Long-term effects of prenatal progesterone exposure: neurophysiological development and hospital admissions in twins up to 8 years of age.

OBJECTIVES: To perform a neurophysiological follow-up at 48 or 60 months of age in children exposed prenatally to progesterone compared with a placebo and evaluate their medical histories up to 8 years of age. METHODS: In this study, Danish participants of the PREDICT study, including 989 surviving children from 498 twin pregnancies, were followed-up. PREDICT was a placebo-controlled randomized clinical trial examining the effect of progesterone for prevention of preterm delivery in unselected twin pregnancies. Medical histories of the children were reviewed and neurophysiological development was evaluated by the parent-completed Ages and Stages Questionnaire (ASQ) at either 48 or 60 months after the estimated date of delivery. We used the method of generalized estimating equation to account for the correlation within twins. RESULTS: A total of 492 children had been exposed prenatally to progesterone and 497 to placebo. There was no difference in the number of admissions to or length of stay in hospital between the treatment groups, and we found no overall difference in the rates of diagnoses made. However, the odds ratios (ORs) for a diagnosis concerning the heart was 1.66 (95% CI, 0.81-3.37), favoring placebo, among all children, 2.38 (95% CI, 1.07-5.30) in dichorionic twins and 8.19 (95% CI, 1.02-65.6) in all children when excluding diagnoses made at outpatient clinic visits. ASQ scores were available for 437 children (progesterone, n = 225; placebo, n = 212). Mean ASQ score was slightly higher in the progesterone group compared with the placebo group (P = 0.03). In dichorionic twins, the risk of having a low ASQ score (< 10(th) centile) was decreased in the progesterone group (OR, 0.34 (95% CI, 0.14-0.86)). CONCLUSION: Second- and third-trimester exposure of the fetus to progesterone does not seem to have long-term harmful effects during childhood, but future studies should focus on cardiac disease in the child. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Outcome of fetuses with short femur length detected at second-trimester anomaly scan: a national survey.

OBJECTIVE: To assess the relationship between the finding of fetal femur diaphysis length (FL) below the 5(th) percentile at the second-trimester scan and pregnancy outcome, in a population in which more than 90% of women attend first-trimester screening. METHODS: This was a retrospective study of all Danish singleton pregnancies with a 17-22-week anomaly scan between 1 January 2008 and 30 June 2011. Information on FL and gestational age (GA) at anomaly scan, on birth weight and GA at delivery and on chromosomal abnormalities was obtained from the Danish Fetal Medicine Database. RESULTS: Short FL was identified in 2718 (1.8%) of 147,766 fetuses and was present in 11 (16.2%) of the 68 fetuses affected by trisomy 21 (positive likelihood ratio (LR+) 8.8 (95% CI, 5.1-15.2)). Trisomy 13/18 and unbalanced autosomal structural abnormalities were also associated with a short FL in three (12.0%, LR+ 6.5 (95% CI, 2.3-18.9)) and eight (32.0%, LR+ 17.4 (95% CI, 9.8-30.9)) of the cases, respectively. The risk of a fetus having trisomy 21, trisomy 18, trisomy 13 or an unbalanced autosomal structural abnormality was 1 : 123 (95% CI, 79-192), given a short FL. Pregnancies with a fetus with short FL were more often affected by early preterm delivery (before 34 weeks) (5.6%; odds ratio (OR) = 4.2 (95% CI, 3.5-4.9)) and small-for-gestational-age (SGA) infants (13.9%; OR = 4.3 (95% CI, 3.8-4.8)). CONCLUSION: Short FL at the second-trimester anomaly scan is associated with a significantly higher relative risk of chromosomal abnormalities, and a substantially higher absolute risk for SGA and early preterm delivery.

Detection of triploidy at 11-14 weeks' gestation: a cohort study of 198 000 pregnant women.

