Wajdi M. Zoghaib

Synthesis, antimicrobial activity, structural and spectral characterization and DFT calculations of Co(II), Ni(II), Cu(II) and Pd(II) complexes of 4-amino-5-pyrimidinecarbonitrile

Co(II), Ni(II), Cu(II) and Pd(II) complexes of 4-amino-5-pyrimidinecarbonitrile (APC) have been synthesized and characterized using elemental analysis, magnetic susceptibility, mass spectrometry, infrared (4000-200 cm(-1)), UV-Visible (200-1100 nm), (1)H NMR and ESR spectroscopy as well as TGA analysis. The molar conductance measurements in DMSO imply non-electrolytic complexes, formulated as [M(APC)2Cl2] where M=Co(II), Ni(II), Cu(II) and Pd(II). The infrared spectra of Co(II), Ni(II) and Cu(II) complexes indicate a bidentate type of bonding for APC through the exocyclic amino and adjacent pyrimidine nitrogen as donors whereas APC coordinated to Pd(II) ion as a monodentated ligand via a pyrimidine nitrogen donor. The magnetic measurements and the electronic absorption spectra support distorted octahedral geometries for Co(II), Ni(II) and Cu(II) complexes however a square planar complex was favored for the Pd(II) complex (C2h skeleton symmetry). In addition, we carried out B3LYP and ω-B97XD geometry optimization at 6-31G(d) basis set except for Pd(II) where we implemented LanL2DZ/6-31G(d) combined basis set. The computational results favor all trans geometrical isomers where amino N, pyrimidine N and Cl are trans to each other (structure 1). Finally, APC and its divalent metal ion complexes were screened for their antibacterial activity, and the synthesized complexes were found to be more potent antimicrobial agents than APC against one or more microbial species.

Raman, infrared and NMR spectral analysis, normal coordinate analysis and theoretical calculations of 5-(methylthio)-1,3,4-thiadiazole-2(3H)-thione and its thiol tautomer.

Raman (3400-100 cm(-1)) and infrared (4000-200 cm(-1)) spectra of 5-(methylthio)-1,3,4-thiadiazole-2(3H)-thione (C3H4N2S3; MTT) were measured in the solid state, and the (1)H/(13)C NMR spectra were obtained in DMSO-d6. Initially, twelve structures were proposed as a result of thiol-thione tautomerism and the internal rotation about the C-S bonds. The energies and vibrational frequencies of the optimized structures were calculated using the 6-31G(d) basis set with the methods of MP2 and DFT/B3LYP with Gaussian 98 quantum calculations. Additionally, (1)H/(13)C NMR chemical shifts were predicted for the thiol (structure 5) and thione (structure 9) tautomers by means of B3LYP/6-311+G(d,p) calculations utilizing the GIAO approximation and the PCM solvation model. After complete relaxation of twelve candidate isomers, the thione tautomer (structure 9) was favored owing to its low energy and its predicted real spectral frequencies. These results agree with the recorded infrared and Raman results, in addition to the observed/calculated (1)H and (13)C NMR spectra. Aided by normal coordinate analysis and potential energy distributions (PEDs), complete vibrational assignments have been proposed for all observed fundamentals for the thione tautomer. With the aid of MP2/6-31G(d) potential surface scans, CH3, CH3S, and SH barriers to internal rotations were estimated with the optimized structural parameters from the MP2 method with the 6-31G(d) basis set. The results are discussed herein and compared with similar model compounds whenever appropriate.

Vibrational assignments, normal coordinate analysis, B3LYP calculations and conformational analysis of methyl-5-amino-4-cyano-3-(methylthio)-1H-pyrazole-1- carbodithioate

