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Fluorescence Experiments (fluorescence + experiment)

Distribution by Scientific Domains

Chemistry	50%
Life Sciences	20%

Selected Abstracts

Polycaprolactone- b -Poly(ethylene oxide) Biocompatible Micelles as Drug Delivery Nanocarriers: Dynamic Light Scattering and Fluorescence Experiments

MACROMOLECULAR SYMPOSIA, Issue 1 2005
Cristiano Giacomelli
Abstract Summary: Dynamic light scattering (DLS) and fluorescence experiments were carried out to study PCL44 - b -PEO114 biocompatible micelles used as nanocarriers in drug delivery. Micelles prepared by a simple procedure (THF removal under nitrogen flow) exhibited a narrow size distribution with an average diameter of 100 nm. For micelles containing a hydrophobic model compound (pyrene) within the PCL core, a smaller average micellar size of 80 nm was observed, with a simultaneous broadening in the size distribution profile. In parallel to DLS results, fluorescence experiments showed evidence of pyrene encapsulation, and that the onset of the micellization process occurs at approximately 10/90 (v/v) THF/water mixtures in the case of PCL44 - b -PEO114 polymer. [source]

Interaction between amyloid ,-protein aggregates and membranes

JOURNAL OF PEPTIDE SCIENCE, Issue 10 2004
Atsuko Kakio
Abstract The conversion of soluble, nontoxic amyloid ,-protein (A,) to aggregated, toxic A, rich in ,-sheet structures is considered to be the key step in the development of Alzheimer's disease. Therefore, extensive studies have been carried out on the mechanisms involved in A, aggregation and the characterization of A, aggregates formed in aqueous solutions mimicking biological fluids. On the other hand, several investigators pointed out that membranes play an important role in A, aggregation. However, it remains unclear whether A, aggregates formed in solution and membranes are identical and whether the former can bind to membranes. In this study, using a dye-labeled A,-(1,40) as well as native A,-(1,40), the properties of A, aggregates formed in buffer and raft-like membranes composed of monosialoganglioside GM1/cholesterol/sphingomyelin were compared. Fourier transform infrared spectroscopic measurements suggested that A, aggregates formed in buffer and in membranes have different ,-sheet structures. Fluorescence experiments revealed that A, aggregated in buffer did not show any affinity for membranes. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source]

On-line identification of lysergic acid diethylamide (LSD) in tablets using a combination of a sweeping technique and micellar electrokinetic chromatography/77 K fluorescence spectroscopy

ELECTROPHORESIS, Issue 6 2003
Ching Fang
Abstract This work describes a novel method for the accurate determination of lysergic acid diethylamide (LSD) in tablets. A technique involving sweeping-micellar electrokinetic chromatography (MEKC) was used for the initial on-line concentration and separation, after which a cryogenic molecular fluorescence experiment was performed at 77 K. Using this approach, not only the separation of LSD from the tablet extract was achieved, but on-line spectra were readily distinguishable and could be unambiguously assigned. The results are in agreement with analyses by gas chromatography-mass spectrometry (GC-MS). Thus, this method, which was found to be accurate, sensitive and rapid, has the potential for use as a reliable complementary method to GC-MS in such analyses. [source]

Fluorescent proteins for single-molecule fluorescence applications

JOURNAL OF BIOPHOTONICS, Issue 1 2008
Britta Seefeldt
Abstract We present single-molecule fluorescence data of fluorescent proteins GFP, YFP, DsRed, and mCherry, a new derivative of DsRed. Ensemble and single-molecule fluorescence experiments proved mCherry as an ideally suited fluorophore for single-molecule applications, demonstrated by high photostability and rare fluorescence-intensity fluctuations. Although mCherry exhibits the lowest fluorescence quantum yield among the fluorescent proteins investigated, its superior photophysical characteristics suggest mCherry as an ideal alternative in single-molecule fluorescence experiments. Due to its spectral characteristics and short fluorescence lifetime of 1.46 ns, mCherry complements other existing fluorescent proteins and is recommended for tracking and localization of target molecules with high accuracy, fluorescence resonance energy transfer (FRET), fluorescence lifetime imaging microscopy (FLIM), or multicolor applications. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Polycaprolactone- b -Poly(ethylene oxide) Biocompatible Micelles as Drug Delivery Nanocarriers: Dynamic Light Scattering and Fluorescence Experiments

