Optical properties of humic substances and CDOM: effects of borohydride reduction

Treatment of Suwanee River humic (SRHA) and fulvic (SRFA) acids, a commercial lignin (LAC), and a series of solid phase extracts (C18) from the Middle Atlantic Bight (MAB extracts) with sodium borohydride (NaBH(4)), a selective reductant of carbonyl-containing compounds including quinones and aromatic ketones, produces a preferential loss of visible absorption (> or = 50% for SRFA) and substantially enhanced, blue-shifted fluorescence emission (2- to 3-fold increase). Comparison of the results with those obtained from a series of model quinones and hydroquinones demonstrates that these spectral changes cannot be assigned directly to the absorption and emission of visible light by quinones/hydroquinones. Instead, these results are consistent with a charge transfer model in which the visible absorption is due primarily to charge transfer transitions arising among hydroxy- (methoxy-) aromatic donors and carbonyl-containing acceptors. Unlike most of the model hydroquinones, the changes in optical properties of the natural samples following NaBH(4) reduction were largely irreversible in the presence of air and following addition of a Cu(2+) catalyst, providing tentative evidence that aromatic ketones (or other similar carbonyl-containing structures) may play a more important role than quinones in the optical properties of these materials.

[Effect of reduction by sodium borohydride on the structural characteristics of brown-rotted lignin]

The FTIR, UV-Visible, 1H NMR and GPC were used to study structural changes of brown-rotted lignin after sodium borohydride reduction. FTIR spectra showed that, after reduction, the band at 1,677 cm(-1) attributed to the conjugated carbonyl groups disappeared, and the band intensity at 1,715 cm(-1) attributed to the nonconjugated carbonyl groups decreased. On the other hand, the band at 1,509 and 1,603 cm(-1) attributed to aromatic skeletal vibration remained almost unchanged. UV spectra showed the decreased absorptions at 288 nm and 300-400 nm after reduction. 1H NMR spectra showed that, after reduction, the number of aromatic methoxyl and aromatic hydroxyls decreased, the number of aliphatic hydroxyls and the proton number attributed to many linkage structures connecting the phenylpropane units increased. GPC results showed that the molecular weight of reduced brown-rotted lignin increased and the molecular distribution got wider, as a consequence of the large molecular weight molecules generated during the reduction reaction. Our results suggest that the conjugated carbonyl groups can be totally reduced to the hydroxyl groups, but only some nonconjugated carbonyl groups can be reduced to the hydroxyl groups. The chemical structure of the brown-rotted lignin changed, but the benzyl ring kept stable. The condensation reaction took place during the sodium borohydride reduction process.

Solid phase extraction of cadmium on 2-mercaptobenzothiazole loaded on sulfur powder in the medium of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate and cold vapor generation-atomic absorption spectrometric determination

A novel solid phase extractor for preconcentration of cadmium at ng L(-1) levels has been developed. Cadmium ions were retained on a column packed with sulfur powder modified with 2-mercaptobenzothiazole (2-MBT) in the medium of 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim](+)PF(6)(-)) ionic liquid. The presence of ionic liquid during modification of sulfur enhanced the retention of cadmium ions on the column. The retained cadmium ions were eluted with 2 mol L(-1) solution of HCl and measured by cold vapor generation-atomic absorption spectrometry (CVG-AAS). By using reaction cell-gas liquid separator (RC-GLS), gaseous cadmium vapors were produced and reached the atomic absorption spectrometer, instantaneously. The influence of different variables on both processes of solid phase extraction and CVG-AAS determination of cadmium ions was investigated. The calibration curve was linear in the range of 10-200 ng L(-1)of cadmium in the initial solution with r=0.9992 (n=8) under optimum conditions. The limit of detection based on three times the standard deviation of the blank (3S(b), n=10) was 4.6 ng L(-1). The relative standard deviation (R.S.D.) of 25 and 150 ng L(-1) of cadmium was 4.1 and 2.2% (n=8), respectively. The procedure was validated by the analysis of a certified reference material (DORM-3), water and fish samples.

