... How to Cite. Fürstner, A., Nevado, C., Tremblay, M., Chevrier, C., Teplý, F., Aïssa, C. and W... more ... How to Cite. Fürstner, A., Nevado, C., Tremblay, M., Chevrier, C., Teplý, F., Aïssa, C. and Waser, M. (2006), Total Synthesis of Iejimalide B. Angewandte Chemie International Edition, 45: 5837–5842. ... C. Aïssa, C. Chevrier, F. Teplý, C. Nevado, M. Tremblay, Angew. Chem. ...
The secondary structure of nucleic acids containing quartets of guanines, termed G-quadruplexes, ... more The secondary structure of nucleic acids containing quartets of guanines, termed G-quadruplexes, is known to regulate the transcription of many genes. Several G-quadruplexes can be formed in the HIV-1 long terminal repeat promoter region and their stabilization results in the inhibition of HIV-1 replication. Here, we identified helquat-based compounds as a new class of anti-HIV-1 inhibitors that inhibit HIV-1 replication at the stage of reverse transcription and provirus expression. Using Taq polymerase stop and FRET melting assays, we have demonstrated their ability to stabilize G-quadruplexes in the HIV-1 long-terminal repeat sequence. Moreover, these compounds were not binding to the general G-rich region, but rather to G-quadruplex-forming regions. Finally, docking and molecular dynamics calculations indicate that the structure of the helquat core greatly affects the binding mode to the individual G-quadruplexes. Our findings can provide useful information for the further ration...
Collection of Czechoslovak Chemical Communications, 2011
Reactions triggered by light constitute a treasure trove of unique synthetic methods that are ava... more Reactions triggered by light constitute a treasure trove of unique synthetic methods that are available to chemists. Photoinduced redox processes using visible light in conjunction with sensitizing dyes offer a great variety of catalytic transformations useful in the realm of organic synthesis. The recent literature amply shows that this preparative toolbox is expanding substantially. This review discusses historical and contemporary work in the area of photoredox catalysis with [Ru(bpy)3]2+. Elegant examples from the most recent literature document the importance of this fast developing area of research. The photoredox chemistry has also emerged as a promising bond-making and bond-breaking tool for chemical biology and materials chemistry. A review with 96 references.
General Methods: All reactions were carried out in flame-dried glassware under Ar. The solvents w... more General Methods: All reactions were carried out in flame-dried glassware under Ar. The solvents were purified by distillation over the drying agents indicated and were transferred under Ar: THF, Et 2 O, 1,4-dioxane (Mg-anthracene), CH 2 Cl 2 (P 4 O 10), MeCN, Et 3 N, pyridine (CaH 2), MeOH (Mg), DMF (Desmodur ® , dibutyltin dilaurate), hexane, toluene (Na/K). Flash chromatography: Merck silica gel 60 (230-400 mesh). NMR: Spectra were recorded on a Bruker DPX 300, AV 400, or DMX 600 spectrometer in the solvents indicated; chemical shifts (δ) are given in ppm relative to TMS, coupling constants (J) in Hz. The solvent signals were used as references and the chemical shifts converted to the TMS scale (CDCl 3 : δ C ≡ 77.0 ppm; residual CHCl 3 in CDCl 3 : δ H ≡ 7.24 ppm; CD 2 Cl 2 : δ C ≡ 53.8 ppm; residual CH 2 Cl 2 in CD 2 Cl 2 : δ H ≡ 5.32 ppm). IR: Nicolet FT-7199 spectrometer, wavenumbers (ν) in cm −1. MS (EI): Finnigan MAT 8200 (70 eV), ESI-MS: Finnigan MAT 95, accurate mass determinations: Bruker APEX III FT-MS (7 T magnet). Melting points: Büchi melting point apparatus B-540 (corrected). Elemental analyses: H. Kolbe, Mülheim/Ruhr. Unless stated otherwise, commercially available compounds (Fluka, Lancaster, Aldrich) were used as received. 1
Positive-sense single-stranded RNA (+RNA) viruses have proven to be important pathogens that are ... more Positive-sense single-stranded RNA (+RNA) viruses have proven to be important pathogens that are able to threaten and deeply damage modern societies, as illustrated by the ongoing COVID-19 pandemic. Therefore, compounds active against most or many +RNA viruses are urgently needed. Here, we present PR673, a helquat-like compound that is able to inhibit the replication of SARS-CoV-2 and tick-borne encephalitis virus in cell culture. Using in vitro polymerase assays, we demonstrate that PR673 inhibits RNA synthesis by viral RNA-dependent RNA polymerases (RdRps). Our results illustrate that the development of broad-spectrum non-nucleoside inhibitors of RdRps is feasible.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Developments in the field of visible-light photoredox catalysis have considerably enriched toolbo... more Developments in the field of visible-light photoredox catalysis have considerably enriched toolbox of preparative organic chemists in recent years. This fast-growing area of research has emerged after seminal studies mainly by MacMillan, Yoon, and Stephenson groups were published in 2008 and 2009. This chapter focuses on the twentieth-century roots of photoredox catalysis with [Ru(bpy)3]2+, and the key properties of this species are briefly summarized.
