A study of some trace elements in infant foods

Seven trace elements were determined in milk formulas, powder milk and infant food. Instrumental neutron activation analysis was used for the analysis of Fe, Zn, Co, Cr and Rb, while As and Cu content was determined using radiochemical neutron activation analysis. Differences were found in the trace element content of foods of the same type. Milk formulas are comparable with human milk according to the results obtained for the elements analyzed. The samples of powder cow's milk presented similar concentrations of the elements studied. Liver with vegetables was found to have the highest Cu content. A meal prepared at home, made of beef and fresh vegetables showed a higher trace element content than its similar commercial one. An estimation of the daily intake of the elements analyzed was made and compared with minimum recommended daily ingestion.     

Synthesis of Carboxylated Monodisperse Latexes and Their Self-Organization in Thin Films

The capability of carboxylated latexes of poly(methyl methacrylate) and copolymers of styrene with glycidyl methacrylate or methacrylic acid for self-organization in thin films was studied in relation to the compositions of the dispersion medium and polymer and to the latex particle size.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 1, 2005, pp. 161–167.Original Russian Text Copyright © 2005 by Men’shikova, Shabsel’s, Evseeva, Shevchenko, Bilibin.     

Glycoprotein synthesis as a function of epithelial cell arrangement: biosynthesis and release of glycoproteins by human breast and prostate cells in organ culture.

We demonstrate that a technique is available to investigate glycoprotein synthesis in organ cultures of human breast and prostate surgical specimens where the 3-dimensional epithelial cell arrangement remains intact. Malignant breast and prostate epithelium maintained their capacity to synthesize glycoproteins for at least 3 days as followed by the incorporation of [3H]glucosamine into macromolecules. Over 70% of incorporation was by malignant cells as judged by autoradiography. Labeled glycoproteins were released into glandular lumina and consequently into the culture fluid. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed predominantly one group of macrmolecules released with an apparent molecular weight of 48,000 +/- 6,000 daltons. This glycoprotein was found in all of the breast specimens studied, which included 1 medullary, 1 infiltrating lobular, and 8 infiltrating duct carcinomas. The pattern was independent of the availability of estrogen receptors. A similar glycoprotein was also observed in the culture media from a Grade I and a Grade II well-differentiated infiltrating prostate carcinoma. Incorporation was below the level of detection in 4 of 6 cases of benign prostatic hyperplasia. A more complex pattern of labeled glycoproteins was found in the media of a Grade II and a Grade III poorly-differentiated prostate carcinoma. The established human mammary carcinoma cell line MCF-7 synthesized and released a similar 48,000 molecular weight glycoprotein but additional components with larger molecular weights were also released. An intriguing interpretation that 3-dimensional tissue integrity restricts some glycoprotein synthesis is discussed. Cells grown in 2-dimensional monolayers could escape from such a topographic restriction and express additional families of glycoproteins.     

A LASER FLASH SPECTROSCOPY STUDY OF THE KINETICS OF ELECTRON TRANSFER FROM SPINACH PHOTOSYSTEM I TO SPINACH AND ALGAL FERREDOXINS

Laser flash absorption spectroscopy has been used to investigate the kinetics of electron transfer from P700 in Photosystem I (PSI)-enriched particles from spinach to the ferredoxins from spinach and the green alga Monoraphidium braunii. Very similar behavior for the interaction of both ferredoxins with the PSI complex was observed, although the algal ferredoxin appears to be slightly more effective as an electron acceptor. For both proteins, a non-linear protein concentration dependence of the rate constant for reduction was obtained, indicating complex formation preceding electron transfer. Estimates of 3 times 10⁷M^?1 s^?1 and 140–180 s^?l were obtained from these data for the second order rate constants for complex formation, and the limiting first order rate constants for electron transfer, respectively. At neutral pH, a biphasic dependence of the rate constant for ferredoxin reduction on the concentration of NaCl or MgCl₂ was observed. This was interpreted in terms of the electrostatic interactions which occur between ferredoxin and the PSI membrane. In addition, magnesium cations appear to play a specific role in the interaction between PSI and ferredoxin. Thus, the addition of these ions under optimal conditions induces a 6-f-old increase in the electron transfer reaction rate constant, compared with a 2-f-old increase in the presence of an optimal amount of NaCI. This cannot be explained as arising from ionic strength effects. To our knowledge, this is the first time that a direct measurement of the rate constant for the reduction of ferredoxin by the PSI complex has been reported.     

