Optical sensing of hydrogen sulphate using rhodamine 6G hydrazide from aqueous medium.

This communication reports the application of rhodamine 6G hydrazide (L) for the selective colorimetric and turn-on fluorescent sensing of hydrogen sulphate ions from aqueous medium. The ring opening of the colourless spirocyclic form of L was selectively triggered in the presence of HSO4- among the other tested anions (F-, Cl-, Br-, I-, AcO-, H2PO4-, NO3-, ClO4-, CN-, HO-, AsO33- and SO42-), which gives rise to a pink colour and strong fluorescence in the visible region. Sensor L showed a detection limit down to micromolar range without any interference from the other tested competitive anions. Sensor L was applied for the construction of two inputs (HO- and HSO4-) INHIBIT type molecular logic gate and naked-eye detection of HSO4- using test paper strips.

Acetate selective fluorescent turn-on sensors derived using vitamin B6 cofactor pyridoxal-5-phosphate.

Two new Schiff base receptors have been synthesized by condensation of pyridoxal-5-phosphate with 2-aminophenol (L(1)) or aniline (L(2)). In DMSO, the receptors showed both chromogenic and 'turn-on' fluorescence responses selectively in the presence of AcO(-) and F(-). However, in mixed DMSO-H2O medium, the receptors showed AcO(-) selective 'turn-on' fluorescence without any interference from other tested anions including F(-). The detection limit for AcO(-) was found to be 7.37 µM and 22.9 µM using the receptors L(1) and L(2), respectively.

An aqueous friendly chemosensor derived from vitamin B6 cofactor for colorimetric sensing of Cu²âº and fluorescent turn-off sensing of Fe³âº.

Chemosensor L derived from vitamin B6 cofactor pyridoxal-5-phosphate was investigated for the selective detection of Cu(2+) and Fe(3+) in aqueous medium. Sensor L formed a 1:1 complex with Cu(2+) and displays a perceptible color change from colorless to yellow brown with the appearance of a new charge transfer band at ~450 nm. In contrast, the fluorescence of L was quenched selectively in the presence of Fe(3+) without any interference from other metal ions including Cu(2+).

Design, synthesis and ¹H NMR study of C3v-symmetric anion receptors with urethane-NH as recognition group.

C3v-Symmetric anion receptors 3 and 4 with urethane groups were synthesized by using trindane triol as tripodal molecular framework. In (1)H NMR titration study, the receptors showed noticeable downfield shift/disappearance of the urethane-NH peak in presence of H2PO4(-) and F(-) due to the host-guest complexation occurred through multiple hydrogen bonding and/or the deprotonation of urethane-NH groups. Other tested anions such as Cl(-), Br(-), HSO4(-), and NO3(-) showed either no or negligible chemical shift of the urethane groups. The deprotonation event in 4 allowed selective detection of F(-) by perceptible color change from colorless to yellowish-red with the appearance of a new charge transfer absorption band at 450 nm.

Virgin silver nanoparticles as colorimetric nanoprobe for simultaneous detection of iodide and bromide ion in aqueous medium.

A simple colorimetric nanoprobe based on virgin silver nanoparticles (AgNPs) was developed for the selective detection of iodide and bromide ions via aggregation and anti-aggregation mechanism. With addition of I(-) ions, virgin AgNPs, in presence of Fe(3+), showed perceptible color change from yellow to colorless along with disappearance of surface plasmon resonance (SPR) band of AgNPs at 400 nm. But in presence of Cr(3+), AgNPs turned yellow upon addition of I(-)and Br(-) anions. The developed virgin AgNPs probe showed high specificity and selectivity with the detection limits down to 0.32 µM and 1.32 µM for I(-) ions via two different mechanistic routes. Also, the designed probe detects Br(-) with a detection limit down to 1.67 µM.

Remarkable change in fluorescence emission of poly(diphenylacetylene) film via in situ desilylation reaction: correlation with variations in microporous structure, chain conformation, and lamellar layer distance.