The Raman and infrared spectra of solid methyl-5-amino-4-cyano-3-(methylthio)-1H-pyrazole-1-carbodithioate (MAMPC, C7H8N4S3) were measured in the spectral range of 3700-100 cm(-1) and 4000-200 cm(-1) with a resolution of 4 and 0.5 cm(-1), respectively. Room temperature 13C NMR and (1)H NMR spectra from room temperature down to -60 °C were also recorded. As a result of internal rotation around C-N and/or C-S bonds, eighteen rotational isomers are suggested for the MAMPC molecule (Cs symmetry). DFT/B3LYP and MP2 calculations were carried out up to 6-311++G(d,p) basis sets to include polarization and diffusion functions. The results favor conformer 1 in the solid (experimentally) and gaseous (theoretically) phases. For conformer 1, the two -CH3 groups are directed towards the nitrogen atoms (pyrazole ring) and CS, while the -NH2 group retains sp2 hybridization and C-CN bond is quasi linear. To support NMR spectral assignments, chemical shifts (δ) were predicted at the B3LYP/6-311+G(2d,p) level using the method of Gauge-Invariant Atomic Orbital (GIAO) method. Moreover, the solvent effect was included via the Polarizable Continuum Model (PCM). Additionally, both infrared and Raman spectra were predicted using B3LYP/6-31G(d) calculations. The recorded vibrational, 1H and 13C NMR spectral data favors conformer 1 in both the solid phase and in solution. Aided by normal coordinate analysis and potential energy distributions, confident vibrational assignments for observed bands have been proposed. Moreover, the CH3 barriers to internal rotations were investigated. The results are discussed herein are compared with similar molecules whenever appropriate.

Analysis of UV and vibrational spectra (FT-IR and FT-Raman) of hexachlorocyclotriphosphazene based on normal coordinate analysis, MP2 and DFT calculations

The Raman (1400-100 cm(-1)) and infrared (4000-400 cm(-1)) of solid hexachlorocyclotriphosphazene, P(3)N(3)Cl(6) (HCCTP) were recorded. The conformational energies were calculated using MP2 and DFT (B3LYP and B3PW91) methods utilizing a variety of basis sets up to 6-311+G(d). On the basis of D(3h) symmetry, the simulated vibrational spectra of P(3)N(3)Cl(6) from MP2 and DFT methods were in excellent agreement with those obtained experimentally. Additionally, Frontier Molecular Orbitals and electronic transitions were predicted using steady state and time dependent DFT(B3LYP)/PCM calculations respectively, each employing the 6-311+G(d,p) optimized structural parameters. The predicted wavelengths were in excellent agreement with experimental values when CH(2)Cl(2) was used as solvent. The (14)N and (31)P chemical shifts were predicted with B3LYP/6-311+G(2d,p) calculations using the GIAO technique with solvent effect modeled using the PCM method. The computed structural parameters of the planar P(3)N(3)Cl(6) (D(3h)) agree well with experimental values from both X-ray and electron diffraction data with slight distortions observed due to lattice defects in the solid phase. The experimental/computational results favor a slightly distorted D(3h) symmetry for the title compound in the gas and solid phases and in solution (τPNPN and τNPNP ranged from 0.018° to 0.90°). Aided by normal coordinate analysis, and the simulated vibrational spectra utilizing MP2, B3LYP and B3PW91 methods at 6-31G(d) basis set, revised and complete vibrational assignments for all fundamentals are provided herein.

Novel fluorinated ferroelectric organosiloxane liquid crystals

A progress report on the synthesis and characterisation of a series of fluorinated chiral bi-mesogen low molar mass organosiloxane materials is presented. The mesogenic moiety is identical to that in the TSiKN65F mono-mesogen material reported by Naciri et al., which displays a de Vries-type SmA* phase. The parameter varied across the series is the length of the alkyl chain linking the mesogen moiety to the siloxane. The material with 10 carbon atoms in the chains displays a stable smectic phase with ferroelectric response at room temperature, whereas the materials with 6, 7 and 8 carbon atoms tend to crystallize.

A Novel Series of Chiral Fluorinated Organosiloxane Liquid Crystals

The synthesis and characterization of a series of chiral fluorinated low molar mass organosiloxane materials is presented. The mesogenic moiety is similar to that in the TSiKN65F mesogen reported by Naciri et al., which displays a de Vries-type SA* phase. The one parameter varied across the series reported herein is the length of the alkyl chain linking the mesogen moiety to the siloxane tail.