Size-controlled synthesis of Pd nanocrystals using a specific multifunctional peptide

Here we report a peptide-mediated synthesis of Pd NCs in aqueous solution with controllable size in the sub-10 nanometre regime. The specific multifunctional peptide Q7 selected using the phage display technique can bind to the Pd NC surface and act as a stabilizer to mediate Pd crystal nucleation and growth. At the nucleation stage, Q7 bound to and helped stabilize the different-sized small Pd NC nuclei achieved using different concentrations of the external reducing agent, NaBH4. At the growth stage, Q7 played the dual role of binding to and reducing the precursor onto the existing nuclei, which led to the further controllable growth of the Pd NCs. By using the variable sizes of nuclei as seeds, and by introducing different amounts of precursors Pd NCs with tunable sizes from 2.6 to 6.6 nm were achieved with good size distribution.

Ultrasensitive detection of DNA in diluted serum using NaBH4 electrooxidation mediated by [Ru(NH3)6]3+ at indium-tin oxide electrodes

There is a crucial need for simple and highly sensitive techniques to detect DNA in complicated biological samples such as serum. Here we present an ultrasensitive electrochemical DNA sensor using (i) single DNA hybridization with peptide nucleic acid (PNA), (ii) selective binding of [Ru(NH(3))(6)](3+) to hybridized DNA, (iii) fast NaBH(4) electrooxidation mediated by [Ru(NH(3))(6)](3+), and (iv) low background currents of NaBH(4) at indium-tin oxide (ITO) electrodes. The [Ru(III)(NH(3))(5)NH(2)](2+) formed from [Ru(III)(NH(3))(6)](3+) in borate buffer (pH 11.0) is readily electrooxidized to both [Ru(IV)(NH(3))(5)NH(2)](3+) and Ru complex with a higher oxidation state. In the absence of [Ru(NH(3))(6)](3+) bound to the DNA-sensing ITO electrodes, the oxidation currents of NaBH(4) are very low. However, in the presence of [Ru(NH(3))(6)](3+), the oxidation currents of NaBH(4) are highly enhanced due to electron mediation of the oxidized Ru complexes. The significant enhancement in the electrocatalytic activity of sensing electrodes after [Ru(NH(3))(6)](3+) binding facilitates to obtain high signal-to-background ratios. PNA and ethylenediamine on DNA-sensing electrodes significantly decrease [Ru(NH(3))(6)](3+) binding, also allowing for high signal-to-background ratios. The oxidation charges of NaBH(4) obtained from chronocoulometry are highly reproducible. All combined effects enable the detection of DNA with a detection limit of 1 fM in ten-fold diluted human serum. The simple and fast detection procedure and the ultrasensitivity make this approach highly promising for practical DNA detection.

Carboxymethylation of the fibrillar collagen with respect to formation of hydroxyapatite

Control over crystal growth by acidic matrix macromolecules is an important process in the formation of many mineralized tissues. Highly acidic macromolecules are postulated intermediates in tissue mineralization, because they sequester many calcium ions and occur in high concentrations at mineralizing foci in distantly related organisms. A prerequisite for biomineralization is the ability of cations like calcium to bind to proteins and to result in concert with appropriate anions like phosphates or carbonates in composite materials with bone-like properties. For this mineralization process the proteins have to be modified with respect to acidification. In this study we modified the protein collagen by carboxymethylation using glucuronic acid. Our experiments showed unambigously, that N(epsilon)-carboxymethyllysine is the major product of the in vitro nonenzymatic glycation reaction between glucuronic acid and collagen. We hypothesized that the function of biomimetically carboxymethylated collagen is to increase the local concentration of corresponding ions so that a critical nucleus of ions can be formed, leading to the formation of the mineral. Thus, the self-organization of HAP nanocrystals on and within collagen fibrils was intensified by carboxymethylation.

