Fragmentation Reactions of Methionine-Containing Protonated Octapeptides and Fragment Ions Therefrom: An Energy-Resolved Study

The fragmentation reactions of the MH⁺ ions as well as the b₇, a₇, and a₇* ions derived therefrom have been studied in detail for the octapeptides MAAAAAAA, AAMAAAAA, AAAAMAAA, and AAAAAAMA. Ionization was by electrospray using a QqToF mass spectrometer, which allowed a study of the evolution of the fragmentation channels as a function of the collision energy. Not surprisingly, the product ion mass spectra for the b₇ ions are independent of the original precursor sequence, indicating macrocyclization and reopening to the same mixture of protonated oxazolones prior to fragmentation. The results show that this sequence scrambling results in a distinct preference to place the Met residue in the C-terminal position of the protonated oxazolones. The a₇ and a₇* ions also produce product ion mass spectra independent of the original peptide sequence. The results for the a₇ ions indicate that fragmentation occurs primarily from an amide structure analogous to that observed for a₄ ions (Bythell et al. in J Am Chem Soc 132:14766–14779, 2010). Clearly, the rearrangement reaction they have proposed applies equally well to a_n ions as large as a₇. The major fragmentation modes of the MH⁺ ions at low collision energies produce b₇, b_6, and b₅ ions. As the collision energy is increased further fragmentation of these primary products produces, in part, non-direct sequence ions, which become prominent at lower m/z values, particularly for the peptides with the Met residue near the N-terminus.

Non-Direct Sequence Ions in the Tandem Mass Spectrometry of Protonated Peptide Amides—an Energy-Resolved Study

The fragmentation reactions of the MH⁺ ions of Leu-enkephalin amide and a variety of heptapeptide amides have been studied in detail as a function of collision energy using a QqToF beam type mass spectrometer. The initial fragmentation of the protonated amides involves primarily formation of b_n ions, including significant loss of NH₃ from the MH⁺ ions. Further fragmentation of these b_n ions occurs following macrocyclization/ring opening leading in many cases to b_n ions with permuted sequences and, thus, to formation of non-direct sequence ions. The importance of these non-direct sequence ions increases markedly with increasing collision energy, making peptide sequence determination difficult, if not impossible, at higher collision energies.

Thermal studies for preparation of Nb10Hf1Ti Alloy

The aim of this work is to evaluate the feasibility of preparation of Nb10Hf1Ti alloy by magnesiothermic reduction of its oxides. DTA studies were conducted to identify the reduction temperature for co reduction of the mixed oxides of Nb₂O₅, HfO₂, and TiO₂ by magnesium under reducing atmosphere. Based on DTA analysis, experiments were carried out to prepare Nb10Hf1Ti alloy by magnesiothermic reduction of their oxides at 750 °C. The reduced product was analyzed for its phases by X-ray diffraction. The excess Mg was leached out, the alloy mixture was vacuum dried, pelletized, sintered, and electron beam melted to get a consolidated alloy of the required composition. The alloy was characterized using different techniques such as optical microscopy, scanning electron microscopy, and chemical analysis. Microstructural observations revealed the formation of coarse grain structure in the consolidated alloy. The alloy product was also evaluated for its micro hardness.     

Molecular Recognition of Aromatic Nitro Compounds at Cyclodextrin Dithiocarbamate-modified Electrodes

Silver electrodes were modified by the adsorption of α-, β-, and γ-cyclodextrin dithiocarbamates (2α–γ) and characterized by reductive desorption experiments. Their molecular recognition properties were studied by cyclic voltammetry using three families of positional isomers of aromatic nitro compounds. Electrodes modified with 2α and 2β were selective for meta and para isomers while 2γ showed little selectivity. These observations are explained in terms of cavity sizes and guest structure. Computational studies suggest that the main reason for the observed selectivity is the different position of the NO² group in ortho and para isomers with respect to the CD cavity.     

Novel Copolymers of 4-Fluorostyrene. 11. Some Ring-substituted 1,1-dicyano-2-(1-naphthyl)ethylenes

Novel copolymers of trisubstituted ethylene monomers, ring-substituted 1,1-dicyano-2-(1-naphthyl)ethylenes, RC₁₀H₆CH?C(CN)₂ (where R is H, 2-OCH₃, 4-OCH₃) and 4-fluorostyrene were prepared by solution copolymerization in the presence of a radical initiator (ABCN) at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, ¹H and ¹³C-NMR. The order of relative reactivity (1/r ₁) for the monomers is (5.86) > 2-CH₃O (4.28) > 4-CH₃O (2.87). Relatively high T_g of the copolymers in comparison with that of poly(4-fluorostyrene) indicates a decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200–500°C range with residue (7.3–7.7% wt.), which then decomposed in the 500–800°C range.     

Mechanisms of electrochemical nitrogen gas reduction to ammonia under ambient conditions: a focused review

Journal of Solid State Electrochemistry - Electrocatalytic nitrogen reduction reaction (E-NRR) to ammonia is becoming a major topic of interest in the field of large-scale energy storage from...     

