Search results for "circular"
showing 10 items of 856 documents
Orientation and substrate interaction of adsorbed CO and NO molecules probed by circular dichroism in the angular distribution of photoelectrons.
1994
The sensitivity and utility of circular dichroism in the angular distribution of photoelectrons (CDAD) as a probe of molecular orientation is demonstrated for adsorbed CO and NO molecules. A comparison between measured CDAD spectra and calculated values for spatially oriented CO and NiCO clearly confirms the well-known perpendicular adsorption for CO on Ni(100), whereas for CO adsorbed on Fe(100) a tilted adsorption geometry was found. For NO/Ni(100) and for NO on the oxygen-preadsorbed Ni(100) surface, an average tilt angle of α=40±10° was observed. In the case of the oxygen-preadsorbed Ni(100) surface, a higher fraction of NO molecules was found to be in a tilted orientation than on the c…
Chiral spin crossover nanoparticles and gels with switchable circular dichroism
2015
Spin crossover complexes represent spectacular examples of molecular switchable materials. We describe a new approach towards homochiral coordination nanoparticles of [Fe(NH2trz)3](L-CSA)2 (NH2trz = 4-amino-1,2,4-triazole, L-CSA = L-camphorsulfonate) that display an abrupt switch of chiral properties associated with a cooperative spin transition. This is an original method that generates stable and additive-free colloidal solutions of nanoparticles with a spin transition around room temperature. The introduction of a chiral anion to the coordination framework makes these nanoparticles display specific chiro-optical (circular dichroism) properties that are different in high and low spin stat…
Exchange coupling in the correlated electronic states of amorphous GdFe films
2013
The bulk sensitivity of hard x-ray photoelectron spectroscopy in combination with circularly polarized radiation of the P09 beamline at PETRA III enables the investigation of the magnetic properties of capped films. We have determined the temperature dependence of the magnetic circular dichroism in the Fe 2$p$ and in the Gd 3$d$ states in amorphous GdFe films. The magnetic dichroism reflects the stronger temperature dependence of Gd moments compared to Fe moments in agreement with mean-field models. We resolved the exchange split Gd 3${d}_{5/2}$ substates and found a significant temperature dependence of the splitting which is attributed to a temperature dependent part of the exchange energ…
Magnetic Circular Dichroism in Two-Photon Photoemission
2009
We report the observation of magnetic circular dichroism (MCD) in two-photon photoemission (2PPE). The Heusler alloys Ni2MnGa and Co2FeSi were investigated by excitation with femtosecond laser light, showing MCD asymmetries of A=(3.5+/-0.5)x10;{-3} for Ni2MnGa and of A=(2.1+/-1.0)x10;{-3} for Co2FeSi, respectively. A theoretical explanation is provided based on local spin-density calculations for the magnetic dichroic response; the computed 2PPE MCD agrees well with the experiment. The observed 2PPE magnetic contrast represents an interesting alternative for future time-resolved photoemission studies on surface magnetism practicable in the laboratory.
Unconventional dihydrogen-bond interaction induced cyanide-bridged chiral nano-sized magnetic molecular wheel: synthesis, crystal structure and syste…
2019
A pair of cyanide-bridged 4d–3d heterobimetallic chiral macrocyclic enantiomeric magnetic complexes have been successfully assembled from the trans-dicyanoruthenium(III) building block [PPh4][Ru(Salen)(CN)2] (Salen = N,N-ethylenebis(salicylideneaminato)dianion) and [Mn((S,S/R,R)-Salcy)(H2O)2]ClO4 (Salcy = N,N′-(1,2-cyclohexanediylethylene)bis(salicylideneiminato)dianion) with the great help of the dihydrogen bond (DHB) interaction and characterized by elemental analysis, IR spectroscopy, circular dichroism (CD) and magnetic circular dichroism (MCD) spectroscopy. Single X-ray diffraction reveals that complex 1, {[Ru(Salen)(CN)2][R,R-Mn(Salcy)]}6·PPh3·6CH3CN·6CH3OH·12H2O, is a neutral dodecan…
Dynamic Light Scattering Investigation of the Kinetics and Fidelity of Supramolecular Copolymerizations in Water
2017
The self-assembly of supramolecular copolymers facilitates the preparation of multifunctional materials, with tunable mechanical, electronic, or bioactive properties. Compared to covalent copolymerization protocols, controlling the molecular weight, stability, and monomer sequence of a multicomponent supramolecular copolymer remains limited. Here, we report a light scattering investigation of the charge-regulated supramolecular copolymerization in neutral buffer of physiological ionic strength, supported with electron microscopy and circular dichroism spectroscopy experiments. Dendritic anionic and cationic peptide comonomers self-assemble into AB-type heterocopolymers with a nanorod-like m…
Copper(ii) and zinc(ii) dependent effects on Aβ42 aggregation: a CD, Th-T and SFM study
2013
A? aggregation is a central event in Alzheimer's disease (AD). In vitro evidence indicates that A? aggregation and fibrillogenesis are significantly influenced by the employed experimental conditions. Indeed, although it is widely established that metal ions, such as copper and zinc, have significant effects on the A? aggregation process, their actual role in A? fibrillogenesis is still debated. In this work the effects of a molar excess of zinc(ii) and/or copper(ii) ions on the A?42 aggregation process and the morphology of the resultant aggregates have been compared in samples exhibiting different initial conformations. CD spectroscopy, Th-T-induced fluorescence and Scanning Force Microsc…
Sensing Chiral Drugs by Using CdSe/ZnS Nanoparticles Capped withN-Acetyl-L-Cysteine Methyl Ester
2013
Chiral quantum dots (QDs), differing in their core or shell size and, consequently, in their optical properties, were synthesized by the treatment of commercially available amine-capped quantum dots with methyl ester N-acetyl-L-cysteine (CysP). Interestingly, their colloidal methanol solutions remain stable for several months. Their NMR and IR spectra were in accordance with CysP binding to the QD surface through two anchoring groups; its thiolate (strongly bound) and the carbonyl group of its ester (weaker bound) group, whereas their circular dichroism (CD) spectra showed a new broad redshifted band, suggesting that the attachment to the QD surface modified the conformational equilibrium t…
Influence of pH on the benzodiazepine-human serum albumin complex. Circular dichroism studies.
1974
The influence of pH on the binding of benzodiazepine derivatives to HSA was studied by circular dichroism measurements and by gel filtration. The binding of nearly all benzodiazepines is increased by rising the pH from 6.60 to 8.20. For flurazepam, clonazepam, and nitrazepam this increase in binding is due to an increase of the affinities, while for the other substances the affinity remains constant and the number of binding sites is increased from one to two. The changes in binding of the benzodiazepines by rising the pH are explained by a cationic amino acid residue near or at the benzodiazepine binding site of the HSA molecule. This second binding site is not detectable by circular dichr…
Influencing the Self‐Sorting Behavior of [2.2]Paracyclophane‐Based Ligands by Introducing Isostructural Binding Motifs
2020
Abstract Two isostructural ligands with either nitrile (Lnit) or isonitrile (Liso) moieties directly connected to a [2.2]paracyclophane backbone with pseudo‐meta substitution pattern have been synthesized. The ligand itself (Lnit) or its precursors (Liso) were resolved by HPLC on a chiral stationary phase and the absolute configuration of the isolated enantiomers was assigned by XRD analysis and/or by comparison of quantum‐chemical simulated and experimental electronic circular dichroism (ECD) spectra. Surprisingly, the resulting metallosupramolecular aggregates formed in solution upon coordination of [(dppp)Pd(OTf)2] differ in their composition: whereas Lnit forms dinuclear complexes, Liso…