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Nanostructured Drug Delivery of Nutraceuticals for Counteracting Oxidative Stress
Published in Bhupinder Singh, Minna Hakkarainen, Kamalinder K. Singh, NanoNutraceuticals, 2019
Shobhit Kumar, Bharti Gaba, Jasjeet K. Narang, Javed Ali, Sanjula Baboota
Age progression is an inevitable characteristic of life. The susceptibility of degenerative disorders increases with aging and has been affecting millions of people each year, thus becoming a major problem of modern society. Free radicals are the major contributing reason for aging (loss of muscle strength and stamina). Free radicals contain unpaired electron(s), usually present in the outer orbit, and are responsible for changing the chemical reactivity behavior of a molecule. They make the unstable molecule highly reactive and electron acceptor, wherein these molecules accept electrons from other molecules, leading to damage to cells and their cellular components such as DNA and proteins (Sies et al., 2017). Both peroxynitrite (ONOO–) and hydrogen peroxide (H2O2) are responsible for free radicals’ formation, as they are highly reactive (Aprioku, 2013). Generally, these molecules and free radicals are known as reactive oxygen species (ROS), which cause harmful effects, including low cellular energy production, impaired cell reproduction leading to cancer, and arterial clogging and blockage, eventually leading to heart attacks and strokes (Parker et al., 2017; Sultana et al., 2017).
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Published in William H. Bush, Karl N. Krecke, Bernard F. King, Michael A. Bettmann, Radiology Life Support (Rad-LS), 2017
The mechanism whereby paramagnetic agents provide contrast differs from the way in which radiographic contrast media work. X-ray contrast media are observed directly on radiographic images because of their ability to absorb X-rays. However, the paramagnetic MRI contrast agents operate in an indirect manner by altering the local magnetic environment of tissues. Chemicals that have unpaired electrons (e.g. transition or lanthanide metal ions, organic free radicals) are the most effective paramagnetic contrast enhancers. This is so because the magnetic moments of unpaired electrons are 657 times larger than the magnetic moments of unpaired protons or neutrons. Thus paramagnetic substances have a permanent magnetism due to their spin moment caused by an unpaired electron. In the absence of external magnetic fields, the magnetic moments of paramagnetic substances are randomly aligned. However, with the application of a strong external magnetic field, the magnetic moments align with the field and generate strong local magnetic fields that shorten both T-l and T-2 relaxation times of neighboring protons. When paramagnetic ions are added to water, the relaxation process of water molecules is more enhanced in the vicinity of these paramagnetic centers.
Ionizing Radiation
Published in Ivan G. Draganić, Zorica D. Draganić, Jean-Pierre Adloff, Radiation and Radioactivity on Earth and Beyond, 2020
Ivan G. Draganić, Zorica D. Draganić, Jean-Pierre Adloff
These consist of atoms or groups of atoms which show increased chemical reactivity owing to the presence of an unpaired electron. Free radicals are produced when a molecule is severed in such a manner that one of the bonding electrons, designated by a dot, remains associated with each fragment: H:OH→H•+OH• The dot representing the unpaired electron is more often used for complex radicals but generally omitted for simple ones such as those produced in water radiolysis.
