Roger M. Leblanc

Peptide-coated CdS quantum dots for the optical detection of copper(II) and silver(I).

Gly-His-Leu-Leu-Cys coated CdS quantum dots detected Cu2+ and Ag+ selectively with high sensitivity, below 0.5 microM.

A dansylated peptide for the selective detection of copper ions

A new peptidyl fluorescent chemosensor for the selective detection of copper ions was studied.

Photoacoustic spectroscopy of Anacystis nidulans: III. Detection of photosynthetic activities

Photosynthetic activities of Anacystis nidulans can be detected by photoacoustic spectroscopy. Algae treated by a photosynthetic inhibitor are used to provide the signal from the photochemically inactive sample. The results of these measurements correspond well with the activities which can be monitored by conventional biochemical assays. Acoustic data from A. nidulans are used to obtain the action spectrum for photochemical energy storage. It is concluded that phycocyanin harvests light for both photoreactions but that chlorophyll alpha molecules convey most of their excitation energy to photoreaction I. As judged from the relationship between the modulation frequency and the acoustic signal intensity, at least 60% of the photons absorbed at 630 nm perform photochemical work and about half of the useful energy is stored at stable products. Although it cannot be separated from the purely thermal effect, the contribution of modulated oxygen evolution to the acoustic signal of algae is estimated to be relatively small. Due to structural peculiarities, the opposite situation predominates in low frequency measurements performed with leaves from Impatiens petersiana.

Design and characteristics of a cell for photoacoustic spectroscopy of condensed matter.

We describe a photoacoustic cell which is simple to use, easy to construct, and which gives a great sensitivity, expressed as a signal-to-noise ratio of 3000. Calibration of the cell indicates that it can be used with confidence as a general purpose photoacoustic cell.

Increased heat emission and its relationship to the xanthophyll cycle in pea leaves exposed to strong light stress

Abstract In vivo thermal energy dissipation was photoacoustically monitored in pea leaves before and after strong light treatment. Concomitant with the conversion of the carotenoid violaxanthin into zeaxanthin, a marked increase in the heat emission signal was observed in the light-stressed leaves. However, when the xanthophyll cycle was blocked by dithiothreitol, the photothermal signal still increased, indicating that there was no causal relationship between these two phenomena. Increased heat emission was shown to result from pigment uncoupling, which caused the inhibition of the energy transfer from carotenoids to chlorophyrs. It was also observed that the maintenance of a very low zeaxanthin level by dithiothreitol led to an increase in both the oxygen evolution and the photothermal components of the photoacoustic signal in control leaves and to a strong increase in lipid degradation in light-stressed leaves. These results may suggest that a possible function of the xanthophyll cycle is to provide an accessory pigment (violaxanthin) in weak light and to furnish the hpid matrix of the thylakoid membranes with an efficient photoprotector (zeaxanthin) in strong light.

Photoacoustic spectroscopy of Anacystis nidulans. I. Effect of sample thickness on the photoacoustic signal.

A photoacoustic spectroscopy study of the cyanobacteria Anacystis nidulans has been undertaken. It is demonstrated, by using a filter deposition technique, that the photoacoustic signal intensity becomes progressively saturated as the thickness of the algal layer is increased. This saturation effect originates mostly from the limited optical penetration of the sample and distorts the photoacoustic spectrum from its true shape. A theoretical model is proposed to explain these results, and practical means to obviate the limitations of this spectroscopic technique are suggested.

A Novel Photoscissile Poly(ethylene glycol)‐Based Hydrogel

drawbacks, such as slow gelation rate, need for potentially toxic initiators, and thermal or storage instability. In addition, a limited number of these photoinduced systems demonstrate photoreversibility. [2,3,9,10] Andreopoulos et al. [3] have synthesized a partially reversible hydrogel via photopolymerization of cinnamylidene-terminated PEG. The physical properties of the hydrogel membrane such as pore size and swellability were controlled in a predictive way by alternating the wavelength (>300/254 nm) and sequence of irradiation. The photoreversibility efficiency of the PEG-cinnamylidene hydrogel, however, was compromised by photoscission light inefficiency, cinnamylidene photodegradation, and side polymerization reactions. [10] In the work reported here, we designed a new photocrosslinked and photoscissile hydrogel based on an eight-branched PEG with nitrocinnamate as pendant groups. Cinnamate is known to undergo trans‐cis isomerization and [2+2] cycloaddition upon UV irradiation at wavelengths longer than 290 nm, and the formed cyclobutane ring can be cleaved to regenerate the starting cinnamate groups at wavelengths below 260 nm. [11] The photocrosslinking property of cinnamates has been broadly utilized in the field of photolithography and the semiconductor industry. [12] However, the application of nitrocinnamate photoreactivity in PEG chemistry, especially in PEG-based hydrogel formation, has rarely been reported. [6,13] On the other hand, cinnamate derivatives possess excellent thermal and storage stability superior to cinnamylidene systems. [14] PEG-cinnamylidene polymers have been shown to be unstable and undergo gelation when they are kept at room temperature for a period of a few weeks. Nitrocinnamate demonstrates the stability characteristics of the unsubstituted cinnamate and at the same time is 350 times more photoreactive. [11,15]

Linear dichroism and orientational studies of carotenoid Langmuir-Blodgett films

Abstract The linear dichroism of single monolayers of lutein, zeaxanthin and a mixture of lutein and synthetic phosphatidylcholine has been measured. The angle of orientation of the carotenoid molecules was found to lie between 45° and 51° relative to the plane of the solid support. Although the adsorbed monolayers were mostly in a monomeric state, microscopic observations, as well as the II-A isotherms, indicated the existence of crystalline islets. The results have been interpreted in connection with Haidingers polarization brushes.

Cotinine reduces amyloid-β aggregation and improves memory in Alzheimer's disease mice

Alzheimers disease (AD) affects millions of people world-wide and new effective and safe therapies are needed. Cotinine, the main metabolite of nicotine, has a long half-life and does not have cardiovascular or addictive side effects in humans. We studied the effect of cotinine on amyloid-β (Aβ) aggregation as well as addressed its impact on working and reference memories. Cotinine reduced Aβ deposition, improved working and reference memories, and inhibited Aβ oligomerization in the brains of transgenic (Tg) 6799 AD mice. In vitro studies confirmed the inhibitory effect of cotinine on Aβ1-42 aggregation. Cotinine stimulated Akt signaling, including the inhibition of glycogen synthase kinase 3β (GSK3β), which promotes neuronal survival and the synaptic plasticity processes underlying learning and memory in the hippocampus and cortex of wild type and Tg6799 AD mice. Simulation of the cotinine-Aβ1-42 complex using molecular dynamics showed that cotinine may interact with key histidine residues of Aβ1-42, altering its structure and inhibiting its aggregation. The good safety profile in humans and its beneficial effects suggest that cotinine may be an excellent therapeutic candidate for the treatment of AD.

Coumaryl crown ether based chemosensors: Selective detection of saxitoxin in the presence of sodium and potassium ions

Two novel fluorescent chemosensors in which an aza-crown is linked to 4-coumaryl fluorophores by a methylene spacer have been synthesized for sensing saxitoxin. Fluorescence enhancement was observed upon binding of the dicationic toxin molecule, whereas several metal ions produced no effect.