Fluorescence (FL) emission properties, microporous structures, energy-minimized chain conformations, and lamellar layer structures of the silicon-containing poly(diphenylacetylene) derivative of p-PTMSDPA before and after desilylation were investigated. The nitrogen-adsorption isotherms of p-PTMSDPA film before and after desilylation were typical of type I, indicating microporous structures. The BET surface area and pore volume of the p-PTMSDPA film were significantly reduced after the desilylation reaction, simultaneously, its FL emission intensity remarkably decreased. The theoretical calculation on both model compounds of p-PTMSDPA and its desilylated polymer, PDPA, showed a remarkable difference in chain conformation: The side phenyl rings of p-PTMSDPA are discontinuously arranged in a zig-zag pattern, while the PDPA is continuously coiled in a helical manner. The lamellar layer distance (LLD) in the p-PTMSDPA film significantly decreased after the desilylation reaction.

Substitution position effect on photoluminescence emission and chain conformation of poly(diphenylacetylene) derivatives.

The significant variation in photoluminescence emission of poly(diphenylacetylene) derivatives according to the substitution position is due to the differences in the intramolecular pi-stack structure and chain conformation.

New deep cavitand with imidazoquinoxaline flaps: formation of static helical alkane inclusion complexes by enhanced CH/pi interactions.

A new deep imidazoquinoxaline cavitand formed static helical alkane inclusion complexes by CH/pi stabilization of alkanes with the enlarged aromatic pi surfaces of the cavity inside.

Multivariate approach to the Fenton process for the treatment of landfill leachate.

Fenton process has been widely used to treat landfill leachate. The "design of experiments" methodology was used to study the main variables affecting the Fenton process as well as their most relevant interactions. Results of two-level-factorial-design indicated that pH, COD, and the interaction of pH and COD gave negative effects, but Fe(II) dosage and H(2)O(2)/Fe(II) mole ratio showed positive effect, respectively. The quadratic model was derived based on the results of both two-level-factorial-design experiment and further runs of star points and center points. The response surface plots of quadratic model were obtained accordingly and the optimal conditions were derived from the quadratic model.

Building a novel vitronectin assay by immobilization of integrin on calixarene monolayer.

Membrane proteins possess significant hydrophobic domains and are likely to deplete their native activity immobilized on the solid surface relative to those occurring in a membrane environment. To investigate an efficient immobilization method, calix[4]crown-ether monolayer as an artificial protein linker system was constructed on the gold surface and characterized by Fourier transform infrared reflection absorption spectroscopy (FTIR-RAS), atomic force microscopy (AFM) and cyclic voltammetry (CV). Integrin alpha(v)beta3 was functionally immobilized onto the monolayer and the integrin-vitronectin interaction was investigated by surface plasmon resonance (SPR). It was found that calix[4]crown-ether was assembled as a monolayer on the gold surface. Orientation and accessibility of integrin alpha(v)beta3 was assessed by sensitive binding of its natural ligand, vitronectin at pg mL(-1) level. Moreover, surface coverage of integrin layer and thickness calculated through SPR curve simulation verified that integrin layer was a monolayer in activated form. In combination with the SPR method, this calix[4]crown monolayer provided a reliable and simple experimental platform for the investigation of isolated membrane proteins under experimental conditions resembling those of their native properties.

Cation selectivity of ionophores based on tripodal thiazole derivatives on benzene scaffold.

The synthesis and potentiometric evaluation of new 1,3,5-tris(thiazolylcarbethoxy)-2,4,6-trimethylbenzene (3), 1,3,5-tris(thiazolylhydroxy)-2,4,6-trimethylbenzene (4), 1,3,5-tris(thiazolylmethyl)-2,4,6-trimethylbenzene (5), and 1,3,5-tris(thiazolylphenyl)-2,4,6-trimethylbenzene (6), toward mono and divalent cations under various pH conditions are outlined. The ion-selective properties of the newly synthesized compounds were studied by measuring the potentiometric responses of the 3-, 4-, 5-, and 6-based membrane electrodes to alkali metal, alkaline earth metal, ammonium, and transition metal ions, under various pH conditions. The 3-based electrode exhibited a Nernstian response to ammonium and potassium under alkaline pH conditions, while the other three electrodes showed a poor potentiometric performance. All electrodes showed substantial responses to silver ion under acidic condition, but there was almost nil response to other transition metal ions (Fe(2+), Co(2+), Zn(2+), Ni(2+), Pb(2+), Cd(2+), Cu(2+) and Hg(2+)). The 3- and 5-based electrodes resulted in near Nernstian responses (51.3mV and 59.5mV/pAg(+), respectively) with low detection limits (approximately 100ppt), while the 4- and 6-based ones showed sub-Nernstian below 40mV/pAg(+). The results were interpreted with semi-empirically modeled structures.

