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PubMed2003

Causes of thrombocytopenia in triplet gestations.

OBJECTIVE: The purpose of this study was to determine the incidence and cause of thrombocytopenia in triplet gestations. STUDY DESIGN: All triplet gestations that received prenatal care and were delivered at our hospital between 1993 and 2001 were identified. Serial platelet values were reviewed from the earliest gestational age available until the postpartum period. Mild and severe thrombocytopenia were defined as a platelet count of 100000 to 150000/microL and <100000/microL, respectively. The cause of the thrombocytopenia was determined from a review of medical records. RESULTS: One hundred twenty-six triplet pregnancies met the inclusion criteria. The mean maternal age was 34.3 +/- 5.4 years, 85.7% of the patients were nulliparous, and at least 92.1% of the patients had received infertility treatment. The overall rate of thrombocytopenia in our triplet population was 36.5%. Mild thrombocytopenia occurred in 19.0% of pregnancies, and severe thrombocytopenia occurred in 17.5% of pregnancies. The causes of thrombocytopenia were severe preeclampsia (54.3%), gestational (23.9%), mild preeclampsia (8.7%), HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet count syndrome; 4.3%), atypical preeclampsia (4.3%), idiopathic thrombocytopenic purpura (2.2%), and familial (2.2%). Thrombocytopenia occurred significantly earlier before the diagnosis of preeclampsia. CONCLUSION: Approximately one third of triplet gestations are complicated by thrombocytopenia, one half of which are severe. This represents a much higher frequency as compared with the 6.6% to 11.6% that was reported for singleton gestations. Hypertension-associated disorders of pregnancy account for 71.7% of thrombocytopenia in triplets, unlike singleton gestations in which 75% of thrombocytopenia is gestational. The single most common cause of thrombocytopenia in triplets is severe preeclampsia. This is the first study to evaluate the incidence and cause of thrombocytopenia in a large set of triplet gestations.

Adult↗

PubMed2003

Excess risk of mortality in very low birthweight triplets: a national, population based study.

BACKGROUND: Neonatal morbidity and mortality differ between singletons, twins, and triplets. OBJECTIVE: To evaluate whether plurality is associated with excess risk of neonatal morbidity and poor outcome (death, chronic lung disease, or adverse neurological findings) in very low birthweight (VLBW) infants from a national, population based cohort. METHODS: The Israel national VLBW infant database has prospectively collected extensive perinatal and neonatal data on all liveborn VLBW infants since 1995. The study sample (n = 5594) consisted of all singletons (n = 3717) and all complete sets of twins (n = 1394) and triplets (n = 483) born during 1995-1999. To account for differences in case-mix, both univariate and multivariate comparisons that included confounding variables such as antenatal steroid treatment and mode of delivery were performed for each of the outcome variables. RESULTS: There was a small inverse correlation between gestational age (GA) and birth weight (BW) and the number of fetuses (singletons: GA 28.9 (2.6) weeks, BW 1096 (269) g; twins: GA 28.4 (2.3) weeks, BW 1062 (271) g; triplets: GA 28.5 (2.4) weeks, BW 1049 (259) g). Triplets were significantly more likely to have been conceived following fertility treatments, to have received antenatal steroids, and to be delivered by caesarean section. Respiratory distress syndrome was significantly more common in twins and triplets in spite of the increased exposure to antenatal steroids. Multivariate logistic regression analysis using all significant perinatal covariates showed that triplets were at increased risk of death (odds ratio (OR) 1.54, 95% confidence interval (CI) 1.13 to 2.11), but not of adverse neurological outcome (OR 1.29, 95% CI 0.91 to 1.85) or chronic lung disease (OR 0.69, 95% CI 0.46 to 1.02). CONCLUSION: Despite considerable differences in the incidence of confounding variables between the groups, VLBW triplets are at increased risk of death compared with twins and singletons. In addition, VLBW twins and triplets more often have respiratory distress syndrome but not chronic lung disease or adverse neurological findings.

Analysis of Variance↗

PubMed2005

Characteristics of mothers who delivered the heaviest, average-weight, and lightest triplet sets.

