Detection of dopamine in the presence of excess ascorbic acid at physiological concentrations through redox cycling at an unmodified microelectrode array

The electrochemical behavior of dopamine was examined under redox cycling conditions in the presence and absence of a high concentration of the interferent ascorbic acid at a coplanar, microelectrode array where the area of the generator electrodes was larger than that of the collector electrodes. Redox cycling converts a redox species between its oxidized and reduced forms by application of suitable potentials on a set of closely located generator and collector electrodes. It allows signal amplification and discrimination between species that undergo reversible and irreversible electron transfer. Microfabrication was used to produce 18 individually addressable, 4-μm-wide gold band electrodes, 2 mm long, contained in an array having an interelectrode spacing of 4 μm. Because the array electrodes are individually addressable, each can be selectively biased to produce an overall optimal electrochemical response. Four adjacent microbands were shorted together to serve as the collector, and were flanked on each side by seven microbands shorted as the generator (a ratio of 1:3.5 of electroactive area, respectively). This configuration achieved a detection limit of 0.454?±?0.026 μM dopamine at the collector in the presence of 100 μM ascorbic acid in artificial cerebrospinal fluid buffer, concentrations that are consistent with physiological levels. Enhancement by surface modification of the microelectrode array to achieve this detection limit was unnecessary. The results suggest that the redox cycling method may be suitable for in vivo quantification of transients and basal levels of dopamine in the brain without background subtraction.

Tuning of Ti-doped mesoporous silica for highly efficient enrichment of phosphopeptides in human placenta mitochondria

Extraction of phosphopeptides from rather complex biological samples has been a tough issue for deep and comprehensive investigation into phosphoproteomes. In this paper, we present a series of Ti-doped mesoporous silica (Ti-MPS) materials with tunable composition and controllable morphology for highly efficient enrichment of phosphopeptides. By altering the molar ratio of silicon to titanium (Si/Ti) in the precursor, the external morphology, Ti content, internal long-rang order, and surface area of Ti-MPS were all modulated accordingly with certain regularity. Tryptic digests of standard phosphoprotein α- and β-casein were employed to assess the phosphopeptide enrichment capability of Ti-MPS series. At the Si/Ti molar ratio of 8:1, the optimum enrichment performance with admirable sensitivity and capacity was achieved. The detection limit for β-casein could reach 10 fmol, and 15 phosphopeptides from the digest of α-casein were resolved in the spectrum after enrichment, both superior to the behavior of commercial TiO₂ materials. More significantly, for the digest of human placenta mitochondria, 396 phosphopeptides and 298 phosphoproteins were definitely detected and identified after enrichment with optimized Ti-MPS material, demonstrating its remarkable applicability for untouched phosphoproteomes. In addition, this research also opened up a universal pathway to construct a composition-tunable functional material in pursuit of the maximum performance in applications.

Synthesis and self-assembly behaviors of four-armed amphiphilic polystyrene-b-poly(N-isopropylacrylamide) copolymers

Four-armed amphiphilic block copolymers polystyrene-b-poly(N-isopropyl acrylamide) (PSt-b-PNIPAAM)₄ were synthesized by atom transfer radical polymerization (ATRP) in two steps. Star narrow dispersed polystyrene, (PSt-Br)₄, with controlled number-average molecular weight was firstly synthesized by ATRP of styrene (St) using pentaerythritol tetrakis (2-bromoisobutyrate) (4Bri-Bu) as four-armed initiator. Then, (PSt-b-PNIPAAM)₄ was prepared using (PSt-Br)₄ as macroinitiator by ATRP. The structures of (PSt-Br)₄ and (PSt-b-PNIPAAM)₄ were confirmed by characterization by nuclear magnetic resonance (¹H NMR). The apparent viscosity of the four-armed (PSt-b-PNIPAAM)₄ was significantly lower than that of the linear PSt-b-PNIPAAM with the same amount of repeat units of PSt and PNIPAAM. The self-assembly behavior of the four-armed amphiphilic block copolymers (PSt-b-PNIPAAM)₄ in mixed solution (DMF/H₂O) and the lower critical solution temperature (LCST) of the resulting micelles were investigated by scanning electron microscopy (SEM), dynamic light scattering (DLS) and UV-VIS spectroscopy. The results show that the size of the mono-dispersed spherical micelles decreased with the increment of the chain length of PNIPAAM in the block copolymers, while LCST increased.     

