Lipophilic porphyrin microparticles induced by AOT reverse micelles: a fluorescence lifetime imaging study

Fluorescence Spectroscopy of Porphyrins and Phthalocyanines: Some Insights into Supramolecular Self-Assembly, Microencapsulation, and Imaging Microscopy

The molecular interactions of anionic tetrasulfonate phenyl porphyrin (TPPS) with poly(amido amine) (PAMAM) dendrimers of generation 2.0 and 4.0 (G2 and G4, respectively) forming H- or J-aggregates, as well as with human and bovine serum albumin proteins (HSA and BSA), were reviewed in the context of self-assembly molecular complementarity. The spectroscopic studies were extended to the association of aluminum phthtalocyanine (AlPCS4) detected with a PAMAM G4 dendrimer with fluorescence studies in both steady state and dynamic state, as well as due to the fluorescence quenching associated to electron-transfer with a distribution of lifetimes. The functionalization of TPPS with peripheral substituents enables the assignment of spontaneous pH-induced aggregates with different and well-defined morphologies. Other work reported in the literature, in particular with soft self-assembly materials, fall in the same area with particular interest for the environment. The microencapsulation of TPPS studies into polyelectrolyte capsules was developed quite recently and aroused much interest, which is well supported and complemented by the extensive data reported on the Imaging Microscopy section of the Luminescence of Porphyrins and Phthalocyanines included in the present review.

Optical spectroscopy and photochemistry of porphyrins and phthalocyanines

Studies of excited singlet and triplet states of porphyrins and phthalocyanines in organized media of reverse micelles, vesicles, monolayers, and Langmuir-Blodgett films along with more complex supramolecular organizates with proteins and dendrimers, are reported. Self-assembly in these systems was followed by imaging and temporal fluorescence techniques.

Reorganization of self-assembled dipeptide porphyrin J-aggregates in water-ethanol mixtures

The self-assembly of a neutral meso-methoxyphenylporphyrin functionalized with a dipeptide glycilglycine substituent (MGG) in water and in water-ethanol mixtures was studied by absorption and fluorescence spectroscopy. In water, hydrophobic interactions and the noncovalent intermolecular hydrogen bonding between the terminal carboxylate group of one porphyrin and the hydrogen atoms of the pyrrolic nitrogens of another porphyrin originate nonspecific disorganized H- and J-aggregates. The addition of ethanol (0.1-25% v/v) to the water creates small clusters within which porphyrin J-aggregates reorganize as revealed by a narrow intense band detected by the Rayleigh light scattering (RLS) at 443 nm. Similar phenomenology is detected in SDS premicellar aggregates. Computational DFT calculations of a model dimer formation stabilized via intermolecular hydrogen bonding estimate an energy gain of -22 kJ mol(-1) and a center-to-center and interplane distances between porphyrin moieties of 16.8 and 3.7 Å, respectively. The kinetics of the J-aggregate formation could be fitted with a time-dependent model, and an activation energy of 96 kJ mol(-1) was estimated. The aggregate's morphology of MGG was followed by transmission electron microscopy (TEM) which showed rod-type structures of 5-8 μm evolving to spherical particles with increased ethanol content. Similar images and sizes were obtained in analogous samples using fluorescence lifetime imaging microscopy (FLIM) and dynamic light scattering (DLS). The formation of excitonically coupled supramolecular MGG structures of brickwork or staircase types is proposed in these water-ethanol mixtures.

Fluorescence lifetime imaging microscopy and fluorescence resonance energy transfer from cyan to yellow fluorescent protein validates a novel method to cluster proteins on solid surfaces

A novel method to distribute proteins on solid surfaces is proposed. Proteins microencapsulated in the water pool of reverse micelles were used to coat a solid surface with well-individualized round spots of 1 to 3 microm in diameter. The number of spots per unit area can be increased through the concentration of reverse micelles, and networks of spots were obtained at high concentrations of large reverse micelles. Moreover, depending on the pool size of the water reverse micelles, proteins can be deposited far from each other or in close proximity within the range of 50 to 70 A. This proximity obtained with small reverse micelles was proved through fluorescence lifetime imaging microscopy and fluorescence resonance energy transfer (FLIM-FRET) measurements for the most relevant FRET pair in cell biology studies, the cyan and yellow fluorescent proteins. This novel procedure has several advantages and reveals the potential for study of protein-protein interactions on solid surfaces and for developing novel biomaterials and molecular devices based on biorecognition elements.

Ordered self-assembly of protonated porphyrin induced by the aqueous environment of biomimetic systems

Water-soluble ionic porphyrins show an interesting self-association pattern in acidic conditions under which highly ordered aggregates are stabilized. Herein we give an overview of the template effect of biological interfaces in tetrakis(4-sulfonatophenyl)porphyrin TSPP self-aggregation, in which we point out the possibility of tuning this process by screening the charge repulsion through ionic strength and pH. We give special emphasis to the use of fluorescence lifetime imaging microscopy and of fluorescence correlation spectroscopy to visualize and characterize these molecular aggregates.

Self-aggregation of free base porphyrins in aqueous solution and in DMPC vesicles

Free base porphyrin (PPhe), derivatized with aminosulfonyl groups linked to the aromatic amino acid phenylalanine at the meso-positions, was mixed with DMPC vesicles. The resulting interaction was studied by absorption, steady-state and transient state fluorescence, at different pHs. At pH=2 to pH=9, the aforementioned porphyrin predominates as an aggregated species, with a co-facial arrangement of the molecules taking into account the blue shift of the Soret band (414 nm for the monomer and 401 nm for the aggregate). Upon interaction with DMPC vesicles, the competing hydrophobic interactions with the bilayer destabilize the aggregated species in favor of monomer incorporation. Fluorescence lifetimes also show that the long component assigned to the monomer contributes only 30% to the overall decay in solution (e.g. pH=7.0) whereas in DMPC vesicles this contribution increases up to 85% independent of the solution pH, which confirms a location of the probe in an environment "protected" from free water. The picture changes completely in the case of TSPP, an anionic porphyrin which does not incorporate in DMPC vesicles. Remarkably, at pH=2.5 all the experimental findings point to the self-assembling of the porphyrin units in J-aggregates induced at the surface of the DMPC vesicle. In fact, upon removal of the aqueous solvent, we could define by fluorescence lifetime imaging microscopy (FLIM) regions where the fluorescence lifetime is that characteristic of the J-aggregate (<tau(F)> 0.11 ns).

Imaging proteins in vivo using fluorescence lifetime microscopy

Fluorescence lifetime imaging (FLIM) represents a key optical technique for imaging proteins and protein interaction in vivo. We review the principles and recent advances in the application of the technique, instrumentation and molecular probe development.