Influencing stability of G-quadruplexes that can be formed in specific guanine-rich sequences has... more Influencing stability of G-quadruplexes that can be formed in specific guanine-rich sequences has emerged as a promising route to anticancer drug design in recent years. These sequences are highly prevalent in human genome and occur in the telomeres as well as in promoters of certain genes upregulated in cancer (e.g. c-Myc, K-ras, VEGF, bcl-2, c-kit, or HIF-1α). Functional role of these G-quadruplex structures has been tested using G-quadruplex-stabilizing ligands in cell-based assays, resulting in suppression of transcription of oncogenes. As c-Myc deregulation is found in many types of human leukemia and lymphoma and its overexpression is often associated with disease progression, we chose it as our primary target. We designed a library of helical structures with cationic aromatic moieties called helquats to find a novel class of G-quadruplex specific ligands. Their non-planar structure minimizes potential of intercalation into DNA duplex. To screen a library of about 1500 compoun...
Synthesis and nontrivial optical resolution of a helicene-like dication, helquat 1, has been acco... more Synthesis and nontrivial optical resolution of a helicene-like dication, helquat 1, has been accomplished. Starting with gram scale of the racemic helquat 1 sample, Dutch Resolution using family of 3 tartrate anions was key to achieve successful separation of M and P helical enantiomers of 1. Hundreds of milligrams of each enantiomer of this configurationally stable C 2-symmetric helquat have been obtained. Racemization barrier of 1 has been determined. To our knowledge this is the first report on Dutch Resolution performed with a helicene-like compound. Moreover, there are no literature precedents for Dutch Resolution of chiral quaternary ammonium cations.
Chemical communications (Cambridge, England), Jan 24, 2017
Electrochemical reduction of an azoniahelicene affords a dimer, accompanied by a strong change in... more Electrochemical reduction of an azoniahelicene affords a dimer, accompanied by a strong change in the electronic circular dichroism. The fast dimerisation event leads to a >500 mV shift of the oxidation potential, affording a large area of bistability, where the chiroptical signal only depends on the redox history.
The journal of physical chemistry. A, Jan 13, 2017
Fourteen new dipolar cations have been synthesized, containing methoxy or tertiary amino electron... more Fourteen new dipolar cations have been synthesized, containing methoxy or tertiary amino electron donor groups attached to helquat (Hq) acceptors. These Hq derivatives have been characterized as their TfO- salts by using various techniques including NMR and electronic absorption spectroscopies. UV-vis spectra show intense, relatively low energy absorptions with λmax ≈ 400-600 nm, attributable to intramolecular charge-transfer (ICT) excitations. Single-crystal X-ray structures have been solved for two of the chromophores, one as its PF6- salt, revealing centrosymmetric packing arrangements (space groups Pica and P-1). Molecular quadratic nonlinear optical (NLO) responses have been determined directly by using hyper-Rayleigh scattering (HRS) with a 800 nm laser, and indirectly via Stark (electroabsorption) spectroscopy for the low energy absorption bands. The obtained static first hyperpolarizabilities β0 range from moderate to large; 9-140 × 10-30 esu from HRS in MeCN and 44-580 × 10...
