pH-switched porphyrin receptor: I. Binding of iodide ions

The basic properties of 5,10,15,20-tetra(4-chlorophenyl)porphyrin in the acetonitrile-perchloric acid system at standard temperature were studied by spectrophotometric titration. The protonation of nitrogen atoms of the tetrapyrrole macrocycle was found to proceed in two steps to give mono- and diprotonated species. The corresponding ionization constants and concentration ranges were determined. Diprotonated porphyrin binds efficiently iodide ions; the stability constants of the 1: 1 and 1: 2 complexes thus formed were determined.     

Noncovalent endo-binding of fullerenes to diprotonated bisporphyrins

Noncovalent binding of fullerenes to bisporphyrins was studied in the gas phase by energy-dependent collision-induced dissociation (CID) with Xe under single-collision conditions. The electrospray ionization mass spectra of calix[4]arene-linked bisporphyrins show that bisporphyrins take up to 3-4 protons, depending on the type of meso-substituents. Of the protonated bisporphyrins, the diprotonated species form stable 1:1 complexes with fullerenes (C(60) and C(70)). CID cracking patterns of the diprotonated bisporphyrins indicate that each monomeric porphyrin moiety is singly protonated. CID yield-energy curves obtained from the 1:1 diprotonated bisporphyrin-fullerene complexes suggest that a fullerene occupies the endo-binding site intercalated between the two singly protonated porphyrin moieties. In the cases of 1:2 diprotonated bisporphyrin-fullerene complexes, CID results show that one fullerene binds inside (endo-binding) and the other outside (exo-binding). The exo-binding mode is energetically almost identical to the binding of fullerenes to singly protonated porphyrin monomers. The endo-binding energy is at least twice the exo-binding energy. To gain insights into the binding mode, we optimized structures of diprotonated bisporphyrins and their 1:1 endo-complexes with fullerenes, and calculated the endo-binding energy for C(60), C(70) (end-on), and C(70) (side-on). The endo-binding of fullerenes to diprotonated bisporphyrins nearly doubles the π-π interactions while reducing the electrostatic repulsion between the two singly protonated porphyrin moieties. The side-on binding of C(70) is favored over the end-on binding because the former exerts less steric strain to the lower rim of calixarene.     

Acid-base equilibria in 5,10,15,20-tetrakis(4-sulfonatophenyl)chlorin: Role of conformational flexibility

The acid-base equilibria in 5,10,15,20-tetrakis(4-sulfonatophenyl)chlorin were studied in aqueous solution and compared with the respective data for the corresponding porphyrin. The reduction of the pyrrole ring in the tetrapyrrolic macrocycle noticeably influences both free base/monoprotonated and mono-/diprotonated species equilibria. In strong acidic solutions protonation of 4-sulfonatophenyl groups takes place in addition to protonation of the macrocycle core. The photophysical properties of all ionic forms are influenced by an enhanced rate of internal S1 --> S0 conversion, leading to about 50% and 90% deactivation through this channel for the free base and diprotonated species, respectively. The enhancement of the rate of the radiationless transitions is explained by an increased conformational flexibility of the chlorin macrocycle with respect to that of a porphyrin. Structural volume change measurements with laser-induced optoacoustic spectroscopy support this explanation. The contraction upon triplet state formation of the free base is about one-half of that measured for the corresponding porphyrin. This contraction should be due to intramolecular structural rearrangements of the macrocycle to adopt a minimum energy conformation in case of the chlorin. On the contrary, for the more rigid porphyrin macrocycle the interactions of the molecule with the solvent environment play a more important role. The diprotonated forms of both porphyrin and chlorin show a high radiationless S1 --> S0 conversion rate and seem to have a similar conformational flexibility. In agreement with previous calculations, the conformational flexibility of the diprotonated forms appears to be higher than that of the free base molecule.     