We analyzed a cohort of 2850 live-born triplet sets to compare age, parity, stature, pre-gravid body mass index (BMI), and weekly weight gain in mothers who delivered triplets with a total weight in the 10th, 5th, and 1st deciles corresponding to the heaviest, average-weight, and lightest triplet sets, respectively. Mothers who delivered the heaviest triplets were significantly older, multiparous, taller, heavily built, and gained more weight compared with mothers of average-weight triplets. In contrast, except for higher parity, mothers of average-weight sets were not significantly different compared with mothers who delivered the lightest triplet sets. We concluded that parity was the only significant factor for increased total triplet weight in the first five deciles. However, the presence of other factors in addition to parity is needed for a triplet pregnancy to be included in the 10th decile.

Adolescent↗

PubMed2003

[Birth weight and height characteristics of triplets].

OBJECTIVE: This study was conducted to assess the birth weight and height in triplets, and to identify associated factors. METHOD: The subjects were 371 sets of triplets (1,113 triplets), who were born after 1986. Data on birth weight, birth height, gender, birth order, mode of delivery, gestational age, maternal weight gain at delivery, and infertility treatment were obtained. Pregravidic body mass index (BMI) was computed to evaluate maternal physique. RESULTS: Mean triplet birth weight was 1,763.3 +/- 420.6 g and mean birth height was 42.2 +/- 3.36 cm. Overall, 96% were low birth weight newborn, 24.4% were very low birth weight newborn, and 4.9% had less than 1,000 g weight. The triplet birth weight was significantly associated with gender (male > female), sex combination (opposite-sexed sets > same-sexed sets), mode of delivery (vaginal delivery > caesarean section), and pregravidic body mass index (BMI) (more than 26.0 kg/m2 > less than 19.8 kg/m2). There was a significant correlation coefficient between maternal weight gain at delivery and birth weight. The triplet birth height was significantly associated with gender (male > famale), sex combination (opposite-sexed sets > same-sexed sets), and pregravidic BMI (more than 26.0 kg/m2 > less than 19.8 kg/m2). Moreover, the birth height was associated with maternal weight gain at delivery and infertility treatment. CONCLUSION: The birth weight and birth height in triplets are much lower than those for singletons and twins. Triplet birth weight is associated with gender, birth order, pregravidic body mass index, mode of delivery, and maternal weight gain at delivery, taking into account gestational age. Birth height is associated with gender, pregravidic body mass index, and infertility treatment.

Birth Weight↗

PubMed2004

A comparative study of twin and triplet pregnancy.

OBJECTIVE: Multiple pregnancy now warrants special attention from the obstetrician. The incidence of multiple pregnancy had increased during the last 15 years. Multiple pregnancy is a high-risk pregnancy since it is associated with increased perinatal morbidity and mortality. In addition, almost every maternal and obstetrical problem occurs more frequently in multiple than in singleton pregnancies. In view of the above we designed our study. METHODS: This was a comparative and descriptive retrospective study conducted during the period January 1985 to December 1999 at Wad Medani Teaching Hospital, Wad Medani, Sudan. The study included the follow up of 597 twin pregnancies and 30 triplet pregnancies. The variables used were the age, the parity, the incidence, the sex of neonates and their weights. The study also concentrated on the mode of delivery, and it highly considered the maternal and perinatal complications. RESULTS: During the period of the study the total number of pregnancies received was 44605. Twin pregnancies accounted for 597/44605 (1.3%), while triplet gestation showed an incidence of 30/44605 (0.1%). In twin pregnancy ovulation occurred spontaneously in 43/597 (7.2%) and it was induced in 167/597 (28%). On the other hand, ovulation occurred spontaneously in triplets 19/30 (63.3%) and it was induced in 11/30 (36.7%). The common maternal complication was pre-term labor, which affected 35.5% in twins and 76.7% in triplets. The rate of cesarean section was 53.1% in twins while in triplet it was 83.3%. The mean birth weight in twin pregnancy was 1890 gm for males and 1780 gm for females. In triplet gestation, the mean birth weight was 1760 gm for males and 1720 gm for females. The maternal mortality rate was 35.8/100.000 live births in twin pregnancies while it was 99/100000 in triplet gestation. The perinatal mortality rate was 115/1000 for twin and 223/1000 for triplet pregnancy. CONCLUSION: Multiple pregnancy is a high-risk pregnancy, and to decrease its maternal and fetal complications it must be diagnosed early. It should also receive almost antenatal care and care at delivery. Early hospitalization plays an important role of reducing these complications. It must be treated by one obstetrician.

