Co-crystallised α- and β-Anomers of 2,3,4,6-Tetra-acetyl-<Emphasis Type="SmallCaps">d</Emphasis>-glucopyranose,in which the α- and β-Anomers are Randomly Distributed in the Hydrogen-bonded Chains of Molecules

Abstract A co-crystallised sample of α- and β-2,3,4,6-tetra-O-acetyl-d-glucopyranose [α:β = 1:2.86(8)], (α,β-1), has been isolated from a solution of 2,3,4,6-tetra-O-acetyl-d-glucopyranose in moist ethyl acetate/diethyl ether. In contrast, pure β-2,3,4,6-tetra-O-acetyl-d-glucopyranose, (β-1) was isolated on crystallisation from diethyl ethyl/petroleum ether. Species (α,β-1) is a solid solution in which approximately one in four of the molecules in the β-form is randomly substituted by a molecule of the α-anomer. The hydrogen bonded zig-zag chain connectivity of the pure β-anomer is maintained in the solid solution along the b direction. Since the parent d-glucopyranose compounds differ in their molecular packing and, therefore in structure, the solid solution phenonmenon in the case of their tetraacetyl derivatives is unexpected. Compound (β-1) and the (α,β-1) solid solution crystallize in the orthorhombic space group P2₁2₁2₁: a = 7.8612(4) ?, b = 10.2045(5) ?, c = 20.7362(11) ?, and Z = 4 for (β-1) at 120(2)K; and a = 7.9674(5) ?, b = 10.2547(4) ?, c = 21.1565(10) ?, and Z = 4 for (α,β-1) at 291(2) K. Index Abstract Co-crystallised α- and β-Anomers of 2,3,4,6-Tetra-acetyl-d-glucopyranose, in which the α- and β-Anomers are Randomly Distributed in the Hydrogen-bonded Chains of Molecules Thomas C. Baddeley, William T. A. Harrison, R. Alan Howie, Janet M. S. Skakle and James L. Wardell α- and β-2,3,4,6-Tetra-O-acetyl-d-glucopyranose can form a crystalline solid solution in which a molecule of the β-form is randomly substituted by a molecule of the α-anomer Co-crystallised α- and β-Anomers of 2,3,4,6-Tetra-acetyl-d-glucopyranose, in which the α- and β-anomers are Randomly Distributed in the Hydrogen-bonded Chains of Molecules Thomas C. Baddeley, ⁽¹⁾ William T. A Harrison, ⁽¹⁾ R. Alan Howie, ⁽¹⁾ Janet M. S. Skakle ⁽¹⁾ and James L. Wardell ^{(1,2)* (1)} Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen, AB24 3UE, Scotland.      

On the nature of pulsars

The paper contains a relatively non-technical summary of some recent work by the author and Jeremy Butterfield. The goal is to find a way of assigning meaningful truth values to propositions in quantum theory: something that is not possible in the normal, instrumentalist interpretation. The key mathematical tool is presheaf theory where multi-valued, contextual truth values arise naturally. We show how this can be applied to quantum theory, with the ‘contexts’ chosen to be Boolean subalgebras of the set of all projection operators.     

Fabrication of a High‐Quality,Porous, Surface‐Confined Covalent Organic Framework on a Reactive Metal Surface

A major goal of heterogeneous catalysis is to optimize catalytic selectivity. Selectivity is often limited by the fact that most heterogeneous catalysts possess sites with a range of reactivities, resulting in the formation of unwanted by‐products. The construction of surface‐confined covalent organic frameworks (sCOFs) on catalytically active surfaces is a desirable strategy, as pores can be tailored to operate as catalytic nanoreactors. Direct modification of reactive surfaces is impractical, because the strong molecule–surface interaction precludes monomer diffusion and formation of extended architectures. Herein, we describe a protocol for the formation of a high‐quality sCOF on a Pd‐rich surface by first fabricating a porous sCOF through Ullmann coupling on a Au‐rich bimetallic surface on Pd(111). Once the sCOF has formed, thermal processing induces a Pd‐rich surface while preserving the integrity of the sCOF architecture, as evidenced by scanning tunneling microscopy and titration of Pd sites through CO adsorption.     

Investigating the mechanism of chiral surface reactions: the interaction of methylacetoacetate with (S)-glutamic Acid modified Ni{111}

The enantioselective hydrogenation of beta ketoesters over Ni-based catalysts is a rare example of a heterogeneously catalyzed chiral reaction. The key step in catalyst preparation is the adsorption from solution of chiral molecules (modifiers). One particularly interesting modifier is (S)-glutamic acid because the dominant enantiomeric product in the catalytic reaction depends upon the modification temperature. We report a reflection absorption infrared spectroscopy (RAIRS) study of the adsorption of methylacetoacetate (the simplest beta ketoester) onto (S)-glutamic acid modified Ni{111} surfaces as functions of the modifier coverage and modification temperature. We show that the sticking probability of methylacetoacetate is close to 0 on saturated (S)-glutamic acid covered surfaces. At lower modifier coverage, methylacetoacetate adsorption can occur. Adsorption of methylacetoacetate onto a Ni{111} surface modified by (S)-glutamic acid at 300 K results in the diketo tautomeric form, with evidence being observed for a 1:1 interaction between zwitterionic (S)-glutamate and methylacetoacetate. In contrast, adsorption of methylacetoacetate onto a Ni{111} surface modified by (S)-glutamic acid at 350 K occurs exclusively in the enol tautomeric form. The implications for the heterogeneous catalytic reaction are discussed.     

