Tze Shyang Chia

Molecular structure, second- and third-order nonlinear optical properties and DFT studies of a novel non-centrosymmetric chalcone derivative: (2E)-3-(4-fluorophenyl)-1-(4-{[(1E)-(4-fluorophenyl)methylene]amino}phenyl)prop-2-en-1-one

In the present work, the title chalcone, (2E)-3-(4-fluorophenyl)-1-(4-{[(1E)-(4-fluorophenyl) methylene]amino}phenyl)prop-2-en-1-one (abbreviated as FAMFC), was synthesized and structurally characterized by single-crystal X-ray diffraction. The compound is crystallized in the monoclinic system with non-centrosymmetric space group P21 and hence it satisfies the essential condition for materials to exhibit second-order nonlinear optical properties. The molecular structure was further confirmed by using FT-IR and 1H NMR spectroscopic techniques. The title crystal is transparent in the Vis-NIR region and has a direct band gap. The third-order nonlinear optical properties were investigated in solution (0.01M) by Z-scan technique using a continuous wave (CW) DPSS laser at the wavelength of 532nm. The title chalcone exhibited significant two-photon absorption (β=35.8×10-5cmW-1), negative nonlinear refraction (n2=-0.18×10-8cm2W-1) and optical limiting (OL threshold=2.73kJcm-2) under the CW regime. In support of the experimental results, a comprehensive theoretical study was carried out on the molecule of FAMFC using density functional theory (DFT). The optimized geometries and frontier molecular orbitals were calculated by employing B3LYP/6-31+G level of theory. The optimized molecular structure was confirmed computationally by IR vibrational and 1H NMR spectral analysis. The experimental UV-Vis-NIR spectrum was interpreted using computational chemistry under time-dependent DFT. The static and dynamic NLO properties such as dipole moments (μ), polarizability (α), and first hyperpolarizabilities (β) were computed by using finite field method. The obtained dynamic first hyperpolarizability β(-2ω;ω,ω) at input frequency ω=0.04282a.u. is predicted to be 161 times higher than urea standard. The electronic excitation energies and HOMO-LUMO band gap for FAMFC were also evaluated by DFT. The experimental and theoretical results are in good agreement, and the NLO study suggests that FAMFC molecule can be a potential candidate in the nonlinear optical applications.

3,3′-[1,2-Phenyl­enebis(methyl­ene)]bis­(1-propyl­benzimidazolium) dibromide hemihydrate

The asymmetric unit of the title compound, C28H32N4 2+·2Br−·0.5H2O, contains one 3,3′-[1,2-phenylenebis(methylene)]bis(1-propylbenzimidazolium) cation, two bromide anions and one half-molecule of water. In the crystal, the whole 3,3′-[1,2-phenylenebis(methylene)]bis(1-propylbenzimidazolium) cation and one of the bromide anions are each disordered over two positions with site-occupancy ratios of 0.751 (6):0.249 (6) and 0.680 (8):0.320 (8). For the major component of the disordered cation, the central benzene ring forms dihedral angles of 83.6 (5) and 88.2 (4)° with its adjacent imidazole rings, while these angles for the minor component are 89.2 (15) and 84.9 (13)°. In the crystal, the cations and anions are linked by C—H⋯Br hydrogen bonds into dimers and then stacked along the c axis. The crystal packing is further stabilized by C—H⋯π and π–π interactions [shortest centroid–centroid distance = 3.646 (4) Å].

Synthesis and Crystal Structures of N-Substituted Pyrazolines

Four pyrazole compounds, 3-(4-fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazole-1-carbaldehyde (1), 5-(4-bromophenyl)-3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazole-1-carbaldehyde (2), 1-[5-(4-chlorophenyl)-3-(4-fluorophenyl)-4,5-dihydro-1H-pyrazol-1-yl]ethanone (3) and 1-[3-(4-fluorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazol-1-yl]propan-1-one (4), have been prepared by condensing chalcones with hydrazine hydrate in the presence of aliphatic acids, namely formic acid, acetic acid and propionic acid. The structures were characterized by X-ray single crystal structure determination. The dihedral angles formed between the pyrazole and the fluoro-substituted rings are 4.64(7)° in 1, 5.3(4)° in 2 and 4.89(6)° in 3. In 4, the corresponding angles for molecules A and molecules B are 10.53(10)° and 9.78(10)°, respectively.

Crystal Structure of Dimeric Flavodoxin from Desulfovibrio gigas Suggests a Potential Binding Region for the Electron-Transferring Partner

Flavodoxins, which exist widely in microorganisms, have been found in various pathways with multiple physiological functions. The flavodoxin (Fld) containing the cofactor flavin mononucleotide (FMN) from sulfur-reducing bacteria Desulfovibrio gigas (D. gigas) is a short-chain enzyme that comprises 146 residues with a molecular mass of 15 kDa and plays important roles in the electron-transfer chain. To investigate its structure, we purified this Fld directly from anaerobically grown D. gigas cells. The crystal structure of Fld, determined at resolution 1.3 Å, is a dimer with two FMN packing in an orientation head to head at a distance of 17 Å, which generates a long and connected negatively charged region. Two loops, Thr59–Asp63 and Asp95–Tyr100, are located in the negatively charged region and between two FMN, and are structurally dynamic. An analysis of each monomer shows that the structure of Fld is in a semiquinone state; the positions of FMN and the surrounding residues in the active site deviate. The crystal structure of Fld from D. gigas agrees with a dimeric form in the solution state. The dimerization area, dynamic characteristics and structure variations between monomers enable us to identify a possible binding area for its functional partners.

