A Circular Dichroic absorption study of the reaction of oxidized pyridine nucleotides with cyanide ions fully confirms the occurence of a very weak Cotton effect around 435 nm in the Circular Dichroic spectrum of the reduced coenzymes and therefore the very faint transition (λmax = 435 nm; ?max ~ 1 M?1 cm?1) from which the Cotton effect originates. 相似文献
Measurements of optical rotatory dispersion (ORD) and circular dichroism (CD) were made in the range of 400–205 nm for polysaccharide tribenzoates such as 2,3,6-tri-O-benzoyl amylose (I), 2,3,4-tri-O-benzoyl dextran (II), tri-O-benzoyl pullulan (III), 2,3,6-tri-O-benzoyl cellulose (IV), 2,3,6-tri-O-benzoyl mannan (V), and polyglycan dibenzoates such as 2,3,-di-O-benzoyl amylose (VI), cellulose (VII), and mannan (VIII). All compounds exhibit Cotton effects in the region of their UV absorption bands (206–285 nm). Comparison of the corresponding di- and tribenzoyl polysaccharides shows a qualitative agreement in number, position and sign of the CD bands but differences in ellipticity magnitude. The disubstituted derivatives exhibit smaller amplitudes than the trisubstituted ones. The contribution of the C(6) chromophore (linked by a CH2-group to the asymmetric C(5) atom) was determined to be of the same sign as the combined contribution of the C(2) and C(3) substituents. The CD bonds of the individual polysaccharide derivatives, which differ in number, sign, and position, were discussed in terms of the steric position of the single chromophores and the steric arrangement and interaction caused by the configuration of the polysaccharides. The optical behavior of these polysaccharide derivatives was found to be not strongly influenced by a definite chain conformation in solution. 相似文献
The circular dichroism (CD) spectra of DNA–acridine orange (DNA–AO) complex in the visible region were measured at DNA phosphate-to-dye ratios (P/D) from 1 to 550. The CD spectrum of DNA–AO complex in the P/D ratio between 1 and approximately 40 consists of four components, i.e., positive CD bands centered at 510 and 480 mμ, and negative CD bands at 497 and 468 mμ. The CD bands at 510 and 468 mμ are optimum at P/D = 4, and the change of ε1 ? εr with P/D suggests that both of them are induced from the interaction between dye molecules bound to adjacent DNA binding sites, each of which is composed of four nucleotides. This is supported by the fact that the values of ε1 ? εr for both decrease with increasing temperature or increasing methylene blue concentration added to the complex. The negative Cotton effect at, 497 mμ is most favored at larger P/D ratio (~8), and the suggested assignment is to the interaction between two dye molecules bound with an empty site between them. A positive Cotton effect at 480 mμ is observed at P/D ratio of less than 4 and is optimum at 1. Above P/D ratio of 40, the CD spectrum of the complex can not be resolved into its components and even at sufficiently high P/D ratio (550) the complex shows a small Cotton effect. 相似文献
Sulphate derivatives (DS 0.8–2.0 for sulphate) of chitosan and N-acylchitosan formed their complexes with Methylene Blue (MB), and the metachromasy and two types of triplet induced Cotton effects (500–700 nm) were produced: the derivatives (DS <0.6 for N-acyl) exhibited three negative-positive-negative extrema at 504–538 (λ1), 544–565 (λ2), and 594–615 nm (λ3), and those (DS >0.7 for N-acyl) exhibited the reverse triplet extrema. When the MB complexes were treated t 70°C for 5 min, both the induced Cotton effects transformed into a novel triplet one with marked changes in the ellipticity and with the sign inversion. The extrema at λ2 and λ3 were just reverse to those of the doublet induced Cotton effect of MB-heparin complexes, which was little affected by temperature. 相似文献
A strong Cotton effect, which practically govern the sign of the optical rotation at 589 nm ([M]d), was studied in phenyl 1-thio-α (and β)-d-glycopyranosides with our new chiroptical technique. The proposal optical rotatory dispersion (ORD) method, with calculations based on a one term Drude equation, showed the presence of a strong Cotton effect at 200–210 nm. Circular dichroism (CD), with accumulation technique, also gave the same Cotton effect. Agreement in these two methods suggests the usefulness of the proposed ORD calculation method. The rotational strengths and the signs were shown to reflect the anomeric configurations and conformations (α-anomer gave positive and β-anomer gave negative signs; axial gave strong and equatorial gave weak bands). This result is an extension of the ring oxygen helicity rule of alkyl and alkyl thioglycosides to phenyl 1-thioglycopyranosides, and probably to other aromatic glycosides. 相似文献
