Alkaline Hydrogen Peroxide Oxidation Research Articles

Eumelanin Detection in Melanized Focal Changes but Not in Red Focal Changes on Atlantic Salmon (Salmo salar) Fillets

Superficial discolored spots on Atlantic salmon (Salmo salar) fillets are a serious quality problem for commercial seafood farming. Previous reports have proposed that the black spots (called melanized focal changes (MFCs)) may be melanin, but no convincing evidence has been reported. In this study, we performed chemical characterization of MFCs and of red pigment (called red focal changes (RFCs)) from salmon fillets using alkaline hydrogen peroxide oxidation and hydroiodic acid hydrolysis. This revealed that the MFCs contain 3,4-dihydroxyphenylalanine (DOPA)-derived eumelanin, whereas the RFCs contain only trace amounts of eumelanin. Therefore, it is probable that the black color of the MFCs can be explained by the presence of eumelanin from accumulated melanomacrophages. For the red pigment, we could not find a significant signature of either eumelanin or pheomelanin; the red color is probably predominantly hemorrhagic in nature. However, we found that the level of pigmentation in RFCs increased together with some melanogenic metabolites. Comparison with a “mimicking experiment”, in which a mixture of a salmon homogenate + DOPA was oxidized with tyrosinase, suggested that the RFCs include conjugations of DOPAquinone and/or DOPAchrome with salmon muscle tissue proteins. In short, the results suggest that melanogenic metabolites in MFCs and RFCs derive from different chemical pathways, which would agree with the two different colorations deriving from distinct cellular origins, namely melanomacrophages and red blood cells, respectively.

Biodegradable, Colorless, and Odorless PLA/PBAT Bioplastics Incorporated with Corn Stover

The effective use of agricultural lignocellulose resources in biodegradable bioplastics has become the focus of people’s attention due to the inappropriate disposal of agricultural waste and plastic materials. However, the repulsive smell and uncontrollable color of agricultural lignocellulose-based materials limit their potential to replace common consumer plastics. In this study, when the corn stover (CS) meal enforced the PLA/PBAT matrix using the melt blending method, the lignin and hemicellulose components were shown to substantially impact the color darkening and unsavory odor release for the resultant bioplastic; therefore, an optimized scalable alkaline hydrogen peroxide oxidation that can be performed using traditional pulp and paper production lines was used to modify CS on a large scale (LCS) to enhance the properties of bioplastics fabricated with the PLA/PBAT matrix. As a result, the appearance color and odor character of the bioplastic enforced by LCS have been significantly improved compared to those of natural CS. In addition, the bioplastic (LCS/PLA/PBAT) exhibited good tensile strength (9.7 MPa), flexural strength (18.1 MPa), elongation at break (61.8%), and surface hydrophobicity with a contact angle value of 91.6°, which could meet the requirement of the Chinese National Standard for Packaging. The reinforcing effect of LCS on these performances lay in its rigid structure with a strong fiber network, high content of cellulose crystalline, and hydrophobic nature of lignin after treatment, as proven by FTIR, XRD, and SEM results. Therefore, our bioplastics filled with treated agricultural waste are attractive appearance-wise, economically competitive, and biodegradable, making them a sustainable alternative to common consumer plastics.

Iron and copper ions accelerate and modify dopamine oxidation to eumelanin: implications for neuromelanin genesis.

Dopamine (DA) is a precursor of neuromelanin (NM) synthesized in the substantia nigra of the brain. NM is known to contain considerable levels of Fe and Cu. However, how Fe and Cu ions affect DA oxidation to DA-eumelanin (DA-EM) and modify its structure is poorly understood. EMs were prepared from 500µM DA, dopaminechrome (DAC), or 5,6-dihydroxyindole (DHI). Autoxidation was carried out in the absence or presence of 50µM Fe(II) or Cu(II) at pH 7.4 and 37℃. EMs were characterized by Soluene-350 solubilization analyzing absorbances at 500nm (A500) and 650nm (A650) and alkaline hydrogen peroxide oxidation (AHPO) yielding various pyrrole carboxylic acids. Pyrrole-2,3,4,5-tetracarboxylic acid (PTeCA) served as a molecular marker of cross-linked DHI units. Importantly, Fe and Cu accelerated DA oxidation to DA-EM and DHI oxidation to DHI-EM several-fold, whereas these metals only weakly affected the production of DAC-EM. The A500 values indicated that DA-EM contains considerable portions of uncyclized DA units. Analysis of the A650/A500 ratios suggests that Fe and Cu caused some degradation of DHI units of DA-EM during 72-h incubation. Results with AHPO were consistent with the A500 values and additionally revealed that (1) DA-EM is less cross-linked than DAC-EM and DHI-EM and (2) Fe and Cu promote cross-linking of DHI units. In conclusion, Fe and Cu not only accelerate the oxidation of DA to DA-EM but also promote cross-linking and degradation of DHI units. These results help to understand how Fe and Cu in the brain affect the production and properties of NM.

