations indicate that Salmonella Enteritidis is the dominant serological type in infections of slaughter chickens, as it is in many countries.     

Highly branched melamine-phenolic novolaks

Summary A convenient synthesis of highly branched melamine-formaldehyde-phenolic oligomers, which can be applied as precursors for dendritic macromolecules, is described. The synthesis comprises the condensation of methylolated melamines with phenol in the presence of stoichiometric amounts of hydrochloric acid (similarly to the Mannich's reaction conditions). A mixture of hydroxyphenylmethylmelamines was obtained of an average content corresponding to the five substituted melamine ring. NMR and mass spectrometry (LSIMS/FAB) analysis showed the products to be almost free of neat melamine-formaldehyde and phenol-formaldehyde condensates. Received: 26 October 2001/Revised version: 8 March 2002/ Accepted: 25 March 2002     

Issues in clustering algorithm consistency in fixed dimensional spaces. Some solutions for k-means

Journal of Intelligent Information Systems - Kleinberg introduced an axiomatic system for clustering functions. Out of three axioms, he proposed, two (scale invariance and consistency) are...