Effect Of Zinc Cations On The Kinetics Of Supramolecular Assembly And The Chirality Of Porphyrin J-Aggregates

Dilute aqueous solutions of anionic meso-4-sulfonatophenyl-porphyrin (TPPS) extract zinc(ii) ions from glass or quartz surfaces at room temperature and efficiently form the corresponding metal complex (ZnTPPS). The partial or complete formation of ZnTPPS has been probed by UV/Vis spectroscopy and both static and time-resolved fluorescence. The source of zinc(ii) ions has been clearly identified through inductively coupled plasma optical emission spectrometry. The presence of increasing amounts of ZnTPPS slows down the rate of TPPS J-aggregate formation in acid solution. This influences the nucleation step and has a profound impact on the onset of chirality in these species. This evidence indicates the important role of this adventitious metal ion in the interpretation of various spectroscopic and kinetic data for the self-assembly of the TPPS porphyrin and provides some insights into controversial findings on their chirality. The use of this metal derivative as the starting compound for in situ formation of monomeric TPPS is suggested

Photoresponsive multilayer films by assembling cationic amphiphilic cyclodextrins and anionic porphyrins at the air/water interface

Densely packed hybrid monolayers of amphiphilic cyclodextrins incorporating hydrophilic porphyrins are formed at the air/water interface through electrostatic interaction and can be transferred onto quartz substrates by Langmuir–Scha¨fer deposition. The resulting multilayers exhibit a good response to light excitation as proven by fluorescence emission, triplet– triplet absorption and singlet oxygen photogeneration

Comportamento all'interfaccia aria-acqua di derivati porfirinici sintetici e naturali e loro deposizione come film sottili tramite tecnica di Langmuir-Blodgett

L'attività dell'Unità di Ricerca di Lecce ha riguardato la deposizione e caratterizzazione morfologico-strutturale ed ottica di film di Langmuir-Blodgett di porfirine. Le principali tecniche utilizzate sono state la Microscopia all'angolo di Brewster e la spettroscopia in riflessione direttamente sul floating film, la spettroscopia UV-Vis in luce polarizzata sui film cresciuti su supporto solido

Deposizione, caratterizzazione ed applicazioni in ambito tecnologico di film sottili di sistemi ciclici tetrapirrolici

Il Progetto di ricerca si è sviluppato lungo le seguenti linee principali: a) studio del trasporto elettronico fotoindotto in sistemi costituiti da film di Langmuir-Blodgett di derivati fullerenici e porfirinici; b) studio di equilibri conformazionali in film di Langmuir e di Langmuir-Blodgett di derivato bis-porfirinici; c) realizzazione di sensori piezoelettrici in fase liquida nei quali lo strato attivo è sato cresciuto con la tecnica di Langmuir-Blodgett; d) Modifica del set-up di uno spettrofotometro ATR-FTIR, opportunamente potenziato per acquisire spettri in modalità differenziale

Interaction With DNA Of The Novel Cationic Complex (2, 2′: 6′, 2″-Terpyridine)Methyl Platinum(II)

The planarity and electron delocalization of the 2, 2′:6′, 2″-terpyridine (terpy) moiety in salts of the type [Pt(terpy)Me]X leads to extensive stacking interactions in aqueous solution. UV/VIS, 1H NMR and resonance light scattering spectra provide evidence for the tendency of the complex to form large aggregates even under low ionic strength conditions. The interaction of the cationic complex with calf thymus DNA was investigated by spectroscopic techniques and mobility assays. At high r f ratios the complex seems to form extended aggregates on the surface of the nucleic acid but at lower r f evidence was obtained for intercalation

Deposizione e caratterizzazione di film sottili per applicazioni (bio)tecnologiche e biomediche

