Adjustable Cavity for Host / Guest Recognition in Cofacial Bisporphyrinic Tweezers.

Abstract not Available.</jats:p

Rigid and Flexible Bis-Porphyrinic Tweezers: Efficient Molecular Recognition of Bidentate Bases.

Increasing efforts are devoted to the synthesis of cofacial bis-porphyrinic tweezers able to complex various bidentate guests through axial coordination of the Zn(II) porphyrins by the two nitrogen atoms. Elaboration of rigid receptors appeared up to now as the ideal way to pre-organize a bis-porphyrinic cavity and increase the stability of the formed host/guest complexes. However, the choice of using rigid spacer to attach the two porphyrins together may cost a lot as far as solubility and stability are concerned. The synthetic pathways necessary to achieve the synthesis of rigid systems are frequently long and tedious. We report here the synthesis and studies of new flexible bis-porphyrinic tweezers bearing uridine as linkers and offering pre-organized cavities able to welcome bidentate guests with extremely high association constants. As part of our studies concerning complexation of bidentate Lewis bases by bis-porphyrinic tweezers, we have synthesized two new bis-porphyrins bearing a flexible nucleosidic linker. Both uridine and 2’-deoxyuridine spacers were chosen on account of some observations we made a few years ago on the unexpected blocked conformations adopted by a pentaporphyrin consisting of four Zn(II) porphyrins attached to a central free-base porphyrin by four nucleosidic linkers. Since we observed no such blocked conformations in other flexible pentaporphyrins, we thought this might be due to the nucleosidic nature of the linkers. We thus synthesized two dimers, which differ by the attachment positions of the two porphyrins. The ability of these two tweezers to accomodate guests was investigated through ligand binding studies carried out in dichloromethane with DABCO as bidentate base. The complexation of DABCO by these dimers was monitored by UV-visible spectrophotometric titration in CH2Cl2. The binding constants between these two tweezers and DABCO were calculated from UV-visible spectroscopic data. These association constants are unexpectedly increased by more than one order of magnitude as compared to the association constants of the same bidentate ligand with a reference Zn(II) mono-porphyrin. This enhanced stability of the complexes may be ascribed to a pre-organization of the bis-porphyrinic tweezers forming a cavity, and provides convincing evidence that the bidentate base is inserted into the cavity of the dimers via host/guest interactions. We demonstrated that similar association constants can be obtained with flexible tweezers bearing uridine as linker and rigid tweezers. However, the stability of these flexible complexes isn’t as convincing as for our rigid tweezers bearing a tris-anthracenic spacer since the addition of an excess of DABCO destroys all the flexible complexes. Molecular modelling of one of the flexible tweezers and its 1/1 complex with DABCO is represented below, as well as our rigid tweezers bearing a tris-anthracenic spacer. Acknowledgements This work was supported by the CNRS and the French Ministry of Research. Figure 1 <jats:p /

