Host-guest complexes of anionic porphyrin sensitizers with cyclodextrins

Abstract

The photodynamic sensitizers zinc(II)- and palladium(II)-5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrins and 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin form 1:1 and/or 1:2 supramolecular complexes with native cyclodextrins (CD) and 2-hydroxypropyl cyclodextrins (hpCD) in aqueous neutral solutions. The formation of these assemblies causes a bathochromic shift of the porphyrin Soret band in the UV-vis spectra and a red shift of the fluorescence emission bands. The binding constants span over three orders of magnitude, from 8.1 × 102 M −1 to 5.4 × 105 M −1 (or 1.1 × 106 M −2) depending on the size of the CD cavity and on the functionalization by adding 2-hydroxypropyl groups. The highest binding constants were obtained for hpβCD and hpγCD. The Nuclear Overhauser spectroscopy signals (ROESY) revealed three binding modes: i) inclusion of the porphyrin 4-sulfonatophenyl or 4-carboxyphenyl groups via the secondary face of βCD and hpβCD with sulfonic or carboxylic groups oriented towards the primary hydroxyl groups. ii) inclusion of the porphyrin groups via the primary face of γCD and hpγCD. iii) non-specific binding of the porphyrin monomers or aggregates on the cyclodextrin exterior. The inclusion host-guest complexation via i) or ii) does not influence the inherent photophysical properties of the monomeric porphyrins such as the quantum yields of fluorescence, the triplet states, and the singlet oxygen formation. Due to the deaggregation effect of cyclodextrins, the inclusion complexes remain efficient supramolecular sensitizers of singlet oxygen even under conditions of extensive aggregation in aqueous solutions.

Probing the Interactions of Porphyrins with Macromolecules Using NMR Spectroscopy Techniques

“…Further proof that the TPPS 4 macrocycle was closer located to the primary face in γ-CD was obtained from ROESY data: In addition to strong NOEs between TPPS 4 phenyl and inner H-3 and H-5 protons, weak NOEs were also and only detected in γ-CD with H(6,6′) located at the rim of the primary face [ 176 ]. Similarly, formation of CD-inclusion complexes could be shown by NMR spectroscopic methods (induced shifts and/or NOE) for the metal complexes Mn(III)TPPS 4 [ 177 ], Zn(II)TPPS 4 [ 178 , 179 ], and Pd(II)TPPS 4 [ 179 ] with respect to α, β and γ-CD binding affinity and geometry [ 179 ]. In these studies, selective changes were also reported for the 13 C NMR shifts of the inner CD carbon nuclei (C-5 and C-3) of the CD-inclusion complexes [ 177 , 179 ].…”

Complexation of a guanidinium-modified calixarene with diverse dyes and investigation of the corresponding photophysical response

“…The fluorescence intensity of TPPS was slightly enhanced upon PMCD encapsulation, accompanied by a sharpening of the fluorescence band [36]. The 2:1 PMCD–TPPS complex has been applied in photodynamic therapy with improved photoactivity due to the inhibition of TPPS aggregation and the shielding effect of PMCD against quenching of the TPPS triplet state [37]. Also, it has been employed in the construction of photovoltaic materials and light-harvesting systems [38–39].…”

Use of Cyclodextrins in Anticancer Photodynamic Therapy Treatment

“…However, with respect to articles involving the potential use of CD-PS inclusion complexes in anticancer PDT (without in vitro and/or in vivo biological studies), we can emphasize that several studies have estimated benefit of CD–PS inclusion complexes on the physicochemical properties of PSs. For porphyrinoid PSs, various studies showed that CD–PS inclusion complexes could (1) increase some of the photophysical properties of PSs (fluorescence intensity [ 108 , 109 ], tripling the lifetime in neutral aqueous solutions [ 110 ], 1 O 2 production [ 111 ], and quantum yield [ 112 ] in aqueous solutions), (2) reduce some drawbacks of PSs (such as poor water solubility [ 113 ], self-aggregation [ 111 , 114 ], protonation of pyrrole nitrogens [ 110 ], metalation [ 110 ], thermal degradation [ 115 ]), and (3) enhance drug delivery [ 110 , 115 ] and lipid membrane penetration [ 116 ]. Similar results were also obtained for non-porphyrinoids PSs, i.e., the improvement of photophysical properties (fluorescence lifetime, emission, and quantum yield) [ 117 ], drug delivery [ 117 , 118 ], and photostability [ 119 ].…”