Long-term impacts of reservoir operation on the spatiotemporal variation in nitrogen forms in the post-Three Gorges Dam period (2004-2016).

Nitrogen (N) is an essential nutrient limiting life, and its biochemical cycling and distribution in rivers have been markedly affected by river engineering construction and operation. Here, we comprehensively analyzed the spatiotemporal variations and driving environmental factors of N distributions based on the long-term observations (from 2004 to 2016) of seven stations in the Three Gorges Reservoir (TGR). In the study period, several water quality indexes of the river reach improved, whereas N pollution was severe and tended to be aggravated after the TGR impoundment. The anti-seasonal reservoir operation strongly affected the variations in N forms. The total nitrogen (TN) concentration in the mainstream of the Yangtze River continuously increased, although it was still lower than that in the incoming tributaries (Wu and Jialing rivers). Further analysis showed that this increase occurred probably because of external inputs, including the upstream (76%), non-point (22%), and point source pollution inputs (2%). Additionally, different N forms showed significant seasonal variations; among them, the TN and nitrate nitrogen concentrations were the lowest in the impoundment season (October-February), and the ammonia nitrogen concentrations were the highest in the sluicing season (March-May). Redundancy analysis revealed that the water level and distance to the Three Gorges Dam were significant contributors to N forms distribution. Our findings could provide a basis for managing and predicting the water quality in the Yangtze River.

Visible-light driven photodegradation on Ag nanoparticle-embedded fullerene (C60) heterostructural microcubes.

Three-dimensional Ag(I)-fullerene hybrid microcrystal is fabricated by AgNO3 assisted liquid-liquid interfacial precipitation, containing the abundant sp2-π-electron system. With a mild chemical reduction, it produces the massive Ag nanocluster/fullerene junctions, on which fullerene doubles role as the excellent electron acceptor and photon scavenger, enabling the Plasmon-driven catalytic reaction. Ag nanocluster employed alone could not perform this photocatalytic reaction, neither of fullerene (C60) crystal. It implicates that Ag-fullerene interface is a key to drive catalytic process. Relative to conventional TiO2 nanostructures, fullerene expands light absorption to most solar wavelength and possesses a tightened bandgap which intrinsically expedites the charge transfer and charge separation from coinage metals. Demonstrated by photodegradation of organic molecules, this Ag(I)-fullerene (C60) composite, consisted of a plethora of electron donor-acceptor dyads renders an additional member to photocatalyst family, potentially implemented for photo-electron conversion, water remedy and beyond.

Ag(I)-Hived Fullerene Microcube as an Enhanced Catalytic Substrate for the Reduction of 4-Nitrophenol and the Photodegradation of Orange G Dye.

We report a facile approach to fabricate an Ag-embedded fullerene (C60) catalyst by the chemical reduction of the AgNO3 complex encapsulated fullerene microcrystal, which showed an enhanced catalytic reduction of 4-nitrophenol because of the strong absorption and propagation of H2 along the fullerene surface. With the aid of visible-light radiation, photodegradation of orange G dye is achieved through the formation of an electron donor-acceptor dyad between plasmon Ag nanostructures and fullerene molecules, which effectively offsets the "electron-hole" recombination. Neither Ag nanoparticle nor fullerene crystal used in isolation could perform this chemical conversion, implying that the metal-fullerene hybrid structure is imperative for performing the catalytic reaction. The obtained Ag-embedded fullerene crystal is characterized by scanning electron microscopy (SEM), associated energy-dispersive X-ray spectroscopy (EDX) imaging, and X-ray photoelectron spectroscopy (XPS) and demonstrates that the present hybrid materials would add a supplemental member to a family of photocatalysts toward the organic synthesis and wastewater remediation.

Unraveling a self-assembling mechanism of isomeric aminothiophenol on Ag dendrite by correlated SERS and matrix-free LDI-MS.

