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Query: UNIPROT:Q86TM3 (cage)
 29,987 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have examined the reactions of peroxynitrite with short-chain aliphatic aldehydes to model the reaction of the peroxynitrite anion (ONOO-) with CO2. Aldehydes, like CO2, react rapidly with peroxynitrite and catalyze its decomposition. The pH dependence of the reaction is consistent with the addition of ONOO- (not ONOOH) to the carbonyl carbon atom of the free aldehyde forming a 1-hydroxyalkylperoxynitrite anion adduct (5), which structurally resembles the nitrosoperoxycarbonate adduct (1) formed from the reaction of ONOO- with CO2. Intermediate 5, or the secondary products derived from it, decays to give NO3- and regenerated aldehyde, with small but significant yields of H2O2, organic acids, and organic nitrates. In analogy with the peroxynitrite/CO2 system, it is suggested that 5 undergoes homolytic or heterolytic cleavage at the O-O bond, giving a caged radical pair [RCH(OH)O./ .NO2] (7) or intimate ion pair [RCH(OH)O -/+ NO2] (8). The radicals and ions in intermediates 7 and 8 can recombine within the solvent cage to form 1-hydroxyalkylnitrate [RCH(OH)ONO2] (6), which can then dissociate to give nitrate and regenerate the aldehyde. The aldehyde/ peroxynitrite adducts 5-8 mediate the oxidation of 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) but not the nitration of 4-hydroxyphenylacetate. The significance of these findings is discussed in relation to the mechanism(s) of the CO2-catalyzed isomerization of peroxynitrite to nitrate and biological nitrations involving peroxynitrite/CO2 adducts.
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PMID:Reactions of peroxynitrite with aldehydes as probes for the reactive intermediates responsible for biological nitration. 943 22

A centered icosahedral 12-coordinate samarium cluster formed by six bis(L-prolinato)nickel(II) ([Ni(pro)2]) ligands, [Sm(Ni(pro)2)6]3+, was prepared. The reaction of Sm with [Ni(pro)2] in a small excess (a 2-fold excess) and also in a large excess (even a 10-fold excess) of the latter produced the cluster. Therefore, this system is a self-assembly. In the cluster, each nickel atom is surrounded by six atoms: two amino nitrogens, two carboxylate oxygens which form chelate rings with the nitrogen atoms, and two carboxylate oxygen atoms which link the neighboring nickel atoms. The samarium atom is coordinated by six [Ni(pro)2] ligands, and the metal is in an icosahedral environment formed by 12 oxygen atoms. The icosahedral geometry is almost ideal. Crystals of [Sm(Ni(pro)2)6](ClO4)3.6MeOH, which were prepared from a methanol solution, immediately decompose after filtration because of loosely trapped MeOH molecules in the crystal lattice. Therefore, crystals without MeOH molecules, which must be stable, were prepared by recrystallization from acetonitrile with tetramethylammonium perchlorate (TMAP). According to the X-ray crystal analysis, the cluster is TMA[Sm(Ni(pro)2)6](ClO4)4, cubic of space group F23, with a = 21.273(9) A, V = 9626(1) A3, and Z = 4; R = 0.053 (Rw = 0.049) for 1296 reflections. In addition, several crystals of cluster salts that have different counteranions, i.e., tetrafluoroborate (BF4-), hexafluorophosphate (PF6-), iodide (I-), and nitrate (NO3-), were prepared. The order of increasing ease of crystallization of the cluster salts was I- > PF6- approximately ClO4- > BF4- >> NO3-. The cluster structure is retained in alcohol and acetonitrile solutions; the UV-vis spectra of the solutions are perfectly consistent with the powder diffuse reflection spectrum. Cyclic voltammograms of [Sm(Ni(pro)2)6]3+ in acetonitrile proved that the structure of [Sm(Ni(pro)2)6]3+ is retained in the redox process and that the nickel atoms electrochemically interact with one another. Thermal analysis of the cluster salts with different counteranions was investigated. The results imply that the cluster is very stable until bis(L-prolinato)nickel(II) ligands, which form the cage structure, disintegrate and that the thermal decomposition processes of the cluster salts depend on their counteranions.
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PMID:Synthesis of stable crystals of a self-assembled centered icosahedral samarium cluster formed by bis(L-prolinato)nickel(II) ligands. 1119 3

