Narrow Results

In previous researches it is demonstrated that reactivity and sensitivity of boron nitride nanotubes (BNNTs) toward gas molecules can be modified by impurity. In this work, oxygen defect for three nitrogen sites was used to study the adsorption of NO molecule through the surface of boroxol ring of oxygen doped BNNT (7,0) with different adsorption patterns, including side-on and end-on. All calculations are performed using the DFT-B3LYP/6-31G${}^{\ast }$ level of theory, and their electronic energies are corrected by gCP and D3 correction terms. High binding energies indicate that NO molecule undergoes chemical adsorption with large charge transfer from the tube which can significantly change electronic properties of the tube. Density of state (DOS) and partial DOS (PDOS) analyses revealed that adsorption of NO molecule on the boroxol ring position is covalent in nature with significant effect on the electronic properties of tube. The Laplacian of electron density, Lagrangian kinetic energy density, Hamiltonian kinetic energy density and potential energy density at bond critical points between the tube and NO indicate that the interaction between the tube and NO molecule is covalent in nature. Topological analysis of the electron localization function shows that electrons in the new formed bonds are approximately localized, meaning that the nature of adsorption process is chemical covalent. The studied nanotube is a suitable candidate to filter and eliminate NO gas molecule.

In this paper, two numerical methods are used to calculate quasi-normal modes (QNMs) of near-extremal black holes/strings in the generalized spherically/cylindrically symmetric background, the Asymptotic Iteration Method (AIM) and the Spectral Method. The numerical results confirm the accuracy of the approximate analytic formula using the Pöschl–Teller potential. Our analytic formula is used to investigate the Strong Cosmic Censorship conjecture of extremal and near-extremal black holes in (P. Burikham, S. Ponglertsakul and T. Wuthicharn, Eur. Phys. J. C80 (2020) 954, arXiv:2010.05879 [gr-qc]).

Interaction of CO and NO molecules by different orientations on (BN)_n=3-5 clusters have been studied at the B3LYP/6-311+G* level of theory. Total electronic energies have been corrected for geometrical counterpoise (gCP) and dispersion (D3) energies at the B3LYP/6-31G* level. Formation of a new sigma bond between the gas and (BN)₃ cluster, atom in molecules (AIM) results, density of states spectrums (DOS), molecular electrostatic potential (MEP) surfaces, and visualization of wave function of molecular orbitals in the nearest bonding regions to the Fermi level have confirmed that adsorption of CO by carbon end atom, and NO by nitrogen end atom is covalent in nature, so that the charge transfer is occurred from gas molecule to the cluster.

Ab initio calculations were performed to study the applicability and reliability of the semi quantitative model based on the local hard-soft acid-base principle in studying the interaction of metal ions with ligands. The particular attention is devoted to the interaction of CO, CN^- and SCN^- as the base with some hard metal ions (Li⁺, Na⁺, K⁺) and some soft metal ions (Pd⁺², Ag⁺², Cd⁺²) as acids. The interaction energies were calculated using the HSAB principle and compared with the values obtained by the conventional MP2 method. The results show that the HSAB principle does not work in many cases and it fails to predict correct values for interaction energies. The AIM and NBO analyses were also performed to characterize the nature of the metal ion-ligand interaction. It is found that the charge transfers have great significance in the interaction of metal ions with ligands.

A theoretical investigation about the cooperative effect on (HCN)_n homo and (HCN)_n ⋯ HF heterochains was performed in terms of structural parameters and topological properties obtained in concordance with the protocol of Bader's atoms in molecules theory. Initially, the hydrogen bonding distances, electronic densities, and Laplacian descriptors were used to characterize small (HCN)_n and (HCN)_n ⋯ HF chains formed by n = 2–4 units of HCN. Hydrogen bond distances and distribution of charge density have revealed that the cooperative effect on (HCN)_n ⋯ HF heterochains is ruled by the polarity of the extreme hydrofluoric acid species. Furthermore, we investigated larger homo and heterochain systems formed by n = 2–8 molecules of HCN. In this insight, the drastic polarized effect caused by HF molecule which was considered very substantial at prior, in fact is seriously limited by an excessive number of HCN molecules connected to the heterochain. This leads to a stabilization of the (N ⋯ HF) hydrogen bonds with invariable electronic density in the range of . In this stage and henceforth, the cooperative effect is re-established with n = 4 molecules of HCN. Thereby, the electronic density of the hydrogen bonds become unaltered within the (HCN)_n ⋯ HF heterochains.