Adult↗

PubMed1997

The outcome of triplet pregnancies at Hartford Hospital--1989-1996.

The advent of artificial induction of ovulation has increased the incidence of triplet pregnancies. Although the outcome of triplet pregnancies has improved through advanced technology, several studies have suggested that triplets conceived by artificial induction of ovulation have worse prenatal and perinatal outcomes than those conceived naturally. Our study examined the outcome of 14 sets of triplets conceived at Hartford Hospital between 1989 and 1996. Five of 14 sets of triplets were conceived by artificial methods and nine of 14 were conceived naturally. The mean gestational age was 31.8 weeks for artificially conceived infants vs 29.7 weeks for naturally conceived infants. Average weight at birth was 1.625 kg in the artificially conceived study group and 1.377 kg in the naturally conceived group. Time spent in the neonatal intensive care unit was 4.67 weeks for the artificially conceived study group and 3.57 weeks for the naturally conceived group. It is concluded that there was no difference in outcome in the triplets conceived by artificial induction of ovulation vs natural conception. Maternal age and sex of triplets were important factors determining perinatal outcomes of triplets.

Adult↗

PubMed2000

Interaction between TOAC free radical and photoexcited triplet chromophores linked to peptide templates.

The intramolecular quenching of photoexcited triplet states by free radicals linked to peptide templates was studied by time-resolved electron paramagnetic resonance (EPR) with pulsed laser excitation. The systems investigated are 3(10)-helix forming peptides, having in the amino acid sequence the free radical 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) and a triplet precursor, such as Bin, Bpa, or Trp, incorporated at different relative positions. Upon interaction with the excited triplet the TOAC radical spin sublevel populations assume values that differ from the Boltzmann equilibrium values. This spin polarization effect produces EPR lines in emission whose time evolution reflects the triplet quenching rate. In particular, in a series of peptides labeled with Bpa and TOAC at successive positions in the 3(10)-helix, radical-triplet interaction was observed in all cases. However, for the peptide where Bpa and TOAC are at positions 2 and 4 the rate of triplet quenching is lower than for the other peptides in the series. In addition, the radical-excited triplet complex in the quartet spin state was observed in a peptide containing fullerene (C(60)) as a triplet precursor and TOAC.

Carbon↗

PubMed1980

Quantum yield and rate of formation of the carotenoid triplet state in photosynthetic structures.

The formation of the triplet state of carotenoids (detected by an absorption peak at 515 nm) and the photo-oxidation of the primary donor of Photosystem II, P-680 (detected by an absorption increase at 820 nm) have been measured by flash absorption spectroscopy in chloroplasts in which the oxygen evolution was inhibited by treatment with Tris. The amount of each transient form has been followed versus excitation flash intensity (at 590 or 694 nm). At low excitation energy the quantum yield of triplet formation (with the Photosystem II reaction center in the state Q-) is about 30% that of P-680 photo-oxidation. The yield of carotenoid triplet formation is higher in the state Q- than in the state Q, in nearly the same proportion as chlorophyll alpha fluorescence. It is concluded that, for excited chlorophyll alpha, the relative rates of intersystem crossing to the triplet state and of fluorescence emission are the same in vivo as in organic solvent. At high flash intensity the signal of P-680+ completely saturates, whereas that of carotenoid triplet continues to increase. The rate of triplet-triplet energy transfer from chlorophyll alpha to carotenoids has been derived from the rise time of the absorption change at 515 nm, in chloroplasts and in several light-harvesting pigment-protein complexes. In all cases the rate is very high, around 8 . 10(7) s-1 at 294 K. It is about 2--3 times slower at 5 K. The transitory formation of chlorophyll triplet has been verified in two pigment-protein complexes, at 5 K.

Carotenoids↗

PubMed1981

The primary charge separation, cytochrome oxidation and triplet formation in preparations from the green photosynthetic bacterium Prosthecochloris aestuarii.

