Removal of trace arsenic(V) and phosphate from water by a highly selective ligand exchange adsorbent.

A highly selective ligand exchange type adsorbent was developed for the removal of trace arsenic(V) (As(V)) and phosphate from water. This adsorbent was prepared by loading zirconium(IV) on monophosphonic acid resin. This adsorbent was able to remove toxic anions efficiently at wide pH ranges. However, low pH was preferable for maximum breakthrough capacity in an adsorption operation. The effect of a large amount of competing anions such as chloride, bicarbonate, and sulfate on the adsorption systems of As(V) and phosphate anions was investigated. The experimental findings revealed that the As(V) and phosphate uptakes were not affected by these competing anions despite the enhancement of the breakthrough points and total adsorption. Phosphate anion was slightly preferable than As(V) in their competitive adsorption by the adsorbent. The adsorbed As(V) and phosphate on the Zr(IV)-loaded resin were quantitatively eluted with 0.1 mol/L sodium hydroxide solution, and the adsorbent was regenerated by 0.5 mol/L sulfuric acid. During several cycles of adsorption-elution-regeneration operations, no Zr(IV) was detected in the column effluents. Therefore, the Zr(IV)-loaded monophosphonic acid resin is an effective ligand exchange adsorbent for removing trace concentrations of As(V) and phosphate from water.

Reversible circularization of an anthracene-modified DNA conjugate through bimolecular triplex formation and its analytical application.

We prepared an oligodeoxyribonucleotide conjugate (5-3ant(2)18) carrying two anthracenes, each of which was tethered to both ends of the conjugate through hexamethylene linker chains. The conjugate has a mirror repeat of two heptamer sequences, such that it forms a bimolecular triplex with the single stranded target, forming a two-fold U-shaped conformation. The conformation of the conjugate in its triplex structure could be frozen instantaneously by circularization through photodimerization of the anthracenes. Compared with the duplex formation of linear probes with relevant sequences, bimolecular triplex formation of 5-3ant(2)18 shows a unique feature in its target recognition; it binds the target tightly, yet still retains high sequence selectivity. Circularization of 5-3ant(2)18 by UV photoirradiation was verified as the probe reaction for a DNA assay. The probe reaction could be performed in a few seconds over a wide range of temperatures, at least between 0 and 25 °C. In addition, the reaction could be regarded as a reversible method for the preparation of circular DNA that shows higher affinity for the target.

Xylitol Separation from a Polyol Mixture Using Lanthanide Ion-loaded Resins.

Xylitol separation from a polyol mixture of the byproducts from bioethanol production processes was performed by liquid chromatography using short columns packed with lanthanide ion-loaded ion-exchange resins. Xylitol was successfully separated with sufficiently high resolution using adsorbents with medium rare-earth metal ions, such as Nd3+ and Sm3+. The adsorbents' specific nature is explained by the so-called "gadolinium break," which is known as a discontinuous behavior of thermodynamic parameters in complexation of the lanthanide series. From the observed behavior, the optimum lanthanide ions could be chosen to prepare appropriate adsorbents for ligand-exchange chromatography of given polyol mixtures.

Silver ion unusually stabilizes the structure of a parallel-motif DNA triplex.

A simple and easy method for stabilizing DNA triplexes using Ag(+) is reported. A silver ion displaces the N3 proton of cytosine in Hoogsteen base-pairing to form the base triplet CG.CAg(+). By the addition of an equimolar amount of Ag(+), the third-strand 15-mer sequence containing five cytosines was stabilized by approximately 30 degrees C in melting temperature at pH 7. The triplex structure was stable even under weakly basic conditions.

Cooperative DNA probing using a beta-cyclodextrin-DNA conjugate and a nucleobase-specific fluorescent ligand.

