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Reactive stepping

Stéphanie Essafi, Jeremy N Harvey
For condensed-phase reactions, commonly used kinetic models assume that energy exchange from and to solvent molecules is much faster than any reactive steps. However, it is becoming increasingly evident that this does not always hold true. In this work, we use molecular dynamics simulations to explore the timescale for energy transfer between solvent and solute in some typical organic solvents. As a reference, energy transfer between solvent molecules is also considered. The timescale is found to depend most strongly on the identity of the solvent...
March 16, 2018: Journal of Physical Chemistry. A
M R Kholghy, G A Kelesidis, S E Pratsinis
Nucleation is an important, yet poorly understood step in soot formation. Here, the importance of reactive PAH dimerization in reducing soot nucleation reversibility is investigated by simulating soot formation in a so-called "nucleation" flame (P. Desgroux et al., Combust. Flame, 2017, 184, 153-166). There, inception of soot particles is prolonged at minimal subsequent growth. With only reversible PAH dimerization, the simulated soot concentration is negligible. Accounting however for PAH chemical bond formation after physical dimerization, stabilizes dimers by covalent bonds and increases the soot concentration by four orders of magnitude, in good agreement with Laser Induced Incandescence measurements...
March 15, 2018: Physical Chemistry Chemical Physics: PCCP
Guner Cicek, Osman Imamoglu, Abdullah Gullu, Oguzhan Celik, Oguzhan Ozcan, Esin Gullu, Faruk Yamaner
The purpose of this study is to investigate the effect of 16 weeks step-aerobic exercises and core exercises on left ventricular structure and function with some physiological parameters in sedentary women. Methods: To achieve the purpose of this study, a total of 45 volunteers including (step-aerobic group (SAG, n = 25), core exercise group (CEG, n = 20) were selected as participants. Two different exercises were applied for 4 days a week, throughout 16 weeks, within 60 minutes for each exercise with the intensity of heart rate (HR) 60-70 percent...
December 2017: Journal of Exercise Science and Fitness
In-Yup Jeon, Hyuk-Jun Noh, Jong-Beom Baek
Hyperbranched macromolecules (HMs, also called hyperbranched polymers) are highly branched three-dimensional (3D) structures in which all bonds converge to a focal point or core, and which have a multiplicity of reactive chain-ends. This review summarizes major types of synthetic strategies exploited to produce HMs, including the step-growth polycondensation, the self-condensing vinyl polymerization and ring opening polymerization. Compared to linear analogues, the globular and dendritic architectures of HMs endow new characteristics, such as abundant functional groups, intramolecular cavities, low viscosity, and high solubility...
March 14, 2018: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Gaspar Epro, Andreas Mierau, Christopher McCrum, Michael Leyendecker, Gert-Peter Bruggemann, Kiros Karamanidis
The plantar flexors play a crucial role in recovery from sudden disturbances to gait. The objective of this study was to investigate whether medium (months) or long-term (years) exercise-induced enhancement of triceps surae (TS) neuromuscular capacities affects older adults' ability to retain improvements in reactive gait stability during perturbed walking acquired from perturbation training sessions. Thirty-four female adults (65{plus minus}7y) were recruited to a perturbation training group (n=13) or a group which additionally completed 14 weeks of TS neuromuscular exercise (n=21), 12 of whom continued with the exercise for 1...
March 14, 2018: Journal of Neurophysiology
N Valiente, R Carrey, N Otero, A Soler, D Sanz, A Muñoz-Martín, F Jirsa, W Wanek, J J Gómez-Alday
Endorheic or closed drainage basins in arid and semi-arid regions are vulnerable to pollution. Nonetheless, in the freshwater-saltwater interface of endorheic saline lakes, oxidation-reduction (redox) reactions can attenuate pollutants such as nitrate (NO3 - ). This study traces the ways of nitrogen (N) removal in the Pétrola lake-aquifer system (central Spain), an endorheic basin contaminated with NO3 - (up to 99.2mg/L in groundwater). This basin was declared vulnerable to NO3 - pollution in 1998 due to the high anthropogenic pressures (mainly agriculture and wastewaters)...
March 10, 2018: Science of the Total Environment
Caixia Zhang, Guangyan Li, Tingting Chen, Baohua Feng, Weimeng Fu, Jinxiang Yan, Mohammad Rezaul Islam, Qianyu Jin, Longxing Tao, Guanfu Fu
BACKGROUND: Pollen tube elongation in the pistil is a key step for pollination success in plants, and auxins play an important role in this process. However, the function of auxins in pollen tube elongation in the pistil of rice under heat stress has seldom been previously reported. RESULTS: Two rice genotypes differing in heat tolerance were subjected to heat stress of 40 °C for 2 h after flowering. A sharp decrease in spikelet fertility was found in the Nipponbare (NPB) and its mutant High temperature susceptible (HTS) under heat stress, but the stress-induced spikelet sterility was reversed by 1-naphthaleneacetic acid (NAA), especially the HTS...