Directed Markov Point Processes as Limits of Partially Ordered Markov Models

In this paper, we consider spatial point processes and investigate members of a subclass of the Markov point processes, termed the directed Markov point processes (DMPPs), whose joint distribution can be written in closed form and, as a consequence, its parameters can be estimated directly. Furthermore, we show how the DMPPs can be simulated rapidly using a one-pass algorithm. A subclass of Markov random fields on a finite lattice, called partially ordered Markov models (POMMs), has analogous structure to that of DMPPs. In this paper, we show that DMPPs are the limits of auto-Poisson and auto-logistic POMMs. These and other results reveal a close link between inference and simulation for DMPPs and POMMs.     

Supercooling of the disordered vortex lattice in Bi(2)Sr(2)CaCu(2)O(8+delta)

Time-resolved local induction measurements near the vortex lattice order-disorder transition in optimally doped Bi(2)Sr(2)CaCu(2)O(8+delta) crystals show that the high-field, disordered phase can be quenched to fields as low as half the transition field. Over an important range of fields, the electrodynamical behavior of the vortex system is governed by the coexistence of ordered and disordered vortex phases in the sample. We interpret the results as supercooling of the high-field phase and the possible first-order nature of the order-disorder transition at the "second magnetization peak."     

Ethyl 1,2,3,4-tetra-O-acetyl-β-D-glucopyranuronate

The crystal structure, at 120 K, and solution ¹H and ¹³C NMR spectra of ethyl 1,2,3,4-tetra-O-acetyl--D-glucopyranuronate, (8) have been determined. Compound 8 crystallizes in the triclinic space group, P1 (Z = 1) with a = 6.0209(3) Å, b = 8.9698(5) Å, c = 9.9818(8) Å, = 104.965(2)°, = 98.522(3)°, = 106.790(5)°. The Cremer and Pople puckering parameters [Q = 0.602(4) Å, = 7.1(4)°, = 325(3)°] for the pyranose ring in the solid state indicate a near ideal ⁴C₁ chair conformation with a slight distortion in the direction towards ⁰H₅. A number of weak, soft intermolecular C–H O hydrogen bonds set up a 3D array. NMR spectra and FAB and EIMS data have been obtained. Solution NMR parameters suggest that the solid state conformation is maintained in solution in chloroform.     

A highly selective Bi(OTf)3 mediated fragmentation-contraction of δ-ortholactones. A facile route to functionalized γ-lactones

A very selective method for the formation of γ-lactones from pyranyl ortholactones has been developed which occurs via a fragmentation-acetate migration-ring contraction process. The reaction is very functional group tolerant, providing functionalized γ-lactones as a single isomeric product following the ring contraction. Mechanistic studies indicate the reaction is mediated by triflic acid liberated from Bi(OTf)₃ in a slow and controlled manner providing excellent chemo and regioselectivity. We propose the triflic acid acts as both a proton and a nucleophile source with triflate anion mediating the fragmentation process.     

Structure-function studies of modular aromatics that form molecular organogels

Three urea-based aromatics 1-3, each with distinct steric and electronic characteristics, have been synthesized and their ability to undergo hierarchical assembly and gel organic solvents investigated. We have found that compound 1 promotes the sol-gel phase transition in primary alcohols (from CH3OH to C10H21OH; CGC < 15 mg/mL), while 2 and 3 do not. IR spectroscopy, X-ray powder diffraction (XRPD), and transmission electron microscopy (TEM) measurements show that 1 organizes into "cylinders" in primary alcohols, using three-centered hydrogen bonds and pi-pi aromatic interactions. The cylinders further organize into pairs through interdigitation of the methyl groups of the adjacent aromatic rings. Importantly, the lateral packing of the cylinders is enhanced as the bulk solvent polarity increases providing a mechanism for controlling the material's morphology via the solvophobic effect. Molecular mechanics (Amber) and semiempirical (AM1) calculations suggested similar conformational behavior but distinct electronic properties of 1-3. Thus, pi-deficient 2 without the methyl groups and pi-rich 3 without aromatic nitrogen fail to promote the sol-gel phase transition in alcohols due to their inability to undergo effective hierarchical assembly, which is necessary for the formation of a 3D fibrillar network. In addition, we have found that the ultrasonication of a supersaturated solution of 1 is necessary for the gelation. Presumably, a fast exchange of the aggregates of 1 is assisted with sonic waves to allow for the effective and "error free" assembly wherein an entangled net of fibers capable of encapsulating solvent molecules is formed.