A dinuclear Ru(II) complex capable of photoinduced ligand exchange at both metal centers.

{[Ru(CH3CN)3]2(tppz)}(4+) (tppz = tetra-2-pyridylpyrazine) undergoes photoinduced CH3CN exchange with λirr ≥ 610 nm in H2O. In contrast, cis-{[Ru(tpy)(L)]2(bpm)}(4+) (tpy = 2,2':6',2''-terpyridine, bpm = 2,2'-bipyrimidine, L = CH3CN) is not reactive, but the complex with L = DMSO is photoactive. These complexes are potentially useful for the release of multiply caged drugs.

Synthesis, spectroscopic and magnetic resonance studies of mercury (II) and methylmercury (II) complexes of azathioprine, a biologically active mercaptopurine derivative.

Synthetic and spectroscopic studies of the Hg(II) and MeHg(II) complexes of azathioprine (AZA), a biologically active 6-mercaptopurine derivative, were undertaken. The altered coordination behavior of AZA with respect to the parent mercaptopurine, with sulfur no longer being the primary donor atom, was confirmed. As concluded by the 1H NMR, 13C NMR, and IR spectroscopic data, Hg(II) binds to the N(9) position of deprotonated AZA, while in the MeHg(II) compound, coordination occurs through the N(3) and N(9) positions of the purine ring. The values of the coupling constants 2J (199Hg-1H), 1J(199Hg-13C) for the MeHg(II) compound further support complexation via nitrogen atoms of the purine. Elemental analyses confirmed the compounds to be Hg(AZA)2 (1) and [(MeHg)2(AZA)](NO3) (2); conductivity measurement values show that 1 is a nonelectrolyte and 2 is a 1:1 electrolyte. Furthermore, the FAB-MS of the compounds confirms direct binding of the metal to the ligand, and in the case of the MeHg(II) compound, the successive loss of one and two MeHg(II) moieties can be clearly observed.

Origin of the single chain magnet behavior of the Co(H2L)(H2O) compound with a 1D structure.

The paper is aimed at the elucidation of the main factors responsible for the single-chain magnet behavior of the cobalt(II) disphosphonate compound Co(H2L)(H2O) with a 1D structure. The model takes into account the spin-orbit interaction, the axial component of the octahedral crystal field acting on the ground-state cubic 4T1 terms of the Co(II) ions, the antiferromagnetic exchange interaction between Co(II) ions as well as the difference in the crystallographic positions of these ions. The conditions that favor the single-chain magnet behavior based on spin canting in a 1D chain containing inequivalent Co(II) centers are discussed. The peculiarities of this behavior in chains containing orbitally degenerate ions are revealed. The qualitative explanation of the experimental data is given.

Modulation of renin by thromboxane: studies with thromboxane synthase inhibitor, receptor antagonists, and mimetic.

The regulation of plasma renin activity (PRA) by thromboxane (Tx) A2 was studied in anesthetized rats by measuring PRA before and after administration of drugs that block cyclooxygenase (CO) (indomethacin [INDO], 5 mg/kg), thromboxane synthase (TS) (UK 38485 [UK], 100 mg/kg), or Tx receptors (SQ 29548 [SQ], 8 mg/kg or L 641953 [L], 50 mg/kg) or that activate Tx receptors (U 46619 [U], 10 ng.kg-1.min-1). PRA (ng ANG I.ml-1.h-1) was unaffected by vehicle; it was reduced by INDO (25 +/- 2 to 13 +/- 3, n = 13, P less than 0.001) but was increased by UK (24 +/- 3 to 50 +/- 6, n = 18, P less than 0.005), SQ (27 +/- 4 to 44 +/- 7, n = 6, P less than 0.05), and L (32 +/- 4 to 51 +/- 7, n = 10, P less than 0.05). U reduced PRA in each rat (17 +/- 3 to 10 +/- 3, n = 6, P less than 0.005). UK caused dose-dependent stimulation of PRA (mean effective dose 50 mg/kg) and inhibition of TxB2 excretion (mean inhibitory dose 15 mg/kg). After INDO, SQ no longer changed PRA (-1 +/- 10, n = 7). Prolonged administration of SQ for 4-6 days (20 mg.kg-1.day-1 ip) did not change Na+ or K+ balances, blood pressure, renal hemodynamics, or urine flow. However, SQ stimulated PRA (P less than 0.007) independent of prior salt intake. In conclusion in anesthetized rats 1) PRA is stimulated by products of CO but inhibited by products of TS and by a Tx mimetic; 2) stimulation of PRA by SQ depends on ongoing PG and Tx synthesis; 3) rise in PRA with Tx antagonists is not closely related to changes in salt balance, blood pressure, or renal hemodynamics.

