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PubMed1997

Solution and Solid State Properties of [N-(2-Hydroxyethyl)iminodiacetato]vanadium(IV), -(V), and -(IV/V) Complexes(1).

A mononuclear vanadium(IV), a mononuclear vanadium(V), and a binuclear mixed valence vanadium(IV/V) complex with the ligand N-(2-hydroxyethyl)iminodiacetic acid (H(3)hida) have been structurally characterized. Crystal data for [VO(Hhida)(H(2)O)].CH(3)OH (1): orthorhombic; P2(1)2(1)2(1); a= 6.940(2), b = 9.745(3), c= 18.539(4) Å; Z = 4. Crystal data for Na[V(O)(2)(Hhida)(2)].4H(2)O (2): monoclinic; P2(1)/c; a = 6.333(2), b = 18.796(2), c = 11.5040(10) Å; beta = 102.53(2) degrees; Z = 4. Crystal data for (NH(4))[V(2)(O)(2)(&mgr;-O)(Hhida)(2)].H(2)O (3): monoclinic; C2/c; a = 18.880(2), b= 7.395(2), c = 16.010(2) Å; beta = 106.33(2) degrees; Z = 4. The mononuclear vanadium(IV) and vanadium(V) complexes are formed from the monoprotonated Hhida(2)(-) ligand, and their structural and magnetic characteristics are as expected for six-coordinate vanadium complexes. An interesting structural feature in these complexes is the fact that the two carboxylate moieties are coordinated trans to one another, whereas the carboxylate moieties are coordinated in a cis fashion in previously characterized complexes. The aqueous solution properties of the vanadium(IV) and -(V) complexes are consistent with their structures. The vanadium(V) complex was previously characterized; in the current study structural characterization in the solid state is provided. X-ray crystallography and magnetic methods show that the mixed valence complex contains two indistinguishable vanadium atoms; the thermal ellipsoid of the bridging oxygen atom suggests a type III complex in the solid state. Magnetic methods show that the mixed valence complex contains a free electron. Characterization of aqueous solutions of the mixed valence complex by UV/vis and EPR spectroscopies suggests that the complex may be described as a type II complex. The Hhida(2)(-) complexes have some similarities, but also some significant differences, with complexes of related ligands, such as nitrilotriacetate (nta), N-(2-pyridylmethyl)iminodiacetate (pmida), and N-(S)-[1-(2-pyridyl)ethyl]iminodiacetate (s-peida). Perhaps most importantly, the mixed valence Hhida(2)(-) complex is significantly less stable than the corresponding pmida and s-peida complexes of similar overall charge but very similar in stability to the nta and V(2)O(3)(3+) complexes with higher charges. Thus, there is the potential for designing stable mixed valence dimers.

Journal Article↗
PubMed1993

Three-dimensional atomic model of F-actin decorated with Dictyostelium myosin S1.

Elucidation of the molecular contacts between actin and myosin is central to understanding the force-generating process in muscle and other cells. Actin, a highly conserved globular protein found in all eukaryotes, polymerizes into filaments (F-actin) for most of its biological functions. Myosins, which are more diverse in sequence, share a conserved globular head of about 900 amino acids in length (subfragment-1 or S1) at the N-terminal end of the molecule. S1 contains all the elements necessary for mechano-chemical force transduction in vitro. Here we report an atomic model for the actomyosin complex produced by combining the atomic X-ray structure of F-actin and chicken myosin S1 with a three-dimensional reconstruction from electron micrographs of frozen-hydrated F-actin decorated with recombinant Dictyostelium myosin S1. The accuracy of the reconstruction shows the position of actin and myosin molecules unambiguously.

Actins↗
PubMed2003

Slow hydrogen atom self-exchange between Os(IV) anilide and Os(III) aniline complexes: relationships with electron and proton transfer self-exchange.

Hydrogen atom, proton and electron transfer self-exchange and cross-reaction rates have been determined for reactions of Os(IV) and Os(III) aniline and anilide complexes. Addition of an H-atom to the Os(IV) anilide TpOs(NHPh)Cl(2) (Os(IV)NHPh) gives the Os(III) aniline complex TpOs(NH(2)Ph)Cl(2) (Os(III)NH(2)Ph) with a new 66 kcal mol(-1) N-H bond. Concerted transfer of H* between Os(IV)NHPh and Os(III)NH(2)Ph is remarkably slow in MeCN-d(3), with k(ex)(H*) = (3 +/- 2) x 10(-3) M(-1) s(-1) at 298 K. This hydrogen atom transfer (HAT) reaction could also be termed proton-coupled electron transfer (PCET). Related to this HAT process are two proton transfer (PT) and two electron transfer (ET) self-exchange reactions, for instance, the ET reactions Os(IV)NHPh + Os(III)NHPh(-) and Os(IV)NH(2)Ph(+) + Os(III)NH(2)Ph. All four of these PT and ET reactions are much faster (k = 10(3)-10(5) M(-1) s(-1)) than HAT self-exchange. This is the first system where all five relevant self-exchange rates related to an HAT or PCET reaction have been measured. The slowness of concerted transfer of H* between Os(IV)NHPh and Os(III)NH(2)Ph is suggested to result not from a large intrinsic barrier but rather from a large work term for formation of the precursor complex to H* transfer and/or from significantly nonadiabatic reaction dynamics. The energetics for precursor complex formation is related to the strength of the hydrogen bond between reactants. To probe this effect further, HAT cross-reactions have been performed with sterically hindered aniline/anilide complexes and nitroxyl radical species. Positioning steric bulk near the active site retards both H* and H(+) transfer. Net H* transfer is catalyzed by trace acids and bases in both self-exchange and cross reactions, by stepwise mechanisms utilizing the fast ET and PT reactions.

