Aida Ben Altabef

Ab-initio and DFT calculations on molecular structure, NBO, HOMO–LUMO study and a new vibrational analysis of 4-(Dimethylamino) Benzaldehyde

The experimental and theoretical study on the molecular structure and a new vibrational analysis of 4-(Dimethylamino) Benzaldehyde (DMABA) is presented. The IR and Raman spectra were recorded in solid state. Optimized geometry, vibrational frequencies and various thermodynamic parameters of the title compound were calculated using DFT methods and are in agreement with the experimental values. A detailed interpretation of the IR and Raman spectra of the title compound were reported. The stability of the molecule arising from hyper-conjugative interactions and charge delocalization has been analyzed using NBO analysis and AIM approach. The HOMO and LUMO analysis were used to determine the charge transfer within the molecule and some molecular properties such as ionization potential, electron affinity, electronegativity, chemical potential, hardness, softness and global electrophilicity index. The TD-DFT approach was applied to assign the electronic transitions observed in the UV-visible spectrum measured experimentally. Molecular electrostatic potential map was performed by the DFT method. According to DSC measurements, the substance presents a melting point of 72.34°C and decomposes at temperatures higher than 193°C.

Syntheses and characterization of new mononuclear and dinuclear complexes derived from ruthenium polypyridines

Abstract New complexes containing the Ru(bpy)(trpy) 2+ moiety (bpy=2,2′-bipyridine; trpy=2,2′:6′,2″-terpyridine) as a photosensitizer, 4-CNpy (=4-cyanopyridine) as a bridging ligand and Ru(NH 3 ) 5 n+ as an electron donor ( n =2) or acceptor ( n =3) capping group were synthesized and characterized by spectroscopic and electrochemical techniques. In the mononuclear complex [Ru II (bpy)(trpy)(4-CNpy)] 2+ (I) IR, UV-Vis and cyclic voltammetry data ( v CN(nitrile)=2237 cm −1 ; λ max =432 and 464 nm, in CH 3 CN; E 1 2 (Ru III /Ru II )=1.23 V, in CH 3 CN versus SCE) point to a pyridine-bonded isomer of 4-CNpy. In the bridged complex [Ru II (bpy)(trpy)(4-CNpy)Ru II (NH 3 ) 5 ] 4+ ( II ) the nitrile end of 4-CNpy coordinates to a capping Ru II (NH 3 ) 5 group, as disclosed by the shifts in spectral absorptions ( v CN(nitrile)=2174 cm −1 ; λ max =490 nm, in CH 3 CN) and the occurrence of a new voltammetric wave ( E 1/2 =0.74 V, in CH 3 CN versus SCE). A related bridged species, [Ru II (bpy)(trpy)(4-CNpy)Fe II (CN) 5 ] − ( IIl ) was obtained and characterized in aqueous solution (λ max =460 nm, in water). The mixed-valence complex [Ru II (bpy)(trpy)(4-CNpy)Ru III (NH 3 ) 5 ] 5+ ( IV ) can be prepared in CH 3 CN solution (λ max =438 nm) by oxidation of II with Ce(IV); it presents a comproportionation constant K c =2x10 8 , thus indicating a high stability arising from the asymmetric nature of this species. The ‘supramolecular’ systems described in this work can be used as models for systematic studies of intramolecular electron transfers.

A conformational and vibrational study of CF3COSCH2CH3

The molecular structure and conformational properties of S-ethyl trifluorothioacetate, CF(3)COSCH(2)CH(3), were determined in the gas phase by electron diffraction and vibrational spectroscopy (IR and Raman). The experimental investigations were supplemented by ab initio (Moller Plesset of second order) and density functional theory quantum chemical calculations at different levels of theory. Both experimental and theoretical methods reveal two structures with C(s) (anti, anti) and C(1) (anti, gauche) symmetries, although there are disagreements about which is more stable. The electron diffraction intensities are best interpreted with a mixture of 51(3)% anti, anti and 49(3)% anti, gauche conformers. This conformational preference was studied using the total energy scheme and the natural bond orbital scheme. In addition, the infrared spectra of CF(3)COSCH(2)CH(3) are reported for the gas, liquid and solid phases as well as the Raman spectrum of the liquid. Using calculated frequencies as a guide, evidence for both C(s) and C(1) structures is obtained in the IR spectra. Harmonic vibrational frequencies and scaled force fields have been calculated for both conformers.