The uptake and partitioning of cadmium in two cultivars of potato (Solanum tuberosum L.).

The uptake and distribution of Cd in potatoes over the course of a growing season was investigated in two cultivars of potatoes that differed in tuber Cd concentration. Plants were grown in soil with supplemental Cd. The concentrations of Cd in different tissues varied greatly in the order roots>shoots>> tubers. After the initiation of tuber bulking, shoot growth ceased and the increase in total plant Cd was mostly due to accumulation in the tubers. The constancy of the Cd concentration in shoots suggested that import of Cd via the xylem must be matched by export in the phloem, which implied that Cd must have significant phloem mobility. It was found that the differences in tuber Cd between cultivars Wilwash and Kennebec were not due to differences in total uptake or growth, but to differences in Cd partitioning within the plant. This partitioning was specific to Cd and was not observed for a range of nutrient elements. Most of the differences in tuber Cd concentration between the cultivars could be accounted for by a 3-fold higher retention of Cd in the roots of cv. Wilwash. The involvement of root sequestration, and xylem and phloem pathways in the loading of Cd into tubers is considered.

Dinuclear and heteropolynuclear complexes containing Mo2(4+) units.

The quadruply bonded compound Mo2(DpyF)4 (1), where DpyF- is the anion of N,N'-di(2-pyridyl)formamidine, has been prepared by ligand substitution reactions of Mo2(OOCCF3)4 and either the neutral ligand, HDpyF, at ambient temperature or its lithium salt, LiDpyF, under refluxing conditions. An X-ray structural analysis shows that 1 has a paddlewheel structure with a [symbol: see text] distance of 2.1108(6) A. Reaction of 1 with CoCl2 in methanol produces the paramagnetic compound [Mo2Co(DpyF)4][CoCl4].2MeOH (2). The Co(II) atom in the cation [Mo2Co(DpyF)4]2+ resides on a low-spin hexacoordinate environment (S = 1/2) with a Co...Mo separation of 2.979(6) A, suggesting there is no direct bonding interaction between the Co and Mo atoms. The Mo-Mo distance of 2.1096(5) A is similar to that in 1. Reaction of 1 and CuCl in methanol yields [Mo2Cu4(DpyF)4Cl2][CuCl2]2.2MeOHxEt2O (3). In the cation there are two copper atoms on each side of the Mo2 core. Each is coordinated to two pyridyl nitrogen atoms of the cis DpyF- ligands and loosely bridged to the other by a chloride ion. As a result, the Cu(I) atoms are not aligned with the Mo2 unit. The Cu to Mo separations are in the range 3.003(1)-3.015(1) A, and the Mo-Mo distance of 2.127(1) A is comparable to those in 1 and 2.

Metal-metal bonded diruthenium(II, III) assemblies with the polycyano anionic linkers N(CN)2-, C(CN)3-, and 1,4-dicyanamido-2,5-dimethylbenzene (DM-dicyd2-): syntheses, structures, and magnetic properties.

The new metal-metal bonded diruthenium(II,III) compounds [Ru2(O2CCH3)4(mu-L)]infinity (L = N(CN)2-, 1; C(CN)3-, 2) and [[Ru2(O2CCH3)2(mhp)2]2(mu-DM-Dicyd)] (3) (mhp = 2-oxy-6-methylpyridinate, DM-Dicyd = 1,4-dicyanamido-2,5-dimethylbenzene dianion) have been synthesized and fully characterized. Compounds 1 and 2 were synthesized by the reaction of [Ru2(O2CCH3)4(NCCH3)2](BF4) with NaN(CN)2 and KC(CN)3, respectively. The "dimer-of-dimers", 3, was synthesized by a 2:1 reaction of [Ru2(O2CCH3)2(mhp)2(MeOH)](BF4) with [As(Ph)4]2[DM-Dicyd]. Compound 1 crystallizes in the monoclinic space group C2/m with a = 10.174(2) A, b = 13.016(3) A, c = 7.0750(14) A, beta = 101.83(3) degrees, and Z = 2. Compound 2 crystallizes in the orthorhombic space group Fdd2 with a = 29.679(6) A, b = 31.409(6) A, c = 7.3660(15) A, V = 6866(2) A3, and Z = 16. In compound 1, dicyanamide anions (N(CN)2-) bridge the [Ru2(O2CCH3)4]+ units in an end-to-end bridging mode, thereby forming an alternating one-dimensional chain. In compound 2, two cyano groups of tricyanomethanide anion (C(CN)3-) are coordinated to independent [Ru2(O2CCH3)4]+ units to give a chain similar to that found in 1. The Ru-Ru bond distances in 1 and 2 are 2.2788(14) and 2.2756(5) A, respectively, which are typical values for Ru2(O2CR)4Cl and [Ru2(O2CR)4]+ compounds. The Ru-N distances are 2.257(8) A in 1 and 2.259(4) and 2.283(4) A in 2. The temperature dependence of the magnetic susceptibilities of compounds 1-3 reveals a weak antiferromagnetic interaction between Ru2 units (S = 3/2) through each polycyano anionic linker: g = 2.16, zJ = -0.33 cm(-1), D = 63.3 cm(-1) for 1; g = 2.15, zJ = -0.22 cm(-1), D = 58.0 cm(-1) for 2; and g = 2.10, zJ = -0.90 cm(-1), D = 75.0 cm(-1) for 3.

