Formation, reactivity, and photorelease of metal bound nitrosyl in [Ru(trpy)(L)(NO)](n+) (trpy = 2,2':6',2'-terpyridine, L = 2-phenylimidazo[4,5-f]1,10-phenanthroline)

Nitrosyl complexes with {Ru-NO} (6) and {Ru-NO} (7) configurations have been isolated in the framework of [Ru(trpy)(L)(NO)] ( n+ ) [trpy = 2,2':6',2'-terpyridine, L = 2-phenylimidazo[4,5- f]1,10-phenanthroline] as the perchlorate salts [ 4](ClO 4) 3 and [ 4](ClO 4) 2, respectively. Single crystals of protonated material [ 4-H (+)](ClO 4) 4.2H 2O reveal a Ru-N-O bond angle of 176.1(7) degrees and triply bonded N-O with a 1.127(9) A bond length. Structures were also determined for precursor compounds of [ 4] (3+) in the form of [Ru(trpy)(L)(Cl)](ClO 4).4.5H 2O and [Ru(trpy)(L-H)(CH 3CN)](ClO 4) 3.H 2O. In agreement with largely NO centered reduction, a sizable shift in nu(NO) frequency was observed on moving from [ 4] (3+) (1953 cm (-1)) to [ 4] (2+) (1654 cm (-1)). The Ru (II)-NO* in isolated or electrogenerated [ 4] (2+) exhibits an EPR spectrum with g 1 = 2.020, g 2 = 1.995, and g 3 = 1.884 in CH 3CN at 110 K, reflecting partial metal contribution to the singly occupied molecular orbital (SOMO); (14)N (NO) hyperfine splitting ( A 2 = 30 G) was also observed. The plot of nu(NO) versus E degrees ({RuNO} (6) --> {RuNO} (7)) for 12 analogous complexes [Ru(trpy)(L')(NO)] ( n+ ) exhibits a linear trend. The electrophilic Ru-NO (+) species [ 4] (3+) is transformed to the corresponding Ru-NO 2 (-) system in the presence of OH (-) with k = 2.02 x 10 (-4) s (-1) at 303 K. In the presence of a steady flow of dioxygen gas, the Ru (II)-NO* state in [ 4] (2+) oxidizes to [ 4] (3+) through an associatively activated pathway (Delta S++ = -190.4 J K (-1) M (-1)) with a rate constant ( k [s (-1)]) of 5.33 x 10 (-3). On irradiation with light (Xe lamp), the acetonitrile solution of paramagnetic [Ru(trpy)(L)(NO)] (2+) ([ 4] (2+)) undergoes facile photorelease of NO ( k NO = 2.0 x 10 (-1) min (-1) and t 1/2 approximately 3.5 min) with the concomitant formation of the solvate [Ru (II)(trpy)(L)(CH 3CN)] (2+) [ 2'] (2+). The photoreleased NO can be trapped as an Mb-NO adduct.     

反相高效液相色谱法同时测定镉、铅、铜和锌

 研究了meso-四（对羟基苯基）卟啉为柱前衍生化试剂与Cd2+,Pb2+,Cu2+和Zn2+离子的配合反应条件及配合物在C18色谱柱上的分离条件,建立了反相高效液相色谱快速分离光度检测Cd2+,Pb2+,Cu2+和Zn2+的新方法。配合物和试剂在15 min内出峰完毕。4种离子的检出限为: Cd2+0.02 ng,Pb2+0.02 ng, Cu2+0.02 ng,Zn2+0.12 ng;线性范围为:Cd2+0.8 μg/L～150 μg/L,Pb2+0.8 μg/L～300 μg/L,Cu2+0.8 μg/L～500 μg/L,Zn2+5.0 μg/L～1 000 μg/L;方法的日内相对标准偏差为:2.8%～4.8%,测定低、中、高3个浓度的日间相对标准偏差为3.7%～9.7%。     

Effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water coordination on the structure of glycine and zwitterionic glycine