The dependence on chain length of two characteristic properties of amylose, i.e., retrogradation and complex formation with iodine, have been studied by using enzymatically synthesized, homodisperse amyloses. The association rates of amyloses in water containing 5% dimethyl sulfoxide have a sharp maximum at a degree of polymerization P?n of 80; shorter and longer molecules are much more soluble. The iodine complexes of amylose exhibit a strong Cotton effect in the range of the long-wave absorption maximum (position depending on chain length) and two weaker Cotton effects at 480 and 350 nm. The long-wave Cotton effect is most intense at about P?n 50 and decreases rapidly for shorter and longer chains. This behavior is unexpected and is not in accordance with the further increase of λmax and λmax. The experiments can best be interpreted by assuming well ordered, stiff chains in the low molecular weight range (P?n 50–80). For longer chains, the findings are discussed in the light of current concepts of amylose conformation in aqueous solution, namely the model of the broken helical chain (alternating stiff helical segments and unordered regions) and the model of a flexible coil without a significant helical content. However, according to the results given in this paper, a wormlike helical chain seems to be the most adequate model for amylose conformation in neutral solution. 相似文献
Cd-binding peptide 1 (Cd-BP1) from (1) has been purified and characterized. Cd-BP1 has a characteristic shoulder at 265 nm in UV absorption spectrum, and shows two marked Cotton bands at 257 nm (negative) and 275 nm (positive). These are not found in the other Cd-thioneins (2) and are unique properties of Cd-BP1 from . With acidification (pH 2) and successive neutralization, a shoulder at 265 nm in UV spectrum and a Cotton band at 275 nm disappeared, and the molecular weight changed from 4 000 to 1 800. In connection with these changes, two molecular forms of Cd-binding peptide are considered. 相似文献
Optical rotatory dispersion (ORD) and circular dichroism (CD) of 17 amino acid hydantoins were measured between 190 and 600 nm. Most of hydantoins exhibited the negative Cotton effect which showed the trough between 238 and 245 nm. The negative trough of CD was also observed between 212 and 236 nm. The Cotton effect of hydantoins was attributable to n→π* transition of carbonyl group at C-4 of hydantoin ring. 相似文献
We have synthesized (Pro-Pro-βAla)n as a model for collagen. The synthetic polytripeptide, mol wt 6500, exhibits a large negative optical rotation with a very strong negative Cotton effect centered at 216 nm. The optical rotatory dispersion of (Pro-Pro-βAla)n followed a single-term Drude equation and the λc was 195 nm. The rotation decreased markedly on heating with the midpoint of the broad transition at 55°C. Preliminary studies also showed loss of structure in guadinine HCl. The circular dichroism spectrum of the polymer exhibited a deep trough at 190 nm. The marked similarities of solution properties of (Pro-Pro-βAla)n to (Pro-Pro-Gly)n suggest that β-alanine can replace glycine in generating collagen-like helix in solution. 相似文献
The Cotton effect below 200 nm was first studied in aromatic glycopyranosides with our new technique of optical rotatory dispersion (ORD). The phenyl and p-nitrophenyl α- and β-d-glycopyranosides showed a strong Cotton effect at around 180 nm which practically governed the optical rotations in the visible wavelength region. The rotational strength and sign of this Cotton effect were shown to reflect the anomeric configurations and conformations, which led to an extension of the ring oxygen helicity rule for alkyl and alkyl 1-thioglycosides to aromatic glycopyranosides. 相似文献
Changes induced on addition of the coenzyme, NADH or NAD+, to porcine lactic dehydrogenase isoenzymes H4 and M4 have been studied by hydrodynamic and spectroscopic methods. As shown by ultracentrifugal analysis, the native subunit structure remains unchanged on holoenzyme formation; a 5% increase of the sedimentation coefficient, parallelled by a slight decrease of the partial specific volume (<1%) indicate a significant change in the native tertiary and/or quaternary structure of the enzymes, corroborating earlier calorimetric data (Hinz and Jaenicke, 1975). The binding constant for the enzyme from skeletal muslce (M4) and NADH are found to be in agreement with KD-values obtained from equilibrium dialysis, as well as spectroscopic and thermal titration experiments (8 M). Far UV circular dichroism measurements do not show significant changes on ligand binding, indicating unchanged helicity or compensatory conformational effects. In the near UV, ligand binding is reflected by an extrinsic Cotton effect around 340 nm; in the range of aromatic absorption no changes are detectable.The experimental results suggest that there are gross structural changes on coenzyme binding to lactic dehydrogenase which do not affect the intrinsic spectral properties normally applied to analyze transconformation reactions in protein molecules. 相似文献
