Department of Chemistry

The reaction of [Cu(PF 6 ) 2 (py) 4 ] (py = pyridine) with [Cu(CH 3 SO 3 ) 2 (py) 4 ], both of which are Werner-type Cu(II) complexes, in a MeOH solution led to the formation of a onedimensional framework composed of [-{Cu(1) 2 (MeO) 2 }-Cu(2)-Cu(3)-Cu(3)-Cu(2)-] repeating units bridged by inorganic CH 3 SO 3 anions.

We report on attempts towards the synthesis of titanium nanoparticles using a wet chemical approach in imidazolium-based ionic liquids (ILs) under reducing conditions. Transmission electron microscopy finds nanoparticles in all cases. UV/Vis spectroscopy confirms the nanoparticulate nature of the precipitate, as in all cases an absorption band between ca. 280 and 300 nm is visible. IR spectroscopy shows that even after extensive washing and drying, some IL remains adsorbed on the nanoparticles. Raman spectroscopy suggests the formation of anatase nanoparticles, but X-ray diffraction reveals that, possibly, amorphous titania forms or that the nanoparticles are so small that a clear structure assignment is not possible. The report thus shows that (possibly amorphous) titanium oxides even form under reducing conditions and that the chemical synthesis of titanium nanoparticles in ILs remains elusive.

Iron oxides are important minerals in biology and materials science. Using biomimetic synthesis, a variety of iron oxides have been fabricated. However, it is still not clear how growth modifiers like amino acids and peptides select different crystal phases of a complex material like iron oxide. The current paper shows that already with single amino acids, (incomplete) crystal phase selection is achieved in vitro. In particular, L-histidine, L-threonine, and L-cysteine favor the formation of unstable crystal phases like ferrihydrite or lepidocrocite, although sometimes only at high amino acid concentrations. Other amino acids like L-valine have only minor effects when compared to control samples grown in the absence of amino acids. The effects of the amino acids can be rationalized via kinetic trapping and different interaction strengths of the amino acids with the growing iron oxide particles. The effects of the amino acids on the particle morphologies are less significant. The paper therefore shows that single amino acids can be a valuable tool for the materials chemist to fabricate and stabilize even unstable iron oxide crystal phases.

A 3-D metal-organic coordination polymer based on pyrazine-2,3-dicarboxylic acid (pzdcH₂) formulated as {[Mn(pzdc)(H₂O)₂] · 2H₂O} n ( 1 ), was obtained by the treatment of MnCl₂ · 6H₂O with pzdcH₂, 8-hydroxy quinoline (8-HQ), and 2-amino-4-methyl pyridine (ampy). In this study, we describe the synthesis, elemental analysis, IR spectroscopy, TG analysis, and single X-ray diffraction. The X-ray single crystal structure reveals that the chemical environment around each Mn(II) is a distorted octahedral by participating one nitrogen, five oxygens from three (pzdc)²⁻ and two water molecules, O₅MnN. The centrosymmetric 1-D ladder-like structure of 1 is bridged by oxygens of (pzdc)²⁻, and Mn-pzdc-Mn bonds are the rungs for our ladder structure. In the crystal structure, intermolecular O-H ··· O hydrogen bonds result in the formation of a supramolecular structure, effective for the stabilization of the structure. The thermal decomposition of 1 indicates that it is quite thermally stable. The...