Interactions between metal ions and amino acids are common both in solution and in the gas phase. Here, the effect of metal ions and water on the structure of glycine is examined. The effect of metal ions (Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) and water on structures of Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (m = 0, 2, 5) complexes have been determined theoretically by employing the hybrid B3LYP exchange-correlation functional and using extended basis sets. Selected calculations were carried out also by means of CBS-QB3 model chemistry. The interaction enthalpies, entropies, and Gibbs energies of eight complexes Gly.Mn+ (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) were determined at the B3LYP density functional level of theory. The computed Gibbs energies DeltaG degrees are negative and span a rather broad energy interval (from -90 to -1100 kJ mol(-1)), meaning that the ions studied form strong complexes. The largest interaction Gibbs energy (-1076 kJ mol(-1)) was computed for the NiGly2+ complex. Calculations of the molecular structure and relative stability of the Gly.Mn+(H2O)m and GlyZwitt.Mn+(H2O)m (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+; m = 0, 2, and 5) systems indicate that in the complexes with monovalent metal cations the most stable species are the NO coordinated metal cations in non-zwitterionic glycine. Divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ prefer coordination via the OO bifurcated bonds of the zwitterionic glycine. Stepwise addition of two and five water molecules leads to considerable changes in the relative stability of the hydrated species. Addition of two water molecules at the metal ion in both Gly.Mn+ and GlyZwitt.Mn+ complexes reduces the relative stability of metallic complexes of glycine. For Mn+ = Li+ or Na+, the addition of five water molecules does not change the relative order of stability. In the Gly.K+ complex, the solvation shell of water molecules around K+ ion has, because of the larger size of the potassium cation, a different structure with a reduced number of hydrogen-bonded contacts. This results in a net preference (by 10.3 kJ mol(-1)) of the GlyZwitt.K+H2O5 system. Addition of five water molecules to the glycine complexes containing divalent cations Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+ results in a net preference for non-zwitterionic glycine species. The computed relative Gibbs energies are quite high (-10 to -38 kJ mol(-1)), and the NO coordination is preferred in the Gly.Mn+(H2O)5 (Mn+ = Mg2+, Ca2+, Ni2+, Cu2+, and Zn2+) complexes over the OO coordination.     

An allosteric synthetic catalyst: metal ions tune the activity of an artificial phosphodiesterase

A trinuclear metal complex of general formula (L-H)M3(Mf)2 represents the first allosteric low molecular weight catalyst. L is a polyaza ligand having a tetradentate and two bidentate metal binding sites, Ms is a "structural" (allosteric) metal, and Mf are functional (catalytic) metals which interact with a substrate. In mononuclear [(L-H)Ms]+ complexes [(L-H)Cu(MeOH)]ClO4 (1a). [(L-H)Cu]NO3 x 2H2O (1b), [(L-H)Ni]ClO4 x 4H2O (2), and [(L-H)Pd]ClO4 x 2H2O (3), prepared from L and M2+ salts, the metal is strongly bound by an in-plane N4-coordination (confirmed by X-ray crystal structure determination of la). Formation of trinuclear complexes [(L-H)MsCu2]5+, with two functional Cu2+ ions coordinated to the bidentate sites of L, was evidenced in solution by photometric titration and by isolation of [(L-H)Cu3][PO4][ClO4]2 x 9H2O (4). The trinuclear complexes catalyze the cleavage of RNA-analogue 2-(hydroxypropyl)-p-nitrophenyl phosphate (HPNP), an activated phosphodiester. From a kinetic analysis of the cleavage rate at various HPNP concentrations, parameters KHPNP (the equilibrium constant for binding of HPNP to [(L-H)MsCu2]5+ and kcat (first-order rate constant for cleavage of HPNP when bound to the catalyst) were derived: KM= 170 (Ms= Cu2+), 340 (Ms = Ni2+), 2,600 (Ms = Pd2+) M(-1), kcat = 17 x 10(-3) (Ms= Cu2+) 3.1 x 10(-3) (Ms=Ni2+), 0.22 x 10(-3) (Ms = Pd2+) s(-1). Obviously, the nature of the allosteric metal ion Ms strongly influences both substrate affinity and reactivity of the catalyst [(L-H)MsCu2]5+. Our interpretation of this observation is that subtle differences in the ionic radius of Ms and in its tendency to distort the N4-Ms coordination plane have a significant influence on the conformation of the catalyst (i.e., preorganization of functional Cu2+ ions) and thus on catalytic activity.     