OBJECTIVES: To assess the detection rate of triploidy at first-trimester screening for trisomy 21 and evaluate outcome in triploid pregnancies. METHODS: From 2008 to 2011, 198 427 women with singleton pregnancies underwent first-trimester screening between 11 + 2 and 14 + 0 weeks' gestation. Screening parameters included nuchal translucency, maternal serum free ß-human chorionic gonadotropin (ß-hCG) and pregnancy-associated plasma protein-A (PAPP-A). In all triploid fetuses, these parameters were re-evaluated. Karyotypes were established by invasive testing (chorionic villus sampling or amniocentesis) or postabortem and obtained from the Danish Cytogenetic Central Register and the Danish Fetal Medicine Database. RESULTS: A total of 30 triploid fetuses underwent first-trimester screening. Twenty-five were diagnosed as a result of abnormal first-trimester scan findings, a detection rate of 83.3%. Twenty-three fetuses were identified due to a high risk for trisomy 13, 18 or 21 and two fetuses due to structural abnormalities. The incidence of triploidy at first-trimester screening was 1:6614. A smaller crown-rump length than that estimated by date of last menstrual period was found in 95% of the fetuses with data available for evaluation. Eight fetuses had a larger biparietal diameter than expected for gestational age. Fetuses with a 69,XXX karyotype had significantly lower multiples of the median values for ß-hCG and PAPP-A than did 69,XXY fetuses (P = 0.045 and P = 0.02 forß-hCG and PAPP-A, respectively). No infants with triploidy were born in the study period. Among the triploid gestations detected on first-trimester screening, 20 (80.0%) women chose termination of pregnancy, four (16.0%) had spontaneous miscarriage and one (4.0%) was stillborn. CONCLUSION: First-trimester screening for trisomy 21 also provides a high detection rate for triploidy.

Influence of chorionicity on perinatal outcome in a large cohort of Danish twin pregnancies.

OBJECTIVE: To assess outcome in twin pregnancies according to chorionicity. METHODS: A cohort was retrieved from local ultrasound databases at 14 obstetric departments in Denmark, comprising all twin pregnancies with two live fetuses scanned between weeks 11 and 14 in the period 1 January 2004 to 31 December 2006. Outcome data were retrieved from the National Board of Health. RESULTS: Among 2038 twin pregnancies, 1757 (86.2%) were dichorionic (DC) and 281 (13.8%) were monochorionic diamniotic (MC). In MC pregnancies, the rate of spontaneous fetal loss in both second and third trimesters was more than threefold higher than the comparable rate in DC pregnancies: 6.0% vs. 1.9% for at least one fetus in the second trimester (P < 0.001) and 2.1% vs. 0.7% in the third trimester (P = 0.03). In 98.4% of DC pregnancies and in 91.1% of MC pregnancies, at least one infant was liveborn. Amongst pregnancies with two live fetuses at 24 weeks, the proportion with two live infants at 28 days after delivery was 97.5% and 95.1%, respectively. CONCLUSIONS: The increased incidence of fetal loss in MC pregnancies compared with DC pregnancies predominantly occurs before 24 weeks' gestation. After this stage, although the risk of intrauterine fetal death is still higher in MC than in DC pregnancies, if both fetuses are alive at 24 weeks, the chance of a woman having two live infants 1 month after delivery is similar in MC and DC pregnancies.

First-trimester screening for trisomy 21 in Denmark: implications for detection and birth rates of trisomy 18 and trisomy 13.

OBJECTIVES: In Denmark a new national guideline for prenatal screening and diagnosis was issued in 2004 according to which all pregnant women should be offered a first-trimester combined risk assessment for trisomy 21 (T21). The aim of this study was to investigate whether the new screening strategy for T21 has changed the gestational age at which trisomy 18 (T18) and trisomy 13 (T13) are diagnosed prenatally, and the number of infants born with T18 or T13. METHODS: We collected from the Danish Cytogenetic Central Register information on all prenatal and postnatal chromosome analyses for T18 or T13, registered from 1997 to 2007. Information on first-trimester screening results was collected from each department of obstetrics and gynecology performing the nuchal translucency scans. The cut-off used for referral to invasive diagnostic testing for T21 and for T18/T13 was 1 : 300 and 1 : 150 at screening, respectively. RESULTS: In total, there were 435 cases with T18 and 168 cases with T13 between 1997 and 2007 in Denmark. The estimated incidence of T18 and T13 at the time of delivery was calculated as 2.5 and 1.6 per 10 000 deliveries, respectively. The number (proportion) of cases diagnosed before week 18 increased significantly, from 63 (59.4%) in 1997 and 1998 to 90 (80.4%) in 2006 and 2007 (P < 0.001). In addition, the number of T18 and T13 cases diagnosed prenatally after week 22 or postnatally decreased significantly, from 34 (32.1%) in 1997 and 1998 to seven (6.3%) in 2006 and 2007 (P < 0.0001). For women participating in first-trimester risk assessment in 2006 and 2007, the detection rate of T18 and T13 was 78.8% (95% CI, 71.0-86.7%). CONCLUSION: The number of T18 and T13 fetuses diagnosed before week 18 increased significantly after the introduction of a combined first-trimester screening strategy for T21 in Denmark. In addition, the total number of fetuses diagnosed late in pregnancy and infants born with T18 or T13 decreased significantly. The national detection rate for T18 and T13 in the first trimester is comparable with detection rates found in modeled datasets and other prospective studies.

