Semi-Experimental Equilibrium Structures for Molecules of Biological Significance
EMSL Project ID
46191
Abstract
Polyenes are important in biology, where they play central roles in vision, in natural pigments, and in light-harvesting for photosynthesis. Putting fluorine substituents in medicinal substances has become an important strategy for tuning potency and increasing the lifetime of drugs in competition with metabolic breakdown. The goal of the project is to gain a better understanding of the structures of small polyenes and fluorine-substituted ones. We do so by determining semi-experimental equilibrium structures for molecules where effects of pi-electron delocalization and fluorine substitution may have significant effects on bond lengths and bond angles in comparison with reference substances. The new structures have bond lengths good to 0.001 A with atoms seemingly at rest, distinct from standard methods, such as x-ray, which give ~0.02 A resolution because of zero point vibrations of the atoms and which give poor definition of bond parameters for hydrogen atoms. Equilibrium structures are also useful in assessing the quality of high-level quantum chemical (QC) calculations of molecular properties. Semi-experimental equilibrium structures (re) come from equilibrium rotational constants, which are determined from ground state rotational constants secured from the analysis of high-resolution molecular spectra and from the QC calculation of the vibration-rotation constants (alphas). A number of 13C and 2H isotopomers must be synthesized for this work. Two molecular systems are being studied: the cis and trans isomers of 1,3,5-hexatriene and the three isomers of 1,4-difluorobutadiene. Cooperation with scientists in the EMSL provides the essential high-resolution infrared spectra.
Project Details
Project type
Exploratory Research
Start Date
2011-10-01
End Date
2012-10-07
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Craig NC, HA Fuson, T Hengfeng, and TA Blake. 2012. "Analysis of the rotational structure in the high-resolution infrared spectra of trans-hexatriene-1,1-d2 and -cis-1-d1." PNNL-SA-84964, Pacific Northwest National Laboratory, Richland, WA.