Size matters! Fragmentation chemistry of [Cu(L)n]2+ complexes of diacylglycerophosphocholines as a function of coordination number (n = 2-7)

[Cu(L)(n)](2+) complexes of 1,2-dihexanoyl-sn-glycero-3-phosphocholine (L = D6PC) are formed upon electrospray ionization mass spectrometry (ESI-MS) of an 8 mM solution of D6PC with 4 mM CuCl(2) in 10 mM ammonium acetate buffer, pH 6.1. The collision-induced dissociation (CID) reactions of the [Cu(L)(n)](2+) complexes were examined in a linear ion trap mass spectrometer. A rich fragmentation chemistry was observed, including: loss of a neutral ligand; intermolecular ligand-ligand S(N)2 methylation; metal ion induced ligand fragmentation via carboxylate abstraction; and phosphate abstraction. The dominant reaction channel depends on the size (n) of the complex. Thus loss of neutral ligand(s) is the sole reaction channel for n = 5-7. At n = 4, S(N)2 methylation and carboxylate abstraction start to compete with neutral ligand loss. At n = 2 the carboxylate abstraction and phosphate abstraction reactions dominate the CID spectrum. The carboxylate abstraction and phosphate abstraction reactions are likely to be driven via neighboring group pathways. PM3 calculations, carried out to compare competing neighboring pathways based on the relative stabilities of the product ions, suggest a preference for five-membered ring formation for ligand fragmentation involving both carboxylate and phosphate abstraction.     

Trinuclear to dinuclear: a radii dependence lanthanide(III) self-assembly coordination behavior of an amide-type tripodal ligand

Lanthanide nitrate complexes with the heptadentate ligand L (6-[2-(2-(diethylamino)-2-oxoethoxy)ethyl]-N,N,12-triethyl-11-oxo-3,9-dioxa-6,12-diazatetradecanamide), [Ln(2)L(NO(3))(6)] (Ln = La, Nd, Sm, Eu, Ho), have been prepared and characterized. The X-ray crystallographic studies show that, in [La(2)L(NO(3))(6)(H(2)O)].H(2)O (1), two complex cations [LaL(H(2)O)](3+) are linked by a hexanitrato anion [La(NO(3))(6)](3)(-) and form a trinuclear cation. In [Nd(2)L(NO(3))(6)(H(2)O)].CHCl(3).1/2CH(3)OH.1/2H(2)O (2), one complex cation [NdL(H(2)O)](3+) and a hexanitrato complex anion [Nd(NO(3))(6)](3)(-) are linked by a bridging NO(3)(-) to form a dinuclear complex. In both complexes, the bridging nitrate is an unusual tetradentate ligand. The metal ions are 12-coordinated in hexanitrato anions and 10-coordinated in complex cations. The chainlike supramolecular structures of La(3+) complex are parallel and have no hydrogen bonds in between, while, in the Nd(3+) complex, a chiral cavity is formed by hydrogen bonds between two adjacent supramolecular chains. These influences are further investigated by assessing the separation efficiency of L and (1)H NMR spectra of its lanthanide nitrate mixtures in solution.     

Discriminating octahedral transition metal ions: highly selective tripodal tris-(2,2'-bipyridine) functionalized piperazine cyclophane receptor for Cu2+ ions

New tripodal transition metal ion receptors, tris(5-ethoxycarbonyl-2,2'-bipyridine) and tris(5-carboxylate-2,2'-bipyridine) substituted 27-membered trimeric piperazine cyclophanes 5 and 7 as well as tetra(5-ethoxycarbonyl-2,2'-bipyridine) substituted 36-membered tetrameric piperazine cyclophane 6, have been prepared and their transition metal ion complexing properties studied in solution by UV-vis spectroscopy and in the solid state by single-crystal X-ray diffraction. The crystal structures of [H(3)5(3+)·Fe(2+)]·4(ClO(4)(-))·CF(3)COO(-) (V), [H(3)7(2+)·Fe(2+)]·2(SO(4)(2-)) (VII) and the reference complex [tris(5,5'-bis(ethoxycarbonyl)-2,2'-bipyridine)Fe(II) perchlorate] (I) showed that the robust piperazine cyclophane is an optimal platform in preorganizing the 2,2'-bipy moieties to form a very fixed octahedral coordination site. In an acidic water solution, the highly preorganized structure of 5 gives a [5·Fe(2+)] complex, the stability of which is comparable with the classical tris(2,2'-bipy) Fe(2+)-complex but it is a significant 3.7 logK units more stable than the non-preorganized tetrameric analog [6·Fe(2+)]. Detailed studies with other similar divalent octahedral transition metal cations showed that the restricted octahedral coordination in complexes of 5 results in an unusual selectivity. The selectivity order [Zn(2+)相似文献   