Noncovalent molecular interactions between helquats, a new class of dicationic helical extended d... more Noncovalent molecular interactions between helquats, a new class of dicationic helical extended diquats, and several chiral acidic aromatic drugs and catalysts have been investigated using partial-filling affinity capillary electrophoresis (PF-ACE). Helquats dissolved at 1mM concentration in the aqueous background electrolyte (40mM Tris, 20mM acetic acid, pH 8.1) were introduced as ligand zones of variable length (0-130mm) into the hydroxypropylcellulose coated fused silica capillary whereas 0.1mM solutions of negatively charged chiral drugs or catalysts (warfarin, ibuprofen, mandelic acid, etodolac, binaphthyl phosphate and 11 other acidic aromatic compounds) were applied as a short analyte zone at the injection capillary end. After application of electric field, analyte and ligand migrated against each other and in case of their interactions, migration time of the analyte was increasing with increasing length of the ligand zone. From the tested compounds, only isomers of those exhibiting helical chirality and/or possessing conjugated aromatic systems were enantioselectively separated through their differential interactions with helquats. Some compounds with conjugated aromatic groups interacted with helquats moderately strongly but non-enantiospecifically. Small compounds with single benzene ring exhibited no or very weak non-enantiospecific interactions. PF-ACE method allowed to determine binding constants of the analyte-helquat complexes from the changes of migration times of the analytes. Binding constants of the weakest complexes of the analytes with helquats were less than 50L/mol, whereas binding constants of the strongest complexes were in the range 1 000-1 400L/mol.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
A straightforward synthetic approach to a new class of molecules with helical chirality has been ... more A straightforward synthetic approach to a new class of molecules with helical chirality has been developed involving an intramolecular [2 + 2 + 2] cycloisomerization of triynes under CpCo(CO) 2 / PPh 3 catalysis. The cyclization reaction is promoted by visible light irradiation. Starting from 1,2-diarylacetylenes with two terminal or methyl-substituted tethered acetylene moieties (1a,b, 4, 5, and 7), the target products (8a,b, 11, 12, and 14) are obtained in 64-89% yield. The triynes bearing terminal trimethylsilyl groups (1c, 2, and 3) are less reactive and afford the products (8c, 9a,b, and 10) in 23-71% yield. The ability of the trimethylsilylated derivatives to cycloisomerize strongly depends on the tether length. The cyclized products (8-14) with five, six, and seven orthofused rings structurally resemble classical helicenes. Several representatives (8b, 11, 12, and 14) have been resolved into enantiomers by HPLC on a chiral column. Thus, the methodology exhibits a considerable versatility and allows the preparation of a variety of helical objects.
Pccp Physical Chemistry Chemical Physics, Feb 3, 2010
Helicene-viologen structural hybrids, like [5]helquat, 6,7,10,11-tetrahydrodipyrido[2,1-a:1 0 ,2 ... more Helicene-viologen structural hybrids, like [5]helquat, 6,7,10,11-tetrahydrodipyrido[2,1-a:1 0 ,2 0-k]-[2,9]phenanthrolinediium, and its four methylated derivatives, are characterized by electrochemical admittance and EPR spectroscopy. All compounds are reversibly reduced in two one-electron steps. Formal redox potentials correlate with the calculated LUMO energies. The electron transfer is coupled with a weak adsorption of the reactants. The analysis of the frequency dependence of the electrode admittance is used for the separation of Faradaic and double layer contributions and finally to the estimation of heterogeneous rate constants. Heterogeneous rate constants determined this way are in the range 0.1 to 3 cm s À1. In all cases the second electron transfer is faster than the first redox step by a factor of three. The Frumkin correction for the acceleration by the double layer potential further amplifies this difference. The heterogeneous rate constants of derivatives correlate with the solvent reorganization energy estimated from the Marcus model. EPR spectra confirm the radical cation formation. The radical of [5]helquat participates in an extremely fast self-exchange process with the parent dication characterized by the self-exchange rate constant k ET = (2.4 AE 0.5) Â 10 9 M À1 s À1 .
