Singlet oxygen quenching activity of furan fatty acids: Kinetic and thermodynamics study

We have undertaken a detailed study of the reactivity of furan fatty acids (F-acids) with singlet oxygen (¹O₂) produced by thermal decomposition of endoperoxide and photosensitizer reaction of rose bengal in ethanol. Accordingly, we measured the second order rate constant (k_Q) for the reaction of F-acids with ¹O₂. As a result, the reactivity of F-acids against ¹O₂ exhibited a decrease in the order tetra-alkyl F-acid (F₃) > tri-alkyl F-acid (F₂) > di-alkyl F-acid (NMF). In addition, we also employed the density functional theory (DFT) and quantum chemical calculations to predict the chemical reactivity, stability, and thermodynamic properties of F-acids with respect to the quenching ¹O₂. In consequence, it is clear that log k_Q values of F-acids correlate with the energy level of the highest occupied molecular orbital (E_HOMO), and HOMO of F-acids may react with the lowest unoccupied molecular orbitals (LUMO) of ¹O₂. Moreover, the reaction of F-acids with ¹O₂ proceeds spontaneously in ethanol based on the calculation by thermodynamics method. These results suggest that the F-acids may contribute to the protection of oxidative damage in animals by quenching ¹O₂.     

Singlet oxygen lifetime in polymer films

Singlet oxygen lifetimes [τ(¹O₂)] in polymer matrices were calculated using the strong exponential correlation between the incremental rate constant (K_xy) of energy transfer from ¹O₂ to terminal oscillators X—Y contained in solvent molecules and the energy (E_xy) of the highest fundamental vibration of the oscillator X—Y. The lifetimes in polymers correspond very well to experimental data in the literature. They depend only on the nature and quantity of molecular oscillators in the medium but not on the state of aggregation. The computed lifetimes in common polymers vary only from 10 to 50 μs. Therefore the lifetime of ¹O₂ in singlet oxygen reactions in polymers is of secondary importance in comparison to the diffusion coefficient.     

Characterization of naturally occurring α-hydroxylinolenic acid

The seed oil ofThymus vulgaris L. (Labiatae) contains 13% of a new unsaturated hydroxy fatty acid which has been characterized as α-hydroxylinolenic acid. This oil also contains the previously unknown norlinolenic (all-cis-8,11,14-heptadecatrienoic) acid (2%) and linolenic acid (55%). The co-occurrence of these three acids suggests that the C₁₇ acid is biosynthesized by α-oxidation of linolenic acid. Presented at the AOCS-AACC Joint Meeting, Washington, D. C., April 1968. No. Utiliz. Res. Dev. Div., ARS, USDA.     

Bioassay of naturally occurring allelochemicals for phytotoxicity

The bioassay has been one of the most widely used tests to demonstrate allelopathic activity. Often, claims that a particular plant species inhibits the growth of another are based entirely on the seed germination response to solvent extracts of the suspected allelopathic plant; few of these tests are of value in demonstrating allelopathy under natural conditions. The veracity of the bioassay for evaluating naturally occurring compounds for phytotoxicity depends upon the physiological and biochemical response capacity of the bioassay organism and the mechanism(s) of action of the allelochemicals. The possibility that more than one allelochemical, acting in concert at very low concentrations, may be responsible for an observed allelopathic effect makes it imperative that bioassays be extremely sensitive to chemical growth perturbation agents. Among the many measures of phytotoxicity of allelochemicals, the inhibition (or stimulation) of seed germination, radicle elongation, and/or seedling growth have been the parameters of choice for most investigations. Few of these assays have been selected with the view towards the possible mechanism of the allelopathic effect.     

Berberine: A naturally occurring phototoxic alkaloid

The isoquinoline alkaloid berberine, present in nine different plant families was found to be phototoxic to mosquito larvae. In the presence of near UV the LC₅₀ for acute 24-hr toxicity was 8.8 ppm compared to 250 ppm for dark controls. Mosquito larvae that were treated with 10 ppm berberine plus near UV for 24 hr and then transferred to berberine-free water showed decreased larval survival and resulted in a smaller cumulative number of pupae and adults as compared to controls, during a subsequent 4-week development period. Berberine was found to be a singlet O₂ generator in experiments with the chemical trap 2,5-dimethyl furan. A slight increase in chromosome aberrations in Chinese hamster cells was also observed with berberine plus near UV treatment. The significance of the phototoxicity of berberine is discussed in relation to plant-insect relations.     

Lipoxygenase inhibition by naturally occurring monoenoic fatty acids

Lipoxygenase activity was not detected in preparations from several varieties of rapessed. Erucic acid, one of the main components of rapessed oil, competitively inhibited both soybean and peanut lipoxygenases. Various other long-chain monoenoic fatty acids were assayed for their effects on lipoxygenase activity with linoleic acid as substrate. Fatty acid chain length, from C₁₆, to C₂₄, was not a significant factor, but position of the point of unsaturation did affect enzyme activity. The position of the double bond from the carboxyl group seemed to be more significant than the distance between the point of unsaturation and the methyl terminal group in terms of inhibition.     

