Optical Rotatory Dispersion Curves Research Articles

The circular dichroism and optical rotatory dispersion of protoberberines

Circular dichroism and optical rotatory dispersion curves of protoberberines and the corresponding benzyltetrahydroisoquinolines have been measured. Allotment of absolute configuration cannot be made by direct comparison between members of the two series, since for the same absolute configuration the two series show curves of opposite signs.Protoberberine alkaloids are formed by the Mannich reaction of benzyltetrahydroisoquinolines with formalin. This reaction gives products of high optical purity, and can therefore be used for the allotment of configuration to protoberberine alkaloids. The stability of the asymmetric centre was confirmed in the present work; tetrahydropapaverine labelled with deuterium at C-1 retained the isotope during the Mannich reaction.

Optical rotatory dispersion. Part LIII. Diterpenecarboxylic acids and related compounds

The optical rotatory dispersion curves of a number of diterpenecarboxylic acids have been examined. The results are discussed in terms of the preferred conformations of carboxylic acids and the carboxyl sector rule.

The synthesis and conformational analysis of epimeric 16-bromo-5-alpha, 13-alpha-androstan-17-ones.

Epimeric 3β-acetoxy-16-bromo-5α, 13α-androstan-17-ones were synthesized starting from 3β-acetoxy-5α, 13α-androstan-17-one, and their structures were confirmed by the standard method of Fieser and Ettorre. An equilibrated mixture obtained from each one of epimers with hydrogen bromide was found to consist of 23% 16β and 77% 16α. On the basis of infrared, ultraviolet, nuclear magnetic resonance spectra and optical rotatory dispersion curves the conformation of ring D was discussed.

Conformation of aspergillopeptidase A in aqueous solution: II. Ultraviolet optical rotatory dispersion of aspergillopeptidase A

The optical rotatory dispersion of acid proteinase of Aspergillus sailoi (aspergillopeptidase A, EC 3.4.4.17) was investigated between 195 to 250 mμ as a function of pH, temperature, and solvent composition. The optical rotatory dispersion curves for these states differ considerably. In the native state, aspergillopeptidase A had a minimum at 220 mμ with [ m′] = −2400 and a maximum at 203 mμ with [ m′] = 900, respectively. The optical rotatory properties of aspergillopeptidase A did not change at pH's between 2.7 to 5.7. It was concluded that aspergillopeptidase A is devoid of a complete α-helical strand, as judged from the ultraviolet optical rotatory dispersion curve at 233 and 198 mμ spectral zone. On weak alkali (above pH 7.0) denaturation and heat denaturation at 55°, the flat maximum at 203 mμ vanished, and the optical rotatory dispersion spectra were altered in such a way as to suggest the presence of a randomly coiled form in the denaturated proteins. The conformation of aspergillopeptidase A was apparently converted by the anionic detergent, sodium lauryl sulfate, into a partially α-helical conformation, as judged from the optical rotatory dispersion curve in the ultraviolet region. The [ m′] 233 and [ m′] 198 values were found to be −3400 and 11600, respectively.

Characterization of 3-Amino-3,6-dideoxy-d-glucose from a Bacterial Lipopolysaccharide

Abstract Lipopolysaccharides were isolated from Citrobacter freundii ATCC 8090 by 44% aqueous-phenol fractionation. The lipopolysaccharides were isolated from the phenol phase and phenol-water interphase fractions. Acid hydrolysis yielded glucosamine and a 3-amino sugar identified as 3-amino-3,6-dideoxyglucose by comparison with authentic 3-amino-3,6-dideoxyhexoses by ion exchange chromatography. Comparison of the 3-acetamido-1,2,4-tri-O-acetyl-3,6-dideoxyhexose with 3-acetamido-1,2,4-tri-O-acetyl-3,6-dideoxy-l-glucose was made. The infrared spectra were identical, while the optical rotatory dispersion curves were identical in shape but opposite in sign. The compound isolated from C. freundii was thus assigned the structure 3-amino-3,6-dideoxy-d-glucose.

Circular dichroism of rhodopsin and isorhodopsin.

A COMPARISON between the optical rotatory dispersion curves of rhodopsin before and after irradiation has been previously reported1. Unbleached rhodopsin solutions show a weak Cotton effect in the visible range, and another distinguishable Cotton effect in the ultra-violet range, attributable to the polypeptide conformation (probably α-helix) of the protein moiety, opsin. After bleaching, however, the samples have a simple dispersion curve showing lower values of optical rotation in the visible range. The Cotton effect in the visible range is thus presumably caused by the optical activity of the prosthetic-group conformation (11-cis), although this is not certain. We have made measurements of the circular dichroism of rhodopsin and isorhodopsin (the artificial pigment with a prosthetic group in the 9-cis configuration) in order to elucidate the weak Cotton effect demonstrated by optical rotatory dispersion.

