Structure and fragmentation of dimethyl methylphosphonate and trimethyl phosphite

The structures and fragmentation pathways of two isomeric organophosphorus esters, dimethyl methylphosphonate (DMMP) and trimethyl phosphite (TMP) have been determined. The long-lived, low-energy molecular ions of DMMP were found to undergo a keto-to-enol isomerization prior to collision-induced dissociation. This isomerization was established through the comparison of the collision spectra from DMMP, TMP, isotopically labeled DMMP and a model precursor ion. Electron ionization and charge exchange reactions were used to study the isomerization as a function of the internal energy of the molecular ion. The structure of the TMP molecular ion retained the structure of the neutral molecule. The daughter ion spectra of the isomeric fragment ions from DMMP and TMP were used to infer the fragment ion structures. Negative ions of DMMP and TMP were also studied, and their collision spectra were found to be indistinguishable.     

More Than 12 % Polarization and 20 Minute Lifetime of 15N in a Choline Derivative Utilizing Parahydrogen and a Rhodium Nanocatalyst in Water

Hyperpolarization techniques are key to extending the capabilities of MRI for the investigation of structural, functional and metabolic processes in vivo. Recent heterogeneous catalyst development has produced high polarization in water using parahydrogen with biologically relevant contrast agents. A heterogeneous ligand‐stabilized Rh catalyst is introduced that is capable of achieving ¹⁵N polarization of 12.2±2.7 % by hydrogenation of neurine into a choline derivative. This is the highest ¹⁵N polarization of any parahydrogen method in water to date. Notably, this was performed using a deuterated quaternary amine with an exceptionally long spin‐lattice relaxation time (T₁) of 21.0±0.4 min. These results open the door to the possibility of ¹⁵N in vivo imaging using nontoxic similar model systems because of the biocompatibility of the production media and the stability of the heterogeneous catalyst using parahydrogen‐induced polarization (PHIP) as the hyperpolarization method.     

Ultrasmall Zeolite L Crystals Prepared from Highly Interdispersed Alkali‐Silicate Precursors

The preparation of nanosized zeolites is critical for applications where mass‐transport limitations within microporous networks hinder their performance. Often the ability to generate ultrasmall zeolite crystals is dependent upon the use of expensive organics with limited commercial relevance. Herein, we report the generation of zeolite L crystals with uniform sizes less than 30 nm using a facile, organic‐free method. Time‐resolved analysis of precursor assembly and evolution during nonclassical crystallization highlights key differences among silicon sources. Our findings reveal that a homogenous dispersion of potassium ions throughout silicate precursors leads to the formation of a metastable nonporous phase, which undergoes an intercrystalline transformation to zeolite L. The generation of highly interdispersed alkali‐silicate precursors is seemingly critical to enhancing the rate of nucleation and facilitating the formation of ultrasmall crystal.     

Heteroleptic Copper(I)‐Based Complexes for Photocatalysis: Combinatorial Assembly,Discovery, and Optimization

A library of 50 copper‐based complexes derived from bisphosphines and diamines was prepared and evaluated in three mechanistically distinct photocatalytic reactions. In all cases, a copper‐based catalyst was identified to afford high yields, where new heteroleptic complexes derived from the bisphosphine BINAP displayed high efficiency across all reaction types. Importantly, the evaluation of the library of copper complexes revealed that even when photophysical data is available, it is not always possible to predict which catalyst structure will be efficient or inefficient in a given process, emphasizing the advantages for catalyst structures with high modularity and structural variability.     

L3C3P3: Tricarbontriphosphide Tricyclic Radicals and Cations Stabilized by Cyclic (alkyl)(amino)carbenes

Alkynes usually oligomerize to give rings with a conjugated π‐electron system. In contrast, phosphaalkynes, R?C≡P, frequently give compounds with polycyclic structures, which are thermodynamically more stable than the corresponding π‐conjugated isomers. The syntheses of the first C₃P₃ tricyclic compounds are reported with either radical or cationic ground states stabilized by cyclic (alkyl)(amino)carbenes (CAACs). These compounds may be considered as examples of tricarbontriphosphide coordinated by carbenes and are likely formed via trimerization of the corresponding mono‐radicals CAAC‐CP^.. The mechanism for the formation of these tricarbontriphosphide radicals has been rationalized by a combination of experiments and DFT calculations.     

