Synthesis and characterization of a photocleavable collagen-like peptide.

A 34-amino acid long collagen-like peptide rich in proline, hydroxyproline, and glycine, and with four photoreactive N-acyl-7-nitroindoline units incorporated into the peptide backbone was synthesized by on-resin fragment condensation. Its circular dichroism supports a stable triple helix structure. The built-in photochemical function enables the decomposition of the peptide into small peptide fragments by illumination with UV light of 350 nm in aqueous solution. Illumination of a thin film of the peptide, or a thin film of a photoreactive amino acid model compound containing a 5-bromo-7-nitroindoline moiety, with femtosecond laser light at 710 nm allows for the creation of well-resolved micropatterns. The cytocompatibility of the peptide was demonstrated using human mesenchymal stem cells and mouse embryonic fibroblasts. Our data show that the full-length peptide is cytocompatible as it can support cell growth and maintain cell viability. In contrast, the small peptide fragments created by photolysis are somewhat cytotoxic and therefore less cytocompatible. These data suggest that biomimetic collagen-like photoreactive peptides could potentially be used for growing cells in 2D micropatterns based on patterns generated by photolysis prior to cell growth.

Synthesis and Photoreactivity of 7-Nitroindoline-S-thiocarbamates.

The photolytic properties of N-acyl-7-nitroindolines make these compounds attractive as photocleavable protecting groups and "caged" compounds for the light-induced release ("uncaging") of biologically active compounds and as acylating reagents under neutral conditions. However, the synthesis of N-acyl-7-nitroindolines usually requires multiple steps, and the direct acylation of 7-nitroindolines can be quite challenging. 7-Nitroindolines with other types of N-carbonyl-containing groups may also be photoreactive and could potentially be better accessible. Here we demonstrate the short and efficient synthesis of 5-bromo-7-nitroindoline-S-thiocarbamates, a new class of photoreactive compounds, and the study of some of their photochemical and photophysical properties. Using 5-bromo-7-nitroindoline-S-ethylthiocarbamate as a model compound, we show that it can undergo one-photon and two-photon photolysis at 350 and 710 nm, respectively. Our experimental data and quantum chemistry calculations support a photolysis pathway that differs from photolysis pathways previously reported for N-acyl-7-nitroindolines. The photolysis with 350 nm light results in 5-bromo-7-nitrosoindoline, which is in equilibrium with its dimeric form(s), as supported by experiment and theory. This study expands the scope of photoreactive 7-nitroindoline derivatives and informs the development of novel photocleavable compounds.

Development of Conductive Boron-Doped Diamond Electrode: A microscopic, Spectroscopic, and Voltammetric Study.

Building on diamond characteristics such as hardness, chemical inertness and low electron emission threshold voltage, the current microscopic, spectroscopic and voltammetric investigations are directed towards improving the properties of electrode coating materials for their future use in clinical studies of deep brain stimulation via fast-scan cyclic voltammetry (FSCV). In this study we combine the capabilities of confocal Raman mapping in providing detailed and accurate analysis of local distributions of material constituents in a series of boron-doped polycrystalline diamond films grown by chemical vapor deposition, with information from the more conventional techniques of scanning electron microscopy (SEM) and infrared absorption spectroscopy. Although SEM images show a uniform distribution of film crystallites, they have the limitation of being unable to differentiate the distribution of boron in the diamond. Values of 1018-1021 atoms/cm³ of boron content have been estimated from the absorption coefficient of the 1290 cm-1 infrared absorption band and from the 500 cm-1 Raman vibration. The observed accumulation of boron atoms and carbon sp² impurities at the grain boundaries suggests that very high doping levels do not necessarily contribute to improvement of the material's conductivity, corroborating with voltammetric data. FSCV results also indicate an enhanced stability of analyte detection.