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Principles Of Fluorescence Spectroscopy

Melatonin was found to be a potent free radical scavenger in 1993. Since then over 800 publications have directly or indirectly confirmed this observation. Melatonin scavenges a variety of reactive oxygen and nitrogen species including hydroxyl radical, hydrogen peroxide, singlet oxygen, nitric oxide and peroxynitrite anion. Based on the analyses of structure-activity relationships, the indole moiety of the melatonin molecule is the reactive center of interaction with oxidants due to its high resonance stability and very low activation energy barrier towards the free radical reactions. However, the methoxy and amide side chains also contribute significantly to melatonins antioxidant capacity. The N-C=O structure in the C3 amide side chain is the functional group. The carbonyl group in the structure of N-C=O is key for melatonin to scavenge the second reactive species and the nitrogen in the N-C=O structure is necessary for melatonin to form the new five membered ring after melatonins interaction with a reactive species. The methoxy group in C5 appears to keep melatonin from exhibiting prooxidative activity. If the methoxy group is replaced by a hydroxyl group, under some in vitro conditions, the antioxidant capacity of this molecule may be enhanced. However, the cost of this change are decreased lipophility and increased prooxidative potential. Therefore, in in vivo studies the antioxidant efficacy of melatonin appears to be superior to its hydroxylated counterpart. The mechanisms of melatonins interaction with reactive species probably involves donation of an electron to form the melatoninyl cation radical or through an radical addition at the site C3. Other possibilities include hydrogen donation from the nitrogen atom or substitution at position C2, C4 and C7 and nitrosation. Melatonin also has the ability to repair damaged biomolecules as shown by the fact that it converts the guanosine radical to guanosine by electron transfer. Unlike the classical antioxidants, melatonin is devoid of prooxid ative activity and all known intermediates generated by the interaction of melatonin with reactive species are also free radical scavengers. This phenomenon is defined as the free radical scavenging cascade reaction of the melatonin family. Due to this cascade, one melatonin molecule has the potential to scavenge up to 4 or more reactive species. This makes melatonin very effective as an antioxidant. Under in vivo conditions, melatonin is often several times more potent than vitamin C and E in protecting tissues from oxidative injury when compared at an equivalent dosage (mmol / kg). Future research in the field of melatonin as a free radical scavenger might be focused on: 1), signal transduction and antioxidant enzyme gene expression induced by melatonin and its metabolites, 2), melatonin levels in tissues and in cells, 3), melatonin structure modifications, 4), melatonin and its metabolites in plants and, 5), clinical trials using melatonin to treat free radical related diseases such as Alzheimers, Parkin sons, stroke and heart disease.

Chemical and physical properties and potential mechanisms: melatonin as a broad spectrum antioxidant and free radical scavenger.

Oxidative damage in the central nervous system: protection by melatonin.

Porphyrins and phthalocyanines have outstanding chemical and thermal stability. The macrocyclic structure and chemical reactivity of tetrapyrroles offers architectural flexibility and facilitates the tailoring of chemical, physical and optoelectronic parameters. The specific optical properties of the tetrapyrrole macrocycle combined with the synthetic methodologies now available and the already available theoretical and spectroscopic knowledge on their optical behavior make porphyrins a target of choice for this area. They are versatile organic nanomaterials with a rich photochemistry and their excited state properties are easily modulated through conformational design, molecular symmetry, metal complexation, orientation and strength of the molecular dipole moment, size and degree of conjugation of the π-systems, and appropriate donor-acceptor substituents. Here we review the structural chemistry and optical properties of recently synthesized porphyrin derivatives that offer potential for nonlinear optical (NLO) applications and complement existing studies on phthalocyanines. Classes of interest include the classic A4 symmetric tetrapyrroles, while optimized systems include push-pull porphyrins, oligomeric and supramolecular self-assembled systems, films and nanoparticle systems, and highly conjugated porphyrin arrays.

Nonlinear Optical Properties of Porphyrins

Methylene blue in photodynamic therapy: From basic mechanisms to clinical applications.