Linear trichromium complexes with direct Cr to Cr contacts. 1. Compounds with Cr3(dipyridylamide)4(2+) cores.

The preparation and structures of seven compounds that contain the Cr3(dpa)4(2+) core (dpa = the anion di(2-pyridyl)amide) are reported. The magnetic properties of several have been measured. In each case there are anionic ligands at each end of the Cr3(6+) chain, sometimes identical (2Cl-, 2CCPh-), sometimes different (Cl-, BF4-; Cl-, PF6-). Several of these compounds have a symmetrical arrangement of the three Cr atoms, with the two Cr-Cr distances equal at ca. 2.36 A, while others have an unsymmetrical arrangement. In the most extreme case the two Cr-Cr distances are 2.00 and 2.64 A. The electronic structures and the remarkable flexibility of the Cr3 arrangement are discussed.

Linear trichromium complexes with direct Cr to Cr contacts. 2. Compounds with Cr3(dipyridylamide)4(3+) cores.

Seven compounds having in common a Cr3(dpa)4(3+) core (dpa = di(2-pyridyl)amide ion) have been prepared and all shown to have an unsymmetrical chain of three Cr atoms. This chain can be described as a pair of quadruply bonded Cr(II) atoms to which a Cr(III) atom is attached. No symmetrical chain has been found, contrary to a previous preliminary report. The seven compounds have been well characterized crystallographically, and their short and long Cr to Cr distances (A, in parentheses) are: 1 [Cr3(dpa)4Cl2]Cl.2CH2Cl2.THF (2.12, 2.47), 2 [Cr3(dpa)4Cl2]AlCl4.CH2Cl2 (2.011, 2.555), 3 [Cr3(dpa)4Cl2]FeCl4.CH2Cl2 (2.009, 2.562), 4 [Cr3(dpa)4Cl2]I3.THF.2H2O (2.08, 2.49), 5 [Cr3(dpa)4Cl2]PF6.2CH2Cl2 (2.08, 2.48), 6 [Cr3(dpa)4(BF4)F]BF4.2CH2Cl2 (1.900, 2.595), 7 [Cr3(dpa)4ClF]BF4.CH2Cl2.C6H14 (2.039, 2.507). Magnetic susceptibility measurements on 1 and 2 reveal mueff = 3.85 +/- 0.05 muB from 10 to 300 K.

Linear trichromium complexes with the anion of 2,6-di(phenylimino)piperidine.

The anion of 2,6-di(phenylimino)piperidine (DPhIP) has been found to support linear chains of three metal atoms. Three new compounds, [Cr3(DPhIP)4Cl]Cl.(1).5CH2Cl2.0.5H2O (1.1.5CH2Cl2.0.5H2O), [Cr3(DPhIP)4(CH3CN)]- (PF6)2.H2O.4CH3CN (2.H2O.4CH3CN), and [Cr3(DPhIP)4(F)(CH3CN)](BF4)2.5CH3CN (3.5CH3CN), have been synthesized and characterized by X-ray crystallography. Compound 1 has a linear chain of three chromium atoms arranged in an unsymmetrical fashion, with two of them forming a quadruply bonded unit (Cr-Cr distance 1.932(2) A) and the third being a non-metal-metal-bound 5-coordinate unit (Cr...Cr distance 2.659(2) A). The fifth coordination site is occupied by a chloride ion, and another chloride ion is located in the interstices of the crystal. The trimetal unit in compound 2 is structurally similar to that in compound 1 except that the axial ligand in 2 is a CH3CN molecule. Compound 3 is an oxidation product prepared by reaction of 1 with AgBF4. Here, a square pyramidal CrIII unit, FCrN4, and a Cr-Cr quadruply bonded (Cr-Cr distance 1.968(2) A) unit, with an axially coordinated acetonitrile molecule, form the trichromium chain. The CrIII...CrII separation of 2.594(2) A in 3 is too long to be considered a bonding interaction.

New linear tricobalt complex of di(2-pyridyl)amide (dpa), [Co3(dpa)4(CH3CN)2][PF6]2.

