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To investigate the relation between protein stability and the predicted stabilities of individual secondary structural elements, residue Pro86 in an alpha-helix in phage T4 lysozyme was replaced by ten different amino acids. The x-ray crystal structures of seven of the mutant lysozymes were determined at high resolution. In each case, replacement of the proline resulted in the formation of an extended alpha-helix. This involves a large conformational change in residues 81 to 83 and smaller shifts that extend 20 angstroms across the protein surface. Unexpectedly, all ten amino acid substitutions marginally reduce protein thermostability. This insensitivity of stability to the amino acid at position 86 is not simply explained by statistical and thermodynamic criteria for helical propensity. The observed conformational changes illustrate a general mechanism by which proteins can tolerate mutations.

Measurements of changes in structure and stability caused by 13 different substitutions for threonine 157 in phage T4 lysozyme show that the most stable lysozyme variants contain hydrogen bonds analogous to those in the wild-type enzyme and that structural adjustments allow the protein to be surprisingly tolerant of amino-acid substitutions.

A rare “five-ling” twinned crystal of TiCN was obtained by chemical vapor deposition on a cemented tungsten carbide substrate at a pressure of 1 atm and temperatures from 1000 to 1150°C. The “five-ling” twinned crystal nucleated after the first thin layer of TiCN coating was formed and then grew quickly. The size of the “five-ling” twinned crystal was about 4 μm. It grew in the [220] direction and on the {111} twin planes. The lattice parameter at different deposition conditions varied from 4.250 to 4.275 A.

A chemical vapour deposition process was used to deposit aluminium onto a pure nickel substrate which was not in contact with the powder mixture. After deposition for about 1 h the aluminium content at the surface reached a high value and then remained almost constant with time. The kinetics of the process is governed by a combination of solid and gas diffusion rates, and a qausi-steady-state appears to exist at the gas-coating interface. The experimental results can be explained satisfactorily by a combination of a stagnant film model for gaseous diffusion and solid diffusion rates.

A gas phase aluminum deposition was developed for Ni by CVD process. The specimen surface quickly came to equilibrium and remained close to equilibrium for the duration of the coating runs. The kinetics of the process was governed by a combination of solid and gas diffusion rates, and a steady-state appeared to exist at the gas phase-coating interface. By combining Levine, Caves, Sivakumar, and Seigle’s model for gaseous diffusion and calculation of solid diffusion rates, some success has been achieved in explaining the results.

A modification of the pack aluminization process has been developed for nickel-base superalloy IN 713 by c chemical vapour deposition (CVD) method, i.e. the substrate to be coated was out of contact with a powder mixture of aluminium and aluminium oxide. It was shown that the growth of aluminide coating increased with the saturation temperature of AlCl 3 and deposition temperature in this study. The CVD method was demonstrated to have sufficient throwing power to deposit aluminium uniformly on the internal surface of the specimens. The coating material (aluminium) is delivered to the specimen surface and controlled by gas phase diffusion. The growth of aluminide coating was found to increase almost linearly with deposition time.

Thin films of Ti(C,N) were prepared by chemical vapour deposition onto cemented tungsten carbide substrates. It was found that the growth rate of the Ti(C,N) coatings increased with the total flow rate of the reactant gas and with the deposition temperature. The microstructure and morphology of the Ti(C,N) coatings vary with their deposition temperature and composition. The composition of the Ti(C,N) determines the extent of the secondary growth features, and the characteristic morphology of the Ti(C,N) coatings is determined by the deposition temperature. It is also shown that the lattice constant of the Ti(C,N) coatings increases with the carbon content of the coatings.

Determination experimentale des conditions de croissance des revetements de chrome obtenus par depot chimique en phase vapeur sur des substrats de nickel pur

Twenty-five different temperature-sensitive point mutations at 20 sites in the lysozyme gene of bacteriophage T4 have been identified. All of the mutations alter amino acid side chains that have lower than average crystallographic thermal factors and reduced solvent accessibility in the folded protein. This suggests that the amino acids with well-defined conformations can form specific intramolecular interactions that make relatively large contributions to the thermal stability of the protein. Residues with high mobility or high solvent accessibility are much less susceptible to destabilizing substitutions, suggesting that, in general, such amino acids contribute less to protein stability. The pattern of the sites of ts substitutions observed in the folded conformation of T4 lysozyme suggests that severe destabilizing mutations that primarily affect the free energy of the unfolded state are rare. These results indicate that proteins can be stabilized by adding new interactions to regions that are rigid or buried in the folded conformation.