Chemistry of Essential Oils
K. Hüsnü Can Başer, Gerhard Buchbauer in Handbook of Essential Oils, 2020
Many enzymes need cofactors as reagents or energy providers. Coenzyme-A has already been mentioned earlier. It is a thiol and is used to form thioesters with carboxylic acids. This has two effects on the acid in question. First, the thiolate anion is a better leaving group than alkoxide and so the carbonyl carbon of the thioester is reactive toward nucleophiles. Second, the thioester group increases the acidity of the protons adjacent to the carbonyl group and therefore promotes the formation of the corresponding carbanions. In biosynthesis, a key role of adenosine triphosphate (ATP) is to make phosphate esters of alcohols (phosphorylation). One of the phosphate groups of ATP is added to the alcohol to give the corresponding phosphate ester and adenosine diphosphate. Another group of cofactors of importance to biosynthesis includes pairs such as NADP/NADPH, TPN/TPNH, and DPN/DPNH. These cofactors contain an N-alkylated pyridine ring. In each pair, one form comprises an N-alkylated pyridinium salt and the other the corresponding N-alkyl-1,4-dihydropyridine. The two forms in each pair are interconverted by gain or loss of a hydride anion and therefore constitute redox reagents. In all of the cofactors mentioned here, the reactive part of the molecule is only a small part of the whole. However, the bulk of the molecule has an important role in molecular recognition. The cofactor docks into the active site of the enzyme through recognition, and this holds the cofactor in the optimum spatial configuration relative to the substrate.
Quantum Dots as Biointeractive and Non-Agglomerated Nanoscale Fillers for Dental Resins
Mary Anne S. Melo in Designing Bioactive Polymeric Materials for Restorative Dentistry, 2020
Currently, other routes to synthesize quantum dots have been proposed through ionic liquids (ILs) (Dupont and Scholten 2010). Most liquids are made up of neutral molecules because charged species generally lead to strong ionic interactions that drive the material to the solid arrangement. On the other side, “molten salts at room temperature” or “ionic liquids” are organic salts with low melting points (below 100°C), and they are often liquid at room temperature (Dupont and Scholten 2010). ILs have low vapor pressure, high thermal and chemical stability, and different density and viscosity depending on their cations and anions (Luczak et al. 2016). These salts comprise a cationic nucleus, usually an organic nitrogen group (such as those from imidazole and pyridine), attached to an alkyl chain (Modaressi et al. 2007). This cationic part of the IL interacts with an anion, that can be as simple as halides, or more complex such as negatively charged sugars and amino acids. Due to the fact that the charge is displaced in bulky cyclic nuclei, there is a lack of salt symmetry (Earle and Seddon 2002), leading to poor coordination and ionic packaging, preventing the formation of a stable crystal lattice, resulting in low melting point and liquid physical state (Pendleton and Gilmore 2015).
Physical Chemistry of Bilirubin: Binding to Macromolecules and Membranes
Karel P. M. Heirwegh, Stanley B. Brown in Bilirubin, 1982
The solubility of bilirubin acid in several solvents has been measured (Figure 3).2 The solubility in apolar media, such as n-hexane, is low, less than 1 µM, and generally increases with solvent polarity, to more than 10 mMin dimethylsulfoxide (DMSO). Aromatic hydrocarbons (benzene) are better solvents than the aliphatic, and an asymmetric structure seems to promote dissolution (toluene, xylene). Pyrrole and pyridine, which are asymmetric aromatic and polar, are good solvents. Dichloromethane and chloroform are asymmetric and are better solvents than carbon tetrachloride. Aliphatic alcohols do not dissolve bilirubin acid, indicating that ability to form hydrogen bonds is not sufficient. Acetone, on the other hand, dissolves some bilirubin, and here again the asymmetric ketones are better solvents. It is interesting to note that increasing chain length does not increase solubility, as illustrated by di-isobutyl ketone which dissolves less bilirubin than methyl isobutyl ketone or acetone. Also, ethyl acetate is a better solvent than long-chain esters, olive oil and lard, which in fact dissolve very little bilirubin.