Enhancement of BSA Binding on Au Surfaces by calix[4]bisazacrown Monolayer.

Effective investigation of biomolecular structure and function with chip-basedmodern instruments often requires reliable and steady attachment of designatedbiomolecules on substrate. Here, we investigated the formation of self-assembled monolayer(SAM) with a new calix[4]arene derivative containing bisazacrown ether at the lower rim(calix[4]bisazacrown) where ammonium moieties of proteins can mainly be interacted with.Immobilization process of protein using bovine serum albumin (BSA) on the Au surfacemodified with calix[4]bisazacrown monolyer as an artificial linker system was monitored bysurface plasmon resonance (SPR) technique. The surface concentration of BSA calculatedby the simulation of SPR experimental data was higher than that of a well-known similarcommercial protein linker. These results can help in modeling and understanding of proteinimmobilization on solid surface as well as further development lab-on-a-chip (LOC) devicesfor biomedical diagnosis kit of certain protein related diseases as biomarkers.

Treatment of landfill leachate by Fenton's reagent in a continuous stirred tank reactor.

The treatment of landfill leachate by Fenton process was carried out in a continuous stirred tank reactor (CSTR). The effect of operating conditions such as reaction time, hydraulic retention time, pH, H(2)O(2) to Fe(II) molar ratio, Fenton's reagent dosage, initial COD strength, and temperature on the efficacy of Fenton process was investigated. It is demonstrated that Fenton's reagent can effectively degrade leachate organics. Fenton process reached the steady state after three times of hydraulic retention. The oxidation of organic materials in the leachate was pH dependent and the optimal pH was 2.5. The favorable H(2)O(2) to Fe(II) molar ratio was 3, and organic removal increased as dosage increased at the favorable H(2)O(2) to Fe(II) molar ratio. Temperature gave a positive effect on organic removal.

Optimization of Fenton process for the treatment of landfill leachate.

The treatment of landfill leachate by Fenton process was carried out in a batch reactor. The effect of operating conditions such as reaction time, pH, H2O2 to Fe(II) molar ratio, Fenton's reagent dosage, initial COD strength, feeding mode, the type of polymer, and temperature on the efficacy of Fenton process was investigated. It is demonstrated that Fenton's reagent can effectively degrade leachate organics. Fenton process was so fast that it was complete in 30 min. The oxidation of organic materials in the leachate was pH dependent and the optimal pH was 2.5. The favorable H2O2 to Fe(II) molar ratio was 1.5, and organic removal increased as dosage increased at the favorable H2O2 to Fe(II) molar ratio. The efficacy of Fenton process was improved by adding Fenton's reagent in multiple steps than that in a single step. Furthermore, the stepwise addition of both hydrogen peroxide and ferrous iron was more effective than that of hydrogen peroxide only. Sludge settling characteristics were much improved with the addition of the proper polymer. Temperature gave a positive effect on organic removal.

Structural properties of benzimidazole cavitand and its selective recognition toward 4-methylbenzamide over 4-methylanilide.

The conformations and properties of cavitand 5 with four benzimidazole flaps are studied by (1)H NMR. The benzimidazole cavitand 5 can form very stable vase structures with an enforced concave cavity by intermolecular hydrogen bonding with four hydroxyl-containing molecules, X-OH, such as methanol (X = Me), acetic acid (X = CH(3)CO), and trifluoroacetic acid (X = CF(3)CO). The stronger hydrogen bond donor strengths of X-OH are, the stronger hydrogen bonds are formed between the NH and N atoms of the neighboring benzimidazole fragments and the more vase structures of 5.4HOX are stable. The annular tautomerism of 5 in CDCl(3)/CD(3)OD (9:1, v/v) due to the proton exchange between NH and N atoms of the neighboring benzimidazole fragments is observed by 400 MHz (1)H NMR, and the free energy of activation is measured as DeltaG++(210) = 10.2 kcal/mol at a coalescence temperature of 210 K. Cavitand 5 forms inclusion complexes with 4-methylbezamide guests such as 4-methyl-N-p-tolylbenzamide 6 and N,4-dimethylbenzamide 7 in water-saturated CDCl(3). However, an isomorphic 4-methylanilide guest such as N-4-tolylacetamide 8 cannot be recognized in the concave cavity of 5. This high selectivity toward 4-methylbenzamide over 4-methylanilide seems attributable to the hydrogen-binding interaction between the NH proton of 4-methylbezamide guest 7 and the oxygen atom of the closest water molecule.