Light fastness of naturally occurring anthraquinone dyes on nylon

Nylon fabric has been dyed with two purified components of Indian madder, purpurin (1,2,4-trihydroxyanthraquinone) and munjistin (1,3-dihydroxy-2-carboxyanthraquinone). The light and wash fastness of dyed and mordanted samples has been studied. Purpurin showed much better resistance to photofading than munjistin. It was found that the type of mordant and the method of mordanting significantly affected the rate and extent of photofading. The use of copper or ferrous sulphate gave high resistance to fading, whereas stannous chloride or alum did not. On the other hand, light fastness was improved when postmordanting was conducted with copper or ferrous iron, but pre-mordanting was superior in the case of stannous chloride or alum.     

Singlet oxygen in copper-catalyzed lipid peroxidation in erythrocyte membranes

Lipid hydroperoxide was generated in human erythrocyte membranes by irradiation with near ultraviolet (UV) light in the presence of a photosensitizer, hematoporphyrin, but no production of 2-thiobarbituric acid-reactive materials (malonaldehyde and its precursors) was detected. Incubation of the irradiated membranes with CuSO₄ led to increased levels of hydroperoxide and formation of malonaldehyde. Hydroperoxides were essential for initiating the Cu(II)-catalyzed peroxidation as no significant activity was observed with nonirradiated membranes and Cu(II) unless an organic peroxide, either t-butyl hydroperoxide or cumene hydroperoxide, was added. Catalytic activity was also found with Fe(II), but not with other metal ions tested. The peroxidation catalyzed with Cu(II) was partially inhibited by several singlet oxygen quenchers but was not affected by superoxide dismutase, catalase or OH^• radical scavengers. The possible involvement of singlet oxygen in the Cu(II)-catalyzed peroxidation reaction was further supported by a 3-fold enhancement of malonaldehyde production in D₂O.     

Effects of quenching mechanisms of carotenoids on the photosensitized oxidation of soybean oil

The effects of 0, 1.0 × 10”⁻⁵, 2.5 × 10⁻⁵, and 5.0 × 10⁻⁵ M β-apo-8'-carotenal, β-carotene, and canthaxanthin on the photooxidation of soybean oil in methylene chloride containing 3.3 × 10⁻⁹ M chlorophyll b were studied by measuring peroxide values and conjugated diene content. β-Apo-8'-carotenal, β-carotene, and canthaxanthin contain 10,11, and 13 conjugated double bonds, respectively. The peroxide values and conjugated diene contents of oils containing the carotenoids were significantly lower (P<0.05) than those of control oil containing no carotenoid. As the number of conjugated double bonds of the carotenoids increased, the peroxide values of soybean oils decreased significantly (P<0.05). The quenching mechanisms and kinetics of the carotenoids in the photosensitized oxidation of soybean oil were studied by measuring peroxide values. The steady-state kinetics study showed that carotenoids quenched singlet oxygen to reduce chlorophyll-sensitized photooxidation of soybean oil. The singlet-oxygen quenching rate constants ofβ- apo-8'-carotenal, β-carotene, and canthaxanthin were 3.06 × 10⁹, 4.60 × 10⁹, and 1.12 × 10¹⁰ M⁻¹sec⁻¹, respectively.     

A quantitative determination of phosphonate phosphorus in naturally occurring aminophosphonates

A new method is described for the quantitative determination of naturally occurring aminophosphonates. Samples are treated sequentially with hydrochloric acid and alkaline phosphatase to convert esters to inorganic phosphate without destruction of phosphonates. The difference between inorganic phosphate and total phosphorus is then a measure of phosphonate phosphorus.     

Synthesis and antifungal activity of analogues of naturally occurring botrydial precursors

Analog compounds of the proposed intermediates of the biogenetic pathway to botrydial have been synthesized. These compounds were tested for their potential antifungal activity against the phytopathogenBotrytis cinerea. Our results showed a fungistatic effect of some compounds on mycelium growth. The most significant effect was exerted by 2--hydroxy-2,3-dihydro-1-epiprobotrydial, which inhibited growth ofB. cinerea. Some aspects of structure-activity relationships are discussed.     

A naturally occurring all-cis 6,9,12,15-Octadecatetraenoic acid in plant oils

Oil extracted from freshly ground seed ofOnosmodium occidentale contains 9-oleic, 9,12-linoleic, 6,9,12-linolenic, 9,12,15-linolenic, 6,9,12, 15-octadecatetraenoic and 11-eicosenoic as unsaturated fatty acids. Column chromatography employing silicic acid-silver nitrate, and oxidation with permanganate-periodate was used in conjunction with GLC to confirm the structures of the unsaturated acids. Oils extracted from other members of the Boraginaceae family also contain the 6,9,12, linolenic and octadecatetraenoic acids.     

Singlet oxygen microscope: from phase-separated polymers to single biological cells

The lowest excited electronic state of molecular oxygen, singlet molecular oxygen (a1Deltag), is an intermediate in many chemical and biological processes. Tools and methods have been developed to create singlet-oxygen-based optical images of heterogeneous samples that range from phase-separated polymers to biological cells. Such images provide unique insight into a variety of oxygen-dependent phenomena, including the photoinitiated death of cells.     

