Vacuum Ultraviolet Circular Dichroism Research Articles

Vacuum ultraviolet circular dichroism of poly(galacturonic acid), sodium polygalacturonate and calcium polygalacturonate

Vacuum ultraviolet circular dichroism spectra are reported for poly(galacturonic acid) solution and film, sodium polygalacturonate solution and film, and calcium polygalacturonate gel. In addition to the positive c.d. band near 208 nm previously observed, we find a pair of higher energy bands at 170 180 nm (negative) and 145 nm (positive). The low energy band, assigned to an n-π ∗ carboxyl transition, is blue-shifted upon gelation or film formation.

Conformation of the complex oligosaccharides of glycoproteins. A vacuum ultraviolet circular dichroism study.

Circular dichroism spectroscopy in the 170-220-nm range of the ultraviolet and measurements of the amide proton coupling constants in nmr have been used to investigate the conformation of asparagine-linked glycopeptides having oligosaccharide chains of the complex antenna type. The CD spectra can be explained as the sum of three contributions, the first of which is a pair of large bands of opposite sign resulting from coupling of the adjacent chromophores of the 2-acetamido-1-N-(4-aspartyl)-2-deoxy-beta-D-glucopyranosylamine linkage. Secondly the amide chromophore of the core N-acetylglucosamine residue substituted at carbon 4 by a beta-mannosyl residue contributes a negative band at 210 nm along with a small negative signal in the 180-190-nm region. The amides of the antenna N-acetylglucosamine residues, which in some cases are substituted by beta-galactosyl residues at carbon 4, contribute a negative band at 210 and a strong positive band at 185-190 nm. Since these three contributions are approximately independent, we can detect no long range interactions between nonreducing termini and the glycopeptide linkage region. Both CD and nmr data imply that the glucosaminyl-asparagine linkage is rigidly fixed in a conformation having the amide protons trans to the sugar ring protons. These results are consistent with an extended conformation in the shape of a "Y" or a "T" for complex type asialo-oligosaccharide chains.

Z-DNA: vacuum ultraviolet circular dichroism.

In concentrated salt or ethanolic solutions, the self-complementary copolymer poly(dG-dC).poly(dG-dC) forms a left-handed double-helical structure that has been termed "Z-DNA." The first evidence for this structure came from changes observed in the circular dichroism (CD) spectrum between 230 and 300 nm for low- and high-salt solutions (Pohl, F. M. & Jovin, T. M. (1972) J. Mol. Biol. 67, 675-696). In 3 M NaCl, the CD spectrum is approximately inverted compared to the B-form spectrum observed in low-salt solution. We measured the vacuum ultraviolet CD spectrum of poly(dG-dC).poly(dG-dC) down to 180 nm under conditions in which the 230- to 300-nm spectrum is inverted. Below 200 nm, where the B form exhibits the large positive peak at 187 nm that is characteristic of right-handed double-helical DNAs, the Z form exhibits a large negative peak at 194 nm and a positive band below 186 nm. Therefore, the Z-form vacuum ultraviolet CD spectrum resembles an inverted and red-shifted B-form spectrum. The magnitudes of the differences observed between the B and Z forms in the CD spectrum below 200 nm are about 10 times greater than those observed between 230 and 300 nm. The vacuum ultraviolet CD spectrum of poly(dG-dC).poly(dG-dC) in 3 M Cs2SO4 also is inverted compared to the B-form spectrum; however, between 230 and 300 nm, it is nonconservative with a negative maximum at 290 nm and a weak positive CD signal above 300 nm, presumably reflecting differential light scattering and indicating the existence of molecular aggregates. Our results suggest that the vacuum ultraviolet CD spectrum is sensitive to the handedness of double-helical DNA structures. The CD spectrum in this region should complement other spectroscopic methods in relating the structures of poly(dG-dC).poly(dG-dC) existing in solution to those determined in the solid state by x-ray crystallography.

