Chiral discrimination of β‐3‐homo‐amino acids using the kinetic method

Chiral discrimination of seven enantiomeric pairs of β‐3‐homo‐amino acids was studied by using the kinetic method and trimeric metal‐bound complexes, with natural and unnatural α‐amino acids as chiral reference compounds and divalent metal ions (Cu²⁺ and Ni²⁺) as the center ions. The β‐3‐homo‐amino acids were selected for this study because, first of all, chiral discrimination of β‐amino acids has not been extensively studied by mass spectrometry. Moreover, these β‐3‐homo‐amino acids studied have different aromatic side chains. Thus, the emphasis was to study the effect of the side chain (electron density of the phenyl ring, as well as the difference between phenyl and benzyl side chains) for the chiral discrimination. The results showed that by the proper choice of a metal ion and a chiral reference compound, all seven enantiomeric pairs of β‐3‐homo‐amino acids could be differentiated. Moreover, it was noted that the β‐3‐homo‐amino acids with benzyl side chains provided higher enantioselectivity than the corresponding phenyl ones. However, increasing or decreasing the electron density of the aromatic ring by different substituents in both the phenyl and benzyl side chains had practically no role for chiral discrimination of β‐3‐homo‐amino acids studied. When copper was used as the central metal, the phenyl side chain containing reference molecules (S)‐2‐amino‐2‐phenylacetic acid (L ‐Phg) and (S)‐2‐amino‐2‐(4‐hydroxyphenyl)‐acetic acid (L ‐4′‐OHPhg) gave rise to an additional copper‐reduced dimeric fragment ion, [Cu^I(ref)(A)]⁺. The inclusion of this ion improved noticeably the enantioselectivity values obtained. Copyright © 2010 John Wiley & Sons, Ltd.     

紫外光照射下 Fe-碳纳米管/TiO2 复合材料降解罗丹明 B

 The composites comprising Fe-carbon nanotubes (CNTs) on TiO2 were prepared by a modified sol-gel method and characterized by nitrogen adsorption, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and energy dispersive X-ray analysis. The photocatalytic decomposition of rhodamine B (Rh.B) under UV irradiation and air aeration catalyzed by the composites was measured. The photocatalytic activity of TiO2 nanoparticles was significantly enhanced by the large CNT network that facilitated electron transfer between adsorbed Rh.B molecules and the catalyst substrate and the simultaneous occurrence of the photo-Fenton reaction in the presence of Fe particles. A marked acceleration of the decomposition rate was observed with aeration by flowing air aeration due to the formation of the circulatory photo-Fenton system. Chemical oxygen demand of piggery waste was measured at regular intervals to evaluate the mineralization of wastewater.     

Reacting to spontaneous feedback from external customers in a university hospital laboratory

Modern quality standards for laboratories recommend the use of customer feedback in quality improvement. Spontaneous customer feedback is one method to obtain information from customers. In the present study, we analysed the feedback data from external customers (health centres and other hospitals) to our university hospital laboratory during 2001–2006. The most common subject matters of the feedback, covering 87% of a total of 95 reports, were lacking test results, suspicion of the validity of test results, return of samples in transportation boxes to customers and delays in service. On investigation, errors or defects were revealed in 78 cases. The most common errors were lacking (45 cases; 58%), erroneous (20 cases; 26%) or delayed test results (7 cases; 9%). As much as 68% of these errors took place in the pre-analytical phase of the laboratory process, occurring most commonly during specimen transfer, when entering orders into the laboratory information system at the university hospital or during sample processing. The most common underlying causes for errors were unintended errors and non-compliance with operating instructions. Latent errors were identified in 14% of the cases. Corrective actions were performed in 79% of the reported cases. It is important that the feedback reports are investigated to find out possible errors and their underlying causes so that appropriate corrective actions can be taken. When processed properly, spontaneous customer feedback is a method that can be used supplementarily to other methods to detect errors and defects in clinical laboratories and to aid in quality improvement.     

Electronic and structural properties of the InP(1 0 0)(2 × 4) surface studied by core-level photoemission and scanning tunneling microscopy

The (2 × 4)-reconstructed InP(1 0 0) surfaces have been investigated by scanning tunneling microscopy (STM) and synchrotron-radiation core-level photoelectron spectroscopy. STM observations show that the α2 model describes the atomic structure of the InP(1 0 0)(2 × 4) surface in a limited range of the surface-preparation conditions, as predicted theoretically but not previously observed. STM results also support the accuracy of the previously found mixed-dimer structure for the InP(1 0 0)(2 × 4) surface under less P-rich conditions. A study of P 2p core-level photoelectron spectra, measured with different surface-sensitivity conditions, demonstrates that P 2p photoemission from the mixed-dimer InP(1 0 0)(2 × 4) surface consists of at least two surface-core-level-shift (SCLS) components which have kinetic energies approximately 0.4 eV higher and 0.3 eV lower than the bulk emission. On the basis of the surface-sensitivity difference between these SCLSs, they are related to the third-layer and top-layer P sites in the mixed-dimer structure, respectively.     

