Biomedical subjects

Mark M Green

Publications and source records attributed to Mark M Green.

3 recordsLinked to original sources

PubMed2004

Chiral effect on a self-assembling bicopper complex.

A bicopper complex was prepared with chiral ligands. The self-assembly of the complex in trans-decalin differed greatly for the racemic and nonracemic ligands. With the latter the resulting gel formed at a lower concentration and exhibited a higher thermal transition temperature. A large optical activity was found in the nonracemic bicopper complex, which was used to probe the process of filament formation, i.e., the aggregation-dissociation process. The material with nonracemic ligands may form a longer nanoscopic filament.

Journal Article↗

PubMed2003

Chiral conflict. The effect of temperature on the helical sense of a polymer controlled by the competition between structurally different enantiomers: from dilute solution to the lyotropic liquid crystal state.

Helical polymers appended with paired structurally different enantiomers, which have opposing helical sense preferences, yield a new kind of relationship between optical activity and temperature, and also reveal unusual details of the nature of chiral interactions. Consistent with a statistical physical theory developed for these experiments, the proportion of the competing chiral groups, determined by synthesis, fixes the compensation temperature at which the helical senses are equally populated. The lyotropic liquid crystal state formed by these polymers yields therefore a nematic state at any chosen temperature over a very wide range, with a cholesteric state arising with tightening pitch as temperature deviates from this point. Far from the nematic temperature, the pitch reaches the nanometer scale and therefore the reflection of visible light. Before crossing zero at the nematic temperature, the optical activity becomes so large that it may be observed with the unaided eye through crossed polarizers.

Biopolymers↗

PubMedDate not supplied

Atropisomerism as a probe of restrictions to motion above and below the glass transition temperature of Polymers.

This short review and interpretation of work conducted in the authors' laboratory concerns the use of atropisomeric 1,1'-binaphthyl derivatives to gain information about the glassy properties of polymers. Bridged binaphthyls appended with oligophenyl paddles are found to yield a series of probes whose racemization kinetics reveal new kinds of information concerning the basis of the time scale and length scale for the restrictions to motion and the heterogeneity of the polymeric glassy state. Because the time scale of the racemization is slower than all other glass probes used previously, new kinds of information were gained for the first time below the glass transition temperature.

Journal Article↗