Structural and vibrational properties of tetraoxaporphyrin dication, the oxygen analogue of porphyrin, and of isoelectronic diprotonated porphyrin

Structural calculations by means of the density functional method have been performed on tetraoxaporphyrin dication and on isoelectronic diprotonated porphyrin as well as on the sulfur and carbon analogues of porphyrin. A detailed study of the stable conformations of these compounds is reported starting with the most symmetrical conformations and lowering the symmetry along the vibrational coordinates with imaginary frequency. The calculated geometries are related to experimental structures available from X-ray diffraction studies. The Raman spectra of tetraoxaporphyrin dication exciting with micro-Raman instrumentation at 785 nm and of diprotonated porphyrin in near-resonance conditions with the Soret band have been measured. The correlation between frequencies calculated with the DF/B3-LYP/cc-pVDZ procedure for porphyrin, diprotonated porphyrin, and tetraoxaporphyrin dication has allowed for making a vibrational assignment for the latter two systems in excellent agreement with experiment using a single frequency scale factor.     

Study on nonlinear spectroscopy of tetraphenylporphyrin and dithiaporphyrin diacids

The nonlinear absorption of two porphyrin diacids (H4TPP2+ and H2DSP2+), the diprotonated forms of free base tetraphenylporphyrin (H2TPP) and dithiaporphyrin (DSP), were studied in the wavelength range of 500-650 nm. The two porphyrin diacids exhibited perturbed static and dynamic characteristics and enhanced nonlinear absorption properties relative to their parent neutral complexes in solution. Furthermore, for the dithiaporphyrin diacid, the introduction of S-atoms into the porphyrin core makes it a better candidate for optical limiting relative to the simple porphyrin. Their photophysical parameters such as ground and excited states absorption cross-sections, together with fluorescence lifetime and intersystem crossing time, were determined.     

NMR determination of the microscopic constants of diprotonated diamines in aqueous solution

The microscopic acidity constants of the diprotonated asymmetric N-methyl-substituted ethylenediamines and N-methylpiperazine were determined by using the change of the chemical shift of the methyl protons with varying acidity. The determination was carried out at 25 degrees in aqueous solution and in an ionic medium of 1M KNO(3). The basicity of the amino-functions follows the expected sequence: secondary > primary 2 > tertiary. The influence of the substituent on the basicity of the end-group is primary > secondary 2 > tertiary.     

π-Extension in expanded porphyrins: cyclo[4]naphthobipyrrole

The π-extended cyclo[4]naphthobipyrrole 1a has been prepared via an Fe(III)-mediated oxidative cyclization of an alkyl-substituted naphthobipyrrole. The structure of this new expanded porphyrin, isolated as the deprotonated sulfate salt, was characterized by spectroscopic means, as well through a single crystal X-ray diffraction analysis. Salt 1a displays a total of four well-resolved redox waves as determined by cyclic voltammetry. It also displays bathochromically shifted near-IR absorption maxima compared to the diprotonated forms of nonannulated cyclo[8]pyrroles.     

Excited states of porphyrin macrocycles

S1 --> S(n) spectra of porphyrin, diprotonated porphyrin, and tetraoxaporphyrin dication have been measured in the energy range 2-3 eV above S1 at room temperature in solution by means of transient absorption spectroscopy exciting with femtosecond pulses. Highly excited pi pi* states not active in the conventional S0 --> S(n) spectrum have been observed. The experimental data are discussed on the basis of the time dependent density functional theory taking advantage of large scale calculations of configuration interaction between singly excited configurations (DF/SCI). The DF/SCI calculation on porphyrin has allowed to assign g states active in the S1 --> S(n) spectrum. Applying the same calculation method to tetraoxaporphyrin dication the S0 --> S(n) spectrum is reproduced relatively to the Q and B (Soret) bands as well as to the weaker E(u) bands at higher energy. According to our calculation the S1 --> S(n) transient spectrum is related to states of g symmetry mainly arising from excitations between doubly degenerate pi and pi* orbitals such as 2e(g) --> 4e(g). In the case of diprotonated porphyrin it is shown that the complex of the macrocycle with two trifluoroacetate anions plays a significant role for absorption. Charge transfer excitations from the anions to the macrocycle contribute to absorption above the Soret band, justifying the intensity enhancement of the S0 --> S(n) spectrum with respect to the other two macrocyclic systems.     

