Photochemistry of macrocyclic ketones within zeolites: competition between norrish type I and type II reactivity

Photolysis of macrocyclic mono- and diketones (1 and 2) included in X and Y zeolites gives Norrish type I products in addition to the products obtained via the Norrish type II process, the only observed process in isotropic media. Enhancement of the type I over the type II process is cation-dependent and especially large enhancements are obtained with Li and Na as cations. The zeolite effect is attributed to a reduction in the rate of the Norrish type II -hydrogen abstraction process.     

Enolate addition to a 2-alkylidene[1,3]dithiane-derived bissulfoxide. A new a(2)-acceptor

Reaction of enolates derived from esters and ketones to an easily prepared alkylidene[1,3]dithiane-1,3-dioxide afforded the respective adducts with good yields and selectivities generally exceeding 85:15. The base used for enolate addition played no significant role for the reaction outcome, and addition of a silyl enole ether gave similar results. The thus formed oxygenated S,S-acetals were transformed into the corresponding 1,4-dicarbonyls by a reduction/oxidation sequence with 84% yield. [reaction: see text]     

Quasi-continuous growth of ultralong carbon nanotube arrays

We report the growth of ultralong (>10 cm) multi-walled and single-walled carbon nanotubes such that the length is limited by the size of the furnace rather than by the termination of growth. The disturbance of microscale laminar flows results in disordered or shorter growth of carbon nanotubes. By downsizing reaction pipes, reaction gas flows are stabilized with low Reynolds numbers. In this way, the catalyst nanoparticles at the end of growing carbon nanotubes can travel a longer distance to grow ultralong nanotubes.     

Frustrated Lewis Pair Catalyzed Dehydrogenative Oxidation of Indolines and Other Heterocycles

An acceptorless dehydrogenation of heterocycles catalyzed by frustrated Lewis pairs (FLPs) was developed. Oxidation with concomitant liberation of molecular hydrogen proceeded in high to excellent yields for N‐protected indolines as well as four other substrate classes. The mechanism of this unprecedented FLP‐catalyzed reaction was investigated by mechanistic studies, characterization of reaction intermediates by NMR spectroscopy and X‐ray crystal analysis, and by quantum‐mechanical calculations. Hydrogen liberation from the ammonium hydridoborate intermediate is the rate‐determining step of the oxidation. The addition of a weaker Lewis acid as a hydride shuttle increased the reaction rate by a factor of 2.28 through a second catalytic cycle.     

High Resolution Mass Spectrometry of Polyfluorinated Polyether-Based Formulation

High resolution mass spectrometry (HRMS) was successfully applied to elucidate the structure of a polyfluorinated polyether (PFPE)-based formulation. The mass spectrum generated from direct injection into the MS was examined by identifying the different repeating units manually and with the aid of an instrument data processor. Highly accurate mass spectral data enabled the calculation of higher-order mass defects. The different plots of MW and the nth-order mass defects (up to n = 3) could aid in assessing the structure of the different repeating units and estimating their absolute and relative number per molecule. The three major repeating units were -C₂H₄O-, -C₂F₄O-, and -CF₂O-. Tandem MS was used to identify the end groups that appeared to be phosphates, as well as the possible distribution of the repeating units. Reversed-phase HPLC separated of the polymer molecules on the basis of number of nonpolar repeating units. The elucidated structure resembles the structure in the published manufacturer technical data. This analytical approach to the characterization of a PFPE-based formulation can serve as a guide in analyzing not just other PFPE-based formulations but also other fluorinated and non-fluorinated polymers. The information from MS is essential in studying the physico-chemical properties of PFPEs and can help in assessing the risks they pose to the environment and to human health.

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Peptide-based SAMs that resist the adsorption of proteins

In this paper we present a modular approach for the fabrication of surfaces to characterize protein-protein interactions. The approach is based on azido peptides with an optimized sequence which are then thiol-functionalized using an alkynyl thiol and "click" chemistry. From these peptide thiols we fabricated SAMs on gold to evaluate the protein resistance, using surface plasmon resonance spectroscopy, toward streptavidin, bovin serum albumin (BSA), and fibronectin.     