Vacuum‐ultraviolet circular dichroism of chondroitins and their complexes with poly(L‐arginine)

AbstractThe vacuum‐ultraviolet circular dichroism (VUCD) of chondroitin and chontroitin‐6‐sulfate has been measured to 160 nm for films and to 170 nm for D2O solutions. The pD‐dependent dichroic behavior of these glycosaminoglycans in D2O is similar above 200 nm and is in agreement with previous studies. Near 190 nm, the CD band sign is also dependent on pD. VUCD spectra were recorded for films and solutions of poly(L‐arginine). In trifluoroethanol the polypeptide is α‐helical, while in D2O it exists as a random coil. The well‐characterized coil–helix transition of poly(L‐arginine) during complexation with chondroitin‐6‐sulfate was observed by VUCD, including the previously inaccessible entire π → π* band. By construction of difference spectra it was also possible to monitor the VUCD of the polysaccharide component during complexation.

Structure and Conformation of Human Pancreatic Carboxyl‐Ester Hydrolase

Human pancreatic carboxyl-ester hydrolase is a glycoprotein with a molecular weight of 100 000 and a high content in carbohydrate, 20%. Sedimentation studies indicate that the molecule resembles an ellipsoid. The results of hydrodynamic and vacuum-ultraviolet circular dichroism investigation allow one to propose a model of the carboxyl-ester hydrolase three-dimensional structure. The enzyme belongs to the "all beta" class of proteins; about 54-60% of its residues are in beta-sheets and in beta-turns, most probably forming the surface of an ellipsoid. A similarity with prealbumin structure is proposed and a comparison with structure of other pancreatic enzymes is presented.

Vacuum‐ultraviolet circular dichroism of acetylated glucans

AbstractWe have measured the solution and film vacuum ultraviolet circular dichroism of a series of acetylated glucans containing α‐ and β‐(1→3), (1→4), and (1→6) linkages. In addition to the 210‐nm band studied previously, we observe the entire π‐π* band near 190 nm; these bands are negative for all triacetates regardless of configuration and conformation. A band near 170 nm shows configurational sensitivity for (1→3)‐ and (1→6)‐linked polysaccharides. The band is positive for both (1→4)‐linked triacetates, but when cellulose triacetate is partially deacetylated, the 170‐nm band becomes negative, thus making the correlation complete. The positive 170‐nm band in cellulose triacetate films is more than an order of magnitude more intense than in any other case and, further, is accompanied by an equally large negative band near 153 nm, raising the possibility that the dichroism in the triacetate arises from strong excitonic interactions which are disrupted upon partial deacetylation.

Cation-specific vacuum ultraviolet circular dichroism behaviour of alginate solutions, gels and solid films

The vacuum ultraviolet circular dichroism of alginate solutions, gels and solid films is reported. Two previously observed bands at ∼215 and ∼203 nm are assigned to n → π ∗ transitions of carboxy groups under different conditions of local environment. Three bands not previously observed are at ∼185 nm, assigned to carboxy π → π ∗ transitions, and at ∼169 and ∼149 nm, assigned to transitions of the polymer backbone. In the course of the sol (Na +)-gel (Ca 2+), the sol (Na +-film (Na +) and the gel (Ca 2+)-film (Ca 2+) transitions, intensity changes are observed in both the low energy and high energy bands. The c.d. changes during the three transitions differ in magnitude, but are qualitatively the same, from which we conclude that the chain conformations in the gel and films are similar, and that the principal spectral changes have their origin in perturbation of chromophores by site-bound cations.

Vacuum ultraviolet circular dichroism of (1 → 6)-β- d-glucan

V.u.c.d. spectra recorded for freshly prepared aqueous solutions of (1 → 6)-β)- D-glucan(pustulan) contained a single positive band near 177 nm. This band was similar in position and magnitude to the single positive band observed in the spectrum of (1 → 6)-α- D-glucan (dextran). Pustulan solutions (20 mg/ml) were observed to gel with time at 10 C. Concurrently, a negative band at 190 nm developed in the pustulan v.u.c.d. spectrum followed by a blue shift of both bands with continued aging. Crystalline films of pustulan yield spectra which resembled the blue shifted spectra of aged gels. The time dependent development of the negative band was attributed to pustulan attaining a helical conformation in solution, and the blue shift to aggregation of helices, Na + and Ca 2+ were found to accelerate gelation presumably by decreasing the activity of the aqueous solvent.