... How to Cite. Fürstner, A., Nevado, C., Tremblay, M., Chevrier, C., Teplý, F., Aïssa, C. and W... more ... How to Cite. Fürstner, A., Nevado, C., Tremblay, M., Chevrier, C., Teplý, F., Aïssa, C. and Waser, M. (2006), Total Synthesis of Iejimalide B. Angewandte Chemie International Edition, 45: 5837–5842. ... C. Aïssa, C. Chevrier, F. Teplý, C. Nevado, M. Tremblay, Angew. Chem. ...
The secondary structure of nucleic acids containing quartets of guanines, termed G-quadruplexes, ... more The secondary structure of nucleic acids containing quartets of guanines, termed G-quadruplexes, is known to regulate the transcription of many genes. Several G-quadruplexes can be formed in the HIV-1 long terminal repeat promoter region and their stabilization results in the inhibition of HIV-1 replication. Here, we identified helquat-based compounds as a new class of anti-HIV-1 inhibitors that inhibit HIV-1 replication at the stage of reverse transcription and provirus expression. Using Taq polymerase stop and FRET melting assays, we have demonstrated their ability to stabilize G-quadruplexes in the HIV-1 long-terminal repeat sequence. Moreover, these compounds were not binding to the general G-rich region, but rather to G-quadruplex-forming regions. Finally, docking and molecular dynamics calculations indicate that the structure of the helquat core greatly affects the binding mode to the individual G-quadruplexes. Our findings can provide useful information for the further ration...
Collection of Czechoslovak Chemical Communications, 2011
Reactions triggered by light constitute a treasure trove of unique synthetic methods that are ava... more Reactions triggered by light constitute a treasure trove of unique synthetic methods that are available to chemists. Photoinduced redox processes using visible light in conjunction with sensitizing dyes offer a great variety of catalytic transformations useful in the realm of organic synthesis. The recent literature amply shows that this preparative toolbox is expanding substantially. This review discusses historical and contemporary work in the area of photoredox catalysis with [Ru(bpy)3]2+. Elegant examples from the most recent literature document the importance of this fast developing area of research. The photoredox chemistry has also emerged as a promising bond-making and bond-breaking tool for chemical biology and materials chemistry. A review with 96 references.
General Methods: All reactions were carried out in flame-dried glassware under Ar. The solvents w... more General Methods: All reactions were carried out in flame-dried glassware under Ar. The solvents were purified by distillation over the drying agents indicated and were transferred under Ar: THF, Et 2 O, 1,4-dioxane (Mg-anthracene), CH 2 Cl 2 (P 4 O 10), MeCN, Et 3 N, pyridine (CaH 2), MeOH (Mg), DMF (Desmodur ® , dibutyltin dilaurate), hexane, toluene (Na/K). Flash chromatography: Merck silica gel 60 (230-400 mesh). NMR: Spectra were recorded on a Bruker DPX 300, AV 400, or DMX 600 spectrometer in the solvents indicated; chemical shifts (δ) are given in ppm relative to TMS, coupling constants (J) in Hz. The solvent signals were used as references and the chemical shifts converted to the TMS scale (CDCl 3 : δ C ≡ 77.0 ppm; residual CHCl 3 in CDCl 3 : δ H ≡ 7.24 ppm; CD 2 Cl 2 : δ C ≡ 53.8 ppm; residual CH 2 Cl 2 in CD 2 Cl 2 : δ H ≡ 5.32 ppm). IR: Nicolet FT-7199 spectrometer, wavenumbers (ν) in cm −1. MS (EI): Finnigan MAT 8200 (70 eV), ESI-MS: Finnigan MAT 95, accurate mass determinations: Bruker APEX III FT-MS (7 T magnet). Melting points: Büchi melting point apparatus B-540 (corrected). Elemental analyses: H. Kolbe, Mülheim/Ruhr. Unless stated otherwise, commercially available compounds (Fluka, Lancaster, Aldrich) were used as received. 1
Positive-sense single-stranded RNA (+RNA) viruses have proven to be important pathogens that are ... more Positive-sense single-stranded RNA (+RNA) viruses have proven to be important pathogens that are able to threaten and deeply damage modern societies, as illustrated by the ongoing COVID-19 pandemic. Therefore, compounds active against most or many +RNA viruses are urgently needed. Here, we present PR673, a helquat-like compound that is able to inhibit the replication of SARS-CoV-2 and tick-borne encephalitis virus in cell culture. Using in vitro polymerase assays, we demonstrate that PR673 inhibits RNA synthesis by viral RNA-dependent RNA polymerases (RdRps). Our results illustrate that the development of broad-spectrum non-nucleoside inhibitors of RdRps is feasible.