5,6-Dihydroxyindole eumelanin content in human skin with varying degrees of constitutive pigmentation.

Human skin contains two distinct components: brown to black, insoluble eumelanin and light colored, alkaline-soluble pheomelanin. Eumelanin consists of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) moieties, while pheomelanin consists of benzothiazine (BT) and benzothiazole (BZ) moieties. These melanin monomer units can be quantitatively analyzed through specific degradation products by high-performance liquid chromatography (HPLC). Alkaline hydrogen peroxide oxidation (AHPO) of eumelanin gives rise to pyrrole-2,3,5-tricarboxylic acid (PTCA) and pyrrole-2,3-dicarboxylic acid (PDCA) as specific degradation products of the DHICA and DHI moieties, respectively. BZ moiety in pheomelanin can be analyzed as thiazole-2,4,5-tricarboxylic acid (TTCA). By reductive hydrolysis with hydroiodic acid, BT moieties in pheomelanin can be analyzed as 4-amino-3-hydroxyphenylalanine (4-AHP). As a recently improved AHPO-HPLC method enabled a better characterization of PDCA, this prompted us to address the question of DHI to DHICA ratio in human skin samples with varying degrees of constitutive pigmentation ranging from very light to dark. Results showed for the first time the ratio of 4 moieties: DHI 35%, DHICA 41%, BZ 20%, and BT 4%. The ratio is constant regardless of the degree of pigmentation. The high content of DHICA moiety may impart an antioxidant property to the epidermis melanin.

Improvement of Biomethane Production from Organic Fraction of Municipal Solid Waste (OFMSW) through Alkaline Hydrogen Peroxide (AHP) Pretreatment

The organic fraction resulting from the separate collection of municipal solid waste (OFMSW) is an abundant residue exploitable for biofuel production. Anaerobic digestion (AD) is one of the most attractive technologies for the treatment of organic wastes thanks to the generation of biogas with a high methane content. However, because of its complex composition, the direct digestion of OFMSW can be less effective. To overcome these difficulties, many pretreatments are under development. In this work, the efficacy of alkaline hydrogen peroxide (AHP) oxidation was assessed for the first time as a pretreatment of OFMSW to enhance its anaerobic biodegradability. In this regard, many AHP batch tests were executed at pH 9 and by changing the peroxide dosages up to 1 gH2O2/gCOD, under room temperature and pressure conditions. Afterwards, biomethane potential tests (BMP) were conducted to evaluate the performance of anaerobic digestion both on raw and pretreated OFMSW. The pretreatment tests demonstrated that AHP induces only a weak reduction in the organic load, reaching a maximum COD removal of about 28%. On the other hand, notable productions of volatile fatty acids (VFA) were found. In fact, by applying a peroxide dose of just 0.025 gH2O2/gCOD, there was a doubling in VFA concentration, which increased by five times with the highest H2O2 amount. These results indicate that AHP mainly causes the conversion of complex organic substrates into easily degradable compounds. This conversion made it possible to achieve much better performance during the BMP tests conducted with the pretreated waste compared to that carried out on fresh OFMSW. Indeed, a low methane production of just 37.06 mLCH4/gTS was detected on raw OFMSW. The cumulated CH4 production in the pretreated samples increased in response to the increase in H2O2 dosage applied during AHP. Maximum specific productions of about 463.7 mLCH4/gTS and 0.31 LCH4/gCODremoved were calculated on mixtures subjected to AHP. On these samples, the satisfactory evolution of AD was confirmed by the process parameters calculated by modeling the cumulated CH4 curves through a new proposed formulation of the Gompertz equation.