Generation of High-Oxidation States of Myoglobin in the Nanosecond Time-Scale by Laser Photoionization

Abstract— The 248 nm laser flash photolysis of myoglobin in various redox states (oxy, met and ferryl) in neutral aqueous solution yielded hydrated electrons with concurrent changes in the visible absorption spectrum of the heme. The results could be ascribed to the photoionization of both the peptide and the heme group, in approximately equal yields. The ionization of met- and ferrylmyoglobin was biphotonic, but that of oxymyoglobin was a mixture of mono- and biphotonic processes. Using appropriate electron and radical scavengers, the changes in the heme absorption could be investigated at times ≥100 ns and were shown to be associated with a +1 increase of the formal oxidation state of the heme. Using this method, the formal iron(V) state of native myoglobin could be spectroscopically characterized for the first time. Its absorption, blue-shifted and less intense relative to the ferryl state, is reminiscent of that of the compound I of peroxidases, which contains a ferryl-oxo (iron[IV]) group and a porphyrin radical cation. On this basis, the same structure is proposed for the formal iron(V) state of native myoglobin. The transition from oxy- to metmyoglo-bin took -5 μs, which may reflect the kinetics of exchange of oxygen with water as ligand. The transitions from the met to the ferryl state, and from ferryl to iron(V) states were faster (∽250 ns), consistent with processes that involve proton or electron movements but no changes in the iron coordination state.     

Investigation of isomerization of n-pentane over supported Pt catalyst modified by adsorbed Bi and Pd

-Al₂O₃-supported Bi–Pt and Pd–Pt bimetallic catalysts were prepared by electrochemical metal adsorption. Isomerization of n-pentane was studied over these catalysts in a pulse reactor. It can be concluded from the results that the properties of these catalysts differ substantially from the base Pt/-Al₂O₃ catalyst. On the modified catalysts conversion and the yield of i-pentane was found to be lower although selectivity was better. The ratio of cracking reactions was also lower than over the base catalyst.It is very probable that the adsorbed bismuth was slowly desorbing from the catalyst surface during the experiments.

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Bi–Pt Pd–Pt -Al₂O₃. -, . , Pt/Al₂O₃. , - , . , . , .

     

An unexpected P-cluster like intermediate en route to the nitrogenase FeMo-co

The nitrogenase MoFe protein contains two different FeS centers, the P-cluster and the iron–molybdenum cofactor (FeMo-co). The former is a [Fe₈S₇] center responsible for conveying electrons to the latter, a [MoFe₇S₉C-(R)-homocitrate] species, where N₂ reduction takes place. NifB is arguably the key enzyme in FeMo-co assembly as it catalyzes the fusion of two [Fe₄S₄] clusters and the insertion of carbide and sulfide ions to build NifB-co, a [Fe₈S₉C] precursor to FeMo-co. Recently, two crystal structures of NifB proteins were reported, one containing two out of three [Fe₄S₄] clusters coordinated by the protein which is likely to correspond to an early stage of the reaction mechanism. The other one was fully complemented with the three [Fe₄S₄] clusters (RS, K1 and K2), but was obtained at lower resolution and a satisfactory model was not obtained. Here we report improved processing of this crystallographic data. At odds with what was previously reported, this structure contains a unique [Fe₈S₈] cluster, likely to be a NifB-co precursor resulting from the fusion of K1- and K2-clusters. Strikingly, this new [Fe₈S₈] cluster has both a structure and coordination sphere geometry reminiscent of the fully reduced P-cluster (P^N-state) with an additional μ²-bridging sulfide ion pointing toward the RS cluster. Comparison of available NifB structures further unveils the plasticity of this protein and suggests how ligand reorganization would accommodate cluster loading and fusion in the time-course of NifB-co synthesis.

The K-cluster of NifB as a key intermediate in the synthesis of the nitrogenase active site supports [Fe₄S₄] cluster fusion occurs before carbide and sulfide insertion and displays ligand spatial arrangement reminiscent to that of the P-cluster.     

Conversion of hydrocarbons on supported catalysts prepared via decomposition of surface complexes. Preparation and properties of (Ga+Pt)/SiO2 and (Ga+Pt)/Al2O3 catalysts

The addition of gallium is shown to increase Pt dispersity and its stability to deactivation in n-hexane dehydrocyclization, to decrease the rate of n-hexane hydrogenolysis and to increase the selectivity to benzene, apparently, due to the interaction of Pt clusters with surface Ga ions.

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, -, - . .

     

Constituents of labiatae—XIV: Vierol and powerol,two new diterpenes from Sideritis canariensis

The two new diterpenes, vierol (1) [(?)kaurane-16α,18-diol] and powerol (3) [(?)kaurane-7β,16α-diol] have been isolated from Sideritis canariensis Ait. 1 was obtained by partial synthesis from epicandicandiol (7), and 3 was related with (?)kauranol (6) and (?)kauren-7β-ol acetate (11). Reduction of the acetoxy-aldehyde 14 by the method of Huang-Minlon and posterior acetylation gave 11, (?)isokauren-7β-ol acetate (17) and (?)kauran-7β-ol acetate (18).     

Zusammenhang zwischen Struktur und Komplexbildungseigenschaften der C1–C6-Xanthogenate mit Hg(II)-, Cd(II)- und Zn(II)-Ionen

The thermodynamic parameters D[`(H)], D[`(G)], D[`(S)]₂₉₈\Delta \bar H, \Delta \bar G, \Delta \bar S_{298} and lg _n resp. of the reactions indicated in the title have been computed from polarographic data. The numerical values obtained are nearly independent from the xanthate used. The overall formation constants increase as follows: Zn(II)<>相似文献