Supramolecular Assemblies of Functional Nanoporphyrins in Therapeutics

Rodica-Mariana Ion

ICECHIM, Bucharest, Romania; Valahia University, Targoviste;

E-mail: rodica_ion2000@yahoo.co.uk

Simina Dreve INCDTIM, Cluj-Napoca;

E-mail: siminadreve@yahoo.com

Abstract

New supramolecular systems have been assembled with the use of bridging unities such as tetrapyridylporphyrins, porphyrazines and polypyrazines. The assembly involves the orientation of the pi-conjugated rings, which are kept together by means of strong hydrophobic intermolecular interactions, as well as by the electrostatic interactions between the peripheral cationic and anionic residues. The porphyrins and ruthenium polypyridines are two classes of compounds exhibiting most of the above mentioned molecular properties. In the present study new cationic porphyrin as tetraruthenium (bipyridine)porphyrin (4+)(TRPyP) was synthesized and its association with anionic porphyrin (TSPP) forming heteroaggregates, is investigated. Potential applications in photodynamic therapy of cancer are discussed. Keywords: porphyrins, nanoporphyrins, supramolecular assemblies, heterroagregates, therapeutics 1. Introduction

Supramolecular chemistry is expected to keep a high developing pace in the next years, giving support to the advancement of molecular devices and nanotechnology. Supramolecular chemistry deals with the association of several chemical species, in an organized way and according to well defined purposes. Based on a molecular engineering approach, supramolecular structures can be designed from pre-formed building blocks, providing a promising route from chemistry to molecular nanotechnology. New supramolecular systems have been assembled in our laboratory with the use of bridging unities such as tetrapyridylporphyrins, porphyrazines and polypyrazines, connecting transition metal complexes and clusters [1]. An important property of the supramolecular systems is their ability to form assembly of suitable anionic and cationic porphyrins [2]. The assembly involves the orientation of the pi-conjugated rings, which are kept together by means of strong hydrophobic intermolecular interactions, as well as by the electrostatic interactions between the peripheral cationic and anionic residues.

The porphyrins and ruthenium polypyridines [3] are two classes of compounds exhibiting most of the above mentioned molecular properties. A relevant series of symmetric polynuclear species has been obtained by attaching four [RuII (bipy)2Cl] groups to the pyridyl substituents of meso-tetra(4-pyridyl)porphyrin and its metallated derivatives. These compounds display rich photochemical properties, associated with the ruthenium-bipyridine complexes and the porphyrin ring. So, by using an "in-situ" ion-exchange method involving tetraruthenium (bipyridine)porphyrin (TRPyP) – a cationic species- and tetra-(4-sulphonatephenyl) porphyrin (TSPP) –an anionic species- we are able to obtain supramolecular assembly.

978-0-7695-3621-7/09 $25.00 © 2009 IEEE

DOI 10.1109/CANS.2008.29

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2008 First International Conference on Complexity and Intelligence of the Artificial and Natural Complex Systems. Medical Applications of the Complex Systems. Biomedical Computing

978-0-7695-3621-7/09 $25.00 © 2009 IEEE

DOI 10.1109/CANS.2008.29

189

2008 First International Conference on Complexity and Intelligence of the Artificial and Natural Complex Systems. Medical Applications of the Complex Systems. Biomedical Computing

978-0-7695-3621-7/09 $25.00 © 2009 IEEE

DOI 10.1109/CANS.2008.29

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Figure 1. The structure of [meso-5, 10, 15, 20-tetra (pyridyl) porphyrin] tetrakis [bis-(bipyridine) chloride ruthenium (II)] (TRPyP)

2. Experimental part 2. 2.1. Chemicals

All other reagents were of analytical grade and used as supplied. Tetraruthenium (bipyridine)porphyrin (TRPyP) was synthesized and characterized as previously described [2]. Stock solutions were prepared using bidistilled, deionized MilliQ water and then kept in the dark at 4degC.

5, 10, 15, 20-tetrakis-p-sulfonato-phenyl porphyrin (TSPP) was prepared and purrified in the lab as we reported elsewhere [4]. The porphyrin has the structure as in figure 2.

All the solutions were prepared in DMSO (Fluka). 1,3-diphenylisobenzofuran (DPBF) was synthesized and purrified after the literature data [5].

Figure 2. The structure of TSPP

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2.2. Apparatus

The UV-Vis spectra were recorded with a SPECORD M 400 Carl Zeiss Jena spectrophotometer with microprocessor and double beam. 2.3. Singlet oxygen test

Measurements were carried out in a quartz cell (1cm x 1cm) at 20oC. A DMSO solution (2.3 ml) containing sensitizer (4.8 x 10 -5 M) and DPBF (2.7 x 10-5 M) was irradiated with light beam from a UV-Vis spectrophotometer. Solutions of sensitizers were freshly prepared and kept in the dark before measurements. The decreasing of the DPBF concentration was followed by a special programm ruled on a computer at the absorbance from 415 nm (the molar coefficient of absorption for DPBF is 23300 M-1. cm-1) as function of the irradiation time (irradiation cycles 50 x 25 s). The reaction showed a zero order-kinetics in the first 100 s. The incident photon flow was 4.65 x 10-9 M.s-1. Using the absorption spectra of the photosensitizers the absorbed photon flow (Iabs) was evaluated. The quantum yield of the photooxidation of DPBF was calculated from the eq. l

ΦDPBF = ([DPBF]/Iabs.V); V=3 cm 3 (1)

The quantum yield for singlet oxygen generation was calculated from eq.2.

