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Jonathan L Sessler

Publications and source records attributed to Jonathan L Sessler.

70 records · Page 4Linked to original sources
PubMed2003

Novel guanosine-cytidine dinucleoside that self-assembles into a trimeric supramolecule.

[reaction: see text] Synthesis and assembly studies of a guanosine-cytidine dinucleoside 1 that self-assembles into a trimeric supramolecule (I) are presented. Dinucleoside 1 was obtained by utilizing two consecutive palladium-catalyzed cross-coupling reactions. Ensemble I was analyzed by ESI-MS, NMR spectroscopies, size exclusion chromatography (SEC), and vapor pressure osmometry (VPO).

Chromatography, Gel↗
PubMed2003

Single side strapping: a new approach to fine tuning the anion recognition properties of calix[4]pyrroles.

Three calix[4]pyrroles bearing m-orcinol-derived diether straps of different lengths on one side of the tetrapyrrolic core have been synthesized and characterized. Structural information for an analogous diester bridged strapped system reported previously (Yoon, D. W.; Hwang, H.; Lee, C. H. Angew. Chem., Int. Ed. Engl. 2002, 41, 1757-1759) is also provided as are bromide and chloride anion affinities for all four systems determined by Isothermal Titration Calorimetry (ITC) in acetonitrile. Although both sets of the strapped calix[4]pyrroles displayed enhanced affinities for chloride and bromide anion, differences were seen among the various receptors that support the conclusion that the anion binding ability of calixpyrrole-type systems can be effectively tuned by modifying the length and nature of the bridging straps. In the specific case of the diether systems, the largest chloride affinity was seen with the shortest strap, whereas the largest affinity for bromide anion was recorded in the case of the longest strap. On the basis of these findings, as well as supporting (1)H NMR spectroscopic studies, it is postulated that not only cavity size per se, but also the ability of the aryl portion of the strap to serve as a CH hydrogen bond donor site are important in regulating the observed anion affinities.

Anions↗
PubMed2003

Formation and properties of cyclo[6]pyrrole and cyclo[7]pyrrole.

Oxidative coupling of a tetraalkylbipyrrole under FeIII-mediated coupling conditions in the presence of HCl results in a mixture of cyclo[6]- and cyclo[7]pyrroles, as well as the known cyclo[8]pyrrole. This "matched set" of heteroannulenes was analyzed by spectroscopic, electrochemical, and X-ray diffraction methods.

Journal Article↗
PubMed2003

In vitro interaction of macrocyclic photosensitizers with intact mitochondria: a spectroscopic study.

Six water-soluble macrocyclic photosensitizers, the members of two groups of expanded porphyrins (metallotexaphyrins and free-base sapphyrins) containing hydrophilic substituents and meso-tetra(4-sulfonatophenyl)-porphyrin, were tested by UV-Vis absorption and resonance Raman spectroscopy in the in vitro binding experiments with intact mitochondria isolated from swine liver. Studied macrocycles showed markedly different affinity to mitochondria. The highest uptake was observed for sapphyrin-sugar conjugate and metallotexaphyrins. Sapphyrin-polyamine conjugates exhibit something less affinity to mitochondria, while the porphyrin of anionic character showed very low mitochondrial uptake. Obtained spectroscopic results confirm that the binding process altered the self-aggregation degree of expanded porphyrins.

Algorithms↗
PubMed2002

Quinoxaline-bridged porphyrinoids.

Quinoxaline-bridged porphyrinoids (3), the first macrocycles containing dipyrrolylquinoxaline (DPQ, 1) subunits, were synthesized from the condensation of the diformyl-substituted DPQ derivatives (2) and 1,8-diaminoanthracene. The resulting structures were confirmed by X-ray analyses, which showed encapsulation of CHCl(3) molecules within the columnar channels established by the stacked arrangement of the individual macrocycles. The solution phase interactions with fluoride and dihydrogenphosphate anions were studied in the case of the unsubstituted system 3a in CH(2)Cl(2). The binding affinities for these anions, studied at the tetrabutylammonium salts, were found to be enhanced relative to those of the simple, unsubstituted monomeric DPQ "parent" system (1a), presumably as the result of the combined effects of preorganization and cooperative binding permitted by the pyrrole NH donor groups. Positive homotropic allosteric anion binding was observed and is ascribed to the structurally coupled nature of the two binding cavities present in the macrocycles. Support for this latter contention came from energy minimization studies.

Anions↗
PubMed2002

Theoretical study of anion binding to calix[4]pyrrole: the effects of solvent, fluorine substitution, cosolute, and water traces.

