"Turn on" electron-transfer-based selective detection of ascorbic acid via copper complexes immobilized on glass

"Turn-on" optical detection of parts-per-million (ppm) levels of ascorbic acid (AA) in water has been determined using a redox-active monolayer on glass.     

Effect of the TBP and water on the complexation of uranyl nitrate and the dissolution of nitric acid into supercritical CO2. A Theoretical Study

We report theoretical studies on the complexation of uranyl nitrate and the dissolution of nitric acid in supercritical CO2 by TBP. According to quantum mechanical calculations, TBP (modeled by trimethyl phosphate TMP) displays stronger hydrogen-bonding interactions with HNO3 than with H2O, and this has been modeled in force-field calculations. Different combinations of water, TBP, and acid are compared in SC-CO2 and simulated by molecular dynamics (MD), demonstrating the importance of TBP and water concentrations. In MD simulations, which started from "random" mixtures of water, TBP, nitric acid, and uranyl nitrate, complexation of uranyl by TBP is observed and the yield increases with the TBP concentration. TBP molecules are also necessary to dissolve nitric acid in the supercritical phase. Indeed, without TBP, nitric acid alone self aggregates via hydrogen-bonding interactions. Adding water to this solution leads to the formation of water microdomains containing the acid and uranyl salts. The simulations show that a high TBP/nitric acid ratio is needed to fully dissolve the acid in the supercritical phase and to form CO2-philic UO2(NO3)2(TBP)2 complexes. The resulting hydrogen-bonding and solvation patterns are analyzed. The results are consistent with experimental observations and provide microscopic views of this important extraction system.     

Amphiphilic Block Copolymers from a Direct and One‐pot RAFT Synthesis in Water

The syntheses of amphiphilic block copolymers are successfully performed in water by chain extension of hydrophilic macromolecules with styrene at 80 °C. The employed strategy is a one‐pot procedure in which poly(acrylic acid), poly(methacrylic acid) or poly(methacrylic acid‐co‐poly(ethylene oxide) methyl ether methacrylate) macroRAFTs are first formed in water using 4‐cyano‐4‐thiothiopropylsulfanyl pentanoic acid (CTPPA) as a chain transfer agent. The resulting macroRAFTs are then directly used without further purification for the RAFT polymerization of styrene in water in the same reactor. This simple and straightforward strategy leads to a very good control of the resulting amphiphilic block copolymers.

     

Design of Supramolecular Cyclodextrin Complex Sensors for Ion and Molecule Recognition in Water

The design and function of novel supramolecular fluoroionophore/cyclodextrin (CyD) complex sensors for ion and molecule recognition in water are reviewed. For the crown ether fluoroionophore/-CyD complex, the dimerization of the fluoroionophore inside the -CyD is found to be selectively promoted by alkali metal ion binding, thereby resulting in metal-ion-selective pyrene dimer emission in water. This supramolecular function is successfully utilized in the design of a podand fluoroionophore/-CyD complex for sensing toxic lead ion in water. The boronic acid fluoroionophore/-CyD complex binds sugars and produces increased fluorescence emission in water. The response mechanism appears to be due to the suppression of the photoinduced electron transfer (PET) from pyrene donor to trigonal phenylboronic acid acceptor. This is a novel emission function provided by the boronic acid fluoroionophore/-CyD complex sensors in water.     

Two strategies for the self-assembly of gold nanoparticles: Photoreaction and radical reaction

Poly(N-isopropylacrylamide)-b-poly(vinylpyridine) (PNIPAAm-b-PVP) and poly(N-isopropylacrylamide-co-hydroxylethyl methacrylate)-b-poly(vinylphenol) (P(NIPAAm-co-HEMA)-b-PVPhol) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Above two copolymers could form complex in pure water and in DMF/water environment with the DMF content lower than 40% by hydrogen bondings. The morphologies of the complex were investigated by transmission electron microscope (TEM). It was found that the dimension of the complex in strong acid (pH 1.0) or base environment (pH 12.0) was smaller than the one in weak acid or in neutral environment. After the shell cross-linking of the complex, the complex showed a type of "swollen" state in acid or base environment which is similar to the properties of microgel.     

Water mediated proton transfer in a mesostructured aluminosilicate framework: an ab initio molecular dynamics study

The proton transfer process mediated by water molecules adsorbed in an aluminosilicate framework has been studied using ab initio molecular dynamics simulations. This investigation has been carried out using a quasi-one-dimensional model simulating the mesoporous aluminosilicate channel structures. The effects of both the water loading and temperature of the system have been considered. At low coverage (one water molecule per acid site), the hydroxonium ion (H(3)O)(+) is found to be a transition state, in agreement with earlier studies on zeolites. At a higher water coverage (two water molecules per acid site), the (H(5)O(2))(+) species and the hydrogen bonded "neutral complex" structure are both found to be stable complexes at finite temperatures. The vibrational frequency spectrum is simulated by performing a Fourier transform of the velocity autocorrelation function (VAF), and the peak positions in the VAF are compared with IR measurements and zero-temperature calculations.     