A Photophysical and Photochemical Study of 6-Methoxy-2-naphthylacetic Acid, the Major Metabolite of the Phototoxic Nonsteroidal Antiinflammatory Drug Nabumetone

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2000
F. Boscá
ABSTRACT Nabumetone is a phototoxic nonsteroidal antiinflammatory drug used for the treatment of osteoarthritis. However, nabumetone is considered a prodrug with its metabolite 6-methoxy-2-naphthylacetic acid the active form. Photophysical and photochemical studies on this metabolite have been undertaken. It undergoes photodecarboxylation in aerated aqueous and organic solvents. In addition to the accepted photodegradation pathway for related molecules, a new mechanism that implies generation of the naphthalene radical cation from the excited singlet and addition of O2 prior to the decarboxylation process has been demonstrated. Evidence for the involvement of the excited singlet state in this mechanism have been obtained by steady-state and time-resolved fluorescence experiments. The fluorescence quenching by O2 and the shorter singlet lifetime in aerated solvents support this assignment. Laser flash photolysis also supports this mechanism by showing the noninvolvement of the triplet in the formation of the naphthalene radical cation. Finally, the well-known electron acceptor CCl4 acts as an efficient singlet quencher, enhancing the route leading to the radical cation, preventing intersystem crossing to the triplet and thus resulting in a dramatic increase in the yield of 6-methoxy-2-naphthaldehyde, the major oxidative decarboxylation product; this constitutes unambiguous proof in favor of the new mechanistic proposals. [source]

The solution structure of the Mg2+ form of soybean calmodulin isoform 4 reveals unique features of plant calmodulins in resting cells

PROTEIN SCIENCE, Issue 3 2010
Hao Huang
Abstract Soybean calmodulin isoform 4 (sCaM4) is a plant calcium-binding protein, regulating cellular responses to the second messenger Ca2+. We have found that the metal ion free (apo-) form of sCaM4 possesses a half unfolded structure, with the N-terminal domain unfolded and the C-terminal domain folded. This result was unexpected as the apo-forms of both soybean calmodulin isoform 1 (sCaM1) and mammalian CaM (mCaM) are fully folded. Because of the fact that free Mg2+ ions are always present at high concentrations in cells (0.5,2 mM), we suggest that Mg2+ should be bound to sCaM4 in nonactivated cells. CD studies revealed that in the presence of Mg2+ the initially unfolded N-terminal domain of sCaM4 folds into an ,-helix-rich structure, similar to the Ca2+ form. We have used the NMR backbone residual dipolar coupling restraints 1DNH, 1DC,H,, and 1DC,C, to determine the solution structure of the N-terminal domain of Mg2+ -sCaM4 (Mg2+ -sCaM4-NT). Compared with the known structure of Ca2+ -sCaM4, the structure of the Mg2+ -sCaM4-NT does not fully open the hydrophobic pocket, which was further confirmed by the use of the fluorescent probe ANS. Tryptophan fluorescence experiments were used to study the interactions between Mg2+ -sCaM4 and CaM-binding peptides derived from smooth muscle myosin light chain kinase and plant glutamate decarboxylase. These results suggest that Mg2+ -sCaM4 does not bind to Ca2+ -CaM target peptides and therefore is functionally similar to apo-mCaM. The Mg2+ - and apo-structures of the sCaM4-NT provide unique insights into the structure and function of some plant calmodulins in resting cells. [source]

Denaturation of replication protein A reveals an alternative conformation with intact domain structure and oligonucleotide binding activity

