Dose Calculation
William Y. Song, Kari Tanderup, Bradley R. Pieters in Emerging Technologies in Brachytherapy, 2017
A chemical compound is an entity consisting of two or more different atoms that associate via chemical bonds. For instance, a water molecule consists of two atoms of hydrogen and one atom of oxygen. As the mass of one entity (e.g., a molecule), m(X), is an inconveniently small number, the mass of 1 mol of entities is used in practice. This so-called molar mass, M(X), can be calculated as M(X) = NAm(X), where NA ≅ 6.022 × 1023 mol−1 is the Avogadro’s constant (Mohr et al. 2012). In case of an entity consisting of ai atoms of element Xi, the molar mass is where M(Xi) and Ar(Xi) are the molar mass and relative atomic mass of element Xi, respectively, Mu = 10−3 kg/mol is the molar mass constant and N is the number of elements in the entity. For instance, M(H2O) = 2M(H) + 1M(O) = 2 ⋅ 1.008 + 1 ⋅ 15.995 = 18.011 g/mol. Mass fraction, wi, of element Xi in the compound X is then
Basic Principles in Photomedicine and Photochemistry
Henry W. Lim, Nicholas A. Soter in Clinical Photomedicine, 2018
When a molecule absorbs a photon, the electron distribution in the orbitals is changed and the energy of the photon converts the molecule from its ground state (a singlet state) to an excited singlet state molecule. Not all photons (wavelengths) can be absorbed: only those with an energy that matches the difference between the ground state and the excited singlet states of a molecule. Each chemical compound has a unique set of energy levels determined by the chemical structure of the molecule. Compounds containing many conjugated double bonds (i.e., porphyrins) have small energy gaps between the ground and excited state and absorb visible radiation. Compounds containing fewer rings or conjugated unsaturated bonds have larger energy gaps and absorb higher-energy UV photons (i.e., tryptophan). In reality, the energies of vibrations and rotations in the chemical structure (shown as lighter lines in Fig. 2) combine with the electronic energy to give the total molecular energy. In order to be absorbed, the energy of the photon must match the energy gap between the total energy (electronic, vibrational, rotational) of the ground state and the total energy of an excited singlet state.
Practical Considerations When Selecting and Using Gloves for Chemical Protection
Robert N. Phalen, Howard I. Maibach in Protective Gloves for Occupational Use, 2023
Ideally, the glove will only be required to protect against the residual hazard identified in the risk assessment for that task. It is essential to ensure that the hazard is that which arises when one or more chemicals are used. This is rarely the same as the hazard stated on the safety data sheet(s). In the UK this has been recognized by the Health and Safety Executive, whose guidance on risk assessment states:Employers should regard a substance as hazardous to health if it is hazardous in the form in which it may occur in the work activity. A substance hazardous to health need not be just a chemical compound, it can also include mixtures of compounds, micro-organisms or natural materials, such as flour, stone or wood dust. (HSE ACoP)6
Microencapsulation of reactive isocyanates for application in self-healing materials: a review
Published in Journal of Microencapsulation, 2021
Amanda N. B. Santos, Demetrio J. dos Santos, Danilo J. Carastan
The term “isocyanate” may refer to the chemical group with formula R-N=C=O, but it is also the generic name of the chemical compounds which have one or more –NCO groups in their structure. The carbon atom in these compounds has an electropositive charge, making it extremely reactive with chemical groups which have an active atom of hydrogen (nucleophilic reagent), such as alcohols, amines and water. The reaction of NCO with the mentioned chemical groups usually forms urethane or urea bonds (Sharmin and Zafar 2012, Cherng et al.2013, Gogoi et al.2014). NCO is available in a large number of chemical compounds with a wide range of reactivity levels. They are usually classified as aliphatic, such as isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), and 4,4′-bis-methylene cyclohexane diisocyanate (HMDI), or aromatic, such as toluene diisocyanate (TDI), methylene diphenyl diisocyanate (MDI) and polyaryl polymethylene isocyanate (PAPI). The chemical structure of these isocyanates is presented in Figure 2. These compounds are usually combined with other monomers to form polymeric materials covering a vast array of properties, more often based on urethane and urea bonds.
25X-NBOMe compounds – chemistry, pharmacology and toxicology. A comprehensive review
Published in Critical Reviews in Toxicology, 2023
Monika Herian, Paweł Świt
In contrast to known psychoactive substances, the effects of NPS on the human body can be unpredictable and are poorly understood. This fact may be explained by the significant rate of synthesis of subsequent chemical compounds and the delay in characterizing properties of new substances. However, there are some online sources providing data on drug seizures, indicating the number of fatal or non-fatal overdoses and outcomes of laboratory testing. An example of such sources is the National Drug Early Warning System (NDEWS) newsletters giving “weekly briefings” and monthly reports of the current situation on the NPS market (National Drug Early Warning System and NDEWS 2023). Unavailability of full pharmacological and toxicological characteristics, as well as the lack of information regarding their safety, create a problem in situations related to intoxication with a substance of unknown origin.
Genotoxicity of selected pharmaceuticals, their binary mixtures, and varying environmental conditions – study with human adenocarcinoma cancer HT29 cell line
Published in Drug and Chemical Toxicology, 2021
Monika Wieczerzak, Jacek Namieśnik, Błażej Kudłak
Mixtures of chemicals may be genotoxic despite the fact that the same compounds do not possess such properties when act separately, additionally, under environmental conditions, they may undergo various chemical or physical transformations, which can affect the toxicity of chemical compounds. Residues of drugs always occur in mixtures with other pollutants in the environment, impact of these environmental mixtures on human and animal organisms is a huge gap in knowledge as far as the environmental fate of these compounds is in stake. The lack of cheap and green technology that eliminates this type of chemical pollution from sewage causes the human and animal organisms to be constantly exposed to residues of pharmaceuticals. In our studies, we determined that environmental conditions such as a change in the pH of the solution resulted in increased toxicity of diclofenac, oxytetracycline, and fluoxetine, but only in a limited range of pH, chloramphenicol showed lower genotoxicity at low pH ranges. All ions, in particular, potassium, fluoride, and bromide, contributed to the reduction of toxicity of the pharmaceuticals tested, however, only in the case of diclofenac and fluoxetine antagonism was observed. The results indicate that synergism was mainly observed for mixtures of fluoxetine h. with diclofenac s. and chloramphenicol with oxytetracycline h. with fluoxetine h., chloramphenicol showed antagonistic interactions depending on the concentrations used.
Related Knowledge Centers
- Atom
- Chemical Reaction
- Chemistry
- Molecule
- Oxygen
- Molecular Entity
- Coordination Complex
- Coordinate Covalent Bond
- NON-Stoichiometric Compound
- Chemical Formula