Carboxylic acid reductases (CARs) catalyze the reduction of a broad range of carboxylic acids to aldehydes using the cofactors adenosine triphosphate and nicotinamide adenine dinucleotide phosphate, and have become attractive biocatalysts for organic synthesis. Mechanistic understanding of CARs was used to expand reaction scope, generating biocatalysts for amide bond formation from carboxylic acid and amine. CARs demonstrated amidation activity for various acids and amines. Optimization of reaction conditions, with respect to pH and temperature, allowed for the synthesis of the anticonvulsant ilepcimide with up to 96 % conversion. Mechanistic studies using site-directed mutagenesis suggest that, following initial enzymatic adenylation of substrates, amidation of the carboxylic acid proceeds by direct reaction of the acyl adenylate with amine nucleophiles.

We present microlensing calculations for a Galactic model based on that of Han & Gould, which is empirically normalized by star counts. We find good agreement between this model and data recently published by the MACHO and OGLE collaborations for the optical depth in various Galactic fields, and the trends thereof with Galactic longitude l and latitude b. We produce maps of optical depth and, by adopting simple kinematic models, of average event time‐scales for microlensing towards the Galactic bulge. We also find that our model predictions are in reasonable agreement with the OGLE data for the expected time‐scale distribution. We show that the fractions of events with very long and short time‐scales owing to a lens of mass M are weighted by M2 n(M) dM and M−1 n(M) dM, respectively, independent of the density and kinematics of the lenses.

We present a direct detection of the gravitational lens that caused the microlensing event . This is the first fully resolved microlensing system involving a source in the Galactic bulge, and the second such system in general. The lens and source are clearly resolved in images taken with the High Resolution Channel of the Advanced Camera for Surveys on board the Hubble Space Telescope (HST ) $9 yr after the microlensing event. The currently available data are not sufficient for the final, unambiguous identification of the gravitational lens and the microlensed source. While the light-curve models combined with the high-resolution photometry for individual objects indicate that the source is red and the lens is blue, the color-magnitude diagram for the line of sight and the observed proper motions strongly support the opposite case. The first scenario points to a metal-poor lens with mass M % 0:6 M at the distance D l % 4 kpc. In the second scenario, the lens could be a main-sequence star with M ¼ 0:8Y0.9 M about halfway to the Galactic bulge or in the foreground disk, depending on the extinction.