Ordinal algorithms for packing with target center of gravity

The problem of arranging N unit length weights on a line segment of length N, given a target center of gravity on this line segment, is examined under the assumption that the only information we have about the weights is their order, i.e., a ₁ a ₂ ... a _N . Lower bounds on worst case performance of algorithms for this problem are developed, and algorithms (permutations) which come close to achieving these bounds are provided.This work was partially supported under Natural Sciences and Engineering Research Council (NSERC) of Canada research grant number OGP0002507.     

Schütte's tautology and the Kochen-Specker theorem

I present a new 33-ray proof of the Kochen and Specker no-go hidden variable theorem in ₃, based on a classical tautology that corresponds to a contingent quantum proposition in ₃ proposed by Kurt Schütte in an unpublished letter to Specker in 1965. 1 discuss the relation of this proof to a 31-ray proof by Conway and Kochen, and to a 33-ray proof by Peres.     

Direct evaluation of DLVO theory for predicting long-range forces between a yeast cell and a surface

Using a combined gradient optical trap and evanescent wave light-scattering force-measurement technique, long-range colloidal forces were measured between a single Candida albicans yeast cell and a flat, bare glass surface in electrolyte concentrations ranging from 0.1 to 100 mM NaCl. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was compared to experimentally measured equilibrium force curves and found to provide a close approximation to the decay length of the measured forces for electrolyte concentrations up to about 0.23 mM NaCl. At higher electrolyte concentrations (>/=0.5 mM NaCl), decay lengths of force curves in experimental measurements were consistently longer than Debye lengths calculated from the electrolyte concentrations. In electrolyte concentrations of 10 and 100 mM NaCl, most cells attached rapidly, which prevented measurements of long-range forces. The small fraction of cells remaining unattached in these higher electrolyte concentrations displayed purely repulsive forces. These results show that the DLVO theory accurately describes cell-surface interactions when the Debye length is in the range of 20-30 nm but underpredicts the decay length of the interactions at higher electrolyte concentrations.     

A survey of acid catalysis and oxidation conditions in the two-step, one-flask synthesis of meso-substituted corroles via dipyrromethanedicarbinols and pyrrole

The reaction of dipyrromethanedicarbinols with pyrrole leading to meso-substituted corroles was investigated to determine whether mild acid catalysts [Dy(OTf)(3), Yb(OTf)(3), Sc(OTf)(3), and InCl(3)] known to provide porphyrins from dipyrromethanecarbinol species while suppressing undesired reversibility (resulting in scrambling) are applicable to reactions affording corrole, and to explore the requirements of the oxidation step. We examined a model reaction leading to meso-triphenylcorrole (TPC) to survey the effect of acid catalyst, acid concentration, ratio of pyrrole to dipyrromethanedicarbinol, oxidant, oxidant quantity, and reaction time on the yield of TPC (by UV-vis) in reactions performed at room temperature in CH(2)Cl(2). Key to this survey was a modification of the well-known spectrophotometric method for monitoring reactions leading to porphyrin. The survey revealed that TPC could be prepared via a subset of the mild acid catalysts [Dy(OTf)(3) and Yb(OTf)(3)], and a preparative-scale reaction afforded an isolated yield of TPC of 49%, devoid of porphyrin. Suppression of reversible processes was further demonstrated by the synthesis of three corroles bearing different meso substituents in defined locations in isolated yields ranging from 50% to 80%. The reaction conditions were applicable to a dipyrromethanedicarbinol bearing electron-withdrawing pentafluorophenyl substituents-provided that the reaction time of the condensation step was increased. We identified circumstances under which DDQ can cause severe interference with the detection and isolation of some corroles, we found that the yield and purity of the corrole depend on judicious selection of oxidation conditions, and we assessed the sensitivity toward light of dilute solutions of the corroles prepared in this study.