Photobleached Oxidative Degradation of Melanins: Chemical Characterization of Melanins Present in Alpaca Fiber.

In order to characterize the phenotype and to examine the effects of sun exposure on the color and structure of eumelanin (EM) and pheomelanin (PM) in alpaca fibers, we applied Soluene-350 solubilization, alkaline hydrogen peroxide oxidation (AHPO) and hydroiodic acid (HI) hydrolysis to the base and tip fibers of 20 true-black (TB) and 20 warm-black (WB) alpacas. We analyzed absorbances at 500 nm (A500) and 650 nm (A650), Free and Total pyrrole-2,3,5-tricarboxylic acid (PTCA), 2,3,4,5-tetracarboxylic acid (PTeCA) as degradative products from EM, and 4-amino-3-hydroxyphenylalanine (4-AHP), 3-amino-4-hydroxyphenylalanine (3-AHP) and thiazole-2,4,5-tricarboxylic acid (TTCA) as degradative products from PM. We found that the ratio of PTeCA/Total PTCA increased significantly from the base to the tip in both colors of alpaca fibers, while the ratios of A650/A500 and 4-AHP/3-AHP decreased significantly. These results show that structures made of both EM and PM in alpaca fibers are modified significantly by sun exposure inducing color change. This study indicates that the ratios of A650/A500, PTeCA/Total PTCA and 4-AHP/3-AHP are highly sensitive markers of color change and photodegradation of EM and PM, respectively.

Improved HPLC Conditions to Determine Eumelanin and Pheomelanin Contents in Biological Samples Using an Ion Pair Reagent.

Alkaline hydrogen peroxide oxidation (AHPO) of eumelanin and pheomelanin, two major classes of melanin pigments, affords pyrrole-2,3,5-tricarboxylic acid (PTCA), pyrrole-2,3-dicarboxylic acid (PDCA) and pyrrole-2,3,4,5-tetracarboxylic acid (PTeCA) from eumelanin and thiazole-2,4,5-tricarboxylic acid (TTCA) and thiazole-4,5-dicarboxylic acid (TDCA) from pheomelanin. Quantification of these five markers by HPLC provides useful information on the quantity and structural diversity of melanins in various biological samples. HPLC analysis of these markers using the original method of 0.1 M potassium phosphate buffer (pH 2.1):methanol = 99:1 (85:15 for PTeCA) on a reversed-phase column had some problems, including the short lifetime of the column and, except for the major eumelanin marker PTCA, other markers were occasionally overlapped by interfering peaks in samples containing only trace levels of these markers. These problems can be overcome by the addition of an ion pair reagent for anions, such as tetra-n-butylammonium bromide (1 mM), to retard the elution of di-, tri- and tetra-carboxylic acids. The methanol concentration was increased to 17% (30% for PTeCA) and the linearity, reproducibility, and recovery of the markers with this improved method is good to excellent. This improved HPLC method was compared to the original method using synthetic melanins, mouse hair, human hair, and human epidermal samples. In addition to PTCA, TTCA, a major marker for pheomelanin, showed excellent correlations between both HPLC methods. The other markers showed an attenuation of the interfering peaks with the improved method. We recommend this improved HPLC method for the quantitative analysis of melanin markers following AHPO because of its simplicity, accuracy, and reproducibility.

Chemical characterization of pterosaur melanin challenges color inferences in extinct animals

Melanosomes (melanin-bearing organelles) are common in the fossil record occurring as dense packs of globular microbodies. The organic component comprising the melanosome, melanin, is often preserved in fossils, allowing identification of the chemical nature of the constituent pigment. In present-day vertebrates, melanosome morphology correlates with their pigment content in selected melanin-containing structures, and this interdependency is employed in the color reconstruction of extinct animals. The lack of analyses integrating the morphology of fossil melanosomes with the chemical identification of pigments, however, makes these inferences tentative. Here, we chemically characterize the melanin content of the soft tissue headcrest of the pterosaur Tupandactylus imperator by alkaline hydrogen peroxide oxidation followed by high-performance liquid chromatography. Our results demonstrate the unequivocal presence of eumelanin in T. imperator headcrest. Scanning electron microscopy followed by statistical analyses, however, reveal that preserved melanosomes containing eumelanin are undistinguishable to pheomelanin-bearing organelles of extant vertebrates. Based on these new findings, straightforward color inferences based on melanosome morphology may not be valid for all fossil vertebrates, and color reconstructions based on ultrastructure alone should be regarded with caution.

