Absorption Spectroscopy and the Structures of the Diosterols

Fieser, Louis; Fieser, Mary; Rajagopalan, S.

doi:10.1021/jo01164a003

Cited by 63 publications

(33 citation statements)

References 6 publications

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“…For example, the shoulder of absorbance for polyethylene after 1600 sec of PIII treatment is observed at 2.5 µm wavelength, corresponding to large islands consisting of conjugated aromatic rings arranged in graphite-like structures -nanographite islands. Using the Woodward-Fieser rule [76,77], the absorbance at 2.5 nm wavelength corresponds to graphitic island containing about 40 conjugated aromatic rings, that would have characteristic size of about 1.5 nm. This value is comparable with the 1 nm size of graphite islands estimated from the Raman spectra.…”

Section: Structure Changes In Polyethylene Surface Layer Resulting Frmentioning

confidence: 99%

Mechanisms for Covalent Immobilization of Horseradish Peroxidase on Ion-Beam-Treated Polyethylene

et al. 2012

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The surface of polyethylene was modified by plasma immersion ion implantation. Structure changes including carbonization and oxidation were observed. High surface energy of the modified polyethylene was attributed to the presence of free radicals on the surface. The surface energy decay with storage time after treatment was explained by a decay of the free radical concentration while the concentration of oxygen-containing groups increased with storage time. Horseradish peroxidase was covalently attached onto the modified surface by the reaction with free radicals. Appropriate blocking agents can block this reaction. All aminoacid residues can take part in the covalent attachment process, providing a universal mechanism of attachment for all proteins. The native conformation of attached protein is retained due to hydrophilic interactions in the interface region. The enzymatic activity of covalently attached protein remained high. The long-term activity of the modified layer to attach protein is explained by stabilisation of unpaired electrons in sp2 carbon structures. A high concentration of free radicals can give multiple covalent bonds to the protein molecule and destroy the native conformation and with it the catalytic activity. The universal mechanism of protein attachment to free radicals could be extended to various methods of radiation damage of polymers.

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Section: Structure Changes In Polyethylene Surface Layer Resulting Frmentioning

confidence: 99%

Mechanisms for Covalent Immobilization of Horseradish Peroxidase on Ion-Beam-Treated Polyethylene

et al. 2012

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“…The absorption spectra of extracted polyenes, including carotenoids, depend largely on the number of conjugated double bonds in their molecules. According to the well‐known Woodward–Fieser rules, the wavelengths of maximum absorption would exhibit higher values of approximately 30 nm for each additional conjugated double bond, due to the fact that an increase in the number of conjugated double bonds in polyene backbone would decrease the energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). This gap lowers the absorption energy, and thus, the maximum absorption in the ultraviolet–visible spectrum (λmax) shifts to the longer wavelength.…”

Section: Discussionmentioning

confidence: 99%

Chemical basis of molluscan shell colors revealed with in situ micro‐Raman spectroscopy

Ishikawa

Kagi

Sasaki

et al. 2019

J Raman Spectroscopy

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Molluscan shells exhibit a wide variety of color tones and patterns that are thought to increase fitness in different natural habitats. However, the chemical aspects of shell pigments have not been well understood. We studied the chemical basis of molluscan shell colors via resonance Raman microspectroscopy using a 514.5‐nm laser on six gastropod, 15 bivalve, and one cephalopod species. Polyene specific signals for C═C (ν1) or C─C (ν2) stretching bands were detected principally from the pigmented regions, and those peak positions correlated with the pigment colors. Because Raman shifts of those bands depend on the conjugation length of polyene backbones, which in turn, affect the highest occupied molecular orbital/lowest unoccupied molecular orbital energy gap, our observations suggest that the conjugation length of polyene is a determinant factor of shell color. Further, our observations and data from previous studies seemed to reveal a quantitative relationship between polyene backbone length and shell color. From an analysis of 89 polyene‐based pigments in 45 molluscan species, we found that yellow, orange/red, and purple/brown/black pigments originate from polyenes with conjugation lengths of 7–9, 9–10, and 10–12, respectively. The shell color shifts from yellow, orange, and red to purple as the polyene chain length increases as reported for free carotenoids. The biological mechanisms underlying the spatial regulations of polyene conjugation systems in molluscan shells will be the most important and intriguing issue to be addressed in the future.

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“…The latter was prepared by oxidation of the isolated "triol" using N-bromosuccinimide in 10 Oi0 aqueous dioxan [14]. Thin layer chromatography of the oxidation product showed that the radioactivity was localised in a compound having the characteristics of cholestan-3/3,5~x-diol-6-one.…”

Section: Identification Of Productsmentioning

confidence: 99%

The Oxidation of Cholesterol in Rat Liver Sub‐Cellular Particles

Mitton¹,

Scholan²,

Boyd³

1971

European Journal of Biochemistry

103

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Various sub‐cellular fractions of rat liver exert catalytic effects on the oxidation of [4‐14C]‐cholesterol to 7α‐hydroxy‐[4‐14C]cholesterol and to other [4‐14C]cholesterol oxidation products. Some of these oxidation products created in these studies in vitro appear to be aberrant oxidation products in that there is no evidence that they are intermediates in the physiological oxidation of cholesterol. These aberrant oxidation products have been classified as autoxidation products despite the fact that the autoxidation reactions in these cell fractions appear to require the participation of NADPH, native proteins and perhaps certain nucleotides for the production of these compounds. The enzyme system catalysing the oxidation of [4‐14C]cholesterol to 7α‐hydroxy‐[4‐14C]cholesterol could be assayed in a 18000 ×g supernatant fraction of rat liver. This enzymic reaction was adversely affected by extensive homogenisation of liver tissue and by prolonged incubation periods, both of which tended to increase the autoxidation reactions. The cholesterol‐7α‐hydroxylase enzyme showed optimal activity in the presence of NADPH and oxygen. In the washed liver microsomal fraction, [4‐14C]cholesterol was extensively oxidised in the presence of NADPH, ADP and ferrous ions to 7β‐hydroxycholesterol, cholestan‐3β, 5α, 6β‐triol and 7‐ketocholesterol. Further investigation showed that another compound was also formed, having the same mobility as 7‐ketocholesterol in the thin layer solvent systems used. Reduction and further metabolism of this compound compared with reference standards suggested that it may be a cholesterol oxide, formed under conditions where peroxidation of microsomal lipids could occur. A comparison of the effects of Tris and phosphate buffers, and various nucleotides suggests that cholesterol autoxidation in the microsomal fraction may be related to the general lipid peroxidation systems. The boiled 100000 ×g liver supernatant preparation or 2‐mercaptoethylamine both effectively quenched cholesterol peroxidation, at the same time stimulating the cholesterol‐7α‐hydroxylase system. A scheme has been suggested to explain the liver microsomal cholesterol autoxidation or peroxidation and to contrast this process with the mixed function oxidase involved in the enzymic cholesterol‐7α‐hydroxylase reaction.

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Absorption Spectroscopy and the Structures of the Diosterols

Cited by 63 publications

References 6 publications

Mechanisms for Covalent Immobilization of Horseradish Peroxidase on Ion-Beam-Treated Polyethylene

Mechanisms for Covalent Immobilization of Horseradish Peroxidase on Ion-Beam-Treated Polyethylene

Chemical basis of molluscan shell colors revealed with in situ micro‐Raman spectroscopy

The Oxidation of Cholesterol in Rat Liver Sub‐Cellular Particles

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