A single nucleotide polymorphism (SNP) base on the target is displayed at a gap in a ternary duplex carrying beta-cyclodextrin-modified DNA. A stable tandem duplex forms regardless of the type of SNP base. A nucleobase-specific ligand is then added to this system. The dansyl moiety in the ligand is expected to form a luminous inclusion complex with nearby beta-CyD, only when the ligand recognizes the specific base displayed in the gap.

Efficient guest inclusion by ß-cyclodextrin attached to the ends of DNA oligomers upon hybridization to various DNA conjugates.

Two types of 5'-ß-CyD-DNA conjugates were synthesized using two different strategies and were hybridized with cDNA conjugates bearing various possible guest compounds at the 3' ends. One of the ß-CyD conjugates was synthesized on the basis of solid-phase postmodification of DNA with a monoamino-ß-CyD derivative on a synthesis column for automated DNA synthesis. The other ß-CyD conjugate was synthesized by the solution-phase coupling of DNA with a monomercapto-ß-CyD derivative using a heterobifunctional cross-coupling reagent. When these 5'-ß-CyD-DNA conjugates were hybridized with cDNA conjugates bearing 1-adamantaneacetic acid at the 3' ends, significant stabilization of the duplexes was observed as compared with the control duplex without ß-CyD. Duplexes of 5'-ß-CyD-DNA conjugates and complementary 3'-dansyl-glycine-DNA conjugates were also moderately stabilized. Thermodynamic measurements revealed that the host-guest inclusion interactions between ß-CyD and 1-adamantaneacetic acid or dansyl-glycine are roughly as strong as those found in bulk solution even if they are tethered to the ends of the DNA.

Anthracene-DNA conjugates as building blocks of designed DNA structures constructed by photochemical reactions.

We present the photochemical ligation of anthracene-ODN (oligodeoxyribonucleotide) conjugates through cycloaddition of anthracenes. Anthracene-DNA conjugates were synthesized by linking the 5'- or 3'-end of ODNs to the anthracene group. The sequences of the conjugates were designed to hybridize to neighboring sites on the target ODN with their anthracene units facing each other. When the ternary duplex consisting of the two conjugates and the target forms, the conjugates can be dimerized by light irradiation. The dimerization efficiency was affected by the substitution position of the anthracene group and by a one-base displacement in the template sequence. Furthermore, it is demonstrated that the capping of the duplex and connecting third strands in a triplex structure could also be the target of the photochemical ligation.

Rapid column-mode removal of arsenate from water by crosslinked poly(allylamine) resin.

Performances of crosslinked poly(allylamine) resin (PAA) as arsenate (As(V)) adsorbent were studied using a column packed with PAA in hydrochloride form. PAA has a high amino group content of 14.6 mmol/g in free amine form and a high chloride content of 10.2 mmol/g in hydrochloride form. Its wet volumes in water were 4.5 and 3.1 mL/g in hydrochloride and free amine forms, respectively, indicating its high hydrophilicity. Breakthrough capacities for As(V) were evaluated changing conditions of adsorption operations: pH of feeds from 2.2 to 7.0, concentration of As(V) in feeds from 0.020 to 2.0 mM, and feed flow rate from 250 to 4000 h(-1) in space velocity. Breakthrough capacities increased from 2.6 to 3.4 mmol/g with a decrease in pH from 7.0 and 2.2, and also from 0.81 to 2.8 mmol/g with an increase in As(V) concentration from 0.020 to 2.0mM. When feed flow rate increased from 250 to 4000 h(-1), breakthrough capacities changed form 3.5 to 0.81 mmol/g. Because of non-Hofmeister anion selectivity behavior of PAA, the interference of chloride and nitrate was minor. Although PAA slightly preferred As(V) to sulfate, the latter more markedly interfered with uptake of As(V) than chloride and nitrate. Competitive uptake of As(V) and phosphate revealed that PAA slightly preferred phosphate to As(V). The adsorbed As(V) was quantitatively eluted with 2M HCl and PAA was simultaneously regenerated into hydrochloride form. All results were obtained using the same column without change of the packed PAA and any deterioration in column performances for 4 months.