B3LYP/6-311++G** calculations have been carried out to simulate the influence of substitutions in position R₁ and R₂ of 3-amino 2-iminomethyl acryl aldehyde on intramolecular hydrogen bond strength. The following substituents are taken into considerations: CN, NO₂, Cl, F, CH₃, CHO, NH₂, C₂H₅, SH, SCH₃, CF₃ and CH₃CO and their vibrational frequencies are calculated at the same level of theory. Quantum theory of "Atoms in Molecules" and Natural Bond Orbitals method were applied to analyzed H-bond interactions. The electron density (ρ) and Laplacian (∇²ρ) properties, estimated by AIM calculations, indicate that N⋯H bond possesses low ρ and positive ∇²ρ values which are in agreement with electrostatic character of the HBs, whereas N–H bonds have covalent character (∇²ρ < 0). Natural population analysis data, the electron density and Laplacian properties, as well as, ν_(N-H) and γ_(N-H) have been used to evaluate the hydrogen bonding interactions.

The reaction mechanism of SiHF radical with HNCO has been investigated by the B3LYP method of density functional theory (DFT), while the geometries and harmonic vibration frequencies of reactants, intermediates, transition states and products have been calculated at the B3LYP/6-311++G** level. To obtain more precise energy result, stationary point energies were calculated at the CCSD(T)/6-311++G**//B3LYP/6-311++G** level. In temperature range of 100 K to 1900 K, the statistical thermodynamics and Eyring transition state theory with Winger correction are used to study the thermodynamic and kinetic characters of the channel with low energy barrier at 1.0 Atm. SiHF + HNCO → IM8 → TS8 → SiFNHCHO(P3) was the main channel with low potential energy in the singlet state, SiFNHCHO was the main product. The analyses for the combining interaction between SiHF radical and HNCO with the atom-in-molecules (AIM) theory have been performed. There are three reaction channels in the triplet.

The pnicogen bonding interactions of PCl₃ and π-electron systems (acetylene, ethylene, benzene) were calculated by using MP2/aug-cc-pVDZ method and the effect of hydrogen bond on pnicogen bond systems were investigated. It has been indicated that the hydrogen bonding and the pnicogen bonding interactions have influence on each other and the positively cooperative effect has been detected. The interaction energies of pnicogen bonded supramolecular system were also calculated by using DFT method (M06-2X) and some simple comparisons with those by using MP2 method were made. It has been disclosed from natural bond orbitals (NBO) analysis that more the amount of charge transfer of pnicogen bonding interaction, the greater the stability of the corresponding complex. Through AIM topological analysis, it has been revealed that the electron density of pnicogen bond BCP point is positively correlated with the stability of trimeric complex. Electron localization function (ELF) was also adopted to analyze the nature of pnicogen bonding interactions. Furthermore, density difference function (DDF) method was adopted to analyze the variation of electron density of pnicogen bond system because of hydrogen bond.

The computational investigations on 1:1 complexes of the nitrogen trifluoride (NF${}_3)$ species with the nitroxyl (HNO) species have been carried out, which reveal the existence of the nine complexes on the singlet potential energy surface (PES). The atoms in molecules (AIM) theory and the electron localization function (ELF) along with the identification of noncovalent interaction (NCI) regions and the investigation of electron transfer of all the obtained complexes have been carried out to provide suitable insight into the electronic and structural properties of these complexes. The calculated results reveal that the N-atom of the NF₃ species and the O-atom of the HNO species have more key roles compared with the F-atom of the NF₃ species and the N-atom of the HNO species in the obtained complexes.