Coupling of ultrasound‐assisted extraction and expanded bed adsorption for simplified medicinal plant processing and its theoretical model: Extraction and enrichment of ginsenosides from Radix Ginseng as a case study

A high‐efficient and environmental‐friendly method for the preparation of ginsenosides from Radix Ginseng using the method of coupling of ultrasound‐assisted extraction with expanded bed adsorption is described. Based on the optimal extraction conditions screened by surface response methodology, ginsenosides were extracted and adsorbed, then eluted by the two‐step elution protocol. The comparison results between the coupling of ultrasound‐assisted extraction with expanded bed adsorption method and conventional method showed that the former was better than the latter in both process efficiency and greenness. The process efficiency and energy efficiency of the coupling of ultrasound‐assisted extraction with expanded bed adsorption method rapidly increased by 1.4‐fold and 18.5‐fold of the conventional method, while the environmental cost and CO₂ emission of the conventional method were 12.9‐fold and 17.0‐fold of the new method. Furthermore, the theoretical model for the extraction of targets was derived. The results revealed that the theoretical model suitably described the process of preparing ginsenosides by the coupling of ultrasound‐assisted extraction with expanded bed adsorption system.     

Separation,interconversion, and insecticidal activity of the cis‐ and trans‐isomers of novel hydrazone derivatives

A series of cis‐ and trans‐isomers of hydrazone derivatives were separated and analyzed through HPLC with diode‐array detection and HPLC‐MS/MS using ESI and ion trap MS. Two single crystals (A‐5‐1 and C‐2‐1) of the trans‐isomers were obtained and determined using X‐ray crystallography data, and the cis‐ to trans‐isomerization under different conditions was discussed. Both of the cis‐ and trans‐isomers of A‐4 and A‐5 exhibited good insecticidal activities against Plutella xylostella.     

Rapid determination of catecholamines in urine samples by nonaqueous microchip electrophoresis with LIF detection

A method was developed for the rapid separation of catecholamines by nonaqueous microchip electrophoresis (NAMCE) with LIF detection, A homemade pump‐free negative pressure sampling device was used for rapid bias‐free sampling in NAMCE, the injection time was 0.5 s and the electrophoresis separation conditions were optimized. Under the optimized conditions, the samples were separated completely in <1 min. The average migration times of the epinephrine (E), dopamine (DA), and norepinephrine (NE) were 34.26, 43.81, and 50.07 s, with an RSD of 1.05, 1.26, and 0.89% (n = 7), respectively. The linearity of the method ranged from 0.0125 to 2.0 mg/L for E and 0.025～4.0 mg/L for DA and NE, with correlation coefficients ranging between 0.9978 and 0.9986. The detection limits of E, DA, and NE were 2.5, 5.0, and 5.0 μg/L, respectively. The recoveries of E, DA, and NE in spiked urine samples were between 86 and 103%, with RSDs of 4.5～6.8% (n = 5). The proposed NAMCE with LIF detection combined with a pump‐free negative pressure sampling device is a simple, inexpensive, energy efficient, miniaturized system that can be successfully applied for the determination of catecholamines in urine samples.     

Wrinkling and Growth Mechanism of CuO Nanowires in Thermal Oxidation of Copper Foil

We report a systematic study on wrinkling and CuO nanowires （NWs） growth in the thermal oxidation of copper foil. Copper foils with thickness of 0.5 mm were thermally oxidized in air at 500℃ for 0.5-10 h. It is found that all the samples have wrinkles and the size of the wrinkles increases with the oxidation time increasing. CuO NWs can grow on both the sidehill and hilltop of wrinkle. The CuO NWs on sidehill are longer and denser than those on hilltop. The growth direction of the CuO NWs on sidehill is not vertical to the substrate but vertical to their growth surfaces. The process of wrinkling and CuO NWs growth can be divided into three stages： undulating, voiding, and cracking. The CuO NWs on both sidehill and hilltop grow at the undulating stage. However, only the CuO NWs on sidehill grow and those on hilltop stop growing at the voiding and cracking stages because of the void in hilltop. The local electric field in a wrinkle at undulating stage was calculated, and it is found that the difference of local electric field strengths between hilltop and sidehill is small, which indicates that the predominant driving force for the diffusion of Cu ion during CuO NWs growth is internal stress.     