March 12, 2018: Rice
Sei Kuriyama, Tadahiro Tsuji, Tetsushi Sakuma, Takashi Yamamoto, Masamistu Tanaka
The anti-apoptotic nature of cancer cells often impedes the effects of anti-cancer therapeutic agents. Multiple death signals influence mitochondria during apoptosis, and though many studies have attempted to elucidate these complicated pathways, Bax oligomerization, an important step in the process, remains controversial. Here we demonstrate that pleckstrin-homology N1 (PLEKHN1), also known as cardiolipin phosphatidic acid binding protein, plays pro-apoptotic roles during reactive oxygen species (ROS)-induced apoptosis...
December 2018: Cell Death Discovery
Aurélien Dupré, Hassan Z Malik
Chronic inflammation is an aberrantly prolonged form of a protective response to a loss of tissue homeostasis and it is involved in several steps of the carcinogenesis process. As a result, many cancers are inflammation-related. The systemic inflammatory response is associated with survival in advanced and localized cancers. Two categories of scores have been proposed to monitor the systemic inflammatory response, those derived from protein measurement and those based on counting inflammatory cells. This review aims to provide a critical appraisal of these 2 categories of surrogate markers...
March 2, 2018: European Journal of Surgical Oncology
Michael Lucas, Aaron M Thomas, Ralf I Kaiser, Eugene K Bashkirov, Valeriy N Azyazov, Alexander Moiseevich Mebel
We explored the elementary reaction of atomic carbon (C;3 Pj ) with pyridine (C5 H5 N; X1 A1 ) at a collision energy of 34 ± 4 kJ mol-1 utilizing the crossed molecular beams technique. Forward-convolution fitting of the data was combined with high-level electronic structure calculations and statistical (RRKM) calculations on the triplet C6 H5 N potential energy surface (PES). These investigations reveal that the reaction dynamics are indirect and dominated by large range reactive impact parameters leading via barrier-less addition to the nitrogen atom and to two chemically non-equivalent 'aromatic' carbon-carbon bonds forming three distinct collision complexes...
March 12, 2018: Journal of Physical Chemistry. A
Wen-Wen Yong, Huan Lu, Han Li, Shu Wang, Ming-Tian Zhang
Artificial photosynthesis is a chemical process that seeks to capture energy from sunlight to produce solar fuels. Light absorption by a robust and efficient photosensitizer is one of the key steps in solar energy conversion. However, common photosensitizers, including [Ru(bpy)3]2+, remain far from the ideal. In this work, we exploited the performance of conjugated polymers (CPs) as photosensitizers in photodriven hydrogen evolution in aqueous solution (pH 6). Interestingly, CPs, such as poly(fluorene-co-phenylene) derivative (PFP, 429 mmolH2•gCP-1•h-1), exhibit steady and high reactivity towards hydrogen evolution; this performance can rival that of a phosphonated [Ru(bpy)3]2+ (RuP) under the same conditions, indicating that CPs are promising metal-free photosensitizers for future application in photocatalysis...
March 12, 2018: ACS Applied Materials & Interfaces
Abhishek De, Murlidhar Rajagopalan, Aarti Sarda, Sudip Das, Projna Biswas
Drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome, is also known as drug induced hypersensitivity syndrome and by various other names. It is now recognised as one of the severe cutaneous adverse reaction (SCAR) and can be potentially life-threatening. Historically, it was most frequently linked with phenytoin and was initially described as phenytoin hypersensitivity syndrome. However, it was later found to be caused by various other medications. Anticonvulsants and sulfonamides are the most common offender...
January 2018: Indian Journal of Dermatology
A R Ramirez, O L Acosta, M B Maya, M El-Hafidi
In metabolic diseases such as obesity, metabolic syndrome and type II diabetes, the over-expression of uncoupling proteins (UCPs) in a response to increased reactive oxygen species (ROS) generation by mitochondrial respiratory complexes, and to the excess of free fatty acid (FFA) supply from adipose tissue, may protect cells from oxidative stress, lipotoxicity and in turn from death. UCPs by reducing superoxide anion and H2O2 generation trigger several signals to cell for their adaptation to the lipotoxic microenvironment...
March 7, 2018: Current Molecular Medicine
Manju Ohri, Smriti Parashar, Venkatesh S Pai, Sujata Ghosh, Anuradha Chakraborti
Group B streptococcus (GBS) or Streptococcus agalactiae, is an opportunistic pathogen causing a wide range of infections like pneumonia, sepsis, and meningitis in newborn, pregnant women and adults. While this bacterium has adapted well to asymptomatic colonization of adult humans, it still remains a potentially devastating pathogen to susceptible infants. Advances in molecular techniques and refinement of in vitro and in vivo model systems have elucidated key elements of the pathogenic process, from initial attachment to the maternal vaginal epithelium to penetration of the newborn blood-brain barrier...
