The development of efficient biological systems for the direct photoproduction of H(2) gas from water faces several challenges, the more serious of which is the sensitivity of the H(2)-evolving enzymes (hydrogenases) to O(2), an obligatory by-product of photosynthesis. This high sensitivity is common to both FeFe and NiFe hydrogenases, and is caused by O(2) binding to their respective metallocatalytic sites. This overview describes approaches to (i) molecular engineering of algal FeFe-hydrogenase to prevent O(2) access to its catalytic site; (ii) transform a cyanobacterium with an O(2)-tolerant bacterial NiFe hydrogenase or (c) partially inactivate algal O(2)-evolution activity to create physiologically anaerobiosis and induce hydrogenase expression.

Recent high-pressure X-ray experiments show that, contrary to traditional expectations and numerous calculations, the NaCl structure is not present in covalent semiconductors, the diatomic b-Sn structure is absent in all compound semiconductors, and the CsCl structure is not seen in ionic semiconductors. We explain these systematic absences in terms of dynamical phonon instabilities of the NaCl, b-Sn, and CsCl crystal structures. Covalent materials in NaCl structures become dynamically unstable with respect to the transverse acoustic TA½001 phonon, while ionic compounds in the b-Sn structure exhibit phonon instabilities in the longitudinal optical LO½00x branch. The latter lead to predicted new high pressure phases of octet semiconductors. For InSb, we find no phonon instability that could prevent the CsCl phase from forming, but for the more ionic GaP, GaAs, InP, and InAs, we find that the CsCl phase is dynamically unstable at high pressures with respect to TA½xx0 phonons. Analysis of the soft normal modes via ''isotropy subgroup" suggests two candidate structures that will replace the CsCl structure at high pressure: the tP4 (B10) InBi-type and the oP4 (B19) AuCd-type. Experimental examination of these predictions is called for.