Butyllithium Polymerization of Butadiene. II. Effects of Solvent and Temperature on Association of Polybutatadienyl Lithium

Abstract

In the butyllithium polymerization of butadiene in aliphatic solvents at 25°C, the first few monomer units are incorporated largely in a 1, 2 manner. With increasing degree of polymerization the extent of 1, 2 addition decreases to a limiting value of about 10% at a degree of polymerization of about 50. However, within this region of high 1, 2-addition increasing solvent basicity, i.e., changing from aliphatic to aromatic solvents, markedly reduces extent of 1, 2 addition and also narrows the molecular weight distribution. Further, in aliphatic solvents, increasing polymerization temperature from 25 to 60°C also results in a marked reduction in 1, 2 addition. These results are consistent with the concept that an ion pair of the associated organolithium complex, [R (_n-1 Li_n] ⊕R?, is the active polymerization species and that changes in mode of monomer incorporation are due to changes in the degree of association of the entire organolithium system.     

Wahl von Radionukliden und deren Aktivität für hydrologische Untersuchungen

Die mit Hilfe von radioaktiven Wässern durchgeführten hydrogeologischen und hydrotechnischen Untersuchungen waren hinsichtlich der richtigen Wahl geeigneter Radionuklide und noch mehr bezüglich der Festlegung der notwendigen Aktivität mit gewissen Schwierigkeiten verbunden.

Dieser Bericht umfaβt praktisch alle bisher in Polen unternommenen Versuche, ein definiertes Modell für solche vorversuche aufzustellen, damit man auf eine lergleichbare Il'eise die Faktoren fiir die verschiedenen liadionuklide unler ungleichen physiko- chemischen und hydraulischen Bedingungen festlegen kann. Die mit diesem Modell an Wassersäulen von verschiedener Dimension durchgeführten Versuche haben zu einer experimenlellen Gleichung geführt, die in einer einfachen Form die Abhäingigkeit der Konzentralions¯nderung eines radioaktiven Tracers mit dem Verlauf seiner Strömung darstellt. Der einzige in dieser Gleichung auftretende Koeffizient genügt, um die Gesamtcharakteristik der Dispersionsfaktoren, die von der Art der Nuklide, des Strömungscharakters und der physiko-chemischen Eigenschajten des Grund- und Wassermediums abluingig sind. zu kennzeichnen.     

Highly efficient broadband double-sided Fresnel lens for THz range

Modern passive THz setups require effective optical elements with a large numerical aperture. Here we propose a new type of the optical element for THz applications, which is a broadband double-sided Fresnel-like lens with an optimized thickness. The optimization is performed to obtain a very low attenuation, low material cost, and small weight in the element media. It also provides achromatic properties for the assumed wavelength range. The experimental evaluation of the proposed diffractive lens by means of time-domain spectroscopy is presented and discussed.     

Compendium on the Principle of the Minimum of the Dissipation Potential for Non-Isothermal Processes

In this paper we present a compendium of the original paper “The Principle of the Minimum of the Dissipation Potential for Non-Isothermal Processes”, published in Continuum Mechanics and Thermodynamics [1]. There, a contribution to the methodology of material modeling was introduced by presenting a potential-based approach for non-isothermal processes. It was based on the principle of the minimum of the dissipation potential which was used previously only for isothermal material models. In contrast to the principle of maximum dissipation, the presented procedure resulted in mathematically simplified equations. Due to its potential character, the inclusion of constraints was very simple. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Two phosphonodehydrotripeptides: Boc0–Gly1–Δ(Z)Phe2–α‐Abu3PO3Me2 and Boc0–Gly1–Δ(Z)Phe2–α‐Nva3PO3Et2

The present paper reports the crystal structures of two short phosphonotripeptides (one in two crystal forms) containing one ΔPhe (dehydrophenylalanine) residue, namely dimethyl (3‐{[tert‐butoxycarbonylglycyl‐α,β‐(Z)‐dehydrophenylalanyl]amino}propyl)phosphonate, Boc⁰–Gly¹–Δ(Z)Phe²–α‐Abu³PO₃Me₂, C₂₁H₃₂N₃O₇P, (I), and diethyl (4‐{[tert‐butoxycarbonylglycyl‐α,β‐(Z)‐dehydrophenylalanyl]amino}butyl)phosphonate, Boc⁰–Gly¹–Δ(Z)Phe²–α‐Nva³PO₃Et₂, as the propan‐2‐ol monosolvate 0.122‐hydrate, C₂₄H₃₈N₃O₇P·C₃H₈O·0.122H₂O, (II), and the ethanol monosolvate 0.076‐hydrate, C₂₄H₃₈N₃O₇P·C₂H₆O·0.076H₂O, (III). The crystals of (II) and (III) are isomorphous but differ in the type of solvent. The phosphono group is linked directly to the last C_α atom in the main chain for all three peptides. All the amino acids are trans linked in the main chains. The crystal structures exhibit no intramolecular hydrogen bonds and are stabilized by intermolecular hydrogen bonds only.     