Optical Rotation of Oriented Helices. III. Calculation of the Rotatory Dispersion and Circular Dichroism of the Alpha- and 310-Helix

We have carried out a calculation of the optical rotatory dispersion (ORD) of α-and 310-helices which is essentially complete within the limitations of the Kirkwood approximation and its extensions. This treatment predicts that right-handed helices will exhibit three rotatory bands at wavelengths greater than 190 mμ. The sign and position of these predicted bands are in good agreement with experiment. The predicted rotational strengths do not agree so well, but are in sufficiently good accord to provide strong support to the assignment of the longest-wavelength band to the amide nπ* transition, and the shortest-wavelength band thus far observed to a composite band due both to the perpendicular-polarized exciton component and to the intrinsic rotational strength of the NV1 transition. Calculation of the ORD and CD (circular dichroism) of the α-helix from the calculated rotational strengths gives results in fair agreement with experiment, especially when the nπ* rotational strength is adjusted to agree with that observed in CD experiments. An analysis of the calculated ORD curves according to the Moffitt—Yang and Shechter—Blout procedures leads to values for the parameters in these equations which agree well with experiment in the case of the α-helix. A similar treatment of the 310-helix indicates that this helix can be distinguished from the α-helix by: (a) appreciably more positive rotations in the visible region, (b) appreciably larger absolute values of b0, A(α, ρ)225 and A(α, ρ)193. The dependence of various rotatory parameters on the length of the helix has been studied. The dispersion parameters b0, A(α, ρ)225 and A(α, ρ)193, as well as the depth of the 233 mμ trough appear to be the least sensitive to chain length. The magnitude of the maximum at 198 mμ, however, seems quite chain-length dependent, and therefore is probably not suitable as a measure of helix content.

The use of computed optical rotatory dispersion curves for the evaluation of protein conformation.

The use of computed optical rotatory dispersion curves for the evaluation of protein conformation.

Asymmetric triglycerides from Impatiens edgeworthii seed oil

Impatiens edgeworthii Hook F. seed oil, which contains acetate, parinarate, and the more common fatty acyl groups, was hydrogenated to give mainly α-acetodistearin. The hydrogenated oil produced a plain negative optical rotatory dispersion curve. Comparison of the dispersion curve with those of α-acetodiacyl triglycerides synthesized by stereoselective methods indicates that the triglycerides of Impatiens edgeworthii seed oil have the ( S)-configuration.

Physico-chemical studies of three variants of Mengo virus and their constituent ribonućleates

Methods are described for the isolation in pure form of three variants of Mengo virus and their constituent ribonucleates. The resulting preparations have been subjected to a detailed physico-chemical investigation using the techniques of sedimentation velocity, diffusion at low centrifugal fields (method of Möller, 1964), optical rotatory dispersion and electron microscopy. It was established that all three variants are identical with respect to the measured hydro dynamic parameters (S 20,w 0 and D 20,w 0), and a similar conclusion was drawn for their RNA constituents. The particle weight of the virus, as estimated from the Svedberg equation, is 8.32 ± 0.7 × 10 6, while that of the RNA is 1.74 ± 0.2 × 10 6. In the electron microscope the three Mengo variants are indistinguishable from each other and appear as spherical particles with diameters of 26.2 to 27.2 mμ. The hydrated diameter calculated from the experimental diffusion coefficient is 29.3 mμ, which is consistent with a hydrated sphere having 0.23 g water per gram dry virus. The frictional ratio of the virus particle, estimated from S 20,w 0 and D 20,w 0, is 1.10, which also suggests that it is essentially spherical in shape. A comparison of the optical rotatory dispersion of the three variants of Mengo virus and their constituent ribonucleates, shows that the curves are essentially identical to one another, with similar cross-over points, positions of troughs and peaks, and amplitudes. This would suggest that the manner in which the proteins are arranged around the RNA chain in the virus is precise and similar in all three cases. By subtracting the contribution of the RNA from that of the virus, the optical rotatory dispersion curve of the protein in situ was obtained. The small amplitude of [ m′] 234 suggests that the protein in its native environment possesses negligible α-helical content.

Some remarks on the interpretation of natural and magnetically induced optical activity data

1. Introduction—A classification for optically active chromophores One of the most useful concepts that emerges from the perturbation approach to the theory of natural optical activity is that of the ‘rotational strength’ of a transition (Condon 1937). This signed quantity conveniently and effectively measures how strongly a particular transition contributes to both the dispersive and absorp­tive aspects of the optical activity of a molecule (Moscowitz 1962); it is obtainable experimentally from either the pertinent partial optical rotatory dispersion curve or the partial circular dichroism curve (Djerassi 1960), and it is amenable to theo­retical calculation for homogeneous isotropic media as the following scalar product (Condon 1937; Moscowitz 1962; Djerassi 1960; Rosenfield 1928). R ba = I {( a | μ e | b ). ( b | μ m | a )}. Here ( a | μ e | b ) and ( b | μ m | a ) are the electric and magnetic dipole transition moments, respectively, connecting the ground state a and the excited state b , and I means imaginary part. Accessible as such to both theory and experiment, the rotational strength provides one of the most suitable foundations on which to build quanti­tative correlations between optical activity data and molecular structure.

