Lack of coupling between secondary structure formation and collapse in a model polypeptide that mimics early folding intermediates, the F2 fragment of the Escherichia coli tryptophan-synthase beta chain

The isolated, 101-residue long C-terminal (so called F2) fragment of the beta chain from Escherichia coli tryptophan synthase was shown previously to fold into an ensemble of conformations that are condensed, to contain large amounts of highly dynamic secondary structures, and to behave as a good model of structured intermediates that form at the very early stages of protein folding. Here, solvent perturbations were used to investigate the forces that are involved in stabilizing the secondary structure (monitored by far-UV CD) and the condensation of the polypeptide chain (monitored by dynamic light scattering) in isolated F2. It was observed that neither the ionic strength, nor the pH (between 7 and 10), nor salts of the Hofmeister series affected the global secondary structure contents of F2, whereas some of these salts affected the collapse slightly. Addition of trifluoroethanol resulted in a large increase in both the amount of secondary structure and the Stokes radius of F2. Conversely, F2 became more condensed upon raising the temperature from 4 to 60 degrees C, whereas in this temperature range, the secondary structure undergoes significant melting. These observations lead to the conclusion that, in isolated F2, there is no coupling between the hydrophobic collapse and the secondary structure. This finding will be discussed in terms of early events in protein folding.     

Free radical addition of hydrogen sulfide and thiols to linseed oil and methyl oleate

Free radical additions of hydrogen sulfide, ethanedithiol, and 1,6-hexanedithiol have been made to methyl oleate and linseed oil with ultraviolet radiation. Reactions were carried out in dichloromethane at −70C and in benzene at 25C. With the dithiols, a new dibasic ester has been prepared from methyl oleate in which bridging is accomplished through a dithiol moiety. Hydrogen sulfide has been added to linseed oil in suitable solvents at both −70C and 25C. It appears that zero-order kinetics control the additions at both temperatures. Infrared data show a linear relationship between mercapto absorption and the amount of sulfur incorporated. Nuclear magnetic resonance (NMR) spectra demonstrate a decrease in olefinic protons with an increase in sulfur content. Fair agreement on the extent of reaction exists between data from NMR, sulfur content, and infrared analyses. Hydrogen sulfide-treated linseed oil films air-dry slowly at room temperature; at 250C for 1 hr under a CO₂ atmosphere these oils cure to brown films with Sward Rocker values of 24 to 32 and pencil hardness values of five to greater than six. Pencil hardness and alkali resistance increased with sulfur content. The film from the 4.2% sulfur sample resisted alkali at room temperature for 24 hr. Presented at the AOCS Meeting, Philadelphia, October 1966. No. Utiliz. Res. and Dev. Div., ARS. USDA.     

Acute and chronic toxicity of copper to the fathead minnow in a surface water of variable quality

Acute and chronic toxicity tests conducted with the fathead minnow and copper used as the source of dilution water a natural stream to which a sewage treatment plant upstream contributed a variety of materials known to affect acute copper toxicity. Nominal total copper 96-h median tolerance limit values (96-h TL50), determined with static testing procedures, ranged from 1.6 to 21 mg l⁻¹. Dissolved copper 96-h TL50 values ranged from 0.60 to 0.98 mg l⁻¹. The maximum acceptable toxicant concentration (MATC) based on survival, growth, reproduction, and hatchability of eggs was between 0.066 and 0.118 mg l⁻¹.     

High Chromium Cast Irons: Destabilized-Subcritical Secondary Carbide Precipitation and Its Effect on Hardness and Wear Properties

This work evaluates the effect of a destabilization treatment combined with a subcritical diffusion (SCD) and a subsequent quenching (Q) steps on precipitation of secondary carbides and their influence on the wear properties of HCCI (16%Cr). The destabilization of the austenite at high temperature leads to a final microstructure composed of eutectic and secondary carbides, with an M₇C₃ nature, embedded in a martensitic matrix. An improved wear resistance was observed in the SCD?+?Q samples in comparison with the Q one, which was attributed to the size of secondary carbides.     

Sperm oil replacements from selectively hydrogenated soybean and linseed esters: Special lubricants

Soybean and linseed oils were selectively hydroenated with copper-on-silica gel catalyst. The linolenate content of the oils was reduced to diene and monoene with no appreciable increase in saturates. Hydrogenated soybean oils contained 68–76% monoene, 11–18% diene, 0% conjugated diene and triene, 1–6% conjugatable diene, 0–0.3% conjugatable triene, and 23–40% isolatedtrans double bonds. Hydrogenated linseed oils contained 44–54% monoene, 35–45% diene, 0% conjugated diene and triene, 0–7% conjugatable diene, 0–02% conjugatable triene, and 44–59% isoaltedtrans double bonds. Esters of fatty acids, derived from these selectively hydrogenated oils, were prepared with trimethylolethane, trimethylolpropane, trimethylolbutane, pentaerythritol, ethylene glycol, C₁₈ saturated cyclic alcohols, primary C₁₂–C₁₈ saturated (nC₁₂, nC₁₄, nC₁₆, nC₁₈) alcohol, and primary C₁₆–C₁₈ saturated (nC₁₆, nC₁₈) alcohol blends. Measurements of viscosities and of smoke, flash, and fire points indicate that these esters are possible replacements for sperm oil. Certain of them, after sulfurization, also have potential as extreme pressure lubricant additives. Presented at the AOCS meeting in Philadelphia, September 1974.     

Polyesteramides from linseed oil for protective coatings low acid-value polymers

Linseed and soybean diethanolamides, from the sodium alkoxide-catalyzed reaction of the corresponding oil with diethanolamine, were used as diols to prepare a series of polyesteramides. The diols and dibasic acids or anhydrides were heated in refluxing xylene until the theoretical amount of water was collected in a trap. Low acid-value linseed polymers were prepared with 10, 20, and 30 mole percent excess diol over the dibasic acid, and the effect of the excess diol on molecular weight, viscosity, and film properties of the polymers was examined. Polyesteramides which contained 10 mole percent excess fatty diethanolamide were made with 11 dibasic acids or anhydrides. The polymers were brown-orange oils with Gardner viscosities of Z7 to >>Z10. Number-average molecular weights ranged from 2,200 to 5,200. Data on drying characteristics, hardness, and chemical resistance of films were obtained. The better polymers air-dried rapidly to give hard, glossy films (Sward rocker 20–60). Films baked at 190C for 10 min were softer than the corresponding air-dried films. Xylene resistance of soybean and linseed polymer films was generally excellent, and alkali resistance was moderate. Soybean films showed the better alkali resistance. Presented at Division of Organic Coatings and Plastics Chemistry, 153rd ACS meeting, Miami Beach, Fla., April 1967. No. Utiliz. Res. Dev. Div., ARS, USDA.