Syntheses, structures and magnetic properties of three Co(II) coordination architectures based on a flexible multidentate carboxylate ligand and different N-donor ligands

Three new cobalt complexes, {[Co₅(tci)₂(bimb)₃(µ₃-O)₂(H₂O)₂]·3DMF·4H₂O} _n (1), {[Co₃(tci)₂(bib)]·2DMF·2H₂O} _n (2) and {[Co(Htci)(bpea)_0.5]·H₂O} _n (3) (H₃tci = tris(2-carboxyethyl)isocyanurate, bimb = 4,4′-bis(imidazol-1-yl)biphenyl, bib = 1,4-bis(imidazol-1-yl)benzene, bpea = 1,2-bis(4-pyridyl)ethane, DMF = N,N′-dimethylformamide), have been successfully synthesized through the assembly of Co(II) ions, H₃tci and different N-donor ligands, respectively. All complexes were structurally characterized by single crystal X-ray diffraction, elemental analyses, IR spectra, thermogravimetric (TG) analyses and X-ray powder diffraction (XRPD). Complex 1 exhibits a 3D three-fold parallel interpenetrated 3D → 3D structure with (6⁵·8) CdSO₄ topology. Complex 2 is built from [Co₃(µ₂-O_carboxyl)₂(CO₂)₄] clusters and linear bib ligands, displaying a two-fold parallel interpenetrated (3,8)-connected (4³)₂(4⁶·6¹⁸·8⁴) topology, while complex 3 is a 3D pillar-layered structure involving an infinite -Co-(µ₂-Ocarboxyl)(CO₂)-Co-chain. The diverse structures of the three complexes indicate that the skeletons of different N-donor ligands play an important role in the assembly of such different frameworks. In addition, magnetic investigation indicates that besides spin-orbit coupling of Co(II) ions, there exist antiferromagnetic exchange interactions in Co₅ and Co₃ clusters of 1 and 2, respectively.     

Predicting hiCE inhibitors based upon pharmacophore models derived from the receptor and its ligands

Human intestinal carboxyl esterase (hiCE) is a drug target for ameliorating irinotecan-induced diarrhea. By reducing irinotecan-induced diarrhea, hiCE inhibitors can improve the anti-cancer efficacy of irinotecan. To find effective hiCE inhibitors, a new virtual screening protocol that combines pharmacophore models derived from the hiCE structure and its ligands has been proposed. The hiCE structure has been constructed through homology techniques using hCES1’s crystal structure. The hiCE structure was optimized via molecular dynamics simulations with the most known active hiCE inhibitors docked into the structure. An optimized pharmacophore, derived from the receptor, was then generated. A ligand-based pharmacophore was also generated from a larger set of known hiCE inhibitors. The final hiCE inhibitor predictions were based upon the virtual screening hits from both ligand-based and receptor-based pharmacophore models. The hit rates from the ligand-based and receptor-based pharmacophore models are 88% and 86%, respectively. The final hit rate is 94%. The two models are highly consistent with one another (85%). This proves that both models are reliable.     

Adsorption behavior of uranium on polyvinyl alcohol-g-amidoxime: Physicochemical properties, kinetic and thermodynamic aspects

Amidoxime-based adsorbents are widely studied as the main adsorbent in the recovery of uranium from seawater.However,the adsorption rate and loading capacity of such adsorbents should be further improved due to the economic viability consideration.In this paper,polyvinyl alcohol functionalized with amidoxime(PVA-g-AO)has been prepared as a new adsorbent for uranium(Ⅵ)adsorption from aqueous solution.The physicochemical properties of PVA-g-AO were investigated using infrared spectroscopy(IR),scanning electron microscope(SEM),X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).Results showed that the ligand monomers were successfully grafted onto the matrixes.The XRD and XPS analysis showed that uranium was adsorbed in metal ionic form rather than in crystal form.Uranyl(U(Ⅵ))adsorption properties onto PVA-g-AO were evaluated.The adsorption of U(Ⅵ)by PVA-g-AO was fast,with an equilibrium time of less than 50 min.Additionally the maximum adsorption capacity reached 42.84 mg/g at pH 4.0.