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The Modification of Cysteine
Published in Roger L. Lundblad, Chemical Reagents for Protein Modification, 2020
The modification of cysteinyl residues in proteins with 2-bromoethane sulfonate has been reported.103 This derivatization procedure was developed in response to a need for a strongly hydrophilic substituent in samples for the Edman degradation. The modification time is longer than for the corresponding carboxymethyl derivatives, taking 12 h for lysozyme, 24 h for insulin, and 48 h for glutathione. This derivative has considerable utility since the S-sulfoethylated lysozyme derivative is soluble between pH 5.0 and 10.0 while the S-carboxymethylated derivative is not. This procedure has potential for primary structure analysis.
Production of Radionuclides by 14 MeV Neutron Generator
Published in Frank Helus, Lelio G. Colombetti, Radionuclides Production, 2019
For 80Br and 80mBr preparation, 0.1 g I2 is added to the bromoethane in order to increase the inorganic yield. After irradiation of 30 min the I2 is reduced by titration with 0.1 N thiosulfate solution. To increase the inorganic yield the extraction was done with 20 mℓ which were boiled down to 5 cc. The preparation takes about 20 min. The aqueous solution contains about 10 μCi of 78Br, 150 μCi of 80Br and 20 μCi of 80mBr. Higher activities are obtained with bromoform (CHBr3) and dibromomethane (CH2Br2) as target material. However, due to their high boiling point, their traces cannot be removed by partial evaporation.
Reproductive System and Mammary Gland
Published in Pritam S. Sahota, James A. Popp, Jerry F. Hardisty, Chirukandath Gopinath, Page R. Bouchard, Toxicologic Pathology, 2018
Justin D. Vidal, Charles E. Wood, Karyn Colman, Katharine M. Whitney, Dianne M. Creasy
Endometrial adenomas or adenocarcinomas are generally rare tumors in most standard strains and species used in nonclinical toxicology testing. Exceptions include the Han-Wistar rat and the rabbit, which can have high background incidences of endometrial carcinomas (Deerberg et al. 1981; Elsinghorst et al. 1984). In Wistar rats, these tumors can be induced by chronic disruption of the HPG axis, leading to decreased prolactin, corpus luteum function, and progesterone; reduced antagonism of estrogenic effects in the uterus by progesterone; and increased endometrial gland hyperplasia and tumors (Harleman et al. 2012). This mechanism is generally considered to have low human relevance given that prolactin does not have a key luteotropic role in the normal human ovarian cycle. In mice, endometrial tumors have been induced by a number of xenobiotics including estrogens, bromoethane, chloroethane, and ethylene oxide, administered either chronically, or during critical windows of development (Highman et al. 1978; Newbold et al. 1990, 2001; Picut et al. 2003). Perinatal estrogen exposure may induce neoplasia via a combination of estrous cycle disruption with luteal dysfunction and altered patterns of uterine epithelial differentiation (Kurita 2011; Suen et al. 2016). In macaques, endometrial adenocarcinomas are exceedingly rare; only a few cases have been reported either as spontaneous or treatment-related lesions (Cline et al. 2008).
Halogen bonding in halocarbon-protein complexes and computational tools for rational drug design
Published in Expert Opinion on Drug Discovery, 2019
Paulo J. Costa, Rafael Nunes, Diogo Vila-Viçosa
Also using models, in this case methanol, phenol, acetamide, imidazole, indole, methanethiol, methylammonium, methylguanidinum, and acetate as hydrogen bond donors (HBDs), MacKerell and Lin [35] performed QM calculations to find which type of interactions dominate in halocarbon–ligand systems, i.e. do halogens act preferentially as halogen bond donors or as hydrogen bond acceptors? Taking fluorobenzene, fluoroethane, chlorobenzene, chloroethane, bromobenzene, and bromoethane as halogenated molecules, the authors computed potential energy scans (RIMP2/cc-pVQZ) as a function of the X···HBD distance at two limiting angles, C-X···HBD = 90º and C-X···HBD = 180º. For chlorinated species, the C−Cl···HBD angle was also scanned. In these scans, perpendicular interactions are preferred, i.e. when the halogen is acting as a hydrogen bond acceptor, the favorable C-X···HBD angle is ~90º as the proton from the HBD points towards the negative region of the electrostatic potential of the halogen, as expected. Notably, these perpendicular X···HBD interactions (hydrogen bonds) are more favorable than the corresponding halogen bonds for aliphatic compounds bearing Cl and Br (I was not considered), indicating that this type of interactions may contribute to halocarbon-protein binding. On the other hand, halogen bonds are, according to the authors, primarily limited to halogenated aromatic species. Although not mentioned by the authors, these results might simply be a consequence of the different halogen-bonding capability of the ligands: unsubstituted aliphatic halocarbon molecules are typically poor halogen bond donors (small σ-hole), and therefore, it is not surprising that they behave as ‘classical’ negatively charged species.