Direct coupling of polymer-based microchip electrophoresis to online MALDI-MS using a rotating ball inlet

We report on the coupling of a polymer-based microfluidic chip to a MALDI-TOF MS using a rotating ball interface. The microfluidic chips were fabricated by micromilling a mold insert into a brass plate, which was then used for replicating polymer microparts via hot embossing. Assembly of the chip was accomplished by thermally annealing a cover slip to the embossed substrate to enclose the channels. The linear separation channel was 50 microm wide, 100 microm deep, and possessed an 8 cm effective length separation channel with a double-T injector (V(inj) = 10 nL). The exit of the separation channel was machined to allow direct contact deposition of effluent onto a specially constructed rotating ball inlet to the mass spectrometer. Matrix addition was accomplished in-line on the surface of the ball. The coupling utilized the ball as the cathode transfer electrode to transport sample into the vacuum for desorption with a 355 nm Nd:YAG laser and analyzed on a TOF mass spectrometer. The ball was cleaned online after every rotation. The ability to couple poly(methylmethacrylate) microchip electrophoresis devices for the separation of peptides and peptide fragments produced from a protein digest with subsequent online MALDI MS detection was demonstrated.     

反式共轭类碳烯CH_2CH—CHC∶LiF的构型及异构化反应

用MP2 / 6 - 31G 解析梯度方法研究了反式共轭类碳烯CH2CH—CHC∶LiF的结构 .得到 3个平衡构型和 2个异构化反应的过渡态 .计算结果表明 ,反式共轭类碳烯有两种比较稳定的平衡构型 .分析了各平衡构型的结构特点及稳定性 ,给出了各种平衡构型及过渡态结构的Mulliken集居数 ,并讨论了两种稳定构型的化学活性     

Separation and identification of organic acid-coenzyme A thioesters using liquid chromatography/electrospray ionization-mass spectrometry

A method has been developed for the direct determination of coenzyme A (CoA) and organic acid-CoA thioesters in mixtures using directly combined liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS). Mixtures of CoA and organic acid-CoA thioesters were analyzed by LC/ESI-MS with detection of protonated molecular ions and characteristic fragment ions for each compound. The identities of the CoA-thioesters were established based on LC retention times and simultaneously recorded mass spectra. Monitoring of the CoA specific fragment ion at m/z 428 throughout the chromatogram provides a unique fingerprint for CoA content in the samples that corroborates the identification of organic acid-CoA thioesters in the mixtures. Furthermore, fragment ions arising from the ester linkage portion of the molecule allow unambiguous identification of the CoA esters in the samples. A second LC elution system was developed that allows the simultaneous separation and identification of 2-hydroxypropionyl-CoA (lactyl-CoA) and 3-hydroxypropionyl CoA (3HP-CoA), which have the same mass and identical MS fragmentation behavior. The utility of LC/ESI-MS employing this elution system is demonstrated by the determination of 3HP-CoA and lactyl-CoA (converted to CoA-thioesters from their corresponding free acids using CoA-transferase) in fermentation broths from Escherichia coli strains engineered for the production of 3-hydroxypropionic acid (3HP). External calibration employing a purified 3HP-CoA standard allowed indirect quantification of 3HP content in the broth with a precision of 1% (RSD). The feasibility of extending the method described above to perform LC/selected reaction monitoring-tandem mass spectrometry for direct determination of organic acid-CoA thioesters in cells was also demonstrated.     

Immunotoxic effects of cis-urocanic acid exposure in C57BL/6N and C3H/HeN mice

Exposure to ultraviolet radiation results in increased levels of intradermal cis-urocanic acid (cUCA) and alters cutaneous immunity by interfering with processing and presentation of antigen by Langerhans cells. Reports on effects of systemic immunotoxicity with 30 day cUCA exposure in laboratory rodents include thymic atrophy, thymic hypocellularity and decreased T-cell-mediated immunity; however, immune effects of single exposure or 5 day cUCA administration, which may better mimic human exposures, are poorly defined. The present study initially evaluated immune effects of single, 5 day, and 4 week cUCA exposure in C57BL/6N mice. Single administration of intradermal cUCA resulted in decreased splenocyte phagocytosis that persisted for 30 days after cUCA exposure. Five day consecutive cUCA exposure decreased numbers of phenotypically mature CD4(+)CD8(-) and CD4(-)CD8(+) (single positive) thymocytes, increased CD4(+)CD8(+) (double positive) immature thymocytes and increased splenocyte proliferation. Prolonged cUCA exposure (4 weeks) caused profound thymic hypocellularity and splenic hypercellularity and increased splenic macrophage chemiluminescence. Because of this apparent sensitivity of C57BL/6N mice to cUCA, thymic hypocellularity was compared between C57BL/6N and C3H/HeN mice dosed with cUCA, and was found to be more pronounced in the C57BL/6N strain. These results are an extension of previous conclusions on immune modulation caused by cUCA in the spleen and thymus. Further, the observed variation in sensitivity between the mouse strains is consistent with known genetic susceptibility of these strains to the immunomodulatory effects of exposure to sunlight.     

