Synthesis of Benzo[c]cinnolinium Salts from 2-Azobiaryls by Copper(II) or Electrochemical Oxidation.

Synthesis of benzo[c]cinnolinium salts by copper(II)-promoted or electrochemical oxidation of 2-azobiaryls is described. A variety of diversely functionalized benzo[c]cinnolinium salts were easily constructed by this strategy with excellent functional group tolerance and high efficiency. An interesting fluorescence centered at 571 nm is revealed by a benzo[c]cinnolinium salt with electron push-pull substitutions. The mechanism is proposed to go through single-electron transfer driven by oxidant and intramolecular cyclization via nucleophilic addition, followed by an anion exchange.

Design and synthesis of fluorinated peptides for analysis of fluorous effects on the interconversion of polyproline helices.

The unique interaction between fluorine atoms has been exploited to alter protein structures and to develop synthetic and analytical applications. To expand such fluorous interaction for novel applications, polyproline peptides represent an excellent molecular nanoscaffold for controlling the presentation of perfluoroalkyl groups on their unique secondary structure. We develop approaches to synthesis fluorinated peptides to systematically investigate how the number, location and types of the fluorous groups on polyproline affect the conformation by monitoring the transition between the two major polyproline structures PPI and PPII. This work provides valuable information on how fluorous interaction affects the peptide structure and also benefits the design of functional fluorous molecules.

Strategy and Effects of Polyproline Peptide Stapling by Copper(I)-Catalyzed Alkyne-Azide Cycloaddition Reaction.

Polyproline is a unique type of peptide that has a stable, robust, and well-defined helical structure in an aqueous environment. These features have allowed polyproline to be used as a nanosized scaffold for applications in chemical biology and related fields. To understand its structural properties and to expand the applications, this secondary structure was tested systematically by stapling the peptide at different locations with staples of various lengths. Using the efficient copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC), we successfully prepared stapled polyproline and investigated the impact of this peptide macrocyclization through circular dichroism analysis. Whereas the stapling seems to have no significant effect on polyproline helix II (PPII) conformation in water, the location and the length of the staple affect the transformation of conformation in n-propanol. These results provide valuable information for future research using peptide stapling to manipulate polyproline conformation for various applications.

Solubility and thermal response of fractionated cyanophycin prepared with recombinant Escherichia coli.

Cyanophycin, also known as cyanophycin granule polypeptide (CGP), is a non-ribosomal polypeptide consisting of aspartic acid as a backbone with arginine and lysine as the side chains. CGP has soluble (sCGP) and insoluble (iCGP) forms based on its aqueous solubility. In order to investigate the role of lysine in its physical properties, CGP was prepared with recombinant Escherichia coli cultivated at different temperatures, and the purified sCGP and iCGP were further fractionated with different ethanol concentrations and pHs, respectively. Low temperature cultivation was found to favor the production of more sCGP. The ratio of iCGP/sCGP increased from 0.12 to 0.35 when the cultivation temperature being raised from 17 to 37°C. After fractionation the same fraction of either sCGP or iCGP contained an approximate content of lysine, and therefore showed expectantly similar physical properties, irrespective of the cultivation temperatures. A high arginine/lysine ratio was found to result in low solubility and high molecular weight. Fractions of sCGP showed upper critical solution temperatures (UCST) below 5°C in phosphate buffered saline whereas iCGP exhibited a UCST around 28-31°C at pH 3. The particle size of iCGP was around 300-500nm as revealed by transmission electron microscopy. The thermal responses of CGP present a potential in biomedical applications, such as drug delivery.