Strong Induced-Fit Binding of Viologen and Pyridine Derivatives in Adjustable Porphyrin Cavities

Novel and Innovative Interface as Potential Active Layer in Chem-FET Sensor Devices for the Specific Sensing of Cs. ACS APPLIED MATERIALS & INTERFACES 2019;11:47635-47641. [PMID: 31769645 DOI: 10.1021/acsami.9b18188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

An innovative novel interface has been designed and developed to be used as a potential active layer in chemically sensitive field-effect transistor (Chem-FET) sensor devices for the specific sensing of Cs⁺. In this study, the synthesis of a specific Cs⁺ probe based on calix[4]arene benzocrown ether, its photophysical properties, and its grafting onto a single lipid monolayer (SLM) recently used as an efficient ultrathin organic dielectric in Chem-FETs are reported simultaneously. On the basis of both optical and NMR titration experiments, the probe has shown high selectivity and specificity for Cs⁺ compared to interfering cations, even if an admixture is used. Additionally, Attenuated Total Reflectance Fourier Transform Infra Red (ATR-FTIR) spectroscopy was successfully used to characterize and prove the efficient grafting of the probe onto a SLM and the formation of the innovative novel sensing layer.

Crystal structure of (15,20-bis-(2,3,4,5,6-penta-fluoro-phen-yl)-5,10-{(4-methyl-pyridine-3,5-di-yl)bis-[(sulfanediyl-methyl-ene)[1,1'-biphen-yl]-4',2-di-yl]}porphyrinato)nickel(II) di-chloro-methane x-solvate (x > 1/2)

The title compound, [Ni(C64H33F10N5S2)]·xCH2Cl2, consists of discrete NiII porphyrin complexes, in which the five-coordinate NiII cations are in a distorted square-pyramidal coordination geometry. The four porphyrin nitro-gen atoms are located in the basal plane of the pyramid, whereas the pyridine N atom is in the apical position. The porphyrin plane is strongly distorted and the NiII cation is located above this plane by 0.241 (3) Å and shifted in the direction of the coordinating pyridine nitro-gen atom. The pyridine ring is not perpendicular to the N4 plane of the porphyrin moiety, as observed for related compounds. In the crystal, the complexes are linked via weak C-H⋯F hydrogen bonds into zigzag chains propagating in the [001] direction. Within this arrangement cavities are formed, in which highly disordered di-chloro-methane solvate mol-ecules are located. No reasonable structural model could be found to describe this disorder and therefore the contribution of the solvent to the electron density was removed using the SQUEEZE option in PLATON [Spek (2015 ▸). Acta Cryst. C71, 9-18].

Crystal structure of (15,20-bis-(2,3,4,5,6-penta-fluoro-phen-yl)-5,10-{(pyridine-3,5-di-yl)bis-[(sulfane-diyl-methyl-ene)[1,1'-biphen-yl]-4',2-di-yl]}porph-yrin-ato)nickel(II) di-chloro-methane x-solvate (x > 1/2) showing a rare CN5 coordination

The crystal structure of the title compound, [Ni(C63H31F10N5S2)]·xCH2Cl2 (x > 1/2), consists of Ni-porphyrin complexes that are located in general positions and di-chloro-methane solvent mol-ecules that are disordered around centers of inversion. The NiII ions are in a square-pyramidal (CN5) coordination, with four porphyrin N atoms in the equatorial and a pyridine N atom in the apical position and are shifted out of the porphyrine N4 plane towards the coordinating pyridine N atom. The pyridine substituent is not exactly perpendicular to the N4 plane with an angle of inter-section between the planes planes of 80.48 (6)°. The di-chloro-methane solvent mol-ecules are hydrogen bonded to one of the four porphyrine N atoms. Two complexes are linked into dimers by two symmetry-equivalent C-H⋯S hydrogen bonds. These dimers are closely packed, leading to cavities in which additional di-chloro-methane solvent mol-ecules are embedded. These solvent mol-ecules are disordered and because no reasonable split model was found, the data were corrected for disordered solvent using the PLATON SQUEEZE routine [Spek (2015 ▸). Acta Cryst. C71, 9-18].

Porphyrin cage compounds based on glycoluril – from enzyme mimics to functional molecular machines

This Feature Article gives an overview of the application of glycoluril-based porphyrin cage compounds in host–guest chemistry, allosterically controlled self-assembly, biomimetic catalysis, and polymer encoding.