Arsenate removal from water by a weak-base anion exchange fibrous adsorbent.

A weak-base anion exchange fiber named FVA with primary amino groups for selective and rapid removal of arsenate species was prepared by means of electron irradiation induced liquid phase graft polymerization of N-vinylformamide onto polyethylene coated polypropylene fibers and by the subsequent alkaline hydrolysis of amide group on the grafted polymer chains. Two types of FVA were prepared. One was a non-woven cloth type named FVA-c for the batch-mode study, which clarified that uptake of arsenate species decreases with an increase in pH, and chloride and sulfate do not strongly interfere with uptake of arsenate species different from conventional anion exchange resins based on crosslinked polystyrene matrices. The other was a filamentary type one named FVA-f used in the column-mode study, which clarified that arsenate species were successfully removed from neutral pH arsenate solutions containing 1.0-99 mg of As/L at feed flow rates of 100-1050 h(-1) in space velocity (SV). The most important findings are that the 1% breakthrough point in uptake from the arsenate solution containing 1.0mg of As/L at the high feed flow rate of 1050h(-1) in SV was as large as 4670 bed volumes, giving the 1% breakthrough capacity of 0.298 mmol/g of FVA-f. Adsorbed arsenate was able to be quantitatively eluted with 1M hydrochloric acid and FVA-f was simultaneously regenerated. Then, the repeated use of FVA-f was possible.

The effect of local structural disruption on the yield of photochemical ligation between anthracene-oligonucleotide conjugates.

The techniques of chemical ligation have attracted great attention as an alternative to enzymatic joining of DNA ends. Here we introduce the photoligation of anthracene-modified ODN conjugates through anthracene cyclodimer formation. The effect of the positions and the kinds of single base mismatch on the template was evaluated using eight templates with one-base displacements. We found out that the yield of the ligation was affected by mispairing in a position-dependent manner. Such results would be attributed to the disruption of the local structure at the ligation site.

Metal ion-directed cooperative DNA binding of small molecules.

Compound (1), which consists of an oxine and a pyridinium group, was synthesized as a metal-responsive DNA binding ligand. Two 1s coordinate to a Cu(II) to form a stable dimer (1(2)-Cu), even in the presence of DNA. The binding of 1 with sonicated calf thymus DNA was enhanced by ca. 10(3) times after forming the dimer; the binding constants were estimated to be 3.2 x 10(4)M(-1) and 2.4 x 10(7)M(-1) in the absence and the presence, respectively, of a half mole of Cu(II). The enormous acceleration of the binding is partly attributed to the generation of a dicationic charge by the formation of the dimer. High cooperativity between dimers could be also responsible; dimers would gather along the duplex as a template to form 1D spiral aggregates.

Preparation of DNA-modified nanoparticles and preliminary study for colorimetric SNP analysis using their selective aggregations.

DNA-modified nanospheres were prepared by anchoring amino-terminated oligodeoxynucleotides (ODNs) with carboxylates onto a colored polystyrene sphere surface through amido bonds. About 220 ODN molecules were immobilized onto a nanosphere 40 nm in diameter. Preliminary studies using the microspheres with 1 microm diameter reveal that the specificity of hybridization was retained after modification. Three kinds of differently colored (RGB, red/green/blue) nanospheres bearing unique ODNs on their surface were prepared for detecting the p53 gene. Each ODN is complementary to a different part in the 45mer sample that is a part of a conservative region of the p53 gene containing one of the hot spots. In a binary system using spheres R and G, the wild-type 45mer made the aggregates with yellow emission as the result of mixing both colors. The mutant 45mer containing one nucleotide displacement did not give such aggregates with distinct colors. The study of fluorescence resonance energy transfer (FRET) showed that spheres R and G directly contact each other in the aggregates with the wild type. The RGB ternary system gave aggregates with specific colors corresponding to the added ODN samples, wild type or mutant. In addition, in the presence of both samples, all of the spheres formed aggregates with white emission as a consequence of mixing three primary colors of light. This means that the present technique should allow us to conduct an allele analysis.