Potentials to differentiate milk composition by different feeding strategies.

To investigate the effect of the dietary intake of the cow on milk composition, bulk-tank milk was collected on 5 occasions from conventional (n = 15) and organic (n = 10) farms in Denmark and on 4 occasions from low-input nonorganic farms in the United Kingdom, along with management and production parameters. Production of milk based on feeding a high intake of cereals, pasture, and grass silage resulted in milk with a high concentration of alpha-linolenic acid (9.4 +/- 0.2 mg/kg of fatty acids), polyunsaturated fatty acids (3.66 +/- 0.07 mg/kg of fatty acids), and natural stereoisomer of alpha-tocopherol (RRR-alpha-tocopherol, 18.6 +/- 0.5 mg/kg of milk fat). A milk production system using a high proportion of maize silage, by-products, and commercial concentrate mix was associated with milk with high concentrations of linoleic acid (LA; 19.7 +/- 0.4 g/kg of fatty acids), monounsaturated fatty acids (27.5 +/- 0.3 mg/kg of fatty acids), and a high ratio between LA and alpha-linolenic acid (4.7 +/- 0.2). Comparing these 2 production systems with a very extensive nonorganic milk production system relying on pasture as almost the sole feed (95 +/- 4% dry matter intake), it was found that the concentrations of conjugated LA (cis-9,trans-11; 17.5 +/- 0.7 g/kg of fatty acids), trans-11-vaccenic acid (37 +/- 2 g/kg of fatty acids), and monounsaturated fatty acids (30.4 +/- 0.6 g/kg of fatty acids) were higher in the extensively produced milk together with the concentration of antioxidants; total alpha-tocopherol (32.0 +/- 0.8 mg/kg of milk fat), RRR-alpha-tocopherol (30.2 +/- 0.8 mg/kg of milk fat), and beta-carotene (9.3 +/- 0.5 mg/kg of milk fat) compared with the organic and conventional milk. Moreover, the concentration of LA (9.2 +/- 0.7 g/kg of fatty acids) in milk from the extensive milk production system was found to approach the recommended unity ratio between n-6 and n-3, although extensive milk production also resulted in a lower daily milk yield.

Dizygotic monochorionic twin pregnancy conceived following intracytoplasmic sperm injection treatment and complicated by twin-twin transfusion syndrome and blood chimerism.

We report a case of a dizygotic monochorionic twin pregnancy preceded by intracytoplasmic sperm injection treatment including assisted hatching. On ultrasound examination at 25 weeks' gestation the twins, which had been assumed to be monochorionic, were found to be of different sexes. Karyotyping and zygocity determination were performed on amniotic fluid and showed the twins to be dizygotic with normal female and male karyotypes. There were clinical and sonographic signs of twin-twin transfusion syndrome (TTTS), and Cesarean delivery was performed at 32 weeks' gestation. At birth the twins were phenotypically a normal male and a normal female. Histology of the placenta showed it to be monochorionic diamniotic. Blood chimerism was found postnatally as both infants had the karyotypes 46,XX[13]/46,XY[17]. Chimerism was not found in cells from a buccal swab at 6 months of age. This is one of only a few reported cases of dizygotic monochorionic twins. Nearly all of these cases have been conceived after assisted reproductive technology procedures. It is of clinical importance to be aware of this rare phenomenon in relation to TTTS, prenatal screening and parental counseling.

Birth weight variants are associated with variable fetal intrauterine growth from 20 weeks of gestation.