Conformational studies on lectins from castor beans (Ricinus communis), RCAI and RCAII, were performed by using circular dichroism (CD). The CD spectra were similar showing several negative bands at 270–320 nm, a positive region at 230–250 nm, several negative bands at 205–225 nm, and a positive peak at about 195 nm. However, significant differences were observed in the band strength between RCAI and RCAII. Lactose, melibiose, and d-fucose induced marked Conformational alterations in RCAI, whereas weaker effects were produced by d-galactose and l-rhamnose. Saccharide-induced conformational alterations were weaker in RCAII than in RCAI, with only lactose and melibiose inducing significant alterations. d-Glucose and 2-acetamido-2-deoxy-d-glucose, which do not inhibit hemagglutination by RCAI or RCAII, did not influence lectin conformation. Acetylation of tyrosyl groups with N-acetylimidazole produced changes in the CD bands in the near uv indicating involvement of tyrosine residues. The saccharide effect was most pronounced at 285 nm, a band that was assigned to a tyrosine chromophore. Analysis of the CD bands in the far-uv zone indicated the presence of approximately 50% pleated sheet (β) structure, and 13–15% α-helix in both RCAI and RCAII. According to the CD results, the polypeptide chain backbone in the lectins was not affected by the saccharides, whereas significant disorganization occurred in 7 m guanidine-HCl. 相似文献
BackgroundSchistosomiasis is a parasitic disease that is transmitted by skin contact with waterborne schistosome cercariae. Mass drug administration with praziquantel is an effective control method, but it cannot prevent reinfection if contact with cercariae infested water continues. Providing safe water for contact activities such as laundry and bathing can help to reduce transmission. In this study we examine the direct effect of UV light on Schistosoma mansoni cercariae using ultraviolet light-emitting diodes (UV LEDs) and a low-pressure (LP) mercury arc discharge lamp.MethodologyS. mansoni cercariae were exposed to UV light at four peak wavelengths: 255 nm, 265 nm, 285 nm (UV LEDs), and 253.7 nm (LP lamp) using bench scale collimated beam apparatus. The UV fluence ranged from 0–300 mJ/cm2 at each wavelength. Cercariae were studied under a stereo-microscope at 0, 60, and 180 minutes post-exposure and the viability of cercariae was determined by assessing their motility and morphology.ConclusionVery high UV fluences were required to kill S. mansoni cercariae, when compared to most other waterborne pathogens. At 265 nm a fluence of 247 mJ/cm2 (95% confidence interval (CI): 234–261 mJ/cm2) was required to achieve a 1-log10 reduction at 0 minutes post-exposure. Cercariae were visibly damaged at lower fluences, and the log reduction increased with time post-exposure at all wavelengths. Fluences of 127 mJ/cm2 (95% CI: 111–146 mJ/cm2) and 99 mJ/cm2 (95% CI: 85–113 mJ/cm2) were required to achieve a 1-log10 reduction at 60 and 180 minutes post-exposure at 265 nm. At 0 minutes post-exposure 285 nm was slightly less effective, but there was no statistical difference between 265 nm and 285 nm after 60 minutes. The least effective wavelengths were 255 nm and 253.7 nm. Due to the high fluences required, UV disinfection is unlikely to be an energy- or cost-efficient water treatment method against schistosome cercariae when compared to other methods such as chlorination, unless it can be demonstrated that UV-damaged cercariae are non-infective using alternative assay methods or there are improvements in UV LED technology. 相似文献
