CD spectra of

Fig. 2.2. CD spectra of (S)- and (R)-2 amino-l-phenyl-l-propanone hydrochloride. [Reproduced with permission from Helv. Chim. Acta 69 1498 (1986).]...

The substance chaetochromin A, structure A, has been shown by X-ray dif action to have the absolute configuration indicated in the structure. The CD spectra of A and the related compounds cephalochromin (B) and ustilaginoidin (C) are shown in the figure. Deduce the absolute stereochemistry of cephalochromin and ustilaginoidin trom these data, and draw perspective structures indicating the absolute configuration. 

Fig. 2. CD-spectra of (L-Lys HBr) in reversed micellar systems of AOT/octane/H20 at different w0-values 65). T 20 °C...

Fig. 13. CD-spectra of random and alternating (L-Leu, L-Lys) u2, u(. a) in water b) in trifluoro-ethanol...

Fig. 14. CD-spectra of alternating (L-Leu-L-Lys) in water-methanol mixtures at different pH of the starting solution "2-"9)...

Fig. 15. CD-spectra of random (L-Leu0,48, L-Lys0,52) in water-methanol mixtures as a function of methanol concentration at 20 °C and pH 7,0. The insert shows [0]2O8 and —[0]2jo dependent on the methanol content112113 ...

Neutral salt-soluble collagen as well as add-soluble collagen show a CD spectrum (Fig. 8) having bands at 198 nm, 0 = -53 (MX) (deg cm2 dmol-1), and at 223 nm, 0 = 7500 (deg cm2 dmol-1), the ratio between both being 7 1. Pysh has calculated the CD spectra of a-helix, -structure, polyproline I and II127 ... 

Fig. 8. CD spectra of collagen in 0.01 m acetic add. (A) At 24 °C in the native state, (B) at 44 °C in a randomly coiled state. Data from Piez et al.la)...

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. 

Fig. 1.6 A comparison of the CD spectra of oligopeptoids with achiral Npm side chains (1) and with a-chiral, aromatic sidechains of S and R chirality (2 and 6, respectively). Sample concentration was 60 j,M in acetonitrile. Spectra were acquired at room temperature. Npm = (N-[l-phenylmethyljglycine) Nspe= (S)-N-(l -phenylethyl)glycine Nrpe= (R)-N-(l -phenylethyl)glycine...

Surprisingly, in contrast to a- and y9-peptides, CD spectra of y-peptides gave only a very hmited amount of stmctural information. Experiments conducted on heh-cal y" -hexapeptides did not reveal any characteristic CD signature (no Cotton effect) [200, 201]. Similarly, y -peptides built from 2,4-disubstituted y-amino acids of like configuration and shown to adopt a more stable 2.6-helical structure, do not display typical CD curves either [201]. However, CD spectra of the 2.6-helical -peptide 147 and its Boc-protected derivative recorded in MeOH and CD3CN present an intense maximum around 215 nm with a shoulder at ca. 200 nm [207]. 

As a prelude to our binding studies, the secondary structure of aPNA itself was examined using CD spectroscopy [52]. The first aPNA to be studied was the tail-to-tail bl dimer, [Ac-Cys-Gly-Ser -Asp-Ala-Glu-Ser -Ala-Ala-Lys-Ser -Ala-Ala-Glu-Ser -Ala-Aib-Ala-Ser -Lys-Gly-NH2]2- The far-UV CD spectra of this aPNA in water at 30 °C showed the double minimum at 220 nm (n-n transition) and 206 nm (n-n transition) as well as the maximum at 193 nm (n-n transition), characteristic of a peptide a-hehx. Upon increasing the temperature, the intensity of the minimum at 200 nm decreased indicating a transition from a-helix to random stracture. An isodichroic point at 202 nm was suggestive of a temperature-depen-dent a-helix to random coil transition. The helical content of this T5(bl)-dimer at 20°C in water was estimated to be 26% [40]. 

Next, the CD spectra of the backbone 2 aPNA Ac-Cys -Lys-Ser -Ala-Ala-Lys-Ser -Ala-Ala-Lys-SerhAla-Ala-Lys-Ser -Ala-Ala-Lys-Ser -Gly-Lys-NH2, was measured as a function of pH in phosphate buffer. At pH 7, the secondary structure of this aPNA was largely random coil. However, the a-hehcity of this aPNA increased with the pH until it reached a maximum at pH 11. Analogous pH-depen-dent secondary structure has also been reported for the amphipathic KALA peptide Trp-Glu-Ala-Lys-Leu-Ala-[Lys-Ala-Leu-Ala]2-Lys-His-Leu-Ala-Lys-Ala-Leu-Ala-Lys-Ala-Leue-Lys-Ala-Cys-Glu-Ala-OH [53]. In our case however, maximum a-helicity... 