Correlated spectroscopic analysis can provide complementary chemical insights that are often unattainable by either approach used in isolation. We distinguished the different self-assembling behavior of isomeric aminothiophenols (ATPs) on Ag dendrite by the correlation of surface-enhanced Raman spectroscopy and laser-induced desorption ionization mass spectrometry, demonstrating that steric effect impinged significantly upon surface molecular density and plasmon-driven catalytic reaction yield, which led to drastic variations in the resulting SERS spectra. The correlative measurement shows that ortho-substitute barely formed a self-assemble monolayer, relative to the para-isomer, which can form a close-packed self-assembled monolayer and perform a decent azo-coupling reaction. Comparison between normal and SERS spectra of ATP isomers supports the fact that additional disulfide- or hydrogen-bonding interactions are established in para-ATP solid crystal, but neither of ortho- nor meta-isomers. This work is expected to create a significant impact on the development of an orthogonally correlated spectroscopic tool in deciphering chemical insights and underlying reaction mechanism. Graphical abstract.

Quantitative Determining of Ultra-Trace Aluminum Ion in Environmental Samples by Liquid Phase Microextraction Assisted Anodic Stripping Voltammetry.

Direct detecting of trace amount Al(III) in aqueous solution by stripping voltammetry is often frustrated by its irreversible reduction, resided at −1.75 V (vs. Ag/AgCl reference), which is in a proximal potential of proton reduction. Here, we described an electroanalytical approach, combined with liquid phase microextraction (LPME) using ionic liquid (IL), to quantitatively assess trace amount aluminum in environmental samples. The Al(III) was caged by 8-hydroxyquinoline, forming a superb hydrophobic metal⁻chelate, which sequentially transfers and concentrates in the bottom layer of IL-phase during LPME. The preconcentrated Al(III) was further analyzed by a square-wave anodic stripping voltammetry (SW-ASV). The resulting Al-deposited electrodes were characterized by scanning electron microscopy and powder X-ray diffraction, showing the intriguing amorphous nanostructures. The method developed provides a linear calibration ranging from 0.1 to 1.2 ng L−1 with a correlation coefficient of 0.9978. The LOD attains as low as 1 pmol L−1, which reaches the lowest report for Al(III) detection using electroanalytical techniques. The applicable methodology was implemented for monitoring Al(III) in commercial distilled water.

Surface invasive cleavage assay on a maskless light-directed diamond DNA microarray for genome-wide human SNP mapping.

The surface invasive cleavage assay, because of its innate accuracy and ability for self-signal amplification, provides a potential route for the mapping of hundreds of thousands of human SNP sites. However, its performance on a high density DNA array has not yet been established, due to the unusual "hairpin" probe design on the microarray and the lack of chemical stability of commercially available substrates. Here we present an applicable method to implement a nanocrystalline diamond thin film as an alternative substrate for fabricating an addressable DNA array using maskless light-directed photochemistry, producing the most chemically stable and biocompatible system for genetic analysis and enzymatic reactions. The surface invasive cleavage reaction, followed by degenerated primer ligation and post-rolling circle amplification is consecutively performed on the addressable diamond DNA array, accurately mapping SNP sites from PCR-amplified human genomic target DNA. Furthermore, a specially-designed DNA array containing dual probes in the same pixel is fabricated by following a reverse light-directed DNA synthesis protocol. This essentially enables us to decipher thousands of SNP alleles in a single-pot reaction by the simple addition of enzyme, target and reaction buffers.

Nanoporous GaN-Ag composite materials prepared by metal-assisted electroless etching for direct laser desorption-ionization mass spectrometry.

Three-dimensional nanoporous gallium nitride(PGaN) produced by metal-assisted electroless etching is chemically embedded with silver nanoparticles via electroless deposition, forming a metallized semiconductor membrane with large surface area and nanoscale metal features. A new application utilizing the unique chemical and morphological features of these composite nanostructures is described here, laser induced desorption-ionization(LDI) of biomolecules(e.g., cholesterol and nucleotides) for direct mass analysis, without use of additional organic matrix. Although PGaN itself is a poor matrix for direct LDI mass spectrometry, the combination of Ag and PGaN greatly improves ion signals relative to PGaN or Ag nanostructure surfaces alone. This behavior is attributed to the combination of strong UV absorption, enhanced surface area, and favorable thermal properties of PGaN. Importantly, Ag-PGaN is shown to facilitate the formation of Ag adduct ions in some cases, for example adenine, where adducts are not observed from either porous anodic aluminum membranes or surfaces presenting Ag nanoparticles in isolation. Nanopore-embedded Ag nanostructures serve a dual role: as cationization agents and to assist thermal desorption under UV laser irradiation. The results reported here suggest that the combination of Ag nanostructures embedded in PGaN has the capacity for high quality matrix-free LDI mass analysis.

