Characterization Of Chemical Bonds Research Articles

Crystal structure, Hirshfeld surface analysis, optical properties and stability of organic-inorganic compound (C6H5CH2NH3)2(CH3CH3NH2)3Bi2Br11

A novel bismuth-based zero-dimensional organic-inorganic hybrid material (C6H5CH2NH3)2(CH3CH3NH2)3Bi2Br11 was synthesized by a hydrothermal method. The crystal structure, intermolecular interactions, chemical groups, chemical bond characterization, optical and thermal stability of the sample were systematically investigated by single crystal X-ray diffraction, powder X-ray diffraction, Hirshfeld surface analysis, field scanning electron microscopy, Fourier transform infrared spectrometer, Raman spectra, thermogravimetric analysis, and Ultraviolet–visible diffuse reflectance spectra. The results indicated that the (C6H5CH2NH3)2(CH3CH3NH2)3Bi2Br11 crystal displayed a triclinic crystal system with a P-1 space group at room temperature with a = 8.5290(4) Å, b = 14.2484(10) Å, c = 18.9386(10) Å, α = 94.418(5) °, β = 102.260(4) °, γ = 106.595(5) °, V = 2131.9(2) Å3, Z = 2, R1 = 0.0936, wR2 = 0.1536. The compound displayed typical zero-dimensional consisting of two benzylamine organic [C6H5CH2NH3]+ cations, three dimethylamine organic [CH3CH3NH2]+ cations and a corner-sharing dimer unit [Bi2Br11]5–. Infrared and Raman vibrational study indicates the presence of [CH3CH3NH2]+. The 2D fingerprint plot of Hirshfeld surface analysis shows that H⋯Br/Br⋯H (56.8 %) and H⋯H (31.4 %) are major contributions to the intermolecular contact of (C6H5CH2NH3)2(CH3CH3NH2)3Bi2Br11. The sample presented relatively perfect thermal stability up to 240 °C and a wide band gap of about 2.75 eV. It provides some reference value for exploring organic-inorganic hybrid materials with low toxicity and high thermal stability.

Synthesis and characterization of gadolinium nanoparticles using polyol method as a candidate for MRI Contrast Agent

This research is related to the preparation and initial characterization of gadolinium nanoparticles as a Magnetic Resonance Imaging (MRI) contrast agent. Nanomaterial-based contrast agents aim to improve clearer imaging, longer examination retention times with lower toxicity than gadolinium ion-based contrast agents, and evaluate the potential use of MRI contrast agents for early detection of cancer. Gadolinium nanoparticles were synthesized using polyol method with stabilizer and chemical reaction process at high temperature. The stabilizers used are diethylene glycol (DEG) and triethylene glycol (TEG). The reaction process was carried out at 180°C for 4 hours to obtain gadolinium nanoparticles with uniform size and shape. The results of hydrodynamic and visual measurements using DLS and HRTEM instruments on the gadolinium nanoparticles produced were 50 nm and 18 nm, respectively. The results of the characterization of the crystal structure obtained the X-ray diffraction pattern in the crystal plane (222), which is a typical for the Gd2O3 crystal phase. Characterization of chemical bonds using FTIR showed absorption at 1438-1627 cm−1, 1000-1138 cm−1 and 450-795 cm−1 indicated the presence of Gd-O bond vibrations, while absorption at 1310-1466 cm−1 indicated the presence of Gd-O-Gd bonds. This is evidenced by the similarity with the absorption peak of commercial Gd2O3. The content of free Gd3+ ions found in the synthesized products detected was only about 0.99% of the Gd3+ precursors used.

