Force-Induced Shuttling of Rotaxanes Controls Fluorescence Resonance Energy Transfer in Polymer Hydrogels

The molecular shuttling function of rotaxanes can be exploited to design mechanoresponsive reporter molecules. Here, we report a new approach to such rotaxane-based mechanophores, in which the fluorescence resonance energy transfer (FRET) between a donor-acceptor pair is mechanically controlled. A cyclic molecule containing a green-light-emitting FRET donor connected to a red-light-emitting FRET acceptor was threaded onto an axle equipped with a quencher at its center and two stoppers in the peripheral positions. In the force-free state, the green emitter is located near the quencher so that charge transfer interactions or photo-induced electron transfer between the two moieties suppress green emission and prevent the FRET from the green to the red emitter. The mechanophore was covalently incorporated into a linear polyurethane-urea (PUU), and stretchable hydrogels were prepared by swelling this polymer with water. Upon deformation of the PUU hydrogels and under an excitation light that selectively excites the donor, the intensity of the red fluorescence increases, as a result of a force-induced separation of the green emitter from the quencher, which enables the FRET. The switching contrast is much more pronounced in the gels than in dry films, which is due to increased molecular mobility and hydrophobic effects in the hydrogel, which both promote the formation of inclusion complexes between the ring containing the green emitter and the quencher.

A study of the structure-activity relationship for diazaborine inhibition of Escherichia coli enoyl-ACP reductase

Enoyl acyl carrier protein (ACP) reductase catalyses the last reductive step of fatty acid biosynthesis, reducing the enoyl group of a growing fatty acid chain attached to ACP to its acyl product using NAD(P)H as the cofactor. This enzyme is the target for the diazaborine class of antibacterial agents, the biocide triclosan, and one of the targets for the front-line anti-tuberculosis drug isoniazid. The structures of complexes of Escherichia coli enoyl-ACP reductase (ENR) from crystals grown in the presence of NAD+ and a family of diazaborine compounds have been determined. Analysis of the structures has revealed that a mobile loop in the structure of the binary complex with NAD+ becomes ordered on binding diazaborine/NAD+ but displays a different conformation in the two subunits of the asymmetric unit. The work presented here reveals how, for one of the ordered conformations adopted by the mobile loop, the mode of diazaborine binding correlates well with the activity profiles of the diazaborine family. Additionally, diazaborine binding provides insights into the pocket on the enzyme surface occupied by the growing fatty acid chain.

Comparative study of pinning in situ and open epiphysiodesis in 105 patients with slipped capital femoral epiphyses

One hundred five patients were treated for slipped capital femoral epiphyses during the period from 1964 to 1976. Attempts were made to evaluate the differences in results of multiple pinning and open epiphysiodesis performed to treat this problem. Pinning in situ was performed in 61 hips, and open epiphysiodesis was performed in 33 hips. The average follow-up period was seven years four months for pinning in situ and six years seven months for open epiphysiodesis. The average slippage was 22 degrees for patients treated by pinning in situ and 30 degrees for patients treated by open epiphysiodesis. At follow-up evaluation 91.7% of the patients treated by pinning in situ had good or excellent results, as compared with 71.6% of the patients treated by epiphysiodesis. For the patients treated by pinning in situ, 5% had poor results, and 3.3% were considered failures. For the patients treated by epiphysiodesis, 3.4% had poor results, while 25% were considered failures. Pinning in situ is the treatment of choice. It is more predictable, has less complications, and provides better long-term results.

Photosynthetic adaptation of Solanum dulcamara L. to sun and shade Environments : IV. A comparison of North American and European genotypes

Clonal replicates of six genotypes of Solanum dulcamara L. grown in eight different environments were compared for photosynthesis and growth. Four of the genotypes were native to shaded habitats, two to sun habitats. The experimental growth environments differed in light level, daily temperature amplitude and substrate moisture availability. Treatments elicited large differences in lightsaturated photosynthetic rates and growth. Genotypic differences in response to the treatments were identified. However, when genotypes native to sun and shade habitats were compared, there were no consistent differences in photosynthesis or total plant dry weight. It was concluded that previously reported differences in the photosynthetic response of genotypes native to sun and shade habitats to treatment light level may have been the result of the persistent after-effects to changes in leaf water potential and not an adaptive response to growth light level.