Central metal dependent modulation of induced-fit gas uptake in molecular porphyrin solids

The induced-fit accommodation of a variety of gaseous molecules including non-polar molecules has been demonstrated in porphyrin-based supramolecular architectures for the first time. Moreover, the gas uptake behaviour can be modulated by changing the central cation of porphyrin.

Unexpected Interactions between Alkyl Straps and Pyridine Ligands in Sulfur-Strapped Porphyrin Nanorings

Strapped or “basket-handle” porphyrins have been investigated previously as hemoglobin mimics and catalysts. The facial selectivity of their interactions with axial ligands is a sensitive test for noncovalent bonding. Here the binding of pyridyl ligands to zinc porphyrins with thioester-linked alkyl straps is investigated in solution by NMR spectroscopy and UV–vis titration, and in the solid state by X-ray crystallography. We expected that coordination of the axial ligand would occur on the less hindered face of the porphyrin, away from the strap. Surprisingly, attractive interactions between the strap and the ligand direct axial coordination to the strapped face of the porphyrin, except when the strap is short and tight. The strapped porphyrins were incorporated into π-conjugated cyclic porphyrin hexamers using template-directed synthesis. The strap and the sulfur substituents are located either inside or outside the porphyrin nanoring, depending on the length of the strap. Six-porphyrin nanorings with outwardly pointing sulfur anchors were prepared for exploring quantum interference effects in single-molecule charge transport.

Doubly Cavitand-Capped Porphyrin Capsule by Hydrogen Bonds

The components of a 1:2 mixture of meso-tetrakis(4-dodecyl-3,5-dihydroxyphenyl)porphyrin (1) and a bowl-shaped tetrakis(4-pyridylethynyl)cavitand (2) in CDCl3 or C6 D6 self-assemble quantitatively into the doubly cavitand-capped porphyrin capsule 2⋅1⋅2 through eight ArOH⋅⋅⋅Npy hydrogen bonds. Capsule 2⋅1⋅2 possesses two cavities divided by the porphyrin ring and encapsulates two molecules of 1-acetoxy-3,5-dimethoxybenzene (G) as a guest to form G/G@(2⋅1⋅2). Remarkable solvent effect was observed, in which the apparent association constant of 2⋅1⋅2 with G in C6 D6 was much greater than that in CDCl3.

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.

High Sensitivity Viologen for a Facile and Versatile Sensor of Base and Solvent Polarity in Solution and Solid State in Air Atmosphere

Viologen cations are excellent electro- and photochromic materials. They generally have no response or very low sensitivity to bases. In this paper, three compounds, 1,1'-bis(2-oxo-2-phenylethyl)-4,4'-bipyridinium (viologen) with different substituents, including H (1), Cl (2), and OH (3), were synthesized. All three, especially 1 and 2, have very high sensitivity to base in both solution and solid state in air atmosphere. These viologens are responsive not only to bases but also to solvent polarity. NMR shows 1 became enolic and then a radical, whereas 3 is colored only in the radical form. These results are in agreement with EPR spectra. Crystal structures show that the C-C that links two pyridinium and N-C distances in coplanar pyridinium in the colored (radical) form is clearly longer than that of the pale-yellow form, indicating that the color is due to the viologen radical. Viologens containing an electron-withdrawing phenacetyl group are the most sensitive compounds for fast, naked eye detection of base and solvent polarity.

Limitations and extensions of the lock-and-key principle: differences between gas state, solution and solid state structures

The lock-and-key concept is discussed with respect to necessary extensions. Formation of supramolecular complexes depends not only, and often not even primarily on an optimal geometric fit between host and guest. Induced fit and allosteric interactions have long been known as important modifications. Different binding mechanisms, the medium used and pH effects can exert a major influence on the affinity. Stereoelectronic effects due to lone pair orientation can lead to variation of binding constants by orders of magnitude. Hydrophobic interactions due to high-energy water inside cavities modify the mechanical lock-and-key picture. That optimal affinities are observed if the cavity is only partially filled by the ligand can be in conflict with the lock-and-key principle. In crystals other forces than those between host and guest often dominate, leading to differences between solid state and solution structures. This is exemplified in particular with calixarene complexes, which by X-ray analysis more often than other hosts show guest molecules outside their cavity. In view of this the particular problems with the identification of weak interactions in crystals is discussed.