PROTEIN SCIENCE, Issue 5 2004
Jonathan E. Nuss
Abstract Replication protein A (RPA) is a heterotrimeric, multidomain, single-stranded DNA-binding protein. Using spectroscopic methods and methylene carbene-based chemical modification methods, we have identified conformational intermediates in the denaturation pathway of RPA. Intrinsic protein fluorescence studies reveal unfolding profiles composed of multiple transitions, with midpoints at 1.5, 2.7, 4.2, and 5.3 M urea. CD profiles of RPA unfolding are characterized by a single transition. RPA is stabilized with respect to the CD-monitored transition when bound to a dA15 oligonucleotide. However, oligonucleotide binding appears to exert little, if any, effect on the first fluorescence transition. Methylene carbene chemical modification, coupled with MALDI-TOF mass spectrometry analysis, was also used to monitor unfolding of several specific RPA folds of the protein. The unfolding profiles of the individual structures are characterized by single transitions similar to the CD-monitored transition. Each fold, however, unravels with different individual characteristics, suggesting significant autonomy. Based on results from chemical modification and spectroscopic analyses, we conclude the initial transition observed in fluorescence experiments represents a change in the juxtaposition of binding folds with little unraveling of the domain structures. The second transition represents the unfolding of the majority of fold structure, and the third transition observed by fluorescence correlates with the dissociation of the 70- and 32-kD subunits. [source]

Ortho-aminobenzoic acid-labeled bradykinins in interaction with lipid vesicles: Fluorescence study

BIOPOLYMERS, Issue 5 2002
R. F. Turchiello
Abstract The peptide hormone bradykinin (BK) (Arg1 -Pro2 -Pro3 -Gly4 -Phe5 -Ser6 -Pro7 -Phe8 -Arg9) and its shorter homolog BK1,5 (Arg1 -Pro2 -Pro3 -Gly4 -Phe5) were labeled with the extrinsic fluorescent probe ortho -aminobenzoic acid (Abz) bound to the N-terminal and amidated in the C-terminal carboxyl group (Abz-BK-NH2 and Abz-BK1,5 -NH2). The fragment des-Arg9 -BK was synthesized with the Abz fluorescent probe attached to the 3-amino group of 2,3-amino propionic acid (DAP), which positioned the Abz group at the C-terminal side of BK sequence, constituting the peptide des-Arg9 -BK-DAP(Abz)-NH2. The spectral characteristics of the probe were similar in the three peptides, and their fluorescent properties were monitored to study the interaction of the peptides with anionic vesicles of dimyristoylphosphatidylglycerol (DMPG). Time-resolved fluorescence experiments showed that the fluorescence decay of the peptides was best described by double-exponential kinetics, with mean lifetimes values around 8.0 ns in buffer pH 7.4 that increased about 10% in the presence of DMPG vesicles. About a 10-fold increase, compared with the values in aqueous solution, was observed in the steady-state anisotropy in the presence of vesicles. A similar increase was also observed for the rotational correlation times obtained from time-resolved anisotropy decay profiles, and related to the overall tumbling of the peptides. Equilibrium binding constants for the peptide,lipid interaction were examined monitoring anisotropy values in titration experiments and the electrostatic effects were evaluated through Gouy,Chapman potential calculations. Without corrections for electrostatic effects, the labeled fragment Abz-BK1,5 -NH2 presented the major affinity for DMPG vesicles. Corrections for the changes in peptide concentration due to electrostatic interactions suggested higher affinity of the BK fragments to the hydrophobic phase of the bilayer. © 2002 Wiley Periodicals, Inc. Biopolymers 65: 336,346, 2002 [source]

The Effect of an Amino-Acid Bridge on Binding Affinity and Cleavage Efficiency of Pyrenyl-Macrocyclic Polyamine Conjugates toward DNA

CHEMISTRY & BIODIVERSITY, Issue 8 2009
Qiao-Sen Lu
Abstract A series of pyrenyl-macrocyclic polyamines 5a,5c have been prepared and characterized. Their DNA-cleavage properties were examined under physiological conditions. Without the presence of other additives, the DNA cleavage ability of 5a,5c showed the order of 5c>5a>5b. Absorption and fluorescence experiments showed the binding affinity of 5a,5c to DNA. The interactions of 5a,5c with CT-DNA indicated that the DNA binding ability followed an order according to their cleavage efficiency. All the results indicated that the structures of amino-acid bridge in the ligands may affect the DNA binding and cleavage ability. The cleavage-mechanism studies indicated that singlet oxygen and superoxide free radicals were involved in the catalytic DNA cleavage process. [source]