Molecular deconvolution

Enantioresolution in capillary electrophoresis (CE) is typically achieved with the help of chiral additives dissolved in the background electrolyte. A number of low as well as high molecular weight compounds such as proteins, antibiotics, crown ethers, and cyclodextrins have already been tested and optimized. Since the mechanism of retention and resolution remains ambiguous, the selection of an additive best suited for the specific separation relies on the one-at-a-time testing of each individual compound, a tedious process at best. Obviously, the use of a mixed library of chiral additives combined with an efficient deconvolution strategy has the potential to accelerate this selection. 

Figure 10.4 All spectra obtained between 20 and 66 minutes are combined into a single spectrum and then deconvoluted using MaxEnt 1. The resulting molecular weight spectrum is noisy and hampers the identification of low abundance proteins. The asterisks indicate where proteins of mass 7274 and 10652 should be observed but are not.

Natural products continue to demonstrate their utility both as therapeutics and as molecular probes for the discovery and mechanistic deconvolution of various cellular processes. However, this utility is dampened by the inherent difficulties involved in isolating and characterizing new bioactive natural products, in... 

The copolymer prepared without DEZ is clearly shown to be bimodal by GPC, with MJMn = 13.8 (Fig. 16). The GPC trace was deconvoluted into components of Mw 240,000 and 9600 g mol reflecting the differing propensities for hydrogen-induced termination between the two catalysts. The molecular weight distribution narrows as DEZ is added, as expected for an efficient chain shuttling polymerization ... 

Example The ESI mass spectrum and the charge-deconvoluted molecular weights (inset) of bovine serum albumine (BSA) as obtained from a quadrupole ion trap instrument are compared below (Fig. 11.19). Ion series A belongs to the noncovalent BSA dimer, series B results from the monomer. [24]... 

Fig. 11.19. Partial ESI mass spectrum of BSA and molecular weights after charge deconvolution (inset). Charge states are assigned to both series of peaks. Reproduced from Ref. [24] by permission. John Wiley Sons, 2000.

The relative molecular mass determination of an unknown protein is generally performed automatically using various deconvolution algorithms, but the procedure is limited to relatively simple mixtures. 

Fig. 1.10 (A) Positive mode electrospray spectrum of human gamma interferon on a quadrupole mass analyzer. (B) Deconvoluted spectrum of human gamma interferon. The molecular mass was measured at 16908 2 Da.

Table 3.1 A portion of the membership of the ALIS screening library, composed of NG LI 27A443 (library 3 in this table) and four other libraries, which yields DHFR ligand 1 (NCD-157, entry 11). Compounds of similar exact molecular weight (EMW) are distributed among the five pooled libraries to minimize mass overlap and simplify hit deconvolution. Reprinted from [40] with permission from Elsevier.

There are many facets of this study which we feel merit further investigation. In particular it is necessary to consider am extension of the proposed model, which in its present form is confined to the performance of a simple column, to cover the behaviour of any set of columns since it is column sets which are normally used. In addition, it is important to consider the input to the model which should be truly representative of polymers with a molecular weight distribution and not merely a concentration pulse of perfectly monodisperse polymer. In relation to this latter suggestion it would be significant if it were possible to link this model to the very real problem of deconvolution, i.e. the removal of instrumental and column broadening from the observed chromatogram to produce the true molecular weight distri-... 

In liquids the interactions between neighboring molecules are considerably more complicated than in gases. The resultant broadening obliterates the fine line structure seen in gas spectra, leaving only broad band profiles. There are many possible contributors to this broadening. In some cases, adequate approximation is obtained by assuming that the band contour is established by collisions. Ramsay (1952) has noted that substitution of appropriate molecular density and collision diameter numbers in the collision broadening formula results in realistic band widths for certain liquid-phase systems. In such systems, the bands typically show an approximately Lorentzian profile. Approximate deconvolution of inherently broadened liquid-phase spectra may therefore be obtained on the basis of the assumption of Lorentzian shape (Kauppinen et al., 1981). 

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