Charge site manipulation to enhance top-down fragmentation efficiency

In recent years, top-down mass spectrometry has become a widely used approach to study proteoforms; however, improving sequence coverage remains an important goal. Here, two different proteins, α-synuclein and bovine carbonic anhydrase, were subjected to top-down collision-induced dissociation (CID) after electrospray ionisation. Two high-boiling solvents, DMSO and propylene carbonate, were added to the protein solution in low concentration (2%) and the effects on the top-down fragmentation patterns of the proteins were systematically investigated. Each sample was measured in triplicate, which revealed highly reproducible differences in the top-down CID fragmentation patterns in the presence of a solution additive, even if the same precursor charge state was isolated in the quadrupole of the instrument. Further investigation supports the solution condition-dependent selective formation of different protonation site isomers as the underlying cause of these differences. Higher sequence coverage was often observed in the presence of additives, and the benefits of this approach became even more evident when datasets from different solution conditions were combined, as increases up to 35% in cleavage coverage were obtained. Overall, this approach therefore represents a promising opportunity to increase top-down fragmentation efficiency.

Thermally Hypsochromic or Bathochromic Emissions? The Silver Nuclei Does Matter

Structural modulation of core-shell silver nanoclusters from the inside is a huge challenge but of great importance in their syntheses. Herein, two silver nanoclusters [Ag₃ S₉ @Ag₄₂ ] (SD/Ag45b) and [Ag₉ S₉ @Ag₄₂ ] (SD/Ag51a) are isolated in the presence of different kinds of sulfonic acids. Uniquely, SD/Ag45b and SD/Ag51a show typical core-shell structures with the similar Ag₄₂ shell but different cores. The outer shell of 42 silver atoms comprises two Ag₃ trigons at two poles encircled by three equatorial distorted square cupolas (J₄ , Ag₁₂ ). The core in SD/Ag45b is a silver trigon ligated by nine S^2- ions (Ag₃ S₉ ), while a tricapped triangular prismatic Ag₉ also ligated by the same amount of S^2- ions (Ag₉ S₉ ) is observed in the inner core of SD/Ag51a. The electrospray ionization mass spectrometry (ESI-MS) indicates that the introduction of p-toluenesulfonic acid can realize the transformation from SD/Ag45b to Ag₅₁ . SD/Ag45b and SD/Ag51a show inverse luminescence thermochromic behaviors in the near-infrared (NIR) region, mainly dictated by the inner silver cores. This work not only realizes the synthesis of new silver nanoclusters by core modulation but also provides a prototype to get molecular-level insight into the correlation between structure and luminescence thermochromism.

[Determination of the binding of natural products to the human c-myb oncogene promoter G-quadruplex DNA by capillary electrophoresis and electrospray ionization mass spectrometry]

The relationship between a drug and its target directly affects its pharmacology and efficacy. Drug-target binding ability and binding stoichiometry are essential characterization data in pharmaceutical research. The c-myb proto-oncogene encodes a crucial transcription factor that is involved in proliferation, differentiation, and maturation during hematopoiesis. Recent studies have found that the human oncogene c-myb is overexpressed in cancer tissues such as colorectal cancer. C-myb has become a potential therapeutic target for colorectal cancer, leukemia, and other cancers. A guanine (G)-rich DNA sequence located in the promoter region of c-myb can be spontaneously folded to form an intra-molecular G-quadruplex (G4) with cationic induction. The specific recognition of small molecules can stabilize this G4 folding, thus regulating the transcription and expression of c-myb. In this study, pressure assisted capillary electrophoresis frontier analysis (PACE-FA) combined with electrospray ionization mass spectrometry (ESI-MS) was used to investigate the interactions between the human c-myb promoter G4 and natural product molecules. In PACE-FA, an external pressure (no more than 13.8 kPa) in the same direction of the migration of the analyte was used in capillary electrophoresis frontier analysis (CE-FA), which greatly sped up the analysis while maintaining the accuracy of the results. Meanwhile, the combination of PACE-FA and ESI-MS could rapidly determine the affinity and stoichiometric relationship between binding molecules and targets. First, the intramolecular parallel-stranded G4 formation of the c-myb promoter sequence in the presence of cations (K⁺, NH₄⁺) was investigated by circular dichroism (CD) and ESI-MS. Then, ESI-MS was used to rapidly screen the natural products for candidate molecules that bound the target G4 DNA. The binding interactions were measured by mixing the c-myb DNA with each natural product separately in a 1:4 molar ratio, and then directly infusing these mixtures into the ESI-MS system. From the ESI-MS spectra, IR_a values calculated from the relative intensities of DNA and its complex ions were used to probe the binding affinities of the natural products. This parameter denotes the relative binding affinity for a small molecule with the G4 DNA. Three natural products were identified through the screen, and their binding affinities to G4 DNA were ranked as follows:pseudolaric acid B > scopolamine butylbromide > nuciferine. Considering that both specific and non-specific binding existed in the solution phase, a free solution method using PACE-FA was developed to further test the binding ability of these products to the c-myb promoter G4 DNA. In the PACE-FA experiments, the pre-equilibrated mixture of the c-myb G4 DNA and the selected ligand was injected into the capillary prior to separation. Upon applying voltage and an external pressure (6.9 kPa) to the capillary, different species of analytes in the sample migrated at their own rates due to their different sizes and charges. The results showed that scopolamine butylbromide could bind specifically to target G4 DNA with 1:1 stoichiometry and a binding constant of 1.18×10⁵ L/mol. Nuciferine's binding to G4 DNA showed a linear increasing trend due to nonspecific binding; thus nuciferine is a nonspecific binder. Although pseudolaric acid B showed high affinity for the c-myb G4 DNA and 1:1 and 1:2 G4-bound complex ions were observed in ESI-MS measurements, the PACE-FA results indicated that pseudolaric acid B did not bind to target G4 DNA in free solution. Therefore, scopolamine butylbromide could be the best candidate to regulate the transcription of the c-myb oncogene, and is expected to be a precursor for anticancer drugs. In this work, PACE-FA has allowed for significant improvements to the conventional CE-FA technique. This combination of PACE-FA and ESI-MS not only reduced the time needed for binding analysis, but also improved the accuracy and specificity of the affinity analysis compared to conventional binding approaches. Furthermore, this combination could be used to screen other targeted drug candidates and to evaluate their interaction mechanisms.

