Mechanistic studies of (porphinato)iron-catalyzed isobutane oxidation. Comparative studies of three classes of electron-deficient porphyrin catalysts

We report herein a comprehensive study of (porphinato)iron [PFe]-catalyzed isobutane oxidation in which molecular oxygen is utilized as the sole oxidant; these catalytic reactions were carried out and monitored in both autoclave reactors and sapphire NMR tubes. In situ 19F and 13C NMR experiments, coupled with GC analyses and optical spectra obtained from the autoclave reactions have enabled the identification of the predominant porphyrinic species present during PFe-catalyzed oxidation of isobutane. Electron-deficient PFe catalysts based on 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin [(C6F5)4PH2], 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(pentafluorophenyl) porphyrin [Br8(C6F5)4PH2], and 5,10,15,20-tetrakis(heptafluoropropyl) porphyrin [(C3F7)4PH2] macrocycles were examined. The nature and distribution of hydrocarbon oxidation products show that an autoxidation reaction pathway dominates the reaction kinetics, consistent with a radical chain process. For each catalytic system examined, PFeII species were shown not to be stable under moderate O2 pressure at 80 degrees C; in every case, the PFeII catalyst precursor was converted quantitatively to high-spin PFeIII complexes prior to the observation of any hydrocarbon oxidation products. Once catalytic isobutane oxidation is initiated, all reactions are marked by concomitant decomposition of the porphyrin-based catalyst. In situ 17O NMR spectroscopic studies confirm the incorporation of 17O from labeled water into the oxidation products, implicating the involvement of PFe-OH in the catalytic cycle. Importantly, Br8(C6F5)4PFe-based catalysts, which lack macrocycle C-H bonds, do not exhibit augmented stability with respect to analogous catalysts based on (C6F5)4PFe and (C3F7)4PFe species. The data presented are consistent with a hydrocarbon oxidation process in which PFe complexes play dual roles of radical chain initiator, and the species responsible for the catalytic decomposition of organic peroxides. This modified Haber-Weiss reaction scheme provides for the decomposition of tert-butyl hydroperoxide intermediates via reaction with PFe-OH complexes; the PFeIII species responsible for hydroperoxide decomposition are regenerated by reaction of PFeII with dioxygen under these experimental conditions.     

Androgynous porphyrins. Silver(II) quinoxalinoporphyrins act as both good electron donors and acceptors

The metal-centered and macrocycle-centered electron-transfer oxidations and reductions of silver(II) porphyrins were characterized in nonaqueous media by electrochemistry, UV-vis spectroelectrochemistry, EPR spectroscopy, and DFT calculations. The investigated compounds are {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrinato}silver(II), {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b']porphyrinato}silver(II), {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b':7,8-b']porphyrinato}silver(II), and {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b':12,13-b']porphyrinato}silver(II). The first one-electron oxidation and first one-electron reduction both occur at the metal center to produce stable compounds with Ag(III) or Ag(I) metal oxidation states, irrespective of the type of porphyrin ligand. The electrochemical HOMO-LUMO gap, determined by the difference in the first oxidation and first reduction potentials, decreases by introduction of quinoxaline groups fused to the Ag(II) porphyrin macrocycle. This provides a unique androgynous character to Ag(II) quinoxalinoporphyrins that enables them to act as both good electron donors and good electron acceptors, something not previously observed in other metalloporphyrin complexes. The second one-electron oxidation and second one-electron reduction of the compounds both occur at the porphyrin macrocycle to produce Ag(III) porphyrin pi-radical cations and Ag(I) porphyrin pi-radical anions, respectively. The macrocycle-centered oxidation potentials of each quinoxalinoporphyrin are shifted in a negative direction, while the macrocycle-centered reduction potentials are shifted in a positive direction as compared to the same electrode reactions of the porphyrin without the fused quinoxaline ring(s). Both potential shifts are due to a stabilization of the radical cations and radical anions by pi-extension of the porphyrin macrocycle after fusion of one or two quinoxaline moieties at the beta-pyrrolic positions of the macrocycle. Introduction of quinoxaline groups fused to the Ag(II) porphyrin macrocycle provides a unique androgynous character to Ag(II) quinoxalinoporphyrins that enables them to act as both good electron donors and good electron acceptors.     

