Lead


Lay summary
It was about half a century ago that the handedness, or sense of chirality, of the microscopic world of molecules could finally be related to the handedness of our macroscopic everyday world. The feat was accomplished by anomaleous x-ray scattering. One of the reasons why the knowledge of the handedness of molecules is so important is that the living world tends to strongly discriminate the image and mirror image forms of molecules, i.e. their enantiomeric forms. Amino acids, e.g., which make up much of the living tissues, are all of one kind, and if a molecule has two enantiomeric forms they can have entirely different physiological properties.There are few practically useful physical methods which can distinguish enantiomers, and even fewer ones capable of assigning absolute configurations, i.e. able to tell if one deals with the left-handed or the right-handed form of a molecule. Anomaleous x-ray scattering cannot be used in a majority of cases. Electronic optical activity is not always reliable. Vibrational optical activity, in contrast, though it became first measurable only about 35 years ago, has proved highly effective, generally applicable, and reliable. Its two forms, vibrational circular dichroism (VCD) and Raman optical activity (ROA) are often complementary.We use ROA to determine absolute configurations and to investigate molecular conformations. The absolute configuration of pyridinophane, which resisted a determination for over 40 years, is currently being assigned. As sample size is one of the most important aspects of any analytical method, we work on improving the reliable measurement of the ROA of small samples, at present at the sub-milligram level. The more efficient computation of ROA and Raman spectra, and the the better understanding of how spectra depend on molecular structure, are likewise important aspects of our work, expected to lead to generally useful rules for correlating configuration and structure with measured spectra in many cases without the need of individual calculations.