Study on the supramolecular system of meso-tetrakis (4-sulfonatophenyl) porphyrin and cyclodextrins by spectroscopy

The ability of beta-cyclodextrin (beta-CD), sulfurbutylether-beta-CD (SBE-beta-CD) and hydroxypropyl-beta-CD (HP-beta-CD) to break the aggregate of the meso-Tetrakis (4-sulfonatophenyl) porphyrin (TPPS4) and to form 2:1 inclusion complexes has been studied by adsorption and fluorescence spectroscopy. The formation constants are calculated, respectively by fluoremetry, from which the inclusion capacity of different CDs is compared and the inclusion mechanism of charged-beta-CD (SBE-beta-CD) is quite different from that of parent beta-CD. At lower pH, the complexation between HP-beta-CD and H2TPPS(2+)4 (the form of the diprotonated TPPS4) hampers the continuous protonation of the pyrrole nitrogen of TPPS4 and the hydrophobic cavity may prefer to bind an apolar neutral porphyrin molecule. 1HNMR data support the inclusion conformation of the porphyrin-cyclodextrin supramolecular system, indicating the interaction of meso-phenyl groups of TPPS4 with the cavity of CDs. For this host-guest inclusion model, cyclodextrin, being regarded as the protein component, which acts as a carrier enveloping the active site of heme prosthetic group within its hydrophobic environment, provides a protective sheath for porphyrin, creating artificial analogues of heme-containing proteins. However, the TPPS4, encapsulated within this saccharide-coated barrier, its physico-chemical, photophysical and photochemical properties changed strongly.     

Aerial oxidation kinetics of a phenolic porphyrin in acid solution

The rate of aerial oxidation of the title porphyrin ( 1 ) in dichloromethane (DCM), acidified with trifluoro-acetic acid (TFA), was found to be first-order in 1 and second-order in TFA at low TFA concentrations, and second-order in both 1 and TFA at higher TFA concentrations. At the lower TFA concentrations, aerial oxidation gives the two-electron oxidised product 2 , while at the higher TFA concentrations, a porphyrin pication radical 3 is formed. These results are rationalised by a kinetic scheme requiring, (i), preequilibrium involving transient formation of a porphyrin tetracation 4 , (ii), two-electron oxidation of 4 to a diprotonated oxidised porphyrin 5 , (iii) reaction of 5 with solvent water and (iv), conproportionation of 5 with 1 to generate 3 .     

Study on the Supramolecular System of TAPP and Cyclodextrins by Spectroscopy

The ability of β-cyclodextrin (β-CD), γ-CD, hydroxypropyl-β-CD (HP-β-CD), trimethyl-β-CD (TM-β-CD), sulfurbutylether-β-CD (SBE-β-CD) and carboxymethyl-β-cyclodextrin (CM-β-CD) to break the aggregate of the meso-tetrakis(4-N-trimethylaminobenzyl)porphyrin (TAPP) and to form 2:1 inclusion complexes has been studied by absorption and fluorescence spectroscopy. The formation constants are calculated, respectively, by fluorimetry, from which the inclusion capacity of different CDs is compared and the inclusion mechanism of charged-β-CD (SBE-β-CD and CM-β-CD) is quite different from that of the parent β-CD. At lower pH, the complexation between TM-β-CD and H²TAPP²⁺ (the form of the diprotonated TAPP) hampers the continuous protonation of the pyrrole nitrogen of TAPP and the hydrophobic cavity may prefer to bind an apolar neutral porphyrin molecule. ¹HNMR data support the inclusion conformation of the porphyrin–cyclodextrin supramolecular system, indicating the interaction of the meso-phenyl groups of TAPP with the cavity of CDs. For this host–guest inclusion model, cyclodextrin being regarded as the protein component, which acts as a carrier enveloping the active site of heme prosthetic group within its hydrophobic environment, provides a protective sheath for the porphyrin, creating artificial analogues of heme-containing proteins. However, for TAPP, encapsulated within this saccharide-coated barrier, its photophysical and photochemical properties changed strongly.     

Laser flash photolysis generation and kinetic studies of porphyrin-manganese-oxo intermediates. Rate constants for oxidations effected by porphyrin-Mn(V)-oxo species and apparent disproportionation equilibrium constants for porphyrin-Mn(IV)-oxo species