Synthesis and spectral properties of a new binuclear iron complex: The ion tetracyano(4-cyanopyridine) ferrate(II)-μ-cyano-pentacyanoferrate(II)☆

Abstract A new cyano-bridged binuclear complex of Fe(II) can be prepared by mixing pentacyano(ammine)ferrate(II) with 4-cyanopyridine at a mole ratio 2:1. IR and UV-VIS spectra, together with kinetic data on ligand substitution, point to the following structure; (NC)5Fe-NC-Fe(CN)4(N -CN)6−, both in solid state and in aqueous solution, thus demonstrating that cyanide forms a bridge between two iron atoms which is much more stable than that formed by 4-cyanopyridine.

Layered crystal structure, conformational and vibrational properties of 2,2,2-trichloroethoxysulfonamide: an experimental and theoretical study.

The molecular structure of 2,2,2-trichloroethoxysulfonamide, CCl3CH2OSO2NH2, has been determined in the solid state by X-ray diffraction data and in the gas phase by ab initio (MP2) and DFT calculations. The substance crystallizes in the monoclinic P21/c space group with a = 9.969(3)Å, b = 22.914(6)Å, c = 7.349(2)Å, β = 91.06(3)°, and Z = 8 molecules per unit cell. There are two independent, but closely related molecular conformers in the crystal asymmetric unit. They only differ in the angular orientation of the sulfonamide (SO2NH2) group. The conformers are arranged in the lattice as center-symmetric NH · · · O(sulf)-bonded dimers. Neighboring dimers are linked through further NH · · · O(sulf) bonds giving rise to a crystal layered structure. The solid state infrared and Raman spectra have been recorded and the observed bands assigned to the molecular vibration modes. Also, the thermal behavior of the substance was investigated by TG-DT analysis. The stability of the molecule arising from hyper-conjugative interactions and charge delocalization has been analyzed using natural bond (NBO) analysis.

DFT calculations of structure and vibrational properties of 2,2,2-trichloroethylacetate, CH3CO2CH2CCl3

The molecular structure and conformational properties of 2,2,2-trichloroethylacetate, CH(3)CO(2)CH(2)CCl(3), were determined by ab initio (MP2) and DFT quantum chemical calculations at different levels of theory. The theoretical study was complemented with experimental measurements such as IR and Raman spectroscopy. The experimental and calculations confirm the presence of two conformers, one with anti, gauche conformation (C1 symmetry) and another with anti, anti form (Cs symmetry). The conformational preference was studied using the total energy scheme, NBO and AIM analysis. The infrared spectra of CH(3)CO(2)CH(2)CCl(3) are reported in the liquid and solid phases and the Raman spectrum in liquid phase. Using calculated frequencies as a guide, evidence for both C1 and Cs conformers is obtained in the IR and Raman spectra.

Synthesis, crystal structure, conformational and vibrational properties of 6-acetyl-2,2-dimethyl-chromane

The 6-acetyl-2,2-dimethyl-chromane compound was synthesized and characterized by IR, Raman, UV-Visible and (1)H NMR spectroscopies. Its solid state structure was determined by X-ray diffraction methods. The substance crystallizes in the triclinic P-1 space group with a=5.9622(5) Å, b=10.342(1) Å, c=10.464(1) Å, α=63.81(1)°, β=81.923(9)°, γ=82.645(9)°, and Z=2 molecules per unit cell. Due to extended π-bonding delocalization a substantial skeletal fragment of the molecule is planar. The vibrational modes were calculated at B3LYP/6-31G(d,p) level and all of them assigned in the IR and Raman spectra. The DFT calculated (1)H NMR spectrum (chemical shifts) were in good agreement with the experimental data. The electronic (UV-Visible) spectrum was calculated using TD-DFT method in gas phase and it was correlated with the experimental data. The assignment and analysis of the frontier HOMO and LUMO orbitals indicate that the absorption bands are mainly originated from π→π(*) transitions. According to DSC measurements the substance presents a melting point of 93°C and decomposes at temperatures higher than 196°C.