Circular dichroism of helical polynucleotide chains

In contrast to relatively well developed experimental and theoretical studies on polypeptides and proteins (see Gratzer 1967 and McLachlan 1967, this volume) the investigation of optical activity of polynucleotides and nucleic acids were very restricted. The optical rotatory dispersion curves of polynucleotides examined in the visible and near u. v. fit one-term Drude equation regardless of the conformation (Fresco 1961; Levedahl & James 1957; Ts’o, Helmkamp & Sander 1962). Recent circular dichroism (c. d.) measurements of several polynucleotides and nucleic acids (figure 1) indicated clearly the presence of dichroic bands in the u. v. region of base absorption which can be related to the dissymmetrical helical conformation (Brahms 1963). The intensity of circular dichroic bands decreases strongly under the conditions in which the helical structure is unstable and goes to random coil form (Brahms 1964; Brahms & Mommaerts 1964). Thus polyadenylic acid (poly A ) is known according to X-ray data to exist at acid pH in a helical two strand and right handed conformation (Rich, Davies, Crick & Watson 1961). In acid solution the same polyadenylic acid exhibits strong circular dichroic bands which disappear at high temperature (figure 2).

Optical rotatory dispersion of indole alkaloids from the yohimban, corynanthean, and quebrachamine groups

AbstractIt has been shown that optical rotatory dispersion curves can be used to determin‐ the absolute stereochemistry at C(3) of indole alkaloids of the yohimban and corynane thean types. This is dependent on the absence of strong chromophores other than that of the aromatic system.

The optical rotatory dispersion of tetrahydropyranyl ethers

Optical rotatory dispersion curves have been measured for a number of pairs of anomeric tetrahydropyranyl ethers. By comparison with 2-deoxyglycosides of known configuration it is possible to allot absolute configurations to C-2′ of the tetrahydropyranyl ring.

Optical rotatory dispersion. Part XLVIII. Some 3,3-diarylprop-1-enes and related quinones: the absolute configuration of latifolin

The optical rotatory dispersion (o.r.d.) curves of latifolin and its derivatives, which are substituted 3,3-diarylprop-1-enes, have been compared in the short wavelength region with those of related quinol diacetates of known absolute configuration; the characteristic Cotton effects at 235 mµ show that the absolute configuration of latifolin is R. The o.r.d. curves of the related quinones of the dalbergione series confirm this assignment.

Optical rotatory dispersion curves of some N-salicylidene amino-sugars.

Optical rotatory dispersion curves of some N-salicylidene amino-sugars.

Optical rotatory dispersion. XLIV. Steroid acetates.

The optical rotatory dispersion curves of a large number of steroid acetates show the first extremum of an ester Cotton effect at ca. 227 mµ. The signs of these Cotton effects can be rationalised in terms of the carboxyl sector rule.

Optical rotatory dispersion. XL. Protected derivatives of the tri- and tetra-peptides of alanine and serine.

The optical rotatory dispersion curves of all the possible protected diastereoisomeric tri- and tetra-peptides of alanine and serine have been measured in methanol; the protected serine derivatives have also been examined in hexane. Arithmetical treatment of the results enables the contributions of the individual chromophores to the total molecular rotation to be calculated.

The identification of (+)-abscisin II [(+)-dormin] in plants and measurement of its concentrations

(+)-Abscisin II[(+)-dormin] has been identified in the ether soluble acid fraction of twenty plant species, including mono-and dicotyledons and a fern. (+)-Abscisin II was identified by its general physical properties, biological activity, chromatographic behaviour and optical rotatory dispersion. Synthetic abscisin II runs on paper chromatograms at the same RF as inhibitor-β from potato tuber and lemon fruit in the solvent mixtures used by previous workers, furthermore the growth-inhibitory activity of these extracts was attributable to the (+)-abscisin II contents. The concentrations of (+)-abscisin II in extracts of a number of plants were calculated from the specific rotation at the first, positive extremum (289 mμ) of the optical rotatory dispersion curve after extraction and chromatographic procedures.A new method of measurement was evolved, analogous to inverse isotope dilution, where a known quantity of racemic abscisin II was added to a tissue homogenate and then the total abscisin II in a highly purified extract was measured spectrophotometrically and the natural (+)-abscisin II measured spectropolarimetrically. The (+)-abscisin II content in the original sample was then calculated from the ratio of these two measurements and the known weight of racemic material added. Concentrations of (+)-abscisin II within tissues obtained by this technique were about three times higher than by the standard extraction procedure.Identification of several previously described growth-inhibitory compounds as (+)-abscisin II has extended the known physiological effects of the compound; its roles as a dormancy and an abscission factor and as a germination inhibitor are discussed.

Optical rotatory dispersion curves of N-salicylidene derivatives of amino-sugar antibiotics.

Optical rotatory dispersion curves of N-salicylidene derivatives of amino-sugar antibiotics.