化学淀积银膜上卤素电解质对吡啶的表面增强喇曼散射(SERS)的影响

本文是载玻片上化学沉淀1000左右粗糙度的银膜,对其吡啶/KX/H_2O 体系(x=F~-,Cl~-,Br~-,I~-)的 SERS 光谱进行了实验研究。分析了不同的卤素电解质,其SERS 光谱峰值大小、位移及吸附态的变化。实验表明:适当的卤素电解质和吡啶的共吸附是产生 SERS 的必要条件。     

关于超平行体的几个不等式

设x_1,x_2,…,x_m是n维内积空间R~n中m个线性无关的向量,以这m个向量为梭所构成的超平行多面体的体积记为V[x_1,x_2,…,x_m]。则经典的Hadamard不等式可表达为: V[x_1,x_2,…,x_m]≤multiply from k=1 to m(‖X_k‖)     

A semi-empirical and ab initio combined approach for the full conformational searches of gaseous lysine and lysine–H2O complex

A full structural search of the canonical, zwitterionic, protonated and deprotonated lysine conformers in gas phase is presented. A total of 17,496 canonical, 972 zwitterionic, 11,664 protonated and 1458 trial deprotonated structures were generated by allowing for all combinations of internal single-bond rotamers. All the trial structures were initially optimized at the AM1 level, and the resulting structures were determined at the B3LYP/6-311G^* level. A total of 927 canonical, 730 protonated and 193 deprotonated conformers were found, but there were no stable zwitterionic structures in the gas phase. The most stable conformers of the canonical, protonated and deprotonated lysine were further optimized at the B3LYP/6-311++G^** level. The energies of the most stable structures were determined at the MP2/6-311G(2df,p) level and the vibrational frequencies were calculated at the B3LYP/6-311++G^** level. The rotational constants, dipole moments, zero-point vibrational energies, harmonic frequencies, vertical ionization energies, enthalpies, Gibbs free energies and conformational distributions of gaseous lysine were presented. Numerous new structures are found and the lowest-energy lysine conformer is more stable than the existing one by 1.1 kcal/mol. Hydrogen bonds are classified and may cause significant red-shifts to the associated vibrational frequencies. The calculated proton affinity/dissociation energy and gas-phase basicity/acidity are in good agreement with the experiments. Calculations are also presented for the canonical lysine–H₂O and zwitterionic lysine–H₂O clusters. Interaction between lysine and H₂O significantly affects the relative conformational stabilities. Only one water molecule is sufficient to produce the stable zwitterionic structures in gas phase. The lowest-energy structure is found to be zwitterions when applying the conductor-like polarized continuum solvent model (CPCM) to the lysine–H₂O complexes.     

Sparse optimal scoring for multiclass cancer diagnosis and biomarker detection using microarray data

Gene expression data sets hold the promise to provide cancer diagnosis on the molecular level. However, using all the gene profiles for diagnosis may be suboptimal. Detection of the molecular signatures not only reduces the number of genes needed for discrimination purposes, but may elucidate the roles they play in the biological processes. Therefore, a central part of diagnosis is to detect a small set of tumor biomarkers which can be used for accurate multiclass cancer classification. This task calls for effective multiclass classifiers with built-in biomarker selection mechanism. We propose the sparse optimal scoring (SOS) method for multiclass cancer characterization. SOS is a simple prototype classifier based on linear discriminant analysis, in which predictive biomarkers can be automatically determined together with accurate classification. Thus, SOS differentiates itself from many other commonly used classifiers, where gene preselection must be applied before classification. We obtain satisfactory performance while applying SOS to several public data sets.     

Application of methyl parathion hydrolase (MPH) as a labeling enzyme

Methyl parathion hydrolase (MPH) is an enzyme that catalyzes the degradation of methyl parathion, generating a yellow product with specific absorption at 405 nm. The application of MPH as a new labeling enzyme was illustrated in this study. The key advantages of using MPH as a labeling enzyme are as follows: (1) unlike alkaline phosphatase (AP), horseradish peroxidase (HRP), and glucose oxidase (GOD), MPH is rarely found in animal cells, and it therefore produces less background noise; (2) its active form in solution is the monomer, with a molecular weight of 37 kDa; (3) its turnover number is 114.70 ± 13.19 s⁻¹, which is sufficiently high to yield a significant signal for sensitive detection; and (4) its 3D structure is known and its C-terminal that is exposed to the surface can be easily subjected to the construction of genetic engineering monocloning antibody–enzyme fusion for enzyme-linked immunosorbent assay (ELISA). To demonstrate its utility, MPH was ligated to an single-chain variable fragment (scFv), known as A1E, against a white spot syndrome virus (WSSV) with the insertion of a [–(Gly–Ser)₅–] linker peptide. The resulting fusion protein MPH-A1E possessed both the binding specificity of the scFv segment and the catalytic activity of the MPH segment. When MPH-A1E was used as an ELISA reagent, 25 ng purified WSSV was detected; this was similar to the detection sensitivity obtained using A1E scFv and the HRP/Anti-E Tag Conjugate protocol. The fusion protein also recognized the WSSV in 1 μL hemolymph from an infected shrimp and differentiated it from a healthy shrimp. Figure The 3-D structure of MPH. (a) monomer showing C- and N-terminals; (b) the crystal structure of the dimer W. Yang and Y.-F. Zhou contributed equally to this work.     

