The CID mass spectra of the MH(+) ions and the b(5) ions derived therefrom have been determined for the hexapeptides YAAAAA, AYAAAA, AAYAAA, AAAYAA, and AAAAYA. The CID mass spectra for the b(5) ions derived from the five isomers are essentially identical and show abundant ion signals for nonsequence b ions. This result is consistent with cyclization of the b(5) ions to a cyclic pentapeptide before fragmentation; this cyclic peptide can open at various positions, leading to losses of amino acid residues that are not characteristic of the original amino acid sequence. These nonsequence b ions are also observed in the fragmentation of the MH(+) ions and increase substantially in importance with increasing collision energy. A comparison of the fragmentation of AAAYAA and Ac-AAAYAA indicates that N-acetylation eliminates the cyclization of b(5) ions and, thus, eliminates the nonsequence ions in the CID mass spectra of both b(5) and MH(+) ions.
Download full-text PDF |
Source |
|---|---|
| http://dx.doi.org/10.1016/j.jasms.2008.06.025 | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Metal-Assisted Synthesis of Diverse Porphyrinoids by Cyclization of an N-Confused Thia-Pentapyrrane.
Chem Asian J
January 2025
East China University of Science and Technology, Institute of Fine Chemicals, Meilong Road, 200237, Shanghai, CHINA.
Oxidation of thia-pentapyrrane S-P4 with terminal β-linked pyrrole and thiophene units in the presence of various metal ions has been found to afford distinct porphyrinoids. Specifically, N-confused thiasapphyrin (1), Cu(III) norrole (2), neo-confused phlorin (3), and p-benzinorrole (4) were obtained, when S-P4 was oxidized with p-chloranil in acetonitrile in the presence of Ni2+, Cu2+, Cd2+, and Co2+, respectively. The structures of 1-4 have been clearly elucidated by NMR spectroscopy, HRMS, and X-ray crystal diffraction (for 2-4).
View Article and Find Full Text PDFGas-Phase Fragmentation of Coenzyme Q Radical Anion Generated by APCI: A Study by High/Low-Resolution Tandem/Sequential Mass Spectrometry.
J Am Soc Mass Spectrom
January 2025
Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro, Via G. Amendola 165/a, 70126 Bari, Italy.
Coenzyme Q (CoQ) and closely related compounds with varying isoprenoid tail lengths (CoQ, = 6-9) are biochemical cofactors involved in many physiological processes, playing important roles in cellular respiration and energy production. Liquid chromatography (LC) coupled with single or tandem mass spectrometry (MS) using electrospray (ESI) or atmospheric pressure chemical ionization (APCI) is considered the gold standard for the identification and quantification of CoQ in food and biological samples. However, the characteristic fragmentation exhibited by the CoQ radical anion ([M], / 862.
View Article and Find Full Text PDFMultifunctional Cyclized Polyacrylonitrile (cPAN) as a Coating for Sb-Based Anodes in Sodium-Ion Batteries.
ACS Appl Mater Interfaces
January 2025
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States.
Conversion electrodes, such as antimony (Sb), are high energy density electrode materials for sodium-ion batteries (NIBs). These materials are limited in their performance due to the mechanical instability of these systems resulting from volume expansion of the material during cycling. Stabilizing conversion materials using a conductive polymer binder (CPB) protective layer is an effective way to enhance the performance of these materials.
View Article and Find Full Text PDFDirect Stereoselective Synthesis of 2-Deoxyglycosides via Visible-Light-Induced Photoacid-Catalyzed Activation of Glycosyl -[1-(-MeO-Phenyl)vinyl]benzoates (PMPVBs) as Donors.
J Org Chem
January 2025
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India.
The photoacid-catalyzed synthesis of 2-deoxy glycosides is presented using stable glycosyl -[1-(-MeO-Phenyl)vinyl]benzoate (PMPVB) donors and employing the eosin Y and diphenyl disulfide (PhSSPh) catalytic system in the presence of blue LED lights. The remote activation of the alkene functionality under the photoacid catalysis followed by a 5-- cyclization led to the generation of oxocarbenium ions that were trapped to provide the glycosylated products in excellent yields and decent selectivities under mild conditions. This method is also useful for the photoacid-catalyzed synthesis of -methoxybenzyl-alkyl ethers.
View Article and Find Full Text PDFPhotoredox/Sulfide Dual Catalysis for Modular Synthesis of Multi-substituted Furan Rings via Catalytic Indirect Reductive Quenching.
Chem Asian J
January 2025
Department Laboratory of Organic and Medicinal Chemistry, Meiji Pharmaceutical University, 2-522-1, Noshio, Kiyose, Tokyo, 204-8588, Japan.
The catalytic indirect reductive quenching method is facilitated by a combination of Ir(III) photoredox and sulfide dual-catalysis system. This study demonstrated a method for synthesizing multi-substituted furans by using a photoredox/sulfide dual-catalysis system. This method enables the synthesis of various furan derivatives, including spirofurans and phthalans.
View Article and Find Full Text PDFWant AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!