Synthesis, spectroscopic analysis and photolabilization of water-soluble ruthenium(III)-nitrosyl complexes

In this paper, the synthesis, structural and spectroscopic characterization of a series of new Ru(III)-nitrosyls of {RuNO}(6) type with the coligand TPA (tris(2-pyridylmethyl)amine) are presented. The complex [Ru(TPA)Cl(2)(NO)]ClO(4) (2) was prepared from the Ru(III) precursor [Ru(TPA)Cl(2)]ClO(4) (1) by simple reaction with NO gas. This led to the surprising displacement of one of the pyridine (py) arms of TPA by NO (instead of the substitution of a chloride anion by NO), as confirmed by X-ray crystallography. NO complexes where TPA serves as a tetradentate ligand were obtained by reacting the new Ru(II) precursor [Ru(TPA)(NO(2))(2)] (3) with a strong acid. This leads to the dehydration of nitrite to NO(+), and the formation of the {RuNO}(6) complex [Ru(TPA)(ONO)(NO)](PF(6))(2) (4), which was also structurally characterized. Derivatives of 4 where nitrite is replaced by urea (5) or water (6) were also obtained. The nitrosyl complexes obtained this way were then further investigated using IR and FT-Raman spectroscopy. Complex 2 with the two anionic chloride coligands shows the lowest N-O and highest Ru-NO stretching frequencies of 1903 and 619 cm(-1) of all the complexes investigated here. Complexes 5 and 6 where TPA serves as a tetradentate ligand show ν(N-O) at higher energy, 1930 and 1917 cm(-1), respectively, and ν(Ru-NO) at lower energy, 577 and 579 cm(-1), respectively, compared to 2. These vibrational energies, as well as the inverse correlation of ν(N-O) and ν(Ru-NO) observed along this series of complexes, again support the Ru(II)-NO(+) type electronic structure previously proposed for {RuNO}(6) complexes. Finally, we investigated the photolability of the Ru-NO bond upon irradiation with UV light to determine the quantum yields (φ) for NO photorelease in complexes 2, 4, 5, and additional water-soluble complexes [Ru(H(2)edta)(Cl)(NO)] (7) and [Ru(Hedta)(NO)] (8). Although {RuNO}(6) complexes are frequently proposed as NO delivery agents in vivo, studies that investigate how φ is affected by the solvent water are lacking. Our results indicate that neutral water is not a solvent that promotes the photodissociation of NO, which would present a major obstacle to the goal of designing {RuNO}(6) complexes as photolabile NO delivery agents in vivo.     

A metallic cobalt electrode for the indirect potentiometric determination of calcium and magnesium in natural waters using flow injection analysis

A flow injection analysis of Ca(2+) and Mg(2+) using indirect potentiometric detection in natural waters is proposed, where Ca(2+) or Mg(2+) are injected into a buffer carrier containing phosphate, resulting in the formation of Ca(3)(PO(4))(2) or Mg(3)(PO(4))(2). The consequent reduction in free phosphate in the carrier solution is detected using a metallic cobalt wire electrode. Indirect electrode response was used and the experimental conditions affecting electrode response were optimized. Responses were linear in the concentration range 5x10(-4) to 5x10(-3) M with a detection limit of 1x10(-5) M in 20 mM phosphate buffer at pH 8.0. The relative standard derivation at 1 mM of Ca(2+) and Mg(2+) were 3.9 and 3.7% (n=10), respectively. EGTA and 8-hydroxyquinoline were used as the masking agents for Ca(2+) and Mg(2+), respectively. Concentrations of Ca(2+) and Mg(2+) in natural waters were successfully determined by the proposed method.     

