Publications by authors named "Bernd Küstner"

6 Publications

  • Page 1 of 1

Vibrational circular dichroism studies of exceptionally strong chirality inducers in liquid crystals.

Phys Chem Chem Phys 2021 Apr;23(16):10021-10028

Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.

7,7'-Disubstituted 2,2'-methylenedioxy-1,1'-binaphthyls are highly efficient chirality inducers in nematic liquid crystals. The absolute configuration of these compounds is, however, hard to determine as they only crystallize as racemic mixtures. In this work a Vibrational Circular Dichroism (VCD) study is reported that provides an unambiguous determination of the absolute configuration of these compounds. An in-depth General Coupled Oscillator (GCO) analysis of the source of the VCD signal reveals that the unusual structure of these binaphthyl compounds inherently leads to strong and robust VCD bands. Combined with linear transit calculations, our VCD studies allow for the determination of key structural parameters.
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http://dx.doi.org/10.1039/d1cp00854dDOI Listing
April 2021

Reactions of Superoxide with Iron Porphyrins in the Bulk and the Near-Surface Region of Ionic Liquids.

Inorg Chem 2015 Jul 9;54(14):6862-72. Epub 2015 Jul 9.

†Department of Chemistry and Pharmacy, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.

The redox reaction of superoxide (KO2) with highly charged iron porphyrins (Fe(P4+), Fe(P8+), and Fe(P8-)) has been investigated in the ionic liquids (IL) [EMIM][Tf2N] (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and [EMIM][B(CN)4] (1-ethyl-3-methylimidazolium tetracyanoborate) by using time-resolved UV/vis stopped-flow, electrochemistry, cryospray mass spectrometry, EPR, and XPS measurements. Stable KO2 solutions in [EMIM][Tf2N] can be prepared up to a 15 mM concentration and are characterized by a signal in EPR spectrum at g = 2.0039 and by the 1215 cm(-1) stretching vibration in the resonance Raman spectrum. While the negatively charged iron porphyrin Fe(P8-) does not react with superoxide in IL, Fe(P4+) and Fe(P8+) do react in a two-step process (first a reduction of the Fe(III) to the Fe(II) form, followed by the binding of superoxide to Fe(II)). In the reaction with KO2, Fe(P4+) and Fe(P8+) show similar rate constants (e.g., in the case of Fe(P4+): k1 = 18.6 ± 0.5 M(-1) s(-1) for the first reaction step, and k2 = 2.8 ± 0.1 M(-1) s(-1) for the second reaction step). Notably, these rate constants are four to five orders of magnitude lower in [EMIM][Tf2N] than in conventional solvents such as DMSO. The influence of the ionic liquid is also apparent during electrochemical experiments, where the redox potentials for the corresponding Fe(III)/Fe(II) couples are much more negative in [EMIM][Tf2N] than in DMSO. This modified redox and kinetic behavior of the positively charged iron porphyrins results from their interactions with the anions of the ionic liquid, while the nucleophilicity of the superoxide is reduced by its interactions with the cations of the ionic liquid. A negligible vapor pressure of [EMIM][B(CN)4] and a sufficient enrichment of Fe(P8+) in a close proximity to the surface enabled XPS measurements as a case study for monitoring direct changes in the electronic structure of the metal centers during redox processes in solution and at liquid/solid interfaces.
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http://dx.doi.org/10.1021/acs.inorgchem.5b00770DOI Listing
July 2015

Synthesis of glass-coated SERS nanoparticle probes via SAMs with terminal SiO2 precursors.

Small 2010 Mar;6(6):733-7

Department of Physics, University of Osnabrück, D-49069 Osnabrück, Germany.

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http://dx.doi.org/10.1002/smll.200902065DOI Listing
March 2010

SERS labels for red laser excitation: silica-encapsulated SAMs on tunable gold/silver nanoshells.

Angew Chem Int Ed Engl 2009 ;48(11):1950-3

Institut für Physikalische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.

In a glass house: Silica-encapsulated self-assembled monolayers (SAMs) on tunable gold/silver nanoshells were used as labels for surface-enhanced Raman scattering (SERS). This concept combines the spectroscopic advantages arising from maximum surface coverage and uniform molecular orientation of the Raman reporter molecules within the complete monolayer together with the high chemical and mechanical stability of the glass shell.
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http://dx.doi.org/10.1002/anie.200804518DOI Listing
April 2009

UV resonance Raman spectroscopic monitoring of supramolecular complex formation: peptide recognition in aqueous solution.

Phys Chem Chem Phys 2007 Aug 27;9(32):4598-603. Epub 2007 Jul 27.

Institut für Physikalische Chemie, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.

The formation of a supramolecular complex between a tetrapeptide and an artificial receptor , is monitored at submillimolar concentrations in water by UV resonance Raman spectroscopy. Using 275 nm excitation, we selectively probe the carboxylate binding site (CBS) within the receptor, a moiety which is very efficient in binding the carboxy terminus of peptides in aqueous media. Complexation of the receptor with the tetrapeptide involves the formation of a H-bond enforced ion pair, resulting in significant changes in the corresponding UV resonance Raman spectra. Our qualitative interpretation is based on experimental reference and calculated Raman spectra on model systems. First preliminary calculations show that for a quantitative analysis, also the distinct contributions of multiple CBS conformers must be considered in addition to the H-bond induced changes upon complexation.
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http://dx.doi.org/10.1039/b709142gDOI Listing
August 2007

Direct and label-free detection of solid-phase-bound compounds by using surface-enhanced Raman scattering microspectroscopy.

Angew Chem Int Ed Engl 2007 ;46(25):4786-9

Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.

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http://dx.doi.org/10.1002/anie.200605190DOI Listing
October 2007