Unusually stable molecular capsule formation of a tetraphenyleneurea cavitand.

An unusually stable molecular capsule was formed by heating phenyleneurea-spanned resorcinarene cavitand with 4-methyl-N-p-tolylbenzamide. The molecular capsule behaved as a discrete molecular entity showing a cylindrical D(4d) structure and showed no guest exchange in toluene-d(8) even at 100 degrees C. [structure: see text]

Syntheses, conformations, and basicities of bicyclic triamines.

The multistep syntheses of several bicyclic triamines are described, all of which have an imbedded 1,5,9-triazacyclododecane ring. In 1,5,9-triazabicyclo[7.3.3]pentadecanes 12, 13, 15, and 16, two nitrogens are bridged by three carbons. The monoprotonated forms of these triamines are highly stabilized by a hydrogen-bonded network involving the bridge and both bridgehead nitrogens, producing a difference of more than 8 pK(a) units in acidities of their monoprotonated and diprotonated forms. The one- and zero-carbon bridges in 1,5,9-triazabicyclo[9.1.1]tridecane (23) and 7-methyl-1,5,9-triazabicyclo[5.5.0]dodecane (39) do not enhance the stabilities of their monoprotonated forms. X-ray crystal structures and computational studies of 12.HI and 16.HI reveal similar, but somewhat weaker, hydrogen-bonded networks, relative to 15.HI. The activation free energies for conformational inversion of 13.HI (14.4 +/- 0.2 kcal/mol), 16.HI (15.0 +/- 0.1 kcal/mol) and 16 (8.8 +/- 0.3 kcal/mol) were measured by variable-temperature (1)H and (13)C NMR spectroscopy. These experimental barriers give an estimate of 6.2 kcal/mol for the strength of the bifurcated hydrogen bond between the bridge nitrogen and cavity proton in 16.HI. Computational studies support the hypothesis that N-inversion occurs in an open conformation, leading to an estimate of 10.32 kcal/mol for the enthalpy of the bifurcated hydrogen bond in 16.HI in the gas phase.

The Anti-HIV potency of cyclotriazadisulfonamide analogs is directly correlated with their ability to down-modulate the CD4 receptor.

9-Benzyl-3-methylene-1,5-di-p-toluenesulfonyl-1,5,9-triazacyclododecane (CADA) has been identified as a novel antiviral lead compound with significant anti-human immunodeficiency virus and anti-human herpesvirus 7 activity. Surprisingly, this compound selectively decreased the expression of the CD4 glycoprotein, the primary receptor needed for the entry of both viruses. Herein, we describe the CD4 down-modulating and antiviral potencies of more than 25 CADA derivatives. Flow cytometric evaluation of cellular CD4 receptor expression in T cells demonstrated the specific CD4 down-modulating capacity of the CADA derivatives, with IC(50) values similar to those obtained in the antiviral assays. The close correlation observed between the CD4 down-regulating and anti-HIV potencies of the CADA derivatives further points to CD4 receptor down-modulation as the primary mode of antiviral action for this group of compounds.

Formation of a self-assembled phenylboronic acid monolayer and its application toward developing a surface plasmon resonance-based monosaccharide sensor.

For the surface-optoelectronic study of sugar sensing, we synthesized and characterized dithiobis(4-butyrylamino-m-phenylboronic acid) (DTBA-PBA) as a recognition molecule. DTBA-PBA has a boronic acid group that has been known to form covalently bonded complexes with the 1,2- or 1,3-diol of sugars. A self-assembled monolayer (SAM) of DTBA-PBA was formed on a gold surface and characterized by atomic-force microscopy, Fourier transform infrared reflection absorption spectroscopy, and surface electrochemical measurements. An interaction study between monosaccharides and DTBA-PBA SAM was performed using surface plasmon resonance spectroscopy. The increase in molecular interactions between DTBA-PBA SAM and monosaccharides resulted in an optically induced electron excitation change on the Au surface through a refractive index change of the interfacial recognition layer. This correlation between electron excitation and molecular interaction was measurable at very low monosaccharide concentrations (1.0 x 10(-12)M). DTBA-PBA SAM shows a selective fructose sensing among four kinds of monosaccharides, even in a low concentration range.