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Flexible high-resolution broadband sum-frequency generation vibrational spectroscopy for intrinsic spectral line widths
No full textThe difficulty in achieving high spectral resolution and accurate line shape in sum-frequency generation vibrational spectroscopy (SFG-VS) has restricted its use in applications requiring precise detection and quantitative analysis. Recently, the development of high-resolution broadband sum-frequency generation vibrational spectroscopy (HR-BB-SFG-VS) with sub-wavenumber resolution generated by synchronizing two independent amplifier lasers have opened new opportunities for probing an intrinsic SFG response. Here, we present a new flexible approach to achieve HR-BB-SFG-VS. In this system, two regeneration amplifiers shared the same oscillator laser as the seed, and a time-asymmetric visible pulse with a nearly Lorentzian line shape filtered by an etalon was used to overlap with a femtosecond broadband infrared pulse. This Lorentzian line shape of the visible pulse can greatly simplify the spectral fitting and analysis. We also demonstrated that the single-sided long visible pulse provided both high spectral resolution (1.4 cm(-1)) and effective suppression of the non-resonant background by detuning the time delay between visible and infrared pulses in SFG-VS measurements. With this new SFG setup, a pair of spectral splittings by 3.1 +/- 0.7 and 3 +/- 0.2 cm 1 for the symmetric and antisymmetric stretching of the CH3 group was resolved at the CH3CN/TiO2(110) surface, which are tentatively attributed to two different orientational methyl groups. These technological advancements can help broaden the applications of HR-BB-SFG-VS and provide solid ground for a better understanding of complex molecular structures and dynamics at interfaces. Published under license by AIP Publishing
Toward Fundamentals of Confined Electrocatalysis in Nanoscale Reactors
No full textA number of experiments have demonstrated that electrochemical reactions are feasible in confined nanoscale reactors, while what the fundamentals of confined electrochemistry are is not clear. Using first-principles calculations and electrochemical modeling, we find that the capacitance in the confined nanoscale reactors can be significantly enhanced, compared to an open electrode interface, essentially promoting the electrochemical reactions and charge transfer efficiency in nanoscale reactors. More importantly, this is a general character, as found in a variety of electrochemical and thermochemical reactions. At the end, we use the recently defined new concept of "confinement energy" for understanding the nature of confined electrochemistry from both thermochemical and electrochemical points of view
Magnetic contributions to the low-temperature specific heat of Sc79Fe21 nanoglass
No full textThe specific heat (Cp) of the Sc79Fe21 nanoglass and Sc75Fe25 melt-spun ribbons was measured in zero and non-zero applied magnetic fields for a temperature range of 1.9 to 7 K. The plots for the C-p/T-vs-T-2 without an applied magnetic field show an "upturn" at lower temperatures. Based on the variations of the "upturn" with applied magnetic fields and the magnetism of the alloys, the "upturn" was attributed to the effect of the ferromagnetic clusters. The calculated number of ferromagnetic clusters within the Sc79Fe21 nanoglass was much smaller than that within the Sc75Fe25 melt-spun ribbon, most likely because of the chemically heterogeneous structure of the nanoglass. Published under license by AIP Publishing
Cytochrome P450 3A Enzymes Are Key Contributors for Hepatic Metabolism of Bufotalin, a Natural Constitute in Chinese Medicine Chansu
No full textBufotalin (BFT), one of the naturally occurring bufodienolides, has multiple pharmacological and toxicological effects including antitumor activity and cardiotoxicity. This study aimed to character the metabolic pathway(s) of BFT and to identify the key drug metabolizing enzyme(s) responsible for hepatic metabolism of BFT in human, as well as to explore the related molecular mechanism of enzymatic selectivity. The major metabolite of BFT in human liver microsomes (HLMs) was fully identified as 5 beta-hydroxylbufotalin by LC-MS/MS and NMR techniques. Reaction phenotyping and chemical inhibition assays showed that CYP3A4 and CYP3A5 were key enzymes responsible for BFT 5 beta-hydroxylation. Kinetic analyses demonstrated that BFT 5 beta-hydroxylation in both HLMs and human CYP3A4 followed the biphasic kinetics, while BFT 5 beta-hydroxylation in CYP3A5 followed substrate inhibition kinetics. Furthermore, molecular docking simulations showed that BFT could bind on two different ligand-binding sites on both CYP3A4 and CYP3A5, which partially explained the different kinetic behaviors of BFT in CYP3A4 and CYP3A5. These findings are very helpful for elucidating the phase I metabolism of BFT in human and for deeper understanding the key interactions between CYP3A enzymes and bufadienolides, as well as for the development of bufadienolide-type drugs with improved pharmacokinetic and safety profiles
