Conformation-dependent charge distributions

Grandori, R. Origin of the conformation dependence of protein charge-state distributions in electrospray ionization mass spectrometry. I. Mass Spectrom. 2003,38, 11-15. 

An empirical increment system permits prediction of charge distribution in a,/ -unsaturated carbonyl compounds, assuming additivity of electronic effects and neglecting the conformational dependence of carbon-13 chemical shifts [290]. Moreover, carbonyl and alkenyl carbon shifts of a, /3-unsaturatcd ketones may be used to differentiate between planar and twisted conjugated systems, as shown in Table 4.29 [291] and outlined for phenones in Section 3.1.3.8. 

U. Koch and A. J. Stone,/. Chem. Soc., Faraday Trans., 92, 1701 (1996). Conformational Dependence of the Molecular Charge Distribution and Its Influence on Intermolecular Interactions. 

As an ion travels through the drift gas, there are several types of interactions between the ion and the nentral molecules of the drift gas (see Chapter 10). These interactions depend on the characteristics of the ion (size, total charge, charge distribution within the ion, and shape) and the drift gas molecnle (size, dipole and qnadrnpole moments, and polarizability). The magnitude of these interactions determines the drift velocity of the ion, namely, the mobility. This is the basis for elncidation of ion structure or conformation from mobility measurements and has been applied to elncidate the strnctnre of small ions like anilines and diamines as well as that of large ions like protonated polyglycine and polyalanine. ... 

We point out to the reader that DMA provides an expansion— rather than a fit—of the charge density. As such, the individual MTP coefficients derived from DMA will not depend on the order of the expansion. Despite its overwhelming use in the field, the method suffers from being tied to a single conformation Koch et al. showed that MTP can be highly conformation dependent [57] and may thus show a lack of transferability across the distribution... 

Because proteins play key roles in nearly all biological processes, their physicochemical properties have attracted scientists worldwide and been the subject of extensive study for decades. It is, therefore, impossible to cover all physicochemical properties of proteins in this section. Physicochemical properties that govern a protein s surface activity include protein size, shape, amino acid composition, net charge and charge distribution, amino acid sequence and their higher structure, surface hydrophobicity or hydrophilicity, and molecular flexibility and rigidity. All these properties are related to the amino acid composition and sequence of proteins. The structure and functions of proteins depend on their amino acid sequences and the dynamic behavior of protein conformations. 

---