Analysis of diacylglycerols by ultra performance liquid chromatography-quadrupole time-of-flight mass spectrometry: Double bond location and isomers separation

Diacylglycerols (DAGs) are important lipid intermediates and have been implicated in human diseases. Isomerism complicates their mass spectrometric analysis; in particular, it is difficult to identify fatty acid substituents and locate the double bond positions in unsaturated DAGs. We have developed an analytical strategy using ultra-performance liquid chromatography–quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF MS) in conjunction with dimethyl disulfide (DMDS) derivatization and collision cross-section (CCS) measurement to characterize DAGs in biological samples. The method employs non-aqueous reversed-phase chromatographic separation and profile collision energy (CE) mode for MS^E and MS/MS analyses. Three types of fragment ions were produced simultaneously. Hydrocarbon ions (m/z 50–200) obtained at high CE helped to distinguish unsaturated and saturated DAGs rapidly. Neutral loss ions and acylium ions (m/z 300–400) produced at low CE were used to identify fatty acid substituents. Informative methyl thioalkane fragment ions were used to locate the double bonds of unsaturated DAGs. Mono-methylthio derivatives were formed mainly by the reaction of DAGs with DMDS, where methyl thiol underwent addition to the first double bond farthest from the ester terminus of unsaturated fatty acid chains. The addition of CCS values maximized the separation of isomeric DAG species and improved the confidence of DAG identification. Fourteen DAGs were identified in mouse myotube cells based on accurate masses, characteristic fragment ions, DMDS derivatization, and CCS values.     

Current Development and Challenges of Mixed Matrix Membranes for CO2/CH4 Separation

In the early stage of membrane technology development in gas separation, utilization of polymeric membranes has gained attention due to their robustness and ease of fabrication. However, the performance of polymeric membranes is limited by the trade-off between permeability and selectivity. Meanwhile, inorganic membrane is capable to exhibit great enhancement in separation performance but unfortunately its fabrication process is hard and costly. Thus, development of mixed matrix membranes (MMMs) by incorporating inorganic fillers into the polymer matrix has become a potential alternative to overcome the limitations of polymeric and inorganic membranes in gas separation. Nevertheless, fabrication of defect-free MMMs with improved separation performance and without compromising the mechanical and thermal stability is extremely difficult and challenging. In the current review paper, various types of inorganic fillers for MMMs fabrication and recent reported efforts to tailor the underlying problems on MMMs fabrication were discussed. The future outlook to advance the performance of MMMs in gas separation especially for CO₂/CH₄ separation was highlighted.     

Mass spectrometric analysis of free fatty acids in infant milk powders by frozen pretreatment coupled with isotope‐labeling derivatization

In combination with frozen pretreatment and carboxyl group derivatization, a novel workflow was developed for the determination of free fatty acids in milk powder. The workflow showed a significantly enhanced performance for comprehensive free fatty acid analysis owing to a highly efficient frozen extraction method. In addition, the advantages of the workflow also involved high sensitivity and great tolerance to a complex matrix. Characteristic fragment ions of derivatization reagents also provide clear evidence for the qualitative analysis of free fatty acids. Fourteen types of free fatty acids in a number of domestic and overseas infant milk powders have been successfully detected. The content of free fatty acids in the different samples was different, which probably indicates the diverse quality of infant milk powder. The workflow is expected to be a pragmatic tool for the analysis of free fatty acids in intricate matrices.     

Determination of nitrophenolate sodium in aquatic products by HPLC–MS/MS with atmospheric pressure chemical ionization

The paper describes an efficient method for the determination of nitrophenolate sodium in aquatic products by HPLC combined with atmospheric pressure chemical ionization with tandem mass spectrometry (LC–APCI-MS/MS). Analytes were extracted from aquatic products by acetonitrile, the extracts were degreased by alumina and concentrated, the concentrated solution was further purified by Oasis HLB cartridge. Finally, the analytes were separated and detected by LC–APCI-MS/MS in negative ion mode. Excellent linearity with correlation coefficients of more than 0.995 was observed in the concentration range of 2–200 μg/L for p-nitrophenol sodium and 2-methoxy-5-nitrophenolate sodium, and 5–200 μg/L for ο-nitrophenol sodium. Recovery rates of nitrophenolate sodium between 86.1–94.3% were achieved. Limit of quantitation of p-nitrophenol sodium and 2-methoxy-5-nitrophenolate sodium was 2 μg/kg and ο-nitrophenol sodium was 5 μg/kg, with relative standard deviations <10%. This method was employed in the practical analysis of spiked and naturally contaminated aquatic products.