We present femtosecond transient absorption measurements on \(\pi\)-conjugated supramolecular assemblies in a high pump fluence regime. Oligo(\emph{p}-phenylenevinylene) monofunctionalized with ...ureido-\emph{s}-triazine (MOPV) self-assembles into chiral stacks in dodecane solution below 75\(^{\circ}\)C at a concentration of \(4\times 10^{-4}\) M. We observe exciton bimolecular annihilation in MOPV stacks at high excitation fluence, indicated by the fluence-dependent decay of \(1^1\)B\(_{u}\)-exciton spectral signatures, and by the sub-linear fluence dependence of time- and wavelength-integrated photoluminescence (PL) intensity. These two characteristics are much less pronounced in MOPV solution where the phase equilibrium is shifted significantly away from supramolecular assembly, slightly below the transition temperature. A mesoscopic rate-equation model is applied to extract the bimolecular annihilation rate constant from the excitation fluence dependence of transient absorption and PL signals. The results demonstrate that the bimolecular annihilation rate is very high with a square-root dependence in time. The exciton annihilation results from a combination of fast exciton diffusion and resonance energy transfer. The supramolecular nanostructures studied here have electronic properties that are intermediate between molecular aggregates and polymeric semiconductors.
These studies were undertaken to quantify cholesterol balance across the plasma space and the individual organs of the mouse, and to determine the role of the low density lipoprotein receptor (LDLR) ...in these two processes. In the normal mouse (129 Sv), sterol was synthesized at the rate of 153 mg/d per kg body weight of which 78% occurred in the extrahepatic tissues while only 22% took place in the liver. These animals metabolized 7.1 pools of LDL-cholesterol (LDL-C) per day, and 79% of this degradation took place in the liver. Of this total turnover, the LDLR accounted for 88% while the remaining 12% was receptor independent. 91% of the receptor-dependent transport identified in these animals was located in the liver while only 38% of the receptor-independent uptake wsa found in this organ. When the LDLR was deleted, the LDL-C production rate increased 1.7-fold, LDL-C turnover decreased from 7.1 to 0.88 pools/d, and the plasma LDL-C level increased 14-fold, from 7 to 101 mg/dl. Despite these major changes in the circulating levels of LDL-C, however, there was no change in the rate of cholesterol synthesis in any extrahepatic organ or in the whole animal, and, further, there was no change in the steady-state cholesterol concentration in any organ. Thus, most extrahepatic tissues synthesize their daily sterol requirements while most LDL-C is returned directly to the liver. Changes in LDLR activity, therefore, profoundly alter the plasma LDL-C concentration but have virtually no affect on cholesterol balance across any extrahepatic organ, including the brain.
This study examines the question of whether apolipoprotein E (apoE) alters steady-state concentrations of plasma cholesterol carried in low density lipoproteins (LDL-C) by acting as a competitive ...inhibitor of hepatic LDL uptake or by altering the rate of net cholesterol delivery from the intestinal lumen to the liver. To differentiate between these two possibilities, rates of cholesterol absorption and synthesis and the kinetics of hepatic LDL-C transport were measured in vivo in mice with either normal (apoE+/+) or zero (apoE-/-) levels of circulating apoE. Rates of cholesterol absorption were essentially identical in both genotypes and equaled approximately 44% of the daily dietary load of cholesterol. This finding was consistent with the further observation that the rates of cholesterol synthesis in the liver (approximately 2000 nmol/h) and extrahepatic tissues (approximately 3000 nmol/h) were also essentially identical in the two groups of mice. However, the apparent Michaelis constant for receptor-dependent hepatic LDL-C uptake was markedly lower in the apoE-/- mice (44 +/- 4 mg/dl) than in the apoE+/+ animals (329 +/- 77 mg/dl) even though the maximal transport velocity for this uptake process was essentially the same (approximately 400 micrograms/h per g) in the two groups of mice. These studies, therefore, demonstrate that apoE-containing lipoproteins can act as potent competitive inhibitors of hepatic LDL-C transport and so can significantly increase steady-state plasma LDL-C levels. This apolipoprotein plays no role, however, in the regulation of cholesterol absorption, sterol biosynthesis, or hepatic LDL receptor number, at least in the mouse
A survey of egg parasitoids of the genus
Trichogramma (Hymenoptera, Trichogrammatidae) was carried out in olive groves in Portugal, Greece, Egypt, and Tunisia during the years 2002–2004. Parasitoids ...were obtained either by exposing sentinel eggs (
Sitotroga cerealella Olivier or
Ephestia kuehniella Zeller) on olive trees or by collecting eggs of lepidopterous olive pests. Parasitized egg samples were reared separately in the laboratory for emergence of parasitoids. These were further reared in separate lines and processed by morphological and molecular biology techniques for species characterization. The recorded fauna of
Trichogramma parasitoids in olive groves was species poor and consisted of species mainly known from the Mediterranean region.
Trichogramma bourarachae Pintureau and Babault was found in Tunisia and Egypt,
T. cordubensis Vargas and Cabello, and
T. euproctidis Girault in Egypt,
Trichogramma cacoeciae Marchal in Portugal, Greece, Egypt, Tunisia and
Trichogramma nerudai Pintureau and Gerding in Portugal. Apart from that,
Trichogramma oleae Voegelé and Pointel was collected in Tunisia. This species is probably not indigenous, but has established after several releases of a French strain were made in recent years. For selected strains, the sequence of the internal transcribed spacer 2 (ITS-2) region of rDNA was determined and deposited in the GenBank database. Differences in important biological attributes were found among collected strains of
T. bourarachae, suggesting the existence of biotypes. The results contribute to the limited knowledge on distribution and biodiversity of the genus
Trichogramma in the Mediterranean region. They can be helpful for the preservation and use of indigenous
Trichogramma species in biological control of lepidopterous pests in olive and other local crops.
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