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Alternate Methods for Visualizing and Constructing
Published in Patrick E. McMahon, Rosemary F. McMahon, Bohdan B. Khomtchouk, Survival Guide to General Chemistry, 2019
Patrick E. McMahon, Rosemary F. McMahon, Bohdan B. Khomtchouk
The donor atom in a coordinate covalent bond donates both electrons to the covalent bond. A lone pair is converted to a bonding pair, and, thus, the donor atom forms one additional bond at the expense of one fewer lone pairs. This type of bonding does not change the bonding valence shell electron number; atoms following octet bonding will still have eight outer shell bonding valence electrons. The difference in bonding occurs because two lone pair valence electrons must now be shared; the donor atom changes its formal charge by (+1) to indicate that the two electrons originally held by the atom all to itself must now be equally shared with the other bonding atom. For counting purposes, the donor atom appears to be providing the acceptor’s contribution of one electron to a normal covalent bond.
Preparation of Low Molecular Weight Copper Complexes
Published in Robert A. Greenwald, CRC Handbook of Methods for Oxygen Radical Research, 2018
The term “complex” is a generic reference to any compound formed via bonding interactions between a metalloelement and a ligand. A “ligand” is any base (Lewis orBronstead-Lowry) that can form a covalent type and/or dative bond with a metalloelement. This bonding is referred to as coordinate covalent bonding by coordination chemists to distinguish it from other types of covalent bonding. Coordinate covalent bond strengths vary widely depending on the ligand and metalloelement. If anhydrous cupric chloride is exposed to air containing water vapor, a hydrate is formed immediately through weak dative bonding between the nonbonded valence electrons of oxygen with copper.1
The 1,2,3-triazole ‘all-in-one’ ring system in drug discovery: a good bioisostere, a good pharmacophore, a good linker, and a versatile synthetic tool
Published in Expert Opinion on Drug Discovery, 2022
Deniz Lengerli, Kübra Ibis, Yahya Nural, Erden Banoglu
1,2,3-Triazoles are a class of π-excessive five-membered heterocycles containing three consecutive nitrogen atoms with intriguing physicochemical properties [1,12]. The triazole ring has an aromatic character owing to its sp2 hybridized atoms with available 6π electrons. In the 1,2,3-triazole system, one of the three nitrogen atoms is of the pyrrole type, while the other two are of the pyridine type and are resistant to quaternization. Monocyclic 1,2,3-triazoles appear in three different structures according to the position of NH proton as 1 H-1,2,3-triazole, 2 H-1,2,3-triazole and 4 H-1,2,3-triazoles (Figure 2A) [1], and generally exist as an equally distributed 1 H- and 2 H- tautomeric mixture in the solid state. 1,2,3-Triazoles may display a large dipole moment up to 5 Debye depending on the substitution pattern [35], and also has a high ionization energy of 10.06 eV as a measure of the electron-rich nature of the ring [36]. Regarding the chemical reactivity, the 1,2,3-triazole ring is quite stable against hydrolysis or oxidation, however it may be cleaved under reducing conditions. The 1,2,3-triazole core contains a diazinyl group with two nitrogen atoms, one acidic and the other basic, and a neighboring amine nitrogen. Besides its aromatic character, which is prone to π-π stacking interactions with the biological target, 1,2,3-triazoles have strong H-bond acceptor properties due to the N(2) and N(3) nitrogen lone pairs, while the acidic C(4)-H is also available as a weak H-bond donor (Figure 2B,) [13]. Moreover, the 1,2,3-triazole core can also form coordinate covalent bond with metal cations via free electron pairs on two nitrogen atoms, which may make them as potential inhibitors of cytochrome (CYP) P450 isoforms through binding to the heme iron [37]. However, the only study comparing the CYP inhibition profiles of a small set of 1,4- and 1,5-bisphenyl 1,2,3-triazole analogs demonstrated that these triazoles inhibit CYP function at higher concentrations (>100 µM) as compared to benchmark CYP inhibitor ketoconazole [13]. Additionally, although the compound set was small, significant difference in the CYP inhibitory profile of differently substituted analogs at phenyl groups differed significantly in their inhibitory potential suggesting that this property of 1,2,3-triazole ring should be further explored in lead discovery studies.