Theoretical study of the stereoselective additions of chiral alcohols to ketenes

In 1989, Larsen et al. at Merck discovered that the addition of chiral alcohols to ketenes provided enantiomerically enriched aryl propionic acids, compounds valued for their therapeutic antiinflammatory properties. The high 1,4-asymmetric induction observed (>99:1 dr in the addition, and up to 99% ee after hydrolysis to the acid) is rare. A quantitative model based on B3LYP density functional theory calculations accounts for the stereoselectivity in the addition of (S)-methyl lactate, (S)-3-methyl-2-butanol, and (S)-pantolactone to methylphenylketene. The conformational processes of the intermediates can impact the stereoselectivity of the process, and either the addition step, or the protonation of the enolate intermediate, may be stereoselectivity determining.     

On Modules over Matrix Quantum Pseudo-Differential Operators

We classify all the quasifinite highest-weight modules over the central extension of the Lie algebra of matrix quantum pseudo-differential operators, and obtain them in terms of representation theory of the Lie algebra (, R _m ) of infinite matrices with only finitely many nonzero diagonals over the algebra R _m = [t]/(t ^m+1). We also classify the unitary ones.     

Distinctive MS/MS Fragmentation Pathways of Glycopeptide‐Generated Oxonium Ions Provide Evidence of the Glycan Structure

Post‐translational glycosylation of proteins play key roles in cellular processes and the site‐specific characterisation of glycan structures is critical to understanding these events. Given the challenges regarding identification of glycan isomers, glycoproteomic studies generally rely on the assumption of conserved biosynthetic pathways. However, in a recent study, we found characteristically different HexNAc oxonium ion fragmentation patterns that depend on glycan structure. Such patterns could be used to distinguish between glycopeptide structural isomers. To acquire a mechanistic insight, deuterium‐labelled glycopeptides were prepared and analysed. We found that the HexNAc‐derived m/z 126 and 144 oxonium ions, differing in mass by H₂O, had completely different structures and that high‐mannose N‐glycopeptides generated abundant Hex‐derived oxonium ions. We describe the oxonium ion decomposition mechanisms and the relative abundance of oxonium ions as a function of collision energy for a number of well‐defined glycan structures, which provide important information for future glycoproteomic studies.     

Continuous glucose monitoring by means of mid-infrared transmission laser spectroscopy in vitro

The continuous surveillance of glucose concentration reduces short-term risks and long-term complications for people with diabetes mellitus, a disorder of glucose metabolism. As a first step towards the continuous monitoring of glucose, reagent-free transmission spectroscopy in the mid-infrared region has been carried out in vitro using a quantum cascade laser and an optical silver halide fiber. A 30 μm gap in the fiber allowed for transmission spectroscopy of aqueous glucose solutions at a wavelength of 9.69 μm, which is specific to a molecular vibration of glucose. A noise-equivalent concentration as low as 4 mg/dL was achieved at an average power of 1.8 mW and an integration time of 50 s. This is among the most precise of glucose measurements using mid-infrared spectroscopy. Even with the very low average laser power of 0.07 mW the sensitivity of previous results (using a fiber optical evanescent field analysis) has been improved upon by almost one order of magnitude. Finally, the impact of potentially interfering substances such as other carbohydrates was analyzed.     

Modelling and Optimization of Stability Constants of Cadmium or Zinc with Biological Buffers (DIPSO or TAPS) in Aqueous Solutions by Electrochemical Techniques

