Vithaya Ruangpornvisuti

A-D-A Sensors Based on Naphthoimidazoledione and Boronic Acid as Turn-On Cyanide Probes in Water

Three fluorescence sensors based on naphthoquinoneimidazole and boronic acid (A-D-A system) have been developed with high selectivity for cyanide in water. The fluorescence band at 460 nm was switched on upon substitution of cyanide on sensors in the CTAB micelle.

Synthesis of tripodal aza crown ether calix[4]arenes and their supramolecular chemistry with transition-, alkali metal ions and anions

Abstract Tripodal aza crown ether calix[4]arenes, 5a , 5b , 6a and 6b , have been synthesized. The structure of protonated 5a was elucidated by X-ray crystallography to be a self-threaded rotaxane. Complexation studies of 5a and 5b towards anions using Na+ as countercation were carried out by 1H NMR titration in dimethylsulfoxide-d6 and the mixture of chloroform-d and methanol-d4, respectively. Ligands 5a and 5b were able to form 1:1 complexes with Br−, I− and NO3− and the complexation stability varied as follows: NO3−>I−>Br−. The effect of countercation on anion complexation was also investigated. The results showed that the association constants of 5a towards Br− in the presence of various cations varied as K+>Bu4N+>Na+. The enhancement in anion complexation ability of 5a may result from the rearrangement of the tripodal ammonium unit in the presence of K+. The neutral forms, 6a and 6b , were able to form complexes with transition metal ions such as Co2+, Ni2+, Cu2+ and Zn2+. The stability of the complexes followed the sequence: Ni2+ 6a and 6b may, therefore, potentially be used as either transition metal ion or anion receptors that can be controlled by pH of the solution.

Aza crown ether calix[4]arenes containing cation and anion binding sites: effects of metal ions towards anion binding ability

Abstract Tripodal aza crown ether calix[4]arenes containing both cation and anion binding sites ( 5a and 5b ) have been synthesized. The X-ray analysis shows that 5a forms a self-threaded rotaxane-like structure in the solid state. 1 H NMR titrations of the two ligands with various halide anions indicate that 5a and 5b can form complexes with Br − and I − but not F − . However, both compounds form more stable complexes with I − than with Br − in the presence of Bu 4 N + . The presence of K + enhances the binding ability of 5a towards Br − .

Deacetylation affects the physical properties and bioactivity of acemannan, an extracted polysaccharide from Aloe vera.

Acemannan, an acetylated polymannose from Aloe vera, induces tissue repair. We investigated the role of acemannans acetyl-groups on its physical and biological properties. Deacetylated acemannan (DeAcAM) was prepared and characterized. The physical properties and microscopic structure of DeAcAM were evaluated using water solubility, contact angle, X-ray diffraction, and scanning-electron microscopy. The activity of DeAcAM on cell proliferation and gene expression were assessed. Acemannan and DeAcAM structures were simulated and the acemannan tetramer diad and its completely deacetylated structure were also determined. Increased acemannan deacetylation reduced its water solubility and hydrophilicity. Complete deacetylation altered acemannans conformation to a partial crystal structure. The bioactivity of acemannan was reduced corresponding to its deacetylation. Acemannan induced cell proliferation, and VEGF and Collagen I expression; however, 100% DeAcAM did not. The simulated structures of the acemannan diad and the completely deacetylated diad were different. We conclude acetyl-groups affect acemannans structure and physical/biological properties.

First principles theoretical study of the hole-assisted conversion of CO to CO2 on the anatase TiO2(101) surface.

First principles density functional theory calculations were carried out to investigate the adsorption and oxidation of CO on the positively charged (101) surface of anatase, as well as the desorption of CO(2) from it. We find that the energy gain on adsorption covers the activation energy required for the oxidation, while the energy gain on the latter is sufficient for the desorption of CO(2), leaving an oxygen vacancy behind. Molecular dynamics simulations indicate that the process can be spontaneous at room temperature. The oxidation process described here happens only in the presence of the hole. The possibility of a photocatalytic cycle is discussed assuming electron scavenging by oxygen.

