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Chapter 4 Biocompatibility and Tissue Damage
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
Polymers ‘age’ if they are not in thermodynamic equilibrium and they can change their molecular order with time. The chemical and physical properties of polymeric materials are derived mainly from the nature of the monomer and the extent of cross-linking between chains. Chemical stability depends on the strength of the chemical bonds in the molecule and their availability to the surface. Steric effects may give some protection. Physical factors such as the degree of crystallization may also have an effect; the more crystalline the polymer, the less likely it is to swell and the less susceptible it is to degradation.
Design and molecular docking studies of {N1-[2-(amino)ethyl]ethane-1,2-diamine}-[tris(oxido)]-molybdenum(VI) complex as a potential antivirus drug: from synthesis to structure
Published in Journal of Coordination Chemistry, 2023
The high value of energy gap revealed that 1 has chemical stability with low reactivity. The energy distribution of HOMOs and LUMOs (energy gap (ΔE) = ELUMO-EHOMO; units in eV) are EHOMO (-2.654), ELUMO (-4.711), ΔE (-2.057), EHOMO-1 (-2.792), ELUMO+1 (-5.816), ΔE (-3.024), EHOMO-2 (-1.847), ELUMO+ 2 (-4.917) and ΔE (-3.070). Therefore, the lowest excitation takes place between HOMO and LUMO and the energy gap of HOMO-2 and LUMO + 2 is significant. From the HOMO and LUMO gap, we can predict the molecular hardness and softness of compounds. Hard molecules have large energy gap while soft molecules have small energy gap. The quantum chemical parameters (units in eV), such as ionization potential (IP), electron affinity (EA), electronegativity (χ), chemical potential (μ), global hardness (η), global softness (σ) and global electrophilicity (ω), were calculated using formulas based on Koopman‘s theorem, IP = 2.654, EA = 4.711, χ = 3.682, η = −1.028, μ = −3.682, ω = −6.593, σ = 0.486 eV for 1. Reactivity parameters of 1 showed greater ionization potential than electron affinity; hence, the Mo(VI) complex has greater electron-donating ability. [Mo(dien)O3] also has higher value of hardness and a smaller value of softness. Stability had a direct relation with global hardness and an inverse relationship to its reactivity.
Synthesis, spectral, FMOs and NLO properties based on DFT calculations of dioxidomolybdenum(VI) complex
Published in Journal of Coordination Chemistry, 2021
M. K. Parte, P. K. Vishwakarma, P. S. Jaget, R. C. Maurya
The FMOs of a complex molecule is shown in Figure 7. FMOs analysis viz., HOMOs and LUMOs are the main orbitals taking part in chemical reactions [38]. The HOMO energy represents the ability to donate an electron while the LUMO as an electron acceptor represents the ability to get an electron. The frontier orbital gap helps to characterize the chemical reactivity, kinetic stability, optical polarizability and chemical hardness–softness of the molecule [39]. The HOMO–LUMO energy calculations reveal that there are 102 occupied and 186 unoccupied molecular orbitals associated with complex. Surfaces for the frontier orbitals were drawn to understand the bonding scheme of the present compound. The positive phase is red and the negative one is green. In the HOMO paired electrons are present in the complex, confirming that it is diamagnetic in nature. The selected FMOs energies of the HOMO − 2, HOMO − 1, HOMO, LUMO, LUMO + 1 and LUMO + 2 which are obtained from DFT calculations are −7.471, −6.861, −6.416, −3.210, −3.136 and −2.623 eV, respectively. The energy gap between the HOMO and LUMO, EHOMO-ELUMO for the complex is 3.205 eV. The large HOMO-LUMO gap indicates high chemical stability and low reactivity of the complex [40]. The other parameters viz. absolute electronegativity (χ), absolute hardness (η), hardness is electrophilicity index (w) and global softness (S) are calculated by the equations represented in Mir et al. [24]. The values of the above parameters are presented in Table S4.
Experimental and computational analysis of N-methylcytisine alkaloid in solution and prediction of biological activity by docking calculations
Published in Molecular Physics, 2022
Fanny C. Alvarez Escalada, Elida Romano, Silvia Antonia Brandán, Ana E. Ledesma
In the water solution, the reactivity of NMC is very important, because it exerts a diversity of pharmacological activities, such as hypoglycaemic, analgesic and anti-inflammatory activities and also it is a promising protective agent [35,36]. For these reasons, calculations of frontier molecular orbitals, highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) are important to predict the way the molecule behaves with other species. Their differences (HOMO–LUMO) known as gaps are used to evaluate the reactivity and chemical stability of the molecule, where its larger value is an indicative of the higher chemical stability and lower reactivity. In Table S2, a very important result is the local maximum value of Egap is found in the solution, evidencing that in the medium, the distribution of electrons stabilises the structure, justifying its higher solvation energy, probably due to its highly symmetric distribution in HOMO orbital, as observed in Figure S2. Chemical hardness (η) proposed by Pearson can also be seen as a parameter to measure the relative stability of the molecules. Thus, similar values were calculated for two media and the tendency of (η) is in agreement with the analysis by the HOMO–LUMO gaps. The comparison of hardness of NMC with those predicted for other known alkaloids [36] shows that the NMC can be considered as a hard molecule. The other important descriptor is the electrophilicity index (ω) [37–39], a measure of energy lowering due to charge transfer. The calculated ω value was higher than 1.5 eV; hence this alkaloid has an important attractive electron power.