Transitions in complex molecules

Kasha M (1950) Characterization of electronic transitions in complex molecules. Faraday Soc Discuss 9 14-19... 

Sensitivity levels more typical of kinetic studies are of the order of lO molecules cm . A schematic diagram of an apparatus for kinetic LIF measurements is shown in figure C3.I.8. A limitation of this approach is that only relative concentrations are easily measured, in contrast to absorjDtion measurements, which yield absolute concentrations. Another important limitation is that not all molecules have measurable fluorescence, as radiationless transitions can be the dominant decay route for electronic excitation in polyatomic molecules. However, the latter situation can also be an advantage in complex molecules, such as proteins, where a lack of background fluorescence allow s the selective introduction of fluorescent chromophores as probes for kinetic studies. (Tryptophan is the only strongly fluorescent amino acid naturally present in proteins, for instance.)... 

The main difficulty in MO calculations consists in evaluation of the multi-center integrals. The DV-integration method is one of the powerful methods to avoid such difficulty and has been successfully used in the MO method. When this technique is applied to the calculations of the transition matrix elements, it makes the evaluations of x-ray emission rates in complex molecules easier. 

Methods for lactone synthesis by transition metal catalysis involving C—O formation developed over the past 50 years have demonstrated much promise. Indeed, lactones have inspired the discovery of new organometallic transformations, design of metal catalysts, and detailed understanding of reaction mechanisms. Issues of waste minimization and stereoselectivity have been addressed. Future developments for chiral lactone synthesis will likely focus on establishing efficient transformations with broad scope and application in complex molecule total synthesis, especially in regards to macrolactonization where entropic costs often plague intramolecular reactivity with undesired intermolecular reactions. 

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