March 8, 2018: World Journal of Microbiology & Biotechnology
Peng Liu, Chen Li, Shengyu Wang, Dunyou Wang
Water-assisted proton transfer process is a key step in guanine damage reaction by hydroxyl radical in aqueous solution. In this article, we quantitatively determined the solvent effect in water-assisted proton transfer mechanism of 8-hydroxy guanine radical using combined quantum mechanics and molecular mechanism with an explicit solvation model. Atomic-level reaction pathway was mapped, which shows a synchronized two-proton transfer mechanism between the assistance water molecule and 8-hydroxy guanine radical...
March 8, 2018: Journal of Physical Chemistry. B
Małgorzata Iciek, Magdalena Górny, Anna Bilska-Wilkosz, Danuta Kowalczyk-Pachel
Aldehyde dehydrogenase (ALDH) catalyzes the critical step of ethanol metabolism, i.e. transformation of toxic acetaldehyde to acetic acid. It is a redox sensitive protein with the key Cys in its active site. Recently, it has been documented that activity of some proteins can be modified by sulfur-containing molecules called reactive sulfur species leading to the formation of hydro- persulfides. The aim of the present study was to examine whether ALDH activity can be modified in this way. Studies were performed in vitro using yeast ALDH and various reactive sulfur species, including Na2 S, GSSH, K2 Sx , Na2 S2 O3 , and garlic-derived allyl sulfides...
March 9, 2018: Acta Biochimica Polonica
Ruben Van de Vijver, Maarten K Sabbe, Marie-Françoise Reyniers, Kevin M Van Geem, Guy B Marin
A set of group additivity values for intramolecular hydrogen abstraction reactions of alkanes, alkenes and alkynes is reported. Calculating 448 reaction rate coefficients at the CBS-QB3 level of theory for 1-2 up to 1-7 hydrogen shift reactions allowed the estimation of ΔGAV° values for 270 groups. The influence of substituents on (1) the attacking radical, (2) the attacked carbon atom, and (3) the carbon chain between the attacking and attacked reactive atom has been systematically studied. Substituents have been varied between hydrogen atoms and sp3 , sp2 and sp hybridized carbon atoms...
March 8, 2018: Physical Chemistry Chemical Physics: PCCP
Kyle M Conner, AnnaMaria C Arostegui, Daniel D Swanson, Seth N Brown
The 2,2'-biphenylene-bridged bis(iminosemiquinone) complexes (t BuClip)M [t BuClipH4 = 4,4'-di- tert-butyl- N, N'-bis(3,5-di- tert-butyl-2-hydroxyphenyl)-2,2'-diaminobiphenyl; M = Pd, Pt] can be reduced to the bis(aminophenoxide) complexes (t BuClipH2 )M by reaction with hydrazobenzene (M = Pd) or by catalytic hydrogenation (M = Pt). The palladium complex with one aminophenoxide ligand and one iminosemiquinone ligand, (t BuClipH)Pd, is generated by comproportionation of (t BuClip)Pd with (t BuClipH2 )Pd in a process that is both slow (0...
March 8, 2018: Inorganic Chemistry
Yulei Wang, Zhidao Huang, Xuebing Leng, Huping Zhu, Guixia Liu, Zheng Huang
The first general catalytic approach to effecting transfer hydrogenation (TH) of unactivated alkenes using ethanol as the hydrogen source is described. A new NCP-type pincer iridium complex (BQ- NCO P)IrHCl containing a rigid benzoquinoline backbone has been developed for efficient, mild TH of unactivated C-C multiple bonds with ethanol, forming ethyl acetate as the sole byproduct. A wide variety of alkenes, including multisubstituted alkyl alkenes, aryl alkenes, and heteroatom-substituted alkenes, as well as O- or N-containing heteroarenes and internal alkynes, are suitable substrates...
March 8, 2018: Journal of the American Chemical Society
Melisa Del Barrio, Matteo Sensi, Christophe Orain, Carole Baffert, Sébastien Dementin, Vincent Fourmond, Christophe Léger
Many enzymes that produce or transform small molecules such as O2 , H2 , and CO2 embed inorganic cofactors based on transition metals. Their active site, where the chemical reaction occurs, is buried in and protected by the protein matrix, and connected to the solvent in several ways: chains of redox cofactors mediate long-range electron transfer; static or dynamic tunnels guide the substrate, product and inhibitors; amino acids and water molecules transfer protons. The catalytic mechanism of these enzymes is therefore delocalized over the protein and involves many different steps, some of which determine the response of the enzyme under conditions of stress (extreme redox conditions, presence of inhibitors, light), the catalytic rates in the two directions of the reaction and their ratio (the "catalytic bias")...
March 8, 2018: Accounts of Chemical Research
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