Triplet pi-diradical dication of directly meso-beta-linked porphyrin dimer

Directly linked bisporphyrin, Zn(II)2 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)-2-(10,15,20-tris(3,5-di-tert-butylphenyl)porphyrin-5-yl)porphyrin, was investigated on the basis of the magnetic property of its bis(pi-radical cation). A stable triplet state of the bis(pi-radical cation) of the bisporphyrin, which obeys the Curie law, was successfully observed.     

Peroxynitrite decomposition activity of iron porphyrin complexes

Peroxynitrite (ONOO(-)/ONOOH), a putative cytotoxin formed by combination of nitric oxide (NO.) and superoxide (HO(2)(.)) radicals, is decomposed catalytically by micromolar concentrations of water-soluble Fe(III) porphyrin complexes, including 5,10,15,20-tetrakis(2',4',6'-trimethyl-3,5-disulfonatophenyl)porphyrinatoferrate(7-), Fe(TMPS); 5,10,15,20-tetrakis(4'-sulfonatophenyl)porphyrinatoiron(3-), Fe(TPPS); and 5,10,15,20-tetrakis(N-methyl-4'-pyridyl) porphyrinatoiron(5+), Fe(TMPyP). Spectroscopic (UV-visible), kinetic (stopped-flow), and product (ion chromatography) studies reveal that the catalyzed reaction is a net isomerization of peroxynitrite to nitrate (NO(3)(-)). One-electron catalyst oxidation forms an oxoFe(IV) intermediate and nitrogen dioxide, and recombination of these species is proposed to regenerate peroxynitrite or to yield nitrate. Michaelis-Menten kinetics are maintained accordingly over an initial peroxynitrite concentration range of 40-610 microM at 5.0 microM catalyst concentrations, with K(m) in the range 370-620 microM and limiting turnover rates in the range of 200-600 s(-1). Control experiments indicate that nitrite is not a kinetically competent reductant toward the oxidized intermediates, thus ruling out a significant role for NO(2)(.) hydrolysis in catalyst turnover. However, ascorbic acid can intercept the catalytic intermediates, thus directing product distributions toward nitrite and accelerating catalysis to the oxidation limit. Additional mechanistic details are proposed on the basis of these and various other kinetic observations, specifically including rate effects of catalyst and peroxynitrite concentrations, solution pH, and isotopic composition.     

Selective oxidation of ethylbenzene catalyzed by fluorinated metalloporphyrins with molecular oxygen

This paper reported the oxidation of ethylbenzene catalyzed by fluorinated metalloporphyrins under mild conditions without any additives.The results showed that the cobalt(Ⅱ)(5,10,15,20-tetrakis(pentafluorophenyl))porphyrin was the best catalyst among the fluorinated metalloporphyrins.The conversion of ethylbenzene reached 38.6%,the selectivity to acetophenone reached 94.0%,and the turnover number is 2719 under the optimal conditions.     

Ligand Fluorination to Optimize Preferential Oxidation (PROX) of Carbon Monoxide by Water-Soluble Rhodium Porphyrins

Catalytic, low temperature preferential oxidation (PROX) of carbon monoxide by aqueous [5,10,15,20-tetrakis(4-sulfonatophenyl)-2,3,7,8,12,13,17,18-octafluoroporphyrinato]rhodium(III) tetrasodium salt, (1[Rh(III)]) and [5,10,15,20-tetrakis(3-sulfonato-2,6-difluorophenyl)-2,3,7,8,12,13,17,18-octafluoroporphyrinato]rhodium(III) tetrasodium salt, (2[Rh(III)]) is reported. The PROX reaction occurs at ambient temperature in buffered (4 ≤ pH ≤ 13) aqueous solutions. Fluorination on the porphyrin periphery is shown to increase the CO PROX reaction rate, shift the metal centered redox potentials, and acidify ligated water molecules. Most importantly, β-fluorination increases the acidity of the rhodium hydride complex (pK(a) = 2.2 ± 0.2 for 2[Rh-D]); the dramatically increased acidity of the Rh(III) hydride complex precludes proton reduction and hydrogen activation near neutral pH, thereby permitting oxidation of CO to be unaffected by the presence of H(2). This new fluorinated water-soluble rhodium porphyrin-based homogenous catalyst system permits preferential oxidation of carbon monoxide in hydrogen gas streams at 308 °K using dioxygen or a sacrificial electron acceptor (indigo carmine) as the terminal oxidant.     

