Resonance Raman studies of photochemical molecular devices for multielectron storage

Resonance Raman spectroscopy was utilized for the first time to characterize the nature of the ¹metal‐to‐ligand charge transfer (MLCT) state of a ruthenium complex containing the redoxactive tetraazatetrapyrido‐pentacene (tatpp) ligand. The presented results show that the long‐wavelength absorption is originating from transitions involving the terminal phenanthroline and the tatpp ligands. Copyright © 2008 John Wiley & Sons, Ltd.     

Investigation of substitution effects on novel Ru–dppz complexes by Raman spectroscopy in combination with DFT methods

We present a combined Raman–density functional theory (DFT) study of novel dipyridophenazine (dppz) derivatives and their Ru–bipyridine complexes. Our results show that the molecular architecture of dppz and its Ru complexes can be considered to consist of two independent moieties, the structural ground state properties of which can be tuned independently by means of side‐specific substitution. These results are expected to be of importance for the design of highly specific dppz‐based DNA sensors. Methodologically, the results presented in this paper highlight the power of a combined Raman–DFT approach to unravel the details of the structural properties of complex molecules. Copyright © 2009 John Wiley & Sons, Ltd.     

A new concept for the bioeffects-related analysis of xenoestrogens: Hyphenation of receptor assays with LC-MS

The wide variety of known and unknown endocrine disruptors demands highly efficient methods for detecting the relevant endocrine disrupting pollutants. Bioeffects-related analysis is expected to solve this problem, combining biomolecular recognition processes with chemical analysis, which therefore reduces costs of instrumental chemical analysis to relevant samples. The hyphenation of both steps provides information on potential bioeffects, structure and concentration of the substances of interest. In this work the hyphenation of an enzyme-linked receptor assay (ELRA) with liquid chromatography-tandem mass spectrometry (LC-MSMS) for the analysis of estrogens and xenoestrogens is proposed. Both test systems have been validated with standards and spiked real water samples. The ELRA achieved a detection limit of 0.1 μg/L for 17β-estradiol (without preconcentration). With the LC-MSMS method, steroids could be detected down to 1 ng/L (with preconcentration). Two concepts for a tighter hyphenation of biomolecular interaction and chemical analysis are discussed: the on-line coupling of receptor-affinity chromatography (RAC) to LC-MSMS and the direct measurement of receptor-ligand complexes by LC-MSMS. Received: 30 October 1998 / Revised: 18 December 1998 / Accepted: 26 December 1998     

Coordination of a closo‐Cluster at Rhodium and Iridium

Stanna‐closo‐dodecaborate [Bu₃MeN]₂[SnB₁₁H₁₁] reacts as a nucleophile with the rhodium and iridium electrophiles of type [Cp*M(bipy′)Cl][BF₄] under formation of a transition metal tin bond. The zwitterionic molecules [Cp*M(bipy′)(SnB₁₁H₁₁)] (with M = Rh, Ir) were characterized by NMR spectroscopy, elemental analyses and X‐ray crystal structure analyses. A high dipole moment of 25.67 D was calculated by DFT methods in the case of the rhodium derivative.     

NMR Solution Structure of Phospholamban

Phospholamban (PLN), an amphipathic intrinsic membrane protein of 52 amino acids, is the modulator of the Ca²⁺ pump of cardiac, slow‐twitch, and smooth‐muscle sarcoplasmic reticulum. In response to β‐adrenergic stimulation, it becomes phosphorylated at Ser¹⁶ and/or Thr¹⁷, and dissociates from the pump, which, in turn, achieves its full activity. Here we present the three‐dimensional structure of chemically synthesized, monomeric PLN in an organic solvent. Monomerization (PLN normally forms homopentamers) was obtained by replacing Cys⁴¹ with phenylalanine (Phe=F), a modification that did not affect biological activity. The structure was determined by high‐resolution NMR in CHCl₃/MeOH of the unphosphorylated state of [F⁴¹]PLN (C41F). Of the hydrophilic cytoplasmic parts IA (Met¹ to Pro²¹) and IB (Gln²² to Asn³⁰) and the membrane‐spanning hydrophobic domain II (Leu³¹ to Leu⁵²) of PLN, domain IA, which contains the two phosphorylation sites Ser¹⁶ and Thr¹⁷, and domain II have been suggested to be helical and connected through the less‐structured hinge‐region IB. In the structural study presented here, [F⁴¹]PLN is composed of two α‐helical regions connected by a β‐turn (type III). The residues of the β‐turn (type III) are Thr¹⁷, Ile¹⁸, Glu¹⁹, and Met²⁰, the first being one of the two phosphorylation sites (Ser¹⁶ and Thr¹⁷). The hinge region is located at the C‐terminal end of domain IA, and domain IB is part of a second helix. The two α‐helices comprising amino acids 4 – 16 and 21 – 49 are well‐defined (the root‐mean‐square deviations for the backbone atoms, calculated for a family of the structures, are 0.58 and 0.92 Å, resp.). Pro²¹ is at the beginning of the C‐terminal helix and in the trans conformation.     

Multiple Triplet Metal-Centered Jahn-Teller Isomers Determine Temperature-Dependent Luminescence Lifetimes in [Ru(bpy)3]2+

Understanding the factors that determine the luminescence lifetime of transition metal compounds is key for applications in photocatalysis and photodynamic therapy. Here we show that for (bpy = 2,2’-bipyridine), the generally accepted idea that emission lifetimes can be controlled optimizing the energy barrier from the emissive triplet metal-to-ligand charge-transfer (³MLCT) state to the thermally-activated triplet metal-centered (³MC) state or the energy gap between both states is a misconception. Further, we demonstrate that considering a single relaxation pathway determined from the minimum that is lowest in energy leads to wrong temperature-dependent emission lifetimes predictions. Instead, we obtain excellent agreement with experimental temperature-dependent lifetimes when an extended kinetic model that includes all the pathways related to multiple Jahn–Teller isomers and their effective reaction barriers is employed. These concepts are essential to correctly design other luminescent transition metal complexes with tailored emission lifetimes based on theoretical predictions.