Bacterial peptidoglycan is a mesh-like network comprised of sugars and oligopeptides. Transpeptidases cross-link peptidoglycan oligopeptides to provide vital cell wall rigidity and structural support. It was recently discovered that the same transpeptidases catalyze the metabolic incorporation of exogenous D-amino acids onto bacterial cell surfaces with vast promiscuity for the side-chain identity. It is now shown that this enzymatic promiscuity is not exclusive to side chains, but that C-terminus variations can also be accommodated across a diverse range of bacteria. Atomic force microscopy analysis revealed that the incorporation of C-terminus amidated D-amino acids onto bacterial surfaces substantially reduced the cell wall stiffness. We exploited the promiscuity of bacterial transpeptidases to develop a novel assay for profiling different bacterial species.

Bacterial peptidoglycan is am esh-like network comprised of sugars and oligopeptides.T ranspeptidases crosslink peptidoglycan oligopeptides to provide vital cell wall rigidity and structural support. It was recently discoveredt hat the same transpeptidases catalyze the metabolic incorporation of exogenous d-amino acids onto bacterial cell surfaces with vast promiscuity for the side-chain identity.I ti sn ow shown that this enzymatic promiscuity is not exclusive to side chains, but that C-terminus variations can also be accommodated across ad iverse range of bacteria. Atomic force microscopy analysis revealed that the incorporation of C-terminus amidated d-amino acids onto bacterial surfaces substantially reduced the cell wall stiffness.W ee xploited the promiscuity of bacterial transpeptidases to develop an ovel assayf or profiling different bacterial species.

A series of polycations bearing one, two, and three pendant quaternary ammonium groups per repeat unit has been synthesized and combined with poly­(sodium 4-styrenesulfonate) to produce hyperthin polyelectrolyte multilayers. Incremental addition of quaternary ammonium groups per repeat unit leads to decreased permeances for H2, CO2, and N2 and increased H2/CO2 and CO2/N2 permeation selectivities. These results, together with analysis of the composition from X-ray photoelectron spectra and values of Young’s modulus from nanoindentation analysis, show that oligo pendant ions provide a means for increasing volume charge density and tightening polyelectrolyte multilayers.

A series of polyelectrolyte multilayers (PEMs) has been fabricated using polyanions and polycations that have repeat units (i) similar in structure and composition (matched), (ii) partially similar in structure and composition (semimatched), and (iii) very different in structure and composition (mismatched). The primary aim of this investigation was to determine whether the matching of the polyelectrolytes can significantly influence the permeability properties of hyperthin PEMs. While matching, per se, was not found to be a key factor in defining membrane permeability, large differences in permeability were observed (the permeances of N varied by a factor of 20), which were correlated with the concentration of pendant aryl groups present, i.e., the greater the concentration of these groups, the higher the permeability. Analysis by AFM indentation measurements further revealed that high-permeability PEMs tend to be more compliant than low-permeability PEMs. These findings underscore the need for considering a broad range of polyelectrolyte combinations when optimizing a particular functional property of PEMs.

Chalcogenide glasssilver heterostructures are candidates for photoresist and diffractive optical applications. To optimize their processing, we report the kinetics of Ag photo-dissolution in As2S3 matrix using in-situ optical transmission/reflection measurements and real time atomic force microscopy (AFM) imaging under optical illumination. The results indicate that photo-dissolution occurs in three stages with the extent and kinetics of each stage depending strongly on Ag film thickness. By contrast, the photodissolution is found to be independent of As2S3 matrix thickness. The extent of three stages also depends strongly on the laser dose and can be reduced to two stages at higher laser fluence. A comparative study of two oppositely stacked sample configurations: As2S3/Ag/glass and Ag/As2S3/glass show that the heterostructures respond differently to light illumination. For the former, Ag dissolves completely into As2S3 matrix at a faster rate than for the latter case. The origin of this difference is established by energy dispersive X-ray spectroscopy and AFM measurements.