Activation volumes (delta V++) have been determined for several reactions of peroxynitrite using the stopped-flow technique. Spontaneous decomposition of ONOOH to NO3- in 0.15 M phosphate, pH 4.5, gave delta V++ = 6.0 +/- 0.7 and 14 +/- 1.0 cm3 mol-1 in the presence of 53 microM and 5 mM nitrite ion, respectively. One-electron oxidations of Mo(CN)8(4-) and Fe(CN)6(4-), which are first order in peroxynitrite and zero order in metal complex, gave delta V++ = 10 +/- 1 and 11 +/- 1 cm3 mol-1, respectively, at pH 7.2. The limiting yields of oxidized metal complex were found to decrease from 61 to 30% of the initially added peroxynitrite for Mo(CN)8(3-) and from 78 to 47% for Fe(CN)6(3-) when the pressure was increased from 0.1 to 140 MPa. The bimolecular reaction between CO2 and ONOO- was determined by monitoring the oxidation of Fe(CN)6(4-) by peroxynitrite in bicarbonate-containing 0.15 M phosphate, pH 7.2, for which delta V++ = -22 +/- 4 cm3 mol-1. The Fe(CN)6(3-) yield decreased by approximately 20% upon increasing the pressure from atmospheric to 80 MPa. Oxidation of Ni(cyclam)2+ by peroxynitrite, which is first order in each reactant, was characterized by delta V++ = -7.1 +/- 2 cm3 mol-1, and the thermal activation parameters delta H++ = 4.2 +/- 0.1 kcal mol-1 and delta S++ = -24 +/- 1 cal mol-1 K-1 in 0.15 M phosphate, pH 7.2. These results are discussed within the context of the radical cage hypothesis for peroxynitrite reactivity.
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PMID:Pressure dependence of peroxynitrite reactions. Support for a radical mechanism. 1120 11

High-temperature 33Na MAS NMR experiments up to 873 K for a number of different sodalites (Na8[AlSiO4]6(NO3)2, Na8[AlSiO4]6(NO2)2, Na8[AlSiO4]6I2, Na7.9[AlSiO4]6(SCN)7.9 x 0.5H2O, Na8[AlGeO4]6(NO3)2, and Na7[AlSiO4]6(H3O2) x 4H2O) were carried out. The spectra of the first five sodalites consist of a quadrupolar MAS pattern with different quadrupolar coupling constants. The quadrupolar interaction for the thiocyanate sodalite, the nitrate aluminosilicate, and germanate sodalite decreases strongly passing a coalescence state on heating, while the quadrupolar interaction of the iodide and nitrite sample shows nearly no change. The basic hydrosodalite shows an asymmetric lineshape at room temperature and, between 350 and 370 K, a second line due to the evaporation of cage-water emerges. The linewidth increases with rising temperature. The temperature dependence of the quadrupolar interaction seems to be a function of the sodalite beta-cage expansion. Two conceivable jump mechanisms are proposed for a tetrahedral two-site jump between occupied and unoccupied tetrahedral sites.
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PMID:Influence of sodium ion dynamics on the 23Na quadrupolar interaction in sodalite: a high-temperature 23Na MAS NMR study. 1127 Jul 43

