Understanding the molecular factors of rice degradation during its aging concerns our research team. This article emphasizes oryzenin-amylopectin. It aims to reveal the mechanism of amylopectin deterioration during rice aging. The research exploits the Natural Bond Analysis and ONION method at theory level DFT/B3LYP/6-31+G(d, p) and AM1. This methodological approach allows highlighting amylopectin transformation;oryzenin converts amylopectin into amyloidosis in continuous. This led to monosaccharides and disaccharides.
The paddy rice degradation remains a concern for research;the chemical phenomena underlying this process persists unknown. This research aims to identify the mechanism of starch degradation. It determines the nature of the reactions between two, three and four synthons of amylose with oryzenin using theoretical methods. The ONIOM (DFT/B3LYP/6 - 31 + G(d, p): AM1) level of theory is performed on four monomers and eight complexes. Frequencies make it possible to obtain energy and spectroscopic quantities. Calculations after geometry optimization. Following this, a “single point” allows exploiting the “Natural Bond Orbital (NBO)” analysis. The first three parameters suggest that the main interactions between oryzenin and amylose arise through O29-H30…O46 hydrogen bonds (HB). Furthermore, this result posits that the length of the amylose doesn’t influence this reaction. The NBO analysis shows that this component of starch degrades first at the end of the chain to produce monosaccharides;it can also alter in the middle of the chain to give disaccharides.
N’guessan Boka RobertBamba El Hadji SawalihoKoffi Kouassi Alain
Malaria is a real public health problem. It’s one of the pathologies that mobilize the scientific community. Resistance to existing treatments is the basis for the search for new treatments. Some molecules such as Manzamenones have shown important antimalarial properties. These molecules belong to the family of atypical fatty acid derivatives. This work presents the relative stabilities, some reactivity properties and the privileged sites of interaction by hydrogen bond of fourteen Manzamenones and two antimalarial drugs: quinine and Artemisinin. These analyses were performed using quantum chemical calculations. We employed the two-layer ONIOM calculation method;namely ONIOM (B3LYP/6-311++G (d, p): AM1) for the fourteen Manzamenones. The geometries of the two antimalarials are calculated at B3LYP/6-311++G (d, p). The electrostatic potential (ESP) calculation of all molecules is done at the B3LYP/6-31++G (d, p) level. The formation processes of the molecules are discussed from the thermodynamic quantities we have calculated. The relative stabilities, the energies of the frontier orbitals, the energy gaps, the dipole moment, etc., are evaluated and discussed. The electrostatic potential at the molecular surface has been used to identify the sites favorable to the formation of hydrogen bonds.
This work was undertaken to analyze intramolecular and intermolecular interactions of Manzamenones from natural bond orbitals (NBO method). For their use in the treatment of malaria, the results of these molecules are compared to those of Artemisinin and Quinine. Manzamenones are a class of atypical fatty acids. They are isolated from a marine sponge of the genus Plakortis kenyensis. The analysis of intramolecular interactions compares the results of each molecule (Manzamenones, Artemisinin and Quinine) in the non-complexed state with those of its complex with a water molecule. Thus, for the same electron donors (i) and associated acceptors (j), the electron density (ED), stabilization energy E2 related to the delocalization of i to j, the energies of the NBO orbitals εi and εj of the donor and acceptor, respectively, and element of the Fock matrix Fi,j are determined and compared. The change in E2 is used to deduce whether or not the molecule is stabilized after complex formation. These analyses allowed to match each Manzamenone to one of the two antimalarials. The intermolecular interactions were analyzed, for each molecule (Manzamenones, Artemisinin and Quinine), in two complexes. These complexes are obtained with a water molecule on the one hand and with an alanine molecule on the other hand. For these interactions, the electron donor and its electron density, the electron acceptor and its electron density as well as the donor—acceptor stabilization energy have been calculated. The ONIOM 2 method is used to study Manzamenones. Theoretical calculations were done using density functional theory (B3LYP) by combining one of the two function bases 6-31++G(d,p) and 6-31+G(d,p).
Mycolactone molecules are responsible of Buruli ulcer disease. In this work, we are interested in the geometric, energetic and spectroscopic characterization of the hydrogen bonding interactions in mycolactone A/B, using quantum chemical method, especially ONIOM(HF/6-311+G(d,p):AM1) and ONIOM (B3LYP/6-311+G(d,p):AM1) levels. ONIOM two layers method has been used because mycolactones compounds are very large, taking into account diffuse and polarization functions are important whenever the matter is intermolecular interactions. Geometric, energetic and spectroscopic parameters of hydrogen bonding reaction on each of the nine oxygen heteroatoms of mycolactone A/B have revealed that the O5sp2 heteroatom is far away the hydrogen bonding site. The identification of such a site constitutes a tool for working out a methodology for the annihilation of the destruction effects of mycolactones.
Kadjo François KassiMamadou Guy-Richard KonéSopi Thomas AffiNahossé Ziao
The rate constants of the nucleophilic reactions between amines and benzhydrylium ions were calculated using first-principles theoretical methods. Solvation models including PCM, CPCM, and COSMORS, as well as different types of atomic radii including UA0, UAKS, UAHF, Bondi, and UFF, and several single-point energy calculation methods （B3LYP, B3P86, B3PW91, BHANDH, PBEPBE, BMK, M06, MP2, and ONIOM method） were examined. By comparing the correlation between experimental rate constants and the calculated values, the ONIOM（CCSD（T）/6-311＋＋G（2df,2p）：B3LYP/6-311＋＋G（2df,2p））//B3LYP/6- 31G（d）/PCM/UFF） method was found to perform the best. This method was then employed to calculate the rate constants of the reactions between diverse amines and diarylcarbenium ions. The calculated rate constants for 65 reactions of amines with diarylcarbenium ions are in agreement with the experimental values, indicating that it is feasible to predict the rate constant of a reaction between an amine and a diarylcarbenium ion through ab initio calculation.
