Protein identification by accurate mass matrix-assisted laser desorption/ionization imaging of tryptic peptides

The spatial distribution of proteins in tissue sections can be used to identify potential markers for pathological processes. Tissue sections are often subjected to enzymatic digestion before matrix‐assisted laser desorption/ionization (MALDI) imaging. This study is targeted at improving the on‐tissue identification of tryptic peptides by accurate mass measurements and complementary off‐line liquid chromatography coupled to electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS) analysis. Two adjacent mouse brain sections were analyzed in parallel. The first section was spotted with trypsin and analyzed by MALDI imaging. Direct on‐tissue MS/MS experiments of this section resulted in the identification of 14 peptides (originating from 4 proteins). The second tissue section was homogenized, fractionated by ultracentrifugation and digested with trypsin prior to LC/ESI‐MS/MS analysis. The number of identified peptides was increased to 153 (corresponding to 106 proteins) by matching imaged mass peaks to peptides which were identified in these LC/ESI‐MS/MS experiments. All results (including MALDI imaging data) were based on accurate mass measurements (RMS <2 ppm) and allow a confident identification of tryptic peptides. Measurements based on lower accuracy would have led to ambiguous or misleading results. MS images of identified peptides were generated with a bin width (mass range used for image generation) of Δm/z = 0.01. The application of accurate mass measurements and additional LC/MS measurements increased both the quality and the number of peptide identifications. The advantages of this approach for the analysis of biological tissue sections are demonstrated and discussed in detail. Results indicate that accurate mass measurements are needed for confident identification and specific image generation of tryptic peptides in tissue sections. Copyright © 2011 John Wiley & Sons, Ltd.     

Modification of guanine residues in PNA-synthesis by PyBOP

The phosphonium-type coupling reagent PyBOP, when applied to the synthesis of peptide nucleic acid (PNA) oligomers, was found to form O⁴-phosphonium compounds of the nucleobase guanine which can be converted into C⁴-modified guanine-derived PNAs by nucleophiles.     

Effect of metal and substituents on the quasi-line spectra of some metalloporphyrins

Absorption spectra are reported for a number of metalloporphyrins in n-octane. For ZnP and PdP, sharp quasi-lines with linewidths ≈4 cm^?1 are observed at 15 and 35 K, respectively. The narrowest linewidths for PtP are ≈12 cm at 15 K, while NiP and CuP show no quasi-linear structure. In these latter cases, quasi-linewidth is attributed to electronic radiationless decay of the visible excited state. The various vibronic bands within Q(1, 0) are tabulated. The quasi-line structures for several zinc porphyrins at 77 K are also reported. Generally, these are not as sharp as those found in ZnP; in particular, Zn tetraphenyl porphin shows no quasi-linear structure. In these cases, the quasi-line structure is attributed to inhomogeneous broadening.     

From σ to π Coordination: Tetraisopropylcyclopentadienyl dichlorides [(C5HR4)ECl2] (R = CHMe2) of phosphorus,arsenic, antimony,and bismuth

[(C₅HR₄)PCl₂] ( 1a ), [(C₅HR₄)PBr₂] ( 1 b ), [(C₅HR₄)AsCl₂] ( 2 ), and [(C₅HR₄)SbCl₂] ( 3 ), have been obtained from the corresponding pnicogen trihalides and sodium tetraisopropylcyclopentadienide (R = CHMe₂). The molecular structures of 1, 2 , and 3 as well as the related structure of [(C₅HR₄)BiCl₂] ( 4 ) display increasing π character of hetero atom to cyclopentadienyl bonding with increasing metallic character of the hetero atom.     

Solvolytic Ring-opening of Alkoxychlorofluorocyclopropanes: A Ready Access to Fluorinated α,β-Unsaturated Aldehydes and Ketones

Alkoxychlorofluorocyclopropanes are easily prepared by chlorofluorocarbene addition to en-ethers in a two-phase system and converted by simple heating in an aqueous solvent mixture to 2-fluoro-2-alkenals which can be reduced to the corresponding alcohols.