Porphyrin Host Research Articles

Colorimetric determination of perfluorocarboxylic acids using porphyrin hosts and mobile phone photographs

Functionalized porphyrin molecules were found to change color in the presence of perfluorocarboxylic acids (PFCAs). The porphyrin molecules allow for simple visual- and color space-based detection of PFCAs across a range of concentrations.

Exploring colorimetric detection of perfluorooctane sulfonate using micelle solubilised porphyrin

The harmful pollutant perfluorooctane sulfonate (PFOS) is difficult to detect without extensive laboratory equipment used by trained personnel. Herein, we report the use of a micelle-encapsulated porphyrin host molecule as a rapid colorimetric indicator for PFOS and its anionic salts. A range of common commercially available surfactants were tested and optimised to encapsulate the hydrophobic highly pigmented porphyrin sensor molecule. This method was used for the detection of PFOS in aqueous solutions at concentrations as low as 3 ppm. Colour space RGB information was extracted from a mobile phone photograph and parameterised, allowing for threshold PFOS detection, demonstrating the applicability of this method as an easily accessible approach to inform an untrained user.

Thiourea Organocatalysts as Emerging Chiral Pollutants: En Route to Porphyrin-Based (Chir)Optical Sensing

Environmental pollution with chiral organic compounds is an emerging problem requiring innovative sensing methods. Amino-functionalized thioureas, such as 2-(dimethylamino)cyclohexyl-(3,5-bis(trifluoromethyl)phenyl)thiourea (Takemoto’s catalyst), are widely used organocatalysts with virtually unknown environmental safety data. Ecotoxicity studies based on the Vibrio fischeri luminescence inhibition test reveal significant toxicity of Takemoto’s catalyst (EC50 = 7.9 mg/L) and its NH2-substituted analog (EC50 = 7.2–7.4 mg/L). The observed toxic effect was pronounced by the influence of the trifluoromethyl moiety. En route to the porphyrin-based chemosensing of Takemoto-type thioureas, their supramolecular binding to a series of zinc porphyrins was studied with UV-Vis and circular dichroism (CD) spectroscopy, computational analysis and single crystal X-ray diffraction. The association constant values generally increased with the increasing electron-withdrawing properties of the porphyrins and electron-donating ability of the thioureas, a result of the predominant Zn⋯N cation–dipole (Lewis acid–base) interaction. The binding event induced a CD signal in the Soret band region of the porphyrin hosts—a crucial property for chirality sensing of Takemoto-type thioureas.

Porphyrin bearing phenothiazine pincers as hosts for fullerene binding via concave–convex complementarity: synthesis and complexation study

Free base porphyrin hosts, m-(PTZ)4-H2P and p-(PTZ)4-H2P, tethered with four phenothiazine moieties at the meso-position via a flexible ethoxy phenyl linker were synthesized and used for the selective complexation of fullerenes, C60 and C70.

Supramolecular chirogenesis in zinc porphyrins: Complexation with enantiopure thiourea derivatives, binding studies and chirality transfer mechanism

Complexation of three (1[Formula: see text],2[Formula: see text]-2-aminocyclohexyl arylthioureas (aryl [Formula: see text] 3,5-bis(trifluoromethyl)phenyl; phenyl; 3,5-dimethylphenyl) as the guests to ZnTPP and ZnOEP hosts has been studied by means of UV-vis, CD spectroscopies and computational simulation. The complexation proceeds via coordination of the primary amino group to the zinc ion of the metalloporphyrin and induces a moderate circular dichroism signal in the Soret band of the porphyrins. The association constants increase with larger electron-withdrawing properties of the porphyrin host and larger electron-donating ability of the guest, indicating predominantly electrostatic (Lewis acid-base) character of the complexation. Computational study of the (1[Formula: see text],2[Formula: see text]-2-aminocyclohexyl-(3,5-bis(trifluoromethyl)phenyl)thiourea and ZnTPP complex revealed slight asymmetric distortion of the porphyrin plane caused by the chiral guest and additional [Formula: see text]–[Formula: see text] interactions between the host and guest molecules. The calculated CD spectrum for the same system reproduces the experimentally observed one.

