Biomedical subjects

Orde Q Munro

Publications and source records attributed to Orde Q Munro.

12 recordsLinked to original sources

PubMed2006

Synthesis, electrochemistry and luminescence of [Pt{4'-(R)trpy}(CN)](+) (R = Ph, o-CH(3)C(6)H(4), o-ClC(6)H(4) or o-CF(3)C(6)H(4); trpy = 2,2':6',2''-terpyridine): crystal structure of [Pt{4'-(Ph)trpy}(CN)]BF(4) x CH(3)CN.

The synthesis and characterization of [Pt{4'-(R)trpy}(CN)]X (R = Ph, X = BF(4) or SbF(6); R = o-CH(3)C(6)H(4), X = SbF(6); R = o-ClC(6)H(4), X = SbF(6); or R = o-CF(3)C(6)H(4), X = SbF(6)) are described where trpy = 2,2':6',2''-terpyridine. Single crystals of [Pt{4'-(Ph)trpy}(CN)]BF(4).CH(3)CN were grown by vapour diffusion of diethyl ether into an acetonitrile solution of [Pt{4'-(Ph)trpy}(CN)]BF(4). An X-ray crystal structure determination of the solvated complex confirms the near linear coordination of the cyanide ligand to the platinum centre. The cation is almost planar as evidenced by a twist of only 1.9 degrees of the phenyl group out of the plane of the terpyridyl moiety. Cyclic voltammograms were recorded in DMF/0.1 M TBAH for the [Pt{4'-(R)trpy}(CN)](+) cations. Two quasi-reversible one-electron reduction (cathodic) waves are observed with E(1/2) values that show the trend expected for an increasingly lower energy of the trpy-based LUMO of the complex i.e., [Pt{4'-(Ph)trpy}(CN)](+) approximately [Pt{4'-(o-CH(3)C(6)H(4))trpy}(CN)](+) < [Pt{4'-(o-ClC(6)H(4))trpy}(CN)](+) < [Pt{4'-(o-CF(3)C(6)H(4))trpy}(CN)](+). All the [Pt(4'-(R)trpy}(CN)](+) cations are photoluminescent in dichloromethane. Emission by [Pt{4'-(Ph)trpy}(CN)](+) is from an excited state with largely (3)MLCT orbital parentage, but with some intraligand (3)pi-pi* character mixed-in (tau = 0.1 micros). In contrast, the other three cations display emission that appears exclusively intraligand (3)pi-pi* in origin (tau approximately 0.8 micros). Emission spectra have been recorded in a low concentration frozen DME {1 : 5 : 5 (v/v) DMF-MeOH-EtOH} glass. For the R = o-CH(3)C(6)H(4), o-ClC(6)H(4) and o-CF(3)C(6)H(4) cations the envelope of vibronic structure and energies of the vibrational components are essentially the same as that recorded in dichloromethane. However, for the [Pt{4'-(Ph)trpy}(CN)](+) cation, there is a blue-shift in the energies of the vibrational components as compared to that recorded in dichloromethane, as well as a change in the envelope of vibronic structure to a more "domed" pattern; this has been interpreted in terms of a higher percentage of intraligand (3)pi-pi* character in the emitting state for the glass. Increasing the concentration of the glass invariably leads to aggregation of the cations and the consequent development of new low energy bands, such that at 0.200 mM broad peaks centred at ca. 650 and 700 nm dominate the spectrum; these bands are assigned to excimeric (3)pi-pi* and (3)MMLCT emission, respectively.

Journal Article↗

PubMed2006

Molecular recognition: preorganization of a bis(pyrrole) Schiff base derivative for tight dimerization by hydrogen bonding.

Multiple techniques have been used to delineate the self-assembly of a bis(pyrrole) Schiff base derivative (compound 4, C(16)H(14)N(4)), which forms an unusual dimer through complementary N-H...N=C hydrogen bonds between twisted, C2-symmetric monomer units. The asymmetric unit of the crystal structure comprises one and a half dimer units, with one dimer exhibiting approximate D2 point-group symmetry and the other exact D2 symmetry (space group C2/c). The dimers pack into columns whose axes are collinear with the a axis of the unit cell. The columns assemble into discrete layers with two distinct types of hydrogen-sized voids residing between the layers. Despite the promising architecture of the voids within the lattice of 4, the absence of genuine channels to interconnect the voids precludes the uptake of hydrogen gas, even at elevated pressures (10 bar). AM1 calculations of the structure of dimeric 4 indicate that self-recognition through hydrogen bonding depends primarily on favorable electrostatic interactions. The potential-energy surface for monomeric 4 mapped by counter-rotation of an adjacent pair of C=C-N=C torsion angles indicates that the X-ray structures of the four monomeric units are global minima with highly nonplanar conformations that are preorganized for self-recognition by hydrogen bonding. The in vacuo enthalpy of association for the dimer was calculated to be significantly exergonic (DeltaG(assoc)=-21.9 kJ mol(-1), 298 K) and in excellent agreement with that determined by 1H NMR spectroscopy in CDCl3 (DeltaG(assoc)=-16.6(4) kJ mol(-1), 298 K). Using population and bond order analyses, in conjunction with the conformation dependence of the frontier MO energies, we have been able to show that pi-electron delocalization is only marginally diminished in the nonplanar conformers of 4 and that the electronic structures of the constituent monomers of the dimer are well mixed.