Flash-induced absorbance changes were measured in intact cells and subcellular preparations of the green photosynthetic bacterium Prosthecochloris aestuarii. In Complex I, a membrane vesicle preparation, photooxidation of the primary electron donor, P-840, and of cytochrome c-553 was observed. Flash excitation of the photosystem pigment complex caused in addition the generation of a bacteriochlorophyll a triplet. Triplet formation was the only reaction observed after flash excitation in the reaction center pigment-protein complex. The triplet had a lifetime of 90 microseconds at 295 K and of 165 microseconds at 120 K. The amount of triplet formed in a flash increased upon cooling from 295 to 120 K from 0.2 and 0.5 per reaction center to 0.45 and nearly 1 per reaction center in the photosystem pigment and reaction center pigment-protein complex, respectively. Measurements of absorbance changes in the near infrared in the reaction center pigment-protein complex indicate that the triplet is formed in the reaction center and that the reaction center bacteriochlorophyll a triplet is that of P-840. Formation of a carotenoid triplet did not occur in our preparations. Illumination with continuous light at 295 K of the reaction center pigment-protein complex produced a stable charge separation (with oxidation of P-840 and cytochrome c-553) in each reaction center, but with a low efficiency. This low efficiency, and the high yield of triplet formation is probably due to damage of the electron transport chain at the acceptor side of the reaction center of the reaction center pigment-protein complex. The halftime for cytochrome c-553 oxidation in Complex I and the photosystem pigment complex was 90 microseconds at 295 K; below 220 K no cytochrome oxidation occurred. At 120 K P-840+ was rereduced with a halftime of 20 ms, presumably by a back reaction with a reduced acceptor.

Bacteria↗

PubMed2005

Energy and structural analysis of double nucleic acid triplets.

In order to investigate the energy and structural character of RNA-RNA triplets and RNA-DNA duplex base triplets, 64 sets of three-dimensional models of RNA-DNA duplex base triplets and mRNA-tRNA triplex base triplets were constructed and optimized by homologous modeling method using the software InsightII. The comparative statistical method and cluster analysis were adopted to study these features. The result showed: (i) all energy parameters of monomer RNA-DNA hybrid triplets and ternary complexes appeared significantly different; and some parameters related with overall molecules such as overall energy, bond energy and coulomb energy have statistically significant correlations between the structures in vacuum and aquatic solutions while other parameters, including theta energy, phi energy, hydrogen bond energy and non-bond energy, changed significantly, but not continuously. (ii) However, the case of mRNA-tRNA triplets was much more complicated in that only the bond energy's correlation coefficient is -0.8. Typically, the main contribution of GC pairs and G/A/U bases were interesting. The models of RNA-DNA hybrid triplets and mRNA-tRNA triplet should be helpful for the study of base pairing in codons and the biological effectiveness of antisense nucleic acids.

Animals↗

PubMed1995

Chlorophyll a and carotenoid triplet states in light-harvesting complex II of higher plants.

Laser-flash-induced transient absorption measurements were performed on trimeric light-harvesting complex II to study carotenoid (Car) and chlorophyll (Chl) triplet states as a function of temperature. In these complexes efficient transfer of triplets from Chl to Car occurs as a protection mechanism against singlet oxygen formation. It appears that at room temperature all triplets are being transferred from Chl to Car; at lower temperatures (77 K and below) the transfer is less efficient and chlorophyll triplets can be observed. In the presence of oxygen at room temperature the Car triplets are partly quenched by oxygen and two different Car triplet spectral species can be distinguished because of a difference in quenching rate. One of these spectral species is replaced by another one upon cooling to 4 Ki demonstrating that at least three carotenoids are in close contact with chlorophylls. The triplet minus singlet absorption (T-S) spectra show maxima at 504-506 nm and 517-523 nm, respectively. In the Chl Qy region absorption changes can be observed that are caused by Car triplets. The T-S spectra in the Chl region show an interesting temperature dependence which indicates that various Car's are in contact with different Chl a molecules. The results are discussed in terms of the crystal structure of light-harvesting complex II.

Aerobiosis↗

PubMed1998

Rate of carotenoid triplet formation in solubilized light-harvesting complex II (LHCII) from spinach.

