Negative bands

The CD spectra reveal several distinct features that are highly significant for both Rieske and Rieske-type clusters. The CD spectra of the oxidized proteins show two positive bands between 310 and 350 nm, a negative band at 375-380 nm, and a set of positive bands between 400 and 500 nm. The CD spectra of the reduced proteins show positive bands at 314 nm, a negative band at 384-390 nm and a negative band around 500 nm. 

In its reduced state, the paramagnetic Rieske cluster shows a temperature-dependent MOD spectrum composed of numerous positive and negative C-terms that originate from the 8 = 1 ground state. The MOD spectra lack the Fe" 8 charge transfer bands that are observed as intense negative bands between 300 and 350 nm and a posi-... 

Extensive studies have been performed on the (1- 6)-)8-D-glucan (pustulan) and the (l- 4)-a-D-glucan (amylose). These are linear polysaccharides that may exist as helical polymers in aqueous solution, as demonstrated by c.d. spectroscopy. Characteristic of the helical structure of these glucans is a negative band at 182 nm, a crossover at 177 nm, and a more intensely positive band at shorter wavelengths (see Figs. 8 and 9). 

Buffington and Stevens measured the c.d. of 2-acetamido-2-deoxy-D-glucose as a film cast from HFIP. The spectrum is considerably more intense than that observed by Dickinson and coworkers for a solution in HFIP, but shows the same general features shifted somewhat towards the red. This vacuum-u.v. c.d. spectrum (see Fig. 18) has, at 218 nm, an intense, positive band due to the mr, an intense negative band due to the amide tttt at 200 nm, and a shoulder at 180 nm, but no other significant features down to 145 nm. 

A change in potential can cause any of several effects, including migration of ions into or out of the thin layer, adsorption, desorption, and faradaic reactions consuming or producing species adsorbed on the surface or in solution. For these reasons a difference spectrum (see Eq. (1.3) can exhibit both negative bands due to species formed and positive bands due to species consumed at the sample potential. 

Fig. 3 shows the spectra of a 50% Raney Ni catalyst (1000 scans, recorded with the sample in air). The uncompensated spectrum S shows, as do other spectra S which follow, a prominent negative band due to atmospheric CO2 the "noise" near 3700 cm l and in the 2000-1300 cm l region is due to the negative... 

The ratioed, scale-expanded insert shows these more clearly. There is a negative band caused by the gaseous SO2 upon which a positive doublet is superimposed. Pumping at room temperature caused the doublet to disappear. The 1375 and 1358 cm l bands are attributed to SO2 weakly coordinated to surface oxide ions... 

Due to the variety of (3-turn types, and the range of qp,ip values at each of the a-carbons involved in the turn, there is no unique CD signature that characterizes (3-turns. Theoretical calculations 125 on a wide range of (3-turn conformations 126 led to the prediction that a variety of CD spectral types could be associated with (3-turns, but one type of spectrum was most prevalent. This type (class B) has a weak negative band between 220 and 230 nm, a... 

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