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The diphosphine complexes cis - or trans -PtCl 2 (P((CH 2 ) n ) 3 P) ( n = b/12, c/14, d/16, e/18) are demetalated by MCX nucleophiles to give the title compounds (P((CH 2 ) n ) 3 )P (3b–e, 91–71%). These “empty cages” react with PdCl 2 or PtCl 2 sources to afford trans -MCl 2 (P((CH 2 ) n ) 3 P). Low temperature 31 P NMR spectra of 3b and c show two rapidly equilibrating species (3b, 86 : 14; 3c, 97 : 3), assigned based upon computational data to in , in (major) and out , out isomers. These interconvert by homeomorphic isomerizations, akin to turning articles of clothing inside out (3b/c: Δ H ‡ 7.3/8.2 kcal mol −1 , Δ S ‡ −19.4/−11.8 eu, minor to major). At 150 °C, 3b, c, e epimerize to (60–51) : (40–49) mixtures of ( in , in / out , out ) : in , out isomers, which are separated via the bis(borane) adducts 3b, c, e·2BH 3 . The configurational stabilities of in , out -3b, c, e preclude phosphorus inversion in the interconversion of in , in and out , out isomers. Low temperature 31 P NMR spectra of in , out -3b, c reveal degenerate in , out / out , in homeomorphic isomerizations (Δ G ‡Tc 12.1, 8.5 kcal mol −1 ). When ( in , in / out , out )-3b, c, e are crystallized, out , out isomers are obtained, despite the preference for in , in isomers in solution. The lattice structures are analyzed, and the D 3 symmetry of out , out -3c enables a particularly favorable packing motif. Similarly, ( in , in / out , out )-3c, e·2BH 3 crystallize in out , out conformations, the former with a cycloalkane solvent guest inside.
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This content will become publicly available on June 17, 2026
Ozonolysis Dissociation Kinetics for the Relative Quantification of Geometrical Phosphatidylcholine Isomers
The structural diversity of lipids presents significant challenges for accurate identification and characterization, ne-cessitating advanced analytical tools. Among these challenges is the differentiation between cis and trans isomers of lipids, which differ only by the geometry of a carbon-carbon double bond. This study employs ozonolysis kinetics to distinguish these isomers based on the reactivity of their gas phase ions with ozone. To achieve precise differentia-tion, it is essential to use an ion adduct that enhances reactivity, thereby improving the sensitivity of the kinetic assays. We evaluated various ion types, including protonated lipids as well as lipids cationized with lithium, sodium, and potassium, using a modified quadrupole ion trap mass spectrometer. Our results demonstrate that lithium-adducted lipids exhibit the highest reaction efficiency and greatest sensitivity for distinguishing between cis and trans isomers. Subsequent analysis of cis and trans isomer mixtures of PC 18:1/18:1 (Δ9), PC 16:1/16:1 (Δ9), and PC 14:1/14:1 (Δ9) confirmed the method's robustness.
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- Award ID(s):
- 2338651
- PAR ID:
- 10608626
- Publisher / Repository:
- ACS
- Date Published:
- Journal Name:
- Analytical Chemistry
- Volume:
- 97
- Issue:
- 23
- ISSN:
- 0003-2700
- Page Range / eLocation ID:
- 12171 to 12179
- Subject(s) / Keyword(s):
- Ozonolysis Lipid Stereochemistry Kinetics
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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