Quantitative proteomics reveals the relationship between protein changes and off-flavor in Russian sturgeon (Acipenser gueldenstaedti) fillets treated with low temperature vacuum heating.

This study aimed to reveal the molecular mechanisms associated with off-flavor generation in sturgeon fillets treated by low temperature vacuum heating (LTVH). Label-free quantitative proteomics was used to identify 120 favor-related proteins, 27 proteins were screened as differentially expressed for bioinformatics analysis. 17 of KEGG pathways were identified. Particularly, proteins involved in proteasome and peroxisome were highly correlated with off-flavor formation. They were primarily implicated in the structures of proteins, including binding and proteasome pathways. The results indicated that the LTVH reduced the binding sites by down-regulating protease and superoxide dismutase expression. LTVH increased the myofibrillar protein and sulfhydryl content and decreased the total volatile basic nitrogen and thiobarbituric acid reactive substance, which confirmed that protein oxidation was related to off-flavor. This proteomics study provided new insights into the off-flavor of sturgeon with LTVH, and proposed potential link between biological processes and off-flavor formation.

Side-Group Effect on Electron Transport of Single Molecular Junctions.

In this article, we have investigated the influence of the nitro side-group on the single molecular conductance of pyridine-based molecules by scanning tunneling microscopy break junction. Single molecular conductance of 4,4'-bipyridine (BPY), 3-nitro-4-(pyridin-4-yl)pyridine (BPY-N), and 3-nitro-4-(3-nitropyridin-4-yl)pyridine (BPY-2N) were measured by contact with Au electrodes. For the BPY molecular junction, two sets of conductance were found with values around 10-3.1 G0 (high G) and 10-3.7 G0 (low G). The addition of nitro side-group(s) onto the pyridine ring resulted in lower conductance of 10-3.8 G0 for BPY-N and 10-3.9 G0 for BPY-2N, respectively, which can be attributed to the twist angle of two pyridine rings. Moreover, the steric hindrance of nitro group(s) also affects the contacting configuration of electrode-molecule-electrode. As a consequence, only one set of conductance value was observed for BPY-N and BPY-2N. Our work clearly shows the important role of side-groups on the electron transport of single-molecule junctions.

Low Tunneling Decay of Iodine-Terminated Alkane Single-Molecule Junctions.

One key issue for the development of molecular electronic devices is to understand the electron transport of single-molecule junctions. In this work, we explore the electron transport of iodine-terminated alkane single molecular junctions using the scanning tunneling microscope-based break junction approach. The result shows that the conductance decreases exponentially with the increase of molecular length with a decay constant ßN = 0.5 per -CH2 (or 4 nm-1). Importantly, the tunneling decay of those molecular junctions is much lower than that of alkane molecules with thiol, amine, and carboxylic acid as the anchoring groups and even comparable to that of the conjugated oligophenyl molecules. The low tunneling decay is attributed to the small barrier height between iodine-terminated alkane molecule and Au, which is well supported by DFT calculations. The work suggests that the tunneling decay can be effectively tuned by the anchoring group, which may guide the manufacturing of molecular wires.

Spirooxindole synthesis via palladium-catalyzed dearomative reductive-Heck reaction.

Palladium-catalyzed intramolecular dearomative reductive-Heck reaction of C2-substituted indoles is developed, which provides access to structurally diverse 3,2'-spiropyrrolidine oxindoles. By changing the hydride source to AcONa base, direct C3-arylation products [2,3-b]quinolinones are achieved in good yields. The reaction of C2-substituted benzofuran is also realized, delivering the desired spiro-product.

Protein-peptide nutritional material prepared from surimi wash-water using immobilized chymotrypsin-trypsin.

BACKGROUND: In the production process of surimi, large quantities of wastewater are produced. Thus it would be interesting to develop an efficient protocol for the recovery of protein from hairtail surimi wash-water. RESULTS: A technique involving the use of immobilized chymotrypsin-trypsin (I-CT) was developed, providing a practical method for the preparation of protein-peptide nutritional material (PPNM). Under optimized reaction conditions, the recovery rate of nitrogen of surimi wash-water was measured as 98.3 ± 2.9%. Nutritional evaluation of the protein-peptide fraction demonstrated that it contained all essential amino acids (EAA) for humans, accounting for 44.1% of the total amino acid (TAA) content, which was determined to be 78.2 g per 100 g dry matter. The essential amino acid index (EAAI) and biological value (BV) were 101.7 (>95) and 76.7 respectively. A wide range of volatile flavor compounds (>50), including aldehydes, ketones, alcohols, hydrocarbons and heterocyclic compounds, were identified in PPNM by gas chromatography/mass spectrometry (GC/MS) analysis. CONCLUSION: An efficient and practical protocol for the recovery of protein from hairtail surimi wash-water has been developed. The PPNM prepared in this work could be used as a nutraceutical and as an ingredient of functional foods. © 2016 Society of Chemical Industry.

Isolation and absolute configurations of diastereomers of 8α-hydroxy-T-muurolol and (1α,6ß,7ß)-cadinane-4-en-8α,10α-diol from Chimonanthus salicifolius.