Coordination and reduction processes in the synthesis of dendrimer-encapsulated Pt nanoparticles

We synthesized Pt nanoparticles encapsulated in poly(amidoamine) (PAMAM) dendrimers by Pt(2+) coordination and subsequent reduction by NaBH(4). To optimize the experimental conditions for the Pt nanoparticle synthesis, we systematically examined the effects of pH, temperature, coordination time, and surface functional groups of the dendrimers on coordination and NaBH(4) reduction by UV-vis spectroscopy and transmission electron microscopy (TEM) measurements. We used generation-4 dendrimers (hydroxyl-terminated PAMAM dendrimers; G4-OH) and generation-4.5 dendrimers (carboxyl-terminated PAMAM dendrimers; G4.5-COO(-)). According to our results, dendrimer-encapsulated Pt nanoparticles with a narrow size distribution were obtained at high Pt(2+) coordination ratios (alpha), while nonencapsulated Pt nanoparticles were formed at low alpha values. To enhance alpha, it was necessary to use a neutral G4-OH solution or an acidic G4.5-COO(-) solution. Temperature had a marked effect on the coordination rate, with an increase in the temperature from room temperature to 50 degrees C, and the coordination time decreased from 10 days to 1-2 days.

A comparison study of the catalytic properties of Au-based nanocages, nanoboxes, and nanoparticles

We have evaluated the catalytic properties of Au-based nanostructures (including nanocages, nanoboxes, and solid nanoparticles) using a model reaction based on the reduction of p-nitrophenol by NaBH(4). From the average reaction rate constants at three different temperatures, we determined the activation energy, the entropy of activation, and the pre-exponential factor for each type of Au nanostructure. The kinetic data indicate that the Au-based nanocages are catalytically more active than both the nanoboxes and nanoparticles probably due to their extremely thin but electrically continuous walls, the high content of Au, and the accessibility of both inner and outer surfaces through the pores in the walls. In addition, a compensation effect was observed in this Au-based catalytic system, which can be primarily interpreted by a model based on kinetic regime switching.

Utilization of sodium borohydride (NaBH4) in kraft pulping process

Aim of this study is to investigate the effect of adding sodium borohydride (NaBH4) in kraft pulping. First of all, six kraft cooks were carried out for varying active alkali and sulfidity. Then, kraft methods for K1 and K6 cooks were modified by adding 1, 2 and 3% NaBH4. The results indicated that modifying kraft method (K1) by adding 3% NaBH4 (KB13) resulted in 9.97% (relative percentage) yield increase and 10.1% (relative percentage) kappa reduction. Although the mechanical properties of NaBH4 modified pulps were lower compared to the kraft pulps, NaBH4 modified pulps were much brighter.

Ag dendrite-based Au/Ag bimetallic nanostructures with strongly enhanced catalytic activity

Dendritic Ag/Au bimetallic nanostructures have been synthesized via a galvanic replacement reaction (GRR) of Ag dendrites in a chlorauric acid (HAuCl4) solution. After short periods of time, one obtains structures with protruding flakes; these will mature into very porous structures with little Ag left over. The morphological, compositional, and crystal structural changes involved with reaction time t were analyzed by using scanning and transmission electron microscopy (SEM and TEM, respectively), energy-dispersive X-ray spectrometry (EDX), and X-ray diffraction. High-resolution TEM combined with EDX and selected area electron diffraction confirmed the replacement of Ag with Au. A proposed formation mechanism of the original Ag dendrites developing pores while growing Au flakes cover this underlying structure at longer reaction times is confirmed by exploiting surface-enhanced Raman scattering (SERS). Catalytic reduction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH4) is strongly enhanced, implying promising applications in catalysis.

Fabrication of functional silver nanobowl arrays via sphere lithography

We report a low-cost and high-throughput method to fabricate large-area silver nanobowl arrays via thermal evaporation of silver on a self-assembled monolayer of nanospheres. The nanobowl array is a hierarchical structure, composed of silver nanoparticles with average diameter size of ca.10 nm, which can serve as a reaction container and catalyst. The optical absorption spectra indicates that surface plasmon resonance of silver nanoparticles exists on the nanobowl array, and it can serve as an excellent surface enhanced Raman scattering (SERS)-active substrate.