Supramolecular Hybrid Material Based on Engineering Porphyrin Hosts for an Efficient Elimination of Lead(II) from Aquatic Medium.

Porphyrins show great promise for future purification demands. This is largely due to their unique features as host binding molecules that can be modified at the synthetic level, and largely improved by their incorporation into inorganic based materials. In this study, we assessed the efficacy of a hybrid material obtained from the immobilization of 5,10,15,20-tetrakis(pentafluorophenyl)-porphyrin on silica surface to remove Pb(II), Cu(II), Cd(II), and Zn(II) ions from water. The new organic-inorganic hybrid adsorbent was fully characterized by adequate techniques and the results show that the hybrid exhibits good chemical and thermal stability. From batch assays, it was evaluated how the efficacy of the hybrid was affected by the pH, contact time, initial metal concentration, and temperature. The adsorption kinetic and isotherms showed to fit the recent developed fractal-like pseudo-second-order model and Langmuir–Freundlich model respectively. The highest adsorption capacities for Pb(II), Cu(II), Cd(II), and Zn(II) ions were 187.36, 125.17, 82.45, and 56.23 mg g−1, respectively, at pH 6.0 and 25 °C. This study also shows that metal cations from real river water samples can be efficient removed in the presence of the new adsorbent material.

Directional threading of a chiral porphyrin cage compound onto viologen guests.

We report the face-selective threading of a chiral porphyrin cage compound onto viologen guests that are provided on both ends with substituents of different sizes. Depending on the types of terminal groups on the guest the cage compound orients itself in one of two possible directions.

Host-Guest Assembly of a Molecular Reporter with Chiral Cyanohydrins for Assignment of Absolute Stereochemistry.

The absolute stereochemistry of cyanohydrins, derived from ketones and aldehydes, is obtained routinely, in a microscale and derivatization-free manner, upon their complexation with Zn-MAPOL, a zincated porphyrin host with a binding pocket comprised of a biphenol core. The host-guest complex leads to observable exciton-coupled circular dichroism (ECCD), the sign of which is easily correlated to the absolute stereochemistry of the bound cyanohydrin. A working model, based on the ECCD signal of cyanohydrins with known configuration, is proposed.

Selective complexation of di-n-hexylammonium salts by tailed porphyrin host

A di-n-hexylammonium ion was selectively encapsulated in the cavity of tailed porphyrins due to induced fit and lipophilic interactions.

A Double‐Cavity‐Containing Porphyrin Host as a Highly Stable Epoxidation Catalyst

AbstractWe describe a manganese porphyrin catalyst containing two adjacent cavities, which can be used for the epoxidation of alkenes by sodium hypochlorite. A pyridine ligand bound in one of the cavities regulates the rate and selectivity of the epoxidation reaction that takes place in the adjoining cavity. Pyridine binding studies suggest that site‐to‐site communication exists between the two cavities. The alkene substrates are completely converted into epoxides by the manganese double‐cavity catalyst, but the observed epoxidation rates are low. These low rates are proposed to be a result of the energetically less favourable binding of the substrate into the cavity containing the active site due to an allosteric pinching effect. In the manganese double‐cavity arrangement the catalytically active manganese complex is efficiently protected against decomposition, leading to a catalytic system with enhanced stability. The presented work may open a new route to the construction of highly stable catalysts of which the activity and selectivity may eventually be controlled by allosteric interactions.

Recognition of mandelate stereoisomers by chiral porphyrin hosts: prediction of stereopreference in guest binding a priori using a simple binding model?