Phytochemical investigation of the aerial parts of Chimonanthus salicifolius resulted in the isolation of two sesquiterpenoids, 8α-hydroxy-T-muurolol and (1α,6ß,7ß)-cadinane-4-en-8α,10α-diol, together with 13 known compounds. The 15 structures were established by means of 1D and 2D NMR spectroscopy. The relative and absolute configurations of 8α-hydroxy-T-muurolol and 8α,11-elemodiol were achieved by NOESY experiments and X-ray crystallography using CuKα radiation. 8α-hydroxy-T-muurolol and (1α,6ß,7ß)-cadinane-4-en-8α,10α-diol showed immunosuppressive activities in a dose-dependent manner.

Isolation, purification, and antioxidant activities of degraded polysaccharides from Enteromorpha prolifera.

In the present study, purification and characterization of enzymatic hydrolysates of polysaccharide from Enteromorpha prolifera (HPE) are described. HPE was sequentially purified by DEAE Cellulose-52 chromatography and Sephadex G-100 chromatography to afford three fractions, namely, PHPE1, PHPE2, and PHPE3. Molecular weights of these three fractions were measured to be 103, 45.4, and 9.8kDa, respectively, using high performance gel permeation chromatography (HPGPC). The three fractions were evaluated for their antioxidant activities by determining their ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl, and superoxide anion radicals. PHPE2 was found to possess the strongest scavenging ability. GC-MS analysis indicates that PHPE2 is mainly composed of mannose, xylose, and glucose.

Mechanistic insights into small molecule activation induced by ligand cooperativity in PCcarbeneP nickel pincer complexes: a quantum chemistry study.

Mechanisms for the activation of water, ammonia, and other small molecules by the PCcarbeneP nickel pincer complex were studied computationally with the aid of density functional theory. The calculation results indicate that the strongly donating, nucleophilic carbene center can engage in a variety of heterolytic splitting of E-H (E=H, C, N, O) bonds, some of which are reversible. The cleavage of E-H bonds across the Ni=C bond represents a new mode of bond activation by ligand cooperativity in nickel pincer complex. On the basis of the calculations, we also demonstrate that reversible H2 activation across the Ir=C bond via the PCcarbeneP iridium pincer complex was observed in the experiments, while other E-H (E=C, N, O) bonds were not activated. Our calculations are in good agreement with experimental observations and could provide new insights into ligand cooperativity in nickel pincer complexes.

Explore the reaction mechanism of the Maillard reaction: a density functional theory study.

The mechanism of Maillard reaction has been investigated by means of density functional theory calculations in the gaseous phase and aqueous solution. The Maillard reaction is a cascade of consecutive and parallel reaction. In the present model system study, glucose and glycine were taken as the initial reactants. On the basis of previous experimental results, the mechanisms of Maillard reaction have been proposed, and the possibility for the formation of different compounds have been evaluated through calculating the relative energy changes for different steps of reaction under different pH conditions. Our calculations reveal that the TS3 in Amadori rearrangement reaction is the rate-determining step of Maillard reaction with the activation barriers of about 66.7 and 68.8 kcal mol(-1) in the gaseous phase and aqueous solution, respectively. The calculation results are in good agreement with previous studies and could provide insights into the reaction mechanism of Maillard reaction, since experimental evaluation of the role of intermediates in the Maillard reaction is quite complicated.

A quantum chemistry study on thermochemical properties of high energy-density endothermic hydrocarbon fuel JP-10.

The density functional theory (DFT) calculations at the M06-2X/6-31++G(d,p) level have been performed to explore the molecular structure, electronic structure, C-H bond dissociation enthalpy, and reaction enthalpies for five isodesmic reactions of a high energy-density endothermic hydrocarbon fuel JP-10. On the basis of the calculations, it is found that the carbonium ion C-6 isomer formed from the catalytic cracking at the C6 site of JP-10 has the lowest energy, and the R-5 radical generated from the thermal cracking at the C5 site of JP-10 is the most stable isomer. Furthermore, a series of hypothetical and isodesmic work reactions containing similar bond environments are used to calculate the reaction enthalpies for target compounds. For the same isodesmic reaction, the reaction enthalpy of each carbon site radical has also been calculated. The present work is of fundamental significance and strategic importance to provide some valuable insights into the component design and energy utilization of advanced endothermic fuels.

A DFT study on the thermal cracking of JP-10.

Density functional theory (DFT) calculations have been carried out to investigate the thermal cracking pathways of JP-10, a high energy density hydrocarbon fuel. Thermal cracking mechanisms are proposed, as supported by our previous experimental results (Xing et al. in Ind Eng Chem Res 47:10034-10040, 2008). Using DFT calculations, the potential energy profiles of the possible thermal cracking pathways for all of the diradicals obtained from homolytic C-C bond cleavage of JP-10 were derived and are presented here. The products of the different thermal cracking pathways are in good agreement with our previous experimental observations.

Intermolecular interactions between gold clusters and selected amino acids cysteine and glycine: a DFT study.

The intermolecular interactions between Au(n) (n = 3-4) clusters and selected amino acids cysteine and glycine have been investigated by means of density functional theory (DFT). Present calculations show that the complexes possessing Au-NH(2) anchoring bond are found to be energetically favored. The results of NBO and frontier molecular orbitals analysis indicate that for the complex with anchoring bonds, lone pair electrons of sulfur, oxygen, and nitrogen atoms are transferred to the antibonding orbitals of gold, while for the complex with the nonconventional hydrogen bonds (Au···H-O), the lone pair electrons of gold are transferred to the antibonding orbitals of O-H bonds during the interaction. Furthermore, the interaction energy calculations show that the complexes with Au-NH(2) anchoring bond have relatively high intermolecular interaction energy, which is consistent with previous computational studies.