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Characterization Techniques in Supramolecular Chemistry

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Special Issue Editor

Dr. Andreas Hennig

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Guest Editor

Department of Life Sciences and Chemistry, Jacobs University Bremen, Bremen, Germany
Interests: supramolecular chemistry; membrane transport; fluorescent probes and sensors; photophysics; optical spectroscopy; bioanalytical applications; enzyme assays; surfaces and interfaces; (nano)bioconjugation

Special Issue Information

Dear Colleagues,

From its infancy in the synthesis, design, and physicochemical investigation of host–guest complexes, supramolecular chemistry has evolved to become a highly interdisciplinary and largely diversified field. It naturally intersects with other scientific areas, because the weak, noncovalent forces that govern supramolecular host–guest complexes are also responsible for the selective association of other molecules. As a consequence, exciting developments for many real and potential applications in the life sciences, materials sciences, and nanosciences can be foreseen.

At the same time, the supramolecular concepts to build up materials and systems with fascinating, emergent properties require a broad range of modern characterization methods and instrumental techniques to investigate supramolecular systems. This includes, for example, NMR spectroscopy, crystallography, isothermal titration calorimetry, mass spectrometry, single molecule spectroscopy, electrochemisty, various steady-state and time-resolved optical spectroscopic methods, as well as functional assays.

For this Special Issue, I would like to kindly invite you to submit review and original research articles on all aspects of characterizing supramolecular systems.

Dr. Andreas Hennig
Guest Editor

Manuscript Submission Information

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Keywords

supramolecular chemistry
self-assembly
self-organization
characterization
UV/VIS spectroscopy
isothermal titration calorimetry
NMR spectroscopy
binding thermodynamics and kinetics

Published Papers (2 papers)

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Research

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10 pages, 897 KiB

Open AccessFeature PaperArticle

EPR Spectroscopy: A Powerful Tool to Analyze Supramolecular Host•Guest Complexes of Stable Radicals with Cucurbiturils

by Fengbo Liu, Hakim Karoui, Antal Rockenbauer, Simin Liu, Olivier Ouari and David Bardelang

Molecules 2020, 25(4), 776; https://doi.org/10.3390/molecules25040776 - 11 Feb 2020

Cited by 7 | Viewed by 3209

Abstract

Stable organic free radicals are increasingly studied compounds due to the multiple and unusual properties imparted by the single electron(s). However, being paramagnetic, classical methods such as NMR spectroscopy can hardly be used due to relaxation and line broadening effects. EPR spectroscopy is thus better suited to get information about the immediate surroundings of the single electrons. EPR has enabled obtaining useful data in the context of host•guest chemistry, and a classical example is reported here for the stable (2,2,6,6-tetramethyl-4-oxo-piperidin-1-yl)oxyl or 4-oxo-TEMPO nitroxide (TEMPONE) inside the macrocycle host cucurbit[7]uril (CB[7]). Generally and also observed here, a contraction of the spectrum is observed as a result of the reduced nitrogen coupling constant due to inclusion complexation in the hydrophobic cavity of the host. Simulations of EPR spectra allowed determining the corresponding binding constant pointing to a weaker affinity for CB[7], compared to TEMPO with CB[7]. We complement this work by the results of EPR spectroscopy of a biradical: bis-TEMPO-bis-ketal (bTbk) with cucurbit[8]uril (CB[8]). Initial investigations pointed to very weak effects on the spectrum of the guest and incorrectly led us to conclude an absence of binding. However, simulations of EPR spectra combined with NMR data of reduced bTbk allowed showing inclusion complexation. EPR titrations were performed, and the corresponding binding constant was determined. ¹H NMR spectra with reduced bTbk suggested a shuttle mechanism, at nearly one equivalent of CB[8], for which the host moves rapidly between two stations. Full article

(This article belongs to the Special Issue Characterization Techniques in Supramolecular Chemistry)

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Review

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38 pages, 4321 KiB

Open AccessReview

Probing Reversible Guest Binding with Hyperpolarized ¹²⁹Xe-NMR: Characteristics and Applications for Cucurbit[n]urils

by Jabadurai Jayapaul and Leif Schröder

Molecules 2020, 25(4), 957; https://doi.org/10.3390/molecules25040957 - 20 Feb 2020

Cited by 9 | Viewed by 3970

Abstract

Cucurbit[n]urils (CB[n]s) are a family of macrocyclic host molecules that find various applications in drug delivery, molecular switching, and dye displacement assays. The CB[n]s with n = 5–7 have also been studied with ¹²⁹Xe-NMR. They bind the noble gas with a large range of exchange rates. Starting with insights from conventional direct detection of bound Xe, this review summarizes recent achievements with chemical exchange saturation transfer (CEST) detection of efficiently exchanging Xe in various CB[n]-based supramolecular systems. Unprecedented sensitivity has been reached by combining the CEST method with hyperpolarized Xe, the production of which is also briefly described. Applications such as displacement assays for enzyme activity detection and rotaxanes as emerging types of Xe biosensors are likewise discussed in the context of biomedical applications and pinpoint future directions for translating this field to preclinical studies. Full article

(This article belongs to the Special Issue Characterization Techniques in Supramolecular Chemistry)

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