Engineered holocytochrome synthases that biosynthesize new cytochromes .

Cytochrome (cyt ), required for electron transport in mitochondria, possesses a covalently attached heme cofactor. Attachment is catalyzed by holocytochrome synthase (HCCS), leading to two thioether bonds between heme and a conserved CXXCH motif of cyt In cyt , histidine (His19) of CXXCH acts as an axial ligand to heme iron and upon release of holocytochrome from HCCS, folding leads to formation of a second axial interaction with methionine (Met81). We previously discovered mutations in human HCCS that facilitate increased biosynthesis of cyt in recombinant Focusing on HCCS E159A, novel cyt variants in quantities that are sufficient for biophysical analysis are biosynthesized.

Oxidative C-C Bond Formation Reactivity of Organometallic Ni(II), Ni(III), and Ni(IV) Complexes.

The use of the tridentate ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (Metacn) and the cyclic alkyl/aryl C-donor ligand -CHCMe-o-CH- (cycloneophyl) allows for the synthesis of isolable organometallic Ni, Ni, and Ni complexes. Surprisingly, the five-coordinate Ni complex is stable both in solution and the solid state, and exhibits limited C-C bond formation reactivity. Oxidation by one electron of this Ni species generates a six-coordinate Ni complex, with an acetonitrile molecule bound to Ni.

Ligand effects on the properties of Ni(iii) complexes: aerobically-induced aromatic cyanation at room temperature.

A series of organometallic Ni and Ni complexes supported by tertadendate N3C ligands were synthesized and fully characterized using X-ray crystallography, CV, and EPR. Based on the solid state structures, the substituents on the two amine N-donors significantly affect the coordination of the Ni centers, while the para substituents of the phenyl C-donor have a reduced effect. This is further supported by electrochemical and spectroscopic measurements that suggest the presence of a less bulky N-substituent of the N3C ligand leads to a more accessible Ni center.

Diffusion of squalene in n-alkanes and squalane.

Squalene, an intermediate in the biosynthesis of cholesterol, has a 24-carbon backbone with six methyl groups and six isolated double bonds. Capillary flow techniques have been used to determine its translational diffusion constant, D, at room temperature in squalane, n-C16, and three n-C8-squalane mixtures. The D values have a weaker dependence on viscosity, η, than predicted by the Stokes-Einstein relation, D = kBT/(6πηr).

Molecular motion of the bis(maleonitriledithiolato)nickel trianion in solution.

Electron spin resonance (ESR) has been used to study the reorientational motion of the bis(maleonitriledithiolato)nickel trianion, [Ni(mnt)(2)](3-), in diethylene glycol dimethyl ether (diglyme). [Ni(mnt)(2)](3-) has one unpaired electron and was prepared by reducing the dianion, [Ni(mnt)(2)](2-), with potassium metal. The trianion and dianion are members of the redox series [Ni(mnt)(2)](n-) with n = 0, 1, 2, and 3.

Diffusion of organic solutes in squalane.

The translational diffusion constants, D, of 26 hydrocarbons have been determined in squalane (2,6,10,15,19,23-hexamethyltetracosane) at room temperature using capillary flow techniques. These new data and previously published room-temperature D values for the same solutes in some (or all) of the n-alkanes n-C(6)-n-C(16) constitute a study of solute diffusion in media spanning a 100-fold change in viscosity; at 23 °C, η = 0.31 cP for n-C(6), 3.