The complexation behavior of four systems involving cadmium(II) or zinc(II) in aqueous solutions with the biological buffers 3-[N,N-bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO), and [(2-hydroxy-1,1-bis(hydroxymethyl)ethyl)amino]-1-propanesulfonic acid (TAPS) was studied by direct current polarography (DCP) and glass electrode potentiometry (GEP), at 25.0 ± 0.1 °C and ionic strength 0.1 mol·dm^?3 KNO₃. Except for the Cd–TAPS system, for which full characterization of the system was possible either by DCP or GEP, full characterization of the other metal-buffer systems (Zn–DIPSO, Zn–TAPS and Cd–DIPSO) was only possible using DCP. For Zn-buffers systems, ZnL⁺ and $ {\text{ZnL(OH)}}_{2}^{ - } $ ZnL(OH) 2 ? (where L stands for buffer) were identified. For the Zn–DIPSO system, the overall stability constant values (as log₁₀ β) are 2.1 ± 0.2 and 13.4 ± 0.2, respectively. For the Zn–TAPS system, the overall stability constants values (as log₁₀ β) are 2.4 ± 0.1 and 12.9 ± 0.3, respectively. For the Cd–DIPSO system, the overall stability constants values (as log₁₀ β) of CdL⁺ and CdL(OH) are 2.9 ± 0.1 and 6.9 ± 0.3, respectively. For the Cd–TAPS system, only the species CdL⁺ was identified with log₁₀ β = 2.5 ± 0.1.     

Modification of crystallinity and pore size distribution in coagulated cellulose films

In this study the effects of altering the coagulation medium during regeneration of cellulose dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate, were investigated using solid-state NMR spectroscopy and NMR cryoporometry. In addition, the influence of drying procedure on the structure of regenerated cellulose was studied. Complete conversion of the starting material into regenerated cellulose was seen regardless of the choice of coagulation medium. Coagulation in water predominantly formed cellulose II, whereas coagulation in alcohols mainly generated non-crystalline structures. Subsequent drying of the regenerated cellulose films, induced hornification effects in the form of irreversible aggregation. This was indicated by solid-state NMR as an increase in signal intensity originating from crystalline structures accompanied by a decrease of signal intensity originating from cellulose surfaces. This phenomenon was observed for all used coagulants in this study, but to various degrees with regard to the polarity of the coagulant. From NMR cryoporometry, it was concluded that drying induced hornification generates an increase of nano-sized pores. A bimodal pore size distribution with pore radius maxima of a few nanometers was observed, and this pattern increased as a function of drying. Additionally, cyclic drying and rewetting generated a narrow monomodal pore size pattern. This study implies that the porosity and crystallinity of regenerated cellulose can be manipulated by the choice of drying condition.     

Enantioselective Alkynylation of Trifluoromethyl Ketones Catalyzed by Cation‐Binding Salen Nickel Complexes

Cation‐binding salen nickel catalysts were developed for the enantioselective alkynylation of trifluoromethyl ketones in high yield (up to 99 %) and high enantioselectivity (up to 97 % ee). The reaction proceeds with substoichiometric quantities of base (10–20 mol % KOt‐Bu) and open to air. In the case of trifluoromethyl vinyl ketones, excellent chemo‐selectivity was observed, generating 1,2‐addition products exclusively over 1,4‐addition products. UV‐vis analysis revealed the pendant oligo‐ether group of the catalyst strongly binds to the potassium cation (K⁺) with 1:1 binding stoichiometry (K_a=6.6×10⁵ m ^?1).     

Algebraic signatures of convex and non-convex codes

A convex code is a binary code generated by the pattern of intersections of a collection of open convex sets in some Euclidean space. Convex codes are relevant to neuroscience as they arise from the activity of neurons that have convex receptive fields. In this paper, we develop algebraic methods to determine if a code is convex. Specifically, we use the neural ideal of a code, which is a generalization of the Stanley–Reisner ideal. Using the neural ideal together with its standard generating set, the canonical form, we provide algebraic signatures of certain families of codes that are non-convex. We connect these signatures to the precise conditions on the arrangement of sets that prevent the codes from being convex. Finally, we also provide algebraic signatures for some families of codes that are convex, including the class of intersection-complete codes. These results allow us to detect convexity and non-convexity in a variety of situations, and point to some interesting open questions.