Supramolecular conduction mechanisms

Because of the vastness of the subject matter, we shall focus our attention on hydrogen bonding interactions between ions and on the possibilities and limitations of their use in the design and construction of molecular materials of desired architectures and/or destined to predetermined functions. Obviously, the crystal engineer (or supramolecular chemist) needs to know the nature of the forces s/he is planning to master, since molecular and ionic crystals, even if constructed with similar building blocks, differ substantially in chemical and physical properties (solubility, melting points, conductivity, mechanical robustness, etc.). 

Once a note of caution is expressed, novel DNA-based molecular design and architectures have, however, reached levels where the emerging supramolecular structures can perhaps become robust to different electronically working environments. Redox- and fluorophor-labeled molecules offer steps towards device-like function where both structural organization and, as noted, additional sophisticated electronic function can be added to the DNA-based molecules. " " " New electronic conductivity mechanisms based on hopping via a chain of well-defined redox probes bound in the DNA-backbone were noted above." Such... 

The present article is centered around macromolecular and supramolecular structures obtained upon use of benzene as a regular building block. While, e.g., the gas permeability of polyethylene tereph-thalate)s,35 the mechanical strength of carbon fibers,36 and the ion conductivity of polybenzimidazoles24 are important features from a practical viewpoint, the focus here is on the occurrence of -conjugation, or lack thereof, originating from the repetition of the aromatic benzene units in various structural motifs. If the reader regards materials... 

Fully understanding the mechanical, electrical, and chemical properties of a material is vital for its successful application. The literature reports confirm that, the properties of PPy s vary widely, and are related to composition and processing conditions in a complex way. Thus, the study of the basic properties must be conducted at a fundamental level, by developing structure-property relationships. This, however, requires a greater understanding of the structure of PPy s, both at the molecular and supramolecular levels. 

Figure 28.6 Solution strategies to align rigid-rod conducting polymers into 2-D arrays by using supramolecular clips, followed by mechanical fixation through the formation of a pseudo-polyrotaxane. Questions have been asked regarding the feasibility of the selective sheet formation. RCM, ring-closing metathesis.

Because of their advanced level of development, high sensitivity, and broad applicability, fluorescence spectroscopy with labeled LUVs and planar bilayer conductance experiments are the two techniques of choice to study synthetic transport systems. The broad applicability of the former also includes ion carriers, but it is extremely difficult to differentiate a carrier from a channel or pore mechanism by LUV experiments. However, the breadth and depth accessible with fluorogenic vesicles in a reliable user-friendly manner are unmatched by any other technique. Planar bilayer conductance experiments are restricted to ion channels and pores and are commonly accepted as substantial evidence for their existence. Exflemely informative, these fragile single-molecule experiments can be very difficult to execute and interpret. Another example for alternative techniques to analyze synthetic transport systems in LUVs is ion-selective electrodes. Conductance experiments in supported lipid bilayer membranes may be mentioned as well. Although these methods are less frequently used, they may be added to the repertoire of the supramolecular chemist. 

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