An entry from the Cambridge Structural Database, the world's repository for small molecule cr... more An entry from the Cambridge Structural Database, the world's repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Developments in the field of visible-light photoredox catalysis have considerably enriched toolbo... more Developments in the field of visible-light photoredox catalysis have considerably enriched toolbox of preparative organic chemists in recent years. This fast-growing area of research has emerged after seminal studies mainly by MacMillan, Yoon, and Stephenson groups were published in 2008 and 2009. This chapter focuses on the twentieth-century roots of photoredox catalysis with [Ru(bpy)3]2+, and the key properties of this species are briefly summarized.
Influencing stability of G-quadruplexes that can be formed in specific guanine-rich sequences has... more Influencing stability of G-quadruplexes that can be formed in specific guanine-rich sequences has emerged as a promising route to anticancer drug design in recent years. These sequences are highly prevalent in human genome and occur in the telomeres as well as in promoters of certain genes upregulated in cancer (e.g. c-Myc, K-ras, VEGF, bcl-2, c-kit, or HIF-1α). Functional role of these G-quadruplex structures has been tested using G-quadruplex-stabilizing ligands in cell-based assays, resulting in suppression of transcription of oncogenes. As c-Myc deregulation is found in many types of human leukemia and lymphoma and its overexpression is often associated with disease progression, we chose it as our primary target. We designed a library of helical structures with cationic aromatic moieties called helquats to find a novel class of G-quadruplex specific ligands. Their non-planar structure minimizes potential of intercalation into DNA duplex. To screen a library of about 1500 compoun...
Synthesis and nontrivial optical resolution of a helicene-like dication, helquat 1, has been acco... more Synthesis and nontrivial optical resolution of a helicene-like dication, helquat 1, has been accomplished. Starting with gram scale of the racemic helquat 1 sample, Dutch Resolution using family of 3 tartrate anions was key to achieve successful separation of M and P helical enantiomers of 1. Hundreds of milligrams of each enantiomer of this configurationally stable C 2-symmetric helquat have been obtained. Racemization barrier of 1 has been determined. To our knowledge this is the first report on Dutch Resolution performed with a helicene-like compound. Moreover, there are no literature precedents for Dutch Resolution of chiral quaternary ammonium cations.
Chemical communications (Cambridge, England), Jan 24, 2017
Electrochemical reduction of an azoniahelicene affords a dimer, accompanied by a strong change in... more Electrochemical reduction of an azoniahelicene affords a dimer, accompanied by a strong change in the electronic circular dichroism. The fast dimerisation event leads to a >500 mV shift of the oxidation potential, affording a large area of bistability, where the chiroptical signal only depends on the redox history.
The journal of physical chemistry. A, Jan 13, 2017
Fourteen new dipolar cations have been synthesized, containing methoxy or tertiary amino electron... more Fourteen new dipolar cations have been synthesized, containing methoxy or tertiary amino electron donor groups attached to helquat (Hq) acceptors. These Hq derivatives have been characterized as their TfO- salts by using various techniques including NMR and electronic absorption spectroscopies. UV-vis spectra show intense, relatively low energy absorptions with λmax ≈ 400-600 nm, attributable to intramolecular charge-transfer (ICT) excitations. Single-crystal X-ray structures have been solved for two of the chromophores, one as its PF6- salt, revealing centrosymmetric packing arrangements (space groups Pica and P-1). Molecular quadratic nonlinear optical (NLO) responses have been determined directly by using hyper-Rayleigh scattering (HRS) with a 800 nm laser, and indirectly via Stark (electroabsorption) spectroscopy for the low energy absorption bands. The obtained static first hyperpolarizabilities β0 range from moderate to large; 9-140 × 10-30 esu from HRS in MeCN and 44-580 × 10...