Size effects on the hydrogen storage properties of nanoscaffolded Li3BN2H8

The use of Li3BN2H8 complex hydride as a practical hydrogen storage material is limited by its high desorption temperature and poor reversibility. While certain catalysts have been shown to decrease the dehydrogenation temperature, no significant improvement in reversibility has been reported thus far. In this study, we demonstrated that tuning the particle size to the nanometer scale by infiltration into nanoporous carbon scaffolds leads to dramatic improvements in the reversibility of Li3BN2H8. Possible changes in the dehydrogenation path were also observed in the nanoscaffolded hydride.

Novel catalytic effects of fullerene for LiBH4 hydrogen uptake and release

The addition of catalysts to complex hydrides is aimed at enhancing the hydrogen absorption desorption properties. Here we show that the addition of carbon nanostructure C60 to LiBH4 has a remarkable catalytic effect, enhancing the uptake and release of hydrogen. A fullerene-LiBH4 composite demonstrates catalytic properties with not only lowered hydrogen desorption temperatures but also regenerative rehydrogenation at a relatively low temperature of 350 degrees C. This catalytic effect probably originates from C60 interfering with the charge transfer from Li to the BH4 moiety, resulting in a minimized ionic bond between Li+ and BH4(-), and a weakened covalent bond between B and H. Interaction of LiBH4 with an electronegative substrate such as carbon fullerene affects the ability of Li to donate its charge to BH4, consequently weakening the B-H bond and causing hydrogen to desorb at lower temperatures as well as facilitating the absorption of H2. Degradation of cycling capacity is observed and is probably due to the formation of diboranes or other irreversible intermediates.

Experimental and theoretical screening of nanoscale oxide reactivity with LiBH4

Experimentation, thermodynamic modeling, and atomic modeling were combined to screen the reactivity of SiO2, Al2O3, and ZrO2 nanoscale oxides with LiBH4. Equilibrium thermodynamic modeling showed that the reactions of oxides with LiBH4 could lead to formation of stable Li-bearing oxide and metal boride phases. Experimentation was conducted to evaluate the discharge/recharge reaction products of nanoscale oxide-LiBH4 mixtures. Thermal gravimetric analyses-mass spectroscopy and x-ray diffraction revealed significant SiO2 destabilization of LiBH4 dehydrogenation, resulting in the formation of lithium silicate and boric acid. A smaller amount of lithium metaborate and boric acid was formed with Al2O3. No destabilization products were observed with ZrO2. Density functional theory atomic modeling predicted much stronger LiBH4 interfacial adsorption on the SiO2 and Al2O3 surfaces than on the ZrO2 surface, which was consistent with the experimental findings. Following dehydrogenation, interfacial Li atoms were predicted to strongly adsorb on the oxide surfaces effectively competing with LiH formation. The interfacial Li interactions with Al2O3 and ZrO2 were equal in strength in the fully hydrided and dehydrided states, so that their predicted net effect on LiBH4 dehydrogenation was insignificant. Zirconia was selected for nanoframework development based on the combined observations of compatibility and weaker associative interactions with LiBH4.

Controlled in-situ synthesis of silver nanoparticles in natural cellulose fibers toward highly efficient antimicrobial materials

In this report, we presented in-situ synthesis of silver nanoparticles in natural cellulose fibers which embody high oxygen (ether and hydroxyl) density and could be considered as aggregated nanoreactors and stabilizers for the nucleation and growth of silver nanoparticles. The morphologies of natural cellulose fibers and silver nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-visible spectroscopy. The content of silver nanoparticles in cellulose fibers was measured by inductive coupled plasma-mass spectrometry (ICP-ms). Experimental results revealed that sodium borohydride (NaBH4) played dual effects in the formation of silver nanoparticles. The mean size (d) and size distribution (sigma) of silver nanoparticles could be adjusted by changing the concentration of NaBH4. Monodisperse silver nanoparticles (d = 2.7 nm, sigma = 0.6 nm) in cellulose fibers were successfully prepared under optimized conditions. When the NaBH4 concentration was very low (0.1 mM), a stable colloidal solution (storage stability > 1 month) of silver nanoparticles was produced, which provides a novel, mild approach to the preparation of stable colloidal solutions of metal nanoparticles. The ability of silver nanoparticle-loaded cellulose fibers to prohibit the propagation of Escherichia coli was estimated by the Minimum Inhibitory Concentration (MIC). Based on the experimental observations, the antibacterial mode of silver nanoparticle-loaded cellulose fibers was discussed in details.