Fetal intrauterine growth is influenced by complex interactions between the maternal genes, environment and fetal genes. The aim of this study was to assess the effect of GWAS-identified genetic variants associated with birth weight on intrauterine fetal growth in 665 children. Fetal growth was estimated by two-dimensional ultrasound scans at 20, 25 and 32 weeks of gestation and growth trajectories were modeled using mixed linear regression. A genetic risk score (GRS) of birth weight-raising variants was associated with intrauterine growth showing an attenuating effect on the unconditional daily reduction in proportional weight gain of 8.92 × 10-6 percentage points/allele/day (p = 2.0 × 10-4), corresponding to a mean difference of 410 g at 40 weeks of gestation between a child with lowest and highest GRS. Eight variants were independently associated with intrauterine growth throughout the pregnancy, while four variants were associated with fetal growth in the periods 20-25 or 25-32 weeks of gestation, indicating that some variants may act in specific time windows during pregnancy. Four of the intrauterine growth variants were associated with type 2 diabetes, hypertension or BMI in the UK Biobank, which may provide basis for further understanding of the link between intrauterine growth and later risk of metabolic disease.

Effect of hop ß-acids as dietary supplement for broiler chickens on meat composition and redox stability.

Addition of ß-acids extracted from hop at different levels (0, 30mgkg-1, 60mgkg-1, 240mgkg-1) to the diet of broiler chickens demonstrated significant effects on the average concentration of polar metabolites and fatty acids of relevance for meat quality. The largest metabolic differences between control group and chicken fed different levels of ß-acids were achieved using 30mgkg-1 of supplement. As determined by EPR spin-trapping, increased redox stability was also obtained for meat from chicken fed 30mgkg-1 of ß-acids which also had highest level of endogenous antioxidants, especially anserine, carnosine, NADH and PUFAs. Diet and storage period were found to affect protein oxidation and myosin and actin were recognized as the main targets of protein oxidation. Myofibrillar proteins from chicken fed hop ß-acids showed to be less susceptible to oxidation. A moderated level of hop ß-acids as dietary supplement accordingly improve the overall redox stability, protecting myofibrillar proteins and fatty acids against oxidation and improve the nutritional properties of meat from broiler chickens.

Comparison of descriptive sensory analysis and chemical analysis for oxidative changes in milk.

Oxidation in 3 types of bovine milk with different fatty acid profiles obtained through manipulation of feed was evaluated by analytical methods quantifying the content of potential antioxidants, the tendency of formation of free radicals, and the accumulation of primary and secondary oxidation products. The milk samples were evaluated in parallel by descriptive sensory analysis by a trained panel, and the correlation between the chemical analysis and the descriptive sensory analysis was evaluated. The fatty acid composition of the 3 types of milk was found to influence the oxidative and lipolytic changes occurring in the milk during chill storage for 4 d. Sensory analysis and chemical analysis showed high correlation between the typical descriptors for oxidation such as cardboard, metallic taste, and boiled milk and specific chemical markers for oxidation such as hexanal. Notably, primary oxidation products (i.e., lipid hydroperoxides) and even the tendency of formation of radicals as measured by electron spin resonance spectroscopy were also highly correlated to the sensory descriptors for oxidation. Electron spin resonance spectroscopy should accordingly be further explored as a routine method for detection of early events in lipid oxidation in milk to predict shelf-life.

Caffeine metabolites not caffeine protect against riboflavin photosensitized oxidative damage related to skin and eye health.

Caffeine metabolites were found to bind riboflavin with dissociation constant in the millimolar region by an exothermic process with positive entropy of reaction, which was found by (1)H NMR and fluorescence spectroscopy to occur predominantly by hydrogen bonding with water being released from riboflavin solvation shell upon caffeine metabolite binding to riboflavin. The caffeine metabolites 1-methyl uric acid and 1,7-dimethyl uric acid were shown by transient absorption laser flash photolysis to be efficient as quenchers of triplet riboflavin with second-order rate constant of 1.4 10(8)Lmol(-1)s(-1) and 1.0 10(8)Lmol(-1)s(-1), respectively, in aqueous solution of pH6.4 at 25°C and more efficient than the other caffeine metabolite 1,7-dimethyl xanthine with second-order rate constant of 4.2 10(7)Lmol(-1)s(-1). Caffeine was in contrast found to be non-reactive towards triplet riboflavin. Caffeine metabolites rather than caffeine seem accordingly important for the observed protective effect against cutaneous melanoma identified for drinkers of regular but not of decaffeinated coffee. The caffeine metabolites, but not caffeine, were by time resolved single photon counting found to quench singlet excited riboflavin through exothermic formation of ground-state precursor complexes indicating importance of hydrogen bounding through keto-enol tautomer's for protection of oxidizable substrates and sensitive structures against riboflavin photosensitization.