Inter-Digitated Photo-Active Strands

In natural photosynthetic systems, the solar energy is collected by pigment molecules attached to the light harvesting complexes. In these units, the chlorophylls are held in a favored spacing and orientation by fairly short a-helical polypeptides.1 When a photon hits one of the chlorophylls, the absorbed energy spreads extremely rapidly to the others until the reaction center is reached within the cell membrane, where the solar energy is converted into chemical energy used by the cell to grow. In this way, the energy contained in a single photon is conducted in a very short time and with minimal loss of energy from the point where it is absorbed to where it is needed. The extraordinary efficiency of the energy migration over long distances with minimal loss of energy is ascribed to the favored spacing and orientation of the chlorophylls which are held in an appropriate parallel conformation. Beyond the control of the structure of multi-chromophoric arrays, monitoring the spatial orientation of the chromophores in artificial light harvesting devices is a challenge of growing interest. Indeed, multi-porphyrinic arrays attract more and more attention for the elaboration of photonic and electronic wires.2 An octapeptide3 and an hexadecapeptide4 derived from the L-lysine and functionalized with porphyrins have been prepared. Beyond a certain degree of oligomerisation, we observed the development of a secondary structure such as a 310 helix which forces the porphyrins to arrange in a defined spatial arrangement. Due to the overlap of the porphyrins in such a conformation, the chromophores undergo a sufficient electronic coupling to favor a good exciton migration.5 The ability of these peptides to accomodate guests was investigated through ligand binding studies carried out in dichloromethane with DABCO as bidentate base. The complexation of DABCO by these peptides was monitored by UV-visible spectrophotometric titration in CH2Cl2. We showed that the enhanced stability of the complexe octapeptide/DABCO can be ascribed to a pre-organization of the octapeptide forming cavities, and provides convincing evidence that the bidentate base is inserted into the cavities of the octapeptide via host/guest interactions. Acknowledgements This work was supported by the CNRS and the French Ministry of Research. References W. Kühlbrandt, Nature 1995, 374, 497-498. a) R. W. Wagner, J. S. Lindsey, J. Seth, V. Palaniappan, D. F. Bocian, J. Am. Chem. Soc. 1996, 118, 3996-3997 and ref. cited therein. b) M. J. Crossley, P. L. Burn, S. J. Langford, J. K Prashar, J. Chem. Soc., Chem. Commun. 1995, 1921-1923. c) A. Osuka, H. Shimidzu, Angew. Chem. Int. Ed. Engl. 1997, 36, 135-137. N. Solladié, A. Hamel, M. Gross, Tet. Lett. 2000, 41, 6075-6078. Unpublished results. a) M. Fujitsuka, M. Hara, S. Tojo, A. Okada, V. Troiani, N. Solladié, T. Majima, J. Phys. Chem B. 2005, 109, 33-35. b) M. Fujitsuka, D. W. Cho, N. Solladié, V. Troiani, H. Qiu, T. Majima, J. Photochem. Photobiol. A 2007, 188, 346-350. Figure 1 <jats:p /

Polypeptides with Pendant Porphyrins: From the Recognition of Bidentate Bases to Inter-Digitated Photo-Active Strands

In natural photosynthetic systems, the solar energy is collected by pigment molecules attached to the light harvesting complexes. In these units, the chlorophylls are held in a favored spacing and orientation by fairly short α-helical polypeptides.1  When a photon hits one of the chlorophylls, the absorbed energy spreads extremely rapidly to the others until the reaction center is reached within the cell membrane, where the solar energy is converted into chemical energy used by the cell to grow.  In this way, the energy contained in a single photon is conducted in a very short time and with minimal loss of energy from the point where it is absorbed to where it is needed. The extraordinary efficiency of the energy migration over long distances with minimal loss of energy is ascribed to the favored spacing and orientation of the chlorophylls which are held in an appropriate parallel conformation. Beyond the control of the structure of multi-chromophoric arrays, monitoring the spatial orientation of the chromophores in artificial light harvesting devices is a challenge of growing interest.  Indeed, multi-porphyrinic arrays attract more and more attention for the elaboration of photonic and electronic wires.2       An octapeptide3 and an hexadecapeptide4 derived from the L-lysine and functionalized with porphyrins have been prepared. Beyond a certain degree of oligomerisation, we observed the development of a secondary structure such as a 310 helix which forces the porphyrins to arrange in a defined spatial arrangement.  Due to the overlap of the porphyrins in such a conformation, the chromophores undergo a sufficient electronic coupling to favor a good exciton migration.5                 The ability of these peptides to accomodate guests was investigated through ligand binding studies carried out in dichloromethane with DABCO as bidentate base. The complexation of DABCO by these peptides was monitored by UV-visible spectrophotometric titration in CH2Cl2. We showed that the enhanced stability of the complexe octapeptide/DABCO can be ascribed to a pre-organization of the octapeptide forming cavities, and provides convincing evidence that the bidentate base is inserted into the cavities of the octapeptide via host/guest interactions. Acknowledgements This work was supported by the CNRS and the French Ministry of Research.  References W. Kühlbrandt, Nature 1995, 374, 497-498. a) R. W. Wagner, J. S. Lindsey, J. Seth, V. Palaniappan, D. F. Bocian, J. Am. Chem. Soc. 1996, 118, 3996-3997 and ref. cited therein. b) M. J. Crossley, P. L. Burn, S. J. Langford, J. K Prashar, J. Chem. Soc., Chem. Commun. 1995, 1921-1923. c) A. Osuka, H. Shimidzu, Angew. Chem. Int. Ed. Engl. 1997, 36, 135-137.  N. Solladié, A. Hamel, M. Gross, Tet. Lett. 2000, 41, 6075-6078. Unpublished results. a) M. Fujitsuka, M. Hara, S. Tojo, A. Okada, V. Troiani, N. Solladié, T. Majima, J. Phys. Chem B. 2005, 109, 33-35. b) M. Fujitsuka, D. W. Cho, N. Solladié, V. Troiani, H. Qiu, T. Majima, J. Photochem. Photobiol. A 2007, 188, 346-350. Figure 1 <jats:p /