Vacuum ultraviolet circular dichroism of galactomannans

The chiroptical behaviour of plant galactomannans has been investigated by a combined vacuum ultraviolet circular dichroism (v.u.c.d) and optical rotatory dispersion (o.r.d.) approach. The samples studied were from Cyamopsis tetragonolobus (guar), Caesalpin'ia spinosa (tara), and Ceratonia siliqua (carob), with galactose levels of 39, 25 and 19%, respectively. V.u.c.d. solid film spectra have been recorded down to 140 nm, and in all cases show a positive band at 169 nm, and a negative band at 149 nm whose relative intensity increases systematically with decreasing galactose content. In solution only the lower energy band is accessible, and has the same position and width as in the solid state but substantially greater amplitude. Residual o.r.d. behaviour, after subtraction of the contribution from the 169 nm band (calculated by Kronig-Kramers transform of fitted c.d. parameters) shows a single band of the same position and width as the high energy solid state transition. The amplitude of both transitions in solution varies linearly with galactose content, consistent with simple additivity of contributions from the two different residues. Extrapolation to 0 and 100% galactose yields molarr ellipticities (10 3 x deg cm 2 dmol −1) at 169 and 149 nm, respectively, of +14 and −33 for mannan, and −8 and −80 for galactan. Reduction in the net intensity of both transitions in the solid state, and to a lesser degree in carob gels, is attributed to conformational restriction of galactose by chain packing, with consequent increase in c.d. intensity from these residues and hence greater cancellation of mannose backbone contributions.

Site and role of the N-terminal fragment of the nucleosomal core histones in their binding to deoxyribonucleic acid as determined by vibrational spectroscopy

The site and role of the binding of the 1-53 N-terminal part of H4 on DNA have been studied by optical spectroscopy. The structure of the 1-53 H4 fragment determined by vacuum ultraviolet circular dichroism and infrared spectroscopy is essentially aperiodic. The site of the interacion between the fragment and free DNA is localized by Raman laser spectroscopy in the small groove of the DNA, similar to the interaction site of the whole histone with DNA in nucleosomes. Infrared linear dichroism measurements show that the two 1-53 and 54-102 H4 fragments play a very important role in the histone-DNA interactions, but the roles are extremely different: the N-terminal part of the histone remains effectless on the DNA conformational flexibility and it is proposed that the structurally important interaction occurs between the globular part of the histone and the DNA. The N-terminal fragment appears to be responsible for finding the correct place on the DNA of the nucleosomal core particles.

The first use of synchrotron radiation for vacuum ultraviolet circular dichroism measurements

Synchrotron radiation (SR) from modern electron storage rings is highly linearly polarized and more intense than conventional vacuum ultraviolet continuum sources. These unique properties make SR ideal for construction of a vacuum ultraviolet circular dichroism (CD) instrument. We report the first use of SR for CD measurements and describe the instrumental setup. These measurements were carried out in the wavelength range 1325–2050 Å on (+)-3-methylcyclopentanone at the Synchrotron Radiation Center of the University of Wisconsin-Madison. The signal to noise ratio, and therefore the resolution, was the best ever obtained for CD measurements in this wavelength range. This resulted in the observation of new structure and dramatic peak height changes in the CD spectrum. In addition, these measurements showed that the extension of CD measurements to higher energies is possible through the use of synchrotron radiation.

Determination of protein secondary structure in solution by vacuum ultraviolet circular dichroism