C(3)-H(2) 0.9300 C(4)-C(5) 1.399(5) C(4)-H(3) 0.9300 C(15)-C(16) 1.357(8) C(15)-H(11) 0.9300 C(16)-C(17) 1.366(8) C(16)-H(12) 0.9300 C(17)-C(18) 1.376(5) C(17)-H(13) 0.9300 C(18)-H(14) 0.9300 C(19)-C(20) 1.389(5) C(19)-C(24) 1.396(5) C(20)-C(21) 1.378(5) C(20)-H(15) 0.9300 C(21)-C(22) 1.383(5) C(21)-H(16) 0.9300 C(22)-C(23) 1.365(5) C(22)-H(17) 0.9300 C(23)-C(24) 1.363(5) C(23)-H(18) 0.9300 C(24)-H(19) 0.9300 C(25)-C(26) 1.455(9) C(25)-H(21) 0.9700 C(25)-H(20) 0.9700 C(26)-C(27) 1.317(8) C(26)-H(22) 0.9700 C(26)-H(23) 0.9700 C(27)-C(28) 1.445(7) C(27)-H(25) 0.9700 C(27)-H(24) 0.9700 C(28)-H(26) 0.9700 C(28)-H(27) 0.9700 C(29)-C(30) 1.519(7) C(29)-H(28) 0.9700 C(29)-H(29) 0.9700 C(30)-C(31) 1.347(7) C(30)-H(31) 0.9700 C(30)-H(30) 0.9700 C(31)-C(32) 1.402(7) C(31)-H(32) 0.9700 C(31)-H(33) 0.9700 C(32)-H(34) 0.9700 ______________________________________________________ Symmetry transformations used to generate equivalent atoms: #1-x+1,-y-1,-z C(32)-H(35) 0.9700 C(33)-C(34) 1.423(6) C(33)-H(36) 0.9700 C(33)-H(37) 0.9700 C(34)-C(35) 1.394(7) C(34)-H(38) 0.9700 C(34)-H(39) 0.9700 C(35)-C(36) 1.501(7) C(35)-H(41) 0.9700 C(35)-H(40) 0.9700 C(36)-H(42) 0.9700 C(36)-H(43) 0.9700 C(37)-C(38) 1.459(6) C(37)-H(45) 0.9700 C(37)-H(44) 0.9700 C(38)-C(39) 1.371(7) C(38)-H(46) 0.9700 C(38)-H(47) 0.9700 C(39)-C(40) 1.477(7) C(39)-H(49) 0.9700 C(39)-H(48) 0.9700 C(40)-H(51) 0.9700 C(40)-H(50) 0.9700 Li(2)-Li(3) 3.310(8) Li(3)-Cl(1)#1 2.308(5) Li(3)-Li(3)#1 2.918(10) C(21)-C(22) 1.370(12) C(21)-H(21) 0.9300 C(22)-C(23) 1.378(12) C(22)-H(22) 0.9300 C(23)-C(24) 1.374(10) C(23)-H(23) 0.9300 C(24)-H(24) 0.9300 C(25)-C(26) 1.362(11) C(25)-O(5) 1.390(8) C(25)-C(30) 1.398(11) C(26)-C(27) 1.386(12) C(26)-H(26) 0.9300 C(27)-C(28) 1.389(17) C(27)-H(27) 0.9300 C(28)-C(29) 1.334(17) C(28)-H(28) 0.9300 C(29)-C(30) 1.386(13) C(29)-H(29) 0.9300 C(30)-H(30) 0.9300 C(31)-C(36) 1.366(11) C(31)-C(32) 1.390(11) C(31)-O(6) 1.390(9) C(32)-C(33) 1.398(14) C(32)-H(32) 0.9300 C(33)-C(34) 1.377(17) C(33)-H(33) 0.9300 C(34)-C(35) 1.330(17) C(34)-H(34) 0.9300 C(35)-C(36) 1.377(13) C(35)-H(35) 0.9300 C(36)-H(36) 0.9300 C(37)-O(7) 1.350(8) C(37)-C(42) 1.363(10) C(37)-C(38) 1.406(10) C(38)-C(39) 1.408(12) C(38)-H(38) 0.9300 C(39)-C(40) 1.358(13) C(39)-H(39) 0.9300 C(40)-C(41) 1.373(13) C(40)-H(40) 0.9300 C(41)-C(42) 1.387(11) C(41)-H(41) 0.9300 C(42)-H(42) 0.9300 C(43)-O(8) 1.366(6) C(43)-C(44) 1.3900 C(43)-C(48) 1.3900 C(44)-C(45) 1.3900 C(44)-H(44) 0.9300 C(45)-C(46) 1.3900 C(45)-H(45) 0.9300 C(46)-C(47) 1.3900 C(46)-H(46) 0.9300 C(47)-C(48) 1.3900 C(47)-H(47) 0.9300 C(48)-H(48) 0.9300 C(49)-O(9) 1.371(8) C(49)-C(50) 1.394(10) C(49)-C(54) 1.406(10) C(119)-H(11S) 0.9700 C(119)-H(11T) 0.9700 C(120)-C(121) 1.509(14) C(120)-H(12A) 0.9700 C(120)-H(12B) 0.9700 C(121)-C(122) 1.496(12) C(121)-H(12C) 0.9700 C(121)-H(12D) 0.9700 C(122)-O(23) 1.449(10) C(122)-H(12E) 0.9700 C(122)-H(12F) 0.9700 C(123)-O(24) 1.414(12) C(123)-C(124) 1.422(18) C(123)-H(12G) 0.9700 C(123)-H(12H) 0.9700 C(124)-C(125) 1.435(18) C(124)-H(12I) 0.9700 C(124)-H(12J) 0.9700 C(125)-C(126) 1.487(15) C(125)-H(12K) 0.9700 C(125)-H(12L) 0.9700 C(126)-O(24) 1.399(13) C(126)-H(12M) 0.9700 C(126)-H(12N) 0.9700 O(1)-Fe(1) 1.908(5) O(1)-Li(1) 1.916(15) O(2)-Li(2) 1.945(15) O(2)-Li(1) 2.025(14) O(2)-Fe(1) 2.059(5) O(3)-Fe(1) 1.891(5) O(3)-Li(2) 1.934(15) O(4)-Li(3) 1.901(13) O(4)-Fe(1) 1.917(5) C(42)-H(42A) 0.9700 C(42)-H(42B) 0.9700 C(41)-H(41A) 0.9700 C(41)-H(41B) 0.9700 C(44)-H(44A) 0.9700 C(44)-H(44B) 0.9700 C(38)-C(39) 1.303(16) C(38)-C(37) 1.420(15) C(38)-H(38A) 0.9700 C(38)-H(38B) 0.9700 C(37)-H(37A) 0.9700 C(37)-H(37B) 0.9700 C(39)-C(40) 1.520(14) C(39)-H(39A) 0.9700 C(39)-H(39B) 0.9700 C(40)-H(40A) 0.9700 C(40)-H(40B) 0.9700