Bis-Porphyrinic Tweezers for the Molecular Recognition of Bidentate Bases of Various Sizes: towards the Purification of Polluted Effluents - Invited

Abstract not Available.</jats:p

Bis-Porphyrinic Tweezers for the Molecular Recognition of Bidentate Bases of Various Sizes: Towards the Purification of Polluted Effluents

Abstract not Available.</jats:p

Polypeptides with Pendant Porphyrins: From the Recognition of Bidentate Bases to Inter-Digitated Photo-Active Strands

In natural photosynthetic systems, the solar energy is collected by pigment molecules attached to the light harvesting complexes. In these units, the chlorophylls are held in a favored spacing and orientation by fairly short a-helical polypeptides.1  When a photon hits one of the chlorophylls, the absorbed energy spreads extremely rapidly to the others until the reaction center is reached within the cell membrane, where the solar energy is converted into chemical energy used by the cell to grow.  In this way, the energy contained in a single photon is conducted in a very short time and with minimal loss of energy from the point where it is absorbed to where it is needed. The extraordinary efficiency of the energy migration over long distances with minimal loss of energy is ascribed to the favored spacing and orientation of the chlorophylls which are held in an appropriate parallel conformation. Beyond the control of the structure of multi-chromophoric arrays, monitoring the spatial orientation of the chromophores in artificial light harvesting devices is a challenge of growing interest.  Indeed, multi-porphyrinic arrays attract more and more attention for the elaboration of photonic and electronic wires.2       An octapeptide3 and an hexadecapeptide4 derived from the L-lysine and functionalized with porphyrins have been prepared. Beyond a certain degree of oligomerisation, we observed the development of a secondary structure such as a 310 helix which forces the porphyrins to arrange in a defined spatial arrangement.  Due to the overlap of the porphyrins in such a conformation, the chromophores undergo a sufficient electronic coupling to favor a good exciton migration.5       The ability of these peptides to accomodate guests was investigated through ligand binding studies carried out in dichloromethane with DABCO as bidentate base. The complexation of DABCO by these peptides was monitored by UV-visible spectrophotometric titration in CH2Cl2. We showed that the enhanced stability of the complexe octapeptide/DABCO can be ascribed to a pre-organization of the octapeptide forming cavities, and provides convincing evidence that the bidentate base is inserted into the cavities of the octapeptide via host/guest interactions. Acknowledgements This work was supported by the CNRS and the French Ministry of Research.  References W. Kühlbrandt, Nature 1995, 374, 497-498. a) R. W. Wagner, J. S. Lindsey, J. Seth, V. Palaniappan, D. F. Bocian, J. Am. Chem. Soc. 1996, 118, 3996-3997 and ref. cited therein. b) M. J. Crossley, P. L. Burn, S. J. Langford, J. K Prashar, J. Chem. Soc., Chem. Commun. 1995, 1921-1923. c) A. Osuka, H. Shimidzu, Angew. Chem. Int. Ed. Engl. 1997, 36, 135-137.  N. Solladié, A. Hamel, M. Gross, Tet. Lett. 2000, 41, 6075-6078. Unpublished results. a) M. Fujitsuka, M. Hara, S. Tojo, A. Okada, V. Troiani, N. Solladié, T. Majima, J. Phys. Chem B. 2005, 109, 33-35. b) M. Fujitsuka, D. W. Cho, N. Solladié, V. Troiani, H. Qiu, T. Majima, J. Photochem. Photobiol. A 2007, 188, 346-350. Figure 1 <jats:p /