Porphyrin-manganese(V)-oxo and porphyrin-manganese(IV)-oxo species were produced in organic solvents by laser flash photolysis (LFP) of the corresponding porphyrin-manganese(III) perchlorate and chlorate complexes, respectively, permitting direct kinetic studies. The porphyrin systems studied were 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TPFPP), and 5,10,15,20-tetrakis(4-methylpyridinium)porphyrin (TMPyP). The order of reactivity for (porphyrin)Mn(V)(O) derivatives in self-decay reactions in acetonitrile and in oxidations of substrates was (TPFPP) > (TMPyP) > (TPP). Representative rate constants for reaction of (TPFPP)Mn(V)(O) in acetonitrile are k = 6.1 x 10(5) M(-1) s(-1) for cis-stilbene and k = 1.4 x 10(5) M(-1) s(-1) for diphenylmethane, and the kinetic isotope effect in oxidation of ethylbenzene and ethylbenzene-d(10) is k(H)/k(D) = 2.3. Competitive oxidation reactions conducted under catalytic conditions display approximately the same relative rate constants as were found in the LFP studies of (porphyrin)Mn(V)(O) derivatives. The apparent rate constants for reactions of (porphyrin)Mn(IV)(O) species show inverted reactivity order with (TPFPP) < (TMPyP) < (TPP) in reactions with cis-stilbene, triphenylamine, and triphenylphosphine. The inverted reactivity results because (porphyrin)Mn(IV)(O) disproportionates to (porphyrin)Mn(III)X and (porphyrin)Mn(V)(O), which is the primary oxidant, and the equilibrium constants for disproportionation of (porphyrin)Mn(IV)(O) are in the order (TPFPP) < (TMPyP) < (TPP). The fast comproportionation reaction of (TPFPP)Mn(V)(O) with (TPFPP)Mn(III)Cl to give (TPFPP)Mn(IV)(O) (k = 5 x 10(8) M(-1) s(-1)) and disproportionation reaction of (TPP)Mn(IV)(O) to give (TPP)Mn(V)(O) and (TPP)Mn(III)X (k approximately 2.5 x 10(9) M(-1) s(-1)) were observed. The relative populations of (porphyrin)Mn(V)(O) and (porphyrin)Mn(IV)(O) were determined from the ratios of observed rate constants for self-decay reactions in acetonitrile and oxidation reactions of cis-stilbene by the two oxo derivatives, and apparent disproportionation equilibrium constants for the three systems in acetonitrile were estimated. A model for oxidations under catalytic conditions is presented.     

Synthesis and properties of fullerene (C70) complexes of 2,6-bis(porphyrin)-substituted pyrazine derivatives bound to a Pd(II) ion

2,6-Bis(porphyrin)-substituted 3,5-dimethylpyrazine and its zinc complex bound C₇₀ to yield 1:1 inclusion complexes, which were characterised by ESI-MS, UV–vis, fluorescence and NMR spectroscopies. Association constants of the C₇₀ complexes were determined by fluorescence and NMR spectral analyses. A decrease in absorbance of the Soret band of the pyrazine derivative by the effect of C₇₀ was observed, suggesting the existence of a charge transfer interaction between C₇₀ and porphyrin. Experimentally reliable values for the association constants were obtained by the NMR method and were about six times larger than those of the corresponding C₆₀ complexes. Palladium complexation of the porphyrin–pyrazine ligand was found to enhance the association with fullerene. The association constant of 2,6-bis(porphyrin-Zn)-substituted 3,5-dimethylpyrazine-Pd(II) complex with C₇₀ was determined to be 8400 ± 900 M^? 1. From the comparison of the association constants, it was found that inclusion room for C₇₀ in the Pd(II) complex was maintained, juxtaposed between porphyrins attached to the opposite sides of the pyrazine ligands.

     

Photophysical properties of glucoconjugated chlorins and porphyrins and their associations with cyclodextrins

Glucoconjugated analogues of the meta-hydroxyphenyl porphyrin (m-THPP) and meta-hydroxyphenyl chlorin (m-THPC) has been recently synthesized. The characteristics of their triplet states have been determined with regard to their involvement in the photodynamic (PDT) efficiency. In the case of porphyrin derivatives, triplet quantum yields (Phi(T)) were ranging from 0.42 to 0.55 and triplet life times (tau(T)) from 1 to 5 micros. High reaction rate constants (k(q)) with molecular oxygen (k(q): 1.2-1.6 x 10(9)s(-1)) have been found. The triplet lifetimes of chlorin derivatives were about four times higher than those of porphyrins whereas the Phi(T) and k(q) values remained quite similar. Singlet oxygen yields of glucosylated and non-glucosylated porphyrins and chlorins were not significantly different within experimental errors (Phi(Delta)((1)O(2)): 0.41-0.58). Furthermore, it has been shown that glucoconjugated photosensitizers could undergo associations with the methyl-beta-cyclodextrin (Me-beta-CD) which exhibit high triplet lifetimes and singlet oxygen yields ranging from 0.27 to 0.48.     