Reactions of MnX2.nH2O with tris(N-(D-mannosyl)-2-aminoethyl)amine ((D-Man)3-tren), which was formed from D-mannose and tris(2-aminoethyl)amine (tren) in situ, afforded colorless crystals of [Mn((D-Man)3-tren)]X2 (3a, X = Cl; 3b, X = Br; 3c, X = NO3; 3d, X = 1/2SO4). The similar reaction of MnSO4.5H2O with tris(N-(L-rhamnosyl)-2-aminoethyl)amine ((L-Rha)3-tren) gave [Mn((L-Rha)3-tren)]SO4 (4d), where L-rhamnose is 6-deoxy-L-mannose. The structures of 3b and 4d were determined by X-ray crystallography to have a seven-coordinate Mn(II) center ligated by the N-glycoside ligand, (aldose)3-tren, with a C3 helical structure. Three D-mannosyl residues of 3b are arranged in a delta(ob3) configuration around the metal, leading to formation of a cage-type sugar domain in which a water molecule is trapped. In 4d, three L-rhamnosyl moieties are in a delta(lel3) configuration to form a facially opened sugar domain on which a sulfate anion is capping through hydrogen bonding. These structures demonstrated that a configurational switch around the seven-coordinate manganese(II) center occurs depending on its counteranion. Reactions of 3a, 3b, and 4d with 0.5 equiv of Mn(II) salt in the presence of triethylamine yielded reddish orange crystals formulated as [[Mn((aldose)3-tren)]2Mn(H2O)X3.nH2O (5a, aldose = D-Man, X = Cl; 5b, aldose = D-Man, X = Br; 6d, aldose = L-Rha, X = 1/2SO4). The analogous trinuclear complexes 6a (aldose = L-Rha, X = Cl), 6b (aldose = L-Rha, X = Br), and 6c (aldose = L-Rha, X = NO3) were prepared by the one-pot reaction of Mn(II) salts with (L-Rha)3-tren without isolation of the intermediate Mn(II) complexes. X-ray crystallographic studies revealed that 5a, 5b, 6c, and 6d have a linearly ordered trimanganese core, Mn(II)Mn(III)Mn(II), bridged by two carbohydrate residues with Mn-Mn separations of 3.845(2)-3.919(4) A and Mn-Mn-Mn angles of 170.7(1)-173.81(7) degrees. The terminal Mn(II) atoms are seven-coordinate with a distorted mono-face-capped octahedral geometry ligated by the (aldose)3-tren ligand through three oxygen atoms of C-2 hydroxyl groups, three N-glycosidic nitrogen atoms, and a tertiary amino group. The central Mn(III) atoms are five-coordinate ligated by four oxygen atoms of carbohydrate residues in the (aldose)3-tren ligands and one water molecule, resulting in a square-pyramidal geometry. In the bridging part, a beta-aldopyranosyl unit with a chair conformation bridges the two Mn(II)Mn(III) ions with the C-2 mu-alkoxo group and with the C-1 N-glycosidic amino and the C-3 alkoxo groups coordinating to each metal center. These structures could be very useful information in relation to xylose isomerases which promote aldose-ketose isomerization by using divalent dimetal centers such as Mn2+, Mg2+, and Co2+.
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PMID:Novel Mn(II)Mn(III)Mn(II) trinuclear complexes with carbohydrate bridges derived from seven-coordinate manganese(II) complexes with N-glycoside. 1127 63

[M2L3] coordination cages and linear [M2L3]infinity polymers of the rigid, bridging diphosphines bis(diphenylphosphino)acetylene (dppa) and trans-1,2-bis(diphenylphosphino)ethylene (dppet) with silver(I) salts have been investigated in the solution and solid states. Unlike flexible diphosphines, 1:1 dppa/AgX mixtures do not selectively form discrete [Ag2(diphos)2(X)2] macrocycles; instead dynamic mixtures of one-, two- and three-coordinate complexes are formed. However, 3:2 dppa/AgX ratios (X = SbF6. BF4, O3SCF3 or NO3) do lead selectively to new [M2L3] triply bridged cage complexes [Ag2(dppa)3(X)2] 1a-d (X = SbF6 a, BF4 b, O3SCF3 c, NO3 d), which do not exhibit Ag-P bond dissociation at room temperature on the NMR time scale (121 MHz). Complexes la-d were characterised by X-ray crystallography and were found to have small internal cavities, helical conformations and multiple intramolecular aromatic interactions. The nucleophilicity of the anion subtly influences the cage shape: Increasing nucleophilicity from SbF6 (1a) through BF4 (1b) and O3SCF3 (1c) to NO3 (1d) increases the pyramidal distortion at the AgP3 centres, stretching the cage framework (with Ag...Ag distances increasing from 5.48 in 1a to 6.21 A in 1d) and giving thinner internal cavities. Crystal packing strongly affected the size of the helical twist angle, and no correlation between this parameter and the Ag-Ag distance was observed. When crystalline 1c was stored in its supernatant for 16 weeks, conversion occured to the isostoichiometric [M2L3]infinity coordination polymer [Ag(dppa)2Ag(dppa)(O3SCF3)2]infinity (1c'). X-ray crystallography revealed a structure with ten-membered Ag2(dppa)2 rings linked into infinite one-dimensional chains by a third dppa unit. The clear structural relationship between this polymer and the precursor cage 1c suggests a novel example of ring-opening polymerisation. With dppet, evidence for discrete [M2L3] cages was also found in solution, although 31P NMR spectroscopy suggested some Ag-P bond dissociation. On crystallisation, only the corresponding ring-opened polymeric structures [M2L3]infinity could be obtained. This may be because the greater steric bulk of dppet versus dppa destabilises the cage and favours the ring-opening polymerisation.
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PMID:Ring-opening polymerisation of silver-diphosphine [M2L3] coordination cages to give [M2L3]infinity coordination polymers. 1146 55