The binding of different anions to calix[4]pyrrole has been studied by means of molecular dynamics coupled to thermodynamic integration calculations. The effect of different apolar solvents, octafluoro substitution, and the change in binding free energy derived from the presence of cosolute and water traces (the hydrated salt used to introduce the anion in the solution) were examined. Calculations allow us to rationalize the differential binding of ions to calix[4]pyrrole and octafluorocalix[4]pyrrole as well as to predict the behavior in new solvents for which experimental data are not available yet. It is found that both calix[4]pyrrole and octafluorocalix[4]pyrrole have a dramatic preference for F- in the gas phase and pure aprotic solvents, but the situation can change dramatically in protic solvents or in the presence of the hydrated cation which is used as cosolute of the anion. Overall, our results provide interesting clues for a better understanding of the process detected experimentally as "binding".

Anions↗
PubMed2002

Metal complexes of porphycene, corrphycene, and hemiporphycene: stability and coordination chemistry.

Porphyrin (P), porphycene (Pc), corrphycene (Cn), and hemiporphycene (Hpc) represent a series of well defined "4-N in" constitutional porphyrin isomers. These isomers, in the form of their octaethyl derivatives, represent a congruent set of porphyrinoids whose properties can be compared. In this study we report how variations in electronic structure and nitrogen-core size in the free-base forms of these four systems are reflected in the properties of their corresponding metal complexes. Specifically, the effects that these differences have on the axial ligation properties of the Zn(II), Mg(II), Ni(II), and Co(II) complexes of P, Pc, Cn, and Hpc in toluene using pyridine as the axial ligand are detailed. Also reported are the relative stabilities of these complexes under acidic conditions. It is shown that for the zinc, magnesium, and cobalt complexes, there are distinct differences in the ability to maintain four-, five-, or six-coordinate geometries in the presence of similar concentrations of pyridine. By contrast, no apparent differences in axial ligand binding affinity are seen for the four nickel complexes. Little difference in stability was likewise seen when these same complexes were subject to acid-mediated demetallation, with all four falling into stability class II, according to the accepted porphyrin stability ranking system. High stabilities were also seen in the case of the cobalt complexes, with the Pc and Cn complexes being of stability class III and the P and Hpc derivatives falling into stability class II. The Zn(II) and Mg(II) complexes were all far less stable than the corresponding Ni(II) and Co(II) complexes. In this case, semiquantitative analyses of the rate of acid-induced decomposition revealed the following stability sequence P>Cn>Hpc>Pc for both the Zn(II) and Mg(II) complexes. Single-crystal X-ray diffraction structures were solved for the Zn(II), Mg(II), and Ni(II) complexes of the octaethyl derivatives of Hpc, Cn, and Pc as well as a Co(II) octamethylcorrphycene and are reported as part of this study. These solid-state structures confirm four-coordinate species for the Ni(II) complexes, four- and five-coordinate species for the Mg(II) and Zn(II) complexes, and a six-coordinate species for the lone Co(II) complex.

Binding Sites↗
PubMed2002

Late first-row transition-metal complexes of texaphyrin.

The preparation of first-row transition-metal complexes of texaphyrin, a porphyrin-like, monoanionic penta-aza macrocyclic ligand, is reported. Specifically, the synthesis of organic-soluble Mn(II) (1), Co(II) (2), Ni(II) (3), Zn(II) (4), and Fe(III) (5) texaphyrin derivatives and their water-soluble counterparts (6-10) from appropriate metal-free, nonaromatic macrocyclic precursors is described. It was found that metal cations of sufficient reduction potential could act to oxidize the nonaromatic macrocyclic precursor in the course of metal insertion. Complexes were characterized by X-ray diffraction analysis, electrochemistry, flash photolysis, and EPR spectroscopy. The structural and electronic properties of these "expanded porphyrin" complexes are compared with those of analogous porphyrins. Notably, the texaphyrin ligand is found to support the complexation of cations in a lower valence and a higher spin state than do porphyrins. Interactions between the coordinated cation and the ligand pi system appear to contribute to the overall bonding. Texaphyrin complexes of Mn(II), Co(II), and Fe(III) in particular may possess sufficient aqueous stability to permit their use in pharmaceutical applications.

Cobalt↗
PubMed2002

Cytosine substituted calix[4]pyrroles: neutral receptors for 5'-guanosine monophosphate.

