A general route to \u03b2,\u03b2-carbocyclic sidechains in peptides: an aqueous metallaphotoredox approach driven by green light

Shapes of MHC Restriction

Peptidoglycan was prepared from purified Bacillus subtilis spores of wild-type and several mutant strains. Digestion with muramidase resulted in cleavage of the glycosidic bonds adjacent to muramic acid replaced by peptide or alanine side chains but not the bonds adjacent to muramic lactam. Reduction of the resulting muropeptides allowed their separation by reversed-phase high-pressure liquid chromatography. The structures of 20 muropeptides were determined by amino acid and amino sugar analysis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. In wild-type spores, 50% of the muramic acid had been converted to the lactam and 75% of these lactam residues were spaced regularly at every second muramic acid position in the glycan chains. Single L-alanine side chains were found on 25% of the muramic acid residues. The remaining 25% of the muramic acid had tetrapeptide or tripeptide side chains, and 11% of the diaminopimelic acid in these side chains was involved in peptide cross-links. Analysis of spore peptidoglycan produced by a number of mutants lacking proteins involved in cell wall metabolism revealed structural changes. The most significant changes were in the spores of a dacB mutant which lacks the sporulation-specific penicillin-binding protein 5*. In these spores, only 46% of the muramic acid was in the lactam form, 12% had L-alanine side chains, and 42% had peptide side chains containing diaminopimelic acid, 29% of which was involved in cross-links.

Peptides, due to their diverse and controllable properties, are used as both liquid and gas phase recognition elements for both biological and chemical targets. While it is well understood how binding of a peptide to a biomolecule can be converted into a sensing event, there is not the same mechanistic level of understanding with regard to how peptides modulate the selectivity of semiconductor/conductor-based gas sensors. Notably, a rational, mechanistic study has not yet been performed to correlate peptide properties to the sensor response for volatile organic compounds (VOCs) as a function of chemical properties. Here, we have designed a peptide that has (1) two amino acid residues that bind the sensor surface, (2) two flexible linkers (GG) that eliminate steric strain, and (3) a five amino-acid repeat that can bind the analyte of interest either by formation of a binding pocket (such as from peptides selected by phage display) or by forming a semiselective adsorption layer. The nine peptide sequences containing both a six amino acid constant sequence (WGGWGG) and a five amino acid variable sequence (XXXXX) were synthesized, and their impact on the selectivity and sensitivity of carbon nanotube (CNT) gas sensors was explored. The response of each sensor to the following VOCs with diverse chemical properties: isopropyl alcohol (polar protic), acetone (polar aprotic), isoprene (nonpolar, linear hydrocarbon), and toluene (nonpolar aromatic), was then recorded and analyzed. This study revealed multiple key factors that influence the response of peptides on CNTs to select VOCs. First, the stability of the CNT-peptide aqueous dispersion correlated to the aromaphilicity of the side chain, strongly suggesting that the side chains of peptides are interfacing with the CNT, and not the peptide backbone. Second, the sensing response profile cannot solely be explained by peptides adsorbing to the gas molecules with similar polarities/dielectrics and may instead be due to analyte displacement of the peptide side chain on the CNT surface as measured by changes in the peptide bond orientation using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). These two observations create a new paradigm to explain how peptides confer selectivity to semiconductor-/conductor-based gas sensors and can provide insights into future design and implementation of peptide-coated solid state sensors for gas targets.

Expert Systems are interactive and reliable computer-based decision-making systems that use both facts and heuristics for solving complex decision-making problems. Generally, the cyclic voltammetry (CV) experiments are executed a random number of times (cycles) to get a stable production of power. However, presently there are not many algorithms or models for predicting the power generation stable criteria in microbial fuel cells. For stability analysis of Medicinal herbs’ CV profiles, an expert system driven by the augmented K-means clustering algorithm is proposed. Our approach requires a dataset that contains voltage-current relationships from CV experiments on the related subjects (plants/herbs). This new approach uses feature engineering and augmented K-means clustering techniques to determine the cycle number beyond which the CV curve stabilizes. We obtain an excellent estimate of the required CV cycles for getting a stable Voltage versus Current curve in this approach. Moreover, this expert system would reduce the time needed and the money spent on running additional and superfluous CV experiments cycles. Thus, it would streamline the process of Bacterial Fuel Cells production using the CV of medicinal herbs.

Because of their unique structural and chemical properties, buckybowl molecules have attracted considerable attention in a wide range of scientific disciplines. The importance and utility of buckybowl molecules significantly increases once they acquire larger π-surface area and/or heteroatoms. The fusion of buckybowl molecules has emerged as a new strategy to extend the π-surface of polycyclic aromatic compounds; however, the π-extension of heteroatom-embedded buckybowls by the fusion strategy is still rare. Here we report the synthesis and propeties of a fused azacorannulene dimer bearing a C62N2 core (1a), which can also be regarded as a double aza[5]helicene. Due to the steric repulsion between two azapentabenzocorannulene moieties, this molecule shows a rigid S-shaped structure where the two azacorannulene bowls face in opposite directions. Stepwise chemical oxidation of 1a resulted in the formation of the corresponding radical cation (1a +) and dication (1a2+), providing an important insight into their aromaticity. The fusion of heteroatom-embedded buckybowls provides a powerful way to synthesize π-extended polycyclic aromatic molecules.

