Dichroic function

Fig. 40. Computer-plot of the dichroic functions of the 1126 cm and 1662 cm absorpticai bands monitored during two independent elongation half-cycles (D/A) of sulfiir-crosslinked natural rubber at 300 K...

Fig. 43. Dichroic functions of the 1126 cm" ( ) and 1662 cm ( ) absorption bands monitored during the elongation/stress-relaxation sequence of Fig. 41...

Fig. 24. Dichroic ratios (A /A X) and stress (a) as function of strain (e) (stretching velocity 0.008 mm/s.x CH2-rocking band (BJp) between 736 and 726 cm"1, V CH2-rocking band (B2)j) between 726 and 710 cm"1, + stress-strain-diagram.

The response of ion-containing ethylene-methacrylic add copolymers has also been investigated 306). The strain amplitude of the samples was 2% and the period of external stress was 50,000microseconds. Changes in the dichroic ratio of the 2673 cm "1 band were observed as a function of strain in times as short as 200 microseconds. Other spectroscopic changes were observed but not interpreted in terms of structural changes. 

Fig. 11. (a) Far ultraviolet rotatory dispersion of ribonuclease. Corrected mean residue specific rotation vs. wavelength [to R = [aLAf/100 [3/(n2 + 2)l where a — specific rotation, M mean residue weight, and n = solvent refractive index. Bars give maximal deviation at peaks. Reproduced from Jirgensons (311). (b) Near ultraviolet rotatory dispersion of 0.48% pancreatic ribonuclease in a 1-mm cell, in (a) 0.15 M phosphate buffer at pH 62 (b) 0.15 M glycine-NaOH buffer at pH 11.5 (c) 0.1 N HC1 (d) 15% sodium dodecyl sulfate. Reproduced from Glazer and Simmons (313). (c) Far ultraviolet circular dichroic spectra of RNase-A, RNase-S, and S-protein at 25° and 3°. Reproduced from Pflumm and Beychok (313). (d) Near ultraviolet circular dichroic spectra of RNase-A as a function of pH. Reproduced from Pflumm and Beychok (313). 

The dichroic ratio is also the following function of the angle Q that the dipole makes with the stretching direction,... 

Equation (167) has been derived assuming the dichroic ratio S2(x) to be independent of the absorption coefficient of the polymer, and S2 per monolayer to be constant for any location within the LED, assumptions which may not always be justified. The relative EL output as a function of the distance from the A1 cathode can thus be obtained by differentiation of the measured relative emission from the parallel organized layer, fix), as given by the right-hand side of Eq. (167). The calculation of Afix)/Ax, made with Ax = 12 nm (10 monolayers) for the ITO/PPP/A1 devices with x varying between 0 and 120 nm, is shown in Fig. 62. Such a calculated profile, like that in single... 

This technique was employed to monitor the B —> A transition of DNA as a function of the relative humidity (Pilet and Brahms, 1973 Pohle et al., 1984). The investigated bands are those which reflect the vibrations of the phosphate groups. As shown by Fig. 4.7-3, which presents the polarized infrared spectra of a salmon sperm DNA hydrated film with 93% RH (top, B form) and 58% RH (bottom, A form), the dichroism of the two phosphate bands changes. The B form of the antisymmetric PO2 stretching vibration around 1230 cm is non-dichroic, while that of the A form is perpendicular. The B form of the symmetric PO2 stretching vibration around 1090 cm is perpendicular, while that of the A form is parallel. A simple computation, for instance for the latter band, shows that the value of the angle between the transition dipole moment of this vibration and the double helical axis varies between 68 ° (B form) and 49 ° (A form). This parameter is an extremely sensitive indicator of a B A transition and may also be employed to show the inhibition of a B —> A transition by various classes of molecules, such as proteins (Liquier et al., 1977 Taillandier et al., 1979) or drugs (Fritzsche and Rupprecht, 1990). 

Tron, T., Crimi, M., Colson, A. M., and Degli Esposti, M., 1991, Structure/function relationships in mitochondrial cytochrome b revealed by the kinetic and circular dichroic properties of two yeast inhibitor-resistant mutants, Eur. J. Biochem. 199 753n760. 