Use of Ag(II) as a removable template in porphyrin chemistry: diol cleavage products of [meso-tetraphenyl-2,3-cis-diolchlorinato]silver(II)

The use of Ag^II as a removable template in synthetic porphyrin chemistry is described. Mild procedures for the insertion of Ag^II into chlorins and the demetallation of the [chlorinato]Ag^II complexes are delineated. The UV-vis spectra of the novel [chlorinato]Ag^II complexes are discussed. The diol cleavage products of [meso-tetraphenyl-2,3-diolchlorinato]silver(II) under a number of conditions are characterized and compared to those resulting from the cleavage of the corresponding free base diol chlorin or its Ni^II complex, highlighting the unique templating effect of Ag^II. The scopes and limits of electrospray ionization mass spectrometry (ESI-MS) for the analysis of Ag^II chlorins is described. The use of Ag^II as a templating metal is superior over Ni^II or Zn^II for the preparation of free base pyrrole-modified porphyrins along metal templated pathways.     

n-Hexane dehydrocyclization over Pt?Ni supported on alumina catalysts

Pt–Ni/-Al₂O₃ catalysts have been prepared and studied in n-hexane dehydrocyclization. The selectivity for benzene and toluene, a chain lengthening product formation was improved by Ni and correlated with its content.

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Pt–Ni/-Al₂O₃ -. Ni . Ni , .

     

Comparison of mass resolution criteria in mass spectrometry

For a single peak, mass spectral resolution can be expressed in terms of peak width or ratio of peak position to peak width. Alternatively, for two equally intense peaks of equal width, resolution can be defined as the minimum peak separation such that the height of the valley between the combined peaks is less than a specified ratio (1%, 10%, 50%, 100%) of the individual (or combined) peak maximum. All these definitions depend on peak shape. Conversion formulae between various mass resolution criteria are presented for each of eight spectral peak shapes: Gaussian, triangular, trapezoidal, Lorentzian (absorption-mode, magnitude-mode, and sine-apodized magnitude-mode), and sinc (absorption-mode and magnitude-mode). From these formulae, mass resolutions based upon different criteria are readily compared for the same or different line shapes.     

Variational reactive scattering calculations: computational optimization strategies

Summary We have developed efficient and accurate techniques for the calculation of quantum mechanical reaction probabilities of atom-diatom exchange reactions in the gas phase, and we have optimized a computer code employing these techniques and applied it sucessfully to several systems. In this paper we consider further strategies for improving the algorithm to allow even more demanding applications. In this context, improvement means that equivalent results can be obtained using fewer computational resources (computer time or storage) or that an equivalent expenditure of resources can yield higher accuracy. The new strategies discussed here lead to improvement in both of these areas. Two areas of special focus in the present paper are (i) the finite difference boundary value method used for calculating distorted wave Green's functions and regular solutions for scattering by the distortion potential and (ii) the choice of the distortion potential itself. Among other results included here is the first application of the outgoing wave or scattered wave variational principle to reactive scattering.     

Role of tin in a PtSb alloy and a Pt-Sn/Al2O3 reforming catalyst

The conversion of n-hexane was studied on a Pt-Sn/Al₂O₃ catalyst, a PtSn alloy and on the corresponding Pt catalysts. The results indicate the same catalytic effect of tin in supported and unsupported catalysts. It is concluded that the role of tin is connected with alloy formation.

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- Pt-Sn/Al₂O₃, PtSn Pt-. . , .

     

NMR chemical shifts in the low–pH form of a-chymotrypsin. A QM/MM and ONIOM–NMR study

 The relationship between hydrogen bonding and NMR chemical shifts in the catalytic triad of low-pH α-chymotrypsin is investigated by combined use of the effective fragment potential [(2001) J Phys Chem A 105:293] and ONIOM–NMR [(2000) Chem Phys Lett 317:589] methods. Our study shows that while the His57 N^δ1−H bond is stretched by a relatively modest amount (to about 1.060 ?) this lengthening, combined with the polarization due to the molecular environment, is sufficient to explain the experimentally observed chemical shifts of 18.2 ppm. Furthermore, the unusual down-field shift of H^ɛ1 (9.2 ppm) observed experimentally is reproduced and shown to be induced by interactions with the C=O group of Ser214 as previously postulated. The free-energy cost of moving H^δ1 from His57 to Asp102 is predicted to be 5.5 kcal/mol. Received: 26 September 2001 / Accepted: 6 September 2002 / Published online: 21 January 2003 Contribution to the Proceedings of the Symposium on Combined QM/MM Methods at the 222nd National Meeting of the American Chemical Society, 2001 Correspondence to: J. H. Jensen e-mail: jan-jensen@uiowa.edu Acknowledgements. This work was supported by a Research Innovation Award from the Research Corporation and a type G starter grant from the Petroleum Research Fund. The calculations were performed on IBM RS/6000 workstations obtained through a CRIF grant from the NSF (CHE-9974502) and on supercomputers at the National Center for Supercomputer Applications at Urbana-Champaign. The authors are indebted to Visvaldas Kairys for help with the CHARMM program, and to Daniel Quinn for many helpful discussions.