Residual solvent amplitude

Residual solvent amplitude Residual solvent amplitude is perhaps the most obvious parameter when judging the effectiveness of a suppression sequence. The magnitude of the remaining solvent resonance(s) is easily identified in the spectra and can be judged in comparison to the solute present in the sample. While certainly not the only criterion, it is indeed important and most sequences realize the need to suppress solvents such as water by a factor of 10 or 10 to bring samples into d)mamic range. 

Residual solvent signal amplitude is only one of the many criteria for evaluating suppression techniques. As spectroscopists, we are certainly interested in any baseline corruption that may result, as this will deter the ability to properly integrate and automatically interpret spectra. We also do not want the inclusion of spurious peaks, or the removal of actual information close to the solvent signal. 

Fig. 6.31 Normalised intermediate scattering function from C-phycocyanin (CPC) obtained by spin-echo [335] compared to a full MD simulation (solid line) exhibiting a good quantitative matching. In contrast the MD results from simplified treatments as from protein without solvent (long dash-short dash /me), with point-like residues (Cpt-atoms) (dashed line) or coarse grained harmonic model (dash-dotted line) show similar slopes but deviate in particular in terms of the amplitude of initial decay. The latter deviation are (partly) explained by the employed technique of Fourier transformation. (Reprinted with permission from [348]. Copyright 2002 Elsevier)...

The five N-terminal residues and the six or seven C-terminal residues cannot be seen in the high resolution electron density map, and the loop referred to above, formed by residues 44 to 53, appears at only one-third to one-half the amplitude of the well-resolved parts of the map. The lack of clarity in these three regions might possibly result from poor phasing or some other crystallographic factor, but we consider it more likely that these predominantly hydrophilic sections of the peptide project in a disordered way into the solvent. In this connection, it is interesting that in the presence of Ca2+ and pdTp trypsin cleaves inhibited nuclease at only two points between residues 5 and 6 and between residues 48 and 49 (36-38) which are at the very extremity of the loop. It also seems relevant that ribonuclease S also shows lack of clarity at the ends of the peptide chains and in the region of a relatively exposed loop (56). 

Polypeptides adopting a 3-structure exhibit CD spectra, the characteristic features of which are a negative band at about 216 nm ([ ] = -18,000) and a positive band of comparable magnitude near 195 nm (Figure 2). However, the CD spectra of (3-struc-tures show much more pronounced variations with solvent and amino acid residues than those of the a-helix, both in amplitude and in the position of the bands. In the presence of sodium dodecyl sulfate, the (3-form of poly(L-lysine), though still a 13-structure by infrared criteria, gives a 218 nm CD band only about half as large as that in the absence of the surfactant.[11]... 

Solid circles are the data points dashed line through the points is from a least-squares comparison of the Cole-Cole expression (Equation I), with the data. Two of the parameters of the fit are indicated A, the amplitude of the major dispensive contribution and D, the residual high field contribution. l/Tj-iy is the proton relaxation rale in protein-free solvent. The solid line that intersects the dashed line is a Lorentrian curve (Equation 2), obtained using the same values for A, D, l/Tiw and v,. as for solid line. After Ref. 7. 

The three-photon transition amplitude has been shown to be obtainable from the single residue of the appropriate CRF [27], although the technique has been employed only rarely. Lin et al. [247] analyzed for instance, solvent effects (accounted for by PCM) on the three-photon absorption spectrum of a symmetric charge transfer molecule using TD-DFT. 

---