Ruthenium nitrosyls derived from polypyridine ligands with carboxamide or imine nitrogen donor(s): isoelectronic complexes with different NO photolability

As part of our search for photoactive ruthenium nitrosyls, a set of {RuNO}6 nitrosyls has been synthesized and structurally characterized. In this set, the first nitrosyl [(SBPy3)Ru(NO)](BF4)3 (1) is derived from a polypyridine Schiff base ligand SBPy3, while the remaining three nitrosyls are derived from analogous polypyridine ligands containing either one ([(PaPy3)Ru(NO)](BF4)2 (2)) or two ([(Py3P)Ru(NO)]BF4 (3) and [(Py3P)Ru(NO)(Cl)] (4)) carboxamide group(s). The coordination structures of 1 and 2 are very similar except that in 2, a carboxamido nitrogen is coordinated to the ruthenium center in place of an imine nitrogen in case of 1. In 3 and 4, the ruthenium center is coordinated to two carboxamido nitrogens in the equatorial plane and the bound NO is trans to a pyridine nitrogen (in 3) and chloride (in 4), respectively. Complexes 1-3 contain N6 donor set, and the NO stretching frequencies (nuNO) correlate well with the N-O bond distances. All four diamagnetic {RuNO}(6) nitrosyls are photoactive and release NO rapidly upon illumination with low-intensity (5-10 mW) UV light. Interestingly, photolysis of 1 generates the diamagnetic Ru(II) photoproduct [(SBPy3)Ru(MeCN)](2+) while 2-4 afford paramagnetic Ru(III) species in MeCN solution. The quantum yield values of NO release under UV illumination (lambda(max) = 302 nm) lie in the range 0.06-0.17. Complexes 3 and 4 also exhibit considerable photoactivity under visible light. The efficiency of NO release increases in the order 2 < 3 < 4, indicating that photorelease of NO is facilitated by (a) the increase in the number of coordinated carboxamido nitrogen(s) and (b) the presence of negatively charged ligands (like chloride) trans to the bound NO.     

Coagulation of bitumen with kaolinite in aqueous solutions containing Ca2+, Mg2+ and Fe3+: effect of citric acid

Heterocoagulation experiments of kaolinite with solvent-diluted-bitumen were carried out to investigate the effect of hydrolyzable metal cations and citric acid on the liberation of bitumen from kaolinite. The adsorption of Ca(2+) and Mg(2+) on kaolinite, and zeta potentials of kaolinite and bitumen droplets in solutions containing 10(-3)mol/L of Ca(2+), Mg(2+) and Fe(3+) with or without citric acid were also measured. It was found that the heterocoagulation of bitumen with kaolinite was enhanced in the presence of the metal cations from pH 7 to pH 10.5, accompanied by a decrease in the magnitude of the zeta potentials and an increase in the adsorption of the metal cations on kaolinite and possibly on bitumen droplets. The addition of 5 x 10(-4)mol/L citric acid reduced the degree of coagulation from 90% to less than 40% in the presence of 10(-3)mol/L Ca(2+) and Mg(2+) cations at pH approximately 10, and at pH approximately 8 for Fe(3+). It was found that hydrolyzable metal cations enhanced bitumen-kaolinite interactions through electrical double layer compression and specific adsorption of the metal hydrolysis species on the surface of kaolinite. The effect of metal cations was removed by citric acid through formation of metal-citrate complexes and/or the adsorption of citrate anions, which restored the zeta potentials of both kaolinite and bitumen. Therefore, electrostatic attraction or repulsion was responsible for the coagulation or dispersion of kaolinite particles from bitumen droplets in the tested system.     

Ruthenium nitrosyl complexes with 1,4,7-trithiacyclononane and 2,2'-bipyridine (bpy) or 2-phenylazopyridine (pap) coligands. Electronic structure and reactivity aspects