Forensic Engineering of Advanced Polymeric Materials-Part VII: Degradation of Biopolymer Welded Joints

Welding technology may be considered as a promising processing method for the formation of packaging products from biopolymers. However, the welding processes used can change the properties of the polymer materials, especially in the region of the weld. In this contribution, the impact of the welding process on the structure and properties of biopolymer welds and their ability to undergo hydrolytic degradation will be discussed. Samples for the study were made from polylactide (PLA) and poly(3-hydroxyalkanoate) (PHA) biopolymers which were welded using two methods: ultrasonic and heated tool welding. Differential scanning calorimetry (DSC) analysis showed slight changes in the thermal properties of the samples resulting from the processing and welding method used. The results of hydrolytic degradation indicated that welds of selected biopolymers started to degrade faster than unwelded parts of the samples. The structure of degradation products at the molecular level was confirmed using mass spectrometry. It was found that hydrolysis of the PLA and PHA welds occurs via the random ester bond cleavage and leads to the formation of PLA and PHA oligomers terminated by hydroxyl and carboxyl end groups, similarly to as previously observed for unwelded PLA and PHA-based materials.

Online Measurement System in Reaction Monitoring for Determination of Structural and Elemental Composition Using Mass Spectrometry

The monitoring of chemical reactions is an important task in chemical engineering, especially in quality control, pharmaceutical and biological processes, or industrial production. The development of new reactions such as catalyst-based procedures requires detailed knowledge about process steps and reaction kinetics. For qualitative and quantitative analysis of reactants and resulting products, proprietary online measurement systems are used, which were designed for special applications. A mobile online reaction monitoring system was developed for a flexible coupling to different mass selective measurement systems for structural (ESI-MS) and elemental (ICP-MS) analysis to determine chemical precursors, reaction products, and internal standard compounds and their elemental composition at any stage of the reaction. Chemical reactions take place in a tempered continuous-flow microreactor. The flow rate in the microreactor can be varied to adjust the residence times in the reactor. An online dilution module was integrated to adapt the concentration of the reaction solutions to the working range of the analyzers. The performance and limitations of the online reaction system were determined using standard solutions and a real chemical reaction. The control software with a graphical user interface enables the adjustment of reaction, sampling, and measurement parameters as well as the system and process control.

High performance liquid chromatography (HPLC) fingerprints and primary structure identification of corn peptides by HPLC-diode array detection and HPLC-electrospray ionization tandem mass spectrometry

Corn peptides (CPs) are reported to have many biological functions, such as facilitating alcohol metabolism, antioxidation, antitumor, antihypertension, and hepatoprotection. To develop a method for quality control, the high-performance liquid chromatography (HPLC) system was applied. Twenty-eight common peaks were found in all the CPs of corn samples from Enshi, China, based on which, a fingerprinting chromatogram was established for use in quality control in future research. Subsequently, the major chemical constituents of these common peaks were identified respectively using the HPLC-diode-array detection electrospray ionization tandem mass spectrometry (DAD-ESI-MS/MS) system, and 48 peptide fractions were determined ultimately. This was the first time for the majority of these peptides to be reported, and many of them contained amino acids of glutamine (Q), L and A, which might play an important role in the exhibition of the bioactivities of CPs. Many peptides had a similar primary structure to the peptides which had been proven to be bioactive such as facilitating alcohol metabolism, scavenging free radicals, and inhibiting lipid peroxidation. This systematical analysis of the primary structure of CPs facilitated subsequent studies on the relationship between the structures and functions, and could accelerate holistic research on CPs.