Table 3 summarizes some of the properties of PS I reaction center and specific functions of its individual subunits. The purified preparation contains about 100 Chi a molecules per P-700 [9,10]. However, this number can be decreased to about 40 while the order of the Chi a molecules increases [70]. Washing out more of the Chi molecules caused a decrease in the dichroic ratio, indicating that those 40 Chls are the highly oriented primary light-harvesting antenna of the reaction center. It was also shown that the S-carotene is in very close proximity to P-700 and it is highly oriented with respect to the latter [70]. P-700 as well as the primary electron acceptor (Aj) may be composed of specialized Chi a molecules [80]. There are at least three more electron acceptors which are part of the reaction center and their function is to slow down the rate of the reaction and thereby stabilize the redox potential difference [72]. It was not until Malkin and Bearden [81] discovered the bound ferredoxins that this part of PS I started to be understood. Today it appears that at least four different clusters are involved in the electron-accepting site of the... 

The orientation function is related to the dichroic ratio R by [5] ... 

PI-1 and PI-2 films exhibit dichroic absorbance after polarized irradiation. Figure 4.15 shows polar plots of the absorbance of linearly polarized probe light (at 488 nm) as a function of the angle, between the polarization of the probe and irradiation light (532 nm 30 mW/cm ). Nonpolar orientation is clearly shown for both PI-1 (left) and PI-2 (right). The highest absorption is observed when the probe and irradiation beams have perpendicular polarizations,... 

A detailed analysis of the UV-VIS spectrum of (spinach) plasto-cyanin in the Cu(II) state has been reported (56). A Gaussian resolution of bands at 427, 468, 535, 599, 717, 781, and 926 nm is indicated in Fig. 7. Detailed assignments have been made from low-temperature optical absorption and magnetic circular dichroic (MCD) and CD spectra in conjunction with self-consistent field Xa-scattered wave calculations. The intense blue band at 600 nm is due to the S(Cys) pvr transition, which is intense because of the very good overlap between ground- and excited-state wave functions. Other transitions which are observed implicate, for example, the Met (427 nm) and His (468 nm) residues. These bonds are much less intense. The low energy of the d 2 orbital indicates a reasonable interaction between the Cu and S(Met), even at 2.9 A. It is concluded that the S(Cys)—Cu(II) bond makes a dominant contribution to the electronic structure of the active site, which is strongly influenced by the orientation of this residue by the... 

Perhaps the simplest (but not the first) example of this approach is a direct descendant of the 180° geometry used in microscopes (Fig. 6.3). A partially reflective mirror or dichroic mirror combines the excitation and collection axes, as shown in Figure 12.18 for a probe built by DLT, Inc. This mirror is commonly referred to as a beamsplitter, even though its function is... 

Figure 3.19. Absolute determination of 8 by in situ autocorrelation. Experiments were performed with a mode locked femtosecond Ti sapphire laser. A prism pair (PC) was used to compensate the group delay dispersion (GDD) of the microscope objective. A long-pass filter eliminates residual argon pump light and Ti sapphire fluorescence. After two sequential beam expanders (BE), the beam was approximately 25 mm in diameter, which was sufficient to overfill the back aperture (10-mm diameter) of the objective. A long-pass dichroic mirror (DC) with reflectivity separates fluorescence from excitation light. The incident power at the sample was measured by recollimating the transmitted beam onto a calibrated power meter. Fluorescence was detected by a photomultiplier tube and recorded as a function of the interferometer delay. (From Ref. [366] with permission of the Optical Society of America.)...

The uniaxial PF2/6 alignment can be quantified in terms of the mean-field theory discussed previously. The degree of alignment in equilibrium (f2) is a function of the number-averaged molecular weight (M ) as described by Eq. 6. This prediction has been studied by photoabsorption in [55] and there it has been shown that the solid angle T2 is expressed in terms of the dichroic ratio in absorption (R) as... 

Fig. 26 Dichroic ratios in absorption (R) as a function of Mn as measured at 380 nm. The open squares correspond to the samples annealed at 80 °C for 10 minutes and the solid squares those at 180 °C for 18 h. A dotted line shows M, the Nem-Hex transition point of PF2/6. An inset shows the region of an exponential drop between Mn = 104-105 g/mol and a linear fit. Reprinted with permission from [55]. (2005) by the American Chemical Society...

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