The neighbor–neighbor interactions in the small ribotrinucleotide ApApCp were investigated with the aid of optical rotatory dispersion measurements. This trinucleotide shows a Cotton effect between 220 and 325 mμ, in the region of its maximum ultraviolet absorption. The specific rotation of the trinucleotide is independent of concentration while the magnitude of the Cotton effect (levorotation) decreases markedly with increasing temperature. Such effects were not observed with the component nucleotides alone, in a simulated hydrolysis mixture, nor with the hydrolyzed trinucleotide. The Cotton effect is attributed to perturbation of the nucleotide base chromophores by neighbor–neighbor intramolecular interaction (stacking), without any hydrogen bonding being involved; this interaction decreases with increasing temperature because of increased internal rotational freedom about the single bonds of the backbone chain with an accompanying disruption of the neighbor–neighbor interaction between the bases. This explanation is supported by a statistical mechanical theory of neighbor-neighbor interactions in polynucleotides, involving the forces between the bases. Application of this technique to further studies of polynucleotides and polypeptides is discussed. 相似文献
The stereochemistry of some dihydrofurano-isoflavones previously isolated from white lupin roots, or obtained following fungal metabolism of prenylated isoflavones, was investigated using CD spectroscopy. The osmate ester/pyridine complex of dextrorotatory lupinisoflavone A (1) exhibited a positive CD Cotton effect at 480 nm, indicating a side-structure configuration (S at C- 2″), opposite to that of natural rotenone (9), which afforded a negative Cotton effect at 474 nm (R- configuration at C-2′ on the side structure [ring E]). The stereochemistry of the laevorotatory luteone metabolite BC-1 (2) and lupinisoflavone D (4) (both ^-configuration at C-2″) was similarly determined after converting to the corresponding dehydrate (10) or trimethyl-dehydrate (1b, 10a). 相似文献
Ultraviolet optical rotatory dispersion curves of mucopolysaccharides exhibit particular Cotton effects in the spectral region of the n–π and π–π amide transitions. Two general patterns emerge: (1) enhancement of negative rotation and of the first negative Cotton effect (troughs 217–220 mμ) and (2) relative dominance of the positive Cotton effect in the π–π transition region (peak ~198 mμ). Groups (1) and (2) can be correlated with a structural difference in the linkages of the amino sugars: (1) occurs with polymers containing 3-1-linked glycosamino sugars and (2) with glycosamino moieties linked 4–1 by either α- or β-glycosidie bonds. Measurements of the circular dichroic absorption bands support the qualitative conclusions from optical rotation. All mucopolysaccharides exhibit a first, negative band centered at 208–211 mμ, while only those in group (2) show, in addition, a positive band centered at 189–192 mμ. A suggested unifying model considers that difference in kind and/or degree of preferred geometry of the amide groups obtains from two forms of secondary order: (1) having a linear hydrogen bond from the N (acceptor) to the (C2)O—H of the preceding uronic acid and (2) having a linear hydrogen bond from the N (acceptor) to the (C2 or 3) O—H of the following sugar. The hydrogen bonds would have similar strength but opposite directions in two systems towards the nonreducing end (1) or towards the reducing end (2)], closing eight-membered rings 相似文献
Platyrrhine (New World) monkeys possess highly polymorphic color vision owing to allelic variation of the single-locus L/M opsin gene on the X chromosome. Most species consist of female trichromats and female and male dichromats. Howlers (genus Alouatta) are an exception; they are considered to be routinely trichromatic with L and M opsin genes juxtaposed on the X chromosome, as seen in catarrhine primates (Old World monkeys, apes, and humans). Yet it is not known whether trichromacy is invariable in howlers. We examined L/M opsin variation in wild howler populations in Costa Rica and Nicaragua (Alouatta palliata) and Belize (A. pigra), using fecal DNA. We surveyed exon 5 sequences (containing the diagnostic 277th and 285th residues for λmax) for 8 and 18 X chromosomes from Alouatta palliata and A. pigra, respectively. The wavelengths of maximal absorption (λmax) of the reconstituted L and M opsin photopigments were 564 nm and 532 nm, respectively, in both species. We found one M–L hybrid sequence with a recombinant 277/285 haplotype in Alouatta palliata and two L–M hybrid sequences in A. pigra. The λmax values of the reconstituted hybrid photopigments were in the range of 546~554 nm, which should result in trichromat phenotypes comparable to those found in other New World monkey species. Our finding of color vision variation due to high frequencies of L/M hybrid opsin genes in howlers challenges the current view that howlers are routine and uniform trichromats. These results deepen our understanding of the evolutionary significance of color vision polymorphisms and routine trichromacy and emphasize the need for further assessment of opsin gene variation as well as behavioral differences among subtypes of trichromacy. 相似文献