Performance of time-dependent density functional theory on twisted intramolecular charge transfer state of emerging visible light photoswitches
No full textHemithioindigo dyes (HTIs) are a class of emerging visible light photoswitches. By using M06, M062X, B3LYP and BMK density functionals, we have investigated the local excited (LE) state and twisted intramolecular charge transfer (TICT) state of HTIs. Both the two excited states are located in HTIs Z1 and Z2 after combining the results of all functionals. The formation of either the LE or TICT state is found to be controlled by the direction of the C-2-C-3 single bond rotation. Different functionals are found to have intrinsic biases on LE and TICT states. Thus, a reasonable combination of various functionals is a convenient method to investigate a system possessing multiple excited-state minima. We recommend a combination of the M06 and M062X functionals
Dummy molecularly imprinted solid phase extraction of climbazole from environmental water samples
No full textDummy molecularly imprinted polymer (DMIP) for climbazole (CBZ) was synthesized for the first time employing miconazole (MNZ) as the dummy template together with methacrylic acid (MAA) monomer, ethylene glycol dimethacrylate (EGDMA) cross-linker and acetonitrile (ACN) porogen. The selectivity and capacity of the prepared MNZ-DMIP was estimated for CBZ by high-performance liquid chromatography (HPLC) and equilibrium binding experiments. Imprinting factor (IF) with a value of 7.0 was achieved, much higher than the CBZ templated MIP (IF = 3.5). Heterogeneous binding sites were found in the MNZ-DMIP, the corresponding saturation capacity and dissociation constant for the high and low affinity binding sites were 6.761 mu mol g(-1) and 0.3027 mmol L-1, 43.60 mu mol g(-1) and 4.055 mmol L-1, respectively. High efficient method based on dummy molecularly imprinted solid phase extraction (DMISPE) coupled with HPLC was established for the selective enrichment of CBZ in river and tap water using MNZ-DMIP as sorbent. DMISPE conditions including sample loading pH/volume, selective washing and elution solvents were carefully optimized. The developed method showed good recoveries (82.3-96.2%) and repeatability (RSDs 0.6-4.9%, n = 5) for samples spiked at three different concentration levels (0.2, 1.0 and 5.0 mu g L-1). The detection limit was determined as 0.012 mu g L-1. The results demonstrated good potential of this method for sample pretreatment of CBZ in environmental water samples
Facile fabrication of zwitterionic magnetic composites by one-step distillation-precipitation polymerization for highly specific enrichment of glycopeptides
No full textHydrophilic interaction chromatography (HILIC) utilizing zwitterion-modified material as solid phase has attracted extensive attention for selective enrichment of glycopeptides. However, a tedious synthesis and low specificity for glycopeptides have restricted its application. Herein, a facile and effective approach was developed to synthesize a zwitterionic (ZIC) polymer-coated magnetic composites (denoted as Fe3O4@PMSA) with a zwitterion ((2-(methacryloyloxy) ethyl)-dimethyl-(3-sulfopropyl) ammonium hydroxide, MSA) via one-step distillation-precipitation polymerization (DPP). The well-designed composites presented clearly ZIC-polymer shell and superior hydrophilicity (water contact angle 30.2), and the performance for selective enrichment of glycopeptides were investigated with standard and real samples, respectively. Owning to the abundant of ZIC molecules with multi-charge and polar groups on the surface of resulting polymer coating, the Fe3O4@PMSA demonstrated high selectivity for glycopeptides enrichment with IgG digest (twenty glycopeptides identified, S/N >= 20) and a mixture of IgG and BSA at the mass ratio of 1:230 (sixteen glycopeptides identified, S/N >= 20). Besides, the detection limit as low as 0.67 fmol for IgG (S/N >= 10) and satisfied recovery yield more than 74% were achieved by the proposed sorbents. Finally, the Fe3O4@PMSA was applied for enriching N-linked glycopeptides from human serum, and 348 unique N-glycosylation sites and 419 glycopeptides from 158 glycoproteins were strictly identified from 1 mL human serum. The results demonstrated that the proposed Fe3O4@PMSA showed a promising potential in glycoproteomics analysis of real biological samples. (C) 2018 Elsevier B.V. All rights reserved
Structural isomer and high-yield of Pt1Ag28 nanocluster via one-pot chemical wet method
