5-[4'-(2,2,5,5-Tetramethyl-3-pyrroline-1-oxyl-3-carbonyl)biphenyl-4-ylethynyl]-2,3,7,8,12,13,17,18-octaethylporphyrinato}copper(II) benzene solvate : corrigendum

In the paper by Bolte [Acta Cryst. (2006), E62, m1609-m1610], the chemical name in the title and the chemical diagram are incorrect. The correct title is {5-[4'-(2,2,5,5-Tetramethyl-3-pyrroline-1-oxyl-3-carbonyloxy)biphenyl-4-ylethynyl]-2,3,7,8,12,13,17,18-octaethylporphyrinato}copper(II) benzene solvate' and the correct diagram is given below

PELDOR measurements on a Nitroxide Labeled Cu(II) Porphyrin:Orientation Selection, Spin-Density Distribution and Conformational Flexibility

Metal ions are functionally or structurally important centers in metalloproteins or RNAs, which makes them interesting targets for spectroscopic investigations. In combination with site-directed spin labeling, pulsed electron-electron double resonance (PELDOR or DEER) could be a well-suited method to characterize and localize them. Here, we report on the synthesis, full characterization, and PELDOR study of a copper(II) porphyrin/nitroxide model system. The X-band PELDOR time traces contain besides the distance information a convolution of orientational selectivity, conformational flexibility, exchange coupling, and spin density distribution, which can be deconvoluted by experiments with different frequency offsets and simulations. The simulations are based on the known experimental and spin Hamiltonian parameters and make use of a geometric model as employed for structurally similar bis-nitroxides and spin density parameters as obtained from density functional theory calculations. It is found that orientation selection with respect to dipolar angles is only weakly resolvable at X-band frequencies due to the large nitrogen hyperfine coupling of the copper porphyrin. On the other hand, the PELDOR time traces reveal a much faster oscillation damping than observed for structurally similar bis-nitroxides, which is mainly assigned to a small distribution in exchange couplings J. Taking the effects of orientation selectivity, distribution in J, and spin density distribution into account leads finally to a narrow distance distribution caused solely by the flexibility of the structure, which is in agreement with distributions from known bis-nitroxides of similar structure. Thus, X-band PELDOR measurements at different frequency offsets in combination with explicit time trace simulations allow for distinguishing between structural models and quantitative interpretation of copper-nitroxide PELDOR data gives access to localization of copper(II) ions.</p

PELDOR on an Exchange Coupled Nitroxide Copper(II) Spin Pair

Transition metal ions play an important role in the design of macromolecular architectures as well as for the structure and function of proteins and oligonucleotides, which makes them interesting targets for spectroscopic investigations. In combination with site directed spin labelling, pulsed electron-electron double resonance (PELDOR or DEER) could be a well-suited method for their characterization and localization. Here, we report on the synthesis and full characterization of a copper(II) porphyrin/nitroxide model system bearing an extended pi-conjugation between the spin centres and demonstrate the possibility to disentangle the dipolar through space interaction from the through bond exchange coupling contribution even in the presence of orientational selectivity and conformational flexibility. The simulations used are based on the known experimental and spin Hamiltonian parameters and on a structural model as previously employed for similar systems. The mean exchange coupling of +4(1) MHz (antiferromagnetic) is in agreement with the value of vertical bar J vertical bar = 3(1) MHz determined from room temperature continuous wave electron paramagnetic resonance (EPR). Thus, as long as the pulse excitation bandwidths are large versus the spin-spin coupling, X-band PELDOR measurements in combination with explicit time trace simulations allow for disentangling the sign and magnitude of through bond electron-electron exchange from the through space dipolar interaction D. (C) 2008 Elsevier B.V. All rights reserved.</p

PELDOR on an Exchange Coupled Nitroxide Copper(II) Spin Pair

Transition metal ions play an important role in the design of macromolecular architectures as well as for the structure and function of proteins and oligonucleotides, which makes them interesting targets for spectroscopic investigations. In combination with site directed spin labelling, pulsed electron-electron double resonance (PELDOR or DEER) could be a well-suited method for their characterization and localization. Here, we report on the synthesis and full characterization of a copper(II) porphyrin/nitroxide model system bearing an extended pi-conjugation between the spin centres and demonstrate the possibility to disentangle the dipolar through space interaction from the through bond exchange coupling contribution even in the presence of orientational selectivity and conformational flexibility. The simulations used are based on the known experimental and spin Hamiltonian parameters and on a structural model as previously employed for similar systems. The mean exchange coupling of +4(1) MHz (antiferromagnetic) is in agreement with the value of vertical bar J vertical bar = 3(1) MHz determined from room temperature continuous wave electron paramagnetic resonance (EPR). Thus, as long as the pulse excitation bandwidths are large versus the spin-spin coupling, X-band PELDOR measurements in combination with explicit time trace simulations allow for disentangling the sign and magnitude of through bond electron-electron exchange from the through space dipolar interaction D. (C) 2008 Elsevier B.V. All rights reserved.</p

Host–Guest Complexes as Water-Soluble High-Performance DNP Polarizing Agents

International audienceDynamic nuclear polarization (DNP) enhancesthe sensitivity of solid-state NMR (SSNMR) spectroscopy byorders of magnitude and, therefore, opens possibilities fornovel applications from biology to materials science. Thismultitude of opportunities implicates a need for highperformancepolarizing agents, which integrate specific physicaland chemical features tailored for various applications. Here,we demonstrate that for the biradical bTbK in complex withcaptisol (CAP), a β-cyclodextrin derivative, host−guestassembling offers a new and easily accessible approach for the development of new polarizing agents. In contrast to bTbK,the CAP-bTbK complex is water-soluble and shows significantly improved DNP performance compared to the commonly usedDNP agent TOTAPOL. Furthermore, NMR and EPR data reveal improved electron and nuclear spin relaxation properties forbTbK within the host molecule. The numerous possibilities to functionalize host molecules will permit designing novel radicalcomplexes targeting diverse applications

Spin labeling of oligonucleotides with the nitroxide TPA and use of PELDOR, a pulse EPR method, to measure intramolecular distances

In this protocol, we describe the facile synthesis of the nitroxide spin-label 2,2,5,5-tetramethyl-pyrrolin-1-oxyl-3-acetylene (TPA) and then its coupling to DNA/RNA through Sonogashira cross-coupling during automated solid-phase synthesis. Subsequently, we explain how to perform distance measurements between two such spin-labels on RNA/DNA using the pulsed electron paramagnetic resonance method pulsed electron double resonance (PELDOR). This combination of methods can be used to study global structure elements of oligonucleotides in frozen solution at RNA/DNA amounts of similar to 10 nmol. We especially focus on the Sonogashira cross-coupling step, the advantages of the ACE chemistry together with the appropriate parameters for the RNA synthesizer and on the PELDOR data analysis. This procedure is applicable to RNA/DNA strands of up to similar to 80 bases in length and PELDOR yields reliably spin-spin distances up to similar to 6.5 nm. The synthesis of TPA takes similar to 5 days and spin labeling together with purification similar to 4 days. The PELDOR measurements usually take similar to 16 h and data analysis from an hour up to several days depending on the extent of analysis.</p