Journal Article↗

PubMed2006

Kinetic and mechanistic study on the reactions of [Pt(bpma)(H2O)]2+ and [Pd(bpma)(H2O)]2+ with some nucleophiles. Crystal structure of [Pd(bpma)(py)](ClO4)2.

Substitution reactions of the complexes [Pd(bpma)(H2O)]2+ and [Pt(bpma)(H2O)]2+, where bpma = bis(2-pyridylmethyl)amine, with TU, DMTU and TMTU for both complexes and Cl-, Br-, I- and SCN- for the platinum complex, were studied in aqueous 0.10 M NaClO4 at pH 2.5 using a variable-temperature stopped-flow spectrophotometer. The pKa value for the coordinated water molecule in [Pd(bpma)(H2O)]2+ (6.67) is a unit higher than that of [Pt(bpma)(H2O)]2+. The observed pseudo-first-order rate constants k(obs) (s(-1)) obeyed the equation k(obs) = k2[Nu] (Nu = nucleophile). The second-order rate constants indicate that the Pd(II) complex is a factor of 10(3) more reactive than Pt(II) complex. The nucleophile reactivity attributed to the steric hindrance in case of TMTU and the inductive effect for DMTU was found to be DMTU > TU > TMTU for [Pt(bpma)(H2O)]2+ and DMTU approximately TU > TMTU for [Pd(bpma)(H2O)]2+. The trend for ionic nucleophile was I- > SCN- > Br- > Cl-, an order linked to their polarizability and the softness or hardness of the metal. Activation parameters were determined for all reactions and the negative entropies of activation (Delta S++) support an associative ligand substitution mechanism. The X-ray crystal structure of [Pd(bpma)(py)](ClO4)2 was determined; it belongs to the triclinic space group P1 and has one formula unit in the unit cell. The unit cell dimensions are a = 8.522(2), b = 8.627(2), c = 16.730(4) A; alpha = 89.20(2), beta = 81.03(2), gamma = 60.61(2) degrees ; V = 1055.7(5) A3. The structure was solved using direct methods in WinGX's implementation of SHELXS-97 and refined to R = 0.054. The coordination geometry of [Pd(bpma)(py)]2+ is distorted square-planar. The Pd-N(central) bond distance, 1.996(3) A, is shorter than the other two Pd-N distances, 2.017(3) and 2.019(3) A. The Pd-N(pyridine) distance is 2.037(3) A.

Journal Article↗

PubMed2004

Venusol from Gunnera perpensa: structural and activity studies.

From the aqueous extract of the dry rhizomes of Gunnera perpensa the minor components pyrogallol, succinic acid, lactic acid, and the trimethyl ether of ellagic acid glucoside were isolated. The major constituent was identified as Z-venusol, a phenylpropanoid glucoside. Its structure was verified by X-ray diffraction. Tests on isolated uterine smooth muscle from rats showed that the whole extract stimulated a direct contractile response and induced a state of continuous contractility of the uterus once all additives had been removed from the organ bath. By contrast, venusol did not trigger the direct contractile response but induced the state of continuous contractility once the organ bath was flushed.

Animals↗

PubMed2004

Minor pyrano-isoflavones from Eriosema kraussianum: activity-, structure-, and chemical reaction studies.

The isolation and identification of two minor pyrano-isoflavones from Eriosema kraussianum is described. New studies on the original pyrano-isoflavones shows that: (i) kraussianone 2 (a major compound in the plant) can be cyclised under acid conditions, (ii) kraussianones 3 and 5 cause contraction (not relaxation as anticipated) of corpus cavernosum tissue and (iii) the structures proposed previously for 4 and 5 are confirmed by the data obtained from an X-ray study of 5.

Crystallography, X-Ray↗

PubMed2003

Self-recognition in a flexible bis(pyrrole) Schiff base derivative: formation of a one-dimensional hydrogen-bonded polymer.

