Circular dichroism spectrum measurement

Fig. 6.—Measured Circular Dichroism Spectrum (-----), Calculated Circular Dichroism...

The determination of the absolute configuration of a carotenoid is only possible by circular dichroism (CD) measurement. The spectrum interpretation can only be done by comparison with reference or model compounds with known chiralities. The sample requirement is as low as 5 to 50 pg, but CD facilities are not so commonly available. Buchecker and Noack reported experimental aspects and discussion of the relationships of carotenoid structures and CD spectra. 

To confirm the importance of ester linkage for chiral formation, we conducted vibrational circular dichroism (VCD) measurements [64]. FT-IR spectrum of this molecule shows many C=0,0-C-O related peaks in addition to peaks of N=N and phenyl and CH2 vibrational modes, as shown in Fig. 22a. It is noted that strong VCD signals are observed in C=0 and O-C-O vibrations, as shown in Fig. 22b. This implies that ester linkage is strongly related to the chiral structure. 

M(A-A)3 complexes are optically active, and the problem can be remedied if a circular dichroism spectrum of one enantiomer can be measured and the sharp electronic lines identified. The bite and twist angles have very different effects on the rotational strengths. The twist angle has a marked effect that is quite plausible when one considers that a 60° twist causes conversion to the opposite enantiomer. Sign changes in the rotational strength can also occur at twist angles near / = 0°. 

The magnetic circular dichroism spectrum of thioxanthone and the circular dichroism spectrum of its inclusion complex with cyclodextrin have been measured and interpreted with the aid of PPP and CNDO/S calculations. The first jtJt state exhibits intramolecular charge transfer characteristics <1994JPC10432>. 

There have been detailed studies on the electronic absorption spectrum of the gas, and the magnetic circular dichroism spectrum has also been recorded and assigned 577,578,580 such spectra were also obtained for the aqueous solution.581 The electronic spectrum of the solid in an argon matrix at 20 K was measured and assigned.580 An energy level diagram was constructed on the basis of the... 

Ru(dmb)j(decb) ] , [Ru(decb) (dmb) ], and (Ru(decb) (dmb -4,4 -dimethyl-2,2 -pyridine, decb 4,4 -bis(ethylcarboxy)-2,2 -bipyridine). Emission properties of [Ru(bpy) nH O and the circular dichroism spectrum of the excited state absorption of (a)-[Ru(bpy)3] have both been reported. The luminescence of Ru(II) and Os(II) polypyridyls has been measured in MeCN as a function of pressure and temperature, and it has been found that at high pressures the radiative and non-radiative transition rates between the luminescent CT level and the ground state are generally increased by 5-10%. Temperature dependence luminescence studies on [Ru(bpy) L] ... 

Ionization constants of hydroxy- and mercaptopyridazines, ° of amino- and diaminopyridazines and their quaternization products,of methylsulfinylpyridazines," and of pyridazinium ylides have been recorded. The basicities of a series of pyridazines have been determined and correlated with substituent constants using the Hammett free-energy relationship. The magnetic susceptibility of pyridazine was measured, and the rate constant for the reaction of hydrogen atoms with pyridazine was determined. The experimental dipole moment, Kerr constant, and molar Cotton-Mouton constant, obtained at 298 K and 633 nm, are reported. The magnetic circular dichroism spectrum of pyridazine has been measured. ... 

The circular dichroism spectrum of the acid proteinase from Endothia parasitica was measured on a Cary61 CD spectrometer at 27 C, at a protein concentration of 0.232 mg/ml in 0.05 M phosphate buffer at pH 4.48. The path length was 10 mm for the near u.v. and 1 mm for the far u.v. The far u.v. circular dichroism is shown in Figure 6b. The spectrum resembles that of pepsin (21) and pepsinogen (22). The spectrum between 195 and 240 nm has been fitted using three sets of standard curves (23-25) with a least squares program (written by... 

We want to be able to deduce the conformation of a polymer in solution from its measured circular dichroism spectrum. For a linear polymer each ordered conformation must be a helix. The limiting cases for a helix are a straight line and a circle. A helix of identical residues is characterized by very few parameters. These are the radius of the helix, the rise per residue (the distance along the helix axis) and the number of residues per turn. A few examples will make this clear. A planar, all trans polyene will have a radius of zero (the helix is a straight line), a rise of 1.44 A and one residue per turn. A polypeptide a-helix has a radius of 2.28 A at the a-carbon, a rise per residue of 1.50 A and 3.6 residues per turn. One strand of a polynucleotide helix in the Watson-Crick B-form of DNA has a radius of 5.72 A at Cr of deoxyribose, a rise per residue of 3.4 A and 10 residues per turn. 

The circular dichroism (CD) measurements are presented and discussed for oligomers up to DP = 50 and compared to those obtained with a polymer of DP - 400. Four possible conformations in aqueous solutions a helix, p sheet, unordered random form and extended structure are demonstrated and can be used to interpret each experimental spectrum [2]. 

In a few instances the technique of magnetic circular dichroism (MCD) spectroscopy has been used to corroborate assignments based on UV-visible spectroscopy. For example, the assignment of the intense 360 nm band for [S,N,Y to a r (2e") r (2a2") (HOMO LUMO) excitation has been confirmed by the measurement of the MCD spectrum of The MCD spectrum of [S4N3] indicates that each of the... 

Circular dichroism (c.d.) spectroscopy measures the difference in absorption between left- and right-circularly polarized light by an asymmetric molecule. The spectrum results from the interaction between neighboring groups, and is thus extremely sensitive to the conformation of a molecule. Because the method may be applied to molecules in solution, it has become popular for monitoring the structure of biological molecules as a function of solvent conditions. 

Measurement of the melting temperature (Tm) and the circular dichroism (CD) spectrum of AQ-DNA(l) shows that it is a duplex at room temperature... 

---