Rigid porphyrin hosts that mimic the spatial arrangement of mandelate recognition motifs lead to stereoselective receptors and illustrate how subtle structural differences in host design have significant impact on guest recognition. The porphyrin hosts are obtained with minimal synthetic effort from readily available chiral amine precursors and are modular in design. The chiral recognition properties of the porphyrin-based hosts with chiral carboxylate-containing guests and chiral amines are described. UV/vis and 1H NMR spectroscopic results indicate some of these porphyrin hosts undergo an induced fit conformational change upon guest binding.

L-Nipecotic Acid-Porphyrin Derivative: A Chiral Host with Introverted Functionality for Chiral Recognition

The synthesis and chiral recognition properties of a porphyrin host with introverted functionality is reported. The host is a hybrid of tetraphenyl zinc porphyrin and the N-phenylamide derivative of (S)-nipecotic acid. The chiral recognition properties of the porphyrin host with chiral carboxylate-containing guests is described. UV/vis and (1)H NMR spectroscopic results indicate the host shows enantioselectivity for (S)-mandelate tetrabutyl ammonium salt.

Enhanced Shape-Selective Recognition of Anion Guests through Complexation-Induced Organization of Porphyrin Hosts

We present a fortuitous discovery of enhanced shape-selective recognition of anion guests that stems from a complexation-induced conformational change in porphyrin hosts upon anion binding. Porphyrin hosts reported here exist in a conformation that is not favorable to guest binding. Anions that bind strongly are those that can induce a conformational change in the host to allow guest binding. Furthermore, guests that mimic the shape of the newly formed pocket bind the strongest.

Enhanced binding strengths of acyclic porphyrin hosts with endohedral metallofullerenes

The complementary use of spectroscopy and electrochemistry shed light onto the supramolecular interactions of calixarene scaffold bearing bisporphyrins 1 and 2 as hosts with a series of fullerenes –C60, Sc3N@C80, and Lu3N@C80 – as guest molecules. Importantly, the present work shows a noticeable variation in binding strength when C60 or endohedral fullerene guests are included into the bisporphyrins hosts. These sizeable differences could be clarified by computational models of the host–guest complexes, on the one hand, and a systematic investigation of the electron transfer chemistry, on the other hand. Detailed studies document an oxidative charge transfer (i.e., electron transfer from the bisporphyrin to the fullerene) for the C60 inclusion complexes, while a reductive charge transfer (i.e., electron transfer from the fullerene to porphyrin) is operative in the endohedral metallofullerene host–guest complexes.

Appending zinc tetraphenylporphyrin with an amine receptor at β-pyrrolic carbon for designing a selective histamine chemosensor

Adopting the rarely used β-functionalisation strategy in porphyrin-based sensor design, an amine receptive site is appended onto the zinc(II) porphyrin molecular framework affording a ditopic chemosensor 4. The assembled chemosensor interacts selectively with histamine in toluene via a ‘two-site’ binding mode. Association constant of the complex evaluated from the respective UV–vis spectra is found to be (2.32 ± 0.57) × 106, which is approximately 4-fold greater than those complexes derived from 4 and nicotine/histidine. On the basis of a combined spectroscopic method and molecular modelling, the binding model of the porphyrin host and biogenic guest molecules is established. Our results clearly demonstrate the viability of the design and development of the porphyrin-based chemosensor by appending a receptor at the β-pyrrolic carbon of the porphyrin scaffold.