The title Schiff base compound, N,N'-bis(pyrrol-2-ylmethylene)propane-1,2-diamine, C(13)H(16)N(4), forms an interesting supramolecular structure (a one-dimensional ladder-like polymer) in the solid state that is based on the existence of complementary intermolecular N-H.N=C hydrogen bonds between the monomer units. The polymer axis is collinear with the c axis of the orthorhombic unit cell. Quantum-chemical AM1 calculations clearly indicate that self-recognition in this system by hydrogen bonding is favoured on electrostatic grounds, since the partial atomic charge on the H atom of the pyrrole NH group (0.274 e) complements the partial atomic charge of the N atom of the C=N group (-0.239 e) on a neighbouring molecule.

Journal Article↗

PubMed2003

The isothiocyanate complex of triphenylborane forms an unusual coordination polymer with [K(18-crown-6)](+), both in the solid state and in solution.

The title salt, (1,4,7,10,13,16-hexaoxacyclooctadecane-kappa(6)O)[(isothiocyanato)triphenylborato-kappaS]potassium(I), [K(C(19)H(15)BNS)(C(12)H(24)O(6))] or [K(SCNBPh(3))(18-crown-6)], where 18-crown-6 is 1,4,7,10,13,16-hexaoxacyclooctadecane and [SCNBPh(3)](-) is the (isothiocyanato)triphenylborate anion, exhibits a supramolecular structure that is best described as a helical coordination polymer or molecular screw. This unusual supramolecular structure is based on a framework in which the SCN(-) ion bridges the chelated K(+) ion and the B atom of BPh(3) in a micro(2) fashion. The X-ray crystal structure of the title salt has been determined at 100 (1) and 293 (2) K. The K(+) ion exhibits axial ligation by the S atom of the [SCNBPh(3)](-) anion, with a K-S distance of 3.2617 (17) A (100 K). The trans-axial ligand is an unexpected eta(2)-bound C=C bond of a phenyl group (meta- and para-C atoms) that belongs to the BPh(3) moiety of a neighboring molecule. The K-C bond distances span the range 3.099 (3)-3.310 (3) A (100 K) and are apparently retained in CDCl(3) solution (as evidenced by (13)C NMR spectroscopy). By virtue of the latter interaction, the supramolecular structure is a helical coordination polymer, with the helix axis parallel to the b axis of the unit cell. IR spectroscopy and semi-empirical molecular orbital (AM1) calculations have been used to investigate further the electronic structure of the [SCNBPh(3)](-) ion.

Journal Article↗

PubMed2003

[Fe(TPP)(4-MePip)(2)]: an axially compressed bis(secondary amine) complex of an iron(II) porphyrin.

The low-spin iron(II) ion of bis(4-methylpiperidine)(5,10,15,20-tetraphenylporphyrinato)iron(II), [Fe(TPP)(4-MePip)(2)], where TPP is 5,10,15,20-tetraphenylporphyrinate (C(44)H(28)N(4)) and 4-MePip is 4-methylpiperidine (C(6)H(13)N), is located at a center of inversion, and there is one molecule in the triclinic unit cell. The axial 4-MePip ligands adopt a chair conformation and the alpha-C atoms are oriented at angles of 21.2 (2) and 32.8 (2) degrees relative to the closest porphyrin N atoms. The equatorial Fe-N(TPP) distances are 1.998 (2) and 1.990 (2) A, while the axial Fe-N distance is 2.107 (2) A. The relatively short axial coordination distance reflects compression of the molecule along its principal axis by intermolecular non-bonded interactions.

Journal Article↗

PubMed2003

Conformational analysis: crystallographic, NMR, and molecular mechanics studies of flexible sulfonic esters.

Two novel X-ray structures of the sulfonic ester derivatives 2-(6-iodo-1,3-benzodioxol-5-yl)ethyl 4-nitrobenzenesulfonate, 3, and 2-(6-iodo-1,3-benzodioxol-5-yl)ethyl 4-methylbenzenesulfonate, 4, have been obtained in a study aimed at analyzing the structures and conformations of sulfonic ester derivatives that are routinely used in alkaloid syntheses. The crystal structure of 4 is highly unusual, containing four independent molecules that belong to two distinct conformational types: (1) a hairpin conformation (stabilized mainly by intramolecular pi-stacking) and (2) a stepped conformation (stabilized mainly by intermolecular pi-stacking). Compound 3, on the other hand, crystallizes exclusively as the hairpin conformer. New MM+ force field parameters for sulfonic esters have been developed using the X-ray data, empirical rules, and DFT calculations to estimate the bond dipole parameters. Grid searches of conformational space for 3 and 4 using MM methods show that there are several gas-phase conformations within 5 kcal/mol of the global minimum and that the lowest energy conformations (by approximately 4.6 kcal/mol) are of the hairpin type. Analysis of the MM conformational energies suggests that the dominant intramolecular interaction stabilizing the hairpin conformations of 3 and 4 is van der Waals attraction. Moreover, the lattice energies for packing the hairpin conformations of 3 and 4 are approximately 4 kcal/mol more favorable than for the stepped conformations. Various intermolecular interactions contribute to the complexity of the observed crystal structures of 3 and 4, including electrostatic attraction between O and I atoms in neighboring molecules. Langevin dynamics (LD) simulations at several temperatures (6.0 ns, friction coefficient = 2.5 ps(-1)) indicate that the conformational exchange rates are approximately 10(10)-10(11) s(-1) over the temperature range 213-400 K, accounting for the temperature-independent (1)H NMR spectra of 3 and 4.

