TY - JOUR A1 - Kreye, Oliver A1 - Toth, Tommy A1 - Meier, Michael A. R. T1 - Introducing multicomponent reactions to polymer science passerini reactions of renewable monomers JF - Journal of the American Chemical Society N2 - Combination of the Passerini three component-reaction (3CR) and olefin metathesis led to the formation of poly[1-(alkyl carbamoyl)alkyl alkanoates], a new class of polyesters with amide moieties in their side chain, from renewable resources. Two different approaches were studied and compared to each other. First, monomers were synthesized by the Passerini-3CR and then polymerized via acyclic diene metathesis. Alternatively, bifunctional monomers were synthesized by self-metathesis and then polymerized by Passerini-3CR. Both approaches led to the formation of high-molecular-weight polymers. Moreover, Passerini-3CRs were shown to be a versatile grafting-onto method. The results clearly demonstrate that the Passerini-3CR offers an interesting new access to monomers and polymers and thus broadens the synthetic portfolio of polymer science. Y1 - 2011 U6 - https://doi.org/10.1021/ja1113003 SN - 0002-7863 VL - 133 IS - 6 SP - 1790 EP - 1792 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schmidt, Bernd A1 - Staude, Lucia A1 - Kelling, Alexandra A1 - Schilde, Uwe T1 - A Cross-Metathesis-Conjugate addition route to enantiopure gamma-Butyrolactams and gamma-Lactones from a C-2-Symmetric Precursor JF - European journal of organic chemistry N2 - A protected derivative of (3R, 4R)-hexa-1,5-diene-3,4-diol, a conveniently accessible C-2-symmetric building block, undergoes single or double cross metathesis with methyl acryl-ate. The cross metathesis products are amenable to stereoselective conjugate addition reactions and can be converted into either gamma-butyrolactones or gamma-lactams. KW - Lactams KW - Lactones KW - Oxygen heterocycles KW - Metathesis KW - Desymmetrization Y1 - 2011 U6 - https://doi.org/10.1002/ejoc.201001528 SN - 1434-193X IS - 9 SP - 1721 EP - 1727 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Yarman, Aysu A1 - Nagel, Thomas A1 - Gajovic-Eichelmann, Nenad A1 - Fischer, Anna A1 - Wollenberger, Ursula A1 - Scheller, Frieder W. T1 - Bioelectrocatalysis by Microperoxidase-11 in a Multilayer Architecture of Chitosan Embedded Gold Nanoparticles JF - Electroanalysis : an international journal devoted to fundamental and practical aspects of electroanalysis N2 - We report on the redox behaviour of the microperoxidase-11 (MP-11) which has been electrostatically immobilized in a matrix of chitosan-embedded gold nanoparticles on the surface of a glassy carbon electrode. MP-11 contains a covalently bound heme c as the redox active group that exchanges electrons with the electrode via the gold nanoparticles. Electroactive surface concentration of MP-11 at high scan rate is between 350+/-50 pmol cm(-2), which reflects a multilayer process. The formal potential (E degrees') of MP-11 in the gold nanoparticles-chitosan film was estimated to be -(267.7+/-2.9) mV at pH 7.0. The heterogeneous electron transfer rate constant (k(s)) starts at 1.21 s(-1) and levels off at 6.45 s(-1) in the scan rate range from 0.1 to 2.0 V s(-1). Oxidation and reduction of MP-11 by hydrogen peroxide and superoxide, respectively have been coupled to the direct electron transfer of MP-11. KW - Microperoxidase KW - Direct electron transfer KW - Nanoparticles KW - Hydrogen peroxide KW - Superoxide KW - Bioelectrocatalysis Y1 - 2011 U6 - https://doi.org/10.1002/elan.201000535 SN - 1040-0397 VL - 23 IS - 3 SP - 611 EP - 618 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Neuvonen, Kari A1 - Neuvonen, Helmi A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - NBO analysis of polar and steric effect using the axial-equatorial equilibrium of cyclohexyl acetates as a probe JF - Computational and theoretical chemistry N2 - The proportion of the axial conformer increases in the ax reversible arrow eq equilibrium of cyclohexyl acetates (RCOOC(6)H(11), R reversible arrow Me, Et, iPr, tBu, CH(2)Cl, CHCl(2), CO(3). CH(2)Br, CHBr(2), CBr(3)) with the increasing size of the acyloxy substitution. The nature of this unexpected steric substituent effect, which is opposite to general stereochemical concepts, was studied by means of ab kiln MO method, accompanied by NBO and isodesmic calculations. NBO parameters seem to be good descriptors for quantitative prediction of the experimental Delta G degrees value of the title conformational equilibrium. The origin and propagation of the substituent effect of the polar substitutions (CH(2)Cl, CHCl(2), CCl(3), CH(2)Br, CHBr(2), CBr(3)) differ, however, from those of the pure alkyl (Me, Et, iPr, tBu) substitutions. The Delta G degrees value of the polar derivatives depends on the qC8 charges, on the occupation of the sigma(center dot)(C1-07) orbital and on the hyperconjugative pi(center dot)(c=O) -> sigma(center dot)(C10-X) and sigma(center dot)(C10-X) -> pi(center dot)(c=O) interactions. The substituent sensitivity of these NBC parameters for the two conformers differ to the effect that the ax reversible arrow eq equilibrium is shifted to the left side with increasing electron withdrawing character of the acyloxy group. The Delta G degrees values of the alkyl derivatives are interpreted in terms of the calculated dipole moments. The destabilization in the non-polar medium (the experimental Delta G degrees values used were measured in CD(2)Cl(2)) due to the enhanced dipolar character is more prominent in the case of the equatorial alkyl conformers. As the consequence, the ax reversible arrow eq equilibrium is shifted to the left despite the increasing size of the R group when going from Me to tBu substitution. KW - Substituent effects KW - Ab initio MO computations KW - Conformational equilibria KW - Cyclohexyl esters KW - NBO analysis Y1 - 2011 U6 - https://doi.org/10.1016/j.comptc.2010.12.033 SN - 2210-271X VL - 964 IS - 1-3 SP - 234 EP - 242 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Mengibar, M. A1 - Ganan, M. A1 - Miralles, B. A1 - Carrascosa, A. V. A1 - Martinez-Rodriguez, Adolfo J. A1 - Peter, Martin G. A1 - Heras, A. T1 - Antibacterial activity of products of depolymerization of chitosans with lysozyme and chitosanase against Campylobacter jejuni JF - Carbohydrate polymers : an international journal devoted to scientific and technological aspects of industrially important polysaccharides N2 - Chitosan has several biological properties useful for the food industry, but the most attractive is its potential use as a food preservative of natural origin due to its antimicrobial activity against a wide range of food-borne microorganisms. Among food-borne pathogens, Campylobacter jejuni and related species are recognised as the most common causes of bacterial food-borne diarrhoeal disease throughout the world. Recently, it has been demonstrated that campylobacters are highly sensitive to chitosan. Even though chitosan is known to have important functional activities, poor solubility makes them difficult to use in food and biomedical applications. Unlike chitosan, the low viscosity and good solubility of chitosan oligosaccharides (COS) make them especially attractive in an important number of useful applications. In the present work, the effect of different COS on C. jejuni was investigated. Variables such as the physicochemical characteristics of chitosan and the enzyme used in COS preparation were studied. The COS had been fractioned using ultrafiltration membranes and each fraction was characterized regarding its FA and molecular weight distribution. It has been demonstrated that the biological properties