A new approach is presented for evaluating the secondary structure of globular proteins in solution by analysis of circular dichroism spectra. Two major improvements are introduced. First, extension of the ultraviolet region down to 165 nm. Extension of the spectral region to the vacuum ultraviolet allows observation of new characteristic bands, which improves substantially the analysis of protein conformation. Secondly, new reference spectra that contain all main protein conformations, including two sets of (β-turns, are taken into account. One set of β-turns representative of all main types of turns, contains the sequences (Ala 2-Gly 2) n, l-Pro- d-Ala, N-acetyl- l-Pro-Gly- l-Leu-OH. A comparison of the results of the analysis with one β-turn and with a set of turns indicates that there is essentially no major improvement; thus one β-turn can be taken as the basis spectrum. In addition, the reference spectra include the β-form represented by polypeptide chains composed of alternating hydrophobic and hydrophilic amino acids, which is more closely related to anti-parallel β-pleated sheet structures in proteins. It appears possible to determine the content of antiparallel and of parallel β-pleated sheets with the present basic β-spectrum. The circular dichroism of aromatic side-chain chromophores was measured in the vacuum ultraviolet in order to take their contribution into account. It appears that for proteins with higher aromatic amino acid content and with weak circular dichroism amide bands, it is necessary to take into account a correction for the aromatic side-chain contribution. The conformation of 13 proteins representative of all main classes of globular proteins was determined from circular dichroism data between 165 nm and 250 nm at 0.2 nm intervals. In particular, the secondary structure of the β-rich class of proteins (concanavalin A, Bence-Jones protein V REI, prealbumin, superoxide dismutase), the α/β class of proteins (lactate dehydrogenase, triose phosphate isomerase, subtilisin, glyceraldehyde-3-phosphate dehydrogenase, flavodoxin and pyruvate kinase) and the (α + β) class of proteins (lysozyme and cytochrome c) were quantitatively characterized in solution. The reliability of the method was also assessed by comparing the data obtained with those available from X-ray crystallography. In general, a good agreement was found between the present circular dichroism data and published X-ray data, except for rubredoxin. By including all types of secondary structure and by enlarging substantially the spectral region, our method permits analysis of the conformation of a variety of proteins, such as nucleic acid-binding proteins, immunoglobulins and β-pleated sheet-rich proteins. It offers new possibilities for investigating the dynamics of protein conformation in solution.

Vacuum ultraviolet circular dichroism spectrometer and its application to N-acetylamino saccharides

Vacuum ultraviolet circular dichroism spectrometer and its application to N-acetylamino saccharides

ChemInform Abstract: SINGLE CRYSTAL, VACUUM ULTRAVIOLET, AND ION ASSOCIATION CIRCULAR DICHROISM SPECTRA OF THE BIS((2R)‐2‐METHYL‐1,4,7‐TRIAZACYCLONONANE)COBALT(III) ION

Chemischer InformationsdienstVolume 10, Issue 36 Physical Organic Chemistry ChemInform Abstract: SINGLE CRYSTAL, VACUUM ULTRAVIOLET, AND ION ASSOCIATION CIRCULAR DICHROISM SPECTRA OF THE BIS((2R)-2-METHYL-1,4,7-TRIAZACYCLONONANE)COBALT(III) ION A. F. DRAKE, A. F. DRAKESearch for more papers by this authorR. KURODA, R. KURODASearch for more papers by this authorS. F. MASON, S. F. MASONSearch for more papers by this author A. F. DRAKE, A. F. DRAKESearch for more papers by this authorR. KURODA, R. KURODASearch for more papers by this authorS. F. MASON, S. F. MASONSearch for more papers by this author First published: September 4, 1979 https://doi.org/10.1002/chin.197936067AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume10, Issue36September 4, 1979 RelatedInformation

Optical rotatory dispersion and vacuum ultraviolet circular dichroism of poly[(R)‐oxypropylene

AbstractThe circular dichroism (CD) spectrum of poly[(R)‐oxypropylene] in a number of solvents has been measured in the vacuum ultraviolet region. Two CD bands were measured for cyclohexane, acetonitrile, and trifluoroethanol solutions. The CD spectrum was extended to 140 nm and three bands were measured in a 1,1,1,3,3,3‐hexafluoro‐2‐propanol solution. The similarity of these four CD spectra in sign, shape, and intensity confirm that poly[(R)‐oxypropylene] has similar conformations in all solvents studied, even though the optical rotatory dispersion (ORD) in the visible region is positive for the cyclohexane solution but negative for the alcohol solutions. A Kronig–Kramers transform of the two CD bands observed for the cyclohexane solution accounts for the observed positive ORD spectrum. In contrast, a third large and negative CD band centered below 160 nm is necessary to account for the negative ORD spectra observed for the alcohol solutions. Apparently the anomalous sign variation of the ORD curves observed in the visible region is due to subtle changes in the interplay of a large number of CD bands. Solvent interaction, observed as a blue shift of the first two CD bands for the alcohol solutions, could produce the subtle changes necessary to change the sign of the ORD curve in the visible region. The first two CD bands of poly[(R)‐oxypropylene] are tentatively assigned as nσ* and the third as an n3s.