Nanoliposomal encapsulation of Bitter Gourd (Momordica charantia) fruit extract as a rich source of health-promoting bioactive compounds

Bitter Gourd fruit is a rich source of antioxidants and anti-diabetic compounds but due to its instability and bitter taste, there are limitations for adding in food formulations. Our goal was to load this charantin-rich extract within nanoliposomes; the studied variables were different concentrations of lecithin (1, 3, 5% w/w) and extract (0.5, 1% w/w). Physicochemical properties including particle size, polydispersity index (PDI), zeta potential and encapsulation efficiency were determined along with characterization of chemical bonds and morphology by FTIR and atomic force microscopy (AFM). It was found that particle size and PDI varied in the range of 125–255 nm and 0.167–0.235, respectively. Z-potential of nanoliposomes (−38.5 to −35.5 mV) indicated a good electrostatic repulsion and high physical stability. Encapsulation efficiency varied from 72.95 to 84.43% so that nanoliposomes containing 1% lecithin and 0.5% extract had the highest encapsulation efficiency. FTIR results suggested the formation of hydrogen bonds between polar areas of lecithin and hydroxyl groups of the extract. AFM images indicated the existence of nano-scaled particles with relatively spherical structures and uniform size distribution. Our study indicated the high efficiency of nanoliposomes for loading bioactive compounds of Bitter Gourd extract and its possible use in food and drink formulations.

Bond Characterization of Chromium−Fischer Carbene Complexes: A Combined Study of Experiment and Theory

Four pentacarbonyl chromium−carbene complexes, (CO)5CrC(XR‘)R, have been studied via X-ray diffraction and molecular orbital calculations. One of the carbene complexes (XR‘ = OCH3, R = −(C⋮CPh)) has been investigated extensively at 110 K by X-ray diffraction using Mo Kα radiation. The electron density distribution of this compound as well as the asphericity in electron density around the Cr atom is clearly demonstrated by deformation density and the Laplacian of electron density. The comparison between experiment and theory is made in terms of deformation density, topological properties, and d orbital populations of Cr. Further chemical bond characterization is based on quantum mechanical molecular orbital calculation and properties associated with bond critical points. The π bond character of a metal carbene can be best represented by a Cr−C−X three-centered four-electron bond with the π electron density mainly located at either the dyz orbital of Cr or the pz orbital of X in the carbene ligand. This makes the carbene carbon an electrophilic site in the pπ direction. The resemblances and differences between amino−(XN) and alkoxy−(XO) carbene complexes are of special interest. Because the energy of π*C-N orbital is fairly close to that of the π*C⋮O (carbonyl on Cr), the π bond character is delocalized toward the M−Ccarbonyl at the trans position i.e., OCM−CN in the amino carbene case; this is in accord with the shortening of bond lengths of the trans M−Ccarbonyl for many amino−carbene complexes. The π bond-delocalization is also illustrated by the Fermi hole distribution. The bond dissociation energies of these carbene complexes are calculated at the CASSCF level and with the density functional method (DFT). The relative orbital energies are also compared with photoelectron spectroscopy (PES) data. The values based on DFT using the transition-state approximation give the best agreement with the experimental results.

Chemical Bonds in Minerals: Topological Analysis of the Electron Localization Function

The characterization of the chemical bonds in minerals and particularly in silicates is a puzzling problem which is related to the criteria used to classify them. As discussed by Tossell and Vaughan (1992), the availability of an absolute description of covalency versus ionicity in terms of observable properties is questionable. From the experimental point of view, the relevant information is provided by the analysis of the electron density. However, different schemes can be applied to partition the crystal into atomic domains which yield slightly different atomic charges. Moreover, the nature of chemical bond is not only a matter of electron distribution, but above all, of distribution of electron pairs. Theoretically most analyses of the bonding rely either on the valence bond (VB) or molecular orbital (MO) schemes, in which the VB and MO functions are themselves expressed in terms of atomic basis functions. Therefore, the guidelines used to characterize the bonding depend upon the level of approximation, they cannot be applied with exact wavefunctions. The characterization of chemical bond is qualitative, not quantitative. The topological analysis of the gradient field of local functions is the mathematically founded approach to go from quantitative to qualitative. This method has been pioneered by Bader (1990) who emphasized the role ofthe electron density. It allows to define bond paths and atomic basins and therefore rationalizes the concept of bonded atoms, provides an objective partitioning scheme and gives a theoretical foundation to structural chemistry. However, as already mentionned, with the electron density alone it is not easy to reveal the formation of electron pairs which are the consequences of the Pauli exclusion principle. In this communication, we apply such a topological analysis to the gradient field of local functions, named hereafter localization functions, which measure the Pauli repulsion. This enables us to propose a new set of criteria to classify chemical bonds which are applied to silica and related materials. A sketch of the topological theory of chemical bonds.