Tetrapyrrolic compounds as hosts for binding of halides and alkali metal cations

In this paper the binding of halides and alkali metal cations with porphyrin hosts is reported. The halide ions are complexed with diprotonated porphyrin macrocycle with high affinity and stable complexes of 1:1 and 1:2 structures with halide ions are formed. Strong (up to 300 times) quenching of the porphyrin fluorescence has been found upon the titration of porphyrin solutions with iodide ions. It was established that both static quenching upon formation of the non-fluorescent complex and dynamic diffusion-controlled quenching took place. It is shown that the halide ions binding isotherms can be linearized with double-logarithmic plots. The alkali metal cations are trapped with mono-meso-arylporphyrins containing a conformationally mobile complexing polyether fragment on the benzene ring with a terminal pyridine ring. The alkali metal cation binding constant depends on the polyether chain length. The five-membered (n = 5) polyether chain provides very high binding selectivity for potassium over lithium or sodium. The potassium complexation constants 3.6 × 105and 7.2 × 104M-1have been obtained for Zn2+complex and diprotonated porphyrin, respectively. For signaling of the alkali cation complexation, it is proposed to use the binding between the terminal pyridine ring with either the Lewis acidic site (chelated Zn2+ion) or the diprotonated macrocycle core ( H4P2+) acting as salt bridging site.

The cage effect on assembly of cyclic-bis-(zinc porphyrin) with 5,15-dipyridylporphyrin

An inclusion complex of cyclic bis(zinc porphyrin) 1 with 5,15-dipyridylporphyrin derivative 3 has been designed and constructed. The complex formation is induced by Zn-N coordination, and is robust (Kassoc ∼ 106 L/mol) due to the presence of the cage effect of cyclic bis(zinc porphyrin). The cage-like complex as an entity is stable enough, and also convenient to achieve relative movement between the bis(zinc porphyrin) host and the dipyridylporphyrin guest connected by Zn-N coordination. The characteristics of these assemblies have been demonstrated by 1 H NMR, UV-vis, and fluorescence spectra. The results show its potential applications as a molecular gyroscope in molecular machines.

Microwave-assisted synthesis of a new series of resorcin[4]arene cavitand-capped porphyrin capsules

Capsule-shaped molecular receptors are fundamental to the modeling of biological host-guest interactions such as those characteristic of enzymatic processes. Among the more versatile and effective synthetic receptors are the hemicarcerand-type hosts. Herein we report the synthesis of six novel resorcin[4]arene cavitand-capped porphyrin capsules, in a new series of molecular capsules modeled on the classical hemicarcerands initially reported by Cram and co-workers. In the first reported instance of its utilisation in the preparation of supramolecularly-capped porphyrin host molecules, microwave (MW) irradiation was used (in conjunction with Adler conditions) in order to form the porphyrin cap in situ. Additionally, the yields obtained via these conditions exhibited a significant improvement, relative to the traditional refluxing protocol hitherto reported. Capsules 20-25 are indefinitely stable, and we observed that 22 and 25 possess the smallest rigidified cavities yet reported for resorcin[4]arene cavitand-capped porphyrin host molecules.

Iron (III) porphyrin bearing 2,6-di- tert-butylphenol pendants deposited onto gold electrodes for amperometric determination of l-histidine

A sensitive amperometric sensor for determination of l-histidine was developed using gold electrode modified with Fe(III)-porphyrin bearing three 2,6-di- tert-butylphenol groups and one palmitoyl chain. Two methods of electrode modification were applied: direct chemisorption and embedment into dodecanethiol monolayer. Both types of electrodes were used for detection of l-histidine using Osteryoung square-wave voltammetry. The sensitivity of sensors presented towards l-histidine depends on the method of electrode modification. The detection limits observed for the electrodes incorporating with Fe(III)-porphyrin host by embedment and chemisorption were in 1 and 100 nM ranges, respectively. In addition, the determination of l-histidine with electrode modified by embedment technique was more precise, in comparison to that obtained by the direct chemisorption. Applicability of gold electrodes modified with Fe(III)-porphyrin for the direct electrochemical determination of l-histidine was demonstrated using the artificial matrix mimicking human serum.

Construction of supramolecular multi-component assemblies by using allosteric interactions

Supramolecular complexes between two cavity-appended porphyrin hosts and three bifunctional guests are described. The host with a single cavity exclusively forms dimers with the bifunctional guests, while the double cavity host yields tetramers and higher order assemblies. The role of allosteric interactions in the binding and assembly process is highlighted.