Polypeptides with Pendant Porphyrins: From the Recognition of Bidentate Bases to Inter-Digitated Photo-Active Strands

In natural photosynthetic systems, the solar energy is collected by pigment molecules attached to the light harvesting complexes. In these units, the chlorophylls are held in a favored spacing and orientation by fairly short a-helical polypeptides. In this way, the energy contained in a single photon is conducted in a very short time and with minimal loss of energy from the point where it is absorbed to where it is needed. The extraordinary efficiency of the energy migration over long distances with minimal loss of energy is ascribed to the favored spacing and orientation of the chlorophylls which are held in an appropriate parallel conformation. Beyond the control of the structure of multi-chromophoric arrays, monitoring the spatial orientation of the chromophores in artificial light harvesting devices is a challenge of growing interest. Indeed, multi-porphyrinic arrays attract more and more attention for the elaboration of photonic and electronic wires. An octapeptide and a hexadecapeptide derived from the L-lysine and functionalized with porphyrins have been prepared. Beyond a certain degree of oligomerisation, we observed the development of a secondary structure such as a 310 helix which forces the porphyrins to arrange in a defined spatial arrangement. Due to the overlap of the porphyrins in such a conformation, the chromophores undergo a sufficient electronic coupling to favor a good exciton migration. The ability of these peptides to accomodate guests was investigated through ligand binding studies carried out in dichloromethane with DABCO as bidentate base. The complexation of DABCO by these peptides was monitored by UV-visible spectrophotometric titration in CH2Cl2. We showed that the enhanced stability of the complexe octapeptide/DABCO can be ascribed to a pre-organization of the octapeptide forming cavities, and provides convincing evidence that the bidentate base is inserted into the cavities of the octapeptide via host/guest interactions. Acknowledgements This work was supported by the CNRS and the French Ministry of Research. </jats:p

Polypeptides with Pendant Porphyrins: From the Recognition of Bidentate Bases to Inter-Digitated Photo-Active Strands

In natural photosynthetic systems, the solar energy is collected by pigment molecules attached to the light harvesting complexes. In these units, the chlorophylls are held in a favored spacing and orientation by fairly short a-helical polypeptides.1 When a photon hits one of the chlorophylls, the absorbed energy spreads extremely rapidly to the others until the reaction center is reached within the cell membrane, where the solar energy is converted into chemical energy used by the cell to grow. In this way, the energy contained in a single photon is conducted in a very short time and with minimal loss of energy from the point where it is absorbed to where it is needed. The extraordinary efficiency of the energy migration over long distances with minimal loss of energy is ascribed to the favored spacing and orientation of the chlorophylls which are held in an appropriate parallel conformation. Beyond the control of the structure of multi-chromophoric arrays, monitoring the spatial orientation of the chromophores in artificial light harvesting devices is a challenge of growing interest. Indeed, multi-porphyrinic arrays attract more and more attention for the elaboration of photonic and electronic wires.2 An octapeptide3 and an hexadecapeptide4 derived from the L-lysine and functionalized with porphyrins have been prepared. Beyond a certain degree of oligomerisation, we observed the development of a secondary structure such as a 310 helix which forces the porphyrins to arrange in a defined spatial arrangement. Due to the overlap of the porphyrins in such a conformation, the chromophores undergo a sufficient electronic coupling to favor a good exciton migration.5 The ability of these peptides to accomodate guests was investigated through ligand binding studies carried out in dichloromethane with DABCO as bidentate base. The complexation of DABCO by these peptides was monitored by UV-visible spectrophotometric titration in CH2Cl2. We showed that the enhanced stability of the complexe octapeptide/DABCO can be ascribed to a pre-organization of the octapeptide forming cavities, and provides convincing evidence that the bidentate base is inserted into the cavities of the octapeptide viahost/guest interactions. Acknowledgements This work was supported by the CNRS and the French Ministry of Research. References W. Kühlbrandt, Nature 1995, 374, 497-498. a) R. W. Wagner, J. S. Lindsey, J. Seth, V. Palaniappan, D. F. Bocian, J. Am. Chem. Soc. 1996, 118, 3996-3997 and ref. cited therein. b) M. J. Crossley, P. L. Burn, S. J. Langford, J. K Prashar, J. Chem. Soc., Chem. Commun. 1995, 1921-1923. c) A. Osuka, H. Shimidzu, Angew. Chem. Int. Ed. Engl. 1997, 36, 135-137. N. Solladié, A. Hamel, M. Gross, Tet. Lett. 2000, 41, 6075-6078. Unpublished results. a) M. Fujitsuka, M. Hara, S. Tojo, A. Okada, V. Troiani, N. Solladié, T. Majima, J. Phys. Chem B. 2005, 109, 33-35. b) M. Fujitsuka, D. W. Cho, N. Solladié, V. Troiani, H. Qiu, T. Majima, J. Photochem. Photobiol. A 2007, 188, 346-350. </jats:p

