Analysis Of Fluorescence Excitation Spectra Research Articles

Fluorescence Excitation Spectra of Total Lipids with Paramagnetic Properties Isolated from Marine Organisms.

Results of analysis of fluorescence excitation spectra of total lipid extracts of marine hydrobionts are presented. Previously, identical paramagnetic centers were recorded in these extracts by EPR spectroscopy. Analysis of fluorescence excitation spectra of total lipid extracts of Mytilus galloprovincialis L. (gonads) and Squalus achantias (liver) showed that, after oxidation with lead dioxide, identical fluorescent products with two similar highs (306 and 321 nm) appeared in hexane.

Incorporation of spheroidene and spheroidenone into light-harvesting complexes from purple sulfur bacteria

Spheroidene and spheroidenone from the non-sulfur bacterium Rhodobacter (Rba.) sphaeroides were incorporated into diphenylamine (DPA) LH1-RC and LH2 complexes from sulfur bacteria Allochromatium (Alc.) minutissimum and Ectothiorhodospira (Ect.) haloalkaliphila in which carotenoid (Car) biosynthesis was inhibited by ~95%. A series of biochemical characteristics of the modified LH2 complexes was studied (electrophoretic mobility, absorption and CD spectra, Car composition, Car-to-BChl energy transfer and thermal stability). It was found that the electrophoretic mobility of the complexes with incorporated Cars did not change compared to that of the control and DPA-complexes, indicating the absence of any significant change in the structure of LH complexes upon DPA-treatment and subsequent incorporation of Cars. The analysis of fluorescence excitation spectra of the spheroidene-incorporated LH2 complex (LH2:sph) and the spheroidenone-incorporated LH2 complex (LH2:sph-ne) showed that spheroidene and spheroidenone exhibited relatively low efficiencies of energy transfer to BChl, when incorporated into the LH2 DPA-complexes from Alc. minutissimum and Ect. haloalkaliphila, although, they showed high efficiencies, being in their natural state in the LH2 complexes from Rba. sphaeroides. A significant increase in thermostability observed for the LH2:sph and LH2:sph-ne complexes with respect to the LH2 DPA-complexes indicated that the two incorporated Cars stabilized the structure of the LH2 complexes.

Molecular structure of trimethyl[(3-indole)ethoxy]silane cooled in a supersonic jet

Conformations of He-jet-cooled trimethyl[(3-indole)ethoxy]silane (TIES) have been studied using a laser spectroscopy technique in combination with quantum-chemical computations. Six probable conformers of the molecule were computed, of which only two conformations were observed. Based on an analysis of fluorescence excitation spectra, fluorescence spectra, shapes of rotational band contours at the electronic S0–S1 transition of TIES, and theoretical computations, the above conformers were assigned to steric structures. Twisted structures have the lowest energy due to intramolecular hydrogen bonds $$ C - H \cdots O <_C^{Si} $$ between hydrogen atoms of methyl groups and an oxygen atom and C–H···π between H and the π-electron cloud of the indole ring.

Vibrational and rotational structure and excited-state dynamics of pyrene

Vibrational level structure in the S(0) (1)A(g) and S(1) (1)B(3u) states of pyrene was investigated through analysis of fluorescence excitation spectra and dispersed fluorescence spectra for single vibronic level excitation in a supersonic jet and through referring to the results of ab initio theoretical calculation. The vibrational energies are very similar in the both states. We found broad spectral feature in the dispersed fluorescence spectrum for single vibronic level excitation with an excess energy of 730 cm(-1). This indicates that intramolecular vibrational redistribution efficiently occurs at small amounts of excess energy in the S(1) (1)B(3u) state of pyrene. We have also observed a rotationally resolved ultrahigh-resolution spectrum of the 0(0) (0) band. Rotational constants have been determined and it has been shown that the pyrene molecule is planar in both the S(0) and S(1) states, and that its geometrical structure does not change significantly upon electronic excitation. Broadening of rotational lines with the magnetic field by the Zeeman splitting of M(J) levels was very small, indicating that intersystem crossing to the triplet state is minimal. The long fluorescence lifetime indicates that internal conversion to the S(0) state is also slow. We conclude that the similarity of pyrene's molecular structure and potential energy curve in its S(0) and S(1) states is the main cause of the slow radiationless transitions.