Astaxanthin diferulate as a bifunctional antioxidant.

Astaxanthin when esterified with ferulic acid is better singlet oxygen quencher with k2 = (1.58 ± 0.1) 10(10) L mol(-1)s(-1) in ethanol at 25°C compared with astaxanthin with k2 = (1.12 ± 0.01) 10(9) L mol(-1)s(-1). The ferulate moiety in the astaxanthin diester is a better radical scavenger than free ferulic acid as seen from the rate constant of scavenging of 1-hydroxyethyl radicals in ethanol at 25°C with a second-order rate constant of (1.68 ± 0.1) 10(8) L mol(-1)s(-1) compared with (1.60 ± 0.03) 10(7) L mol(-1)s(-1) for the astaxanthin:ferulic acid mixture, 1:2 equivalents. The mutual enhancement of antioxidant activity for the newly synthetized astaxanthin diferulate becoming a bifunctional antioxidant is rationalized according to a two-dimensional classification plot for electron donation and electron acceptance capability.

Relative stability of carotenoid radical cations and homologue tocopheroxyl radicals. A real time kinetic study of antioxidant hierarchy.

Real time detection following laser flash photolysis of transient carotenoid radical cations and tocopheroxyl radicals formed in chloroform and bleaching of the carotenoids has allowed interaction between carotenoids and tocopherols to be studied. It is found that alpha-, beta-, and gamma-tocopherol reduce all the carotenoid radical cations investigated whereas the delta-tocopheroxyl radical can be reduced by lycopene and beta-carotene. Astaxanthin, canthaxanthin, and beta-apo-8'-carotenal radical cations are scavenged rapidly by all four tocopherol homologues whereas the other carotenoid radical cations react much more slowly with the tocopherols. The results allow the antioxidant hierarchy to be established: alpha-tocopherol > lycopene approximately beta-tocopherol approximately gamma-tocopherol > beta-carotene > zeaxanthin approximately delta-tocopherol > lutein > echinenone >> canthaxanthin approximately beta-apo-8'-carotenal > astaxanthin.

Reactivity of beta-carotene towards peroxyl radicals studied by laser flash and steady-state photolysis.

Peroxyl radicals, as model for peroxyl radicals formed during autoxidation of lipids, have been generated in three solvent systems (cyclohexane, tetrahydrofuran and tert-butanol/water) by steady-state and laser flash photolysis, and their reaction with beta-carotene studied. Steady-state photolysis experiments showed that alkyl, alkoxyl and alkylperoxyl radicals all react with beta-carotene. However, laser flash photolysis experiments indicated that the reaction with peroxyl radicals (second-order rate constant estimated to be less than 10(6) M(-1) s(-1)) is slower than with alkyl and alkoxyl radicals, and that beta-carotene is hence a poor direct scavenger of peroxyl radicals. Scavenging of peroxyl radicals by beta-carotene is suggested not to proceed via electron transfer but rather by adduct formation and/or hydrogen abstraction. For different phenoxyl radicals, differences in reactivity towards beta-carotene seem to be correlated with standard reduction potential.

Formation of long-lived protein radicals in the reaction between H2O2-activated metmyoglobin and other proteins.

Free radicals formed during the reaction of H2O2 and metmyoglobin in the presence of bovine serum albumin (BSA) were investigated using freeze quench and spin-trap ESR spectroscopy. Increasing concentrations of BSA (0-300 microM) resulted in drastic changes in the characteristic freeze quench ESR signal of H2O2-activated metmyoglobin (perferryl protein radical) under physiological conditions (pH = 7.4; I = 0.16). The radical species formed during reaction of 100 microM H2O2, 100 microM metmyoglobin, and 200 microM BSA have half-lives of approximately 13 min at 25 degrees C, in contrast to the perferryl protein radical that has a half-life of approximately 28 s at 25 degrees C. The radical species formed in the presence of BSA were reactive towards ascorbate, glutathione, cysteine, and tyrosine. Substitution of BSA with defatted BSA, gamma-globulin or beta-lactoglobulin also resulted in formation of long-lived free radical species (half-lives: 13-18 min); however, the ability to form these was dependent of the specific protein and decreased in the following order: BSA > defatted BSA > gamma-globulin > beta-lactoglobulin. The spin-trap alpha-phenyl-tert-butylnitrone (PBN) showed the presence of transient protein radical species formed in the reaction between MMb, H2O2, and BSA. Transient radical species that could be proposed as intermediates in the formation of the long-lived protein radicals detected by freeze-quench ESR. Dityrosine was formed in the reaction between MMb, H2O2, and BSA, showing the involvement of tyrosine residues in the present reaction. The described chemical interaction between H2O2-activated myoglobin and other proteins have major consequences on future interpretations of the significance of the perferryl protein radical in biological systems where proteins are abundant.