Asymmetric cooperativity in tandem hybridization of enantiomeric metal complex-tethered short fluorescent DNA probes.

The complex [Ru(phen)(2)(dppz)](2+)(phen = 1,10-phenanthroline, dppz = dipyrido[3,2-aratio2',3'-c]phenazine) was attached to the 5' end of a short oligonucleotide to form conjugates, the Delta-isomer of which showed a high cooperativity during the recognition of the repetitive sequence, while the Lambda-isomer did not.

Column-mode phosphate removal by a novel highly selective adsorbent.

A phosphoric acid resin RGP was immobilized with zirconium(IV) (Zr(IV)) to investigate its applicability in phosphate removal. When loaded with Zr(IV), RGP was changed into an effective ligand exchanger with phosphate sorption capacity of 0.345 mmol/ml. Little metal leakage was observed. Breakthrough of phosphate sorption depended on solution acidity and phosphate concentration. An increase of solution pH greatly suppressed phosphate removal, but even at pH 8.21, about 56% of the added phosphate (2.8mM) in the feed solution could still be sorbed. Electrolytes in the aqueous solution did not interfere with phosphate sorption; on the contrary, an enhancement effect was observed. Due to the high sorption capacity of Zr(IV)-loaded RGP, low concentration of phosphate can be removed at high flow rate (100 h(-1) in space velocity). The sorbed phosphate on the Zr(IV)-loaded RGP could be quantitatively eluted with 0.5M sodium hydroxide solution. The Zr(IV)-loaded RGP is a promising ligand exchanger for treating wastewater containing trace amounts of inorganic phosphate.

Colorimetric SNP analysis using oligonucleotide-modified nanoparticles.

A point mutation in the p53 gene has been detected by means of fluorescence microscopy and fluorescent resonance energy transfer (FRET) through sequence selective aggregation of DNA-modified nanoparticles, in which fluorescent dyes were impregnated.

Evaluating of arsenic(V) removal from water by weak-base anion exchange adsorbents.

Arsenic contamination of groundwater has been called the largest mass poisoning calamity in human history and creates severe health problems. The effective adsorbents are imperative in response to the widespread removal of toxic arsenic exposure through drinking water. Evaluation of arsenic(V) removal from water by weak-base anion exchange adsorbents was studied in this paper, aiming at the determination of the effects of pH, competing anions, and feed flow rates to improvement on remediation. Two types of weak-base adsorbents were used to evaluate arsenic(V) removal efficiency both in batch and column approaches. Anion selectivity was determined by both adsorbents in batch method as equilibrium As(V) adsorption capacities. Column studies were performed in fixed-bed experiments using both adsorbent packed columns, and kinetic performance was dependent on the feed flow rate and competing anions. The weak-base adsorbents clarified that these are selective to arsenic(V) over competition of chloride, nitrate, and sulfate anions. The solution pH played an important role in arsenic(V) removal, and a higher pH can cause lower adsorption capacities. A low concentration level of arsenic(V) was also removed by these adsorbents even at a high flow rate of 250-350 h(-1). Adsorbed arsenic(V) was quantitatively eluted with 1 M HCl acid and regenerated into hydrochloride form simultaneously for the next adsorption operation after rinsing with water. The weak-base anion exchange adsorbents are to be an effective means to remove arsenic(V) from drinking water. The fast adsorption rate and the excellent adsorption capacity in the neutral pH range will render this removal technique attractive in practical use in chemical industry.

Efficient arsenic(V) removal from water by ligand exchange fibrous adsorbent.