固载化阳离子金属卟啉/杂多阴离子复合催化剂在分子氧氧化乙苯过程中的催化特性

以交联聚苯乙烯微球(CPS)为基质载体, 采用同步合成与固载的方法, 简捷地制得了固载化阳离子苯基卟啉, 继而通过与钴盐的配合反应, 制备了固载化阳离子钴卟啉. 在此基础上, 以Keggin 型杂多酸磷钨酸(HPW)及磷钼酸(HPMo)为试剂, 凭借阳离子钴卟啉(CoP)与杂多阴离子之间的静电相互作用, 制备与表征了固载化的由阳离子钴卟啉与杂多阴离子复合而成的固体催化剂CoPPW-CPS和CoPPMo-CPS. 将两种复合催化剂用于分子氧氧化乙苯的氧化反应, 考察研究了催化特性. 结果表明: 在分子氧氧化乙苯的氧化反应中, 复合催化剂具有很高的催化活性, 可使乙苯高选择性地转化为苯乙酮, 反应12 h, 苯乙酮的产率达30.1%; 复合催化剂的催化活性比单纯的固载化钴卟啉高75%; CoPPW-CPS的催化活性高于CoPPMo-CPS. 在复合催化剂结构组分中, 固载化的杂多阴离子并无催化活性, 起催化作用的组分是钴卟啉; 但是, 杂多阴离子可有效保护钴卟啉, 使其免于被氧化失活, 从而使其保持稳定的高催化活性. 复合催化剂具有最适宜的投加量, 过量催化剂的加入, 会抑制钴卟啉的催化活性. 复合催化剂还具有良好的循环使用性能.     

Synthesis and spectral properties of cobalt(II) and cobalt(III) tetraarylporphyrinates

Reactions of 5,10,15,20-tetraphenylporphin, 5,10,15,20-tetra(4′-methoxyphenyl)porphyrin, and 5,10,15,20-tetra(4′-chlorophenyl)porphyrin with cobalt(II) acetate in dimethylformamide were studied by spectrophotometry. The corresponding cobalt(II) porphyrinates were synthesized and identified. The corresponding cobalt porphyrinates in +3 oxidation state were obtained by reaction of cobalt(II) 5,10,15,20-tetraphenylporphyrinate and cobalt(II) 5,10,15,20-tetra(4′-methoxyphenyl)porphyrinate with 2,3-dichloro-5,6-dicyano-p-benzoquinone in chloroform. The oxidation of cobalt(II) 5,10,15,20-tetra(4′-chlorophenyl)porphyrinate with hydrochloric acid in dimethylformamide leads to cobalt(III) porphyrinate.     

Synthesis and characterization of transition metal complexes of dimeric N-confused porphyrin linked by an o-xylene fragment

Insertion of nickel(II), zinc, cadmium, or silver(III) into both macrocyclic crevices of 2,2'-o-xylene-bis(5,10,15,20-tetrakis(p-tolyl)-2-aza-21-carbaporphyrin) results in homometallic dimeric complexes which were isolated and characterized by NMR, UV-vis, mass spectrometry, and cyclic voltammetry. The 1H NMR study of these systems at low temperatures (203-233 K) allowed determination of most stable conformers with respect to a rotational freedom around the xylene bridge. An unfolded conformation for the dicationic bis(silver(III)) complex was determined on the basis of 2D nuclear Overhauser effect spectrometry experimentation. A mixture of nonequally populated diastereomers is observed for bis(zinc) and bis(cadmium) complexes due to a possibility of two different orientations of the apical anionic ligands with respect to the bridge. In a reaction of 5,10,15,20-tetrakis(p-tolyl)-2-aza-21-carbaporphyrinato nickel(II) with 2-(o-bromoxylene)-5,10,15,20-tetrakis(p-tolyl)-2-aza-21-carbaporphyrin in the presence of a proton scavenger, two isomeric bis(N-confused porphyrin) complexes with one subunit "empty" and the other metalated by nickel(II) were obtained. In the product 10, the o-xylene links external nitrogens of the subunits while product 11 consists of the xylene bridge between external nitrogen of the nonmetalated subunit and internal carbon of the fragment containing a nickel(II) ion. The products were characterized by mass spectrometry, UV-vis, NMR, and, in the case of complex 11, also by X-ray crystallographic analysis (space group P1, a =17.007(3), b = 18.130(3), c = 18.797(2) A, alpha = 105.856(13) degrees, beta = 107.447(13) degrees, gamma = 98.818(15) degrees, V = 5141.1(15) A3, Z = 2). Insertion of zinc or silver(III) into an empty crevice of 10 resulted in heterometallic zinc-nickel(II) or silver(III)-nickel(II) complexes 12 or 13, respectively, which were characterized by NMR, UV-vis, and cyclic voltammetry. The subunits in the bis(porphyrin) systems retain spectroscopic and redox properties typical for monomeric complexes.     

