Spectral simulations empirical

D-correlation spectra were collected. This information was used with empirical spectral simulations of proton and carbon spectra to elucidate the structures. The necessary information was thus provided to demonstrate that multiple dimer-like structures were formed through bonding of residual synthetic precursor to each of the hydroxyl sites of the drug substance itself. Three distinct dimers were identified. These species were tracked by LC-NMR, and two were shown to interconvert over time. Analogous trimer structures were also evident at lower levels. 

The SG uses the empirical formula along with Goodlist and Badlist to generate exhaustively but without redundancy a list of candidate structures for the form of the substance which gave rise to the mass spectrum. These candidates, consonant with the empirical formula, Goodlist and Badlist are then given as input to the third phase of HDP, the spectral simulator, called the Predictor. 

In Sect. 4, some methodical aspects will be investigated, addressing the relative size of intra- and zntermolecular contributions to the chemical shift (Sect. 4.1), the influence of the endgroups on the results (Sect. 4.2), the significance of the atomic basis and the empirical forcefield (Sect. 4.3), as well as some more general remarks on the preconditions of spectral simulation in disordered systems (Sect. 4.4-4.6). 

This benefit comes at a cost, which arises from significantly reduced S/N and some interpretive difficulty as compared to IR. Developments on the latter front are bringing the theoretical prediction capability of VCD for small molecules to a level demonstrably superior to that for ECD (Freedman and Nafie, 1994 Stephens et al., 1994 Stephens and Devlin, 2000), especially for peptide spectra (Kubelka et al., 2002). Most previous protein applications of VCD used empirically based analyses (Keiderling, 1996, 2000). Theoretical methods are limited when applied to large molecules such as proteins however, a hybrid approach using ab initio determination of spectral parameters with modest-sized molecules for transfer to large peptides has made simulation of spectra for large peptides possible (Bour et al., 1997 Kubelka et al., 2002). Theoretical techniques for simulation of small-molecule VCD are the focus of several previous reviews (Stephens and Lowe, 1985 Freedman and Nafie,... 

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