Anisotropic Aromatic side chains

As well as providing a means of measuring 1 H/2H-exchange in proteins, NMR is a most powerful technique for studying the mobility of individual amino acids. For example, the rotational freedom of the aromatic side chains of tyrosine and phenylalanine about the C 3—Cy bond is readily studied by various NMR methods. ]H NMR can detect whether or not the aromatic ring is constrained in an anisotropic environment. In an isotropic environment or where there is rapid rotation on the NMR time scale, the 3 and 5 protons of phenylalanine and tyrosine are symmetrically related, as are the 2 and 6 (structures 1.12). The resultant spectrum is of the AA BB type, containing two pairs of closely separated doublets. But if there is slow rotation in an anisotropic environment, the symmetry breaks down to give four separate resonances (an ABCD spectrum), since the 5 and 6 protons are in different states from the 2 and 3. At an intermediate time... 

Solid-state NMR spectroscopy is well suited for studies of intramolecular dynamics because side chain motions can be analyzed Independent of overall molecular reorientation in crystalline samples. It is an alternative spectroscopic strategy to solution NMR because partial motional averaging of the anisotropic spin interactions occurs. Dipolar, chemical shift, and quadrupolar interactions can be used to describe the dynamics of aromatic rings of proteins and peptides. 

Since side-chain-type LC polyacetylene derivatives were first synthesized [10-18], various types of LC conjugated polymers have been synthesized and evaluated from the standpoint of their electrical and optical properties [19-46]. Among them, LC aromatic conjugated polymers, including LC polythiophene derivatives, have been of recent interest because they are available for linearly polarized luminescent materials, and also anisotropically conducting materials [28-30, 40-53]. 

It has been shown that the hexagonal columnar phase forms honeycombed network and has the microcavity with diameter of ca. 3 nm (Figure 7-6) [30]. It is the first type of aromatic polyester with flexible side chains. Further, it is expected that existence of the microcavity in the hexagonal columnar phase leads to possibility to be used as soft materials with anisotropic field and so may be applied to smart membranes. For this, stmctural and dynamic behavior of the polymers must be characterized with high precision. 

---