Synthesis of glycosylphosphatidylinositol analogues with an unnatural <i>β</i>-D-glucosamine-(1→6)-<i>myo</i>-inositol motif

Glycosylphosphatidylinositol (GPI) anchors contain a unique α-D-glucosamine-(1→6)-myo-inositol [αGlcN(1,6)Ins] motif in their conserved core structure. To facilitate investigations of the functional roles of this structural motif, two GPI analogues containing unnatural βGlcN(1,6)Ins, instead of αGlcN(1,6)Ins, and an alkyne group at different positions of the GPI core were designed and synthesized. To this end, an orthogonally protected pseudopentasaccharide derivative of GPIs with the βGlcN(1,6)Ins motif was convergently constructed via [3 + 2] glycosylation and used as the common intermediate to prepare both GPI analogues by streamlined synthetic protocols. The pseudopentasaccharide intermediate and developed protocols can be widely applicable to access various GPI analogues with the βGlcN(1,6)Ins motif. The target GPI analogues contain an alkyne, which allows their further modification to introduce various molecular labels via click chemistry, making them useful probes for the study of GPI anchorage. The differences in reactivity and NMR behavior of the two GPI analogues, as well as the differences of these analogues from previously reported GPI derivatives of similar structure containing an αGlcN(1,6)Ins motif, suggest that the 2-O-phosphoethanolamine moiety on mannose-I and the linkage form of GlcN in GPIs can have a decisive impact on the structure, which is likely relevant to biology.</p

Diversity-Oriented Synthesis of Glycosylphosphatidylinositol Probes Based on an Orthogonally Protected Pentasaccharide

Two glycosylphosphatidylinositol (GPI) derivatives having an alkynyl group at different positions were derived from the same orthogonally protected pentasaccharide that in turn was assembled by a convergent [3+2] glycosylation strategy. The resultant alkynylated GPIs are useful biological probes and are suitable for further modification by click reaction to obtain other GPI probes. The pentasaccharide is a versatile platform for the synthesis of various uniquely functionalized GPI probes

Time-Scaling in Atomistics and the Rate-Dependent Mechanical Behavior of Nanostructures

Conventional molecular dynamics simulations enable the elucidation of an astonishing array of phenomena inherent in the mechanical and chemical behavior of materials. Unfortunately, current computational limitations preclude accounting for processes whose transition times exceed, at best, microseconds. This limitation severely impacts, among others, a realistic assessment of slow-strain-rate mechanical behavior. In this work, using a simple paradigmatical model of a metallic nanopillar that is often the subject of experimental works, we attempt to circumvent the time-scale bottleneck of conventional molecular dynamics and provide novel physical insights into the rate-dependence of mechanical behavior of nanostructures. Using a collection of algorithms that include a recently developed potential energy surface sampling methodthe so-called autonomous basin climbing approach, kinetic Monte Carlo, and others, we assess the nanopillar mechanical behavior under strain rates ranging from 1 to 10⁸ s^–1. While our results for high-strain rate behavior are consistent with conventional molecular dynamics, we find that the response of nanostructures to slow compression is “liquid-like” and accompanied by extensive surface reconstructions

Time-Scaling in Atomistics and the Rate-Dependent Mechanical Behavior of Nanostructures

Conventional molecular dynamics simulations enable the elucidation of an astonishing array of phenomena inherent in the mechanical and chemical behavior of materials. Unfortunately, current computational limitations preclude accounting for processes whose transition times exceed, at best, microseconds. This limitation severely impacts, among others, a realistic assessment of slow-strain-rate mechanical behavior. In this work, using a simple paradigmatical model of a metallic nanopillar that is often the subject of experimental works, we attempt to circumvent the time-scale bottleneck of conventional molecular dynamics and provide novel physical insights into the rate-dependence of mechanical behavior of nanostructures. Using a collection of algorithms that include a recently developed potential energy surface sampling methodthe so-called autonomous basin climbing approach, kinetic Monte Carlo, and others, we assess the nanopillar mechanical behavior under strain rates ranging from 1 to 10⁸ s^–1. While our results for high-strain rate behavior are consistent with conventional molecular dynamics, we find that the response of nanostructures to slow compression is “liquid-like” and accompanied by extensive surface reconstructions

Highly Efficient and Stable Molecular-Based TiO₂ Photoanodes for Photoelectrochemical Water Splitting Achieved by Pyridyl Anchoring Technique

Photoelectrochemical overall water splitting by semiconductor electrodes modified with functional molecules has attracted considerable attention in recent years. Various kinds of molecular-based photoanodes consisting of a semiconductor thin film modified with both a photosensitizer (PS) and a water oxidation catalyst (WOC) have been developed thus far, and overall water splitting is achieved by using such a molecular-based photoanode and a Pt cathode. Nevertheless, due to the desorption of a PS and/or a WOC from the semiconductor surfaces, almost all the reported molecular-based photoanodes lose their photoelectrocatalytic activity within an hour. Thus, there is a strong demand to greatly improve the long-term stability of the molecular-based photoanodes toward practical applications. Here, we demonstrate the effectiveness of the “pyridyl anchoring technique” developed by us, leading to the long-term stability of our molecular-based photoanodes owing to the high strength of the Ti–N (pyridyl) bonding. A molecular-based TiO2 photoanode modified with both a polypyridyl ruthenium PS, [Ru(dpbpy)2(qpy)]2+ (dpbpy = 4,4′-diphenyl-2,2′-bipyridine, qpy = 4,4′:2′,2″:4″,4‴-quaterpyridine) (Ru-qpy), and a Ru(bda)-type WOC, Ru(bda)(4,4′-bpy)2 (bda = 2,2′-bipyridine-6,6′-dicarboxylic acid, 4,4′-bpy = 4,4′-bipyridine) (Ru(bda)-py) by our technique promotes water oxidation with an almost quantitative Faradaic efficiency (94 ± 6%) at the applied potential of 0.05 V versus SCE over 3 h under solar light irradiation (λ > 410 nm). Moreover, a photoelectrochemical cell (PEC) consisting of this molecular-based photoanode and a Pt cathode promotes overall water splitting only by giving an extra bias of 0.4 V. Our PEC achieves the second highest solar-to-hydrogen (STH) conversion efficiency (0.07%) among such applied bias-compensating PECs, successfully demonstrating the usefulness of the stable anchoring of molecular components in order to fabricate highly efficient PECs for solar water splitting