[A study on decreasing the instrument detection limit of atomic fluorescence spectrometry (AFS-930) for Hg]

In the present study, the detection limit of atomic fluorescence spectrometry (AFS-930) was decreased to 2 ng x L(-1) (n=6) based on several optimizing modifications, including that the sub-high voltage of photomultiplier tube and the current of hollow-cathode lamp were elevated to 280 V and to 30 mA, respectively, and the height of atomization cell was set as 10 mm; In addition, the concentration of KBH4 was decreased to 0.5% (KOH 0.2%). With the optimized parameters, a good standard curve of Hg concentration versus intensity of fluorescence (If) could been obtained readily, after that, a 4-ng x L(-1)-Hg water samples was measured accurately with a little relative standard deviation (RSD) of <5%, while for approximately 2-ng x L(-1)-Hg waters the RSD varied within a wide range of 10.9%-27.2%, likely due to the absorption of Hg by polyethylene vessels used in this study and/or due to the contamination by analysis grade reagents used in this study. By using low-absorption polytetrafluoroethylene (PTFE) materials and the guaranteed reagents, the instrument detection limit was further decreased to 1 ng x L(-1) (n=10).

Total synthesis of vinblastine, vincristine, related natural products, and key structural analogues

Full details of the development of a direct coupling of catharanthine with vindoline to provide vinblastine are described along with key mechanistic and labeling studies. Following an Fe(III)-promoted coupling reaction initiated by generation of a presumed catharanthine radical cation that undergoes a subsequent oxidative fragmentation and diastereoselective coupling with vindoline, addition of the resulting reaction mixture to an Fe(III)-NaBH(4)/air solution leads to oxidation of the C15'-C20' double bond and reduction of the intermediate iminium ion directly providing vinblastine (40-43%) and leurosidine (20-23%), its naturally occurring C20' alcohol isomer. The yield of coupled products, which exclusively possess the natural C16' stereochemistry, approaches or exceeds 80% and the combined yield of the isomeric C20' alcohols is >60%. Preliminary studies of Fe(III)-NaBH(4)/air oxidation reaction illustrate a generalizable trisubstituted olefin scope, identify alternatives to O(2) trap at the oxidized carbon, provide a unique entry into C20' functionalized vinblastines, and afford initial insights into the observed C20' diastereoselectivity. The first disclosure of the use of exo-catharanthine proceeding through Delta(19',20')-anhydrovinblastine in such coupling reactions is also detailed with identical stereochemical consequences. Incorporating either a catharanthine N-methyl group or a vindoline N-formyl group precludes Fe(III)-promoted coupling, whereas the removal of the potentially key C16 methoxy group of vindoline does not adversely impact the coupling efficiency. Extension of these studies provided a total synthesis of vincristine (2) via N-desmethylvinblastine (36, also a natural product), 16-desmethoxyvinblastine (44) and 4-desacetoxy-16-desmethoxyvinblastine (47) both of which we can now suggest are likely natural products produced by C. roseus, desacetylvinblastine (62) and 4-desacetoxyvinblastine (59), as well as a series of key analogues bearing systematic modifications in the vindoline subunit. Their biological evaluation provided additional insights into the key functionality within the vindoline subunit contributing to the activity and sets the foundation on which further, more deep-seated changes in the structures of 1 and 2 will be explored in future studies.

