An Alternative Way to Generalize the Pentagon

We introduce the concept of a pentagonal geometry as a generalization of the pentagon and the Desargues configuration, in the same vein that the generalized polygons share the fundamental properties of ordinary polygons. In short, a pentagonal geometry is a regular partial linear space in which for all points x, the points not collinear with the point x, form a line. We compute bounds on their parameters, give some constructions, obtain some nonexistence results for seemingly feasible parameters and suggest a cryptographic application related to identifying codes of partial linear spaces.     

Hyperpolarization of Amino Acids in Water Utilizing Parahydrogen on a Rhodium Nanocatalyst

NMR offers many possibilities in chemical analysis, structural investigations, and medical diagnostics. Although it is broadly used, one of NMR spectroscopies main drawbacks is low sensitivity. Hyperpolarization techniques enhance NMR signals by more than four orders of magnitude allowing the design of new contrast agents. Parahydrogen induced polarization that utilizes the para-hydrogen's singlet state to create enhanced signals is of particular interest since it allows to produce molecular imaging agents within seconds. Herein, we present a strategy for signal enhancement of the carbonyl ¹³C in amino acids by using parahydrogen, as demonstrated for glycine and alanine. Importantly, the hyperpolarization step is carried out in water and chemically unmodified canonical amino acids are obtained. Our approach thus offers a high degree of biocompatibility, which is crucial for further application. The rapid sample hyperpolarization (within seconds) may enable the continuous production of biologically useful probes, such as metabolic contrast agents or probes for structural biology.     

A tale of hydrogen abstraction,initially detected via X‐ray diffraction

Reaction of a bis‐tetrazinyl pyridine pincer ligand, btzp, with a vanadium(III) reagent gives not a simple adduct but dichlorido{3‐methyl‐6‐[6‐(6‐methyl‐1,2,4,5‐tetrazin‐3‐yl‐κN²)pyridin‐2‐yl‐κN]‐1,4‐dihydro‐1,2,4,5‐tetrazin‐1‐yl‐κN¹}oxidovanadium(IV) acetonitrile 2.5‐solvate, [V(C₁₁H₁₀N₉)Cl₂O]·2.5CH₃CN, a species which X‐ray diffraction reveals to have one H atom added to one of the two tetrazinyl rings. This H atom was first revealed by a short intermolecular N...Cl contact in the unit cell and subsequently established, from difference maps, to be associated with a hydrogen bond. One chloride ligand has also been replaced by an oxide ligand in this synthetic reaction. This formula for the complex, [V(Hbtzp)Cl₂O], leaves open the question of both ligand oxidation state and spin state. A computational study of all isomeric locations of the H atom shows the similarity of their energies, which is subject to perturbation by intermolecular hydrogen bonding found in X‐ray work on the solid state. These density functional calculations reveal that the isomer with the H atom located as found in the solid state contains a neutral radical Hbtzp ligand and tetravalent d¹ V center, but that these two unpaired electrons are more stable as an open‐shell singlet and hence antiferromagnetically coupled.     

Radiometrische Bandwaage mit Rechnerschaltkreis zur Signalaufbereitung

Es wird eine radiometrische Bandwaage zur Koksaustragsmengen-Messung in BHT-Kokereien beschrieben. Voranstellend werden einige analytische Ausdrücke zur theoretischen Behandlung dieses Bandwaagentyps mitgeteilt. Die Waage zeichnet sich durch hohe Stabilität der Anzeige, durch die Möglichkeit des routinemäßigen Umsetzens von Meßstelle zu Meßstelle innerhalb kurzer Zeit und durch einen relativ kleinen Wägefehler (Meßunsicherheit ≦ 2,9%) aus. Die Signalaufbereitung innerhalb der Elektronik erfolgt durchgängig digital unter Verwendung eines Rechnerschaltkreises.     

The Tucson-Melbourne three-nucleon force in the automatized partial-wave decomposition

A recently developed procedure for a partial-wave decomposition of a three-nucleon force is applied to the p \pi -p \pi , p \pi -r \rho and r \rho -r \rho components of the Tucson-Melbourne three-nucleon potential. The resulting matrix elements for the p \pi -p \pi and p \pi -r \rho components are compared with the values obtained using the standard approach to the partial-wave decomposition, in which the p \pi -r \rho expressions for the matrix elements are also derived and presented. Several numerical tests and results for the triton binding energy and the correlation function prove the reliability and efficiency of the new method.     

SURFACE MODIFICATION WITH HYDROGELS VIA MACROINITIATORS FOR ENHANCED FRICTION PROPERTIES OF BIOMATERIALS

ABSTRACT

A general method of surface modification is described which is based on dip-coating of a substrate with a macroinitiator and subsequent free radical polymerization of functional monomers. Using this method, it is possible to fix poly(acrylic acid) hydrogels on polymer surfaces, e.g. on catheters, which drastically reduces the friction of these materials. Similarly, other biological relevant properties, especially reduced protein or bacteria adsorption can be achieved by choosing appropriate monomers.

The substrate was first homogeneously dip-coated with e.g. the water-insoluble macroinitiator poly(octadecene-co-maleic anhydride), partially reacted to the tert.-butyl perester. Homogeneity, thickness, and reactivity of the macroinitiator layer was characterized in detail. After a temper step, surface homo- and copolymerizations of ionic monomers were carried out in water directly from the modified surface. The consistency of the hydrogel coating could be well controlled by the reaction conditions and the monomer composition. The correlation between the experimental parameters, the composition of the surface coating, and the friction properties was established. A relatively thick, slightly crosslinked poly(acrylic acid) hydrogel coating reduces the friction coefficient by 95% compared to that of uncoated surfaces.     

Ammonium Ion Complexes of Tetraethyl Resorcarene: An Ab Initio Study

The complexation of various ammonium ions with a resorcarene host was evaluated by ab initio calculations. The approximations of the binding locations and the interaction energies for each guest are reported. The supramolecular complex formation also affects the conformation of the resorcarene host.     

Systematic Study of the Interaction Between VIV Centres and LnIII Ions in Well Defined {V 2 IV LnIII}{AsIIIW9O33}2 Sandwich-Type Clusters: Part 2

The gadolinium (Gd) member of a new type of heteropolytungstates that contain one lanthanide and two transition metal ions in a triangular arrangement is reported. The compound NaK₆Gd_0.33 [((VO)₂Gd(H₂O)₄K₂(H₂O)₂(Na)(H₂O)₂)(α-B-AsW₉O₃₃)₂]·24H₂O (1) was prepared from acidified aqueous solutions of Na₂WO₄·2H₂O, As₂O₃ and VOSO₄·5H₂O to which Gd³⁺ ions were added. The single crystal X-ray structure analysis (monoclinic, space group P2₁/m) shows that the anion consists of two [α-B-As^IIIW₉O₃₃]^9? trilacunary Keggin-type units linked by two VO²⁺, one Gd³⁺ as well as weakly by two K⁺ and one Na⁺ ions, resulting in a sandwich-type structure with idealized C _2v symmetry. The problem of positioning crystal lattice and special polyoxometalate sites with different cations is discussed also in connection with supramolecular chemistry aspects and as an option for further research. A fit of the magnetic susceptibility yielded exchange coupling constants of J _VV = ?2.55 cm^?1 (anti-ferromagnetic) between the vanadium ions and J _GdV = 0.6 cm^?1 (ferromagnetic) between the Gd and each of the two vanadium ions. The complete magnetochemical analysis also revealed a partial occupancy of the Na⁺ sites in the counter-cation–water system by Gd³⁺ ions (0.33 Gd³⁺ ions in total).