Abstract
For analysis of weak π–π complexes proton-nuclear magnetic resonance (proton-NMR) simultaneously provides information of stacking configurations and association constants left( K right) However, an apparent issue for this approach is inconsistent/impossible constant estimation which often leads to unreasonable interpretation for π–π complexation. Whether or not this proton-dependent constant variation could be attributed to simple experimental uncertainties or to more sophisticated additional unspecific shielding effects (AUS effects) was addressed by means of hypothesis tests using a robust bootstrap technique in this report. Our analysis shows the significance of AUS effects on such variation in constant estimation. A following study using numeric simulation further reveals the variation patterns induced by AUS effects and concludes that the largest K among the obtained K estimates of a complex is considered as the best estimate of K due to minimum deviation from the true value of K and the multiple K estimates of a π–π complex could provide preferable inferences for complex geometries.
Highlights
IntroductionSelf-assembled π electron acceptor–donor molecular complexes (π–π complexes) have been intensively studied in broad fields including conformational structures of biomolecules like DNA, RNA and proteins [1,2,3,4,5,6,7], and design and quantitative analyses [8,9,10,11,12] for drug overdose remediation [13,14,15]. π–π complexes usually involve complexation between a π electron donor and a π electron acceptor
Despite that the statistical analysis adopted in those historical data treatments is not clarified, we assumed that t-test is most likely used for the treatment of observed different K estimates
When proton-NMR is used for analysis of such π–π complexes, upfield shifts of observed protons are often treated as a characteristic of complexation
Summary
Self-assembled π electron acceptor–donor molecular complexes (π–π complexes) have been intensively studied in broad fields including conformational structures of biomolecules like DNA, RNA and proteins [1,2,3,4,5,6,7], and design and quantitative analyses [8,9,10,11,12] for drug overdose remediation [13,14,15]. π–π complexes usually involve complexation between a π electron donor and a π electron acceptor. Lin et al BMC Chemistry (2020) 14:66 It means that K values are proton independent and the experimentally obtained various upfield shifts ( , the difference between the chemical shifts of acceptor protons in the absence and in the presence of donors) primarily result from the difference in C induced by the offset geometry of a complex [17, 19,20,21]. Despite that the statistical analysis adopted in those historical data treatments is not clarified, we assumed that t-test is most likely used for the treatment of observed different K estimates. The numeric simulation provides useful information for treatment of inconsistent K estimates and a new approach for geometric inferences without the need of changing experimental conditions. The results and the complex geometric inferences are presented in “Discussion” section
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