Subcritical Water Hydrolysis of Peptides: Amino Acid Side-Chain Modifications

Previously we have shown that subcritical water may be used as an alternative to enzymatic digestion in the proteolysis of proteins for bottom-up proteomics. Subcritical water hydrolysis of proteins was shown to result in protein sequence coverages greater than or equal to that obtained following digestion with trypsin; however, the percentage of peptide spectral matches for the samples treated with trypsin were consistently greater than for those treated with subcritical water. This observation suggests that in addition to cleavage of the peptide bond, subcritical water treatment results in other hydrolysis products, possibly due to modifications of amino acid side chains. Here, a model peptide comprising all common amino acid residues (VQSIKCADFLHYMENPTWGR) and two further model peptides (VCFQYMDRGDR and VQSIKADFLHYENPTWGR) were treated with subcritical water with the aim of probing any induced amino acid side-chain modifications. The hydrolysis products were analyzed by direct infusion electrospray tandem mass spectrometry, either collision-induced dissociation or electron transfer dissociation, and liquid chromatography collision-induced dissociation tandem mass spectrometry. The results show preferential oxidation of cysteine to sulfinic and sulfonic acid, and oxidation of methionine. In the absence of cysteine and methionine, oxidation of tryptophan was observed. In addition, water loss from aspartic acid and C-terminal amidation were observed in harsher subcritical water conditions.

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Crystalline hydrates of calix[4]arene-<Emphasis Type="Italic">para</Emphasis>-sulfonic acid with <Emphasis Type="Italic">n</Emphasis> (<Emphasis Type="Italic">n</Emphasis> = 6–16) water molecules: a structure modeling

The structures of crystalline hydrates of calix[4]arene-para-sulfonic acid with n (n = 6–16) water molecules and the activation barriers to surface proton migration were calculated within the framework of the density functional theory (DFT) using the PBE gradient-corrected functional, the "hard" basis set of projector-augmented waves (PAW), a corresponding pseudopotential, periodic boundary conditions, and the VASP program package. The energies of formation of crystalline hydrates from calix[4]arene-para-sulfonic acid and n water molecules calculated per water molecule are in the range of 0.4–0.9 eV and depend on n. The adsorption energy of water on the surface is in the range of 0.5–0.7 eV. The activation barriers to proton transfer across the surface calculated for the most stable crystal (n = 8) are close to experimental data and depend on the number of superstoihiometric water molecules, being equal to ~0.2 eV provided three superstoihiometric water molecules per surface SO₃H group.     

Acid–Base Behavior in Supercritical Water: β-Naphthoic Acid–Ammonia Equilibrium

Equilibrium constants for the reaction of -naphthoic acid and ammonia, K _BHA, were measured with UV-vis spectroscopy in water from 25°C to 400°C. At high density K _BHA decreases with temperature, the normal behavior for an exothermic reaction of a stronger acid and base to a weaker acid and base. At low density, the reaction becomes endothermic as the solvation of the ionic products becomes weaker. These data were combined with literature results for the dissociation of water and ammonia to determine equilibrium constants for the dissociation of -naphthoic acid and the reaction of -naphthoic acid and OH^- Whereas the density (and dielectric constant) of water have only a modest effect on the isocoulombic reaction of -naphthoic acid and OH^-, they have a large effect on all of the other reactions which are ionogenic.     

Photo-controlled extraction and active transport of amino acids by functional reversed micelles containing spiropyran derivatives

In a reversed micellarn-decane solution, a spiropyran derivative 3,3-dimethyl-1-octadecyl-6-nitrospiro(2H-benzopyran-2,2-indoline) (PC18) showed normal photochromism, and the reversed micelles provided polar microenvironment increasing stability of a zwitterionic merocyanine (MC) form of PC18. Though the reversed micelles of tetraethyleneglycol dodecylether (TEGDE) alone inn-decane had relatively low ability to extract amino acid from aqueous solutions, the PC18-incorporated TEGDE reversed micelles inn-decane showed good photo-controlled extraction of zwitterionic amino acid under UV-irradiation and release under VIS-irradiation. Extent of the extracted amino acid was higher for tryptophane (Trp) bearing hydrophobic side chain than alanine (Ala), showing amino acid selectivity. Photo-driven active transport of amino acid across a liquid membrane was attained by the PC18-incorporated TEGDE reversed micellar carrier in a water/n-decane/water three-phase system, where one side of an aqueous/organic interface was irradiated by the UV-light and the other side by the VIS-light. When Trp and Ala were present in the aqueous solution, Trp was selectively transported.     