Photodegradation of Eumelanin and Pheomelanin and Its Pathophysiological Implications.

Eumelanin is photoprotective for pigmented tissues while pheomelanin is phototoxic. In this review, we summarize current understanding of how eumelanin and pheomelanin structures are modified by ultraviolet A (UVA) and also by visible light and how reactive oxygen species participate in those processes. Alkaline hydrogen peroxide oxidation was employed to characterize eumelanin and benzothiazole-type pheomelanin, giving pyrrole-2,3,5-tricarboxylic acid (PTCA) and thiazole-2,4,5-tricarboxylic acid (TTCA), respectively. Reductive hydrolysis with hydroiodic acid gives 4-amino-3-hydroxyphenylalanine (4-AHP) from the benzothiazine moiety of pheomelanin. The results show that the photoaging of eumelanin gives rise to free PTCA (produced by peroxidation in situ) and pyrrole-2,3,4,5-tetracarboxylic acid (PTeCA, produced by cross-linking). The TTCA/4-AHP ratio increases with photoaging, indicating the conversion of benzothiazine to the benzothiazole moiety. Analysis of those markers and their ratios show that both eumelanin and pheomelanin in human retinal pigment epithelium melanosomes undergo extensive structural modifications due to their lifelong exposure to blue light. Using synthetic melanins, we also found that singlet oxygen, in addition to superoxide anions, is photogenerated and quenched upon UVA irradiation. The (patho)physiological significance of those findings is discussed in relation to the tanning process, to melanomagenesis in the skin and to age-related macular degeneration in the eyes.

High-performance liquid chromatography estimation of cross-linking of dihydroxyindole moiety in eumelanin

Eumelanin pigments consist of various ratios of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and 5,6-dihydroxyindole (DHI). On alkaline hydrogen peroxide oxidation, these indole moieties give rise to pyrrole-2,3,5-tricarboxylic acid (PTCA) and pyrrole-2,3-dicarboxylic acid (PDCA), respectively. In a recent study, we detected considerable amounts of other pyrrole acids, pyrrole-2,3,4,5-tetracarboxylic acid (PTeCA) and pyrrole-2,3,4-tricarboxylic acid (isoPTCA), among the oxidation products of fossil ink sacs more than 160million years old. PTeCA and isoPTCA arise from the cross-linking of the DHI moiety of eumelanin at the C2 and/or C3 positions. We mimicked the process of cross-linking by heating synthetic eumelanins prepared from various ratios of DHICA and DHI at 100°C for 18days (or at 40°C for 180days). The heated eumelanins were analyzed after alkaline peroxide oxidation as PTCA, PDCA, PTeCA, and isoPTCA by high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection. On heating, PTCA decreased rapidly due to decarboxylation, whereas PDCA decreased gradually. Concurrently, PTeCA increased gradually to levels close to PTCA. IsoPTCA also increased gradually at lower levels. Similar changes were observed at 40°C at a much slower rate. These findings suggest that the PTeCA/PTCA ratio may serve as a good indicator of aging (cross-linking) of eumelanin.

Separating melanins into their primary colors: quantifying contributions from eumelanin and pheomelanin

Separating melanins into their primary colors: quantifying contributions from eumelanin and pheomelanin

Usefulness of alkaline hydrogen peroxide oxidation to analyze eumelanin and pheomelanin in various tissue samples: application to chemical analysis of human hair melanins