Noncovalent molecular interactions between helquats, a new class of dicationic helical extended d... more Noncovalent molecular interactions between helquats, a new class of dicationic helical extended diquats, and several chiral acidic aromatic drugs and catalysts have been investigated using partial-filling affinity capillary electrophoresis (PF-ACE). Helquats dissolved at 1mM concentration in the aqueous background electrolyte (40mM Tris, 20mM acetic acid, pH 8.1) were introduced as ligand zones of variable length (0-130mm) into the hydroxypropylcellulose coated fused silica capillary whereas 0.1mM solutions of negatively charged chiral drugs or catalysts (warfarin, ibuprofen, mandelic acid, etodolac, binaphthyl phosphate and 11 other acidic aromatic compounds) were applied as a short analyte zone at the injection capillary end. After application of electric field, analyte and ligand migrated against each other and in case of their interactions, migration time of the analyte was increasing with increasing length of the ligand zone. From the tested compounds, only isomers of those exhibiting helical chirality and/or possessing conjugated aromatic systems were enantioselectively separated through their differential interactions with helquats. Some compounds with conjugated aromatic groups interacted with helquats moderately strongly but non-enantiospecifically. Small compounds with single benzene ring exhibited no or very weak non-enantiospecific interactions. PF-ACE method allowed to determine binding constants of the analyte-helquat complexes from the changes of migration times of the analytes. Binding constants of the weakest complexes of the analytes with helquats were less than 50L/mol, whereas binding constants of the strongest complexes were in the range 1 000-1 400L/mol.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
A straightforward synthetic approach to a new class of molecules with helical chirality has been ... more A straightforward synthetic approach to a new class of molecules with helical chirality has been developed involving an intramolecular [2 + 2 + 2] cycloisomerization of triynes under CpCo(CO) 2 / PPh 3 catalysis. The cyclization reaction is promoted by visible light irradiation. Starting from 1,2-diarylacetylenes with two terminal or methyl-substituted tethered acetylene moieties (1a,b, 4, 5, and 7), the target products (8a,b, 11, 12, and 14) are obtained in 64-89% yield. The triynes bearing terminal trimethylsilyl groups (1c, 2, and 3) are less reactive and afford the products (8c, 9a,b, and 10) in 23-71% yield. The ability of the trimethylsilylated derivatives to cycloisomerize strongly depends on the tether length. The cyclized products (8-14) with five, six, and seven orthofused rings structurally resemble classical helicenes. Several representatives (8b, 11, 12, and 14) have been resolved into enantiomers by HPLC on a chiral column. Thus, the methodology exhibits a considerable versatility and allows the preparation of a variety of helical objects.
Pccp Physical Chemistry Chemical Physics, Feb 3, 2010
Helicene-viologen structural hybrids, like [5]helquat, 6,7,10,11-tetrahydrodipyrido[2,1-a:1 0 ,2 ... more Helicene-viologen structural hybrids, like [5]helquat, 6,7,10,11-tetrahydrodipyrido[2,1-a:1 0 ,2 0-k]-[2,9]phenanthrolinediium, and its four methylated derivatives, are characterized by electrochemical admittance and EPR spectroscopy. All compounds are reversibly reduced in two one-electron steps. Formal redox potentials correlate with the calculated LUMO energies. The electron transfer is coupled with a weak adsorption of the reactants. The analysis of the frequency dependence of the electrode admittance is used for the separation of Faradaic and double layer contributions and finally to the estimation of heterogeneous rate constants. Heterogeneous rate constants determined this way are in the range 0.1 to 3 cm s À1. In all cases the second electron transfer is faster than the first redox step by a factor of three. The Frumkin correction for the acceleration by the double layer potential further amplifies this difference. The heterogeneous rate constants of derivatives correlate with the solvent reorganization energy estimated from the Marcus model. EPR spectra confirm the radical cation formation. The radical of [5]helquat participates in an extremely fast self-exchange process with the parent dication characterized by the self-exchange rate constant k ET = (2.4 AE 0.5) Â 10 9 M À1 s À1 .
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