Freezing temperatures of aqueous solutions of hexamethylenetetramine with polyols,amides, and ethers

Freezing temperatures of dilute aqueous solutions of hexamethylenetetramine and mixtures of hexamethylenetetramine with myo-inositol, d-mannitol, cyclohexanol, formamide, acetamide, 1,4-dioxane, and 1,3,5-trioxane have been measured. These data yield pairwise molecular Gibbs energies of interaction between the molecules in an aqueous solution. Using the additivity principle, the results also yield the pairwise functional group Gibbs energies of interaction in an aqueous solution for the amine nitrogen with itself and with the hydroxyl, amide, ether, and methylene groups.     

Phase-titration analysis of ternary mixtures containing mutually miscible components

A method, based on phase-titration, for the analysis of ternary mixtures composed of mutually miscible components is described. One of the components is determined by an independent chemical or physical means and its concentration in the original mixture then brought to a fixed value by adding a calculated amount of one of the three components. The resultant mixture is then titrated to the turbidimetric end-point with a titrant which is immiscible with one of the components and the composition of the sample is computed from a calibration curve. The method is illustrated by its application to benzene-methanol-acetic acid and benzene-toluene-acetic acid mixtures.     

Lipidated cyclopropenes via a stable 3-N spirocyclopropene scaffold

Lipidated cyclopropenes serve as useful bioorthogonal reagents for imaging cell membranes due to the cyclopropene’s small size and ability to ligate with pro-fluorescent tetrazines. Previously, the lipidation of cyclopropenes required modification at the C3 position because methods to append lipids at C1/C2 were not available. Herein, we describe C1/C2 lipidation with the biologically active lipid ceramide and a common phospholipid using a cyclopropene scaffold whose reactivity with 1,2,4,5-tetrazines has been caged.     

Synthesis of a hyaluronan neoglycopolymer by ring-opening metathesis polymerization

A hyaluronan (HA)-derived disaccharide was synthesized bearing an n-pentenyl spacer arm, which facilitated disaccharide derivatization with a norbornene template. Subsequent ring opening metathesis polymerization of the monomer produced an HA-mimetic neoglycopolymer of low polydispersity.     

An ELISA-based approach to optimize elution conditions for obtaining hapten-specific antibodies

The correct choice of the elution conditions to break an affinity interaction is important for the successful purification of biomolecules. The optimal elution buffer liberates the bound substance in a minimum volume and maintains the activity of the purified material. The present study demonstrates an enzyme-linked immunosorbent assay (ELISA)-based approach for selection of specific elution conditions for eluting antibodies against a small molecule (atrazine) from pooled sera. Six different elution conditions were tried for the removal of antibodies from the complex. Large-scale purification of anti-atrazine antibodies from the sera was done with a hapten-specific column using an amino-terminal crosslinked agarose gel. Efficacy in terms of total amount of recovery and binding affinities of eluted antibodies from the column were further investigated by ELISA. Results indicate that the ELISA-based elution approach is ideal for the selection of suitable elution buffer that can subsequently be utilized for affinity purification applications.     

The versions of the finite element method for problems with boundary layers

We study the uniform approximation of boundary layer functions for , , by the and versions of the finite element method. For the version (with fixed mesh), we prove super-exponential convergence in the range . We also establish, for this version, an overall convergence rate of in the energy norm error which is uniform in , and show that this rate is sharp (up to the term) when robust estimates uniform in are considered. For the version with variable mesh (i.e., the version), we show that exponential convergence, uniform in , is achieved by taking the first element at the boundary layer to be of size . Numerical experiments for a model elliptic singular perturbation problem show good agreement with our convergence estimates, even when few degrees of freedom are used and when is as small as, e.g., . They also illustrate the superiority of the approach over other methods, including a low-order version with optimal ``exponential" mesh refinement. The estimates established in this paper are also applicable in the context of corresponding spectral element methods.

     

A Pedestrian Approach to Ray Shooting: Shoot a Ray, Take a Walk

We propose a very simple ray-shooting algorithm, whose only data structure is a triangulation. The query algorithm, after locating the triangle containing the origin of the ray, walks along the ray, advancing from one triangle to a neighboring one until the polygon boundary is reached. The key result of the paper is a Steiner triangulation of a simple polygon with the property that a ray can intersect at most O(log n) triangles before reaching the polygon boundary. We are able to compute such a triangulation in linear sequential time, or in O(log n) parallel time using O(n/log n) processors. This gives a simple, yet optimal, ray-shooting algorithm for a simple polygon. Using a well-known technique, we can extend our triangulation procedure to a multiconnected polygon with k components and n vertices, so that a ray intersects at most O(√k log n) triangles.     

Influence of the preparation method on the morphology of templated NiCo<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel

The synthesis of NiCo₂O₄ spinel by several nanocasting strategies (i.e., multi-step nanocasting, one-step nanocasting and soft-templating), in which nickel and cobalt nitrates are used as precursors and Pluronic P123 as surfactant, is explored. First, in the multi-step nanocasting, the effect of the impregnation method (evaporation, solid–liquid and two-solvent) of the SBA-15 silica template on the morphology of NiCo₂O₄ replica is investigated. The evaporation method seems to be the best choice to obtain mesoporous NiCo₂O₄ powder which, after calcination at 375 °C and subsequent template removal, displays the highest surface area (93.1 m²/g). We have also checked the feasibility of the one-step nanoscating approach for the synthesis of ordered NiCo₂O₄ arrays, though this methodology entails severe difficulties, mainly related to the different decomposition temperature of the nitrate precursors and the P123 surfactant. Finally, randomly oriented, aggregated NiCo₂O₄ nanoparticles are obtained by means of P123 surfactant-assisted soft-templating approach.     

Dinuclear Cobalt Complexes with a Decadentate Ligand Scaffold: Hydrogen Evolution and Oxygen Reduction Catalysis

A new decadentate dinucleating ligand containing a pyridazine bridging group and pyridylic arms has been synthesized and characterized by analytical and spectroscopic techniques. Four new dinuclear cobalt complexes featuring this ligand have been prepared and thoroughly characterized both in the solid state (X‐ray diffraction) and in solution (1D and 2D NMR spectroscopy, ESI‐MS, and electrochemical techniques). The flexible but stable coordination environment provided by the ligand scaffold when coordinating Co in different oxidation states is shown to play a crucial role in the performance of the set of complexes when tested as catalysts for the photochemical hydrogen evolution reaction (HER) and chemical oxygen reduction reaction (ORR).