A general procedure, using the commonly employed solid-phase peptide synthesis methodology for obtaining internally quenched fluorogenic peptides with ortho-aminobenzoyl/dinitrophenyl groups as donor-acceptor pairs, is presented. The essential feature of this procedure is the synthesis of an Nα-Boc or-Fmoc derivative of glutamic acid with the α-carboxyl group bound to N-(2,4-dinitrophenyl)-ethylenediamine (EDDnp), which provides the quencher moiety attached to the C-terminus of the substrate. The fluorescent donor group, ortho-aminobenzoic acid (Abz), is incorporated into the resin-bound peptide in the last coupling cycle. Depending on the resin type used, Abz-peptidyl-Gln-EDDnp or Abz-peptidyl-Glu-EDDnp is obtained. Using the procedure described above, substrates for human renin and tissue kallikreins were synthesised. Spectrofluorimetric measurements of Abz bound to the α-amino group of proline showed that strong quenching of Abz fluorescence occurs in the absence of any acceptor group.

Internally quenched fluorogenic protease substrates: Solid-phase synthesis and fluorescence spectroscopy of peptides containing ortho-aminobenzoyl/dinitrophenyl groups as donor-acceptor pairs

Fluorescence of the skin, enamel, dentin, and bone are reviewed. Fluorescence spectroscopy is one of the noninvasive methods that can identify diseases and promote increasing the knowledge in medical diagnosis. The microstructure and composition of biological tissues are presented, followed by a description of chromophores, fluorophores as identified by use of applied fluorescence techniques.

/pdf/fluorescence-spectroscopy-of-biological-tissues-a-review-5dxyob19a7.pdf

Fluorescence Spectroscopy of Biological Tissues—A Review

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/S0014-5793%2897%2901178-2

How melatonin interacts with lipid bilayers: a study by fluorescence and ESR spectroscopies

Treatment of melanoma lesions using methylene blue and RL50 light source

Steady-state and time-resolved fluorescence spectroscopy were employed in the study of the structure and interactions of alpha-MSH (alpha-melanocyte-stimulating hormone) and its analogs, [Nle4,D-Phe7]-alpha-MSH (MSH-I) and Ac-[Nle4,Asp5,D-Phe7,Lys10]-alpha-MSH(4-10)-NH2 (MSH-II). In aqueous buffer, the fluorescence parameters of the single tryptophan of alpha-MSH and MSH-I were similar and did not allow any distinction between these molecules. On the other hand, the tryptophan fluorescence of MSH-II was notably different, reflecting its cyclic lactam turn structure. In the presence of acidic lipid vesicles, the fluorescence properties of the peptides were different, indicating structural changes on incorporation of the peptide into the liquid-crystalline phase of the lipid. No evidence of interaction was observed in the presence of the neutral lipid dimyristoylphosphatidylcholine (DMPC). The association constants for lipid-peptide interactions were compared for binding isotherms which either neglected or accounted for electrostatic effects through Gouy-Chapman potential functions. The relative order of association constants in either treatment was MSH-II > MSH-I > alpha-MSH. These results parallel the reported biological activities that show increased potencies and prolongation of response for the analogs, MSH-II and MSH-I, as compared to the native hormone, alpha-MSH. Time-resolved fluorescence results showed that the fluorescence decay of melanotropins is best described by triple-exponential kinetics. In the lipid-peptide complex, there was a change in the relative concentrations of the components, with the intermediate-lifetime component predominating compared to those in solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Amando Siuiti Ito

Papers

Internally quenched fluorogenic protease substrates: Solid-phase synthesis and fluorescence spectroscopy of peptides containing ortho-aminobenzoyl/dinitrophenyl groups as donor-acceptor pairs

Fluorescence Spectroscopy of Biological Tissues—A Review

How melatonin interacts with lipid bilayers: a study by fluorescence and ESR spectroscopies

Treatment of melanoma lesions using methylene blue and RL50 light source

Structure-activity correlations of melanotropin peptides in model lipids by tryptophan fluorescence studies.