Mechanisms of Cysteine-Lysine Covalent Linkage—The Role of Reactive Oxygen Species and Competition with Disulfide Bonds**

Recently, a new naturally occurring covalent linkage was characterised, involving a cysteine and a lysine, bridged through an oxygen atom. The latter was dubbed as the NOS bond, reflecting the individual atoms involved in this uncommon bond which finds little parallel in lab chemistry. It is found to form under oxidising conditions and is reversible upon addition of reducing agents. Further studies have identified the bond in crystal structures across a variety of systems and organisms, potentially playing an important role in regulation, cellular defense and replication. Not only that, double NOS bonds have been identified and even found to be competitive in relation to the formation of disulfide bonds. This raises several questions about how this exotic bond comes to be, what are the intermediates involved in its formation and how it competes with other pathways of sulfide oxidation. With this objective in mind, we revisited our first proposed mechanism for the reaction with model electronic structure calculations, adding information about the reactivity with alternative reactive oxygen species and other potential competing products of oxidation. We present a network with more than 30 reactions which provides one of the most encompassing pictures for cysteine oxidation pathways to date.     

Towards a Precise NMR Quantification of Acute Phase Inflammation Proteins from Human Serum

Nuclear Magnetic Resonance (NMR) spectra of human serum and plasma show, besides metabolites and lipoproteins, two characteristic signals termed GlycA and B arising from the acetyl groups of glycoprotein glycans from acute phase proteins, which constitute good markers for inflammatory processes. Here, we report a comprehensive assignment of glycoprotein glycan NMR signals observed in human serum, showing that GlycA and GlycB signals originate from Neu5Ac and GlcNAc moieties from N-glycans, respectively. Diffusion-edited NMR experiments demonstrate that signal components can be associated with specific acute phase proteins. Conventionally determined concentrations of acute phase glycoproteins correlate well with distinct features in NMR spectra (R² up to 0.9422, p-value <0.001), allowing the simultaneous quantification of several acute phase inflammation proteins. Overall, a proteo-metabolomics NMR signature of significant diagnostic potential is obtained within 10–20 min acquisition time. This is exemplified in serum samples from COVID-19 and cardiogenic shock patients showing significant changes in several acute phase proteins compared to healthy controls.     

UHV Studies of Methanol Decomposition on Mono‐ and Bimetallic CoPd Nanoparticles Supported on Thin Alumina Films

Bimetallic nanoparticles often turn out to be superior to the corresponding monometallic systems with respect to their catalytic properties. To study such effects for the methanol decomposition reaction, model catalysts were prepared by physical vapor deposition of Pd and Co under ultrahigh‐vacuum (UHV) conditions. Monometallic Pd and Co particles as well as CoPd core–shell particles were generated on an epitaxial alumina film grown on NiAl(110). The interaction with methanol is examined by temperature‐programmed desorption of methanol and carbon monoxide and by X‐ray photoelectron spectroscopy. The decomposition of methanol proceeds in two reaction pathways independent of the particle composition: complete dehydrogenation towards carbon monoxide and hydrogen, and C? O bond scission yielding carbon deposits. Pd is the most active material studied here. The relative importance of the two channels varies for the different particle systems: on Pd dehydrogenation is preferred, whereas the C? O bond cleavage is more pronounced on Co. The bimetallic clusters show a moderate performance for both pathways. Carbon deposition poisons the model catalysts by blocking the adsorption sites for methoxide, which is the first intermediate product during methanol decomposition. In particular on Co, large amounts of carbon deposits can also be caused by dissociation of the final product of the dehydrogenation pathway, carbon monoxide. A comparison with the results of methanol decomposition on Co, Pd, and CoPd catalysts in continuous‐flow reactors demonstrates that the findings of the present UHV study are relevant for catalytic performance under high‐pressure conditions.