Conformational studies of 2-(4-bromophenyl)-2-oxoethyl benzoates

Abstract Phenacyl benzoates possess commercial importance due to their various applications in the fields of synthetic and photochemistry, such as photosensitive blocking groups owing to their ease of cleavage under mild conditions. In the present study, a series of ten new 2-(4-bromophenyl)-2-oxoethyl benzoates 2(a–j), with the general formula Br(C6H4)COCH2OCO(C6H5–nXn), X = Cl, NO2 or NH2, and n = 1 or 2, have been synthesized by reacting 4-bromophenacyl bromide with various substituted benzoic acids using potassium carbonate in DMF medium at room temperature. These reactions proceeded with ease under mild conditions producing high purity products in good yield. Each product was characterized by mass spectra, elemental analysis and melting points, its 3D structure was confirmed by single-crystal X-ray diffraction studies. The X-ray 3D structures showed the flexibility of the C(=O)–O–C–C(=O) connecting bridge in which 7 out of 10 compounds tend to form a torsion angle in the range of 70 to 91°, whereas the rest are slightly twisted with a torsion angles of –160, 163, 176 and 178°. Their molecular conformations are in good agreement with another 22 related structures. These synthesized compounds were screened for their abilities for DPPH radical scavenging and ferric reducing anti-oxidant power. The results indicate that these compounds displayed mild anti-oxidant ability when compared to the standard anti-oxidant BHT.

3,3′-[1,4-Phenyl­enebis(methyl­ene)]­bis­(1-propyl­benzimidazolium) dichloride dihydrate

The asymmetric unit of the title compound, C28H32N4 2+·2Cl−·2H2O, contains half of a 3,3′-[1,4-phenylenebis(methylene)]bis(1-propylbenzimidazolium) cation, one chloride anion and one water molecule. The complete cation is generated by a crystallographic inversion center. The central benzene ring forms a dihedral angle of 66.06 (11)° with its adjacent benzimidazolium ring system. In the crystal, the cations, anions and water molecules are linked by O—H⋯Cl, C—H⋯O and C—H⋯Cl hydrogen bonds into a three-dimensional network. The crystal packing is further stabilized by π–π interactions, with centroid–centroid distances of 3.5561 (15) and 3.6708 (15) Å.

2-[3,5-Bis-(4-fluoro-phen-yl)-4,5-dihydro-1H-pyrazol-1-yl]-4,6-bis(4-fluoro-phenyl)pyrimidine.

In the title compound, C31H20F4N4, the pyrazole ring adopts an envelope conformation and forms a dihedral angle of 9.91 (6)° with the adjacent pyrimidine ring. The pyrimidine ring forms dihedral angles of 9.23 (6) and 2.16 (5)° with its adjacent fluoro-substituted benzene rings, whereas these angles are 88.22 (6) and 9.66 (6)° for the pyrazole ring and its adjacent benzene rings. In the crystal, molecules are linked by C—H⋯F hydrogen bonds into ribbons along [01-1]. The crystal packing is further stabilized by C—H⋯π and by π–π interactions, with centroid–centroid distances of 3.7428 (7) and 3.7630 (6) Å.

5-Bromo-4-(3,4-dimeth-oxy-phen-yl)thia-zol-2-amine.

In the title compound, C11H11BrN2O2S, the thiazole ring makes a dihedral angle of 53.16 (11)° with the adjacent benzene ring. The two methoxy groups are slightly twisted from the attached benzene ring with C—O—C—C torsion angles of −9.2 (3) and −5.5 (3)°. In the crystal, molecules are linked by a pair of N—H⋯N hydrogen bonds into an inversion dimer with an R 2 2(8) ring motif. The dimers are further connected by N—H⋯O hydrogen bonds into a tape along [-110].

Methyl 4,4''-difluoro-5'-meth-oxy-1,1':3',1''-terphenyl-4'-carboxyl-ate.

In the title compound, C21H16F2O3, the pendant fluorobenzene rings form dihedral angles of 22.22 (12) and 50.74 (11)° with the central benzene ring. In the crystal, molecules are linked by C—H⋯O hydrogen bonds into chains along the a axis. The crystal structure also features C—H⋯π interactions.

3-[(N-Methyl-anilino)meth-yl]-5-(thio-phen-2-yl)-1,3,4-oxadiazole-2(3H)-thione.

In the title compound, C14H13N3OS2, the thiophene ring is disordered over two orientations by ca 180° about the C—C bond axis linking the ring to the rest of the molecule, with a site-occupancy ratio of 0.651 (5):0.349 (5). The central 1,3,4-oxadiazole-2(3H)-thione ring forms dihedral angles of 9.2 (5), 4.6 (11) and 47.70 (7)° with the major and minor parts of the disordered thiophene ring and the terminal phenyl ring, respectively. In the crystal, no significant intermolecular hydrogen bonds are observed. The crystal packing is stabilized by π–π interactions [centroid–centroid distance = 3.589 (2) Å].