Self-assembling nanoscaled drug delivery systems composed of amphiphilic poly- N-vinylpyrrolidones

Certain amphiphilic water-soluble polymers including amphiphilic derivatives of poly- N-vinylpyrrolidone (PVP) were found to be an efficient base for drug delivery systems. In this study, one-end functionalized PVP of different molecular weight was hydrophobically modified with long-chain fatty n-alkyl or di( n-alkyl) amines through a coupling reaction using N,N′-dicyclohexyl carbodiimide (DCC). Amphiphilic PVPs have different physico-chemical properties according to the structure of hydrophilic/hydrophobic fragments. Since synthesized polymers have the amphiphilic characteristics in aqueous solution, polymeric nanoparticles of amphiphilic PVPs were prepared in aqueous media. Using the analysis of fluorescence excitation spectra and dynamic light-scattering it was shown that the ability to form nanoparticles of 30–700 nm size for polymers with primary aliphatic end groups increases with decreasing the polymer molecular weight and with increasing n-alkyl group length. Polymers containing di( n-alkyl) end groups form larger aggregates at higher concentrations. Transmission electron micrograph readings showed the spherical morphologies of the polymeric nanoparticles. In all cases the size of aggregates formed in physiological solution is lower than those obtained in distilled water.

Self-assembled polymeric nanoparticles of poly(ethylene glycol) grafted pullulan acetate as a novel drug carrier.

Self-assembling nanospheres of hydrophobized pullulan have been developed. Pullulan acetate (PA), as hydrophobized pullulan, was synthesized by acetylation. Carboxymethylated poly(ethylene-glycol) (CMPEG) was introduced into pullulan acetate (PA) through a coupling reaction using N,N'-dicyclohexyl carbodiimide (DCC). A synthesized PA-PEG-PA (abbreviated as PEP) conjugate was confirmed by Fourier transform-infrared (FT-IR) spectroscopy. Since PEP conjugates have amphiphilic characteristics in aqueous solution, polymeric nanoparticles of PEP conjugates were prepared using a simple dialysis method in water. From the analysis of fluorescence excitation spectra primarily, the critical association concentration (CAC) of this conjugate was found to be 0.0063 g/L. Observations by scanning electron microscopy (SEM) showed the spherical morphologies of the PEP nanoparticles. The particle size distribution of the PEP conjugates was determined using photon correlation spectroscopy (PCS) and the intensity-average particle size was 193.3 +/- 13.53 nm with a unimodal distribution. Clonazepam (CNZ), as a model drug, was easy to entrap into polymeric nanoparticles of the PEP conjugates. The drug release behavior was mainly diffusion controlled from the core portion.

Polymeric nanoparticle composed of fatty acids and poly(ethylene glycol) as a drug carrier

