Higher dissolved oxygen levels promote downward migration of phosphorus in the sediment profile: Implications for lake restoration.

Lake restoration (typically sediment dredging) commonly involves producing a new sediment-water interface (SWI). This study comprehensively investigated the migration and transformation of P during the formation of a new SWI under different dissolved oxygen (DO) levels in the overlying water, based on Fe/Al-rich sediment. The results suggest that DO had a profound effect on the 0-7 cm sediment layer properties and higher DO levels in the overlying water resulted in the diffusion of DO deeper into the sediments. Importantly, besides preventing Fe reductive dissolution and sulfides competition, higher DO levels inhibited the release of P from sediment by inducing the mitigation of P from the upper (0-3 cm) into the bottom (3-7 cm) sediments. The migration of P was found to be closely related to the interactions between organic matter and Al, Fe, and Ca in the sediment profile caused by higher DO levels in overlying water. Particularly, the decrease in organic matter in the upper sediments increased the mobility of Ca and promoted aging of Al and Fe, which increased the migration of the different forms of P. The increased organic matter in the bottom sediments retained the mobile Ca and increased amorphous Fe, which immobilized the P that had migrated from the upper sediments. These results demonstrate the relatively high mobility of P in the upper sediments and the importance of P immobilization capability of bottom sediments on regulating P release from SWI under higher DO levels in overlying water. Accordingly, measures for lake restoration with producing a new SWI were recommended to be applied in combination with P immobilization method to develop more feasible strategies.

Organic matter stabilized Fe in drinking water treatment residue with implications for environmental remediation.

Fe-based materials used to adsorb P are commonly considered to be limited by the increased Fe lability, while Fe in drinking water treatment residue (DWTR) shows stable P adsorption abilities. Accordingly, this study aimed to gain insight into Fe lability in DWTR as compared to FeCl3 and Fe2(SO4)3 using Fe fractionation, EXAFS, and high-throughput sequencing technologies. The results showed that compared to Fe2(SO4)3 and FeCl3, Fe was relatively stable in the DWTR under the effects of organic matter, sulfides, and anaerobic conditions. Typically, the addition of FeCl3 and Fe2(SO4)3 enhanced Fe mobility in sediment and overlying water, promoting the formation of Fe-humin acid and ferrous sulfides (FeS and FeS2). However, the addition of DWTR, even at relatively high doses of Fe, has limited impact on Fe mobility. The addition remarkably increased oxidizable Fe in sediment (by approximately 63%), causing Fe to be dominated by oxidizable and residual fractions (like those in raw DWTR); EXAFS analysis also suggested that Fe-humin acid increased substantially with the addition of DWTR, becoming the main Fe species in sediment (with a relative abundance of 50.1%). Importantly, the Fe distributions were stable in sediment with DWTR added, which demonstrated that organic matter stabilized the Fe in the DWTR. Further analysis indicated that all materials promoted the enrichment of bacterial genera potentially related to Fe metabolism (e.g., Bacteroides, Dok59, and Methanosarcina). Fe2O3 in the FeCl3 and Fe2(SO4)3 groups and Fe-HA in the DWTR group were the key species affecting the microbial communities. Overall, the stabilizing effect of organic matter on Fe in DWTR could be used to develop Fe-based materials to enhance Fe stability for environmental remediation.

Theoretical investigation on exciton-dissociation and charge-recombination processes of PC61BM-PTDPPSe interface.

Designing and synthesizing novel electron-donor polymers with the high photovoltaic performances has remained a major challenge and hot issue in organic electronics. In this work, the exciton-dissociation (k dis ) and charge-recombination (k rec ) rates for the PC61BM-PTDPPSe system as a promising polymer-based solar cell candidate have been theoretically investigated by means of density functional theory (DFT) calculations coupled with the non-adiabatic Marcus charge transfer model. Moreover, a series of regression analysis has been carried out to explore the rational structure-property relationship. Results reveal that the PC61BM-PTDPPSe system possesses the large open-circuit voltage (0.77 V), middle-sized exiton binding energy (0.457 eV), and relatively small reorganization energies in exciton-dissociation (0.273 eV) and charge-recombination (0.530 eV) processes. With the Marcus model, the k dis , k rec , and the radiative decay rate (k s ), are estimated to be 3.167×10(11) s(-1), 3.767×10(10) s(-1), and 7.930×10(8) s(-1) respectively in the PC61BM-PTDPPSe interface. Comparably, the k dis is as 1∼3 orders of magnitude larger than the k rec and the k s , which indicates a fast and efficient photoinduced exciton-dissociation process in the PC61BM-PTDPPSe interface. Graphical Abstract PTDPPSe is predicted to be a promising electron donor polymer, and the PC61BM-PTDPPSe system is worthy of further device research by experiments.