In the present study the rate of triplet transfer from chlorophyll to carotenoids in solubilized LHCII was investigated by flash spectroscopy using laser pulses of approximately 2 ns for both pump and probe. Special attention has been paid to calibration of the experimental setup and to avoid saturation effects. Carotenoid triplets were identified by the pronounced positive peak at approximately 507 nm in the triplet-singlet difference spectra. DeltaOD (507 nm) exhibits a monoexponential relaxation kinetics with characteristic lifetimes of 2-9 micros (depending on the oxygen content) that was found to be independent of the pump pulse intensity. The rise of DeltaOD (507 nm) was resolved via a pump probe technique where an optical delay of up to 20 ns was used. A thorough analysis of these experimental data leads to the conclusion that the kinetics of carotenoid triplet formation in solubilized LHCII is almost entirely limited by the lifetime of the excited singlet state of chlorophyll but neither by the pulse width nor by the rate constant of triplet-triplet transfer. Within the experimental error the rate constant of triplet-triplet transfer from chlorophyll to carotenoids was estimated to be kTT > (0.5 ns)-1. This value exceeds all data reported so far by at least one order of magnitude. The implications of this finding are briefly discussed.

Biophysical Phenomena↗

PubMed1998

Perinatal mortality and morbidity rates among singleton, twin, and triplet gestations.

Objective: To determine rates of perinatal mortality and morbidity from 24 to 43 weeks gestation among singletons, twins, and triplets.Methods: Successfully linked data from 1992 Californian maternal and infant discharge records as well as birth and death certificates from acute care civilian hospitals were examined for perinatal mortality and morbidity. Perinatal mortality was defined as the sum of all stillbirths and neonatal deaths. Deliveries from 24 to 43 weeks gestation among singleton, twin, and triplet pregnancies were collected as separate data sets. Perinatal mortality was identified using birth certificate death indicators excluding deaths caused by congenital anomalies. Neonatal deaths were identified from death indicators found in the death certificates. For the purpose of this study, perinatal morbidities were identified by ICD-9 codes and limited to respiratory distress syndrome (RDS), intraventricular hemorrhage (IVH), and necrotizing enterocolitis (NEC). Perinatal mortality and morbidity rates were expressed as a percent of live births stratified by gestational age. Perinatal mortality data were expressed in log scale and perinatal morbidity rates were statistically compared.Results: There were 571,390 total births in California of which 527,677 (92%) were singleton, 12,535 (2%) were twin, and 367 (0.06%) were triplet gestations. Across gestation, the rate of RDS between triplets and twins was comparable (6.6% vs 6.8%). However, the rates of IVH and NEC were significantly greater in triplets than in twins (20% vs 8%, P <.0001, and 25% vs 9%, P <.0001, respectively). The perinatal mortality rates are shown below.Conclusions: Perinatal mortality rates were comparable among singleton, twin, and triplet gestations delivered between 24 and 30 weeks gestation. Unlike singletons and twins, the triplet perinatal mortality rate did not fall between 31 and 36 weeks gestation and remained at 2.6%. Twin perinatal mortality rate was equivalent to singletons until 36 weeks gestation. IVH and NEC were significantly greater among triplets regardless of gestational age. These data suggest that antepartum fetal surveillance of triplet pregnancies should start as early as 30 weeks gestation while testing for twin pregnancies can begin at 36 weeks gestation.

Journal Article↗

PubMed1998

The influence of aggregation on triplet formation in light-harvesting chlorophyll a/b pigment-protein complex II of green plants.

The influence of aggregation on triplet formation in the light-harvesting pigment-protein complex of photosystem II of green plants (LHCII) has been studied with time-resolved laser flash photolysis. The aggregation state of LHCII has been varied by changing the detergent concentration. The triplet yield increases upon disaggregation and follows the same dependence on the detergent concentration as the fluorescence yield. The rate constant of intersystem crossing is not altered by disaggregation, and variations of the triplet yield appear to be due to aggregation-dependent quenching of singlet excited states. The efficiency of triplet transfer in LHCII aggregates from chlorophyll (Chl) to carotenoid (Car) is 92 +/- 7% at room temperature and 82 +/- 6% at 5 K, and does not change upon disaggregation. The Chl's that do not transfer their triplets to Car's seem to be bound to LHCII and are capable of transfering/accepting their singlet excitations to/from other Chl's. Two spectral contributions of Car triplets are observed: at 525 and 506 nm. Disaggregation of macroaggregates to small aggregates reduces by 10% the relative contribution of Car triplets absorbing at 525 nm. This effect most likely originates from a decreased efficiency of intertrimer Chl-to-Car triplet transfer. At the critical micelle concentration, at which small aggregates are disassembled into trimers, the interactions between Chl and Car are changed. At room temperature, this effect is much more pronounced than at 5 K.

