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Related Topics I: Charge-Transfer Complexes in Biological Systems
Published in Jean-Pierre Farges, Organic Conductors, 2022
Vivian C. Flores, Hendrik Keyzer, Cissy Varkey-Johnson, Karen Leslie Young
The oxygen molecule is preeminent in living systems because it is a universal electron acceptor. Oxygen, however, tends to accept electrons in pairs, which renders it unsuitable as a direct electron acceptor for proteins, because these would then be degraded too rapidly. Charge-transfer interaction usually involves single electron transfer, which may lead to a biradical complex with an unpaired electron on both the donor and the acceptor molecule. The majority of charge-transfer interactions are weaker, generally transferring electronic charge only fractionally. A charge-transfer complex is formed in which no new chemical bonds arise but in which the electron shuttles between the donor and the acceptor, preferring the neighborhood of the donor parent. This behavior may convert a “dead” molecule to a “living” molecule.
Drug Solubility and Solubilization
Published in Sandeep Nema, John D. Ludwig, Parenteral Medications, 2019
Ching-Chiang Su, Lan Xiao, Michael J. Hageman
Some drugs are known to form a charge-transfer complex with certain solvents. A charge-transfer complex or an, electron–donor–acceptor complex is a chemical association of two or more molecules, or of different parts of one very large molecule, in which the attraction between the molecules (or parts) is created by an electronic transition into an excited electronic state, such that a fraction of electronic charge is transferred between the molecules. The resulting electrostatic attraction provides a stabilizing force for the molecular complex. The association does not constitute a strong covalent bond and is subject to significant temperature, concentration, and host (e.g., solvent) dependencies and occurs in a chemical equilibrium with the independent donor (D) and acceptor (A) molecules.
Vibrational Spectroscopy
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Peter Fredericks, Llewellyn Rintoul, John Coates
Other regimes for removing or reducing the impact of fluorescence have been considered, and these include moving to shorter wavelength (as mentioned), the use of quenching agents and time-based discrimination methods. The use of quenching agents may have limited applicability, dependent on the type of compound being investigated. Examples are compounds that form charge-transfer complexes with materials such as butan-2,3-dione and tetracyanoethylene. The types of compounds that interact in this manner with these reagents are aromatic and polycyclic hydrocarbons. Note that relatively high levels of quenching agents may be required to reduce the fluorescence, and their presence may cause a spectral interference.
Thermodynamics and transport properties of binary liquid mixtures at various temperatures (Morpholine, 2-methoxyether, 2-ethoxyether and 2-butoxyether)
Published in International Journal of Ambient Energy, 2022
D. Bala, M. Gowrisankar, D. Ramachandran, Mohan Krishna Murthy
Mulliken's theory of charge-transfer interactions produced between an electron donor and electron acceptor has been applied to many interesting studies. Charge transfer complexes have great attention for their non – linear optical properties and electrical conductivities. In addition, they are known to take part in many chemical reactions like addition, substitution and condensation. Electron donor – acceptor interaction is also important in the field of drug – receptor-binding mechanism, in solar energy storage, in surface chemistry and in many biological fields.
Spectral variations associated with anthocyanin accumulation; an apt tool to evaluate zinc stress in Zea mays L.
Published in Chemistry and Ecology, 2021
E. Janeeshma, Vijisha K. Rajan, Jos T. Puthur
Anthocyanins are powerful antioxidant and it also interacts with metal ions by acting as a chelator and forming coloured complexes; where the concentration of metal ions has a crucial role in the colour intensity of the complex formed [46–49]. When Brassica juncea was exposed to molybdenum and tungsten, the development of blue crystals was observed in their epidermal cells as a result of anthocyanins-metal ions complexation [50,51]. As per these reports, the purple-red colour developed in the leaves of maize plants in the present study could be also due to the complexation between anthocyanins and excess Zn ions. Cyanidin, delphinidin, and petunidin are the three major anthocyanins with considerable metal chelation potential as they have adjacent hydroxyl groups [52]. In the present study, cyanidin was taken as the representative of anthocyanins, to evaluate the affinity towards Zn ion. The charge transfer complex reactions were analysed with the help of molecular orbital analysis. Based on the frontier molecular orbital (FMO) theory, HOMO and LUMO of a molecule determine the chemical reactivity of a molecule [17]. The difference in the delocalisation pattern of LUMO in cyanidin and its Zn complex showed that the LUMO of cyanidin interacts with the Zn ion by accepting electrons, thereby forming a stable complex. The reduction in the bandgap between cyanidin and cyanidin-Zn complex also indicates the stabilisation of cyanidin with a metal ion [53]. The charge transfer between the cyanidin molecule and the metal ion resulted in the stabilisation of the cyanidin-Zn complex. The positive charge in the cyanidin makes them good electron acceptors, which further supports the charge transfer from Zn to cyanidin in the studied complex. Thus as assessed from the above observation, there is every possibility for the accumulated anthocyanins in the leaves of maize plants under Zn stress to act as a strong metal chelator, which helps the plant to tolerate the higher Zn concentrations.