Il progetto di ricerca costituisce una naturale prosecuzione delle indagini già intraprese e sviluppate con le altre Unità di Ricerca di Bari, Catania e Messina. Le tematiche di ricerca proposte comportano: a) lo studio di fenomeni fotoindotti in film sottili contenenti diadi composte da derivati fullerenici o nanotubi di carbonio (CNT) e clorofilla. b) l'indagine su sensori piezoelettrici con strato attivo costituito da porfirine o ftalocianine per la rivelazione di derivati fenolici che sono già stati classificati dall'USEPA come inquinanti prioritari in virtù della loro aggressività verso l'organismo umano. Poiché la maggior parte di questi fenoli è sostituita con atomi di alogeno, si è chiarito quali siano le interazioni fondamentali alla base della rivelazione da parte del cristallo di quarzo (legame a idrogeno, legame alogeno, interazioni p-p , ecc.). c) indagini effettuate nel campo delle biotecnologie biomediche per la cura di neoplasie. Infatti, in questo caso si è usato un approccio analogo alla classica terapia fotodinamica, introducendo due principali modifiche: la prima è l'immobilizzazione tramite tecnica di Langmuir-Blodgett del fotosensibilizzatore (una porfirina) su un supporto solido; la seconda, anche alla luce di quanto suggerito dal Premio Nobel J.L. Ignarro, è l'associazione dell'azione dell'ossigeno di singoletto con quella simultanea dell'ossido nitrico, NO, attraverso la co-deposizione di un sale d'ammonio derivato del composto 4-nitro-3-(trifluorometil)anilina

Sitting-Atop Metallo-Porphyrin Complexes: Experimental and Theoretical Investigations on Such Elusive Species

The interaction between the sodium cation and two meso-aryl porphyrins (tetraphenylporphyrin, TPP, and tetra(4-methoxyphenyl)porphyrin, TMPP) leads to the formation of new species that have been identified as Sitting-Atop (SAT) complexes, where the metal ion interacts with the N atoms of the porphyrin core without the concomitant deprotonation of the N−H groups. These species have been attained in low polarity solvent through the interaction of the porphyrin free bases with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB), and investigated in situ through a combination of spectroscopic techniques, such as UV/vis absorption and fluorescence (static and time-resolved), resonance light scattering, FT-IR, and 1H NMR. All spectroscopic evidence points to the occurrence of a single equilibrium between each parent compound and its SAT complex, ruling out the presence of other metallo-, protonated, or aggregated porphyrins in solution. The 1:1 stoichiometry of the adducts has been determined via continuous variation method (Job’s plot), and an estimate of the corresponding association constants in CH2Cl2 at 298 K have been obtained by UV/vis titration (Keq = (9 ± 4) × 105 L mol−1 and (5 ± 2) × 106 L mol−1 for TPP and TMPP, respectively). Density-functional theory (DFT) calculations on SAT model complexes, [NaTPP(PF6)] and [NaTMPP(PF6)], have provided information on the molecular structure of these elusive species and on the nature and strength of the sodium−porphyrin interaction. It is found that the sodium ion is bound to the four nitrogen atoms of the porphyrin core. The involvement of the pyrrolic N atoms results in a modest but not negligible elongation of the N−H bonds, pyramidalization of the hydrogen atoms, and blue shift of the N−H stretching frequencies. Electronic structure and energy decomposition analysis reveal that covalent interactions, mainly consisting of porphyrin to sodium charge transfer interactions, are an important component of the sodium-porphyrin bond. Time-dependent DFT (TDDFT) calculations of the lowest excited states of the model systems provide an unambiguous interpretation of the absorption and emission properties of the experimentally identified SAT complexes

Biocompatible nanoparticles of amphiphilic cyclodextrins entangling porphyrins as suitable vessels for light-induced energy and electron transfer

In this contribution we explore the capability of biocompatible nanoparticles (NPs) of cationic amphiphilic cyclodextrins entangling the anionic hydrophilic 5,10,15,20-tetrakis(4- sulfonatophenyl)-21H,23H-porphyrin (TPPS) to facilitate photoinduced energy and electron transfer with suitable donor and acceptor guest molecules, by using a combination of absorption, induced circular dichroism and fluorescence spectroscopy. It is shown that anthracene (AN) and anthraquinone-2-sulfonate (AQS), chosen as appropriate energy donor and electron acceptor, respectively, can be trapped within the NPs network. Fluorescence experiments carried out in the presence and, for comparison, in the absence of NPs provide clear evidence that the amphiphilic NPs strongly encourage singlet–singlet energy transfer from AN to TPPS as well as photoinduced electron transfer from TPPS to AQS. In view of the biocompatibility and drug-carring properties of the NPs used, these results can be of interest from the perspective of designing photo-activated drug delivery systems