Two New Devices for Identifying Electrochemical Reaction Intermediates with Desorption Electrospray Ionization Mass Spectrometry

Desorption electrospray ionization mass spectrometry (DESI-MS) previously has been used to capture and identify transient intermediates in electrochemical redox reactions on a platinum-covered rotating waterwheel. We present here two different setups that use a flat surface with porous carbon tape as the working electrode, where analyte-containing microdroplets from the DESI probe contacted with electrolyte supplied onto the surface. One setup had the conducting carbon tape in the form of a grooved inclined plane; the other one was in the form of a flat plane that had the conducting carbon tape as its front surface. Both these setups, which were relatively robust and easy to operate, overcame interference from the electrospray sheath gas that disturbs and dries the flowing electrolyte. By using the inclined-plane device, we observed radical cations and dimer species generated in the electrochemical oxidation of triphenylamine, diimine and imine alcohol in the electrochemical oxidation of uric acid, and the reductive cleavage of disulfide bonds in glutathione disulfide. By using the device with the flat carbon tape, we detected nitrenium ions generated in the electrochemical oxidation of <i>N</i>,<i>N</i>′-dimethyoxydiphenylamine and di-<i>p</i>-tolylamine. Our experience suggests that the flat porous carbon tape surface might be preferable over the inclined plane because of its ease of setup

Formation and Stabilization of Palladium Nanoparticles on Colloidal Graphene Quantum Dots

Metal particles supported by carbon materials are important for various technologies yet not well understood. Here, we report on the use of well-defined colloidal graphene quantum dots as a model system for the carbon materials to study metal–carbon interaction. In the case of palladium, our studies show high affinity between the metal nanoparticles with the graphene. IR spectroscopy reveals covalent nature of the interaction between the two, which had been predicted by theoretical calculations yet never directly proven before

Lipid Isobaric Mass Tagging for Enhanced Relative Quantification of Unsaturated <i>sn</i>-Positional Isomers

Changes in the levels of lipid sn-positional isomers are associated with perturbation of the physiological environment within the biological system. Consequently, knowing the concentrations of these lipids holds significant importance for unraveling their involvement in disease diagnosis and pathological mechanisms. However, existing methods for lipid quantification often fall short in accuracy due to the structural diversity and isomeric forms of lipids. To address this challenge, we have developed an aziridine-based isobaric tag labeling strategy that allows (i) differentiation and (ii) enhanced relative quantification of lipid sn-positional isomers from distinct samples in a single run. The methodology enabled by aziridination, isobaric tag labeling, and lithiation has been applied to various phospholipids, enabling the determination of the sn-positions of fatty acyl chains and enhanced relative quantification. The analysis of Escherichia coli lipid extracts demonstrated the enhanced determination of the concentration ratios of lipid isomers by measuring the intensity ratios of mass reporters released from sn-positional diagnostic ions. Moreover, we applied the method to the analysis of human colon cancer plasma. Intriguingly, 17 PC lipid sn-positional isomers were identified and quantified simultaneously, and among them, 7 showed significant abundance changes in the colon cancer plasma, which can be used as potential plasma markers for diagnosis of human colon cancer

Computational Comparative Study of the Binding of Americium with N‑Donor Ligands

The accessibility of multiple valence states of americium (Am) inspired redox-based protocols aimed at efficient separation of trivalent Am (Am3+) from trivalent lanthanides (Ln3+) alternative to the traditional liquid–liquid extraction. This requires an extensive understanding of the coordination chemistry of Am in its various accessible valence states in the aqueous phase. In this work, by means of DFT calculations, the coordination of AmIII–VI with five typical N-donor ligands, i.e., terpyridine (tpy), bispyrazinylpyridine (dpp), bistriazinylpyridine (BTP), bistriazinyl bipyridine (BTBP), and bistrazinyl phenanthroline (BTPhen), was studied in terms of energy and topological analysis. The results show that the exchange of aqua ligands of hydrated ions by N-donor ligands is an entropy-driven process and enthalpically unfavorable. Topological analysis suggests a distinct mechanism of BTP to modulate the redox potential of Am(III) in that BTP can assist the relay of the leaving electron of AmIII, while the other N-donor ligands can detain the oxidation of Am by offering their electron instead. This comparative study enriches our understanding of the coordination chemistry of high-valent Am with N-donor ligands and recommends the ligand design toward the modulation of redox potentials of hydrated Am(III) ions

Student demand classification method based on the KANO model.

Student demand classification method based on the KANO model.</p