Monitoring Conformational Changes of Lysozyme–Polyelectrolyte Complexes Using Trapped Ion Mobility-Mass Spectrometry (IM-MS)

The conformational changes of lysozyme due to the formation of its complexes with polystyrene sulfonate (PSS) oligomers were monitored at different charge states using trapped ion mobility spectrometry-time-of-flight mass spectrometer (TIMS-TOF-MS). The mixtures of disulfide-intact lysozyme and PSS oligomers were directly infused into the ESI source of the TIMS-TOF-MS instrument. At charge states from 7+ to 12+ in the gas phase, mobilograms obtained from TIMS-TOF-MS analyses were extracted for the protein and each complex ion. Changes occurring in the protein conformation as a result of the binding of PSS oligomers of different chain lengths were evaluated by comparing the obtained integrated peak areas for compact and extended conformers in the extracted ion mobilograms. The increase in the abundance of compact conformers due to the complexation of lysozyme and PSS oligomers was observed more clearly in the 8+ charge state. The number and lengths of PSS chains had little or no effect on the complex conformation in the higher charge states that did not provide compaction in the entire structure. It was observed that the molecular dynamics (MD) simulations of the protein and complexes correlate well with the results obtained by TIMS-TOF-MS. The PSS chains interact with the positively charged sites of the protein and cause compaction in the conformation by changing the locations of the excess charge on the structure in the gas phase that was monitored using TIMS regarding the length and number of the attached polyelectrolyte chain.</p

Synthesis and characterization of the ABA-type poly(ester-ether-ester) block copolymers

Polyethylene glycol with average molar mass of 1,450 Da (PEG-1450) was treated with equivalent amount of sodium hydride to convert hydroxy groups to sodium alkoxide. Assuming the PEG oligomer with alkoxy end-groups as a macroinitiator, anionic ring-opening polymerization of some lactones (β-propiolactone, α-methyl-β-propiolactone, δ-valerolactone and ε-caprolactone) with different ring sizes were performed to obtain the ABA-type poly(ester-ether-ester) block copolymers. Copolymers with various compositions were obtained with high yields. Spectroscopic and thermal characterization of the copolymers were performed by using DSC, TGA, FT-IR, and 1H-NMR spectroscopy. Formation of the block copolymers and their mass distributions were determined by MALDI mass spectrometry. Structural analyses of the copolymers revealed that chain extensions increased in order of α-methyl-β-propiolactone, β-propiolactone, δ-valerolactone and ε-caprolactone.</p

Isolation and Characterization of Rare Flavone Tetraglycosides from the Seeds of the Bioactive Plant: <i>Peganum harmala L.</i>

The phytochemical investigation of Peganum harmala L. seeds yielded two rare flavone tetraglycosides following isolation, purification, and analyses. The compound determined to be diosmetin-7-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→6)]-β-D-glucopyranoside (1) was first isolated from the species while the other compound characterized to be acacetin-7-O-β-D-glucopyranosyl-(1→2)-β-D-glucopyranosyl-(1→2)-[α-L-rhamnopyranosyl-(1→6)]-β-D-glucopyranoside (2) was isolated from the genus Peganum for the first time. Their structures were primarily elucidated by one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) (1H, 13C NMR, DEPT, COSY, HSQC and HMBC) and supported by matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-TOF-MS) and MALDI-TOF-MS/MS analyses.</p

Conformational Characterization of Polyelectrolyte Oligomers and Their Noncovalent Complexes Using Ion Mobility-Mass Spectrometry

Poly-l-lysine (PLL), polystyrenesulfonate (PSS), and a mixture of these polyelectrolytes were investigated by electrospray ionization ion mobility mass spectrometry. The IM step confirmed the formation of noncovalent (i.e., supramolecular) complexes between these polyelectrolytes, which were detected in various charge states and stoichiometries in the presence of their constituents. Experimental and theoretical collision cross sections (CCSs) were derived for both PLL and PSS oligomers as well as their noncovalent assemblies. PSS chains showed higher compactness with increasing size as compared to PLL chains, indicating that the intrinsic conformations of the polyelectrolytes depend on the nature of the functional groups on their side chains. The CCS data for the noncovalent complexes further revealed that assemblies with higher PLL content have higher CCS values than other compositions of similar mass and that PLL–PSS complex formation is accompanied by significant size contraction