Proceedings of the 13th annual conference of INEBRIA

CITATION: Watson, R., et al. 2016. Proceedings of the 13th annual conference of INEBRIA. Addiction Science & Clinical Practice, 11:13, doi:10.1186/s13722-016-0062-9.The original publication is available at https://ascpjournal.biomedcentral.comENGLISH SUMMARY : Meeting abstracts.https://ascpjournal.biomedcentral.com/articles/10.1186/s13722-016-0062-9Publisher's versio

Interference of surface plasmon resonances causes enhanced depolarized light scattering from metal nanoparticles

We show that the strongly depolarized light scattering from noble metal particles is a result of interference of two surface plasmon resonances on the same particle. The maximum depolarization occurs between two resonances. Under favorable conditions the anisotropy of the scattering light can be much lower than what is possible for dielectric particles. This explanation is discussed in relation to earlier published experimental measurements. Comparison of experimental results with theoretical calculations provides information on the shape distribution of metallic particles in the suspension. (c) 2006 Elsevier B.V. All rights reserved

Fluorescence correlation spectroscopy in surface plasmon coupled emission microscope

Study of dynamics of single molecules by Fluorescence Correlation Spectroscopy (PCS) requires that the rate of photon detection per molecule be high, that the background be low, and that there be a large change in fluorescent signal associated with change in a position of a molecule. PCS applied to microscopic Surface Plasmon Coupled Emission (SPCE) suggests a powerful method to meet those requirements. In this method, the observational volume is made shallow by placing a sample on a thin metal film and illuminating it with the laser beam at Surface Plasmon Resonance (SPR) angle through high numerical aperture objective. The illuminating light excites surface plasmons in the metal film that produce an evanescent wave on the aqueous side of the interface. The thickness of the detection volume is a product of evanescent wave penetration depth and distance-dependent fluorescence coupling to surface plasmons. It is further reduced by a metal quenching of excited fluorophores at a close proximity (below 10 nm) to a surface. The fluorescent light is emitted through the metal film only at an SPCE angle. Objective collects emitted light, and a confocal aperture inserted in its conjugate image plane reduces lateral dimensions of the detection volume to a fraction of a micrometer. By using diffusion of fluorescent microspheres, we show that SPCE-FCS is an efficient method to measure molecular diffusion and that on gold surface the height of the detection volume is ∼35 nm

Application of Surface Plasmon Coupled Emission to Study of Muscle

Muscle contraction results from interactions between actin and myosin cross-bridges. Dynamics of this interaction may be quite different in contracting muscle than in vitro because of the molecular crowding. In addition, each cross-bridge of contracting muscle is in a different stage of its mechanochemical cycle, and so temporal measurements are time averages. To avoid complications related to crowding and averaging, it is necessary to follow time behavior of a single cross-bridge in muscle. To be able to do so, it is necessary to collect data from an extremely small volume (an attoliter, 10(−18) liter). We report here on a novel microscopic application of surface plasmon-coupled emission (SPCE), which provides such a volume in a live sample. Muscle is fluorescently labeled and placed on a coverslip coated with a thin layer of noble metal. The laser beam is incident at a surface plasmon resonance (SPR) angle, at which it penetrates the metal layer and illuminates muscle by evanescent wave. The volume from which fluorescence emanates is a product of two near-field factors: the depth of evanescent wave excitation and a distance-dependent coupling of excited fluorophores to the surface plasmons. The fluorescence is quenched at the metal interface (up to ∼10 nm), which further limits the thickness of the fluorescent volume to ∼50 nm. The fluorescence is detected through a confocal aperture, which limits the lateral dimensions of the detection volume to ∼200 nm. The resulting volume is ∼2 x 10(−18) liter. The method is particularly sensitive to rotational motions because of the strong dependence of the plasmon coupling on the orientation of excited transition dipole. We show that by using a high-numerical-aperture objective (1.65) and high-refractive-index coverslips coated with gold, it is possible to follow rotational motion of 12 actin molecules in muscle with millisecond time resolution

Spectroscopy of Photosynthetic Pigment-Protein Complex LHCII

Light-harvesting pigment-protein complex of photosystem II is the most abundant membrane protein in the biosphere, comprising more than half chlorophyll molecules. The protein plays a role of photosynthetic antenna, collecting solar radiation and transferring excitations towards the reaction centers, where electric charge separation takes place. Efficient excitation energy capture and transfer requires unique organization of the complex and unique photophysical properties of the accessory pigments: chlorophylls and carotenoids. LHCII is also a place where extremely harmful singlet oxygen may be generated, under strong illumination conditions. Several physical mechanisms have been found in LHCII, operating to protect the photosynthetic apparatus against light-induced damage, including chlorophyll triplet and singlet excitations quenching by carotenoids. In this paper we discuss the results of our recent studies, carried out with the application of several molecular spectroscopy techniques (electronic absorption, fluorescence, resonance Raman and FTIR), designed to investigate molecular mechanisms responsible for regulation of excitation density in LHCII. Among the most interesting findings are the light-induced molecular configuration changes of the LHCII-bound xanthophylls, leading to conformational rearrangements of the protein. These mechanisms are discussed in terms of excessive excitation quenching in the pigment-protein complex subjected to overexcitation. Such an activity seems to represent a vital regulatory process in the photosynthetic apparatus, at the molecular level, protecting plants against photodegradation