LEAFS determination and concentration of metals in Great Lakes ecosystem

A Laser-Excited Atomic Fluorescence Spectrometric (LEAFS) method for Tl determination has been extended to investigate the direct determination (without preconcentration nor acid digestion) of total Pb, for which the method validation was successfully achieved by using a standard reference material as well as many spike recoveries of digested and undigested unfiltered water samples. The method was applied to study total and dissolved Pb in many water columns collected from different stations in Lake Ontario. Dissolved Pb was found to be about twice as much as dissolved Tl, and total Pb about seven times higher than total Tl. Seventy five percent of Pb is in particulate form versus 11% for Tl. Also, a simple cold dissolution procedure using HNO₃ and HF (not a hot acid digestion) is proposed to liquefy sediments in a form suitable for LEAFS analysis and was used to analyze a sediment core, where pore water samples were also collected. The interaction dynamics of Tl within the natural environment of a water/pore water/sediment system from Lake Erie was assessed. The calculations of fluxes suggest a strong similarity between Tl and Cd geochemical transport. The paper also presents for the first time a genuine sediment pore water profile of Tl concentration, which ranged from sub- to 40 ng/l and which was directly determined by LEAFS.     

Interfacial water structure at polymer gel/quartz interfaces investigated by sum frequency generation spectroscopy

Interfacial structures of water at polyvinyl alcohol (PVA) and poly(2-acrylamido-2-methypropane) sulfonic acid sodium salt (PNaAMPS)/quartz interfaces were investigated by sum frequency generation (SFG) spectroscopy. Two broad peaks were observed in OH stretching region at 3200 and 3400 cm(-1), corresponding to the symmetric OH stretching of tetrahedrally coordinated, i.e., strongly hydrogen bonded "ice-like" water, and the asymmetric OH stretching of water in a more random arrangement, i.e., weakly hydrogen bonded "liquid-like" water, respectively, in both cases. The "liquid-like" water became dominant when the PVA gel was pressed against the quartz surface. The relative intensity of the SFG signal due to the "liquid-like" water to that due to the "ice-like water" at the quartz surface modified with a self-assembled monolayer of aminopropyltrimethoxysilane (APS) became higher when the negatively charged PNaMPS gel was contacted to the APS modified quartz surface in a solution of pH = 12, where the surface was negatively charged and electrostatic repulsive interaction and low friction were present between the PNaMPS gel and the APS modified surface. It, however, did not change in a solution of pH = 2, where the surface was positively charged and electrostatic attractive interaction and very high friction were present between the PNaMPS gel and the APS modified surface. These results suggest the important role of water structure for small friction at the polymer gel/solid interface.     

Speciation of arsenic in water samples by high-performance liquid chromatography-hydride generation-atomic absorption spectrometry at trace levels using a post-column reaction system

Anion-exchange HPLC has been combined with hydride generation – atomic absorption spectrometry (HG-AAS) for the routine speciation of arsenite, arsenate, monomethylarsenic acid and dimethylarsinic acid. The sensitivity of the AAS-detection was increased by a post-column reaction system to achieve complete formation of volatile arsines from the methylated species and arsenate. The system allows the quantitative determination of 0.5 g/l of each arsenic compound in water samples. The stability of synthetical and natural water containing arsenic at trace levels was investigated. To preserve stored water samples, a method for quantitative separation of arsenate at high pH-values with the basic anion-exchange resin Dowex 1×8 was developed.     

Fabrication of superhydrophobic surface of stearic acid grafted zinc by using an aqueous plasma etching technique

A stable superhydrophobic surface of stearic acid grafted zinc was fabricated with two steps, that is, the zinc surface was firstly treated with glow discharge electrolysis plasma (GDEP) and then followed by a grafted reaction of stearic acid onto the treated zinc surface. Results indicated that the wettability of zinc substrate changed from superhydrophily to superhyphodrobicity with a water contact angle (CA) up to 158° and a water sliding angle (SA) less than 5°. The surface morphology and composition were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively.      