Density functional investigation of hydrogen gas adsorption on Fe−doped pristine and Stone−Wales defected single−walled carbon nanotubes

AbstractThe adsorptions of hydrogen molecule of the Fe − doped pristine and Stone − Wales defected armchair (5,5) single − walled carbon nanotubes (SWCNTs) compared with the pristine SWCNT were investigated by using the density functional theory at the B3LYP/LanL2DZ level. The doping of Fe atom into SWCNTs occurring via an exothermic process was found. The adsorptions of hydrogen molecule on the Fe − doped structures of either perfect or SW defected SWCNTs are stronger than on their corresponding undoped structures. The structural and electronic properties of the pristine and SW defected SWCNTs, their Fe − doped structures and their hydrogen molecule adsorptions are reported. FigureThe adsorptions of hydrogen molecule of the Fe−doped pristine and defected (5,5) single−walled carbon nanotubes (SWCNTs) compared with the pristine SWCNT were computed. The adsorptions of hydrogen molecule on the Fe−doped structures of either perfect or defected SWCNTs are stronger than on their corresponding undoped structures

Density functional investigation of CO adsorption on Ni-doped single-walled armchair (5,5) boron nitride nanotubes

AbstractThe adsorption of CO onto Ni-doped boron nitride nanotubes (BNNTs) was investigated using density functional theory at the B3LYP/LanL2DZ level of theory. The structures of the Ni-doped BNNTs and their CO-adsorbed configurations were obtained. It was found that the strength of adsorption of CO onto Ni-doped perfect BNNTs is higher than that on defective BNNTs. The electronic properties of all of the adsorption configurations of CO on Ni-doped BNNTs are reported. FigureThe optimized structures of CO adsorption on Ni-doped BNNTs

A density functional theory study on peptide bond cleavage at aspartic residues: direct vs cyclic intermediate hydrolysis

In this work, peptide bond cleavages at carboxy- and amino-sides of the aspartic residue in a peptide model via direct (concerted and step-wise) and cyclic intermediate hydrolysis reaction pathways were explored computationally. The energetics, thermodynamic properties, rate constants, and equilibrium constants of all hydrolysis reactions, as well as their energy profiles were computed at the B3LYP/6-311++G(d,p) level of theory. The result indicated that peptide bond cleavage of the Asp residue occurred most preferentially via the cyclic intermediate hydrolysis pathway. In all reaction pathways, cleavage of the peptide bond at the amino-side occurred less preferentially than at the carboxy-side. The overall reaction rate constants of peptide bond cleavage of the Asp residue at the carboxy-side for the assisted system were, in increasing order: concerted < step-wise < cyclic intermediate.

Conformational and energetical structures of sulfonylcalix[4]arene, p-tert-butylsulfonylcalix[4]arene and their zinc complexes

Abstract The p -tert-butylsulfonylcalix[4]arene and sulfonylcalix[4]arene conformers have been obtained by AM1 geometry optimizations. The structural cavities of p -tert-butylsulfonylcalix[4]arene and sulfonylcalix[4]arene conformers of which phenol groups are bridged by sulfonyl sulfur have been compared to the calix[4]arene and thiacalix[4]arene. The conformational energies of p -tert-butylsulfonylcalix[4]arene have been compared with the energies of sulfonylcalix[4]arene, calix[4]arene and thiacalix[4]arene. The most stable conformer of sulfonylcalix[4]arene and p -tert-butylsulfonylcalix[4]arene are 1,2-alternate and 0011-AAAA 1,2-alternate conformers, respectively. Two different types of hydrogen bond presented in the sulfonylcalix[4]arene cone and partial cone conformers and p -tert-butylsulfonylcalix[4]arene cone conformer have been found. Ab initio energies of the AM1-optimized structures of sulfonylcalix[4]arene and p -tert-butylsulfonylcalix[4]arene conformers and their complexes with zinc(II) have been computed at HF/6-31G* and B3LYP/6-31G* theoretical levels. The optimized structure of complex species of p -tert-butylsulfonylcalix[4]arene with zinc(II) is in good agreement with recent X-ray geometry data.

Synthesis of stilbene crown ether p-tert-butylcalix[4]arenes

Photo-switchable calixarene crown ether derivatives were synthesized in order to control the ring sizes and shapes of ionophores by isomerization between two different geometrical isomers. Five stilbene crown ether calix[4]arenes were prepared via McMurry coupling of the corresponding bisbenzaldehyde–calix[4]arene derivatives. The coupling reactions yielded both cis- and trans-stilbenes from o- and m-bisbenzaldehydes while only the cis-isomer was obtained from the reaction of the p-isomer. Unlike diazobenzene analogues, the stilbene crown ether calix[4]arene derivatives did not undergo thermal isomerization. Nevertheless, the isomerization of all synthesized stilbene crown ether calix[4]arenes can be photochemically induced.