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Basic Chemical Hazards to Human Health and Safety — I
Published in Jack Daugherty, Assessment of Chemical Exposures, 2020
The chemical reactions in tissues undergo degradation in catabolism and resynthesis in anabolism. Exergonic reactions occur during catabolism, and release energy from within the reaction system. Endergonic reactions occur during anabolism, and require external energy. After the reactant and product substances involved in an endergonic reaction absorb energy, they sometimes start an exergonic reaction going. Oxidation sets off endergonic reactions within cells. When an exergonic reaction drives an endergonic reaction, the two are said to be coupled.
X-Nuclei MRI and Energy Metabolism
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
Metabolic pathways in energy metabolism have the following key characteristics: A metabolic pathway is a series of single chemical reactions.Chemical reactions are generally catalyzed by enzymes which can lower the reaction activation energy in order to accelerate the specific metabolic processes necessary for maintaining life.During metabolic chemical reactions, electrons are transferred between molecules: molecules that lose electrons are oxidized (oxidation reaction), and those that gain electrons are reduced (reduction reaction). Electrons are transferred by electron carriers, such as nicotinamide adenine dinucleotide (NADH), between reactions.Energy is transferred during metabolic reactions by the energy carrier ATP. Exergonic reactions occur spontaneously and release free energy (exothermic). Endergonic reactions are non-spontaneous and require free energy, which can be provided by breaking ATP molecules (endothermic). The ATP/ADP cycle is used to link exergonic and endergonic reactions by what is called energy coupling, where the energy produced by one reaction is used to drive another reaction: ATP hydrolysis (ATP to ADP) is exergonic. The released energy is used to drive endergonic reactions such as active transport of ions or molecules, cell movements and anabolism.ATP synthesis (ADP to ATP) is endergonic. It requires energy from exergonic reactions such as cell respiration and catabolism.
Reaction of Pentanol isomers with OH radical – A theoretical perspective
Published in Molecular Physics, 2018
Basheer Aazaad, Senthilkumar Lakshmipathi
In pathway 4, the fourth –CH2 group undergoes H-atom abstraction reaction and the corresponding energy barrier calculated at M06-2X method is 1.24 kcal/mol. The other functionals of MPW1K, BHandHLYP, MP2 and CCSD(T) also predict the barrier to be 2.66, 5.18, 5.07 and 2.67 kcal/mol, respectively. In TS4, the C4-H8 of 1.15 Å bond length which was 1.09 Å in the reactant complex (RC1). The product complex PC4 and product P4 reside at −20.14 and −18.14 kcal/mol, respectively. In pathway 5, the hydrogen atom (H8) present in the terminal CH3 group is abstracted by OH radical with an energy barrier of 2.95 and 4.47 kcal/mol as calculated at M06-2X and MPW1K methods. The BHandHLYP, MP2 and CCSD(T) functionals also found the barrier to be 7.09, 6.87 and 4.85 kcal/mol, respectively. The corresponding product complex PC5 and product P5 possess the relative energy of −19.73 and −15.23 kcal/mol, respectively. This pathway is also predicted to be exothermic. In pathway 6, the hydrogen atom (H12) residing in hydroxyl group is abstracted by OH radical with an energy barrier of 1.55 and 4.43 kcal/mol calculated at M06-2X and MPW1K methods, respectively. The CCSD(T) method validates the barrier to be 4.93 kcal/mol. This exothermic and exergonic reaction has enthalpy and Gibbs free energy of −13.87 and −14.87 kcal/mol, respectively.