of COS on Campylobacter depend on the composition of the fraction analysed. COS prepared by enzymatic hydrolysis with chitosanase were more active against Campylobacter that lysozyme-derived COS, and this behaviour seems to be related with the acetylation of the chains. On the other hand. the 10-30 kDa fraction was the most active COS fraction, independently of the enzyme used for the hydrolysis. These results have shown that COS could be useful as antimicrobial in the control of C. jejuni. KW - Campylobacter jejuni KW - Chitooligosaccharides KW - Chitosanase KW - Lysozyme KW - Depolymerization Y1 - 2011 U6 - https://doi.org/10.1016/j.carbpol.2010.04.042 SN - 0144-8617 VL - 84 IS - 2 SP - 844 EP - 848 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Vijayakrishnan, Balakumar A1 - Issaree, Arisara A1 - Corilo, Yuri E. A1 - Ferreira, Christina Ramires A1 - Eberlin, Marcos N. A1 - Peter, Martin G. T1 - MSn of the six isomers of (GlcN)(2)(GlcNAc)(2) aminoglucan tetrasaccharides (diacetylchitotetraoses) rules of fragmentation for the sodiated molecules and application to sequence analysis of hetero-chitooligosaccharides JF - Carbohydrate polymers : an international journal devoted to scientific and technological aspects of industrially important polysaccharides N2 - The six possible isomers of di-N-acetylchitotetraoses [AADD, ADDA, ADAD, DADA, DAAD, and DDAA, where D stands for 2-amino-2-deoxy-3-D-glucose (GlcN) and A for 2-acetamido-2-deoxy-beta-D-glucose (GlcNAc)] were analyzed by ESI(+)-MSn. Collision induced dissociation via MSn experiments were performed for the sodiated molecules of m/z 769 [M+Na](+) for each isomer, and fragments were generated mainly by glycosidic bond and cross-ring cleavages. Rules of fragmentation were then established. A reducing end D residue yields the (O.2)A(4) cross-ring [M-59+Na](+) fragment of m/z 710 as the most abundant, whereas isomers containing a reducing end A prefer to lose water to form the [M-18+Na](+) ion of m/z 751, as well as abundant (O.2)A(4) cross-ring [M-101+Na](+) fragments of m/z 668 and B-3 [M-221+Na](+) ions of m/z 548. MS3 of C- and Y-type ions shows analogous fragmentation behaviour that allows identification of the reducing end next-neighbour residue. Due to gas-phase anchimeric assistance, B-type cleavage between the glycosidic oxygen and the anomeric carbon atom is favoured when the glycon is an A residue. Relative ion abundances are generally in the order B >> C > Y, but may vary depending on the next neighbour towards the non-reducing end. These fragmentation rules were used for partial sequence analysis of hetero-chitooligosaccharides of the composition D(2)A(3), D(3)A(3), D(2)A(4), D(4)A(3), and D(3)A(4). KW - Chitosan KW - Fragmentation KW - Oligosaccharides KW - Sequence analysis KW - Tandem mass spectrometry Y1 - 2011 U6 - https://doi.org/10.1016/j.carbpol.2010.04.041 SN - 0144-8617 VL - 84 IS - 2 SP - 713 EP - 726 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Wirth, Jonas A1 - Monturet, Serge A1 - Klamroth, Tillmann A1 - Saalfrank, Peter T1 - Adsorption and (photo-) electrochemical splitting of water on rutile ruthenium dioxide JF - epl : a letters journal exploring the frontiers of physics N2 - In this work, the adsorption and splitting of the water molecule by light and/or an external potential is investigated in the frame of (photo-) electrochemical cells using a rutile ruthenium dioxide anode. With the help of periodic density functional calculations, the adsorbed structures of H(2)O and some radicals involved in the splitting process (O, OH, OOH) are obtained and compared with the available experimental results. On the basis of these electronic-structure calculations, we use a method to calculate the stability of the reaction intermediates and conclude on the thermodynamical possibility of the water