High‐Throughput Screening in Olefin‐Polymerization Catalysis: From Serendipitous Discovery Towards Rational Understanding

High–throughput‐screening (HTS) tools and methods are used more and more, especially in industry, in the search for new, selective organometallic catalysts. In most cases, the approach is, in essence, empirical, and the strategy is to increase the number of experiments that can be run at a given place in a given time. Highly miniaturized, parallel reaction setups have been implemented for the rapid assessment of whether novel catalysts resulting from the structural amplification of a basic framework are “good” or “bad” with respect to the properties of interest, and, depending on the response, worthy of a subsequent, more‐careful evaluation. In this article, we demonstrate that it is possible to utilize these state‐of‐the‐art HTS platforms with a different strategy: the rapid generation of reliable kinetic data for mechanistic studies in view of a thorough understanding and rational catalyst design. Ziegler–Natta‐type catalytic olefin polymerization will be used throughout as an example.

     

<Emphasis Type="Italic">Q</Emphasis>-systems as Cluster Algebras II: Cartan Matrix of Finite Type and the Polynomial Property

We define the cluster algebra associated with the Q-system for the Kirillov–Reshetikhin characters of the quantum affine algebra \({U_q(\widehat{\mathfrak {g}})}\) for any simple Lie algebra \({\mathfrak {g}}\), generalizing the simply-laced case treated in (Kedem in Q-systems as cluster algebras. arXiv:0712.2695 [math.RT], 2007). We describe some special properties of this cluster algebra, and explain its relation to the deformed Q-systems which appeared on our proof of the combinatorial-KR conjecture. We prove that the polynomiality of the cluster variables in terms of the “initial cluster seeds”, including solutions of the Q-system, is a consequence of the Laurent phenomenon and the boundary conditions. We also define the cluster algebra associated with T-systems, or general systems which take the form of T-systems in the bipartite case. Such systems describe the recursion relations satisfied by the q-characters of Kirillov–Reshetikhin modules and also appear in the categorification picture in terms of preprojective algebras of Geiss, Leclerc and Schröer. We give a formulation of both Q-systems and generalized T-systems as cluster algebras with coefficients. This provides a proof of the polynomiality of solutions of all such “generalized T-systems” with appropriate boundary conditions.     

A pulsed EPR method to determine distances between paramagnetic centers with strong spectral anisotropy and radicals: The dead-time free RIDME sequence

Methods to determine distances between paramagnetic metal centers and radicals are scarce. This is unfortunate because paramagnetic metal centers are frequent in biological systems and so far have not been employed much as distance markers. Successful pulse sequences that directly target the dipolar interactions cannot be applied to paramagnetic metal centers with fast relaxation rates and large g-anisotropy, if no echos can be detected and the excitation bandwidth is not sufficient to cover a sufficiently large part of the spectrum. The RIDME method Kulik et al. (2002) [20] circumvents this problem by making use of the T₁-induced spin-flip of the transition-metal ion. Designed to measure distance between such a fast relaxing metal center and a radical, it suffers from a dead time problem. We show that this is severe because the anisotropy of the metal center broadens the dipolar curves, which therefore, only can be analyzed if the full curve is known. Here, we introduce five-pulse RIDME (5p-RIDME) that is intrinsically dead-time free. Proper functioning of the sequence is demonstrated on a nitroxide biradical. The distance between a low-spin Fe(III) center and a spin label in spin-labeled cytochrome f shows the complete dipolar trace of a transition-metal ion center and a spin label, yielding the distance expected from the structure.     

Generating CuII–Oxyl/CuIII–Oxo Species from CuI–α‐Ketocarboxylate Complexes and O2: In Silico Studies on Ligand Effects and C?H‐Activation Reactivity

Theoretically speaking : The mechanistic details associated with the generation and reaction of [CuO]⁺ species from Cu^I–α‐ketocarboxylate complexes, especially with respect to modifications of the ligand supporting the copper center, were investigated (see scheme). Theoretical models were used to characterize the electronic structures of different [CuO]⁺ species and their reactivity in C? H activation and O‐atom transfer reactions.

     

Novel copolyesters based on poly(alkylene dicarboxylate)s: 2. Thermal behavior and biodegradation of fully aliphatic random copolymers containing 1,4-cyclohexylene rings

Aliphatic poly(butylene 1,12-dodecanedioate) is an interesting biodegradable polyester characterized by high thermal stability and high crystallinity, but low melting temperature. In order to improve the performances of this polymer some novel fully aliphatic random copolyesters have been prepared starting from 1,4-butanediol and different molar ratio of 1,12-dodecanedioc acid and 1,4-cyclohexanedicarboxylic acid. The copolymers have a notable resistance to thermal degradation, thermal properties which vary as a function of the composition, and maintain the mechanical characteristics of the poly(alkylene dicarboxylate). In particular, the copolymer containing the 70 mol% of 1,4-cyclohexanedicarboxylate units improves the thermal properties of the poly(butylene 1,12-dodecanedioate) and presents a very high biodegradation rate, higher than those of the two parent homopolymers. This behavior has been correlated to the low level of crystallinity of the sample and to the composition of the amorphous phase. Therefore, these novel fully aliphatic copolymers represent an interesting new class of copolyesters which can balance good physical properties and high biodegradability.     

Analysis of pharmaceuticals in indirect potable reuse systems using solid-phase extraction and liquid chromatography–tandem mass spectrometry

A solid-phase extraction (SPE) LC–MS/MS method for 18 commercial drugs in secondary wastewater and product water from water recycling plants using microfiltration (MF) and reverse osmosis (RO) has been developed, optimised and validated. The method incorporates a range of multi-class pharmaceuticals including lipid lowering agents, analgesics, antipyretics, non-steroidal anti-inflammatory drugs, antidepressants, anticoagulants, tranquilizers, cytostatic agents, and antiepileptics. Method limits of quantitation (MLQs) in secondary wastewater ranged from 15 to 250 ng/L, while MLQs in post-RO water ranged from 1 to 25 ng/L. Results from analysis of secondary wastewater from Western Australia are presented, and represent the largest survey of non-antibiotic pharmaceuticals within Australia to date. Analysis of post-RO water from two MF/RO water recycling facilities also demonstrate that MF/RO treatment removes most pharmaceuticals to below the analytical limits of detection, and more importantly, up to seven orders of magnitude below health-based guideline values.     

Selective oxidation of ethanol to acetic acid in highly efficient polymer electrolyte membrane-direct ethanol fuel cells

The selective conversion of ethanol into potassium acetate with concomitant production of electrical energy has been achieved in both passive and active direct fuel cells containing platinum-free electrodes and an anion-exchange polymer membrane. The power densities supplied by the passive systems at r.t. can be as high as 55 mW cm^?2, while the active systems can deliver up to 170 mW cm^?2 at 80 °C. Such high values have never been reported for direct ethanol fuel cells with whatsoever electrocatalyst in either alkaline or acidic media.     

Schatten–von Neumann properties for Fourier integral operators with non-smooth symbols,I

We consider Fourier integral operators with symbols in modulation spaces and non-smooth phase functions whose second orders of derivatives belong to certain types of modulation space. We prove continuity and Schatten–von Neumann properties of such operators when acting on L ².