Treating anisotropic artefacts in circular dichroism spectroscopy enables investigation of lyotropic liquid crystalline polyaspartate solutions

Hirschmann, Max; Merten, Christian; Thiele, Christina M.

doi:10.1039/d0sm02102d

Cited by 20 publications

(26 citation statements)

References 42 publications

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“…In a later publication, the same authors revised their assumption of a symmetry breaking event and attributed the CD signals to measurement artefacts. [ 24 ] Based on our own experiments within this study and on another achiral mesogen (disodium cromoglycate [DSCG]), [ 62 ] we support this second interpretation of the CD signature being an artefact stemming from the sample's macroscopic anisotropy also for BTA 1b .…”

Section: Resultssupporting

confidence: 68%

A supramolecular and liquid crystalline water‐based alignment medium based on azobenzene‐substituted 1,3,5‐benzenetricarboxamides

Knoll

Herold

Hirschmann

et al. 2022

Magnetic Reson in Chemistry

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A supramolecular, lyotropic liquid crystalline alignment medium based on an azobenzene‐containing 1,3,5‐benzenetricarboxamide (BTA) building block is described and investigated. As we demonstrate, this water‐based system is suitable for the investigation of various water‐soluble analytes and allows for a scaling of alignment strength through variation of temperature. Additionally, alignment is shown to reversibly collapse above a certain temperature, yielding an isotropic solution. This collapse allows for isotropic reference measurements, which are typically needed in addition to those in an anisotropic environment, to be performed using the same sample just by varying the temperature. The medium described thus provides easy access to anisotropic NMR observables and simplifies structure elucidation techniques based thereon.

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Section: Resultssupporting

confidence: 68%

A supramolecular and liquid crystalline water‐based alignment medium based on azobenzene‐substituted 1,3,5‐benzenetricarboxamides

Knoll

Herold

Hirschmann

et al. 2022

Magnetic Reson in Chemistry

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“…However, we cannot rule out that genuine CD contributes to the symmetric component of the observed signal, an assessment of which warrants further theoretical research. Regardless, our results emphasize that LDLB can in principle manifest as independent of the light propagation direction and can therefore not be rigorously suppressed by averaging the CD signals resulting from opposite irradiation directions as previously proposed. − …”

Section: Discussionmentioning

confidence: 50%

“…Notably, a macroscopic anisotropy may yield strong LD signals that could interfere with LB interactions in the measurement device, in which case the resulting LDLB contribution is an actual artifact, although one that can be circumvented straightforwardly . But even when sample-intrinsic, LDLB signals may mask genuine CD, the debate of which traces back to measurements on Congo red bound to cellulose or polyvinyl alcohol. , Schemes have been proposed for eliminating the LDLB signals based on averaging the CD spectrum resulting from opposite irradiation directions in order to cancel any antisymmetric contributions. − Perhaps due to its questionable reputation, little is known about how the optical selection rules emerging from LDLB interactions are related to microscopic details of the involved samples, with previous accounts of these interactions being mostly restricted to a macroscopic Jones or Mueller calculus treatment. ,, It has nonetheless been appreciated that LDLB can inform on chiral structural details in certain cases . Perhaps more importantly, however, is that (sample-intrinsic) LDLB signals are due to genuine light–matter interactions, and favorable properties including large g factors and antisymmetric behavior could render them ideal facilitators of photon-to-matter quantum transduction.…”

Section: Introductionmentioning

confidence: 99%

Theory of Apparent Circular Dichroism Reveals the Origin of Inverted and Noninverted Chiroptical Response under Sample Flipping

2021

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Circular dichroism (CD) finds widespread application as an optical probe for the structure of molecules and supramolecular assemblies. Its underlying chiral light−matter interactions effectively couple between photonic spin states and select quantum-mechanical degrees of freedom in a sample, implying an intricate connection with photon-to-matter quantum transduction. However, effective transduction implementations likely require interactions that are antisymmetric with respect to the direction of light propagation through the sample, yielding an inversion of the chiroptical response upon sample flipping, which is uncommon for CD. Recent experiments on organic thin films have demonstrated such chiroptical behavior, which was attributed to "apparent CD" resulting from an interference between the sample's linear birefringence and linear dichroism. However, a theory connecting the underlying optical selection rules to the microscopic electronic structure of the constituent molecules remains to be formulated. Here, we present such a theory based on a combination of Mueller calculus and a Lorentz oscillator model. The theory reaches good agreement with experimental CD spectra and allows for establishing the (supra)molecular design rules for maximizing or minimizing this chiroptical effect. It furthermore highlights that, in addition to antisymmetrically, it can manifest symmetrically such that no chiroptical response inversion occurs, which is a consequence of a helical stacking of molecules in the light propagation direction.

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“…The samples were measured in isotropic solution (1% (wt/wt) polymer concentration in TCE) between two quartz plates at a path length of approximately 0.01 mm (see Supporting Information for details of the path length). Custom-made cuvette holders 25 were used that prevent the solvent from evaporation during the measurement. A background correction was performed by subtracting the signal of pure TCE.…”

Section: ■ Introductionmentioning

confidence: 99%

Copolyaspartates: Uncovering Simultaneous Thermo and Magnetoresponsiveness

2021

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A series of poly-β-benzyl-l-aspartate-co-poly-β-phenethyl-l-aspartates varying in their copolymer composition as well as with selectively introduced deuterium labels in the backbone or the side-chain were synthesized and their temperature-dependent conformation and orientation with respect to an external magnetic field were characterized by measuring 2H quadrupolar splittings [nuclear magnetic resonance (NMR) spectroscopy] and circular dichroism. All copolymers demonstrate a temperature-dependent change of their helical conformation from right-handed to left-handed (helix reversal) and a change of their alignment from perpendicular to parallel with respect to the magnetic field in an anisotropic solution (helix realignment) at different temperatures. Both effects react differently to a change of copolymer composition, but are concentration, dispersity, and molecular weight independent as well as unaffected by the initiator used for polymerization. The helix realignment by 90° in a magnetic field has not been observed previously for these copolyaspartates. Its existence is proven directly by measurement of the quadrupolar splitting of the specifically labeled polymers and comparison to calculated quadrupolar splittings. Furthermore, the temperature of both transitions was found to be dependent on deuteration at the N-position. The uncovering of the thermo and magnetoresponsiveness will lead to an improved understanding and application scope of the copolyaspartates (e.g., in their use as alignment media in NMR spectroscopy).

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Treating anisotropic artefacts in circular dichroism spectroscopy enables investigation of lyotropic liquid crystalline polyaspartate solutions

Abstract: Circular dichroism (CD) spectroscopy is commonly used for investigation of the secondary structure of biomolecular compounds as well as polymers in isotropic solution. In anisotropic solution, the usage of the...

Cited by 20 publications

References 42 publications

A supramolecular and liquid crystalline water‐based alignment medium based on azobenzene‐substituted 1,3,5‐benzenetricarboxamides

A supramolecular and liquid crystalline water‐based alignment medium based on azobenzene‐substituted 1,3,5‐benzenetricarboxamides

Theory of Apparent Circular Dichroism Reveals the Origin of Inverted and Noninverted Chiroptical Response under Sample Flipping

Copolyaspartates: Uncovering Simultaneous Thermo and Magnetoresponsiveness

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