Eumelanin and pheomelanin in tissue samples can be specifically measured as the markers pyrrole-2,3,5-tricarboxylic acid (PTCA) and 4-amino-3-hydroxyphenylalanine after acidic permanganate oxidation and hydroiodic acid hydrolysis, respectively. Those degradation methods, although widely applied, are not easily performed in most laboratories. To overcome this difficulty, we developed alkaline H(2)O(2) oxidation in 1 M K(2)CO(3) that produces, in addition to the eumelanin marker PTCA, thiazole-2,4,5-tricarboxylic acid (TTCA) and thiazole-4,5-dicarboxylic acid (TDCA) as markers for pheomelanin and pyrrole-2,3-dicarboxylic acid (PDCA) as a marker for 5,6-dihydroxyindole-derived eumelanin. Those four degradation products can be easily separated by HPLC and analyzed with ultraviolet detection. The alkaline H(2)O(2) oxidation method is simple, reproducible and applicable to all pigmented tissues. Its application to characterize eumelanin and pheomelanin in human hair shows that PTCA and TTCA serve as specific markers for eumelanin and pheomelanin, respectively, although some caution is needed regarding the artificial production of TTCA from eumelanic tissue proteins.

A Novel Synthesis of (Z)‐2‐(1‐Trimethylgermyl‐1‐alkenyl)‐1,3,2‐dioxaborinanes and Their Conversion into Carboxylic Acids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A novel synthesis of ( Z)-2-(1-trimethylgermyl-1-alkenyl)-1,3,2-dioxaborinanes and their conversion into carboxylic acids

A novel procedure for preparing heterocyclic compounds such as ( Z)-2-(1-trimethylgermyl-1-alkenyl)-1,3,2-dioxaborinanes based on 1-trimethylgermyl-1-alkynes is described. 1-Trimethylgermyl-1-alkynes easily obtainable by deprotonation of 1-alkynes with n-butyllithium followed by treatment with trimethylgermanium chloride, are readily hydroborated in n-pentane in the presence of boron trichloride in hexane at 0 °C for 3 h. The resulting supernatant clear solution was separated from boron trichloride–methyl sulfide complex. It was then reacted with 1,3-propane diol at 0 °C for 0.5 h. The resulting representative ( Z)-2-(1-trimethylgermyl-1-alkenyl)-1,3,2-dioxaborinanes were isolated in good yields (65–86%) and in high stereochemical purities (>98%) as evidenced by NMR spectral data. The carbon skeletons present in these intermediates were confirmed by alkaline hydrogen peroxide oxidation to the corresponding carboxylic acids.

Chain elongations by three carbon atoms at a time in the boron-catalyzed polymerization of methallyltriphenylarsonium ylide.

Methallyltriphenylarsonium ylide polymerized in the presence of catalytic amounts of trialkylboranes. Linear polymers containing a terminal alcohol function were obtained after alkaline hydrogen peroxide oxidation. The chain of these polymers is constituted of methyl-substituted double bonds, separated by one methylene group. Their structure is related to that of natural rubber, in which the double bonds are separated by two methylene groups. These polymers arise from successive chain elongations of three carbon atoms at a time. A cyclic, polymeric ketone was also prepared from a cyclic trialkylborane. The mechanism, which involves a boratropic rearrangement after every insertion of a monomer, is discussed.

Asymmetric hydrogenation of 1-phenylethenylboronic acid and esters for the synthesis of chiral organoboron compounds

The hydrogenation of ethanediol 1-phenylethenylboronic ester was carried out at −20 °C under a hydrogen atmosphere (9 atm) in the presence of [Rh(cod) 2]BF 4–( R)-BINAP (3 mol%). After alkaline hydrogen peroxide oxidation, the reaction gave 1-phenylethanol with 80% e.e.

STRUCTURAL CHARACTERIZATION OF POLY(ϵ-CAPROLACTONE) AND POLY(ϵ-CAPROLACTONE-b-ISOBUTYLENE-b-ϵ-CAPROLACTONE) BLOCK COPOLYMERS BY MALDI-TOF MASS SPECTROMETRY