Peroxidation of linoleate at physiological pH: hemichrome formation by substrate binding protects against metmyoglobin activation by hydrogen peroxide.

Peroxidation by metmyoglobin, MbFe(III), by metmyoglobin/hydrogen peroxide, MbFe(III)/H(2)O(2), to yield the myoglobin ferryl radical (*MbFe(IV)=O), or by ferrylmyoglobin, MbFe(IV)=O, was investigated at physiological pH (7.4) in oil-in-water linoleate emulsions. Linoleate peroxidation was followed using second derivative ultraviolet (UV)-spectroscopy for monitoring formation of conjugated dienes and quantitative determination of specific linoleate hydroperoxides by liquid chromatography with photodiode absorption detection. Modifications of myoglobins during lipid peroxidation were followed simultaneously by changes in the Soret absorption band (410 or 424 nm), and in the visible absorption region (from 450 to 700 nm), combined with electron spin resonance (ESR) spectroscopy for direct detection of changes in the spin state of the iron center. In contrast to MbFe(IV)=O, MbFe(III) and MbFe(III)/H(2)O(2) were not able to initiate linoleate peroxidation in oil-in-water emulsions, and MbFe(III) was converted, by binding of linoleate (but not methyl linoleate), to a low-spin hemichrome derivate, HMbFe(III), with the distal histidine reversibly bound to the iron center. HMbFe(III) is ineffective in initiating lipid peroxidation and cannot be activated to *MbFe(IV)=O or MbFe(IV)=O by addition of moderate amounts of H(2)O(2). Addition of MbFe(III) to linoleate emulsions containing H(2)O(2) results in the competitive formation of *MbFe(IV)=O and HMbFe(III) in favor of HMbFe(III), and little linoleate peroxidation is detected, demonstrating the inherent protection, at physiologic pH, against peroxidation by reversible binding of the substrate to the potential myoglobin catalyst.

Comparative mechanisms and rates of free radical scavenging by carotenoid antioxidants.

The comparative mechanisms and relative rates of nitrogen dioxide (NO2.), thiyl (RS.) and sulphonyl (RSO2.) radical scavenging by the carotenoid antioxidants lycopene, lutein, zeaxanthin, astaxanthin and canthaxanthin have been determined by pulse radiolysis. All the carotenoids under study react with the NO2. radical via electron transfer to generate the carotenoid radical cation (Car.+). In marked contrast the glutathione and 2-mercaptoethanol thiyl radicals react via a radical addition process to generate carotenoid-thiyl radical adducts [RS-Car].. The RSO2. radical undergoes both radical addition, [RSO2-Car]. and electron abstraction, Car.+. Both carotenoid adduct radicals and radical cations decay bimolecularly. Absolute rate constants for radical scavenging were in the order of approximately 10(7)-10(9) M(-1) s(-1) and follow the sequence HO(CH2)2S. > RSO2. > GS. > NO2.. Although there were some discernible trends in carotenoid reactivity for individual radicals, rate constants varied by no greater than a factor of 2.5. The mechanism and rate of scavenging is strongly dependent on the nature of the oxidising radical species but much less dependent on the carotenoid structure.

Free radical transients in photobleaching of xanthophylls and carotenes.