The present article describes ruthenium nitrosyl complexes with the {RuNO}(6) and {RuNO}(7) notations in the selective molecular frameworks of [Ru(II)([9]aneS(3))(bpy)(NO(+))](3+) (4(3+)), [Ru(II)([9]aneS(3))(pap) (NO(+))](3+) (8(3+)) and [Ru(II)([9]aneS(3))(bpy)(NO˙)](2+) (4(2+)), [Ru(II)([9]aneS(3))(pap)(NO˙)](2+) (8(2+)) ([9]aneS(3) = 1,4,7-trithiacyclononane, bpy = 2,2'-bipyridine, pap = 2-phenylazopyridine), respectively. The nitrosyl complexes have been synthesized by following a stepwise synthetic procedure: {Ru(II)-Cl} → {Ru(II)-CH(3)CN} → {Ru(II)-NO(2)} → {Ru(II)-NO(+)} → {Ru(II)-NO˙}. The single-crystal X-ray structure of 4(3+) and DFT optimised structures of 4(3+), 8(3+) and 4(2+), 8(2+) establish the localised linear and bent geometries for {Ru-NO(+)} and {Ru-NO˙} complexes, respectively. The crystal structures and (1)H/(13)C NMR suggest the [333] conformation of the coordinated macrocyclic ligand ([9]aneS(3)) in the complexes. The difference in π-accepting strength of the co-ligands, bpy in 4(3+) and pap in 8(3+) (bpy < pap) has been reflected in the ν(NO) frequencies of 1945 cm(-1) (DFT: 1943 cm(-1)) and 1964 cm(-1) (DFT: 1966 cm(-1)) and E°({Ru(II)-NO(+)}/{Ru(II)-NO˙}) of 0.49 and 0.67 V versus SCE, respectively. The ν(NO) frequency of the reduced {Ru-NO˙} state in 4(2+) or 8(2+) however decreases to 1632 cm(-1) (DFT: 1637 cm(-1)) or 1634 cm(-1) (DFT: 1632 cm(-1)), respectively, with the change of the linear {Ru(II)-NO(+)} geometry in 4(3+), 8(3+) to bent {Ru(II)-NO˙} geometry in 4(2+), 8(2+). The preferential stabilisation of the eclipsed conformation of the bent NO in 4(2+) and 8(2+) has been supported by the DFT calculations. The reduced {Ru(II)-NO˙} exhibits free-radical EPR with partial metal contribution revealing the resonance formulation of {Ru(II)-NO˙}(major)?{Ru(I)-NO(+)}(minor). The electronic transitions of the complexes have been assigned based on the TD-DFT calculations on their DFT optimised structures. The estimated second-order rate constant (k, M(-1) s(-1)) of the reaction of the nucleophile, OH(-) with the electrophilic {Ru(II)-NO(+)} for the bpy derivative (4(3+)) of 1.39 × 10(-1) is half of that determined for the pap derivative (8(3+)), 2.84 × 10(-1) in CH(3)CN at 298 K. The Ru-NO bond in 4(3+) or 8(3+) undergoes facile photolytic cleavage to form the corresponding solvent species {Ru(II)-CH(3)CN}, 2(2+) or 6(2+) with widely varying rate constant values, (k(NO), s(-1)) of 1.12 × 10(-1) (t(1/2) = 6.2 s) and 7.67 × 10(-3) (t(1/2) = 90.3 s), respectively. The photo-released NO can bind to the reduced myoglobin to yield the Mb-NO adduct.     

NMR studies of heteropolyanion [P(2)W(20)O(70)(H2O)2](-10) complexes with metal cations

We have used multinuclear NMR and IR spectroscopy to study the interaction of a number of metal cations with monovacant heteropolyanion [P(2)W(20)O(7)(0)(H(2)O)(2)](10)(-) (P(2)W(20)) in aqueous solutions starting from its K salt. We have also prepared and studied P(2)W(20) in an Na-only medium. The observed differences in the NMR spectra of NaP(2)W(20)and KP(2)W(20)solutions and the importance of K(+) and Na(+) for the formation of P(2)W(20) suggest that this polyanion exists only as a complex with the alkaline cations. When both cations were simultaneously present in solution, we observed the broadening of the NMR signals of P(2)W(20)due to the Na-K exchange. Li(+) does not replace K(+) or Na(+) in such complexes, and in an Li-only medium P(2)W(20) does not form. Of all the M(n)(+) cations studied (Pd(2+), Bi(3+), Sn(4+), Zr(4+), Ce(4+), Ti(4+), V(5+), and Mo(6+)) only Bi(3+), Sn(4+), and Ce(4+) form complexes with P(2)W(20) in strongly acidic solutions. The (183)W and (119)Sn NMR data suggest that Sn(4+) forms in solution two mutually interconvertable P(2)W(20)Sn complexes of the composition P(2)W(20)O(70)(H(2)O)(3)SnOH(7)(-) and (P(2)W(20)O(70)(H(2)O)(3)Sn)(2)O(14)(-) while Bi(3+) forms one complex of the proposed composition P(2)W(20)O(70)(H(2)O)(2)Bi.(7)(-) We obtained complexes with Bi and Sn as free heteropoly acids and studied their thermostability in the solid state.     