Methyl propionate radical cation

Examination of the reactions of the long-lived (>0.5-s) radical cations of CD₃CH₂COOCH₃ and CH₃CH₂COOCD₃ indicates that the long-lived, nondecomposing methyl propionate radical cation CH₃CH₂C(O)OCH ₃ ^+· isomerizes to its enol form CH₃CH=C(OH)OCH ₃ ^+· (ΔH _{isomerization} ? ?32 kcal/mol) via two different pathways in the gas phase in a Fourier-transform ion cyclotron resonance mass spectrometer. A 1,4-shift of a β-hydrogen of the acid moiety to the carbonyl oxygen yields the distonic ion ^·CH₂CH₂C⁺ (OH)OCH₃ that then rearranges to CH₃CH=C(OH)OCH ₃ ^+· probably by consecutive 1,5- and 1,4-hydrogen shifts. This process is in competition with a 1,4-hydrogen transfer from the alcohol moiety to form another distonic ion, CH₃CH₂C⁺(OH)OCH ₂ ^· , that can undergo a 1,4-hydrogen shift to form CH₃CH=C(OH)OCH ₃ ^+· . Ab initio molecular orbital calculations carried out at the UMP2/6-31G** + ZPVE level of theory show that the two distonic ions lie more than 16 kcal/mol lower in energy than CH₃CH₂C(O)OCH ₃ ^+· . Hence, the first step of both rearrangement processes has a great driving force. The 1,4-hydrogen shift that involves the acid moiety is 3 kcal/mol more exothermic (ΔH _{isomerization}=?16 kcal/mol) and is associated with a 4-kcal/mol lower barrier (10 kcal/mol) than the shift that involves the alcohol moiety. Indeed, experimental findings suggest that the hydrogen shift from the acid moiety is likely to be the favored channel.     

In-beam gamma-ray spectroscopy of 190, 197Po

γ -ray transitions in the neutron-deficient nuclei ^{190, 197}Po have been identified using the JUROGAM Ge detector array coupled to the RITU gas-filled separator and the GREAT spectrometer. The yrast band of ¹⁹⁰Po has been firmly established through γ -γ coincidences and extended up to a spin and parity of 14⁺. It displays similar behaviour to its isotones ¹⁸⁶Hg and ¹⁸⁸Pb above the 4⁺ level, thus confirming its prolate nature. In ¹⁹⁷Po the band built upon the 13/2⁺ isomer has been extended up to a spin and parity of 33/2⁺, while the non-yrast band has been observed for the first time. The behaviour of ¹⁹⁷Po is found to be similar to that of the nearby even-mass isotopes, which is consistent with the model in which the i _13/2 neutron is weakly coupled to the states in the even-even core.     

An application of the pixe method: Analysis of trace elements after wet digestion of uterine tissue

The authors present an application of the PIXE (Particle Induced X-ray Emission) method: determination of trace element concentrations in uterine tissue after wet digestion by HNO₃. A method for calibration of the system is described. Results of the analysis of a NBS reference material (National Bureau of Standards), SRM 1577 bovine liver, are given and possible sources of error are discussed. In the authors’ experience, the combination of wet digestion and PIXE provides a tool for reliable analysis of trace element concentrations in tissues.     

Differentiation of diastereomeric cyclic beta-amino acids by varying the neutral reagent in ion/molecule reactions studied by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Stereochemical differentiation of diasteromeric pairs of cis- and trans-2-aminocyclohexane-, -2-amino-4-cyclohexene-, and -2-aminocyclopentanecarboxylic acids was investigated with host-guest complexes where tetraethyl resorcarene was the host molecule. Diastereoselectivity was evaluated by ion/molecule reactions and collision-induced dissociation with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS). The effect of varying the neutral reagent (n-propylamine, i-propylamine, diethylamine, and triethylamine) in ion/molecule reactions was evaluated. Both steric interactions and proton affinity of the neutral reagents influenced the reaction rates. High proton affinity of the neutral reagent apparently had a twofold effect. If the proton affinity of the neutral reagent was too high, the reaction tended to become too exothermic and part of the host-guest complex decomposed instead of transforming to a new host-guest complex, effecting a decrease in the reaction rate. The remaining portion of the host-guest complexes meanwhile reacted very fast with the neutral reagent due to high proton affinity causing an increase in the reaction rate. n-Propylamine and i-propylamine proved to be the best neutral reagents, providing clear diastereoselectivity for beta-amino acids in ion/molecule reactions. Interestingly, diastereoselectivity was better for flexible cyclohexane beta-amino acids (2 and 3) than for more rigid cyclopentane beta-amino acids (6 and 7). The results of ab initio and hybrid density functional theory calculations on the structures of the host-guest complexes of saturated beta-amino acids were in good agreement with the experimental results.