Purification and ATP hydrolysis of the putative cholesterol transporters ABCG5 and ABCG8.

Mutations in the ATP-binding cassette (ABC) transporters ABCG5 and ABCG8 lead to sitosterolemia, a disorder characterized by sterol accumulation and premature atherosclerosis. ABCG5 and ABCG8 are both half-size transporters that have been proposed to function as heterodimers in vivo. We have expressed the recombinant human ABCG5 and ABCG8 genes in the yeast Pichia pastoris and purified the proteins to near homogeneity. Purified ABCG5 and ABCG8 had very low ATPase activities (<5 nmol min(-)(1) mg(-)(1)), suggesting that expression of ABCG5 or ABCG8 alone yielded nonfunctional transporters. Coexpression of the two genes in P. pastoris greatly increased the yield of pure proteins, indicating that the two transporters stabilize each other during expression and purification. Copurified ABCG5/G8 displayed low but significant ATPase activity with a V(max) of approximately 15 nmol min(-)(1) mg(-)(1). The ATPase activity was not stimulated by sterols. The catalytic activity of copurified ABCG5/G8 was characterized in detail, demonstrating low affinity for MgATP, a preference for Mg as a metal cofactor and ATP as a hydrolyzed substrate, and a pH optimum near 8.0. AlFx and BeFx inhibited MgATP hydrolysis by specific trapping of nucleotides in the ABCG5/G8 proteins. Furthermore, ABCG5/G8 eluted as a dimer on gel filtration columns. The data suggest that the hetero-dimer is the catalytically active species, and likely the active species in vivo.

Dual-capillary backscatter interferometry for high-sensitivity nanoliter-volume refractive index detection with density gradient compensation.

A simple, stable, ultrasensitive dual-capillary dual-bicell (DCDB) microinterferometic backscattering detection (MIBD) system was developed. In DCDB MIBD, a He-Ne laser beam passes through a half-wave plate onto the cross section of two capillaries, one for reference and another for sensing analyte. The position of the backscattered fringe from each capillary, which are in proximity or essentially identical thermal environments, was detected with matched bicell photodetectors. The configuration was found to effectively compensate for thermal drift, which is normally the major source of noise in refractive index (RI) detection systems. It is shown that passive environmental compensation leads to greatly enhanced signal in nanoscale refractometry preformed by MIBD. An order of magnitude improvement in detection limits over single channel configurations is possible. Performance reaches the 10(-9) RIU level for like solvents in the presence in extremely large thermally induced RI gradients. At this level of detectability, DCDB MIBD could facilitate nanoliter-volume, femtomole-level universal detection in applications ranging from mu-HPLC and on-chip CE to scanning microcalorimetry.

Attomole sensitivity for unlabeled proteins and polypeptides with on-chip capillary electrophoresis and universal detection by interferometric backscatter.

A universal detector based on backscatter interferometry has been developed to perform nanoliter volume refractive index measurements for on-chip sodium dodecyl sulfate (SDS) gel based (polyethylene oxide gel) separations and quantification label-free proteins. The on-chip interferometric backscatter detector (OCIBD) system consists of a simple, folded optical train based on the interaction of a laser beam with an etched channel in the shape of half cylinder in a fused-silica plate. The backscattered light from the channel takes on the form of a high-contrast interference pattern that contains information related to the bulk properties of the fluid located within the probe or detection volume of 2.32 x 10(-9) L. Depending on capillary electrophoresis (CE) injection method, the positional changes of the interference pattern extrema (fringes) allow for the quantification of unlabeled proteins at levels ranging from 11 to 310 amol (2.7 x 10(-8)mol/L) with a linear dynamic range of 2.5 decades (egg albumin). Using OCIBD microchannel-based SDS capillary gel electrophoresis (SDS/CGE), separation and detection of five label-free proteins was achieved in less than 100 seconds with detection limits ranging from 0.95 pg (1.1 x 10(-16)mol or 2.5 x 10(-7)mol/L) of calmodulin to 7.0 pg (1.0 x 10(-16)mol or 2.4 x 10(-7)mol/L) for bovine serum albumin (BSA) without signal filtering or active thermal control. This development shows that a universal detector based on backscatter interferometry can be used effectively for on-chip label-free solute analysis.