Fluorescent detection of alpha-aminoadipic and gamma-glutamic semialdehydes in oxidized proteins

The oxidative modification of proteins is believed to play a critical role in the etiology and/or progression of several diseases. alpha-Aminoadipic semialdehyde (AAS) and gamma-glutamic semialdehyde (GGS) residues represent major oxidized amino acids generated in oxidized proteins. This paper describes a novel procedure for the specific and sensitive determination of AAS and GGS after their reductive amination with sodium cyanoborohydride and p-aminobenzoic acid, a fluorescence reagent, to their corresponding derivatives, followed by a high-performance liquid chromatography (HPLC) analysis. This fluorescent labeling of protein-associated aldehyde moieties is a simple and accurate technique that may be widely used to reveal increased levels of oxidatively modified proteins with reactive oxygen species during aging and disease.

[Total selenium and se species in vegetables measured with hydride generation-atomic fluorescence spectrometry]

The amounts of total selenium and Se-species including organic and inorganic selenium in vegetables were measured with the method of hydride generation-atomic fluorescence spectrometry. The instrumental parameters and analytical conditions were optimized. In order to obtain the maximum fluorescence signal, the effects of the concentrations of HCI and KBH4 in carrier solution, the concentrations of HCl and HNO3 in sample medium, and the interference from foreign ion (Cu) on the signal were mainly investigated. Under the optimum conditions, the detection limit estimated with 3-fold standard deviation by 11 replicates of procedure blank was 0.35 ng x g(-1). The recovery tested by adding standards ranged from 97.6% to 101%. After being digested with HNO3 by microwave, selenium in several kinds of vegetables was measured. The results indicated that the total amounts of Se in the vegetable samples were low except straw mushroom, in which the content of Se was 0.151 microg x g(-1) (dry weight). In addition, the species of organic selenium were the main existing forms in vegetables.

[Analysis of paraquat in blood and urine by sodium borohydride/nickel chloride chemical reduction-gas chromatography/thermionic specific detector]

OBJECTIVE

To establish a new method for the analysis of paraquat in blood and urine by sodium borohydride/nickel chloride chemical reduction-gas chromatography/thermionic specific detector.

METHODS

An initial procedure of precipitation was performed by adding hydrochloric solution with sodium chloride and a mixture of chloroform and ethanol. Then the analyte contained in supernatant was reduced by a reduction system of sodium borohydride and nickel chloride and extracted by acetic ether. Ethyl paraquat (EPQ) was used as internal standard. GC/TSD was used to identify and quantify the analyte.

RESULTS

The limits of detection (S/N=3) in blood and urine were 0.002 and 0.004 microg/mL, respectively. The linear ranges were 0.050-30.0 microg/mL. Correlation coefficients in blood and urine were 0.999 and 0.998, respectively. The recoveries exceeded 80% both in blood and urine.

CONCLUSION

This method is applicable for quantification of paraquat in biological fluids.

Synthesis and spectroscopic characterization of gold nanoparticles

Photoluminescent nanoparticles of gold with size 3, 4, 6, and 9 nm are prepared by borohydride/citrate reduction in presence of polyethylene glycol (PEG)/tannic acid. The prepared nanomaterials are characterized by UV-vis spectroscopy and dynamic light scattering (DLS) technique. Intense photoluminescence (PL) is observed in nanoparticles prepared by fast reduction with borohydride in presence of PEG. A red shift of PL emission from 408 to 456 nm is observed for the change of size from 4 to 6 nm. Increase in PL intensity is observed for all the nanoparticles on the addition of KCl. Citrate reduced gold colloid which consists of large particles of size approximately 35 nm with anisotropic shapes showing two plasmon peaks is also prepared. The anisotropy is confirmed by TEM measurement. SERS activity of this colloid is tested using glutamic acid as an adsorbate probe. Assignment of the observed bands is given.