No full textIn order to understand the structure-property correlation and explore the application of metal nanoclusters, it is important and intriguing to determine their crystal structure and obtain high-yield. At the same time, this is also a challenge in nanoscience and technology. Here, we report the highly efficient synthesis of Pt1Ag28 nanocluster via one-pot chemical wet method. The crystal structure of Pt1Ag28 nanocluster was determined by X-ray crystallography to be a face centered cubic (FCC) kernel. This novel structure is the structural isomerization of Pt1Ag28 nanocluster reported before. This phenomenon is first discovered in the synthesis of alloy nanoclusters. In addition, Pt1Ag28 nanocluster has high yield and exhibits potential optics in the near infrared (NIR) fluorescent imaging. The time-dependent density functional theory (TD-DFT) calculation implied that the optical property of Pt1Ag28 was sensitive to its structure. This work provides a simple method to synthesize alloy nanoclusters with structural isomerization
Modified metabolites mapping by liquid chromatography-high resolution mass spectrometry using full scan/all ion Cheek for fragmentation/neutral loss acquisition
No full textModified metabolites play important roles in diagnostic monitoring, oxidative response and physiological regulation. Comprehensive analytical methods are greatly needed for improving the coverage of modified metabolites and studying their physiological function. Here, a novel nontargeted profiling method for mapping modified metabolites was developed by liquid chromatography-high resolution mass spectrometry with full scan/all ion fragmentation/neutral loss (FS/AIF/NL) data acquisition. Modified metabolites were unbiasedly defined with less false positive results by mixed standards verification. Thirteen types of modified metabolites in urine were analyzed at the same time, and 198 of 307 modified metabolites at positive mode and 166 of 366 modified metabolites at negative mode were putatively identified. The modified metabolites profiling method was applied for investigating the metabolic differences between the patients with breast cancer and health controls. As a result, many modified metabolites with glu-curonidation, ribosylation and indole acetylation modification were significantly up-regulated in breast cancer and four modified metabolites including 7-methylguanosine, N-4-acetylcytidine, dihyroxy-1H-indole glucuronide I and indole-3-acetic acid-O-glucuronide were identified as potential biomarkers for the diagnose of breast cancer. (C) 2018 Elsevier B.V. All rights reserved
Role of Pt Loading in the Photocatalytic Chemistry of Methanol on Rutile TiO2(110)
No full textAs a cocatalyst, Pt is well-known for accepting photoexcited electrons and lowering the overpotential of hydrogen production in photocatalysis, being responsible for the enhanced photocatalytic efficiency. Despite the above existing knowledge, the adsorption of reactants on the Pt/photon-absorber (for example, Pt/TiO2) interface, a prerequisite to understand the photocatalytic chemistry, is extremely difficult to investigate mainly because of the complexity of the powdered material and solution environment. Combining ultrahigh vacuum and well-ordered single crystals, we study the photocatalytic chemistry of methanol on Pt-loaded rutile TiO2(110) using temperature-programmed desorption (TPD) and ultraviolet photoelectron spectroscopy (UPS). Despite the same photocatalytic chemical products (i.e., formaldehyde and surface hydrogen species) as on Pt-free TiO2(110), the subsequent chemistry of surface hydrogen species and the photocatalytic reaction rate are much different. The bridging hydroxyls desorb as water molecules around 500 K on the Pt-free TiO2(110) surface, and by contrast, this desorption channel disappears completely and water and molecular hydrogen desorb at much lower temperature (<300 K) after Pt deposition, which can prevent the recombination of hydrogen species with formaldehyde. More importantly, methanol dissociates into methoxy at the Pt/TiO2(110) interface, which is crucial in the photocatalytic chemistry of methanol on TiO2 surfaces because methoxy is a more effective hole scavenger than methanol itself. The photocatalytic chemical reaction rate is increased by nearly 1 order of magnitude after 0.12 monolayer Pt deposition. This work suggests that Pt loading can promote the dissociation of methanol into methoxy and lower the desorption barrier of molecular hydrogen, which may work cooperatively with separating photoexcited charges to enhance the photocatalytic efficiency. Our work implies the importance of the cocatalysts in affecting the surface structure and adsorption of reactants and products and then improving the photoactivity, in addition to the well known role in charge separation