CD spectroscopy has been used extensively to study peptide-nucleic acid interactions. Conformation changes induced by either the peptide or nucleic acid can be detected readily using this spectroscopic technique. Although the CD spectra of... 

Fig. 5.5 CD spectra of (a) DNA d(A3GGAGGA3) alone, (b) aPNA CCTCC(b2) alone, and (c) a 1 1 mixture of d(A3GGAGGA3)-rCCTCC(b2) (6 pM each) in HjO. (See [51] for experimental details. Reprinted with permission from Garner P, Dey S, Huang Y. /. Am. Chem. Soc. 2000, 122, 2405)...

These CD studies confirmed the binding stoichiometries of our aPNA-DNA complexes and provided further support for our binding model. Comparisons between the CD spectra of the individual components and the aPNA DNA complex suggest a template effect (not unhke that observed with certain DNA-binding proteins) where the components induce mutual conformational changes upon their interaction with each other. 

Pi 1-2 was found to form self-supporting gels at a concentration of approximately 15 mg mL in pH-neutral water. In water, circular dichroism (CD) spectra of the... 

Such differences in the secondary structure behavior with respect to temperature can be explained by suggesting that molecular close packing of proteins in the film is the main parameter responsible for the thermal stability. In fact, as in the case of BR, we have close packing of molecules even in the solution (membrane fragments) there are practically no differences in the CD spectra of BR solution at least tiU 75°C (denaturation takes place only for the sample heated to 90°C). RC in solution begins to be affected even at 50°C and is completely denatured at 75°C, for the solution contains separated molecules. 

The fact that CD spectra of BR in LB and self-assembled films show similar behavior with respect to temperamre is also not strange. Because the basic block of the fihn in both cases is the membrane fragment, which is already closely packed, there is no principal difference between these samples with regard to packing. The difference in the distribution of these fragments cannot be critical for thermal stability. 

In the case of RC there are big differences in the temperature dependencies of CD spectra of LB and self-assembled films. The differences are due to the different organization of molecular structures in the fihn. In the case of self-assembled films, the molecules... 

Other spectroscopic properties such as nuclear magnetic resonance (NMR), mass spectrometry (MS), infra-red (IR), and circular dichroism (CD) spectra of chlorophyll compounds and derivatives have been valuable tools for structural elucidation. - ... 

The availability of the purified transporter in large quantity has enabled investigation of its secondary structure by biophysical techniques. Comparison of the circular dichroism (CD) spectrum of the transporter in lipid vesicles with the CD spectra of water-soluble proteins of known structure indicated the presence of approximately 82% a-helix, 10% ) -turns and 8% other random coil structure [97]. No / -sheet structure was detected either in this study or in a study of the protein by the same group using polarized Fourier transform infrared (FTIR) spectroscopy [98]. In our laboratory FTIR spectroscopy of the transporter has similarly revealed that... 

Circular dichroism (CD) is another interesting example of an optical property of the small Au SR clusters. Since the first observation of Schaaff et al. [23,24], several reports have appeared regarding the CD activities of gold clusters protected by chiral thiols such as penicillamine [25] and A-isobutyryl-cysteine [26]. Figure 11 shows the CD spectra of 1-9, which is a good reproduction of the original report by Whetten s group [23,24]. 

The introduction of Py at the 2 sugar position of uridine and Ptz at the 5 -end of ODN caused an increase in Tm. The Tm for PtzPy-1 is 39.4 °C, which is 6.9 °C higher than that of unmodified ODN (32.5 °C). Similarly, the introduction of Ptz or Py into ODN showed increases in Tm for Ptz-1 (1.2 °C) and for Py-1 (6.6 °C) compared with unmodified ODN, suggesting that Py intercalated into ODN duplex at the 3 -side, and the 5 -linked-Ptz associated with the 5 -terminus by end-capping [5]. The structures of ODNs conjugated with Py and Ptz were examined by circular dichroism (CD) spectral measurements. The CD spectra of ODNs in 20 mM phosphate buffer were characteristic of the B-form. 

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