2,4-Dimethyl-1,3-thiazole-5-carboxylic acid: an X-ray structural study at 100 K and Hirshfeld surface analysis.

The crystal structure of the title thiazolecarboxylic acid derivative, C(6)H(7)NO(2)S, (I), has been determined from single-crystal X-ray analysis at 100 K. In the crystal packing, an interplay of O-H···N and C-H···O hydrogen bonds connects the molecules to form C(6)R(2)(2)(8) polymeric chains, which are further linked via weak C-H···O hydrogen bonds into a two-dimensional supramolecular framework. The relative contributions of different interactions to the Hirshfeld surface in (I) and a few related thiazolecarboxylic acid derivatives indicate that the H···H, N···H and O···H contacts can account for about 50-70% of the total Hirshfeld surface area in this class of compound.

Synthesis of selenoxo peptides and oligoselenoxo peptides employing LiAlHSeH.

Synthesis of selenoxo peptides by the treatment of N(α)-protected peptide esters with a combination of PCl(5) and LiAlHSeH is delineated. The method is simple, high-yielding, and free from racemization. Thus obtained selenoxo peptides are used as units for N-terminal chain extension through N(α)-deprotection/coupling to yield peptide-selenoxo peptide hybrids. Multiple selenation is demonstrated by conversion of two peptide bonds of tripeptides into selenoxo peptide bonds. Amino acid derived arylamides are also converted into aryl selenoamides. C(6)H(5)-CSeNH-Val-OMe 8f is obtained as single crystal, and its structure was determined through X-ray diffraction study.

A new half-condensed Schiff base compound: highly selective and sensitive pH-responsive fluorescent sensor.

A new probe, 3-[(3-benzyloxypyridin-2-ylimino)methyl]-2-hydroxy-5-methylbenzaldehyde (1-H) behaves as a highly selective fluorescent pH sensor in a Britton-Robinson buffer at 25 °C. The pH titrations show a 250-fold increase in fluorescence intensity within the pH range of 4.2 to 8.3 with a pK(a) value of 6.63 which is valuable for studying many of the biological organelles.

Molecular dynamics study and electronic structure evolution of a DNA duplex d(CCCGATCGGG)2.

The molecular dynamics simulations and electronic structure evolution of a A-DNA decamer, d(CCCGATCGGG)(2), in the presence and absence of [Co(NH(3))(6)](3+) ions have been investigated. In both cases, the results of 2.5 ns MD simulation indicate a A-DNA→B-DNA transition. Ab initio DFT calculations were performed on a series of conformations representing the A→B transitions to reveal the dynamical behavior of the electronic structure of the decamer. The results suggest that the conformational parameters as well as the surrounding environment have no direct correlation with the electronic structures. Instead, the thermal fluctuations play an important role in the electronic structure of the present DNA system.

A highly selective fluorescent chemosensor for zinc ion and imaging application in living cells.

A new 2,6-bis(5,6-dihydrobenzo[4,5]imidazo[1,2-c]quinazolin-6-yl)-4-methylphenol (1) serves as a highly selective and sensitive fluorescent probe for Zn(2+) in a HEPES buffer (50 mM, DMSO:water = 1:9 (v/v), pH = 7.2) at 25 °C. The increase in fluorescence in the presence of Zn(2+) is accounted for by the formation of dinuclear Zn(2+) complex [Zn(2)(C(35)H(25)N(6)O)(OH)(NO(3))(2)(H(2)O)] (2), characterized by X-ray crystallography. The fluorescence quantum yield of the chemosensor 1 is only 0.019, and it increases more than 12-fold (0.237) in the presence of 2 equiv of the zinc ion. Interestingly, the introduction of other metal ions causes the fluorescence intensity to be either unchanged or weakened. By incubation of cultured living cells (A375 and HT-29) with the chemosensor 1, intracellular Zn(2+) concentrations could be monitored through selective fluorescence chemosensing.

4-(3,5-Dimethyl-1H-pyrazol-4-ylmethyl)-3,5-dimethyl-1H-pyrazol-2-ium dihydrogen phosphate: a combined X-ray and DFT study.

The molecular structure of the title salt, C(11)H(17)N(4)(+).H(2)PO(4)(-), has been determined from single-crystal X-ray analysis and compared with the structure calculated by density functional theory (DFT) at the BLYP level. The crystal packing in the title compound is stabilized primarily by intermolecular N-H...O, O-H...N and O-H...O hydrogen bonds and pi-pi stacking interactions, and thus a three-dimensional supramolecular honeycomb network consisting of R(4)(2)(10), R(4)(4)(14) and R(4)(4)(24) ring motifs is established. The HOMO-LUMO energy gap (1.338 eV; HOMO is the highest occupied molecular orbital and LUMO is the lowest unoccupied molecular orbital) indicates a high chemical reactivity for the title compound.

2,2'-Diazinodimethylidyne)di-o-phenyl-ene) dibenzoate.

The title compound, C(28)H(20)N(2)O(4), was synthesized by the reaction of 2-(hydrazonometh-yl)phenyl benzoate with iodine. The mol-ecule possesses a crystallographically imposed center of symmetry at the mid-point of the hydrazine N-N bond. The substituents at the ends of the C=N bonds adopt an E,E configuration. Inter-molecular C-H⋯π(arene) hydrogen bonds and aromatic π-π stacking inter-actions [centroid-centroid distance 3.900 (1) Å] link the mol-ecules into (100) sheets. In addition, there is an inter-molecular C-H⋯O hydrogen-bond inter-action.

Dimethyl 6-methoxy-4abeta-methyl-9-oxo-1,2,3,4,4a,9,10,10abeta-octahydrophenanthrene-1,1-dicarboxylate.

In the title tricyclic keto-diester, C(20)H(24)O(6), a potential intermediate in the synthesis of bioactive podocarpic acid, the outer cyclohexane ring (in a chair conformation) is cis fused to the central cyclohexanone ring (in a half-chair conformation). The conformational analysis of the compound, investigated by semi-empirical quantum mechanical AM1 calculations, shows a good agreement with the X-ray structure, except for the orientation of the methyl, methoxyphenyl and methoxycarbonyl substituents.

(1SR,2RS,5RS,6SR,8RS)-7,7-Dimethyltricyclo[6.2.1.0(1,6)]undecane-2,5,6-triol: a supramolecular framework built from O-H...O hydrogen bonds.

In the title compound, C(13)H(22)O(3), the asymmetric unit has two independent molecules linked by a strong O-H...O hydrogen bond. The cyclohexane ring is trans fused to the cyclopentane ring bridged through an ethyl moiety. The hydroxyl groups act as donors as well as acceptors, resulting in an extensive two-dimensional hydrogen-bonded network in the (011) plane. Intermolecular O-H...O bonds between centrosymmetrically related molecules form a four-membered supramolecular assembly, leading to infinite chains parallel to the [011] direction, crosslinked in the [100] direction.