Acid dissociation constants of mono- and diprotonated species of some polyalkyl substituted 1,10-phenanthrolines and the peculiar effects of 2,9-dialkyl substituents

Acid dissociation constants of protonated species of some selected polyalkyl substituted 1,10-phenanthrolines were determined spectrophotometrically. The results confirm the existence of diprotonated species and indicate that polyalkyl substituents enhance both protonation steps, but not necessarily to the same degree. A peculiar effect, presumably steric in nature, was discovered for the 2,9-dialkyl substituted derivatives which suggests that a different mode of protonation is involved for these than for other substituted 1,10-phenanthrolines.     

Retro‐Diels–Alder Approach to the Synthesis of π‐Expanded Azuliporphyrins and Their Porphyrinoid Aromaticity

Bicyclo[2.2.2]octadiene (BCOD) fused azuliporphyrins were synthesized by 3+1 porphyrin synthesis of azulitripyrranes with diformylpyrroles. Subsequent retro‐Diels–Alder reaction of the BCOD‐fused azuliporphyrins afforded azulibenzo‐, azulidibenzo‐, and azulitribenzoporphyrins 1 – 5 . NMR and UV/Vis spectra, as well as nucleus‐independent chemical shift (NICS) calculations revealed that 1 – 5 and their diprotonated dications exhibit relatively low porphyrinoid aromaticity, which was dependent on the position and number of fused benzene rings present.     

Basicity of octa- and dodecamethyl-substituted tetraphenylporphyrins by phase-transfer spectral potentiometric titration

Phase-transfer potentiometric titration with potentiometric pH control in the system chloroform-aqueous electrolyte solution was used to determine basicity constants for octamethyl-substituted tetraphenylporphyrins. The pH ranges were determined, where the dicationic form of octa- and dodecamethylsubstituted tetraphenylporphyrins is prevailing. It was shown that the basicity of tetraphenylporphyrins is increased by methyl substitution of β-hydrogens (formation of octamethyl-substituted tetraphenylporphyrins). Further methylation of the four central nitrogen atoms of the porphyrin (formation of dodecamethyl-substituted tetraphenylporphyrins) extends the dication stability pH range to 12.     

Complexing ability of dimeric zinc octaalkylporphyrinates with a poly(ethyleneoxy) bridge toward 1,4-diazabicyclo[2.2.2]octane and 1,4-diazine

The formation of “guest-host” complexes from dimeric zinc octaalkylporphyrinates with a poly(ethyleneoxy) bridge and various bidentate ligands containing two N atoms was studied by spectrophotometric titration and ¹H NMR spectroscopy in toluene-methanol (5: 1). The reactions of dimeric porphyrinates with 1,4-diazabicyclo[2.2.2]octane and 1,4-diazine gave 1: 1 or 1: 2 complexes, depending on the molar ratio of metal porphyrin and the ligand. The stability constants of the complexes obtained and the concentration ranges for their formation were determined.     

Determination des constantes d'equilibre conditionnelles et des constantes de vitesse des reactions entre le selenium(IV) et cinq orthodiamines aromatiques

The conditional equilibrium and rate constants, at various pH values, of the reaction between selenium(IV) and five aromatic orthodiamines, were determined. A main reaction of second order occurs first between the monoprotonated species of the diamine and the non-dissociated selenious acid. The hydrogen selenite ion and the diprotonated diamine can also react but more slowly. The reaction products are very stable.     

吸电子取代基(2-硝基)金属卟啉的轴向加合反应的研究

本文报道了用电子吸收光谱和电化学方法系统地研究卟啉环上具有吸电子取代基(—NO_2)的四苯基卟啉[H_2TP(2-NO_2)P]的Zn、Ni、Cu、Co、Mn、Fe的配合物与一系列含N有机碱的加合作用,测定了加合常数、加合分子数,总结了吸电子基团对金属卟啉的轴向效应以及中心金属离子和卟啉环氧化还原性的影响。