Substitution of Aspartic Acid at Position 57 of the DQβ1 Affects Relapse of Autoimmune Pancreatitis

Extraterrestrial amino acids and amines identified in asteroid Ryugu samples returned by the Hayabusa2 mission

Cyclic voltammetry and a.c. impedance studies of Ca 2+-induced ion channels on Pt-BLM

Electrooxidation study of pure ethanol/methanol and their mixture for the application in direct alcohol alkaline fuel cells (DAAFCs)

Electrochemical measurement of corrosive impurities in molten chlorides for thermal energy storage

SUMMARYThe influence of red, blue, green, and white light on growth and photosynthetic rates, carbon metabolism, and rates of release of extracellular compounds in the freshwater alga Chlamydomonas reinhardtii Dangeard was examined. Relative growth constants were 0.28, 0.32, 0.40, and 0.41 in green, white, blue, and red light, respectively. Photosynthetic rates were higher in white, blue, or red than in green light of the same intensity.More than 66% of the 14CO2 assimilated by cells grown under blue or green light was incorporated into the ethanol‐insoluble fraction, compared with about 50% in cells grown under white or red light. The percentage of sugars in this fraction was significantly higher in cells grown under green or red light than in cells cultured in white or blue light, while the percentage of proteins was highest in blue light. Light quality also influenced the composition of the ethanol‐soluble fraction. The percentage of organic acids was highest in cells grown in green and white light, while amino acids were highest in blue and green cultures. The percentage of ethanol‐soluble sugars was greatest in cultures grown in blue and red light.The percentage release of dissolved organic carbon into the medium was highest in white light and lowest in blue or red light. The nature of the extracellular products varied according to the quality of light under which the cells were cultured, but had no consistent relation to the nature or concentration or components in the ethanol‐soluble fraction.

Oligopeptide-binding protein A (OppA) from Lactococcus lactis binds peptides of an exceptionally wide range of lengths (4-35 residues), with no apparent sequence preference. Here, we present the crystal structures of OppA in the open- and closed-liganded conformations. The structures directly explain the protein's phenomenal promiscuity. A huge cavity allows binding of very long peptides, and a lack of constraints for the position of the N and C termini of the ligand is compatible with binding of peptides with varying lengths. Unexpectedly, the peptide's amino-acid composition (but not the exact sequence) appears to have a function in selection, with a preference for proline-rich peptides containing at least one isoleucine. These properties can be related to the physiology of the organism: L. lactis is auxotrophic for branched chain amino acids and favours proline-rich caseins as a source of amino acids. We propose a new mechanism for peptide selection based on amino-acid composition rather than sequence.

Synthetic ion channels containing δ-amino acids can become cation selective! δ-Amino acids with a cyclohexylether unit (see structure) were combined with structural motives from gramicidin A and led to channels with a NH4+/K+ permeability ratio of >10/1. (The current trace for an NH4+ channel is shown.)

Understanding the hydrophilicity/hydrophobicity of amino acid side chains in peptides/proteins is one the most important aspects of biology. Though many hydrophilicity/hydrophobicity scales have been generated, an "intrinsic" scale has yet to be achieved. "Intrinsic" implies the maximum possible hydrophilicity/hydrophobicity of side chains in the absence of nearest-neighbor or conformational effects that would decrease the full expression of the side-chain hydrophilicity/hydrophobicity when the side chain is in a polypeptide chain. Such a scale is the fundamental starting point for determining the parameters that affect side-chain hydrophobicity and for quantifying such effects in peptides and proteins. A 10-residue peptide sequence, Ac-X-G-A-K-G-A-G-V-G-L-amide, was designed to enable the determination of the intrinsic values, where position X was substituted by all 20 naturally occurring amino acids and norvaline, norleucine, and ornithine. The coefficients were determined by reversed-phase high-performance liquid chromatography using six different mobile phase conditions involving different pH values (2, 5, and 7), ion-pairing reagents, and the presence and absence of different salts. The results show that the intrinsic hydrophilicity/hydrophobicity of amino acid side chains in peptides (proteins) is independent of pH, buffer conditions, or whether C(8) or C(18) reversed-phase columns were used for 17 side chains (Gly, Ala, Cys, Pro, Val, nVal, Leu, nLeu, Ile, Met, Tyr, Phe, Trp, Ser, Thr, Asn, and Gln) and dependent on pH and buffer conditions, including the type of salt or ion-pairing reagent for potentially charged side chains (Orn, Lys, His, Arg, Asp, and Glu).

The behavior of hydrogen production on ZnO electrode during the electrolytic reduction of water was investigated by cyclic voltammetry (CV) and cathode polarization experiments combined with in situ Raman and photoluminescence spectroscopy. CV experiments indicate that hydrogen species prefers to diffuse into the ZnO bulk at negative potentials and occupies oxygen vacancies and interstitial sites. Meanwhile, the H2O reduction is self-enhanced during the electroreduction process, as evidenced by the trace crossing of the CV curves and the chronoamperometric experiment. The influence of the H species on the ZnO electrode during the electrocatalytic processes was characterized by the in situ Raman and photoluminescence spectroscopies. These results help us to understand the hydrogen-related catalytic or electrocatalytic processes on ZnO surfaces.