Correlation of surface-enhanced Raman spectroscopy and laser desorption-ionization mass spectrometry acquired from silver nanoparticle substrates.

Applying complementary experiments, like laser desorption-ionization mass spectrometry (LDI-MS) and confocal surface-enhanced Raman microscopy, to the same physical sample location has the potential to elucidate the behavior of complex chemical and biochemical systems in ways that are not available to either method applied in isolation. In these experiments surface-enhanced Raman scattering (SERS) and LDI-MS are applied to the same sample spot using a common structure, deposited Ag colloids, both as ionization matrix and simultaneously as enhancing media for surface-enhanced Raman scattering of small organic molecules, dyes and lipids, and the behavior is compared. Three compounds-p-aminothiophenol (ATP), rhodamine 6G and cholesterol-which exhibit different strengths of interaction with Ag are examined in detail by correlated SERS and LDI-MS. The related mechanisms of nanoparticle-assisted desorption-ionization and Raman enhancement are explored by correlating mass and Raman spectra. The correlated spectra highlight the manner in which the different test compounds interact with plasmonic metal nanostructures. These coupled studies yield new insight into the transition of analyte from the metal-solution interface to gaseous ions, including, in the case of organothiols, a rich set of mixed clusters that provide chemical insight into the ion formation process.

Quantitative high-performance liquid chromatography-electrospray ionization tandem mass spectrometry analysis of bis-N7-guanine DNA-DNA cross-links in white blood cells of cancer patients receiving cyclophosphamide therapy.

Cyclophosphamide (CPA) is a DNA alkylating agent widely used in cancer chemotherapy. CPA undergoes metabolic activation to phosphoramide mustard and nornitrogen mustard (NOR) which alkylate the N-7 position of guanine in DNA to produce N-[2-(N7-guaninyl) ethyl]-N-[2-hydroxyethyl]-amine (G-NOR-OH) monoadducts and N,N-bis[2-(N7-guaninyl) ethyl] amine cross-links (G-NOR-G). G-NOR-G cross-links are strongly cytotoxic and are thought to be responsible for the biological activity of CPA. In the present work, an isotope dilution high-performance liquid chromatography-electrospray ionization (positive ion) tandem mass spectrometry (HPLC-ESI(+)-MS/MS) methodology was developed to accurately quantify G-NOR-G adducts in human blood. In our approach, DNA extracted from white blood cells (5-20 microg) is spiked with an internal standard of [(15)N(10)]-G-NOR-G and subjected to thermal hydrolysis to release G-NOR-G adducts from the DNA backbone. Following solid phase extraction, G-NOR-G conjugates are quantified by capillary HPLC-ESI-MS/MS in the selected reaction monitoring mode. The application of the new methodology is demonstrated for DNA extracted from blood of three cancer patients receiving 50-60 mg/kg of intravenous CPA. The highest numbers of G-NOR-G adduct (up to 18 adducts per 10(6) normal nucleotides) were observed 4-8 h following CPA administration, followed by a gradual decrease over time, probably due to adduct hydrolysis, DNA repair, and white blood cell death. This methodology will be useful for future investigations of the interindividual differences for CPA-induced DNA-DNA cross-linking.

Targeted quantitative analysis of superoxide dismutase 1 in cisplatin-sensitive and cisplatin-resistant human ovarian cancer cells.

Protein quantification in a complex protein mixture presents a daunting task in biochemical analysis. Antibody-based immunoassays are traditional methods for protein quantification. However, there are issues associated with accuracy and specificity in these assays, especially when the changes are small (e.g., <2-fold). With recent developments in mass spectrometry, monitoring a selected peptide, thus protein, in a complex biological sample has become possible. In this study, we demonstrate a simple mass spectrometry-based method for selective measurement of a moderately low abundant protein, superoxide dismutase 1 (SOD1), in cisplatin-sensitive and cisplatin-resistant human ovarian cancer cells. Selected-reaction-monitoring (SRM) technology was employed to specifically analyze the target peptides in a pair of human ovarian cancer cell lines: 2008/2008-C13*5.25 (cisplatin-sensitive/cisplatin-resistant, respectively). The observed 1.47-fold higher expression in the resistant cell line is consistent with findings by other approaches. This robust liquid chromatography/mass spectrometry (LC/MS) method provides a powerful tool for targeted proteomic verification and/or validation studies.