Journal Article↗

PubMed2003

The first phosphite complex of a metalloporphyrin.

(Diphenyl phosphite-kappaO)(5,10,15,20-tetraphenylporphyrinato-kappa(4)N)manganese(III) hexafluoroantimonate(V), [Mn(C(44)H(28)N(4))(C(12)H(11)O(3)P)](SbF(6)), is the first example of a structurally characterized diaryl or dialkyl phosphite complex of a metal-porphyrin ion. The axial phosphite ligand binds to the Mn(III) ion via the P=O O atom, affording a nominally five-coordinate complex with an Mn-O distance of 2.120 (4) A. The mean porphyrin Mn-N distance is 2.000 (4) A and the Mn(III) ion is displaced from the 24-atom porphyrin mean plane by 0.1548 (13) A towards the axial O atom. The porphyrin adopts a marked saddle conformation, with a small domed component. The saddle distortion of the porphyrin ligand reflects the tight back-to-back dimers formed in the lattice by pairs of neighboring cations. The 'non-covalent' dimers in the lattice exhibit an unusual (weak) eta(2)-type coordination of a pyrrole C=C bond from a neighboring molecule, with Mn(III).C distances of 3.697 (5) and 3.537 (5) A.

Journal Article↗

PubMed2003

Electronic tuning of the lability of Pt(II) complexes through pi-acceptor effects. Correlations between thermodynamic, kinetic, and theoretical parameters.

pi-Acceptor effects are often used to account for the unusual high lability of [Pt(terpy)L]((2)(-)(n)+) (terpy = 2,2':6',2' '-terpyridine) complexes. To gain further insight into this phenomenon, the pi-acceptor effect was varied systematically by studying the lability of [Pt(diethylenetriamine)OH(2)](2+) (aaa), [Pt(2,6-bis-aminomethylpyridine)OH(2)](2+) (apa), [Pt(N-(pyridyl-2-methyl)-1,2-diamino-ethane)OH(2)](2+) (aap), [Pt(bis(2-pyridylmethyl)amine)OH(2)](2+) (pap), [Pt(2,2'-bipyridine)(NH(3))(OH(2))](2+) (app), and [Pt(terpy)OH(2)](2+) (ppp). The crystal structure of the apa precursor [Pt(2,6-bis-aminomethylpyridine)Cl]Cl.H(2)O was determined. The substitution of water by a series of nucleophiles, viz. thiourea, N,N-dimethylthiourea, N,N,N',N'-tetramethylthiourea, I(-), and SCN(-), was studied under pseudo-first-order conditions as a function of concentration, pH, temperature, and pressure, using stopped-flow techniques. The data enable an overall comparison of the substitution behavior of these complexes, emphasizing the role played by the kinetic cis and trans pi-acceptor effects. The results indicate that the cis pi-acceptor effect is larger than the trans pi-acceptor effect, and that the pi-acceptor effects are multiplicative. DFT calculations at the B3LYP/LACVP level of theory show that, by the addition of pi-acceptor ligands to the metal, the positive charge on the metal center increases, and the energy separation of the frontier molecular orbitals (E(LUMO) - E(HOMO)) of the ground state Pt(II) complexes decreases. The calculations collectively support the experimentally observed additional increase in reactivity when two pi-accepting rings are adjacent to each other (app and ppp), which is ascribed to "electronic communication" between the pyridine rings. The results furthermore indicate that the pK(a) value of the platinum bound water molecule is controlled by the pi-accepting nature of the chelate system and reflects the electron density around the metal center. This in turn controls the rate of the associative substitution reaction and was analyzed using the Hammett equation.

Journal Article↗

PubMed2002

Pyrano-isoflavones with erectile-dysfunction activity from Eriosema kraussianum.

Five pyrano-isoflavones have been isolated from the rootstock of Eriosema kraussianum N. E. Br (Papilionaceae). Spectral data and single crystal X-ray analyses were used for structural elucidation. The most active of the compounds had an activity of 75% of that found in Viagra in the erectile dysfunction test on rabbit penile smooth muscle.

Animals↗