Synthesis and Spectral and Coordination Properties of meso-Tetraarylporphyrins

Russian Journal of Organic Chemistry - 5,10,15,20-Tetrakis(3,5-dibromophenyl)porphyrin and 5,10,15,20-tetrakis(3-bromo-4-methoxy-phenyl)porphyrin have been synthesized, and their complexing...     

四(4－N-吡啶基)卟啉衍生物的合成及表征

阳离子卟啉配体;配合物;还原电位;四(4－N-吡啶基)卟啉衍生物的合成及表征     

New class of potent catalysts of O2.-dismutation. Mn(III) ortho-methoxyethylpyridyl- and di-ortho-methoxyethylimidazolylporphyrins

Three new Mn(III) porphyrin catalysts of O2.-dismutation (superoxide dismutase mimics), bearing ether oxygen atoms within their side chains, were synthesized and characterized: Mn(III) 5,10,15,20-tetrakis[N-(2-methoxyethyl)pyridinium-2-yl]porphyrin (MnTMOE-2-PyP(5+)), Mn(III)5,10,15,20-tetrakis[N-methyl-N'-(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTM,MOE-2-ImP(5+)) and Mn(III) 5,10,15,20-tetrakis[N,N'-di(2-methoxyethyl)imidazolium-2-yl]porphyrin (MnTDMOE-2-ImP(5+)). Their catalytic rate constants for O2.-dismutation (disproportionation) and the related metal-centered redox potentials vs. NHE are: log k(cat)= 8.04 (E(1/2)=+251 mV) for MnTMOE-2-PyP(5+), log k(cat)= 7.98 (E(1/2)=+356 mV) for MnTM,MOE-2-ImP(5+) and log k(cat)= 7.59 (E(1/2)=+365 mV) for MnTDMOE-2-ImP(5+). The new porphyrins were compared to the previously described SOD mimics Mn(III) 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP(5+)), Mn(III) 5,10,15,20-tetrakis(N-n-butylpyridinium-2-yl)porphyrin (MnTnBu-2-PyP(5+)) and Mn(III) 5,10,15,20-tetrakis(N,N'-diethylimidazolium-2-yl)porphyrin (MnTDE-2-ImP(5+)). MnTMOE-2-PyP(5+) has side chains of the same length and the same E(1/2), as MnTnBu-2-PyP(5+)(k(cat)= 7.25, E(1/2)=+ 254 mV), yet it is 6-fold more potent a catalyst of O2.-dismutation , presumably due to the presence of the ether oxygen. The log k(cat)vs. E(1/2) relationship for all Mn porphyrin-based SOD mimics thus far studied is discussed. None of the new compounds were toxic to Escherichia coli in the concentration range studied (up to 30 microM), and protected SOD-deficient E. coli in a concentration-dependent manner. At 3 microM levels, the MnTDMOE-2-ImP(5+), bearing an oxygen atom within each of the eight side chains, was the most effective and offered much higher protection than MnTE-2-PyP(5+), while MnTDE-2-ImP(5+) was of very low efficacy.     