1/ΦDPBF = 1/Φ 1O2 + (1/Φ 1O2 Kd/Ka) (1/[DPBF]) (2)

From the intercept of the Stern-Volmer plots, we obtained the quantum yield for singlet oxygen generation. 2.4. The Job method

The control of the complex formation and determination of their stoichiometry were carried out according to Job's method [6,7]. This method is based on the spectrophotometric analysis of mixtures of equimolar solutions of all the reagents present in the studied system. It was made for example, by adding the measured volume of the first porphyrin (TRPyP) of 10-4 M in solution to the solution of the second porphyrin (TSPP) of 10-4 M concentration. It was observed that in any order would be add the regeants; the final complex would be the same. Were obtained the absorbance changes of the series of solutions in which the ratio of the three differently charged compounds varied in increments from 10:0 up to 0:10.

3. Results and discussion

Modified porphyrins containing transition metal complexes attached to peripheral pyridine groups have been investigated. The complex, [TPyP {Ru (bipy)2Cl}4]4+ or (TRPyP) is a prototype of a series, containing photochemically active groups directly attached to the porphyrin system.

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The electronic spectra show the characteristic Soret band at 418 nm and the β and α doublets of the porphyrin at 518, 558 and 594, 650 nm, respectively, in addition to the absorption bands of the [Ru(bipy)2Cl]+ moieties at 298 nm (bipy π → π*) and 470 nm (Ru II → bipy charge-transfer). The electronic bands of the peripheral ruthenium complexes remain practically unchanged; however, a new intense band appears around 690 nm. This band decays when the metal ions are oxidized, or when the porphyrin is reduced, indicating a ruthenium (II)-to-protonated porphyrin charge-transfer transition. By aggregation with TSPP, a new supramolecular assembly is formed, as it is shown in Figure 3.

Figure 3. The structure of TSPP-TRPyP

In this situation, the heteroaggregation between TSPP and TRPyP occurs only between the macrocycles which can adopt a close-contact, corner-to-corner mutual configuration, in order to optimize the π−π interactions between aromatic cores.

Table 1.The absorption bands of TRPyP,TSPP and their heterocomplex. Compound Soret Qy(0-1) Qy(0-0) Qx(0-1) Qx(0-0)

TSPP 420 515 552 594 646 TRPyP 418 518 558 594 650

TSPP+TRPyP

418 514 555 595 648

Can be seen very small spectral differences of the absorption maxima of TSPP will be

registered in the presence of TPyP (table 1), probably to the small charges present on this

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molecule, and also to the spatial hindrance induced by the N+ groups from TRPyP molecule in DMSO.

By means of Job method we will establish the stoichiometry and formation constant for such heterocomplex. TSPP could form 1:4 heteroaggregates with TRPyP (k=3.5 x 105 M-1). The K values are low for the heterodimers containing the porphyrins that present the larger meso-substituent, due to the steric hindrance caused by these groups. These results show that many structural features can control the association between tetrapyrrolic macrocycles. The lifetime of the first singlet excited state for all these compounds, are shown in Table 2.

Table 2. The lifetime of the first singlet excited state for the studied compounds System Lifetime(s) x 10 9 Quantum yield of the singlet oxygen generationTRPyP 7.6 0.43 TSPP 0.43 0.78

TSPP/TRPyP 0.690 0.81

The assembly involves the orientation of the pi-conjugated rings, which are kept together by means of π−π strong hydrophobic intermolecular interactions, as well as by the electrostatic interactions between the peripheral cationic and anionic residues. With all these values, it can be seen the ability of the new hetero-complexes to generate singlet oxygen with highly efficiency useful for the photodynamic therapy of cancer [8].

Though the hydrogen-bond interactions were rather weak, stable aggregates are obtained through hydrogen bonds at multiple sites, combined with hydrophobic and π–π interactions between the porphyrin rings.

4. Conclusions

In the present study new cationic porphyrin - tetraruthenium (bipyridine) porphyrin (4+)(TRPyP)- was synthesized and its association with anionic porphyrin (TSPP) forming heteroaggregates, are investigated. Potential applications in photodynamic therapy are discussed. The assembly involves the orientation of the pi-conjugated rings, which are kept together by means of π−π strong hydrophobic intermolecular interactions, as well as by the electrostatic interactions between the peripheral cationic and anionic residues. The obtained complexes have shorter lifetimes for the first excited singlet states and higher efficiencies for generation singlet oxygen useful in photodynamic therapy of cancer. 5. References [1]. RM Ion, Materiale Naocristaline, FMR Ed., Bucharest (2003) [2]. V.Balzani, F.Scandola, Supramolecular Photochemistry, Ellis Horwood: Chichester, UK

(1991) [3]. J.G.Levy, M.Obochi, Photochem. Photobiol.. 64, 1996, pp.747-750 [4]. R.M.Ion, Progr.Catal., 1, 55 (1997)

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[5]. R.M.Ion, A.Planner, K.Wiktorowicz, D.Frackowiak, Acta Biochimica Polonica, 45, 833(1998)

[6]. J.-H.Tran Thi, Coord.Chem.Rev. 160, 53(1997) [7]. R.M.Ion, I.Yilmaz, O.Bekaroglu, Serb.J.Chem.Soc. 2, 81 (1998) [8] D.Frackowiak, A.Planner, R.M.Ion, K.Wiktorowicz, in "Synthesis, properties and

applications of near-infrared dyes in high technology fields", S.Daehne (ed) Kluwer Acad.Publ. (1998).

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