Effects of High Atmospheric CO(2) and Sink Size on Rates of Photosynthesis of a Soybean Cultivar

The effect of sink strength on photosynthetic rates under conditions of long-term exposure to high CO(2) has been investigated in soybean. Soybean plants (Merr. cv. Fiskeby V) were grown in growth chambers containing 350 microliters CO(2) per liter air until pod set. At that time, plants were trimmed to three trifoliolate leaves and either 21 pods (high sink treatment) or 6 pods (low sink treatment). Trimmed plants were either left in 350 microliters CO(2) per liter of air or placed in 1000 microliters CO(2) per liter of air (high CO(2) treatment) until pod maturity. Whole plant net photosynthetic rates of all plants were measured twice weekly, both at 350 microliters CO(2) per liter of air and 1000 microliters CO(2) per liter of air. Plants were also harvested at this time for dry weight measurements. Photosynthetic rates of high sink plants at both measurement CO(2) concentrations were consistently higher than those of low sink plants, and those of plants given the 350 microliter CO(2) per liter of air treatment were higher at both measurement CO(2) concentrations than those of plants given the 1000 microliters CO(2) per liter of air treatment. When plants were measured under treatment CO(2) levels, however, rates were higher in 1,000 microliter plants than 350 microliter CO(2) plants. Dry weights of all plant parts were higher in the 1,000 microliters CO(2) per liter air treatment than in the 350 microliters CO(2) per liter air treatment, and were higher in the low sink than in the high sink treatments.

Photosynthetic Adaptation of Solanum dulcamara L. to Sun and Shade Environments: II. Physiological Characterization of Phenotypic Response to Environment

Photosynthetic and growth properties of Solanum dulcamara L. were studied under controlled environments. The 200 experimentally tested plants were clonal replicates of five field-collected individuals, three from fully exposed habitats and two from deeply shaded habitats. After 4 weeks of growth in one of eight environmental treatments, each plant was measured for leaf adaxial and abaxial conductance to water vapor, specific leaf weight, chlorophyll per square decimeter of leaf, photosynthetic unit size, light-saturated photosynthetic rate, total leaf area, and total leaf, stem, and root dry weights. Changes in light level influenced photosynthesis and growth of each plant more than changes in water availability or temperature. It is strongly suggested that the primary adaptive response of the tested individuals to changes in levels of light involves the regulation of leaf thickness.

Radioimmunoassay of bleomycin in plasma and urine

Antibodies to bleomycin were raised by immunization of sheep and rabbits with bleomycin-albumin conjugates. The combination of a high-titre, high-avidity sheep antiserum and iodinated bleomycin produced a radioimmunoassay sensitive to 8 ng of bleomycin per ml of plasma or urine. Untreated specimens (100 microliter) of plasma or urine could be added directly to the assay tubes. The antiseerum was specific for bleomycin and showed no cross-reaction with other anticancer agents used in combination chemotherapy. Over a concentration range of 20-100 ng/ml, recovery of bleomycin from plasma was 110% and from urine, 93%. Repeated assay of plasma samples showed a decrease in bleomycin levels unless the samples were kept at 4 degrees C or below. Assay of bleomycin levels in plasma and urine from patients under treatment with bleomycin showed similarities with results reported using a microbiological assay. The radioimmunoassay offers a more reliable, rapid and sensitive method for the measurement of bleomycin.

Radioimmunoassay of vinblastine and vincristine

1 The cytotoxic agent, vinblastine, was conjugated to albumin, using the Mannich reaction. Rabbits immunized with two conjugates, containing differing amounts of hapten, produce antibodies which bound [3H]-vinblastine. 2 Antisera from one rabbit cross-reacted with both vinblastine and vincristine and were used to develop radioimmunoassays for measuring their concentration in plasma. 3 The antisera showed no cross-reactivity with other alkaloids or cytotoxic drugs and provided assays sensitive to a concentration of 2.1 ng vinblastine or 3.8 ng vincristine/ml of plasma added direct to the assay tubes. 4 This is sufficiently sensitive to permit the measurement of plasma vinblastine levels for up to 24 h after the intravenous administration of 15 mg of the drug.

Plasma cannabinoids measured by radioimmunoassay in rabbits after intravenous injection of tetrahydrocannibinol, 11-hydroxy-tetrahydrocannabinol, cannabinol and cannabidiol

An antiserum raised in sheep against a conjugate of tetrahydrocannabinol with bovine serum albumin has been used as the basis of a radioimmunoassay for cannabinoids in the blood of rabbits given tetrahydrocannabinol, 11-hydroxy-tetrahydrocannabinol, cannabinol or cannabidiol by rapid intravenous injection. In the case of both 11-hydroxy-tetrahydrocannabinol and cannabinol plasma cannabinoid concentrations fell exponentially from an initial peak plasma level attained immediately after the completion of intravascular distribution of the injected bolus. In the case of tetrahydrocannabinol itself, however, there was a progressive rise in plasma cannabinoid concentration between five and fifteen minutes after the rapid intravenous injection. The reasons for this rise in plasma cannabinoid concentration are discussed.