Carotenoids in chloroform and carbon tetrachloride photobleach upon nanosecond laser flash photolysis in two steps: instantaneously and in a second-order reaction. The rate constant for second-order reaction (first-order in a solvent derived radical and first-order in (excess) carotenoid) is largest for carotenes (9.8.10(8) M-1 for beta-carotene), intermediate for hydroxylated carotenoids, and smallest for carbonyl containing carotenoids (1.0.10(8) M-1 S-1 for astaxanthin) in chloroform at 20 degrees C. Near infrared absorbing transients are formed concomitant with photobleaching in chloroform (not detected in carbon tetrachloride). A species formed instantaneously is tentatively identified as either a carotenoid/solvent adduct or an ion-pair. A second species is formed by decay of instantaneously formed species and is identified as the carotenoid radical action. This species is formed in a first-order reaction with a rate constant of approx. 5.10(4) S-1 and absorbing at longer wavelength than the precursor. The lifetime (second-order decay) of the intermediates appears to be longest for the carotenoids with the longest conjugated system. The results indicate that carotenes are better antioxidants than xanthophylls as the carotenes, at least in the present lipophilic solvents, react faster with free radicals.

Flavonoid deactivation of ferrylmyoglobin in relation to ease of oxidation as determined by cyclic voltammetry.

Fourteen flavonoid aglycones, and the flavonoid glycoside rutin, with redox potentials ranging from 0.20 (myricetin) to 0.83 V (chrysin) vs. NHE, as determined by cyclic voltammetry at 23 degrees C in aqueous 50 mM phosphate, ionic strength 0.16 (NaCl) with pH = 7.4 and compared with redox potentials determined for four cinnamic acid derivatives, were all found to reduce ferrylmyoglobin, MbFe(IV)=O, to metmyoglobin, MbFe(III). Reaction stoichiometry depends strongly on the number of hydroxyl groups in the flavonoid B-ring. All compounds with 3',4'-dihydroxy substitution reduce 2 equivalents of MbFe(IV)=O, whereas naringenin, hesperitin and kaempferol, with one hydroxyl group in the B-ring, reduce with a one-to-one stoichiometry. As studied spectrophotometrically under pseudo-first-order conditions with flavonoids in excess, rutin and apigenin react with MbFe(IV)=O with very similar and moderately high activation enthalpies of deltaH298++ = 69 +/- 1 kJ mol(-1) and deltaH298++ = 65 +/- 3 kJ mol(-1), respectively, and with positive activation entropies of deltaS298++ = 23 +/- 4 J mol(-1) K(-1) and deltaS298++ = 13 +/- 9 J mol(-1) K(-1), respectively, in agreement with outer-sphere electron transfer as rate determining. For the fifteen plant polyphenols only qualitative relations exist between redox potential and rate constants rather than a linear free energy relationship (r2 = 0.503), and especially the flavone apigenin was found more efficient as reducing agent. For the flavanones, a linear relation (r2 = 0.971) indicate that, in the absence of a 2,3 double bond, removal of the 4-carbonyl group or addition of a 3-hydroxy group only has minor effect on reactivity. The flavonols are the most efficient reducing agents, effectively reducing MbFe(IV)=O to MbFe(III) and establishing a steady state distribution between the flavonol and MbFe(III) and oxymyoglobin, MbFe(II)O2. Oxidised flavonols reduces MbFe(III) to MbFe(II)O2 very efficiently and much faster than the parent flavonol.

Kinetics of photobleaching of beta-carotene in chloroform and formation of transient carotenoid species absorbing in the near infrared.

Upon laser flash photolysis of beta-carotene in chloroform instantaneous bleaching of beta-carotene and concomitant formation of near infrared absorbing species are observed. One species, absorbing with maximum at 920 nm, is formed during the laser pulse (10 ns) and is practically gone in one millisecond, the decay showing a bi-exponential behaviour. The second species, absorbing with maximum at 1000 nm, is formed from the species absorbing at 920 nm by first order kinetics with a rate constant of 4.9.10(4) s-1 at 20 degrees C. This second species decays by second order kinetics and is gone within a few milliseconds. An additional slow bleaching of beta-carotene and formation of the species absorbing at 920 nm is observed. This slow bleaching/formation of transient absorption is probably due to processes involving free radicals generated during the instantaneous bleaching. The species absorbing at 920 nm is suggested to be either (i) a free radical adduct formed from beta-carotene and chloroform or (ii) beta-carotene after abstraction of a hydrogen atom. The species absorbing at 1000 nm is most likely the radical cation. Formation and decay of the near infrared absorbing species and bleaching of beta-carotene are independent of whether oxygen is present or absent in the solutions.