Carotenoids↗

PubMedDate not supplied

Fuzzy tricentric pharmacophore fingerprints. 1. Topological fuzzy pharmacophore triplets and adapted molecular similarity scoring schemes.

This paper introduces a novel molecular description--topological (2D) fuzzy pharmacophore triplets, 2D-FPT--using the number of interposed bonds as the measure of separation between the atoms representing pharmacophore types (hydrophobic, aromatic, hydrogen-bond donor and acceptor, cation, and anion). 2D-FPT features three key improvements with respect to the state-of-the-art pharmacophore fingerprints: (1) The first key novelty is fuzzy mapping of molecular triplets onto the basis set of pharmacophore triplets: unlike in the binary scheme where an atom triplet is set to highlight the bit of a single, best-matching basis triplet, the herein-defined fuzzy approach allows for gradual mapping of each atom triplet onto several related basis triplets, thus minimizing binary classification artifacts. (2) The second innovation is proteolytic equilibrium dependence, by explicitly considering all of the conjugated acids and bases (microspecies). 2D-FPTs are concentration-weighted (as predicted at pH=7.4) averages of microspecies fingerprints. Therefore, small structural modifications, not affecting the overall pharmacophore pattern (in the sense of classical rule-based assignment), but nevertheless triggering a pKa shift, will have a major impact on 2D-FPT. Pairs of almost identical compounds with significantly differing activities ("activity cliffs" in classical descriptor spaces) were in many cases predictable by 2D-FPT. (3) The third innovation is a new similarity scoring formula, acknowledging that the simultaneous absence of a triplet in two molecules is a less-constraining indicator of similarity than its simultaneous presence. It displays excellent neighborhood behavior, outperforming 2D or 3D two-point pharmacophore descriptors or chemical fingerprints. The 2D-FPT calculator was developed using the chemoinformatics toolkit of ChemAxon (www.chemaxon.com).

Algorithms↗

PubMed2005

Deactivation of triplet-excited riboflavin by purine derivatives: important role of uric acid in light-induced oxidation of milk sensitized by riboflavin.

The reactivity of purine derivatives (uric acid, xanthine, hypoxanthine, and purine) toward triplet-excited riboflavin in aqueous solution at pH 6.4 is described on the basis of kinetic (laser flash photolysis), electrochemical (square-wave voltammetry), and theoretical data (density functional theory, DFT). Direct deactivation of triplet-excited riboflavin in aqueous solution, pH 6.4 at 24 degrees C, in the presence of uric acid, xanthine, and hypoxanthine strongly suggests a direct electron transfer from the purine to the triplet-excited riboflavin with k = 2.9 x 10(9) M(-1) s(-1) (DeltaH(++) = 14.7 kJ mol(-1), DeltaS(++) = -15.6 J mol(-1) K(-1)), 1.2 x 10(9) M(-1) s(-1) (DeltaH(++) = 34.3 kJ mol(-1), DeltaS(++) = +45.3 J mol(-1) K(-1)), and 1.7 x10(8) M(-1) s(-1) (DeltaH(++) = 122 kJ mol(-1), DeltaS(++) = +319 J mol(-1) K(-1)), respectively. From the respective one-electron oxidation potentials collected in aqueous solution at pH 6.4 for uric acid (E = +0.686 vs normal hydrogen electrode, NHE), xanthine (E = +1.106 vs NHE), and hypoxanthine (E = +1.654 vs NHE), the overall free energy changes for electron transfer from the quencher to the triplet-excited riboflavin are as follows: uric acid (DeltaG(o) = -114 kJ mol(-1)), xanthine (DeltaG(o) = -73.5 kJ mol(-1)), hypoxanthine (DeltaG(o) = -20.6 kJ mol(-1)), and purine (DeltaG(o) > 0). The inertness observed for purine toward triplet-excited riboflavin corroborates with its electrochemical inactivity in the potential range from 0 up to 2 V vs NHE. These data are in agreement with the DFT results, which show that the energy of the purine highest occupied molecular orbital (HOMO) (-0.2685 arbitrary unit) is lower than the energy of the semioccupied molecular orbital (SOMO) (-0.2557 a.u.) of triplet-excited riboflavin, indicating an endergonic process for the electron-transfer process. The rate-determining step for deactivation by purine derivatives can be assigned to an electron transfer from the purine derivative to the SOMO orbital of the triplet-excited riboflavin. The results show that uric acid may compete with oxygen and other antioxidants to deactivate triplet-excited riboflavin in milk serum and other biological fluids leading to a free radical process.

