Im-trityl protection of histidine.

A rational attempt to prepare FmocHis(piTrt)OH regiospecifically gave in fact the well-known tau-trityl isomer, and experiments with model systems indicate that the prospects for access to pi-trityl histidine derivatives, which would be of great value for the racemization-free synthesis of histidine-containing peptides, are poor.     

Respiration rates of some greenhouse cultivated tropical and subtropical species

A comparative study of dark respiration and effects of high and low temperature on dark respiration in five greenhouse cultivated tropical and sub-tropical species was made. The respiration rates determined manometrically were low in all species. Respiration rates increased with increasing temperature. Low temperature treatment accelerated the rate of respiration at 25 °G except in two species. An attempt has been made to determine the critical and optimum temperature for these species. The respiratory behaviour of these species has been discussed with respect to their original habitats and prevailing environmental conditions.     

A process optimization for bio-catalytic production of substituted catechols (3-nitrocatechol and 3-methylcatechol

Background  

Substituted catechols are important precursors for large-scale synthesis of pharmaceuticals and other industrial products. Most of the reported chemical synthesis methods are expensive and insufficient at industrial level. However, biological processes for production of substituted catechols could be highly selective and suitable for industrial purposes.     

Purification and characterization of a gelatinase produced by fibroblasts from human gingiva

An endopeptidase which digests denatured collagen to small, dialysable fragments was purified 2675-fold from medium that had been conditioned by the culture of fibroblasts grown from explants of human gingiva. This enzyme was inhibited by chelating agents, but not by phenylmethylsulphonyl fluoride nor by N-ethylmaleimide, and is therefore probably a metalloproteinase. It showed no demonstrable activity against native collagen or ovalbumin, while alpha-casein was digested slowly, if at all. It therefore belongs to the group of enzymes which have been called tissue gelatinases. This gelatinase was secreted in a latent form or forms and could be activated by proteolysis with trypsin. The active enzyme had an apparent molecular weight of 69 000 (gel chromatography) or 72 000 (gel electrophoresis in sodium dodecyl sulphate) and an apparent isoelectric point of 4.15.     

What Do We Know About Metal Recycling Rates?

The recycling of metals is widely viewed as a fruitful sustainability strategy, but little information is available on the degree to which recycling is actually taking place. This article provides an overview on the current knowledge of recycling rates for 60 metals. We propose various recycling metrics, discuss relevant aspects of recycling processes, and present current estimates on global end‐of‐life recycling rates (EOL‐RR; i.e., the percentage of a metal in discards that is actually recycled), recycled content (RC), and old scrap ratios (OSRs; i.e., the share of old scrap in the total scrap flow). Because of increases in metal use over time and long metal in‐use lifetimes, many RC values are low and will remain so for the foreseeable future. Because of relatively low efficiencies in the collection and processing of most discarded products, inherent limitations in recycling processes, and the fact that primary material is often relatively abundant and low‐cost (which thereby keeps down the price of scrap), many EOL‐RRs are very low: Only for 18 metals (silver, aluminum, gold, cobalt, chromium, copper, iron, manganese, niobium, nickel, lead, palladium, platinum, rhenium, rhodium, tin, titanium, and zinc) is the EOL‐RR above 50% at present. Only for niobium, lead, and ruthenium is the RC above 50%, although 16 metals are in the 25% to 50% range. Thirteen metals have an OSR greater than 50%. These estimates may be used in considerations of whether recycling efficiencies can be improved; which metric could best encourage improved effectiveness in recycling; and an improved understanding of the dependence of recycling on economics, technology, and other factors.     

Determination of dialkyl phosphates in human hair for the biomonitoring of exposure to organophosphate pesticides

A new, simple, fast and sensitive method that enables the measurement of four dialkyl phosphates (DAPs) in human head hair is presented in the current study. The dialkyl phosphates, dimethyl phosphate (DMP), diethyl phosphate (DEP), diethyl thiophosphate (DETP) and diethyl dithiophosphate (DEDTP) are non-selective metabolites of the organophosphate pesticides (OPs). The extraction of DAPs from hair matrix was achieved by one step methanolic extraction. Head hair samples from general population and population occupationally exposed to OPs were analysed using gas chromatography–mass spectrometry (GC–MS) after derivatization with pentafluorobenzylbromide. The recovery of the target compounds was estimated at 84.3% for DMP, 116.1% for DEP, 109.0% for DETP and 91.5% for DEDTP. The limit of quantitation (LOQ) and detection (LOD) was 20 and 6 pg/mg for DMP, 10 and 5 pg/mg for DEP and DETP and 5 and 3 pg/mg for DEDTP, respectively. With-run and between-run precision as well as accuracy was estimated. The percentage of positive hair samples for DMP, DEP, DETP and DEDTP for the group of general population was 63.0%, 96.3%, 66.7%, and 70.4% respectively. The samples from the group with occupational exposure were positive for all dialkyl phosphates analysed. The median concentrations for DMP were 165.0 and 181.7 pg/mg, for DEP were 51.2 and 812.9 pg/mg, for DETP were 54.0 and 660.1 pg/mg, and for DEDTP were 40.0 and 60.6 pg/mg for the general population group and the group with occupational exposure respectively. Significant differences in the levels of the total dialkyl phosphates amongst exposed and not exposed groups were observed (p < 0.001). More specifically, the total ethyl phosphate (DEPs) and DAPs median concentrations were 119.5 and 301.5 pg/mg for the general population group and 1498.8 and 1694.4 pg/mg for the group with occupational exposure.