Toward synthetic tubes for NO2/N2O4: design, synthesis, and host-guest chemistry

Design of molecular nanotubes is proposed for entrapment and conversion of NO2/N2O4 gases. Synthesis of 1,3-alternate bis-calix[4]arene tube 3 of 5 x 11 A internal dimensions is presented, and its reversible reactions with NO2/N2O4 in solution are studied. Exposure of 3 to NO2/N2O4 in chlorinated solvents results in the rapid encapsulation of nitrosonium (NO+) cations within its interior. Mono- and dinitrosonium complexes 4 and 5, respectively, were isolated and characterized by UV-vis, FTIR, and 1H NMR spectroscopies, and also molecular modeling. The NO+ entrapment process is reversible, and addition of water quickly recovered starting tube 3. Encapsulated within the tube NO+ species act as nitrosating agents for secondary amides. These findings open wider perspectives toward NO2/NOx storing and converting materials and also offer a promise for further development of supramolecular chemistry of synthetic nanotubes.     

A ratiometric fluorescent chemosensor for iron: discrimination of Fe2+ and Fe3+ and living cell application

A newly designed probe, 6-thiophen-2-yl-5,6-dihydrobenzo[4,5]imidazo-[1,2-c] quinazoline (HL(1)) behaves as a highly selective ratiometric fluorescent sensor for Fe(2+) at pH 4.0-5.0 and Fe(3+) at pH 6.5-8.0 in acetonitrile-HEPES buffer (1/4) (v/v) medium. A decrease in fluorescence at 412 nm and increase in fluorescence at 472 nm with an isoemissive point at 436 nm with the addition of Fe(2+) salt solution is due to the formation of mononuclear Fe(2+) complex [Fe(II)(HL)(ClO(4))(2)(CH(3)CN)(2)] (1) in acetonitrile-HEPES buffer (100 mM, 1/4, v/v) at pH 4.5 and a decrease in fluorescence at 412 nm and increase in fluorescence at 482 nm with an isoemissive point at 445 nm during titration by Fe(3+) salt due to the formation of binary Fe(3+) complex, [Fe(III)(L)(2)(ClO(4))(H(2)O)] (2) with co-solvent at biological pH 7.4 have been established. Binding constants (K(a)) in the solution state were calculated to be 3.88 × 10(5) M(-1) for Fe(2+) and 0.21 × 10(3) M(-1/2) for Fe(3+) and ratiometric detection limits for Fe(2+) and Fe(3+) were found to be 2.0 μM and 3.5 μM, respectively. The probe is a "naked eye" chemosensor for two states of iron. Theoretical calculations were studied to establish the configurations of probe-iron complexes. The sensor is efficient for detecting Fe(3+)in vitro by developing a good image of the biological organelles.     

Photo-controlled metal-ion (Zn2+ and Cd2+) release in aqueous Tween-20 micelle solution

Photo-controlled metal-ion (Zn(2+) and Cd(2+)) release in aqueous micelle solution (tris-HCl, pH = 7.4) has been described using 2-((2-mercaptophenylimino)methyl) phenol as ligand. It is found that both the ligand-Zn complex (1) and the ligand-Cd complex (2) are stable in micelle solution, and Zn(2+) (Cd(2+)) can be released from the complex with 365 nm light trigger. Accompanying the metal-ion release, the ligand is photo-converted to 2-(benzothiazol-2-yl) phenol (3) as product, and the turn-on fluorescence is detected. The fluorescence intensity increases with the photo-triggered release until Zn(2+) (Cd(2+)) is completely released, which is beneficial for monitoring the process of photo-controlled metal ion release. Control experiments demonstrate that no binding occurs between 3 and Zn(2+) (Cd(2+)) in micelle solution and there is no binding between cations and micelle, either.     