Infrared, 1H and 13C NMR spectra, structural charcterization and DFT calculations of novel adenine-cyclodiphosp(V)azane derivatives

Adenine tetrachlorocyclodiphospha(V)zane derivatives (III(a-c)) were prepared by the reaction of hexachlorocyclodiphospha(V)zane derivatives (I(a-c)) and adenine (II) as precursors. The synthesized compounds and their structures (III(a-c)) were firmly characterized (based on the presence of an inversion center) using FT-IR (4000-200 cm(-1)), UV-vis. (190-800 nm), (1)H, (13)C NMR and Mass spectral measurements in addition to C, H, N, P elemental analysis. The compounds (III(a-c)) were found to be a 1:2 molar ratio of (I(a-c)) and adenine (II) adducts, respectively. Confident and complete vibrational assignments are proposed for nearly all fundamental vibrations, along with detailed interpretation for all observed signals in both (1)H and (13)C NMR spectra of the investigated phospha(V)zanes (III(a-c)). In addition, unconstrained geometry optimization of III(a-c) were carried out by means of DFT-B3LYP/3-21G(d) calculations to provide new insight into the structural parameters and molecular geometries of compounds III(a-c). The results are reported herein and compared with similar molecules whenever appropriate.

Design, Synthesis, and Cytotoxicity of 5-Fluoro-2-methyl-6-(4-aryl-piperazin-1-yl) Benzoxazoles

To design new compounds suitable as starting points for anticancer drug development, we have synthesized a novel series of benzoxazoles with pharmaceutically advantageous piperazine and fluorine moieties attached to them. The newly synthesized benzoxazoles and their corresponding precursors were evaluated for cytotoxicity on human A-549 lung carcinoma cells and non-cancer HepaRG hepatocyes. Some of these new benzoxazoles show potential anticancer activity, while two of the intermediates show lung cancer selective properties at low concentrations where healthy cells are unaffected, indicating a selectivity window for anticancer compounds.

The Electro-Optic Response in a Series of Chiral Bi-Mesogen Low Molar Mass Organosiloxane Liquid-Crystal Materials

The electro-optic response of a series of low molar mass bi-mesogen organosiloxane materials is presented. The materials display an unusual response to the electric field. It is argued that the observed behaviour can be explained if the material has two regimes for switching depending on temperature and the amplitude of the applied field. In one regime the two mesogenic moieties of the molecules respond independently of each other like side pendant in polymeric materials and in the other regime the bi-mesogen molecule responds as a single unit like a bent-core molecule.

Synthesis, characterization, computational studies and biological activities of Co(II), Ni(II) and Cu(II) complexes of 2-amino-1,3,4-thiadiazole derivatives

Abstract Co(II), Ni(II), and Cu(II) complexes of 2-Amino-5-ethyl-1,3,4-thiadiazole (AET) and 2-Amino-5-(ethylthio)-1,3,4-thiadiazole (AEST) have been synthesized and characterized based on elemental analysis, magnetic susceptibility, infrared (4000–400 cm−1), mass spectrometry (ESI and MALDI), UV–Vis (200–1100 nm) and thermal analysis (TGA/DTA). Molar conductance measurements proved that [M(L)2(H2O)2]Cl2·H2O are electrolytic complexes where M represents Co, Ni, and Cu divalent metal ions. The geometrical isomerism of [M(L)2(H2O)2]2+ ions were investigated by DFT-B3LYP calculations incorporated in Gaussian09 package; it favored the all trans isomers due to having the lowest energy points on the potential energy surface. The outcome of DFT-B3LYP quantum mechanical calculations using 6-31G(d) basis set favor six-coordinate sites via a bidentate ligand through exo amino and adjacent endo thiadiazole nitrogen (N3) donors. These results were consistent with magnetic measurements combined with infrared and UV–Vis spectral interpretations. The predicted metal–ligand binding energies from B3LYP/6-31G(d) calculations follow the trend Cu2+>Ni2+>Co2+, in agreement with the Irving–Williams series. Both AET and AEST ligands and the synthesized complexes were screened for their antibacterial activity and the outcome was high antimicrobial activity of the complexes compared to the free ligands against one or more microbial species and in some cases (copper complexes) higher activity than standard drugs. Graphical Abstract