Amide Moieties Modulate the Antimicrobial Activities of Conjugated Oligoelectrolytes against Gram-negative Bacteria

Cationic conjugated oligoelectrolytes (COEs) are a class of compounds that can be tailored to achieve relevant in vitro antimicrobial properties with relatively low cytotoxicity against mammalian cells. Three distyrylbenzene-based COEs were designed containing amide functional groups on the side chains. Their properties were compared to two representative COEs with only quaternary ammonium groups. The optimal compound, COE2−3C−C3-Apropyl , has an antimicrobial efficacy against Escherichia coli with an MIC=2 μg mL⁻¹, even in the presence of human serum albumin low cytotoxicity (IC₅₀=740 μg mL⁻¹) and minimal hemolytic activity. Moreover, we find that amide groups increase interactions between COEs and a bacterial lipid mimic based on calcein leakage assay and allow COEs to readily permeabilize the cytoplasmic membrane of E. coli. These findings suggest that hydrogen bond forming moieties can be further applied in the molecular design of antimicrobial COEs to further improve their selectivity towards bacteria.     

Elemental Analysis of Phytotherapeutic Products by Inductively Coupled Plasma–Tandem Mass Spectrometry

A procedure for the determination of As, Cd, Cr, Ni, Pb, and V in phytotherapy medicines by inductively coupled plasma–tandem mass spectrometry is reported. The use of tandem mass spectrometry with oxygen into an octopole reaction system at various gas flow rates and the combination of on-mass and mass-shift modes was evaluated. Cadmium, Cr, Ni, and Pb were determined as free atomic ions while As and V were determined as the oxides AsO⁺ and VO⁺ in the same run. Samples were prepared by microwave-assisted digestion with dilute nitric acid and hydrogen peroxide. Two plant-certified reference materials (apple leaves and tomato leaves) were used to check the accuracy. For tandem mass spectrometry with 0.5?mL min^?1 O₂, recoveries in the 85–113% were typically obtained and no statistical differences were observed at the 95% confidence level (t-test) in comparison with the certified values. Using these conditions, the limits of detection for the method were 0.01, 0.0002, 0.008, 0.008, 0.003, and 0.002?µg g^?1 for As, Cd, Cr, Ni, Pb, and V, respectively. The procedure was used for the analysis of four phytotherapic drugs and the determined concentrations were up to 0.168?µg g^?1 As, 0.03?µg g^?1 Cd, 0.82?µg g^?1 Cr, 1.18?µg g^?1 Ni, 0.52?µg g^?1 Pb, and 2.4?µg g^?1 V with average precision values of 8% as the relative standard deviation. The found concentrations were compared with limits proposed in official guidelines and, in most cases, the values were below the maximum limits allowed.     

Cloning of the Orange Light‐Producing Luciferase from Photinus scintillans—A New Proposal on how Bioluminescence Color is Determined

Unlike the enchanting yellow‐green flashes of light produced on warm summer evenings by Photinus pyralis, the most common firefly species in North America, the orange lights of Photinus scintillans are infrequently observed. These Photinus species, and likely all bioluminescent beetles, use the same substrates beetle luciferin, ATP and oxygen to produce light. It is the structure of the particular luciferase enzyme that is the key to determining the color of the emitted light. We report here the molecular cloning of the P. scintillans luc gene and the expression and characterization of the corresponding novel recombinant luciferase enzyme. A comparison of the amino acid sequence with that of the highly similar P. pyralis enzyme and subsequent mutagenesis studies revealed that the single conservative amino acid change tyrosine to phenylalanine at position 255 accounted for the entire emission color difference. Additional mutagenesis and crystallographic studies were performed on a H‐bond network, which includes the position 255 residue and five other stringently conserved beetle luciferase residues, that is proximal to the substrate/emitter binding site. The results are interpreted in the context of a speculative proposal that this network is key to the understanding of bioluminescence color determination.     

Optimal Production of a <Emphasis Type="Italic">Rhodococcus erythropolis</Emphasis> ATCC 4277 Biocatalyst for Biodesulfurization and Biodenitrogenation Applications

Rhodococcus sp. has a broad catabolic diversity and unique enzymatic capabilities, and it is able to adapt under extreme conditions. Thereby, the production of this remarkable bacterium has a great biotechnological and industrial importance. In this sense, we sought to improve the R. erythropolis ATCC 4277 growth through a central composite design, by varying the components of nutrient medium (glucose, malt extract, yeast extract, CaCO₃), temperature, and agitation. It was found that the concentrations of glucose and malt extract are not statistically significant, being reduced of 4.0 and 10.0 g L^-1 to 2.0 and 5.0 g L^?1, respectively. The CaCO₃ concentration and temperature were also diminished of 2.0 to 1.16 g L^?1and 28 to 23.7 °C, respectively. Optimal growth conditions provided a 240% increase in final biomass concentration, an increment in specific growth rate, and a growth yield coefficient about five times greater. Application of the optimal conditions in biodesulfurization and biodenitrogenation processes showed that desulfurization capability is not associated with optimal growth conditions; however, it was achieved a 47% of nitrogen removal in the assay containing 10% (w/w) of heavy gas oil.

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