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.

Morphology and functions of astrocytes cultured on water-repellent fractal tripalmitin surfaces.

In the brain, astrocytes play an essential role with their multiple functions and sophisticated structure, as surrounded by a fractal environment which has not been available in our traditional cell culture. Water-repellent fractal tripalmitin (PPP) surfaces can imitate the fractal environment in vivo, so the morphology and biochemical characterization of astrocytes on these surfaces are examined. Water-repellent fractal PPP surface can induce astrocytes to display sophisticated morphology with smaller size of cell area, longer and finer filopodium-like processes, and higher morphological complexity. The super water-repellent fractal PPP surface with water contact angle of 150°âˆ¼160° produces the maximal effects compared with other surfaces at lower water contact angles. The trends of characteristic protein expression, including that of nestin, vimentin, GFAP and glutamine synthetase, for astrocytes cultured on super water-repellent fractal PPP surfaces approximate more to in vivo pattern. The super water-repellent PPP surface also render astrocytes to perform more pronounced promotion of neurogenesis by increasing the release of nerve growth factor in a co-culture system. Altogether, our results suggest that the super water-repellent fractal PPP surface facilitates the astrocytes to mimic their in vivo performance, thus provides a closer-to-natural culture environment for experimental assessment of glial structure and functions.

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.

Relationship between thyroid-stimulating hormone and blood pressure in the middle-aged and elderly population.

INTRODUCTION: Hypothyroidism and subclinical hypothyroidism may be associated with hypertension and metabolic syndrome. The aim of this study was to investigate the relationship between thyroid-stimulating hormone (TSH) and blood pressure, as well as the relationship between thyroid function and insulin resistance in middle-aged and elderly Chinese. METHODS: This was a cross-sectional, community-based study. Serum TSH, fasting glucose and insulin were measured in 2,988 subjects aged 35-80 years. Logistic regression analysis was used to identify the risk factors for hypertension. Analysis of variance and multiple linear regression analysis were performed to characterise the relationship among TSH, insulin resistance and blood pressure. RESULTS: Higher serum TSH concentration was found to be an independent risk factor for hypertension in females (odds ratio 1.4, 95% confidence interval 1.02-1.93; p-value = 0.039). The female group with subclinical hypothyroidism and high normal TSH (2.5-4.8 mIU/L) were more susceptible to high blood pressure than those with low normal TSH (0.3-2.5 mIU/L) (p-value < 0.05). After adjustment for waist-hip ratio and body mass index, neither the correlation between blood pressure and homeostasis model assessment of insulin resistance (HOMA-IR) nor the correlation between TSH and HOMA-IR were found to be significant in this study. CONCLUSION: This study provides evidence that both subclinical hypothyroidism and high normal TSH are independent risk factors for hypertension in middle-aged and elderly Chinese women.

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.

Association between serum fibroblast growth factor 21 and diabetic nephropathy.

Fibroblast growth factor 21 (FGF-21) is a new metabolic regulator with beneficial effects on lipid and glucose metabolism in animal models of diabetes mellitus. The aim of this study was to explore the relationship between FGF-21 and diabetic nephropathy in humans. Serum FGF-21 levels were determined in groups of control (n = 50) and type 2 diabetes mellitus (T2DM) patients with normoalbuminuria (n = 158), microalbuminuria (n = 68), and macroalbuminuria (n = 38) using enzyme-linked immunosorbent assay. Multiple linear regression models were used to analyze the associations between FGF-21 or other biomedical indices and urinary albumin excretion (UAE). Median serum FGF-21 levels were increased in T2DM patients compared with nondiabetic controls and were significantly higher in patients of higher UAE group. In groups of control and T2DM patients with normoalbuminuria, microalbuminuria, and macroalbuminuria, median serum (interquartile range) FGF-21 levels were 467.89 (294.59-519.56), 492.30 (354.59-640.42), 595.01 (480.49-792.31), and 665.20 (448.68-829.75) ng/L (P < .001), respectively. After adjustment for the confounders, FGF-21, fasting plasma glucose, and high-density lipoprotein cholesterol levels were found to be independently associated with UAE in diabetic patients. Serum FGF-21 level is independently correlated with UAE in T2DM patients, indicating that circulating FGF-21 may be involved in diabetic nephropathy.