Appraisal of anti-protozoan activity of nitroaromatic benzenesulfonamides inhibiting carbonic anhydrases from Trypanosoma cruzi and Leishmania donovani
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2019
Alessio Nocentini, Sameh M. Osman, Igor A. Rodrigues, Veronica S. Cardoso, Fatmah Ali S. Alasmary, Zeid AlOthman, Alane B. Vermelho, Paola Gratteri, Claudiu T. Supuran
A set of variably substituted 3-nitrobenzenesulfonamides was prepared starting from 4-hydrobenzenesulfonamide 121. The sulfonamide moiety was protected (compound 2) to avoid decomposition to sulfonic acid that occurs in the nitrating conditions. Both mono- and di-nitro derivatives were obtained in different yields and deprotected in acidic media (compounds 4 and 6). 3,5-Dinitro compound 6 was benzoylated to afford 7. A key intermediate, 3-amino-4-hydroxy-5-nitro-benzenesulfonamide 8 was achieved by reduction of a unique nitro group of 5 with Na2S2O4 and sequential sulfonamide deprotection in acidic media. Intermediate 8 was subjected to several functionalisation reactions. Acylation reactions produced the di-benzoyl compounds 9 and 10. The pyridinium salt 11 was prepared by the reaction of 8 with the proper pyrylium salt. The light-sensitive derivative 12 was obtained by diazonium salt formation and N2 release in aqueous NaNO221. A set of ureas (13–24) was prepared by the reaction of 8 with commercially available isocyanates, in addition to the freshly prepared one obtained from 1,3,4,6-tetra-O-acetyl-glucosamine21. Compound 24 was de-acetylated with sodium methoxide to give the glycoside 25 (Schemes 1 and 2).
Extraction and derivatisation of active polysaccharides
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2019
Chlorosulfonic acid-pyridine method. Chlorosulfonic acid is a very acidic acid. It will decompose violently when it meets water, and it will emit a lot of heat to carbonise polysaccharides. Therefore, the reagent bottle of the reaction must be kept dry, and water cannot be used as a solvent. Therefore, pyridine is generally used as a medium, and ice salt bath cooling is used to prevent excessive temperature. The reaction is relatively simple and rapid. Therefore, attention should be paid to the proportion of reagents, reaction time, and reaction temperature, which will affect the final yield of sulphated polysaccharides. Therefore, the selection of the optimal conditions for this method is also a research hotspot. Orthogonal experiments or response surface experiments are usually used to study the optimal reaction conditions. For example, Wang et al.22 used orthogonal experiment to study various factors (reagent ratio, reaction time, and experimental temperature) that influence the sulphation of SC-FUC (trepang fucoidan sulphate) by HSO3Cl-pyridine method, and discussed the optimal experimental scheme of sulphation: the volume ratio of chlorosulfonic acid to pyridine is 1:1 and reaction time is 2. The reaction temperature is 50 C. The content of sulphuric acid group increased from 10.75% to 59.53%. The Fourier transform infrared spectroscopy results show that the intensity of characteristic absorption peaks of sulphated SC-FUC increases obviously.
Characterization and cytotoxicity assessment of nargile smoke using dynamic exposure
Published in Inhalation Toxicology, 2019
Christian Khalil, Joe Braham Chahine, Brenda Chahla, Tamara Hobeika, Rony S. Khnayzer
Nicotine, one of the main components in nargile smoke, has been well researched in the literature. Its other common names are α-pyridyl-α-methylpyrrolidine and pyridine, 3-(1-methyl-2-pyrrolidinyl). Exposure to nicotine has been reported to trigger hypoxia in addition to its effects on the pituitary adenylate cyclase-activating polypeptide and its receptor 1 in the developing piglet brainstem (Huang et al. 2017). Nicotine exposure has also been reported to trigger severe systemic effects (Mishra et al. 2015) in addition to being a carcinogen in animals and humans (Momi et al. 2013; Chu et al. 2013). Nicotine was also reported to alleviate depression in individuals with depressive disorder (Cosci et al. 2014). Another common component identified in the smoke consisted of Vanillin. Vanillin and ethyl vanillin are commonly used as flavoring compounds in food, beverages, cosmetics, and drugs (Ogawa et al. 2018). Many studies of Nargile smoke identified the vanillin presence in the smoke (Sepetdjian et al. 2013; Shihadeh et al. 2015). Vanillin was reported in the literature as a compound that affects cytochrome P450 activity in vitro and in vivo (Chen et al. 2012).