The structure and properties of the N${}_{(\mathrm{\text{ax}})}$–Mn–O bonds of high valent manganese-oxo of the second and third generation porphyrins in the presence of imidazole have been studied by means of density functional (DFT) method with 6-31G* basis set in the gas phase as well as water solution. The geometric structures, frontier molecular orbitals, thermodynamic parameters, aromaticity indices and physical properties such as chemical potential and chemical hardness of [(TPP)(ImH)MnO]${}^{+}$ and its derivatives were calculated. The obtained results showed that [(TPP)(ImH)MnO]${}^{+}$ bearing halogen atoms at the $\beta$-pyrrole positions had a saddle conformation with low Mn–O strength. The electron density ($\rho )$ and Laplacian (${\nabla }_{\rho }^2)$ properties at critical points of the N${}_{(\mathrm{\text{ax}})}$–Mn–O bonds, estimated by AIM calculations, indicate that Mn–O bonds in third generation porphyrins have lower $\rho$ and Mn–N${}_{(\mathrm{\text{ax}})}$ distances have higher $\rho$ than the second generation ones. The calculations of aromaticity indices for chelated rings at the porphyrin center show that HOMA and NICS in third generation porphyrins are generally lower than that of second ones which is in agreement with their saddle conformation. These results are supported by natural bond orbital (NBO) analysis.

The stereo electronic effects as well as hydrogen bonding effects of imidazole, pyridine and 2,6-dimethylpyridine as N-donor axial ligands on the C–H oxidation activity of high-valent manganese(V)–oxo meso-tetraphenylporphyrin (TPP) and meso-tetrakis(pentaflourophenyl)porphyrin (TPFPP), are investigated by DFT calculations. The electronic and steric properties of axial donors and porphyrin ligands affected on the activation energy of cyclohexane hydroxylation as well as the Mn–O bond strength of the oxo species in transition state. Imidazole with the strong $\pi$-donating ability and the least steric hindrance showed greater co-catalytic activity than those of pyridine and in particularly hindered 2,6-Me₂ pyridine in the presence of simple [(TPP)MnO]${}^{+}$. Nevertheless, the C–H bond activation by hindered and electron-deficient perfluorinated catalyst [(TPFPP)MnO]${}^{+}$ is in the order of pyridine >2, 6-Me₂ pyridine >imidazole. AIM analysis showed hydrogen bonding (HB) between the C–H $\sigma$ bonds of pyridine (C${}_{\mathrm{\text{sp}}2}$-H of ring) and 2,6-Me₂Py (C${}_{\mathrm{\text{sp}}3}$-H of methyl groups) with ortho-C–F bond of phenyl rings of TPFPP in Mn$=$O species (C–H…..F–C hydrogen bond) which might be responsible for this unusual behavior. These results are supported by natural bond orbital (NBO) analysis.

Microfinance was introduced in Malaysia in 1987 to provide financial access to the poorest member of the society and to reduce the persisting income inequality. Poverty and inequality in Malaysia are characterised by the income disparity between urban–rural populations, gender, as well as among ethnic groups and states. This chapter gives an overview of three main Microfinance Institutions (MFIs) in Malaysia, namely Amanah Ikhtiar Malaysia (AIM), Yayasan Usaha Maju (YUM) and Tabung Ekonomi Kumpulan Usaha Niaga (TEKUN). The three MFIs receive financial support from the Malaysian government but differ in the year of establishment, organisation type, lending schemes, service area coverage and target borrowers. MFIs differ in the performance of their loans’ repayment rate where the high Non-Performing Loans (NPL) can be associated with the loans’ lending terms as well as borrowers’ certain individual and household characteristics. MFIs’ microcredit loans positively affect borrowers’ individual, household and microenterprise economic performances but the magnitudes of the impact vary among MFIs and across economic performance measures. The implications of the presented findings and analysis are discussed, both for the MFIs and the policy makers.