Inter-Digitated Photo-Active Strands

In natural photosynthetic systems, the solar energy is collected by pigment molecules attached to the light harvesting complexes. In these units, the chlorophylls are held in a favored spacing and orientation by fairly short α-helical polypeptides.1 When a photon hits one of the chlorophylls, the absorbed energy spreads extremely rapidly to the others until the reaction center is reached within the cell membrane, where the solar energy is converted into chemical energy used by the cell to grow. In this way, the energy contained in a single photon is conducted in a very short time and with minimal loss of energy from the point where it is absorbed to where it is needed. The extraordinary efficiency of the energy migration over long distances with minimal loss of energy is ascribed to the favored spacing and orientation of the chlorophylls which are held in an appropriate parallel conformation. Beyond the control of the structure of multi-chromophoric arrays, monitoring the spatial orientation of the chromophores in artificial light harvesting devices is a challenge of growing interest. Indeed, multi-porphyrinic arrays attract more and more attention for the elaboration of photonic and electronic wires.2 An octapeptide3 and an hexadecapeptide4 derived from the L-lysine and functionalized with porphyrins have been prepared. Beyond a certain degree of oligomerisation, we observed the development of a secondary structure such as a 310 helix which forces the porphyrins to arrange in a defined spatial arrangement. Due to the overlap of the porphyrins in such a conformation, the chromophores undergo a sufficient electronic coupling to favor a good exciton migration.5 The ability of these peptides to accomodate guests was investigated through ligand binding studies carried out in dichloromethane with DABCO as bidentate base. The complexation of DABCO by these peptides was monitored by UV-visible spectrophotometric titration in CH2Cl2. We showed that the enhanced stability of the complexe octapeptide/DABCO can be ascribed to a pre-organization of the octapeptide forming cavities, and provides convincing evidence that the bidentate base is inserted into the cavities of the octapeptide via host/guest interactions. Acknowledgements This work was supported by the CNRS and the French Ministry of Research. References W. Kühlbrandt, Nature 1995, 374, 497-498. a) R. W. Wagner, J. S. Lindsey, J. Seth, V. Palaniappan, D. F. Bocian, J. Am. Chem. Soc. 1996, 118, 3996-3997 and ref. cited therein. b) M. J. Crossley, P. L. Burn, S. J. Langford, J. K Prashar, J. Chem. Soc., Chem. Commun. 1995, 1921-1923. c) A. Osuka, H. Shimidzu, Angew. Chem. Int. Ed. Engl. 1997, 36, 135-137. N. Solladié, A. Hamel, M. Gross, Tet. Lett. 2000, 41, 6075-6078. Unpublished results. a) M. Fujitsuka, M. Hara, S. Tojo, A. Okada, V. Troiani, N. Solladié, T. Majima, J. Phys. Chem B. 2005, 109, 33-35. b) M. Fujitsuka, D. W. Cho, N. Solladié, V. Troiani, H. Qiu, T. Majima, J. Photochem. Photobiol. A 2007, 188, 346-350. Figure 1 <jats:p /