The synthesis and characterization of two cytosine-substituted calix[4]pyrrole conjugates, bearing the appended cytosine attached at either a beta- or meso-pyrrolic position, is described. These systems were tested as nucleotide-selective carriers and as active components of nucleotide-sensing ion-selective electrodes at pH 6.6. Studies of carrier selectivity were made using a Pressman-type model membrane system consisting of an initial pH 6.0 aqueous phase, an intervening dichloromethane barrier containing the calix[4]pyrrole conjugate, and a receiving basic aqueous phase. Good selectivity for the Watson-Crick complementary nucleotide, 5'-guanosine monophosphate (5'-GMP), was seen in the case of the meso-linked conjugate with the relative rates of through-membrane transport being 7.7:4.1:1 for 5'-GMP, 5'-AMP, and 5'-CMP, respectively. By contrast, the beta-substituted conjugate, while showing a selectivity for 5'-GMP that was enhanced relative to unsubstituted calix[4]pyrrole, was found to transport 5'-CMP roughly 4.5 times more quickly than 5'-GMP. Higher selectivities were also found for 5'-CMP when both the beta- and meso-substituted conjugates were incorporated into polyvinyl chloride membranes and tested as ion selective electrodes at pH 6.6, whereas near-equal selectivities were observed for 5'-CMP and 5'-GMP in the case of unsubstituted calix[4]pyrroles. These seemingly disparate results are consistent with a picture wherein the meso-substituted cytosine calix[4]pyrrole conjugate, but not its beta-linked congener, is capable of acting as a ditopic receptor, binding concurrently both the phosphate anion and nucleobase portions of 5'-GMP to the calixpyrrole core and cytosine "tails" of the molecule, respectively, with the effect of this binding being most apparent under the conditions of the transport experiments.

Calixarenes↗
PubMed2002

Missing-link macrocycles: hybrid heterocalixarene analogues formed from several different building blocks.

The synthesis and structural characterization of hybrid heterocalix[4]arene analogues containing pyrrole, benzene, methoxy-substituted benzene, and pyridine subunits is described. Macrocycles 1 and 2, examples of calix[2]benzene[2]pyrrole and calix[1]benzene[3]pyrrole systems, respectively, are synthesized by the condensation of pyrrole and an appropriate phenylbis(carbinol). Macrocycles 3 and 7, examples of calix[2]benzene[1]pyridine[1]pyrrole and calix[1]pyridine[3]pyrrole, respectively, are synthesized by the use of a carbene-based pyrrole-to-pyridine ring-expansion procedure. Single-crystal X-ray analysis reveals that compounds 1a, 1b, and 2b adopt 1,3-alternate conformations in the solid state, whereas compounds 3 and 7 display structures that are best described as "flattened partial cones" in terms of their conformation. (Series a refers to pure benzene-derived systems, whereas series b indicates macrocycles containing 5-methoxyphenyl subunits). In the solid state, the methoxy-functionalized macrocycles 1b and 2b, and the chloropyridine-containing macrocycle 7 exist as dimers. In the case of 1a and 7, these compounds interact with neutral solvent in the solid state. The conformations of the macrocycles in solution were explored by temperature-dependent proton NMR and NOESY spectral analysis. At 188 K, macrocycles 1a and 2a adopt flattened 1,3-alternate conformations, whereas macrocycles 3 and 7 exist in the form of flattened partial-cone conformations. Standard proton NMR titration analyses were carried out in the case of macrocycles 1a and 2a, and reveal that at least the second of these systems is capable of binding fluoride and chloride anions in CD(2)Cl(2) solution at room temperature (K(a)=571 and 17M(-1) in the case of 2a and F(-) and Cl(-), respectively).

Bridged-Ring Compounds↗
PubMed2002

Synthesis and biolocalization of water-soluble sapphyrins.

The synthesis, characterization, and biolocalization properties of new, fully water-soluble sapphyrins is reported. These systems, which display light absorbing features that make them of potential interest as photodynamic therapy (PDT) sensitizers, were found to localize selectively in pancreatic carcinoma tissue in a xenographic murine model. In this model, the concentration ratios for malignant tissue to surrounding muscle tissue were found to be as high as 280 in the most favorable case. The concentrations of the water-soluble sapphyrins reported here, as well as a porphyrin control system, were determined as a function of time and tissue type.

Animals↗
PubMed2002

Phenanthroline complexes bearing fused dipyrrolylquinoxaline anion recognition sites: efficient fluoride anion receptors.

Novel anion recognition host molecules, tris-1,10-phenanthroline cobalt(III) and bis-2,2'-bipyridine mono-1,10-phenanthroline ruthenium(II) complexes bearing fused dipyrrolylquinoxaline moieties have been synthesized. As determined by UV-vis spectroscopic and electrochemical studies, these metal complexes bind fluoride with high affinity in polar media both in absolute terms and relative to the metal-free phenanthroline dipyrrolylquinozaline precursor from which they are derived (fluoride is bound to the tris-1,10-phenanthroline cobalt(III) dipyrrolylquinoxaline system with a 1:1 binding constant of 54 000 M-1 in DMSO). The large observed binding constants are ascribed to two factors, (i) the presence of a phenanthroline-coordinated cationic charge that decreases the electron density on the pyrrole NH protons and (ii) pure electrostatic effects.

Anions↗