Herein we report on the adsorption and photocatalytic decomposition of organic molecules in aqueous environments containing two-dimensional Ti3C2Tx, a representative of the MXene family.
Monolayer-protected clusters were prepared by procedures like those yielding Au25L18 (where L=-SCH2CH2Ph=-SC2Ph) but using, instead, mixtures of Au and Pd salts, as starting materials, with the intent of creating and characterizing Au25-xMxL18 clusters. Isolation of small nanoparticle product followed by partial ligand exchange to introduce thiolated poly(ethylene glycol) (SPEG=-S(CH2CH2O)5CH3) into the nanoparticle ligand shell enabled characterization of the Au25-xMxL18 content by positive mode electrospray ionization mass spectrometry (ESI-MS). For synthetic feed mole ratios of Au:Pd of 9:1 and 13:12, electrospray spectra of the PEGylated MPCs showed that the reaction and isolation produce a mixture of Au25(SC2Ph)18 and a mono-Pd nanoparticle Au24Pd(SC2Ph)18. A higher proportion of the mono-Pd nanoparticle is produced by the 13:12 mole ratio, and also when the thiol:metal ratio was lowered, according to ESI-MS and MALDI-TOF-MS. As the nanoparticle mixture is enriched, by solvent fractionations, in Au24Pd(SC2Ph)18 relative to Au25(SC2Ph)18, the distinctive optical and electrochemical signatures of Au25(SC2Ph)18 are replaced by Au24Pd(SC2Ph)18 nanoparticle responses, which are very different, even though only one Au atom is replaced by a Pd atom.
Measurements of the core and ligand monolayer compositions of small gold nanoparticles (NPs) using electrospray ionization (ESI) mass spectrometry were performed by incorporating ionization tags, methoxy penta(ethylene glycol) thiolate ligands (-S-PEG), into the ligand monolayers via ligand exchange. During ESI, alkali metal ions (M+) coordinate to the -S-PEG ligands and give the NPs positive charge. Atomically precise, high-resolution measurements show unequivocally that the NP composition is Au25(ligand)18. The predominant ions, M4Au25(ligand)18 3+ and M5Au25(ligand)18 4+, have 1− charge on the core. Because ligand exchange is a statistical process, there is a distribution of mixed-monolayer exchange products, which is reflected in the mass spectra.
New approaches to electrospray ionization mass spectrometry (ESI-MS)swith exact compositional assignmentssof small (Au25) nanoparticles with uniform and mixed protecting organothiolate monolayers are described. The results expand the scope of analysis and reveal a rich chemistry of ionization behavior. ESI-MS of solutions of phenylethanethiolate monolayer-protected gold clusters (MPCs), Au25(SC2Ph)18, containing alkali metal acetate salts (MOAc) produce spectra in which, for Na + , K + , Rb + , and Cs + acetates, the dominant species are MAu25(SC2Ph)18 2+ and M2Au25(SC2Ph)18 2+ . Li + acetates caused ligand loss. This method was extended to the analysis of Au25 MPCs with mixed monolayers, where thiophenolate (-SPh), hexanethiolate (-SC6), or biotinylated (-S-PEG-biotin) ligands had been introduced by ligand exchange. In negative-mode ESI-MS, no added reagents were needed in order to observe Au25(SC2Ph)18and to analyze mixed monolayer Au25 MPCs prepared by ligand exchange with 4-mercaptobenzoic acid, HSPhCOOH, which gave spectra through deprotonation of the carboxylic acids. Adducts of tetraoctylammonium (Oct4N + ) with -SPhCOOsites were also observed. Mass spectrometry is the only method that has demonstrated capacity for measuring the exact distribution of ligand-exchange products. The possible origins of the different Au25 core charges (1-, 0, 1+, 2+) observed during electrospray ionization are discussed.
Dissociation of protonated peptides via infrared multiphoton dissociation (IRMPD) provides more extensive sequence information than is obtained with collisionally activated dissociation (CAD) in a quadrupole ion trap due to the lack of the CAD low m/z cutoff and the ability to form secondary and higher order fragments with the non-resonant photoactivation technique. In addition, IRMPD is shown to be useful for the selective dissociation of phosphopeptides over those which are not phosphorylated because the greater photon absorption efficiency of the phosphorylated peptides leads to their more rapid dissociation. Finally, the selectivity of the IRMPD technique for phosphorylated species in complex mixtures is confirmed with the analysis of a mock peptide mixture and a tryptic digest of ␣-casein. I nvestigations into the protein complement of an organism's genome seek to identify the primary structure of the proteins produced including any modifications that take place. Following transcription, the primary sequence of a protein can undergo modifications such as N-terminal acetylation, formation of disulfide bonds, sulfation, and phosphorylation, all of which affect activity. Arguably, the most important post-translational modification of proteins is the reversible phosphorylation of serine, threonine, and tyrosine residues [1,2]. This covalent modification has regulatory influence over cellular processes such as metabolism, growth, and reproduction [3][4][5]. Because phosphorylation has such an impact on living systems, it is of great interest to be able to determine when, where, and to what extent this type of modification takes place. For this, suitable analytical techniques must be developed and applied. The relative speed and sensitivity of tandem mass spectrometry make it a powerful tool [6 -30] when compared with more conventional methods of phosphoprotein mapping, namely 32 P phosphate labeling of a protein sample followed by purification, enzymatic digestion, chromatographic separation, and Edman sequencing.Collisional activated dissociation (CAD) typically reveals sites of phosphorylation based on a mass loss associated with the cleavage of a phosphate moiety from a peptide ion (Ϫ80 (HPO 3 ) and/or Ϫ98 (H 3 PO 4 ) in positive ion MS/MS) [9,14]. Precursor ion scanning [14,19], neutral loss scanning [23], and nozzle-skimmer dissociation [9] can determine the presence, absence, and location of peptide phosphorylation based on the unique mass losses associated with phosphorylated peptides. In MALDI-TOF mass spectrometry, postsource decay (PSD) of metastable ions formed in the source region via these characteristic pathways can also be used to determine sites of phosphorylation [17]. When a peptide is phosphorylated at a tyrosine residue as opposed to a serine or threonine residue, however, the unique neutral losses are not necessarily observed upon dissociation due to the greater phosphate-tyrosine binding energy and the existence of fewer -elimination pathways than are present in the cases of serine and thr...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.