Elektronentransfer (ET) durch Proteine über lange Distanzen ist ein fundamentaler Prozess in biologischen Systemen, der sowohl bei der Umwandlung von Energie in der Photosynthese [1a] und der Atmung [1b] als auch bei metabolischen Prozessen eine große Rolle spielt. [1c] Der Mechanismus dieser ET-Prozesse wird nach wie vor kontrovers diskutiert, wobei zwei Möglichkeiten in Betracht gezogen werden. Zum einen der Superaustausch-Mechanismus (Einstufenreaktion) und zum anderen der Hüpf-Mechanismus (Mehrstufenreaktion), [2] bei dem jeder Schritt der Marcus-Regel [3] folgt. Dieser Hüpf-Mechanismus wird heute für ET über lange Distanzen als wahrscheinlicher angesehen. [4] Allerdings wurde ET durch a-helikale Peptide, die über intramolekulare H-Brücken verfügen, nach wie vor als Einstufenreaktion diskutiert. [5] Rechnungen favorisieren hingegen auch für a-Helices eine Mehrstufenreaktion. [6] Im Falle der Polyprolin-II(PPII)-Helix, die keine H-Brücken aufweist, wurde ein Wechsel von einer ein-zu einer mehrstufigen Reaktion beobachtet, sobald die Anzahl der Prolineinheiten zwischen dem Elektronendonor und dem Elektronenakzeptor größer als vier war. [7] Quantenchemische Rechnungen erklären den Einfluss der Peptidkonformation auf die Distanzabhängigkeit mit einem Tunnel-Pfad-Modell. [8] Vor kurzem konnte gezeigt werden, dass die Geschwindigkeit auch von der Richtung des ET-Prozesses abhängt und somit das Dipolmoment einen entscheidenden Einfluss hat. [9] Ein weiterer Parameter, der den ET beeinflusst, sind Ionen, die als Cofaktoren an die Systeme gebunden sind. [10] Ein analoger Coulomb-Effekt sollte auch in Peptiden mit entschützten Amino-oder Carboxylatgruppen eine Rolle spielen, die unter biologischen Bedingungen als Ionen vorliegen. Hier präsentieren wir unsere neuen Ergebnisse, die zeigen, dass ET in Peptiden tatsächlich von geladenen Endgruppen beeinflusst wird. Die Untersuchungen wurden mit dem kürzlich von uns entwickelten Modellpeptid 1 durchgeführt, in dem der ET zwischen dem Radikalkation einer Dialkoxyphenylgruppe (Elektronenakzeptor am C-terminalen Ende) und Tyrosin als Elektronendonor am N-terminalen Ende stattfindet. In der Mitte des Peptids befindet sich eine Aminosäure mit der Seitenkette X. [11] Diese drei Aminosäuren werden durch Sequenzen von je drei Prolinen voneinander getrennt (Schema 1). Wenn die Seitenkette der Aminosäure X durch den Elektronenakzeptor oxidiert werden kann, fungiert diese zentrale Aminosäure als Zwischenstation (Relais) des Hüpf-Prozesses. [11]

Pairs of reducible pentakis(thiophenyl)benzene subunits are linked by different molecular structures as model compounds for reducible molecular-wire-type synthons showing varying electron-transfer ability as a function of the bridging structures, consisting of either para-divinylbenzene, bis-hydrazone, or diacetylene. Their electron-transfer ability from one reducible subunit to the other was investigated by electrochemical and spectroelectrochemical methods. In the case of the bis-hydrazone bridge and the diacetylene bridge, the solid-state structures support the experimental findings. While the para-divinylbenzene bridge completely isolates the reducible subunits (class I system) the diacetylene bridge electronically connects the two reducible structures (class III system), demonstrating its potential application as a "molecular wire." The bis-hydrazone linked dimer displays electronic communication only to a small extend, which was only observed in the spectroelectrochemical investigation. The diacetylene connection as active electron-transfer linker together with poly(thiophenyl)benzene as reducible subunits was used to design more complex molecular architectures. Linear rodlike struktures did allow adjustment of the length of these type of molecular wires and investigation of the extent of electron mobility. Cyclic structures addressed the possibility of moving electrons on a bent molecular wire.