Synthesis and nanostructures of 5,10,15,20-tetrakis(4-piperidyl)porphyrin

A new water-soluble porphyrin, 5,10,15,20-tetrakis(4-piperidyl)porphyrin (T(4-Pip)P), has been synthesized. T(4-Pip)P is related to the extensively studied water-soluble porphyrin 5,10,15,20-tetrakis(4-pyridyl)porphyrin (T(4-Py)P) but has substituents with different electronic and hydrogen-bonding properties and is soluble over a much larger pH range due to the higher pK_a of its conjugate acid T(4-H-Pip)P⁴⁺. Investigations of the ionic self-assembly reactions of T(4-H-Pip)P⁴⁺ with anionic water-soluble porphyrins reveal that it forms nanoscale materials.     

Oxidation of 2,6-Di-tert-butylphenol by dioxygen catalyzed by tetrasodium phthalocyaninatocobalt(II) tetrasulfonate in aqueous micellar media

The oxidation of 2,6-di-tert-butylphenol by dioxygen has been investigated in aqueous micellar aggregates of cetyltrimethylammonium bromide (CTAB) using tetrasodium phthalocyaninatocobalt(II) tetrasulfonate (CoPcTsNa₄) as catalyst. The CTAB/CoPcTsNa4 system showed enhanced catalytic activity in the oxidation of 2,6-di-tert-butylphenol compared to that observed in the oxidation reaction in the absence of CTAB. 2,6-Di-tert-butyl-1,4-benzoquinone and 3,5,3′,5′-tetra-tert-butyl-4,4-diphenoquinone were identified as reaction products. The initial rate constants of auto-oxidation reaction was found to increase with increasing the pH range from 7.0 to 13.0. The rate constants k_obs of auto-oxidation reaction showed linear dependence on catalyst concentration. The rate of auto-oxidation reaction was found to fit a Michealis-Menten kinetic model for the saturation of catalyst sites with increasing 2,6-di-tert-butylphenol concentration and dioxygen pressure. Tetrasodium phthalocyaninatocobalt(II) tetrasulfonate in aqueous micellar solution of CTAB was found to be mainly monomeric.     

Methoxy-isoporphyrins of water-soluble porphyrins: synthesis,characterization and electrochemical properties

Abstract

Methoxy-isoporphyrins of zinc [5,10,15,20-tetrakis(4-sulfonatophenyl)]porphyrin, ZnTSPP (1a) and zinc [5,10,15,20-tetrakis(4-carboxyphenyl)]porphyrin, ZnTCPP (1b) have been synthesized and characterized using standard spectroscopic techniques (Uv-visible, ¹H NMR) , ESI-mass spectrometry and powder X-ray diffraction studies. The isoporphyrins [5-(methoxy)-5,10,15,20-tetrakis(4-sulfonatophenyl)-5H,15H-porphinato]zinc(II) (2a) and [5-(methoxy)-5,10,15,20-tetrakis(4-carboxyphenyl)-5H,21H-porphinato]zinc(II) (2b) are formed due to nucleophilic attack of the methanol to the zinc porphyrin dication. Ceric ammonium nitrate (CAN) was used to oxidize zinc porphyrin and to form zinc porphyrin dication. The electronic spectra of the isoporphyrin complexes 2a and 2b exhibit an intense peak at near IR region . Electrochemical measurements of the synthesized isoporphyrins showed a typical irreversible reduction peak at lower potential. S-containing nucleophiles, which work as reducing agents, convert the zinc isoporphyrins to their parent porphyrins, which supports the electrochemical observations. Their structural properties have been studied using powder X-ray diffraction. The luminescence properties of isoporphyrins were compared with the parent zinc porphyrins.     

Radical polymerization of methyl methacrylate in the presence of Fe(III) and Co(III) porphyrins

The free-radical polymerization of methyl methacrylate in the presence of chlorine-containing complexes of Fe(III) with 5,10,15,20-tetrakis(3′,5′-di-tert-butylphenyl)porphyrin and 5,10,15,20-tetrakis(3′-butoxyphenyl)porphyrin, as well as in the presence of the acetate complex of Co(III) 5,10,15,20-tetrakis(3′,5′-di-tert-butylphenyl)porphyrin, has been investigated. The kinetic features of the process and the molecular mass characteristics of polymers are studied, and a feasible polymerization mechanism is proposed.     

