Spectrum enhancement

Friedrich B and Herschbach D 1996 Alignment enhanced spectra of molecules in intense non-resonant laser fields Chem. Phys. Lett. 262 41... 

Photoluminescent spectra for methyltetrahydrofolate and the enzyme methyltransferase. When methyltetrahydrofolate and methyltransferase are mixed, the enzyme is no longer photoluminescent, but the photoluminescence of methyltetrahydrofolate is enhanced. (Spectra courtesy of Dave Roberts, DePauw University.)... 

F ure 10. solid-state NMR spectra of calcium pectate in the solid (A) and gel (B) forms. Inset resolution-enhanced spectra. The gel concentration was 290 g/1. 

VCD and FTIR spectra should always be obtained on the same samples, the FTIR at higher resolution and optimized S/N to permit computation of deconvolved (resolution-enhanced) spectra (Kauppinen etal., 1981). VCD spectra of biomolecules are often normalized to the absorbance, since concentration and path lengths are rarely known to good accuracy. Because the absorbance coefficients for different molecules will vary, this is only an approximate correction for concentration variation. 

Nuclear Overhauser effect—The nuclear Overhauser effect (NOE) occurs only between nuclei that share a dipole coupling, i.e., their nuclei are so close that their magnetic dipoles interact. Techniques that use NOE enhance spectra and allow spacial relationships of protons to be determined. 

Almost all spectra were acquired on a AMX-600 Bruker NMR spectrometer equipped with a 5 mm inverse broad-band probe. The only exception were the gradient-enhanced spectra acquired on an INOVA-600 Varian NMR spectrometer using a 5 mm triple-resonance probe with z gradients. The experimental details are given for each spectrum in the figure captions. 

It is evident that relaxation studies in the solid state can look at the motions which are responsible for the mechanical properties of the cured epoxy systems 43). Therefore, Garroway, Moniz and Resing continued to do relaxation studies 61). Garroway, et al. looked at four epoxy polymers based on the DGEBA resin. Two of the epoxy resins were cured with amines and the other two were cured with anhydrides. Proton enhanced spectra of the epoxy systems were generated. The solid state spectra were compared to the solution spectra of the unreacted epoxy. The< epoxy resin of interest was again DGEBA which was reacted with ... 

Hx-X, with X = He, Ne, Ar, Kr, or Xe. At sufficiently low densities, mixtures of monatomic and diatomic gases such as helium and hydrogen feature two types of CIA spectra one arising strictly from H2-H2 pairs and the other from H2-He pairs. (Of course, there are no spectral components arising from He-He interactions.) From exact measurements of the CIA spectra of both, the pure molecular gas and the mixture, the enhancement spectra due to H2-He pairs are obtained by subtracting the spectrum of pure hydrogen from the total absorption obtained in the mixture of helium and hydrogen [37], Fig. 3.12. 

Measurements of enhancement spectra exist for several gases and mixtures. Figure 3.14 shows the collision-induced absorption spectra of H2-X pairs, with X = He, Ne, Ar, Kr, Xe [213]. The translational lines were omitted for technical reasons. Because the spectra are recorded at room temperature, the So(J) lines of H2 are quite diffuse. Most prominent is the So(l) line at 587 cm-1, but lines at other rotational transition frequencies of H2 are also discernible, for example So(0) at 354 cm-1, So(2) at 815 cm-1, and So(3) at 1035 cm-1, especially for the massive pairs. 

H2-X where X is a molecule. If a molecule other than H2 is chosen as the collision al partner X, new absorption bands appear at the rotovi-brational bands of that molecule. As an example, Fig. 3.17 shows the rototranslational enhancement spectra [46] of H2-CH4 for the temperature of 195 K. At the higher frequencies (v > 250 cm-1), these look much like the H2-Ar spectrum of Fig. 3.10 the H2 So(J) lines at 354, 587, and 815 cm-1 are clearly discernible. Besides these H2 rotational lines, a strong low-frequency spectrum is apparent which corresponds to the (unresolved) induced rotational transitions of the CH4 molecule these in turn look like the envelope of the rotational spectra seen in pure methane, Fig. 3.22. This is evident in the decomposition of the spectrum, Fig. 3.17, into its main components [46] the CH4 octopole (dashed curve) and hex-adecapole (dot-dashed curve) components that resemble the CH4-CH4 spectrum of Fig. 3.22, and the H2 quadrupole-induced component (dotted curve) which resembles the H2-Ar spectrum, Fig. 3.14. The superposition (heavy curve) models the measurement (big dots) closely. Similar spectra are known for systems like H2-N2 [58]. 

The binary enhancement spectra of hydrogen-helium mixtures in the... 

Figures 6.21 and 6.22 below (p. 345) show calculations of the three lowest moments of the H2-He enhancement spectra of the fundamental band (left panels). The range of temperatures is a much wider one than those of Table 6.2. We notice that with increasing temperature, the differences between the moments computed with and without the corrections for the vibrational dependences of the interaction potential (solid and dashed lines, respectively) increase substantially for the first moments and decrease for the second moments to the point of insignificance.

Table 6.5. Temperature dependence of the moment of the enhancement spectra of hydrogen-helium mixtures in the fundamental band of H2. The superscripts 12 and 122 stand for H2-He and H2-He-He the term M 122 = M H2 He H9 + M H2—He—He)//. ancj sjmjiar for M n Units are 10-35 J amagat N and 10-22 W amagat N for the zeroth and first moments, with JV = 2 for the binary and N = 3 for the ternary moments [296].

To obtain spectra, equation 21 is used, with the elements of the Green s tensor obtained frcnn equation 19 and 25, and the initial density matrix elements from equation 23. Enhanced spectra are calculated using the results from CDE, as shown in the previous section. The results are seen in Figure 3.5. 

The best method to use for the estimation of protein secondary structure involves band-fitting the amide I band. The parameters required, and the number of component bands and their positions are obtained from the resolution-enhanced spectra. The fractional areas of the fitted component bands are directly proportional to the relative amounts of structure that they represent. The percentages of helices, -structures and turns are estimated by addition of the areas of all of the component bands assigned to each of these structures and then expressing the sum as a fraction of the total amide I area. The... 

Nuclear Overhauser Enhancements. Nuclear Overhauser enhancements (1 -I- ij) of the mobile carbons were measured using the gated decoupling technique IS). The pulse repetition rate for both the Overhauser-suppressed and Overhauser-enhanced spectra was 8 s. Peak integrations were used to determine the NOE. 

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