Clove as antioxidant additive in diesel–biodiesel fuel blends in diesel engines
Published in International Journal of Green Energy, 2019
Nagarajan Jeyakumar, Bose Narayanasamy
Many research works have recorded that usage of biodiesel increases NOx emission from diesel engines (Varatharajan, Cheralathan, and Velraj 2011). NOx is produced by means of thermal, prompt, and fuel mechanisms. Highly reactive atomic nitrogen is produced by means of breakage of strong triple bond present in the nitrogen molecules by means of high temperature produced during combustion reaction. This unstable nitrogen atom reacts with oxygen atom to form thermal NOx. Prompt NOx is produced from the hydrocarbon flame front from the combustion reaction. Fuel NOx is obtained from the reaction between oxygen and nitrogen present in the fuel. Thermal and prompt NOx are produced from biodiesel combustion, since biodiesel does not contain fuel bound nitrogen. Fuel chemistry does not influence the thermal NOx, whereas prompt NOx depends on free-radical formation which determines the kinetics of reaction. Free radicals such as oxygen molecule, nitric oxide, superoxide ion, and hydroxyl (OH) radical are highly reactive due to the presence of unpaired electron(s). Oxidation process is delayed or inhibited by the antioxidants by donating an electron or hydrogen atom to free-radical derivatives (Balaji and Cheralathan 2015). Thermal NO and prompt NO are the two main NOx formation mechanisms in diesel engines. Thermal NO is a result of high-flame temperature, whereas prompt NO is produced in fuel-rich part of the flames. Thermal NO formation mechanism studied by zeldovich is as follows (Anetor, Odetunde, and Osakue 2014):
Techniques to control IC engine exhaust emissions through modification in fuel and intake air – a review
Published in International Journal of Ambient Energy, 2022
Ajai Prasad Nigam, Shailendra Sinha
Increase in fuel density, traces of nitrogen and oxygen bound with vegetable oil biodiesel fuels results in high in-cylinder pressure, temperature and so the higher NOx emissions. NOx formation in the engine exhaust largely depends upon fuel/air equivalence ratio, compression ratio, advancement of fuel injection, percentage of waste gas in fresh inlet air and its temperature (Velmurugan and Sathiyagnanam 2016). Injection of larger mass of dense bio-fuels and its subsequent burning produces more NOx. Denser biofuels (higher bulk modulus) advance the effective injection timing resulting in prolonged ignition delay, i.e. injection of fuel to compressed air at low temperature and pressure causing increase in NOx formation (Gopinath, Puhan, and Nagarajan 2010). It was observed that the use of biodiesel as fuel increases NOx emissions due to the formation of free radicals (Velmurugan and Sathiyagnanam 2016). Oxidation reaction rate is regulated by free radicals which are basically unpaired electron of a molecule. Their literature survey also revealed that the combustion of biodiesel fuel results in higher CH radical formation (other radicals being C, CH2, C2 and C2H) which eventually reacts with nitrogen molecule leading to increased NOx formation. Increase in NOx emission was observed at all speeds (1500 rpm and 3000 rpm) of CRDI engine, using divided injection, and at all loads (50, 100 and 150 Nm) with the increase in proportion of biocomponent (B25, B50 and B75) in mineral diesel, with minor exceptions (Mikulski, Duda, and Wierzbicki 2016). High oxygen level in biodiesel results in high NOx specifically at medium and high speeds (Nguyen and Pham 2015; Velmurugan and Sathiyagnanam 2016). However, the use of Jatropha biodiesel diesel blend comparatively reduces NOx due to the complete combustion at high temperature in the presence of sufficient oxygen (Jain and Sharma 2010).
Low density polyethylene tubular reactor control using state space model predictive control
Published in Chemical Engineering Communications, 2021
D. Muhammad, Z. Ahmad, N. Aziz
In this process, LDPE is produced via high pressure free radical polymerization of ethylene gas. There are many reaction steps involved in the mentioned polymerization process leading to the complex polymer structure with short and long chain branches. Brandolin et al. (1996) and Agrawal et al. (2006) study had been referred to obtain the reaction mechanisms and kinetic parameters for this work. Generally, the free radical polymerization reaction mechanism involves five fundamental reactions:Initiator decomposition - Free radicals are formed due to the breakdown of initiators such as organic peroxides and oxygen. These free radicals are reactive intermediate with an unpaired electron.Chain Initiation – The combination of free radicals with monomer molecules will form polymer radicals. These polymer radicals (also called live polymer) will be the preliminary chain for the polymerization process.Chain Propagation – Polymer radicals propagate by reacting with other monomer molecules in a successive series of reactions to form polymer chains.Chain termination - Polymer radicals are terminated when two polymer radicals of the same or different chain length are combined (termination by combination) or disproportionate to form dead polymer chains (termination by disproportionation).Chain Transfer - Polymer radicals can undergo reaction with the monomer (chain transfer to monomer), agents (chain transfer to agents), and polymer molecules (chain transfer to polymer). It can also break away (e.g., beta scission) or jump on the same or another polymer chain (e.g., back-biting).