This study is an efficient arsenic(V) removal from contaminated waters used as drinking water in adsorption process by zirconium(IV) loaded ligand exchange fibrous adsorbent. The bifunctional fibers contained both phosphonate and sulfonate groups. The bifunctional fiber was synthesised by graft polymerization of chloromethylstyrene onto polyethylene coated polypropylene fiber by means of electron irradiation graft polymerization technique and then desired phosphonate and sulfonate groups were introduced by Arbusov reaction followed by phosphorylation and sulfonation. Arsenic(V) adsorption was clarified in column methods with continuous flow operation in order to assess the arsenic(V) removal capacity in various conditions. The adsorption efficiency was evaluated in several parameters such as competing ions (chloride and sulfate), feed solution acidity, feed flow rate, feed concentration and kinetic performances at high feed flow rate of trace concentration arsenic(V). Arsenic(V) adsorption was not greatly changed when feed solutions pH at 3.0-7.0 and high breakthrough capacity was observed in strong acidic area below pH 2.2. Increasing the flow rate brings a decrease both breakthrough capacity and total adsorption. Trace level of arsenic(V) (0.015 mM) in presence of competing ions was also removed at high flow rate (750 h(-1)) with high removal efficiency. Therefore, the adsorbent is highly selective to arsenic(V) even in the presence of high concentration competing ions. The adsorbent is reversible and reusable in many cycles without any deterioration in its original performances. Therefore, Zr(IV) loaded ligand exchange adsorbent is to be an effective means to treat arsenic(V) contaminated water efficiently and able to safeguard the human health.

DNA analysis based on the local structural disruption to the duplexes carrying a luminous lanthanide complex.

The two DNA conjugates (split probes) carrying a metal chelator form an integrated luminous lanthanide (Ln(3+): Tb(3+) or Eu(3+)) complex on the complementary template DNA (target). The luminous property of this Ln(3+) complex has been used for DNA assay. The intensity of the luminescence was affected by the local structural disruption caused by one-base mispairing around the complex. Among the mispairings systematically introduced around the Ln(3+) center, vicinal mispairings to the center decreased the emission intensity more. This would be a novel nucleobase-discriminating principle, in which the split probes bind the target tightly, yet still retain sequence selectivity.

A weak-base fibrous anion exchanger effective for rapid phosphate removal from water.

This work investigated that weak-base anion exchange fibers named FVA-c and FVA-f were selectively and rapidly taken up phosphate from water. The chemical structure of both FVA-c and FVA-f was the same; i.e., poly(vinylamine) chains grafted onto polyethylene coated polypropylene fibers. Batch study using FVA-c clarified that this preferred phosphate to chloride, nitrate and sulfate in neutral pH region and an equilibrium capacity of FVA-c for phosphate was from 2.45 to 6.87 mmol/g. Column study using FVA-f made it clear that breakthrough capacities of FVA-f were not strongly affected by flow rates from 150 to 2000 h(-1) as well as phosphate feed concentration from 0.072 to 1.6mM. Under these conditions, breakthrough capacities were from 0.84 to 1.43 mmol/g indicating high kinetic performances. Trace concentration of phosphate was also removed from feeds containing 0.021 and 0.035 mM of phosphate at high feed flow rate of 2500 h(-1), breakthrough capacities were 0.676 and 0.741 mmol/g, respectively. The column study also clarified that chloride and sulfate did not strongly interfere with phosphate uptake even in their presence of equimolar and fivefold molar levels. Adsorbed phosphate on FVA-f was quantitatively eluted with 1M HCl acid and regenerated into hydrochloride form simultaneously for next phosphate adsorption operation. Therefore, FVA-f is able to use long time even under rigorous chemical treatment of multiple regeneration/reuse cycles without any noticeable deterioration.

Electrochemical signal modulation in homogeneous solutions using the formation of an inclusion complex between ferrocene and ß-cyclodextrin on a DNA scaffold.

Two DNA conjugates modified with ferrocene and ß-cyclodextrin were prepared as a pair of probes that work cooperatively for DNA sensing, in which the electrochemical signal of ferrocene on one probe was significantly "quenched" by the formation of an inclusion complex with ß-cyclodextrin of the other probe on the DNA templates.