The ascent of man(made oxidoreductases).

Though established 40 years ago, the field of de novo protein design has recently come of age, with new designs exhibiting an unprecedented level of sophistication in structure and function. With respect to catalysis, de novo enzymes promise to revolutionise the industrial production of useful chemicals and materials, while providing new biomolecules as plug-and-play components in the metabolic pathways of living cells. To this end, there are now de novo metalloenzymes that are assembled in vivo, including the recently reported C45 maquette, which can catalyse a variety of substrate oxidations with efficiencies rivalling those of closely related natural enzymes. Here we explore the successful design of this de novo enzyme, which was designed to minimise the undesirable complexity of natural proteins using a minimalistic bottom-up approach.

Thermocapillary Flow and Aggregation of Bubbles on a Solid Wall.

Theory suggests that thermocapillary flow about neighboring bubbles in liquids on hot walls pulls the bubbles together. A temperature gradient perpendicular to the wall establishes a surface tension gradient at the bubble-liquid interface, which in turn sustains a shear stress gradient that pumps adjacent fluid away from the wall. Neighboring bubbles are mutually entrained in this flow and also respond thermophoretically to lateral temperature gradients in the temperature near field. The theory predicts that the aggregation velocity scales with the temperature gradient, the radius of the bubbles, the derivative of the surface tension with respect to temperature, and the reciprocal of the liquid's viscosity. Bubble aggregation experiments under controlled conditions were performed to test the theory. Scaling the experimental bubble trajectories according to the theory substantially collapses all of the data onto a master curve when the interbubble separation is greater than 3 radii, which suggests that the theory is correct. Calculated velocities agree with the experimental results when hindrance of bubble motion due to the wall is included. Values for the parameter that describes the hindrance effect are obtained from fitting the data to the theory, from independent measurements, and from direct hydrodynamic calculation. The results of the three determinations agree within 15% of the possible range of the value of the parameter. Copyright 2000 Academic Press.

Synthesis and characterization of 5-substituted 1,3-diazacyclohexane derivatives

Three synthetic routes to 5-substituted 1,3-diazacyclohexane derivatives 1 are reported. The first method involves treatment of 1, 3-diaminopropan-2-ol 2 with paraformaldehyde to yield 5-hydroxy-1, 3-diazacyclohexane 3. A second method is based on the condensation of 2-bromo-2-nitro-1,3-propanediol with tert-butylamine and formaldehyde to yield 1,3-di-tert-butyl-5-bromo-5-nitro-1, 3-diazacyclohexane 22. The third method relies on the cycloalkylation of methylenebisacetamide with 3-chloro-2-chloromethyl-2-propene to provide 5-exomethylene-1, 3-diacetyl-1,3-diazacyclohexane 28. Functional group manipulations of 3, 22, and 28 provide a number of novel 1,3-diazacyclohexanes functionalized at the 5-position.

Footwall refrigeration along a detachment fault: implications for the thermal evolution of core complexes

Oxygen isotope compositions of epidote and quartz from chloritic breccias that underlie the detachment fault in the metamorphic core complex of the Whipple Mountains yielded quartz-epidote fractionations that range from 4.1 to 6.4 per mil and increase systematically toward the fault. These fractionations give mean temperatures that decrease from approximately 432 degrees C at 50 meters below the fault to approximately 350 degrees C at 12 meters below the fault. This extreme thermal gradient of 82 degrees C over 38 meters (2160 degrees C per kilometer) is best explained by advective heat extraction by means of circulating surface-derived fluids. Models of lithospheric extension consider only conductive cooling resulting from tectonic denudation and thus require revision to include fluid-induced fault-zone refrigeration.

Electrophoretic Motion of Two Spherical Particles with Thick Double Layers

The electrophoretic mobilities of two interacting spheres are calculated numerically for arbitrary values of the double-layer thickness. A general formula for the electrophoretic translational and angular velocities of N interacting particles is derived for low-zeta-potential conditions. The present calculation complements the well-studied case of thin double layers. The results are compared with recent reflection calculations and are used to compute the O(phi) contribution to the electrophoretic mobility of a suspension. Particle interactions can be significant for values of the scaled particle radius kappaa

Boundary Effects on Electrophoretic Motion of Spherical Particles for Thick Double Layers and Low Zeta Potential

The electrophoretic motion of a charged sphere in the presence of a rigid boundary is analyzed for low surface zeta potentials but arbitrary kappaa, where a is the particle radius and kappa is the inverse Debye length. The boundary configurations considered are a single flat wall, a slit, and a long cylindrical tube. Using a method of reflections, we obtain the particle velocity for a constant applied electric field in powers of lambda up to O(lambda6), where lambda is the ratio of the particle radius to the distance from the boundary. This analysis is valid as long as the double layer around the particle does not overlap significantly with the double layer at the boundary. The effect of finite kappaa is to enhance the viscous retardation of the particle, although for large separations the first effect due to the proximity of the boundary is still at O(lambda3) in all cases. When the applied field is parallel to the boundary, the electrophoretic velocity is not proportional to the difference in zeta potential between the particle and the boundary (as occurs for kappaa --> infinity), and the proximity of the boundary may increase the particle velocity or change its direction. An important result of the analysis is that the hindrance to the electrophoretic velocity of a particle in a cylindrical pore increases significantly as kappaa is reduced below 10.