Ion exchange of the sodium hydro sodalites [Na3(H2O)4]2-[Al3Si3O12]2 [Na4(H3O2)]2[Al3Si3O12]2 and [Na4(OH)]2[Al3Si3O12]2 with aqueous Pb(NO3)2 solutions yielded, whichever reactant sodalite phase was used, the same lead hydro sodalite, [Pb2(OH)-(H2O)3]2[Al3Si3O12]2. Thus, in the case of the non-basic reactant [Na3(H2O)4]2-[Al3Si3O12]2 an overexchange occurs with respect to the number of nonframework cationic charges. Rietveld structure refinement of the lead hydro sodalite based on powder X-ray diffraction data (cubic, a = 9.070 A, room temperature, space group P43n) revealed that the two lead cations within each polyhedral sodalite cage form an orientationally disordered dinuclear [Pb2(micro-OH)(micro-H2O)(H2O)2]3+ complex. Due to additional lead framework oxygen bonds the coordination environment of each metal cation (CN 3+3) is approximately spherical, and clearly the lead 6s electron lone pair is stereochemically inactive. This is also suggested by the absence of a small peak at 13.025 keV, attributed in other Pb2+-O compounds to an electronic 2p-6s transition, in the PbL3 edge XANES spectrum. 1H MAS NMR and FTIR spectra show that the hydrogen atoms of the aqua hydroxo complex (which could not be determined in the Rietveld analysis) are involved in hydrogen bonds of various strengths.
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PMID:Lead hydro sodalite [Pb2(OH)(H2O)3]2[Al3Si3O12]2: synthesis and structure determination by combining X-ray rietveld refinement, 1H MAS NMR FTIR and XANES spectroscopy. 1193 Nov 9

Complexation of the ligand 1 with Pd(NO3)2 leads to the self-assembly of a very stable M2L4 type macrotricyclic cage that encapsulates a nitrate ion inside its cavity.
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PMID:Self-assembly of a novel macrotricyclic Pd(II) metallocage encapsulating a nitrate ion. 1224 Apr 27

A tris(3-pyridyl)-substituted C3 symmetric subphthalocyanine (SubPc) was dimerized into a M3L2 cage in the presence of a stoichiometric amount of (en)Pd(NO3)2. NMR studies demonstrated the recognition event to be accompanied by chiral self-discrimination between the two enantiomers of the SubPc. Moreover, the specificity is such that only one of four possible isomers was detected in solution.
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PMID:Chiral self-discrimination in a M3L2 subphthalocyanine cage. 1246 47

The use of a ligand directed strategy in the assembly of discrete clusters, 1D chains, 2D layers, and 3D networks using aliphatic N-donor ligands has been investigated. The ligands are a family of amines with rigid backbones [cis,cis-1,3,5-triaminocyclohexane (cis-tach), cis,trans-1,3,5-triaminocyclohexane (trans-tach), cis-1,3-diaminocyclohexane (cis-dach), and cis-3,5-diaminopiperidine (cis-dapi)], and their complexation with Ag(I) salts results in a diverse set of architectures with the following compositions: [Ag3(cis-tach)2]F3.4CH(3)OH.0.5H2O (1), [Ag3(cis-tach)2]F3.6H2O (2), ([Ag(cis-dach)]ClO4)n (3), ([Ag(cis-tach)]NO3)n (4), ([Ag(trans-tach)]PF6)n(5), and ([Ag(cis-dapi)]CF3SO3)n (6). Structural analysis shows that compounds 1 and 2 are discrete M(3)L(2) cage-type clusters with varying solvent molecule content. Short Ag...Ag contacts (3.021(8) A) are observed to dimerize discrete units in compound 2. Compound 3 is a 1D zigzag chain formed by coordination to the two primary amines of cis-dach, whereas the tridentate ligands in compounds 4 and 5 (cis-tach and trans-tach, respectively) are able to form tubular architectures by virtue of their ability to "wrap" round the channel walls. An infinite 2D coordination network is demonstrated by compound 6, in which the three coplanar amino donors of cis-dapi coordinate to the trigonal planar Ag(I) ions to form a layered structure of 6(3) topology. These are compared with a previously reported 3D structure, ([Ag(trans-tach)]NO3)n (7), that belongs to this family of architectures.
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PMID:Coordination networks through the dimensions: from discrete clusters to 1D, 2D, and 3D silver(I) coordination polymers with rigid aliphatic amino ligands. 1528 72


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