Structural Information on Copper Proteins from Resonance Raman Spectroscopy
René Lontie in Copper Proteins and Copper Enzymes, 1984
All of the OxyHc vibrations listed in Table 7 appear to be in resonance with the ≈345-nm absorption band as indicated in Figure 13. Thus, it is of interest to determine the nature of the electronic transition at ≈345 nm and how it might be responsible for enhancement of a number of different Cu-L vibrations. In our earlier work we assigned it to an imidazole → copper CT,23 and Larrabee et al.100 assigned it to a simultaneous pair excitation of the antiferromagnetically coupled copper center. However, the recent observation of a MetHc which lacks the ≈345-nm absorption, but whose copper ligation to the protein and magnetic coupling remains intact,101 makes it likely that the ≈345-nm absorption is directly related to oxygen binding and arises from a peroxide → Cu(II) CT. The question remains as to the nature of the orbitals involved in this transition. It should be emphasized at this point that the type of molecular orbital description one arrives at depends on the assumptions one makes concerning the relative energies of the different orbitals.103
Radiation Detection and Measurement
Shaheen A. Dewji, Nolan E. Hertel in Advanced Radiation Protection Dosimetry, 2019
The process of thermoluminescence as applied to radiation detection and measurement relies on the behavior of electrons in crystalline solids. Electrons are fermions that have non-integer spins, obey Fermi-Dirac statistics, and the Pauli Exclusion Principle restricts their occupation of certain atomic orbits. The result is the constraint of electrons to atomic orbitals that have been given the identifying letters s, p, d, and f, that correspond to the angular momentum quantum numbers 0, 1, 2, and 3. When atoms form a crystalline lattice, the density of the structure is such that many molecular orbitals are present, resulting in regions, or bands, in energy. Bands are separated by an energy gap, where no electrons are normally present. Metals do not have an energy gap and are therefore good electrical conductors. Insulators have large energy gaps of several eV, making the transition of electrons to the conduction band very difficult. Semiconductors have smaller energy gaps of about 1 eV or less (Kittel 1991). LiF is an insulator with a wide energy gap of 13.6 eV, but in the case of LiF: Mg, Ti, the added dopants of magnesium and titanium provide lattice sites within the energy gap that can be occupied by electrons.
Gold Nanomaterials at Work in Biomedicine *
Valerio Voliani in Nanomaterials and Neoplasms, 2021
The extraordinary enhancement can arise from two different mechanisms of chemical and electromagnetic origins, respectively [383–385]. The chemical mechanism leads to enhancement through charge transfer between the lowest unoccupied molecular orbital (LUMO) or the highest occupied molecular orbital (HOMO) of analyte molecules and the Fermi energy level of the metal substrate [385–387]. The chemical enhancement factor is typically on an order below 102, and it varies depending on the types of analyte and substrate involved, as well as the locations on the substrate. The electromagnetic mechanism is generally believed to be the predominant contributor to SERS, which accounts for an enhancement factor ranging from 106 to 108 [17, 372]. This kind of enhancement is associated with the LSPR of the metal substrate. The collective oscillations of free electrons in a metal substrate can enhance the intensity of the local electric field by a factor of 2–4 orders of magnitude in the vicinity of the metal surface (less than 5 nm from the surface),388 leading to a tremendous enhancement of the Raman scattering cross section.
Mechanistic studies on the drug metabolism and toxicity originating from cytochromes P450
Published in Drug Metabolism Reviews, 2020
Chaitanya K. Jaladanki, Anuj Gahlawat, Gajanan Rathod, Hardeep Sandhu, Kousar Jahan, Prasad V. Bharatam
QC methods are being widely used to address key questions about CYP450-catalyzed reactions. The information being sought from such analysis includes: (i) the electronic structure of reactants, intermediates, products and transition states; (ii) the absolute and the relative energies of all the species; (iii) the details of molecular orbitals (shapes and energies); (iii) estimation of partial atomic charges, electrophilicity and nucleophilicity parameters; (iv) surface properties (molecular electrostatic potential); (v) reaction pathways, by establishing the energy profiles of the metabolic reactions; (vi) internal surface distribution of electron density, spin density (Gao and Truhlar 2002; Friesner and Guallar 2005; Shaik et al. 2010; Siegbahn and Blomberg 2010; Rydberg et al. 2012; Blomberg et al. 2014; Hirao et al. 2014). The transition states on the enzyme-catalyzed metabolic reaction pathways are central and cannot be studied experimentally owing to their short-lived character (Becke 1993), but the same can be obtained using QC methods with sufficient clarity. Moreover, the interactions stabilizing these transition states cannot be determined by experimental methods. Thus, QC methods are utilized for the overall understanding of the complexities and challenges in drug metabolism studies.
Zerumbone binding to estrogen receptors: an in-silico investigation
Published in Journal of Receptors and Signal Transduction, 2018
Eltayeb E. M. Eid, Faizul Azam, Mahmoud Hassan, Ismail M. Taban, Mohammad A. Halim
Molecular interactions of ligands with target proteins are absolutely crucial to various pharmacological activities, which in turn depend on the structural features of the molecules. Density functional theory (DFT) calculations furnish information about electronic effects and intermolecular charge transfer responsible for ligand-protein connections [48–50]. Therefore, computation of the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies describes the reactivity, shape and binding properties of a complete molecule as well as of molecular fragments and substituents. In recent times, the concept of HOMO and LUMO has been successfully executed in explicating the biological activity and molecular properties of the drug candidates [47,51,52].
Exploring space-energy matching via quantum-molecular mechanics modeling and breakage dynamics-energy dissipation via microhydrodynamic modeling to improve the screening efficiency of nanosuspension prepared by wet media milling
Published in Expert Opinion on Drug Delivery, 2021
Jing Tian, Fangxia Qiao, Yanhui Hou, Bin Tian, Jianhong Yang
The aggregation characteristics of drug molecules can affect the stability of nanosuspensions. If bulk drug molecules readily aggregate, then the interactions between the drug molecules may be stronger and nanosuspensions with larger particles are more likely to be produced. The intermolecular interactions might be caused by acceptance/donor and transfer of the electrons, and the frontier molecular orbitals can be used to evaluate the electron regions of molecules to assess where the possible adsorption sites may occur [66,67]. The highest occupied molecular orbital (HOMO) of the donor electrons has the highest energy and the lowest occupied molecular orbital (LUMO) receives electrons with the lowest energy, and they are collectively referred to as the frontier orbitals. The electron cloud regions in HOMO may affect LUMO or electron transition phenomenon can even occur to allow their interaction [38]. After obtaining the adsorption sites, the adsorption module can be used to determine the aggregation conditions for different amounts of drug molecules based on diagrams.
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