Reaction of the linear tricobalt compound Co3(dpa)4Cl2 (1) (dpa = di(2-pyridyl)amide) with silver hexafluorophosphate in acetonitrile yields [Co3(dpa)4(CH3CN)2][PF6]2 (2). Two crystalline forms are obtained from the same solution, namely, a monoclinic (P2(1)) form 2xCH3CNx2Et2O and a triclinic (P1) form, 2x3CH3CN. The tricobalt units in both crystals are essentially symmetrical, though this is not required by crystal symmetry, with Co-Co distances in the range 2298-2304 A. Each of the two terminal Co atoms is coordinated to an acetonitrile molecule with Co-N distances in the range 2068-2111 A at 213 K. The spiral arrangement of ligands gives an overall idealized D4 point group symmetry for the cation [Co3(dpa)4(CH3CN)2]2+ . Chiral crystals of both delta and lambda configurations in the P2(1) form have been isolated. The absolute configurations were determined by X-ray crystallography and their mirror-image circular dichroism spectra measured. The D4 symmetry of the cation appears to be preserved in solution as judged by the presence of only five proton resonance signals in the 1H NMR spectrum. Magnetic susceptibility measurements in the solid state indicates that 2 has a doublet ground state and exhibits an increase of the effective moment at high temperature (approximately 160 K) due to a spin crossover process.

Tuning the metal-metal bonds in the linear tricobalt compound Co3(dpa)(4)Cl2: bond-stretch and spin-state isomers.

Sixteen crystal structures have been determined for the Co3(dpa)(4)Cl2 (1) molecule in the following five crystalline solvates: 1.0.85(C2H5)(2)O.0.15CH2Cl2 (at 120, 213, 296 K); 1.C(4)H(8)O (at 120, 295 K); 1.C(6)H(6) (at 170, 213, 260, 316 K); 1.C(6)H(12) (at 120, 213, 295 K); and 1.1.75C(7)H(8).0.5C(6)H(14) (at 90, 110, 170, 298 K). For 1.0.85(C(2)H(5))(2)O.0.15CH2Cl2 the molecule of 1 is almost symmetrical at 120 K (Co-Co distances of 2.3191(3) and 2.3304(3) A) and remains so at 296 K (2.2320(3) and 2.3667(4) A). For 1.C(4)H(8)O the Co(3) chain is precisely symmetric at both 120 and 295 K though the Co-Co distances increase from 2.3111(4) to 2.3484(4) A as the temperature rises. Compound 1.C(6)H(6) is isomorphous with 1.C(4)H(8)O at 213 and 295 K and has rigorously symmetrical molecules at these two temperatures. Between 213 and 120 K the space group changes from Pccn to P2(1)/c, so that a symmetrical arrangement is no longer required and the two Co-Co distances then differ slightly (by 0.013 A). For 1.C(6)H(6) there is a phase change between 316 K (Pca2(1)) and 260 K (Pna2(1)). At all four temperatures, however, the molecule is almost symmetrical, with the two independent Co-Co distances never differing by more than 0.026 A. 1.1.75C(7)H(8).0.5C(6)H(14) contains, at all temperatures between 90 and 298 K, two crystallographically independent molecules, each of which is distinctly unsymmetrical at 298 K (Co-Co distances of 2.312(2) and 2.442(2) A for one and 2.310(2) and 2.471(2) for the other). In the first of these the distances converge to a much smaller separation (0.056 A) at 90 K while in the second the difference decreases to only 0.006 A at 90 K. Magnetic susceptibility measurements from 1.8 to 350 K indicate in each case that a gradual spin crossover, from a doublet to a quartet state, occurs over this temperature range.

Loss of corticomedullary demarcation on magnetic resonance imaging: an index of biopsy-proven acute renal transplant dysfunction.

A prospective study of 19 cadaveric renal allograft recipients with suspected graft rejection was undertaken to compare the histological findings of the renal transplant biopsy with the results of magnetic resonance imaging (MRI). All 19 patients underwent a biopsy of the transplant allograft. Biopsy results included acute cellular rejection, acute vascular rejection, chronic vascular rejection (CVR), and acute tubular necrosis (ATN). Recipients of cadaveric renal allografts with normal function served as controls. The control showed distinct corticomedullary demarcation (CMD) on T1-weighted imaging. In contrast, CMD was absent or diminished in all the patients with suspected allograft rejection. Unfortunately, the loss of CMD did not correlate with a specific biopsy diagnosis. Patients with biopsy evidence of acute and chronic rejection or ATN demonstrated loss of CMD with similar image patterns. In conclusion, MRI is capable of detecting renal allograft dysfunction, but does not permit the determination of a specific cause.