[Determination of the derivatization reactivity between α/ß-dicarbonyl compounds and standard citrullinated peptides based on matrix-assisted laser desorption ionization-time-of-flight mass spectrometry].

Protein citrullination is an irreversible post-translational modification process regulated by peptidylarginine deiminases (PADs) in the presence of Ca2+. This process is closely related to the occurrence and development of autoimmune diseases, cancers, neurological disorders, cardiovascular and cerebrovascular diseases, and other major diseases. The analysis of protein citrullination by biomass spectrometry confronts great challenges owing to its low abundance, lack of affinity tags, small mass-to-charge ratio change, and susceptibility to isotopic and deamidation interferences. The methods commonly used to study the protein citrullination mainly involve the chemical derivatization of the urea group of the guanine side chain of the peptide to increase the mass-to-charge ratio difference of the citrullinated peptide. Affinity-enriched labels are then introduced to effectively improve the sensitivity and accuracy of protein citrullination by mass spectrometry. 2,3-Butanedione or phenylglyoxal compounds are often used as derivatization reagents to increase the mass-to-charge ratio difference of the citrullinated peptide, and the resulting derivatives have been observed to contain α-dicarbonyl structures. To date, however, no relevant studies on the reactivity of dicarbonyl compounds with citrullinated peptides have been reported. In this study, we determined whether six α-dicarbonyl and two ß-dicarbonyl compounds undergo derivatization reactions with standard citrullinated peptides using matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS). Among the α-dicarbonyl compounds, 2,3-butanedione and glyoxal reacted efficiently with several standard citrullinated peptides, but yielded a series of by-products. Phenylglyoxal, methylglyoxal, 1,2-cyclohexanedione, and 1,10-phenanthroline-5,6-dione also derivated efficiently with standard citrullinated peptides, generating a single derivative. Thus, a new derivatization method that could yield a single derivative was identified. Among the ß-dicarbonyl compounds, 1,3-cyclohexanedione and 2,4-pentanedione successfully reacted with the standard citrullinated peptides, and generated a single derivative. However, their reaction efficiency was very low, indicating that the ß-dicarbonyl compounds are unsuitable for the chemical derivatization of citrullinated peptides. The above results indicate that the α-dicarbonyl structure is necessary for realizing the efficient and specific chemical derivatization of citrullinated peptides. Moreover, the side chains of the α-dicarbonyl structure determine the structure of the derivatives, derivatization efficiency, and generation (or otherwise) of by-products. Therefore, the specific enrichment and precise identification of citrullinated peptides can be achieved by synthesizing α-dicarbonyl structured compounds containing affinity tags. The proposed method enables the identification of citrullinated proteins and their modified sites by MS, thereby providing a better understanding of the distribution of citrullinated proteins in different tissues. The findings will be beneficial for studies on the mechanism of action of citrullinated proteins in a variety of diseases.

Three viologen-derived Zn-organic materials: photochromism, photomodulated fluorescence, and inkless and erasable prints.

Three zinc-viologen compounds, namely, {[Zn(Mebpy)(Hbtc)Cl]·2H2O}n (1), {[Zn3(Cebpy)2(Hbtc) (H2btc)2 (OH)2]·4H2O}n (2), and {[Zn4(Cebpy)2(IPA)3(OH)2]·2H2O}n (3) (Mebpy = N-methyl-4,4'-bipyridinium, Cebpy = N-carboxyethyl-4,4'-bipyridinium, H3btc = 1,3,5-benzenetricarboxylic acid, and H2IPA = isophthalic acid) have been constructed from aromatic carboxylic acid and viologen-derived ligands. In compound 1, the Hbtc2- ligands bridge Zn2+ cations to form a 1D fence-like chain with the Mebpy+ ligand suspended on the chains. Compound 2 possesses a 2D (4, 4) double-layered grid structure based on linear trinuclear Zn3O2 cluster units. The structure of compound 3 can be described as a 3D open-framework based on tetranuclear Zn4O2 cluster units and helical chains with helical channels. All three compounds display photochromic properties from pale yellow to dark blue after being irradiated by a xenon lamp with different photoresponsive rates. Compounds 2 and 3 can be deposited in paper simply by coating them with a solution of ethanol. The papers can be used as inkless and erasable print media. In addition, the photo-modulated luminescence of these compounds was also investigated.

NIR emission and luminescent sensing of a lanthanide-organic framework with Lewis basic imidazole and pyridyl sites.

A series of lanthanide-organic frameworks [Ln(Himdc)(ina)(H2O)]n (Ln = Eu 1a; Sm 1b; and Nd 1c, H3imdc = imidazole-4,5-dicarboxylic acid, Hina = isonicotinic acid) were synthesized under hydrothermal conditions. All compounds 1a-1c consist of a 3D microporous lanthanide carboxylate ([Eu(COO)3]n) framework and uncoordinated Lewis basic pyridyl and imidazole groups hung in the channels. The luminescence investigations show that the compound 1c displays an interesting NIR luminescence property. The compound 1a exhibits a good potential as a luminescent multi-responsive sensing material for Fe3+ ions and Cr2O72- anions.