Poly(ϵ-caprolactone)(PC1) and PC1-polyisobutylene-PC1 (PC1-PIB-PC1) block copolymers were synthesized in anhydrous toluene by in situ conversion of 2-methyl-1-propanol (2M1P) and α,ω-dihydroxy PIB, respectively, to the corresponding aluminum alkoxide by reaction with a stoichiometric amount of triethylaluminum (TEA) followed by the addition of e-caprolactone. Structural characterization of 2M1P-initiated PCl by gel permeation chromatography (GPC) and matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry (MS) demonstrated the presence of cyclic oligomers, which are produced by intramolecular transesterification reactions that become significant at high monomer conversions. A minor fraction of chains bearing carboxylic acid termini was also observed in the MALDI-TOF mass spectrum; however, carboxylic acid chain ends could not be detected by 13C NMR analysis. Thus, the likely origin of the carboxylic acid termini is fragmentation of the initiator residue from the chain end during MALDI-TOF analysis. For PCl-PIB-PCl block copolymers, two different α,ω-telechelic PIB diols were used as macroinitiators, one derived from allyl and one from isopropenyl terminated PIB. Terminal olefins were converted to primary alcohols via regioselective hydroboration followed by alkaline hydrogen peroxide oxidation. After reaction with ϵ-caprolactone, formation of a block copolymer was evidenced by a shift of the polymer peak to lower elution volume in GPC analysis. Block copolymers possessed molecular weight distributions ≤1.4, and molecular weights of the PCl blocks calculated from GPC were in excellent agreement with those found using MALDI-TOF MS. Structural analysis indicated that the PCl end blocks were severed from the crude block copolymer during MS analysis, for both allyl- and isopropenyl-derived materials. For allyl-derived materials the PCl blocks were found to predominantly carry a C2 residue at the point of detachment of the PIB block; however, the isopropenyl-derived block copolymers showed a complex mixture of different residues suggesting a complex fragmentation mechanism during loss of the PIB block.

Latanoprost stimulates eumelanogenesis in iridial melanocytes of cynomolgus monkeys.

Latanoprost, the active principle of Xalatan eye drops, is a prostaglandin F2alpha analogue in widespread use for the treatment of glaucoma. During chronic treatment with the drug, an increased pigmentation of the iris was observed in both primates and man. To gain an insight into the nature of this effect, we analyzed the stroma of the irides of cynomolgus monkeys subjected to 25-38 weeks of treatment. A highly sensitive procedure, based on chemical degradation by alkaline hydrogen peroxide oxidation, or hydriodic acid hydrolysis, was developed, which allowed eumelanin and pheomelanin analysis of a single iris at a time. Untreated monkey irides were found to be essentially pheomelanic, providing further support to the recently reported occurrence of these pigments in human irides. In the Latanoprost-treated eyes, the amount of eumelanin increased from three to sevenfold, while the variation of pheomelanin did not exceed 25%. The increase in eumelanin/pheomelanin ratio in the treated eyes, as compared with the contralateral control eyes, varied from three to fivefold, and the change was statistically significant (P < 0.01; t-test). Based on the results of parallel studies, showing that Latanoprost does not induce proliferation of iridial melanocytes, and that the other pigmented layers of the iris which do not contain melanocytes are not affected by the drug, it can be concluded that the observed effect is a result of a direct interaction with the melanogenic mechanism. This probably involves activation of tyrosinase, as suggested, to account for the stimulation of melanin synthesis by related compounds, including natural prostaglandins.

The Reactions of Lignins with High Temperature Hydrogen Peroxide Part 2. The Oxidation of Kraft Lignin

Summary A technical pine kraft lignin was subjected to alkaline hydrogen peroxide oxidation in the presence of DTMPA and molecular oxygen at various temperatures. In the presence of DTMPA the lignin was found to undergo increasing levels of oxidation and degradation with increasing temperature. At 110°C over 80% of the kraft lignin was degraded. Analyses of the degraded lignins indicated that both phenolic and nonphenolic lignin moieties were degraded. At 90°C the addition of molecular oxygen resulted in further lignin demethoxylation, but did not decrease the amount of phenolic hydroxyl groups or hydrogen peroxide consumed. In the absence of DTMPA the hydrogen peroxide was rapidly degraded, and accompanied by only minimal lignin oxidation.

Melanin biosynthesis in Cryptococcus neoformans.

Pigment production by Cryptococcus neoformans is virulence associated. Dopamine- and 3,4-dihydroxyphenylalanine-melanin products were identified after acidic permanganate oxidation, alkaline hydrogen peroxide oxidation, or hydrolysis with hydriodic acid. These data provide direct chemical evidence for the formation of eumelanin polymers by catecholamine oxidation by laccase alone followed by oxidative coupling of dihydroxyindole.