splitting reaction at the surface. We demonstrate that a moderate overpotential of 0.64 V is required for the reaction to take place at the RuO(2)(110) surface. Y1 - 2011 U6 - https://doi.org/10.1209/0295-5075/93/68001 SN - 0295-5075 VL - 93 IS - 6 PB - EDP Sciences CY - Mulhouse ER - TY - JOUR A1 - Neumann, Mike A1 - Noeske, Robert A1 - Bach, Grete A1 - Glaubauf, Thomas A1 - Bartoszek, Michael A1 - Strauch, Peter T1 - A procedure for rapid determination of the silicon content in plant materials JF - Zeitschrift für Naturforschung : B, Chemical sciences N2 - An efficient, reliable and low-cost procedure to determine the silicon content in plant material is presented which allows to monitor the agricultural aspects like growth and yield. The presented procedure consists of a hydrochloric acid pre-treatment and a subsequent thermal oxidation. The method is compared to other processes like dissolution in hydrofluoric acid combined with ICP OES, energy-dispersive X-ray fluorescence spectroscopy (EDXRF) or aqua regia treatment. KW - Silica Determination KW - Silicon Content KW - Plant Material Y1 - 2011 SN - 0932-0776 VL - 66 IS - 3 SP - 289 EP - 294 PB - De Gruyter CY - Tübingen ER - TY - JOUR A1 - Wessig, Pablo A1 - Matthes, Annika T1 - Preparation of Strained Axially Chiral (1,5)Naphthalenophanes by Photo-dehydro-Diels-Alder Reaction JF - Journal of the American Chemical Society N2 - The preparation of 10 (1,5)naphthalenophanes (10a-j) by photo-dehydro-Diels-Alder (PDDA) reaction is described. Owing to hindered rotation around the biaryl axis, compounds 10 are axially chiral and the separation of enantiomers by chiral HPLC was demonstrated in three cases (10a,b,e). The absolute configuration of the isolated enantiomers could be unambiguously determined by comparison of calculated and measured circular dichroism (CD) spectra. Furthermore, we analyzed ring strain phenomena of (1,5)naphthalenophanes 10. Depending on the length of the linker units, one can distinguish three classes of naphthalenophanes. Compounds 10a-c are highly strained (E-STR = 7-31 kcal/mol), and the strain is caused by small bond angles in the linker unit and deformation of the naphthalene moiety. Another type of strain is observed if the linker unit becomes relatively long (10g,h) originating from transannular interactions and is comparable with the well-known strain of medium sized rings. The naphthalenophanes 10d-f with a linker length of 10-14 atoms are only marginally strained. To clearly discriminate the different sources of strain, we defined two geometrical parameters (average central dihedral angle delta(C) and naphthalene thickness D-N) and demonstrated that they are well-suited to indicate naphthalene deformation of our naphthalenophanes 10 as well as of ten model naphthalenophanes (I-X) with different linker lengths and linking positions. Y1 - 2011 U6 - https://doi.org/10.1021/ja109118m SN - 0002-7863 VL - 133 IS - 8 SP - 2642 EP - 2650 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Reznichenko, Alexander L. A1 - Emge, Thomas J. A1 - Audoersch, Stephan A1 - Klauber, Eric G. A1 - Hultzsch, Kai C. A1 - Schmidt, Bernd T1 - Group 5 metal binaphtholate complexes for catalytic asymmetric hydroaminoalkylation and hydroamination/cyclization JF - Organometallics N2 - 3,3'-Silylated binaphtholate tantalum and niobium complexes were shown to be efficient catalysts for the asymmetric hydroaminoalkylation of N-methylaniline derivatives and N-benzylmethylamine with simple alkenes in enantioselectivities of up to 80% ee. No hydroaminoalkylation was observed with aminoalkenes; rather, exclusive asymmetric hydroamination/cyclization took place in up to 81% ee. Y1 - 2011 U6 - https://doi.org/10.1021/om1011006 SN - 0276-7333 VL - 30 IS - 5 SP - 921 EP - 924 PB - American Chemical Society CY - Washington ER -