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Cutaneous Photosensitization
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
Responses of biological systems to light are based on chemical reactions initiated by molecular absorption of light. Absorption of light by specific molecules in the system results in the promotion of electrons to higher energy states. These “excited-state” molecules possess the necessary energy of activation required to undergo a photochemical reaction. The absorbing molecule may photochemically react in a reagent manner with adjacent biomolecules and thus be exhausted in the reaction or it may resemble a catalytic mechanism causing a modification of a biomolecule without itself undergoing a permanent chemical change. The latter mechanism allows the photosensitizing molecule to return to the unexcited (ground) state and thus be available to absorb another quantum of light and repeat the photochemical reaction cycle again.
Gastrointestinal Tract as a Major Route of Pharmaceutical Administration
Published in Shayne C. Gad, Toxicology of the Gastrointestinal Tract, 2018
The term “metabolism” is derived from the Greek word metabolē meaning “to change.” These changes are the chemical changes which occur to a substance following entry into the body. These chemical biotransformations sustain life within the cells. Enzymes located within specific tissues are responsible for changes in a substance’s structure and subsequently altering the pharmacologic properties of the substance. Biotransformation of a xenobiotic usually occurs within a matter of minutes or hours. The primary location for metabolic changes is the liver. Other locations include the lungs, kidneys, gastrointestinal epithelium, and skin. Some substances can be changed into less toxic substances or can be prevented from metabolizing into toxic derivatives altogether hence the process can be an important defense mechanism. Unfortunately, the reverse is also possible: a substance can enter the body as a nontoxic entity and can be metabolized into a toxic derivative (Kapp, 2014; Lehman-McKeeman, 2015).
Introduction: The significance of radiobiology and radiotherapy for cancer treatment
Published in Michael C. Joiner, Albert J. van der Kogel, Basic Clinical Radiobiology, 2018
Michael C. Joiner, Albert J. van der Kogel, G. Gordon Steel
The chemical phase describes the period in which these damaged atoms and molecules react with other cellular components in rapid chemical reactions. Ionization and excitation lead to the breakage of chemical bonds and the formation of broken molecules, known as ‘free radicals’. These are highly reactive and they engage in a succession of reactions that lead eventually to the restoration of electronic charge equilibrium. Free-radical reactions are complete within approximately 1 ms of radiation exposure. An important characteristic of the chemical phase is the competition between scavenging reactions, for instance with sulphydryl compounds that inactivate the free radicals, and fixation reactions that lead to stable chemical changes in biologically important molecules.
Recent advances in electrochemical and optical sensing of the organophosphate chlorpyrifos: a review
Published in Critical Reviews in Toxicology, 2022
Athira Sradha S, Louis George, Keerthana P, Anitha Varghese
“Analytical devices that can detect physical, chemical, biological changes and convert them to quantifiable signals” are called sensors. Chemical sensors, in particular, “are devices that report chemical changes.” Sensors, in general, consist of three parts: a sensing element, a transducer and a signal processor. The sensing element is responsible for interaction with the analyte and thereby producing a chemical signal. The chemical signal generated is converted to an observable signal by the transducer. The signal processor essentially helps in the amplification of the produced signal (Faridbod et al. 2018). An introduction of biosensor that can be used as an analytical device that possesses a biological recognition element and biological interactions to detect and measure the concentration of a specific analyte. The detecting analyte transforms bio-molecular interactions into an identifiable signal (Raman Suri et al. 2009; Shrikrishna et al. 2021; Sagar et al. 2022). Based on the working principle of the transducer we can broadly classify chemical sensors as electrochemical sensors, optical sensors, mass-sensitive sensors, magnetic sensors, thermometric sensors, etc. (Hulanicki et al. 1991).
Plasma-initiated graft polymerization of carbon nanoparticles as nano-based drug delivery systems
Published in Biofouling, 2022
Tianchi Liu, Christopher Stradford, Ashwin Ambi, Daniel Centeno, Jasmine Roca, Thomas Cattabiani, Thomas J. Drwiega, Clive Li, Christian Traba
Aside from the chemical changes associated with each modification step, significant physical changes were also observed. More specifically, substantial surface topography changes were visualized using SEM (Figure 4B). These highly magnified (200K ×) images of CNPs were acquired in order to help demonstrate the topographical changes throughout the modification process. It was observed that less magnified images were not be helpful in visualizing CNPs due to their small size. Another obstacle encountered when acquiring SEM imaging involved the very high surface energies associated with CNPs, making them inclined to agglomerate (Polidor et al. 2020). In order to avoid this, care was taken to reduce the concentration of the different types of CNPs during their immobilization onto silica wafers. Argon plasma treated CNPs showed very circular and smooth surfaces, with a diameter of ∼80nm (Figure 4B1). On the other hand, the ‘grafting-from’ approach resulted in a nanocoating with uniform surface coverage, and substantial surface topography changes as visualized using SEM (Figure 4B2). The same QA-grafted CNPs demonstrated a significant jump in size to ∼120nm with dry polymer brush lengths of around 90nm (as determined by ellipsometry). When compared with QA-grafted CNPs, NBDDSs demonstrated an even greater change in topography when visualized using SEM (Figure 4B3). The same SEM images again depict NBDDSs with uniform coverage throughout the CNPs with an even larger size of 160nm (Figure 4B3).
LsrB, the hub of ABC transporters involved in the membrane damage mechanisms of heavy ion irradiation in Escherichia coli
Published in International Journal of Radiation Biology, 2021
Xin Li, Lei Chen, Haitao Zhou, Shaobin Gu, Ying Wu, Bing Wang, Miaomiao Zhang, Nan Ding, Jiaju Sun, Xinyue Pang, Dong Lu
With the extensive application and development of nuclear energy in military, industrial and medical fields, the potential harm of ionizing radiation (IR) to human beings is increasing (Matuo et al. 2018; Guo et al. 2020). The nuclear leakage accidents made the harm of radiation to human life become the focus of global attention. IR includes particles, β particles, protons, heavy ions (HIs), and other high-speed charged particles, etc. IR acts on cells, causing the ionization and excitation of atoms or molecules after collision (Dietze et al. 2013; Liu et al. 2019). The chemical properties of ions and excited molecules produced are unstable, quickly turning into free radicals and neutral molecules, causing complex chemical changes, leading to a series of biological effects (Gao et al. 2020).