Diamine-terminated poly(ethylene glycol) (ATPEG) was hydrophobically modified with long-chain fatty acids (FAs) through a coupling reaction using N, N′-dicyclohexyl carbodiimide (DCC). FA–PEG–FA conjugates have different physico-chemical properties according to the chain length of the fatty acid (FA). Synthesized FA–PEG–FA conjugate was confirmed by Fourier transform-infrared (FT-IR). Since FA–PEG–FA conjugates have the amphiphilic characteristics in aqueous solution, polymeric nanoparticles of FA–PEG–FA conjugates were prepared using a simple dialysis method in water. The results of 1H nuclear magnetic resonance (NMR) spectroscopy and fluorescent spectroscopy suggest that the FA–PEG–FA conjugate has a typical core–shell type nanoparticle structure made by a self-assembling process. From the analysis of fluorescence excitation spectra, especially, the critical micelles concentration (CMC) of this conjugate was changed unpredictably, i.e. the critical association concentration (CAC) value was decreased below a FA carbon number of 16 but, above increased a FA carbon number of 16. Transmission electron micrograph readings showed the spherical morphologies of the polymeric nanoparticles. The particle size was continuously decreased until below a FA carbon number of 20, but it was increased above a FA carbon number of 20. Clonazepam (CNZ), as a model drug, was easy to entrap into polymeric nanoparticles of the FA–PEG–FA conjugates. The drug release behavior was changed according to the FA chain length and was mainly diffusion controlled from the core portion.

Xanthophyll pigments in light-harvesting complex II in monomolecular layers: localisation, energy transfer and orientation

Monomolecular layers of the largest light-harvesting pigment-protein complex of Photosystem II (LHCII) were formed at the argon-water interface. The molecular area of the LHCII monomer in monomolecular layers determined from the isotherms of compression is found to be close to 14 nm 2, which corresponds well to the molecular dimensions of the protein evaluated on the basis of crystallographic studies. Monolayers of LHCII were deposited on a glass support by means of the Langmuir-Blodgett technique and subjected to spectroscopic studies: electronic absorption spectrophotometry and spectrofluorometry. The fluorescence excitation spectra of chlorophyll a in monolayers of LHCII were analysed using gaussian deconvolution. Comparison of the absorption and fluorescence excitation spectra enabled calculation of the rate of excitation energy transfer in the system. Excitation energy was found to be transferred to chlorophyll a from chlorophyll b with 97% efficiency, from neoxanthin with 85%, from lutein with 62% and from violaxanthin with at least 54% efficiency. The analysis of the position of the 0-0 absorption band of the xanthophylls revealed that neoxanthin is located in the same protein environment as lutein but in a different environment than violaxanthin. The analysis of fluorescence excitation spectra of chlorophyll a in LHCII, recorded with the excitation light beam polarised in two orthogonal directions, enabled the determination of the mean orientation angle of the accessory xanthophyll pigments with respect to the plane of the sample. The mean orientation of lutein found in this study (approx. 51°) corresponds well to the crystallographic data. Neoxanthin was found to adopt a similar orientation to lutein. The transition dipole moment of violaxanthin was found to form a mean angle of 71° with the axis spanning two polar regions of the protein, perpendicular to the plane of the monolayer, suggesting planar orientation of this pigment with respect to the plane of the thylakoid membrane. These experimentally determined xanthophyll orientations are discussed in terms of importance of peripheral xanthophyll pigments in supramolecular organisation of LHCII and the operation of the xanthophyll cycle within the thylakoid membrane.

Trypsin-induced changes in energy distribution between photosystem I and photosystem II in pea thylakoid membranes

The influence of “mild” trypsin digestion of pea thylakoid membranes on fluorescence emission and excitation spectra was investigated. With increasing trypsin concentration the intensity of fluorescence emission maximum at 735 nm (attributed to PSI) was enhanced and the ratio F 735/ F 685 increased from 1.47 ± 0.12 for control thylakoids up to 3.15 + 0.23 for thylakoids, treated with 8 μg tryp/mg Chl. This increase was more pronounced when the excited light wavelength was 472 nm. In order to clarify which chlorophyll forms are responsible for these changes in the distribution of light energy between both photosystems, an analysis of fluorescence excitation spectra in “blue” and “red” regions was carried out. In the “blue” region an increase of the ratio of intensities 470/436 was observed. In the “red” region an increase of the intensity of the shoulder at 650 nm is observed. Concomitantly, a shift to shorter wavelengths of the excitation maximum at 680 nm was observed. The data presented support the view that the observed increase of photosystem I energy supply involves an increased contribution of Chl b molecules.