Reflected shock tube studies of high-temperature rate constants for OH + NO2 --> HO2 + NO and OH + HO2 --> H2O + O2

The motivation for the present study comes from the preceding paper where it is suggested that accepted rate constants for OH + NO2 --> NO + HO2 are high by approximately 2. This conclusion was based on a reevaluation of heats of formation for HO2, OH, NO, and NO2 using the Active Thermochemical Table (ATcT) approach. The present experiments were performed in C2H5I/NO2 mixtures, using the reflected shock tube technique and OH-radical electronic absorption detection (at 308 nm) and using a multipass optical system. Time-dependent profile decays were fitted with a 23-step mechanism, but only OH + NO2, OH + HO2, both HO2 and NO2 dissociations, and the atom molecule reactions, O + NO2 and O + C2H4, contributed to the decay profile. Since all of the reactions except the first two are known with good accuracy, the profiles were fitted by varying only OH + NO2 and OH + HO2. The new ATcT approach was used to evaluate equilibrium constants so that back reactions were accurately taken into account. The combined rate constant from the present work and earlier work by Glaenzer and Troe (GT) is k(OH+NO2) = 2.25 x 10(-11) exp(-3831 K/T) cm3 molecule(-1) s(-1), which is a factor of 2 lower than the extrapolated direct value from Howard but agrees well with NO + HO2 --> OH + NO2 transformed with the updated equilibrium constants. Also, the rate constant for OH + HO2 suitable for combustion modeling applications over the T range (1200-1700 K) is (5 +/- 3) x 10(-11) cm3 molecule(-1) s(-1). Finally, simulating previous experimental results of GT using our updated mechanism, we suggest a constant rate for k(HO2+NO2) = (2.2 +/- 0.7) x 10(-11) cm3 molecule(-1) s(-1) over the T range 1350-1760 K.     

Recognition of phosphate monoester dianion by an alkoxide-bridged dinuclear zinc(II) complex

Recognition of phosphate monoester dianion by an alkoxide-bridged dinuclear zinc(II) complex (Zn2L3+) has been studied (L = alkoxide species of 1,3-bis[bis(pyridin-2-ylmethyl)amino]propan-2-ol). Potentiometric pH titration study disclosed a 1 : 1 phenyl phosphate complexation with Zn2L3+ in aqueous solution. The dissociation constant (= [Zn2L3+][PhOPO3(2-)]/[Zn2L3+-PhOPO3(2-)]) is an extremely small value of 2.5 x 10(-8) mol dm(-3) at 25 degrees C with I = 0.10 (NaNO3). The X-ray crystal analysis of the dizinc(II) complex with p-nitrophenyl phosphate showed that the phosphate dianion binds as a bridging ligand to the two zinc(II) ions.     

Complex series [Ru(tpy)(dpk)(X)]n+ (tpy = 2,2':6',2''-terpyridine; dpk = 2,2'-dipyridyl ketone; X = Cl-, CH3CN, NO2(-), NO+, NO*, NO-): substitution and electron transfer, structure, and spectroscopy

The complex framework [Ru(tpy)(dpk)]2+ has been used to study the generation and reactivity of the nitrosyl complex [Ru(tpy)(dpk)(NO)]3+ ([4]3+). Stepwise conversion of the chloro complex [Ru(tpy)(dpk)(Cl)]+ ([1]+) via [Ru(tpy)(dpk)(CH3CN)]2+ ([2]2+) and the nitro compound [Ru(tpy)(dpk)(NO2)]+ ([3]+) yielded [4]3+; all four complexes were structurally characterized as perchlorates. Electrochemical oxidation and reduction was investigated as a function of the monodentate ligand as was the IR and UV-vis spectroscopic response (absorption/emission). The kinetics of the conversion [4]3+/[3]+ in aqueous environment were also studied. Two-step reduction of [4]3+ was monitored via EPR, UV-vis, and IR (nu(NO), nu(CO)) spectroelectrochemistry to confirm the {RuNO}7 configuration of [4]2+ and to exhibit a relatively intense band at 505 nm for [4]+, attributed to a ligand-to-ligand transition originating from bound NO-.