Crystallization studies on linear aliphatic polyamides derived from naturally occurring carbohydrates

The thermal behavior of three series of sugar‐derived polyamides (PA‐nSu) made from the arabinaric, mannaric and galactaric acids, respectively, and α,ω‐alkanediamines containing from 6 to 12 methylene units was investigated by DSC supported by polarizing optical microscopy. Crystallization from the melt under both isothermal and nonisothermal conditions was studied in detail. Melting temperatures of PA‐nSu were found to decay steadily with the length of the polymethylene segment. Data registered from isothermally crystallized samples were analyzed by the kinetics Avrami approach, which revealed that crystallization initiated by combination of instantaneous and sporadically nucleation. Crystallization half‐times indicated that “crystallizability” of PA‐nSu increases with the number of methylenes in the diamine unit and decreases with the length of the carbohydrate‐derived unit. Higher crystallinities were attained for polyamides made of shorter aldaric acids. The relation between thermal data and the configuration of the sugar moiety present in PA‐nSu was discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Assembly of naturally occurring glycosides, evolved tactics, and glycosylation methods

Glycosylation of proteins and lipids is critical to many life processes. Secondary metabolites (or natural products), such as flavonoids, steroids, triterpenes, and antibiotics, are also frequently modified with saccharides. The resulting glycosides include diverse structures and functions, and some of them have pharmacological significance. The saccharide portions of the glycosides often have specific structural characteristics that depend on the aglycones. These molecules also form heterogeneous "glycoform" mixtures where molecules have similar glycosidic linkages but the saccharides vary in the length and type of monosaccharide unit. Thus, it is difficult to purify homogeneous glycosides in appreciable amounts from natural sources. Chemical synthesis provides a feasible access to the homogeneous glycosides and their congeners. Synthesis of a glycoside involves the synthesis of the aglycone, the saccharide, the connection of these two parts, and the overall manipulation of protecting groups. However, most synthetic efforts to date have focused on the aglycones, treating the attachment of saccharides onto the aglycones as a dispensable topic. The synthesis of the aglycone and the synthesis of the saccharide belong to two independent categories of chemistry, and different types of the aglycones and saccharides pose as specific synthetic subjects in their own disciplines. The only reaction that integrates the broad chemistry of glycoside synthesis is the glycosidic bond formation between the saccharide and the aglycone. Focusing on this glycosylation reaction in this Account, we string together our experience with the synthesis of the naturally occurring glycosides. We briefly describe the synthesis of 18 glycosides, including glycolipids, phenolic glycosides, steroid glycosides, and triterpene glycosides. Each molecule represents a prototypical structure of a family of the natural glycosides with interesting biological activities, and we emphasize the general tactics for the synthesis of these diverse structures. We provide a rationale for four tactics for the synthesis of glycosides, based on the stage at which the glycosidic bond is formed between the saccharide and the aglycone. This choice of tactic determines the success or failure of a synthesis, and the flexibility and the overall efficiency of the synthesis as well. Toward the synthesis of heterogeneous glycoform mixtures, we discuss successive and random glycosylation reactions. Finally, we have developed two new glycosylation protocols that address the challenges in the glycosylation of aglycones that are poorly nucleophilic, extremely acid labile, or extremely electrophilic. One of these new protocols takes advantage of glycosyl trifluoroacetimidate donors, and a second protocol uses gold(I)-catalyzed glycosylation with glycosyl ortho-alkynylbenzoate donors.     

Recovery of titanium dioxide from naturally occurring ilmenite by high-temperature borate fusion

Fusion of naturally-occurring ilmenite at 1273 K with Li₂O·XB₂O₃ solvents (where X = 2, 4, 5, 6, 7 and 8) gives, after boiling water extraction of the crushed solidified melts, maximum (68.1%) recovery of TiO₂ (as rutile) for X = 6. Extraction with hot 9 mol dm^?3H₂SO₄ of the water-insoluble residue from the fusion of ilmenite with Li₂O·6B₂O₃ yields a product containing 86 weight % TiO₂ and only a trace of iron. The overall process is a possible route for upgrading ilmenite to a rutile-enriched product.     

The fatty acid composition of small and large naturally occurring milk fat globules

Native milk fat globules of various mean diameters, ranging from d₄₃ = 1.5 to 7.3 μm, were obtained using microfiltration of raw whole milk acquired in winter and spring. After total lipid extraction, fatty acid composition was characterized by methyl and butyl ester analysis using gas chromatography. The oleic and linoleic acid content of milk obtained in winter increased with fat globule size, whereas myristic and palmitic acid decreased. There was significantly more lauric, myristic and palmitoleic acid, and less stearic acid in small fat globules compared to large fat globules in milk obtained in both winter and spring. The relative content of oleic and linoleic acids were found to depend on fat globule size and season. Results are interpreted on the basis of the relative content of milk fat globule membrane depending on fat globule size, and on consequences of compositional variations on milk fat globule melting behavior.