Animals↗

PubMed2003

Benzophenones in the higher triplet excited states.

Transient phenomena of benzophenone (BP) in the higher triplet excited state (Tn) have been investigated by the two-colour two-laser excitation method. Triplet energy transfer from BP(Tn) to quenchers (Q) occurred within the duration of a laser pulse (5 ns) to give Q(T1) with higher triplet energy than that of BP(T1). The quantum yield of the triplet energy-transfer quenching of BP(Tn) by CCl4 was found to be 0.0023 +/- 0.0002 from the bleaching of the transient absorption of BP(T1) and the absorbed photon number. It appears that internal conversion from BP(Tn) to BP(T1) is the predominant process. The lifetimes (tauTn) of BP(Tn) and several substituted benzophenones (BPs) in the higher triplet excited state [BPs(Tn)] were estimated from the dependence of the Q concentration on the efficiency of the triplet energy-transfer quenching of BP(Tn) by Q, and found to be 110-450 ps, depending on the nature of the substituents on the BPs. The effect of the substituents on tauTn may be explained by the energy gap between the Tn and T1 states, because the main deactivation pathway for BPs(Tn) is the internal conversion process. In contrast, the substituent effect on the lifetimes of BPs(T1) cannot be explained by the energy gap law. The transient behaviour of Q(T1) depends on the properties of the quencher. Sequential triplet energy transfer from Q(T1) to BP occurred for p-dichlorobenzene and tert-butylbenzene as quenchers, while Q(T1) reacted partly with Q to form triplet excimers (3Q2*) for benzene, chlorobenzene, and o-dichlorobenzene as quenchers. When CCl4 was used as the quencher, the homolytic cleavage of a C-Cl bond of CCl4(T1) occurred to give Cl* and Cl3C* radicals.

Journal Article↗

PubMed1998

Triplet structure of human von Willebrand factor.

Human von Willebrand factor (hp-vWF) is a high-molecular- mass protein found in plasma as a series of multimers. It consists of subunits comprising 2050 amino acids linked by disulphide bonds into multimers of various size ranging in molecular mass up to greater than 10000kDa. Partial proteolysis at position Tyr842-Mer843 of the subunit [Dent et al. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 6306-6310] by a vWF-specific protease [Furlan et al. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 7503-7507] results in the generation of an N-terminal and a C-terminal fragment and the appearance of hp-vWF triplet bands. It has been suggested [Furlan et al. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 7503-7507] that (i) the intermediate triplet band of the primary dimer represents a dimer of two C-terminal fragments, (ii) the slower migrating satellite band of the primary dimer represents an asymmetric structure composed of a mature subunit to which one N-terminal and one C-terminal fragment are linked by disulphide bonds, and (iii) the faster migrating satellite band of the primary dimer contains two N-terminal fragments. Here we used recombinant vWF (r-vWF) for structural analysis of hp-vWF multimers. r-vWF exhibited no proteolytic degradation and all multimers contained mature subunits. High-resolution agarose-gel electrophoresis and two-dimensional electrophoresis demonstrated that (i) r-vWF multimers and hp-vWF intermediate triplet bands exhibited identical molecular mass and electrophoretic mobilities, (ii) the faster and slower migrating satellite bands of hp-vWF differ by less than the molecular mass of one subunit from the corresponding intermediate triplet band, and (iii) the triplet bands of hp-vWF are composed of mature and degraded subunits. The results support a structural model of hp-vWF triplet bands according to which the intermediate triplet bands represent multiple numbers of symmetric and/or asymmetric dimers, the slower migrating satellite bands have one extra N-terminal fragment, and the faster migrating satellite band lacks one N-terminal fragment respectively in comparison with the corresponding intermediate triplet band.

Dimerization↗