Unexpected formation of dinaphthoaza-17-crown-5 ether containing γ-aminopiperidine subunit

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Chlorotrimethylsilane-promoted synthesis of 1,2,4-triazolopyrimidines from 3,5-diamino-1,2,4-triazoles and pentane-2,4-diones

An efficient synthesis of 2-amino-1-R-[1,2,4]triazolo[1,5-a]- pyrimidinium or 3-amino-2-R-[1,2,4]triazolo[4,3-a]pyrimidi- nium chloride derivatives by heterocyclization of 3,5-diamino- 1-R-1,2,4-triazoles (R = Alk or Ar) with pentane-2,4-diones was developed. The process is promoted by chlorotrimethyl- silane which plays the dual role of carbonyl-activating agent and water scavenger.     

Finitely presented monoids with linear Dehn function need not have regular cross-sections

This paper shows that a finitely presented monoid with linear Dehn function need not have a regular cross-section, strengthening the previously-known result that such a monoid need not be presented by a finite complete string rewriting system, and contrasting with the fact that finitely presented groups with linear Dehn function always have regular cross-sections.     

Metal Oxide Assisted Preparation of Core–Shell Beads with Dense Metal–Organic Framework Coatings for the Enhanced Extraction of Organic Pollutants

Dense and homogeneous metal–organic framework (MOF) coatings on functional bead surfaces are easily prepared by using intermediate sacrificial metal oxide coatings containing the metal precursor of the MOF. Polystyrene (PS) beads are coated with a ZnO layer to give ZnO@PS core–shell beads. The ZnO@PS beads are reactive in the presence of 2‐methylimidazole to transform part of the ZnO coating into a porous zeolitic imidazolate framework‐8 (ZIF‐8) external shell positioned above the internal ZnO precursor shell. The obtained ZIF‐8@ZnO@PS beads can be easily packed in column format for flow‐through applications, such as the solid‐phase extraction of trace priority‐listed environmental pollutants. The prepared material shows an excellent permeance to flow when packed as a column to give high enrichment factors, facile regeneration, and excellent reusability for the extraction of the pollutant bisphenol A. It also shows an outstanding performance for the simultaneous enrichment of mixtures of endocrine disrupting chemicals (bisphenol A, 4‐tert‐octylphenol and 4‐n‐nonylphenol), facilitating their analysis when present at very low levels (<1 μg L^?1) in drinking waters. For the extraction of the pollutant bisphenol A, the prepared ZIF‐8@ZnO@PS beads also show a superior extraction and preconcentration capacity to that of the PS beads used as precursors and the composite materials obtained by the direct growth of ZIF‐8 on the surface of the PS beads in the absence of metal oxide intermediate coatings.     

The Michael Addition of Sulfur Anions to β,β-Substituted Nα-Formyl-α, β-Dehydroamino Acid Esters

The addition of lithium benzylthiolates to N^α,-formyl-α,β-dehydro-α-amino acid esters gave protected N^α-formyl-β-S-benzyl-β,β-dialkylcysteine esters. Hydrolysis and N^α-protection produced β,β-dialkyl-cysteines which can be used for peptide synthesis.     

The not-so-peculiar case of calcium oxide: a weakness in atomic natural orbital basis sets for calcium

Atomic natural orbital (ANO) basis sets for calcium may produce surprisingly poor atomic and molecular properties and energetics. The weaknesses in these basis sets may be traced primarily to deficiencies within the sets of d functions which are incapable of effectively correlating the 3s and 3p electrons. Examples are given which show that addition of tight d functions to the ANO basis is required to achieve qualitatively correct energetics and structures for conventionally bonded calcium compounds.     

A Lax type operator for quantum finite W-algebras

Selecta Mathematica - For a reductive Lie algebra $$\mathfrak {g}$$ , its nilpotent element f and its faithful finite dimensional representation, we construct a Lax operator L(z) with coefficients...     

Convex Entire Noncommutative Functions are Polynomials of Degree Two or Less

We establish several new relations between the discrete transition operator, the continuous Laplacian and the averaging operator associated with combinatorial and metric graphs. It is shown that these operators can be expressed through each other in a very explicit way. In particular, the averaging operator appears to be closely related to the solutions of the associated wave equation. The machinery used allows one to study a class of infinite graphs without assumption on the local finiteness.