Large breathing effect induced by water sorption in a remarkably stable nonporous cyanide-bridged coordination polymer

While metal–organic frameworks (MOFs) are at the forefront of cutting-edge porous materials, extraordinary sorption properties can also be observed in Prussian Blue Analogs (PBAs) and related materials comprising extremely short bridging ligands. Herein, we present a bimetallic nonporous cyanide-bridged coordination polymer (CP) {[Mn(imH)]₂[Mo(CN)₈]}_n (1Mn; imH = imidazole) that can efficiently and reversibly capture and release water molecules over tens of cycles without any fatigue despite being based on one of the shortest bridging ligands known – the cyanide. The sorption performance of {[Mn(imH)]₂[Mo(CN)₈]}_n matches or even outperforms MOFs that are typically selected for water harvesting applications with perfect sorption reversibility and very low desorption temperatures. Water sorption in 1Mn is possible due to the breathing effect (accompanied by a dramatic cyanide-framework transformation) occurring in three well-defined steps between four different crystal phases studied structurally by X-ray diffraction structural analysis. Moreover, the capture of H₂O by 1Mn switches the EPR signal intensity of the Mn^II centres, which has been demonstrated by in situ EPR measurements and enables monitoring of the hydration level of 1Mn by EPR. The sorption of water in 1Mn controls also its photomagnetic behavior at the cryogenic regime, thanks to the presence of the [Mo^IV(CN)₈]⁴⁻ photomagnetic chromophore in the structure. These observations demonstrate the extraordinary sorption potential of cyanide-bridged CPs and the possibility to merge it with the unique physical properties of this class of compounds arising from their bimetallic character (e.g. photomagnetism and long-range magnetic ordering).

A cyanide-bridged coordination polymer {[Mn(imH)]₂[Mo(CN)₈]}_n shows exceptional water sorption properties, very large breathing effect and outstanding stability – properties that are unique for this class of compounds – Prussian blue analogs.     

Master equation approach to vibrational energy transfer between two diatomic molecules

In this paper a semiclassical non-markovian master equation is derived. We begin by using the well-known tetradic form of the Liouville equation for a reduced density operator. By projecting the diagonal matrix elements of the operator, we obtain an infinite-order master equation. This equation is then applied in the lowest-order approximation to collinear collisions between the diatomic molecules: H₂H₂, N₂N₂ and Cl₂Cl₂. With an assumed form of the interaction potential for such a problem we have also derived an analytical expression for the V—V transition probabilities. They are then calculated over a wide range of velocities of the colliding molecules and compared with exact semiclassical ones. An excellent agreement of the results is found for small velocities (i.e. υ ≈ 10⁴ cm/s). For larger values of υ (≈ 10⁵ cm/s) the results obtained from the master equation approach agree with the exact ones only in the low-velocity range for light molecules and low oscillatory states.     

Simple physics-based analytical formulas for the potentials of mean force for the interaction of amino acid side chains in water. 2. Tests with simple spherical systems

Simple analytical functions consisting of electrostatic, polarization, Lennard-Jones or modified Lennard-Jones, and cavity terms are proposed to express the potentials of mean force analytically for spherical particles interacting in water. The cavity term was expressed either through the molecular-surface area of the solute or by using the Gaussian-overlap model of hydrophobic hydration developed in paper 1 of this series. The analytical expressions were fitted to the potentials of mean force of a methane homodimer, heterodimers composed of a methane molecule, and an ammonium cation or a chloride anion, respectively, and dimers consisting of two chloride anions, two ammonium cations, or a chloride ion and an ammonium cation. The potentials of mean force for these dimers were determined by umbrella-sampling molecular dynamics simulations with the AMBER 7.0 force field with TIP3P water either in our earlier work or in this work. For all systems, the analytical formulas fitted the potentials of mean force very well. However, using the molecular-surface area to express the cavity term provided a good fit only when the nonbonded interactions were expressed by an all-repulsive modified Lennard-Jones potential but also resulted in non-physical values of some of the parameters. Conversely, the use of our new Gaussian-overlap-based expression for the cavity term provided a good fit to the potentials of mean force (PMFs) with Lennard-Jones nonbonded potential, and the values of all parameters were physically reasonable.