NMR Studies of Cyclodextrins and Cyclodextrin Complexes

Methods for Selective Modifications of Cyclodextrins.

Fundamental Principles. L.W. Jelinsky, Experimental Methods. The Chemical Shift. Coupling of Nuclear Spins. Nuclear Relaxation and Chemical Rate Processes. P.A. Mirau and F.A. Bovey, Two-Dimensional Nuclear Magnetic Resonance Spectroscopy. Macromolecules. NMR of Solids. F.A. Bovey, L.W. Jelinsky, P.A. Mirau, Special Topics. Appendixes. Author Index. Subject Index.

Nuclear magnetic resonance spectroscopy.

An astonishing assortment of structures have been described as "insulated molecular wires" (IMWs), thus illustrating the diversity of approaches to molecular-scale insulation. These systems demonstrate the scope of encapsulation in the molecular engineering of optoelectronic materials and organic semiconductors. This Review surveys the synthesis and structural characterization of IMWs, and highlights emerging structure-property relationships to determine how insulation can enhance the behavior of a molecular wire. We focus mainly on three IMW architectures: polyrotaxanes, polymer-wrapped pi systems, and dendronized polymers, and compare the properties of these systems with those of conjugated polymers threaded through mesoporous frameworks and zeolites. Encapsulation of molecular wires can enhance properties as diverse as luminescence, electrical transport, and chemical stability, which points to applications in electroluminescent displays, sensors, and the photochemical generation of hydrogen.

Insulated molecular wires.

A continual challenge in the field of chemical detection is the development of approaches to designing microsensors and microsensor-based detectors with high selectivity. No single science exists to unite all sensor technologies with a common set of principles and a common approach to achieving selectivity. Nevertheless, in the area of vapor detection, sorption phenomena and solubility interactions can be identified as common features of many sensors. In designing microsensors for vapor detection, interactive coating materials must be chosen that will collect and concentrate analyte molecules at the sensor's surface. The sensitivity and selectivity of each individual sensor is controlled by tailoring the chemical and physical properties of the coating material to maximize particular solubility interactions. The selection of coatings for the complete sensor array is logically made through a systematic variation of the solubility properties of the coating materials, so that each sensor is selective for a different balance of solubility interactions. This account discusses solubility in great detail. Parameters and methodologies for characterizing analyte solubility properties, sensor coating material solubility properties, and their interactions are presented. Specific functional groups are recommended for inclusion in sensor coating materials in order to maximize particular interactions. In addition, the treatment of coating material properties is integrated with consideration of the factors that influence chemical selectivity in sensor arrays. Methods for choosing coatings inteligently for sensor arrays, and for optimizing sensor arrays for particular analytes are considered.

https://apps.dtic.mil/sti/pdfs/ADA224957.pdf

Solubility interactions and the design of chemically selective sorbent coatings for chemical sensors and arrays

Cyclodextrins as second‐sphere ligands for transition metal complexes

Second Sphere Coordination Adducts of Phosphane‐Transition Metal Complexes with β‐Cyclodextrin and its Methylated Derivative

Three chemically modified cyclodextrins have been prepared, characterised by n.m.r. spectroscopy, and studied for their possible role as piezoelectric crystal coating detectors towards benzene vapour. 2,6-Per-O-methyl-β-cyclodextrin 3-perbenzoate (DMsCD-B7) is not recommended. 2,6-Per-O-(t-butyldimethylsilyl)-α-cyclodextrin (DSαCD) was found to be the best for the ca. 0.08–ca. 400 mg dm–3 range of benzene vapour in air. 2,6-Per-O-allyl-α-cyclodextrin (DAαCD) is a possible alternative. Both detector systems function for > 20 days. The detectors are selective towards benzene vapour over methane, propane, butane, pentane, ethyne, ammonia, nitrobenzene, and toluene. Toluene gives rise to the most serious interference. For the preferred DSαCD sensor, toluene only gives < 20% of the decrease in frequency observed with the corresponding amount of benzene. However, the interference is slightly greater for the DAαCD sensor.

Piezoelectric quartz crystal detection of benzene vapour using chemically modified cyclodextrins

Mass spectrometric investigation of adduct formation by methylated cyclodextrins

Samples of 2,6-per-O-methyl-s-cyclodextrin (DMsCD), prepared according to literature procedures, have been shown to be less than 70% pure. The major impurity has been identified as the unsymmetrical over-methylated cyclodextrin derivative (DM+1)sCD. Samples of pure DMsCD and (DM+1)sCD have been prepared by (i) benzoylating a chromatographically homogeneous mixture obtained after methylating sCD with dimethyl sulphate, (ii) separating chromatographically the resulting DMsCD heptabenzoate (DMsCD-B7) and (DM+1)sCD hexabenzoate [(DM+1)sCD-B6], and then (iii) subjecting the pure perbenzoates to de-O-benzoylation. Both DMsCD-B7 and (DM+1)sCD-B6 have been fully characterised. High-resolution 1H and 13C n.m.r. spectroscopy, with use of modern pulse techniques (homonuclear double resonance difference spectroscopy, COSY, J-resolved, JMOD, XHCORRD, and CHORTLE) for signal assignment and n.O.e. difference spectroscopy for residue sequencing, has been used to assign individually (i) 41 out of the 49 heterotopic protons and (ii) 29 out of the 42 heterotopic carbon atoms of the unsymmetrical (DM+1)sCD-B6(nuclei associated with O-methyl and O-benzoyl groups were excluded from consideration). The complete spectroscopic characterisation of unsymmetrical chemically modified cyclodextrins is important in the investigation of these compounds as potential enzyme models. The necessity of preparing pure chemically modified cyclodextrin derivatives cannot be over-emphasised.

Ryszard Zarzycki

Papers

Cyclodextrins as second‐sphere ligands for transition metal complexes

Second Sphere Coordination Adducts of Phosphane‐Transition Metal Complexes with β‐Cyclodextrin and its Methylated Derivative

Piezoelectric quartz crystal detection of benzene vapour using chemically modified cyclodextrins

Mass spectrometric investigation of adduct formation by methylated cyclodextrins

Structural mapping of an unsymmetrical chemically modified cyclodextrin by high-field nuclear magnetic resonance spectroscopy