Sodium borohydride/chloranil-based assay for quantifying total flavonoids

A novel sodium borohydride/chloranil-based (SBC) assay for quantifying total flavonoids, including flavones, flavonols, flavonones, flavononols, isoflavonoids, flavanols, and anthocyanins, has been developed. Flavonoids with a 4-carbonyl group were reduced to flavanols using sodium borohydride catalyzed with aluminum chloride. Then the flavan-4-ols were oxidized to anthocyanins by chloranil in an acetic acid solution. The anthocyanins were reacted with vanillin in concentrated hydrochloric acid and then quantified spectrophotometrically at 490 nm. A representative of each common flavonoid class including flavones (baicalein), flavonols (quercetin), flavonones (hesperetin), flavononols (silibinin), isoflavonoids (biochanin A), and flavanols (catechin) showed excellent linear dose-responses in the general range of 0.1-10.0 mM. For most flavonoids, the detection limit was about 0.1 mM in this assay. The recoveries of quercetin from spiked samples of apples and red peppers were 96.5 +/- 1.4% (CV = 1.4%, n = 4) and 99.0 +/- 4.2% (CV = 4.2%, n = 4), respectively. The recovery of catechin from spiked samples of cranberry extracts was 97.9 +/- 2.0% (CV = 2.0%, n = 4). The total flavonoids of selected common fruits and vegetables were measured using this assay. Among the samples tested, blueberry had the highest total flavonoid content (689.5 +/- 10.7 mg of catechin equiv per 100 g of sample), followed by cranberry, apple, broccoli, and red pepper. This novel SBC total flavonoid assay can be widely used to measure the total flavonoid content of fruits, vegetables, whole grains, herbal products, dietary supplements, and nutraceutical products.

Synthesis and assembly of gold nanoparticles in organized molecular films of gemini amphiphiles

Generation and assembly of gold nanostructures were investigated in the organized molecular films of a series of gemini amphiphiles. The chloroauric acid, dissolved in the aqueous subphase, was incorporated into the monolayers of the gemini amphiphiles containing ethyleneamine spacers through an interfacial assembly. The in situ formed complex monolayers were transferred onto solid substrates, and gold nanoparticles were generated in the film by a chemical or photochemical reduction. Discrete gold nanoparticles with an absorption maximum at 550 nm were generated in the films by photoirradiation, while different gold nanostructures were obtained by chemical reduction. Depending on the chemical reductant, various shape and assembly of gold nanostructures were obtained. When reduced by hydroquinone, a tree-branched assembly of the nanoparticles was obtained and the film showed a broad band centered at around 900 nm. When NaBH 4 was applied, crooked nanowires or assembly of nanoparticles were obtained, depending on concentration, and the film showed absorption at 569 or 600 nm. Furthermore, by combining the photochemical and chemical reduction methods, i.e., the chloroaurate ion-incorporated film was initially irradiated with UV light and then subjected to chemical reduction, the optical absorption of the formed gold nanostructures can be regulated.

Preparation of stable suspensions of gold nanoparticles in water by sonoelectrochemistry

Stable suspensions of gold nanoparticles in water were prepared with high yield by a novel one-step ultrasound assisted electrochemical process. Various strategies based on the addition of either tailor-made polymers or mixtures of commercially available polymers, in the electrochemical bath have been found successful to avoid nanoparticles aggregation commonly observed by sonoelectrochemistry. alpha-Methoxy-omega-mercapto-poly(ethylene oxide) or poly(vinyl pyrrolidone)/polyethylene oxide mixtures were able to build up a coalescence barrier around the gold nanoparticles. The results showed that the size of the gold nanoparticles could be easily tuned between 5 nm and 35 nm by simple control of the electrochemical parameters, i.e. the deposition time (T(ON)) from 10 ms to 20 ms. The properties of as-prepared gold nanoparticles were compared to the ones of gold colloids prepared by the more conventional wet nanoprecipitation method using chemical reductive agents.

Quantitative determination of paraquat in meconium by sodium borohydride-nickel chloride chemical reduction and gas chromatography/mass spectrometry (GC/MS)

The objective of this study was to develop a procedure for the GC/MS assay of paraquat in meconium as a biomarker of fetal exposure to paraquat. The method involved a sodium borohydride-nickel chloride reduction procedure, liquid-liquid extraction of the perhydrogenated product, concentration, and GC/MS assay. The method demonstrated good overall recovery (102.56%) with %CV (inter-assay) of less than 13%, and a limit of detection of 0.0156microg/g. Analysis of meconium samples from a study population in the Philippines (n=70) showed a 2.8% prevalence of fetal exposure to paraquat.