Stretched Polymers in a Poor Solvent

Stretched polymers with attractive interaction are studied in two and three dimensions. They are described by biased self-avoiding random walks with nearest neighbour attraction. The bias corresponds to opposite forces applied to the first and last monomers. We show that both in $d=2$ and $d=3$ a phase transition occurs as this force is increased beyond a critical value, where the polymer changes from a collapsed globule to a stretched configuration. This transition is second order in $d=2$ and first order in $d=3$. For $d=2$ we predict the transition point quantitatively from properties of the unstretched polymer. This is not possible in $d=3$, but even there we can estimate the transition point precisely, and we can study the scaling at temperatures slightly below the collapse temperature of the unstretched polymer. We find very large finite size corrections which would make very difficult the estimate of the transition point from straightforward simulations.Comment: 10 pages, 16 figure

Reversible magnetic mercury extraction from water

A facile and efficient way to decontaminate mercury(II) polluted water with the aid of magnetic, highly stable and recyclable carbon coated cobalt (Co/C) nanoparticles is reported. Comparing non-functionalised Co/C nanomagnets with particles that were functionalised with amino moieties, the latter one proved to be more effective for scavenging mercury with respect to extraction capacity and recyclability. A novel nanoparticle–poly(ethyleneimine) hybrid (Co/C–PEI) prepared by direct ring opening polymerization of aziridine initiated by an amine functionalised nanoparticle surface led to a high capacity material (10 mmol amino groups per g nanomaterial) and thus proved to be the best material for scavenging toxic mercury at relevant concentrations (mg L−1/μg L−1) for at least 6 consecutive cycles. On a large-scale, 20 L of drinking water with an initial Hg2+ concentration of 30 μg L−1 can be decontaminated to the level acceptable for drinking water (≤2 μg L−1) with just 60 mg of Co/C–PEI particles

Phosphabutatriene, Alpha-omega-Diphosphabutatriene Synthese, Struktur und Reaktivität

SIGLEAvailable from TIB Hannover: DW 3208 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Synthesis of a polyisobutylene-tagged fac-Ir(ppy)3 complex and its application as recyclable visible-light photocatalyst in a continuous flow process

The facile synthesis and application of a polyisobutylene-polymer-tagged, iridium(III) photocatalyst is described. The catalytic performance of this complex remains consistently high, while the installed tether allows for its convenient separation from reaction products through a thermomorphic solvent system. Excellent recycling properties were observed both in batch and in flow reactions, and especially in the latter the continuous, automatic recovery and reuse of the catalyst either from a mono-or a biphasic reaction solution is realised, making this approach attractive for large-scale applications

Bromo- or Methoxy-Group-Promoted Umpolung Electron Transfer Enabled, Visible-Light-Mediated Synthesis of 2-Substituted Indole-3-glyoxylates

A visible-light-mediated radical tandem cyclization of ortho-isocyano-alpha-bromo cinnamates to 2-substituted indole-3-glyoxylates is achieved by formation of both C-C/C-S and C-O bonds. The reaction proceeds through a hitherto unprecedented bromine- or methoxy-group-promoted umpolung back electron transfer from an a-carbonyl radical to the photocatalyst. This method allows preparation of diverse 2-arylated or 2-thioarylated indole-3-glyoxylates. The glyoxylate group installed in the products can be utilized for several biologically relevant manipulations

Flow chemistry in undergraduate organic chemistry education

On the basis of already existing (batch-mode) experiments, novel experiments in flow reactors have been developed that are continuous (flow-mode), as analogous to many industrial processes. The new flow-mode experiments have been implemented as experiments in laboratory classes by designing new experimental protocols and incorporating them into existing courses. The flow-type reactions can be controlled easily and students can rapidly apply various reaction conditions and directly monitor the effect on the outcome of the reaction using either off-line or on-line analysis, which is not possible using current (batch-mode) equipment. This gives students a novel type of control over their experiments as they are “space-resolved”. The experiments using flow reactor technology consume much less solvents and chemicals. Students recognize the large impact on sustainability when performing reactions in flow reactors

Visible light photoredox-catalyzed deoxygenation of alcohols

Carbon–oxygen single bonds are ubiquitous in natural products whereas efficient methods for their reductive defunctionalization are rare. In this work an environmentally benign protocol for the activation of carbon–oxygen single bonds of alcohols towards a reductive bond cleavage under visible light photocatalysis was developed. Alcohols were activated as 3,5-bis(trifluoromethyl)-substituted benzoates and irradiation with blue light in the presence of [Ir(ppy)2(dtb-bpy)](PF6) as visible light photocatalyst and Hünig’s base as sacrificial electron donor in an acetonitrile/water mixture generally gave good to excellent yields of the desired defunctionalized compounds. Functional group tolerance is high but the protocol developed is limited to benzylic, α-carbonyl, and α-cyanoalcohols; with other alcohols a slow partial C–F bond reduction in the 3,5-bis(trifluoromethyl)benzoate moiety occurs

Configurational and conformational isomeric antiaromatic [28]tetraoxaporphyrinoids(4.2.4.2) and aromatic [26]tetraoxaporphyrin(4.2.4.2) dications. A new type of molecular dynamics in macrocyclic systems

The [28]tetraoxaporphyrinoids(4.2.4.2) I are synthesized by cyclizing Wittig reaction. An alternative path is the McMurry condensation. Four different configurational isomers of I were isolated and characterized by 1H NMR. The inner and outer protons of the (E,E)-dienediyl bridges in (Z,EE,Z,EE)-I exchange by rotation around the adjacent single bonds. In (Z,EE,E,EE)-I, the (E)-ethenediyl bridge is rotationally active, while in (E,ZE,E,EZ)- and (E,EZ,E,EZ)-I, rotation of both (E)-ethenediyl bridges is obsd. When the rotation of the active (E)-double bonds at temps. T <-90° is frozen, all configurational isomers of I appear to be antiarom. and paratropic. The oxidn. of (E,ZE,E,EZ)- and (E,EZ,E,EZ)-I with DDQ yields 2 arom., diatropic [26]tetraoxaporphyrin(4.2.4.2) dications both with (E,EZ,E,EZ)-configuration but different fixed conformations. (Z,EE,Z,EE)-I is oxidized to give the (Z,EE,Z,EE)-dication, while the oxidn. of (Z,EE,E,EE)-I yields a mixt. of isomer dications. The std. formation enthalpies of the obtained and expected [28]tetraoxaporphyrinoids I and [26]tetraoxaporphyrin dications were calcd. with the AM1 method, showing good accordance with exptl. results