Targeting superoxide dismutase 1 to overcome cisplatin resistance in human ovarian cancer.

PURPOSE: Clinical drug resistance to platinum-based chemotherapy is considered a major impediment in the treatment of human ovarian cancer. Multiple pathways associated with drug resistance have been suggested by many previous studies. Over expression of several key proteins involved in DNA repair, drug transport, redox regulation, and apoptosis has been recently reported by our group using a global quantitative proteomic profiling approach. Superoxide dismutase 1 (SOD1) is one of these proteins consistently over-expressed in cisplatin-resistant ovarian cancer cells as compared to their sensitive counterparts, but its precise role in drug resistance is yet to be defined. METHOD: In the current study, we examined the role of SOD1 in drug resistance by inhibiting its redox activity in cisplatin-resistant ovarian cancer cells using a small-molecule inhibitor, triethylenetetramine (TETA). The effect of TETA was determined by the cell proliferation assay, clonogenic cell survival assay, and SOD1 activity assay. RESULTS: The inhibition of the SOD1 activity enhanced the cisplatin sensitivity in the resistant cells supporting the hypothesis that SOD1 is a key determinant of cisplatin resistance and is an exploitable target to overcome cisplatin drug resistance. CONCLUSION: SOD1 plays an important role in cisplatin resistance and modulation of its activity may overcome this resistance and ultimately lead to improved clinical outcomes.

Quantitative detection of individual cleaved DNA molecules on surfaces using gold nanoparticles and scanning electron microscope imaging.

Single-nucleotide polymorphisms (SNPs) are the most frequent type of human genetic variation. Recent work has shown that it is possible to directly analyze SNPs in unamplified human genomic DNA samples using the surface-invasive cleavage reaction followed by rolling circle amplification (RCA) labeling of the cleavage products. The individual RCA amplicon molecules were counted on the surface using fluorescence microscopy. Two principal limitations of such single-molecule counting are the variability in the amplicon size, which results in a large variation in fluorescence signal intensity from the dye-labeled DNA molecules, and a high level of background fluorescence. It is shown here that an excellent alternative to RCA labeling is tagging with gold nanoparticles followed by imaging with a scanning electron microscope. Gold nanoparticles have a uniform diameter (15 +/- 0.5 nm) and provide excellent contrast against the background of the silicon substrate employed. Individual gold nanoparticles are readily counted using publicly available software. The results demonstrate that the labeling efficiency is improved by as much as approximately 15-fold, and the signal-to-noise ratio is improved by approximately 4-fold. Detection of individual cleaved DNA molecules following surface-invasive cleavage was linear and quantitative over 3 orders of magnitude in amount of target DNA (10(-18)-10(-15) mol).

Scoring single-nucleotide polymorphisms at the single-molecule level by counting individual DNA cleavage events on surfaces.

Single-nucleotide polymorphisms (SNPs) are the most frequent type of human genetic variation. Recent work has shown that it is possible to directly analyze SNPs in unamplified human genomic DNA samples using the surface-invasive cleavage reaction followed by rolling circle amplification (RCA) of the cleavage products. The ability of RCA to produce single-stranded DNA tens of thousands of nucleotides in length from a single cleaved DNA molecule on the surface suggested the possibility of detecting individual cleavage events on the surface. The feasibility of this approach to SNP scoring is shown here. Individual cleavage events on the surface are detected using fluorescence microscopy to visualize the single-stranded DNA product of the RCA reaction labeled with the fluorescent dye SYBR Green I. The surface density of fluorescent features observed is dependent upon the concentration of target DNA. Future reductions of the sample volume and optimization of the reaction conditions offer the potential of being able to perform such analyses on as little as a single copy of genomic DNA target.