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Nitrogen is fundamental to all of life and many industrial processes. The interchange of nitrogen oxidation states in the industrial production of ammonia, nitric acid, and other commodity chemicals is largely powered by fossil fuels. A key goal of contemporary research in the field of nitrogen chemistry is to minimize the use of fossil fuels by developing more efficient heterogeneous, homogeneous, photo-, and electrocatalytic processes or by adapting the enzymatic processes underlying the natural nitrogen cycle. These approaches, as well as the challenges involved, are discussed in this Review.

Colloidal semiconducting nanocrystals (NCs) are powerful elements of a photocatalytic system useful for enabling a variety of chemical transformations owing to their strong light-absorbing properties and high degree of size-, shape-, and composition-tunability. Key to their utility is our understanding of the photoinduced charge transfer processes required for these photochemical transformations. This Perspective will focus on the implementation of semiconductor NCs for photochemical fuel formation. Three general system designs for photocatalytic proton reduction using semiconductor NCs will be reviewed: metal–semiconductor heterostructures, NC photosensitizers with molecular catalysts, and hydrogenase-based systems. Other relevant reactions toward solar fuel targets, such as CO2 and N2 reductions with NCs, will also be highlighted. Illustrating the versatile roles that NCs can play in light-driven chemical reactions, advances made toward NC-catalyzed organic transformations will be discussed. Finally, we will share a few concluding thoughts and perspectives on the future of the field, with a focus on goals toward improving and implementing NC-based technologies for solar fuel development. [ABSTRACT FROM AUTHOR]

Metalloenzymes are remarkable for facilitating challenging redox transformations with high efficiency and selectivity. In the area of alternative energy, scientists aim to capture these properties in bioinspired and engineered biomolecular catalysts for the efficient and fast production of fuels from low‐energy feedstocks such as water and carbon dioxide. In this short review, efforts to mimic biological catalysts for proton reduction and carbon dioxide reduction are highlighted. Two important recurring themes are the importance of the microenvironment of the catalyst active site and the key role of proton delivery to the active site in achieving desired reactivity. Perspectives on ongoing and future challenges are also provided. [ABSTRACT FROM AUTHOR]

A study was conducted to establish the thermodynamic and structural bases for the significant stabilization seen for Pseudomonas aeruginosa upon mutation of Asn64 to Gln. Results revealed that analysis of unfolding thermodynamics indicates that the net charges in stability resulting from the position 64 mutations are primarily attributable to entropic factors.

Protein film voltammetry studies demonstrate the impact of the heme-binding loop 64 positions upon the redox characteristics of cytochromes c from Pseudomonas aeruginosa cyts c551, hydrogenobacter thermophilus, and Nitrosomonas europaea cyts c552. The potential for hydrogen-bonding interactions between the 64 positions and Met61 can be rationalized by an upward shift in the midpoint potential.

The axial methionine (Met) in 'Hydrogenobacter thermophilus' cytochrome C552 (Ht cyt C552) is found to be fluxional which resulted in an unusual compressed range of heme substituent hyperfine shifts. The H NMR hyperfine shift pattern of Ht cyt c(sub552) is drastically altered by making the conservative heme pocket mutation Gln64Asn.

The knowledge of other, unexpected interactions between the two thiol groups of the apocytochrome c and the two vinyl groups of the heme is investigated. In this discussion the descriptions of cytochrome p572 may suggest more detailed study of protein-bound, formyl-containing hemes, as might occur if these can be prepared in vitro.

A nuclear magnetic resonance study of the cubane iron-sulfur clusters and cluster ligand mutants of the four-iron ferredoxin (Fd) from the hyperthermophilic Archaeon Pyrococcus furiosus was conducted to identify the oxidation-reduction reaction between an individual iron ligated by a specific protein ligand. Findings showed a stabilization of the irons ligated to Cys11 and 17 in both D14C- and D14S-Fd and probably reflects on a hydrogen bond between the backbones of Cys21 and Cys17.

Analysis of the solution structure of the oxidized yeast protein Saccharomyces cerevisiae, Iso-1-cytochrome c using the 1H nuclear Overhauser effect experiments have revealed that the flexibility of the structure of the oxidized cytochrome c in solution is determined by the decrease in the number of nonexchanging amide protons found in the loop regions 14-16 and 75-82.

The structure of oxidized and reduced forms of the iso-1-cytochrome c of Saccharomyces cerevisiae was analyzed by nuclear magnetic resonance spectroscopy. Iso-1-cytochrome exhibited high RMSD values in D2O solutions with large numbers of amide NH due to the the rigidity of the cytochrome backbone compared to the cyanide adduct of the Ala 80 protein. Furthermore, iso-1-cytochrome also exhibited hydrogen-bond networks and an additional helix in its 15-18 residues.

The primary and secondary structure of the cyanide adduct of a triple mutant iso-1-cytochrome c of Saccharomyces cerevisiae obtained from an analyses of the (super 1)H NMR spectrum is given. The quality of the mutant protein as determined by the RMSD values is similar to the ferrocytochrome c of the horse heart. The secondary structure and folding of the mutant is similar to that of the wild-type protein. A distal ligand-binding cavity is formed by if alanine is present instead of the axial ligand. Due to four prolines which do not contain amide NH there is no connectivity in the amino acid sequence.

An investigation of the active-site structure of the cyanide derivative of Ala80cis c using 1H NMR spectroscopy reveals that the mutation of the axial methionine residue of iso-i-cytochrome c presents a ligand-binding protein with spectroscopic features identical to myoglobin and peroxidases. The resemblance of heme methyl shifts to those of the wild-type ferricyt c-CN minus shows that the proximal orientation remains unchanged in the mutant, and the large hyperfine shift and the short T1 of the signal attributable to Tyr67 hydroxyl protein indicates that the proton is hydrogen-bonded to the ligated cyanide.

YEp vector with a target nonfunctional variant and a functional cytochrome c gene facilitates the expression and resolution of a recombinant and nonfunctional axial-ligand mutant of iso-1-cytochrome c, Met-80 linked to Ala, in Saccharomyces cerevisiae. The functional cytochrome c gene codes for a gene with an altered metal-cheating dishistidine site, His-39 and Len-58 linked to His, and facilitates the resolution of two isoforms using static metal-attracted chromatography. Cytochromes and variants can be constructed with engineered structural and catalytic features using a double-gene vector for the expressing cytochrome c and a metal-mediates extraction process.