Interaction of S-methyl methanethiosulfonate with DPPC bilayer

The present study is a first step towards the investigation of S-methyl methanethiosulfonate (MMTS) interaction with membrane model systems like liposomes. In this paper, the interaction of MMTS with dipalmitoylphosphatidylcholine (DPPC) bilayers was studied by FTIR and SERS spectroscopy. Lysolipid effect on vesicle stability was studied. The results show that MMTS interacts to different extents with the phosphate and carbonyl groups of membranes in the gel and the liquid crystalline states. To gain a deeper insight into MMTS properties that may be potentially helpful in the design of new drugs with therapeutic effects, we performed theoretical studies that may be the basis for the design of their mode of action.

Determination of the main solid-state form of albendazole in bulk drug, employing Raman spectroscopy coupled to multivariate analysis

Albendazole (ALB) is a broad-spectrum anthelmintic, which exhibits two solid-state forms (Forms I and II). The Form I is the metastable crystal at room temperature, while Form II is the stable one. Because the drug has poor aqueous solubility and Form II is less soluble than Form I, it is desirable to have a method to assess the solid-state form of the drug employed for manufacturing purposes. Therefore, a Partial Least Squares (PLS) model was developed for the determination of Form I of ALB in its mixtures with Form II. For model development, both solid-state forms of ALB were prepared and characterized by microscopic (optical and with normal and polarized light), thermal (DSC) and spectroscopic (ATR-FTIR, Raman) techniques. Mixtures of solids in different ratios were prepared by weighing and mechanical mixing of the components. Their Raman spectra were acquired, and subjected to peak smoothing, normalization, standard normal variate correction and de-trending, before performing the PLS calculations. The optimal spectral region (1396-1280cm(-1)) and number of latent variables (LV=3) were obtained employing a moving window of variable size strategy. The method was internally validated by means of the leave one out procedure, providing satisfactory statistics (r(2)=0.9729 and RMSD=5.6%) and figures of merit (LOD=9.4% and MDDC=1.4). Furthermore, the methods performance was also evaluated by analysis of two validation sets. Validation set I was used for assessment of linearity and range and Validation set II, to demonstrate accuracy and precision (Recovery=101.4% and RSD=2.8%). Additionally, a third set of spiked commercial samples was evaluated, exhibiting excellent recoveries (94.2±6.4%). The results suggest that the combination of Raman spectroscopy with multivariate analysis could be applied to the assessment of the main crystal form and its quantitation in samples of ALB bulk drug, in the routine quality control laboratory.

Combined experimental studies and theoretical calculations to yield the complete molecular structure and vibrational spectra of (CH3)3GeH.

The molecular structure of trimethylgermane has been determined by gas electron diffraction experiments. Infrared spectra for the gaseous, liquid, and solid phases were also recorded. Parallel and perpendicular polarized Raman spectra for the liquid were measured to obtain depolarization values. The experimental studies were supported by a series of computational calculations using HF, B3LYP, and MP2 methods and a variety of basis sets. The force fields obtained from density functional theory using both B3LYP/6-31G* and B3LYP/6-311+G** were scaled with both Pulays SQM methodology and Yoshidas WLS procedure to simulate the vibrational spectra and assist in the assignment of fundamental bands. The Raman intensities were obtained from polarizability derivatives. The vibrational spectra of trimethylgermane were completely assigned on the basis of the experimental data and the theoretical prediction of vibrational frequencies and intensities.