Photophysical investigations on non-covalently linked fullerene/tetraarylporphyrin supramolecular complexes

The host-guest interactions of various tetraarylporphyrins (TP), viz., 5,10,15,20-tetraphenyl-21H,23H-porphyrin (1), 5,10,15,20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (2) and 5,10,15,20-tetrakis(dodecyloxyphenyl)-21H,23H-porphyrin (3) with C60 and C70 have been studied by 1H NMR, UV-vis and fluorescence spectroscopic techniques in toluene medium. All the fullerene/porphyrin complexes are found to be stable with 1:1 stoichiometry. Binding constants (K) of all the fullerene/porphyrin complexes have been determined by fluorescence quenching experiment. The trend in K values revealed that the presence of long chain n-alkyl group in tetraarylporphyrin effectively and remarkably increases the selectivity ratio of C70 over C60. Theoretical calculations have extended a good support in interpreting the stability difference between various fullerene/TP complexes.     

Dioxygen Affinity and Catalytic Performance of Bis-(furaldehyde) Schiff Bases Co(II) Complexes in Cyclohexene Oxidation

As mimetic oxygen carrier or oxidation catalyst, Schiff base cobalt complexes such as Co (II) salen have been widely studied1-4. However their high-price greatly limited their application. The synthesis of cheap furaldehyde Schiff bases and their complexes with Co (II), as well as the dioxygen affinity and biomimetic catalytic oxidation performance of these complexes are worth trying to study. In this paper, the saturated dioxygen uptake of cobalt complexes with different bis-(furaldehyd…     

Monolayers as models for supported catalysts: zirconium phosphonate films containing manganese(III) porphyrins

Organized monolayer films of a manganese tetraphenylporphyrin have been prepared and used as supported oxidation catalysts. Manganese 5,10,15,20-tetrakis(tetrafluorophenyl-4'-octadecyloxyphosphonic acid) porphyrin (1) has been immobilized as a monolayer film by a combination of Langmuir-Blodgett (LB) and self-assembled monolayer techniques that use zirconium phosphonate linkages to bind the molecule to the surface. Analysis by FTIR, XPS, UV-vis and polarized optical spectroscopy show that the films consist of noninteracting molecules effectively anchored and oriented nearly parallel to the surface. The monolayer films are stable to the solvent and temperature conditions needed to explore organic oxidations. The activity of films of 1 toward the epoxidation of cyclooctene using iodosylbenzene as the oxidant was compared to that of Manganese 5,10,15,20-tetrakis(pentafluorophenyl) porphyrin (2) and 1 under equivalent homogeneous conditions. The immobilized porphyrin 1 shows an enhanced activity relative to either homogeneous reaction. The main difference between 1 and 2 is the four alkyl phosphonate arms in 1 designed to incorporate the porphyrin within the films. The increased activity of immobilized 1 is a combination of the porphyrin structure, which prohibits the formation of mu-oxo dimers even in solution, and a change in conformation when anchored to the surface. The study demonstrates that careful monolayer studies can provide useful models for the design and study of supported molecular catalyst systems.     

Molecular imprinting inside dendrimers

Synthetic hosts capable of binding porphyrins have been produced by a mixed-covalent-noncovalent imprinting process wherein a single binding site is created within cross-linked dendrimers. Two synthetic hosts were prepared, using as templates 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin and 5,10,15,20-tetrakis(3,5-dihydroxyphenyl)porphyrin. These two templates were esterified with, respectively, fourth- and third-generation Fréchet-type dendrons containing homoallyl end-groups. The resulting tetra- and octadendron macromolecules underwent the ring-closing metathesis reaction using Grubbs' Type I catalyst, RuCl(2)(P(C(6)H(5))(3))(2)(CHCH(2)C(6)H(5)), to give extensive interdendron cross-linking. Hydrolytic removal of the porphyrin cores afforded imprinted hosts whose ability to bind porphyrins with various peripheral substituents was investigated by UV-visible spectrophotometric titrations and size exclusion chromatography. The results indicate a high yield of imprinted sites that show high selectivity for binding of porphyrins capable of making at least four hydrogen bonds, but only a moderate degree of shape selectivity.