Minimization of detection volume by surface-plasmon-coupled emission

We report theoretical predictions and experimental observations of the reduced detection volume with the use of surface-plasmon-coupled emission (SPCE). The effective fluorescence volume (detection volume) in SPCE experiments depends on two near-field factors: the depth of evanescent wave excitation and a distance-dependent coupling of excited fluorophores to the surface plasmons. With direct excitation of the sample (reverse Kretschmann excitation) the detection volume is restricted only by the distance-dependent coupling of the excitation to the surface plasmons. However, with the excitation through the glass prism at surface plasmon resonance angle (Kretschmann configuration), the detection volume is a product of evanescent wave penetration depth and distance-dependent coupling. In addition, the detection volume is further reduced by a metal quenching of excited fluorophores at a close proximity (below 10 nm). The height of the detected volume size is 40-70 nm, depending on the orientation of the excited dipoles. We show that, by using the Kretschmann configuration in a microscope with a high-numerical-aperture objective (1.45) together with confocal detection, the detection volume can be reduced to 1-2 attoL. The strong dependence of the coupling to the surface plasmons on the orientation of excited dipoles can be used to study the small conformational changes of macromolecules

Effect of temperature during assembly on the structure and mechanical properties of peptide-based materials.

Mutually complementary, self-repulsive oligopeptide pairs were designed to coassemble into viscoelastic hydrogels. Peptide engineering was combined with biophysical techniques to investigate the effects of temperature on the structural and mechanical properties of the resulting hydrogels. Biophysical characterizations, including dynamic rheometry, small-angle X-ray scattering (SAXS), and fluorescence spectroscopy, were used to investigate hydrogelation at the bulk, fiber, and molecular levels, respectively. It has been found that temperature has a significant effect on the structure and mechanical properties of peptide-based biomaterials. Oligopeptide fibers assembled at 25°C are formed faster and are two times thicker, and the resulting material is mechanically seven times stronger than that assembled at 5°C. © 2010, American Chemical Societ

Effects of chain length on oligopeptide hydrogelation

The co-assembly of mutually complementary, but self-repulsive oligopeptide pairs into viscoelastic hydrogels has been studied. Oligopeptides of 6, 10, and 14 amino acid residues were used to investigate the effects of peptide chain length on the structural and mechanical properties of the resulting hydrogels. Biophysical characterizations, including dynamic rheometry, small-angle X-ray scattering (SAXS) and fluorescence spectroscopy, were used to investigate hydrogelation at the bulk, fiber, and molecular levels, respectively. Upon mixing, the 10-mer peptides and the 14-mer peptides both form hydrogels while the 6-mer peptides do not. SAXS studies point to morphological similarity of the cross-sections of fibers underlying the 10 : 10 and 14 : 14 gels. However, fluorescence spectroscopy data suggest tighter packing of the amino acid side chains in the 10 : 10 fibers. Consistent with this tighter packing, dynamic rheometry data show that the 10 : 10 gel has much higher elastic modulus than the 14 : 14-mer (18 kPa vs. 0.1 kPa). Therefore, from the standpoint of mechanical strength, the optimum peptide chain length for this class of oligopeptide-based hydrogels is around 10 amino acid residues. © 2010, Royal Society of Chemistry

Spectroscopy of Photosynthetic Pigment-Protein Complex LHCII

Light-harvesting pigment-protein complex of photosystem II is the most abundant membrane protein in the biosphere, comprising more than half chlorophyll molecules. The protein plays a role of photosynthetic antenna, collecting solar radiation and transferring excitations towards the reaction centers, where electric charge separation takes place. Efficient excitation energy capture and transfer requires unique organization of the complex and unique photophysical properties of the accessory pigments: chlorophylls and carotenoids. LHCII is also a place where extremely harmful singlet oxygen may be generated, under strong illumination conditions. Several physical mechanisms have been found in LHCII, operating to protect the photosynthetic apparatus against light-induced damage, including chlorophyll triplet and singlet excitations quenching by carotenoids. In this paper we discuss the results of our recent studies, carried out with the application of several molecular spectroscopy techniques (electronic absorption, fluorescence, resonance Raman and FTIR), designed to investigate molecular mechanisms responsible for regulation of excitation density in LHCII. Among the most interesting findings are the light-induced molecular configuration changes of the LHCII-bound xanthophylls, leading to conformational rearrangements of the protein. These mechanisms are discussed in terms of excessive excitation quenching in the pigment-protein complex subjected to overexcitation. Such an activity seems to represent a vital regulatory process in the photosynthetic apparatus, at the molecular level, protecting plants against photodegradation

Rates of energy transfer between tryptophans and hemes in hemoglobin, assuming that the heme is a planar oscillator.

Using the Förster equations we have estimated the rate of energy transfer from tryptophans to hemes in hemoglobin. Assuming an isotropic distribution of the transition moments of the heme in the plane of the porphyrin, we computed the orientation factors and the consequent transfer rates from the crystallographic coordinates of human oxy- and deoxy-hemoglobin. It appears that the orientation factors do not play a limiting role in regulating the energy transfer and that the rates are controlled almost exclusively by the intrasubunit separations between tryptophans and hemes. In intact hemoglobin tetramers the intrasubunit separations are such as to reduce lifetimes to 5 and 15 ps/ns of tryptophan lifetime. Lifetimes of several hundred picoseconds would be allowed by the intersubunit separations, but intersubunits transfer becomes important only when one heme per tetramer is absent or does not accept transfer. If more than one heme per tetramer is absent lifetimes of more than 1 ns would appear