IR Study of a Polymer Proton-Conducting Electrolyte Based on Poly(vinyl alcohol) and Phenol-2,4-Disulfonic Acid

The structure and hydration of phenol-2,4-disulfonic acid in the individual state and in the system with poly(vinyl alcohol) at low and high humidity levels are studied by IR spectroscopy. It is shown that all characteristic features of the electrolytic dissociation of phenol-2,4-disulfonic acid via proton transfer from acid molecules to the molecules of water in the liquid phase of the binary system phenol-2,4-disulfonic acid–water are also observed for the viscous solutions of the triple system poly(vinyl alcohol)–phenol-2,4-disulfonic acid–water, although differences make themselves evident if water molecules are in deficiency. It is found that evacuation of the phenol-2,4-disulfonic acid film for several hours at room temperature leads to its dehydration and eventually causes formation of molecular dimers [C₆H₃OH(SO₂OH)₂]₂. A similar operation with the poly(vinyl alcohol)–phenol-2,4-disulfonic acid film is completed by the transfer of a proton from the acid molecule to the–ОН group of poly(vinyl alcohol) according to the following scheme: nC₆H₃OH(SO₂OH)₂ + (–CH₂OH) _n → nC₆H₃OH(SO₃)(SO₂OH)^– + (–CH₂OH₂) _n ⁺ .     

Application of the microwave oven to the pretreatment of macrosamples in environmental radioactivity monitoring

In order to reduce the sample pretreatment in the measurements of - and -emitter radionuclides in environmental analysis, we present the application of the microwave oven to dry different environmental macrosamples such as vegetables, milk, meat, fish, soil and sediment. We have also studied this technique to evaporate water (rain water and seawater) and to optimize acid digestion of sediments. The results show that the microwave oven gives good results for drying environmental macrosamples, for evaporating water samples when applied in acid atack. With the porposed procedures, time of analysis shortened dramatically.     

Molecular Recognition of Nucleic Acid Bases in Water by Hydrogen Bonding of Poly(vinyldiaminotriazine)

Poly(2-vinyl-4,6-diamino-1,3,5-triazine) efficiently binds nucleic acid bases and nucleosides in water by using complementary hydrogen bonding. The binding activity decreases in the order: U, T > A C, G. The corresponding monomer shows virtually no activity, indicating a predominant role of polymer effect for the molecular recognition in water.     

Water mediated self assembly of 5-(2-benzoimidazole-1-yl-ethoxy)-3-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid methyl ester through CH⋯O and OH⋯N interactions

Single crystal X-ray structure analysis of 5-(2-benzoimidazole-1-yl-ethoxy)-3-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid methyl ester (2).0.5H₂O provided experimental proof for H?OC, CH?OH and HO?N interactions. The embedded water molecule bridges between molecules 2 via non-covalent interactions. Thus this molecule behaves as a preorganized host molecule for water, presenting a minimum ring-size molecular environment for water binding. Single crystal X-ray structure analysis of 5-(2-benzoimidazole-1-yl-ethoxy)-3-methyl-1-phenyl-1H-pyrazole-4-carboxylic acid methyl esterhemihydrate provided experimental proof for six hydrogen bonds by one molecule of water. The embedded water molecule bridges six molecules by two types of hydrogen bonding. Theoretical calculations showed that the conformation of the bicyclic hetero-ring alters only slightly due to the presence of the water molecule. Thus this organic molecule behaves as a very interesting preorganized host molecule for water, presenting maximum binding environment for water binding.     

Fluorimetric determination of aluminium in water by sequential injection through column extraction

A fluorimetric procedure for the determination of aluminium with matrix removal in drinking water is proposed. The system is based both on the solid phase extraction of aluminium on a new chelating resin (XAD-4 modified by grafting salicylic acid) and the fluorimetric detection of a complex formed between 8-hydroxyquinoline-5-sulfonic acid (HQS) and Al(III), after elution of the resin by hydrochloric acid. The sorption and elution of aluminium were studied in both competitive and non-competitive conditions, varying pH, flow-rates, volume and concentration of reagents, as well as time contact. The optimised procedure allows determination of Al³⁺ at the sub-ppb level (LOD: 0.2 g L^–1 for 1 ml of sample) within a working range of 0.2–500 g L^–1. The analytical procedure was successfully employed for the determination of aluminium in drinking water during and after flocculation/coagulation treatment processes.     

Inductively coupled plasma mass spectrometry: Application to the determination of arsenic species

The application of ion-pair reversed phase chromatography (HPLC) and inductively coupled plasma mass spectrometry to the determination of six species of arsenic is described: arsenious acid (As^III), arsenic acid (As^V), monomethylarsinic acid (MMA), dimethylarsinic acid (DMA), arsenocholine (AsC) and arsenobetaine (AsB) in marine biota and in natural fresh water. The coupling conditions of HPLC-ICP-MS are given and also the evaluation of the extraction procedure applied to determine these species in marine organisms. The limits of detection are between 6 and 25 g.l^–1.