Vacuum ultraviolet circular dichroism spectrum of β-turn in solution

The vacuum ultraviolet circular dichroism spectrum of an isolated 4 → 1 hydrogen bonded β-turn is reported. The observed spectrum of N-acetyl-Pro-Gly-Leu-OH at − 40°C in trifluoroethanol is in good agreement with the theoretically calculated CD spectrum of the β-turn conformation. This spectrum, particularly the presence of a strong negative band around 180 nm and a large ratio [θ] 201 [θ] 225 , can be taken as a characteristic feature of the isolated β-turn conformation. These CD spectral features can thus be used to distinguish the β-turn conformation from the β-structure in solution.

9] Far (vacuum) ultraviolet circular dichroism

Publisher Summary This chapter provides a description of the special techniques required for measurements of vacuum ultraviolet circular dichroism (VUCD) and a description of the information that can be obtained from VUCD measurements that are not obtainable from circular dichroism (CD) measurements at longer wavelengths. Inasmuch as the first measurements of CD in the vacuum ultraviolet were made only a few years ago, an historical reference ought to be permitted to place that development into a larger perspective. The fundamental principles of optics necessary to know to understand the phenomenon of circular dichroism are described very often. At present, there is no commercially available instrument that allows CD measurements at wavelengths lower than about 185 nm. In commercial instruments, ammonium or potassium dihydrogen phosphate (ADE KDP) is used to produce alternately right and left circularly polarized light through the application of the Pockels' effect, but ADP and KDP are not transparent far into the vacuum ultraviolet region.

Identification of β,β-turns and unordered conformations in polypeptide chains by vacuum ultraviolet circular dichroism

Different conformations of polypeptides were characterized by measurements of the circular dichroism (CD) extended into the vacuum ultraviolet region. (i) The linear beta-pleated sheet structure was characterized in a broad ultraviolet region down to 165 nm by examination of copolypeptides composed of alternating hydrophobic and hydrophilic amino-acid residues, e.g., poly(Lys-Leu-Lys-Leu). A short-wavelength intense band was found at about 169 nm, which is characteristic of beta-pleated sheet conformation. (ii) The beta-turns were experimentally measured using poly(Ala(2)-Gly(2)) in a broad spectral region down to 165 nm with accuracy. The observed CD spectrum is in excellent qualitative agreement with the theoretical curve calculated by Woody for the beta-turns of type II and/or I of Venkatachalam. The similarity in shape between the theoretical curve and the observed CD spectra suggests a dominance of beta-turn segments in the poly(Ala(2)-Gly(2)) structure. The presence of beta-turns in poly(Ala(2)-Gly(2)) is also in agreement with the characterization of this polypeptide by solid state methods (electron microscopy and x-ray diffraction). The CD spectrum of beta-turns is characterized by a very intense band at 207.5 nm and strong negative bands at 191 and 169 nm. Copolypeptides such as poly(Ala(2)-Gly(3)) and poly(Ala(3)-Gly(3)) yielded a similar type of CD spectrum, analysis of which indicates that a large fraction of their residues is contained in beta-turn regions. (iii) The CD spectrum of the unordered chain of these alternating copolypeptides in salt-free solution is observed in the vacuum ultraviolet region.

Vacuum ultraviolet circular dichroism of protected homooligomers derived from L-leucine.

Vacuum ultraviolet circular dichroism of protected homooligomers derived from L-leucine.

Improved circular dichroism instrument in the vacuum ultraviolet

The vacuum ultraviolet circular dichroism instrument developed in this laboratory and originally described in 1970 has been modified and improved. The principal modification is the replacement of two lenses by a collimating mirror, thus converting to reflection optics. As a result, the efficiency of the instrument was considerably improved; particularly at wavelengths shorter than 160 nm. The effectiveness of the polarization optics at short wavelengths was investigated and found to be unimpaired out to 135 nm.