Aniline Compounds↗
PubMed2006

Neutron diffraction studies of Escherichia coli dihydrofolate reductase complexed with methotrexate.

Hydrogen atoms play a central role in many biochemical processes yet are difficult to visualize by x-ray crystallography. Spallation neutron sources provide a new arena for protein crystallography with TOF measurements enhancing data collection efficiency and allowing hydrogen atoms to be located in smaller crystals of larger biological macromolecules. Here we report a 2.2-A resolution neutron structure of Escherichia coli dihydrofolate reductase (DHFR) in complex with methotrexate (MTX). Neutron data were collected on a 0.3-mm(3) D(2)O-soaked crystal at the Los Alamos Neutron Scattering Center. This study provides an example of using spallation neutrons to study protein dynamics, to identify protonation states directly from nuclear density maps, and to analyze solvent structure. Our structure reveals that the occluded loop conformation [monomer (mon.) A] of the DHFR.MTX complex undergoes greater H/D exchange compared with the closed-loop conformer (mon. B), partly because the Met-20 and beta(F-G) loops readily exchange in mon. A. The eight-stranded beta sheet of both DHFR molecules resists H/D exchange more than the helices and loops. However, the C-terminal strand, betaH, in mon. A is almost fully exchanged. Several D(2)Os form hydrogen bonds with exchanged amides. At the active site, the N1 atom of MTX is protonated and thus charged when bound to DHFR. Several D(2)Os are observed at hydrophobic surfaces, including two pockets near the MTX-binding site. A previously unidentified D(2)O hydrogen bonds with the catalytic D27 in mon. B, stabilizing its negative charge.

Binding Sites↗
PubMed1991

Structures of met and azidomet hemerythrin at 1.66 A resolution.

The crystallographic refinement of met and azidomet hemerythrin has been carried out at 1.66 A resolution in an attempt to characterize precisely the binuclear iron center in this protein. Restrained least-squares refinement has produced molecular models giving R-values of 18.9% for met (65,683 reflections from 10 A to 1.66 A) and 17.6% for azidomet hemerythrin (68,747 reflections from 10.0 A to 1.66 A). The protein structure in each derivative is very similar to that of myohemerythrin. The mu-oxo bridged iron center differs between the two forms. The complex in met hemerythrin is asymmetric with the bridging oxygen closer to one of the iron atoms while the complex in azidomet hemerythrin is symmetric. After investigations of the effects of correlation in the refinement, we believe this difference between the two complexes is associated with chemical differences and is not a refinement artefact.

Animals↗
PubMed1995

Atomic model of a pyrimidine dimer excision repair enzyme complexed with a DNA substrate: structural basis for damaged DNA recognition.

T4 endonuclease V is a DNA repair enzyme from bacteriophage T4 that catalyzes the first reaction step of the pyrimidine dimer-specific base excision repair pathway. The crystal structure of this enzyme complexed with a duplex DNA substrate, containing a thymine dimer, has been determined at 2.75 A resolution. The atomic structure of the complex reveals the unique conformation of the DNA duplex, which exhibits a sharp kink with a 60 degree inclination at the central thymine dimer. The adenine base complementary to the 5' side of the thymine dimer is completely flipped out of the DNA duplex and trapped in a cavity on the protein surface. These structural features allow an understanding of the catalytic mechanism and implicate a general mechanism of how other repair enzymes recognize damaged DNA duplexes.

Adenine↗
PubMed2005

Supramolecular architectures assembled by the interaction of purine nucleobases with metal-oxalato frameworks. Non-covalent stabilization of the 7H-adenine tautomer in the solid-state.

The synthesis, crystal structure and variable-temperature magnetic measurements of the compounds [Mn(mu-ox)(H2O)(7H-pur-kappaN9)]n (1), {[Mn(mu-ox)(H2O)2].(7H-ade).(H2O)}n (2) and {[Cu(mu-ox)(H2O)(7H-ade-kappaN9)][Cu(mu-ox)(mu-H2O)(7H-ade-kappaN9)]. approximately 10/3H2O}n (3), (where ox: oxalato dianion, pur: purine, and ade: adenine) are reported. Compounds 1and 2 contain one-dimensional chains in which manganese(II) atoms are bridged by bis-bidentate oxalato ligands. The distorted octahedral geometry around each metal centre is completed in compound 1 by one water molecule and the imidazole N9 donor site of the purine ligand, which is a rare example of direct binding between the Mn(II) ion and the N donor site of an isolated nucleobase. Unlike 1, the adenine moiety in compound 2 is not bonded to manganese atoms and the metal coordination polyhedron is filled by two water molecules in a cis-arrangement. Its crystal building is constructed from pi-stacked layers of Watson-Crick hydrogen-bonded adenine...(H2O2)...adenine aggregates and zig-zag Mn(II)-oxalato chains held together by means of a strong network of hydrogen bonding interactions. The nucleobase exists in the lattice as the 7H-adenine tautomer which represents an unprecedented solid-state characterization of this minor tautomer as free molecule (without metal coordination) stabilized through non-covalent interactions. Compound consists of two slightly different [Cu(ox)(H2O)(7H-ade-kappaN9)] units in which the nucleobase coordinates through the imidazole N9 atom. The planar complex entities are parallel stacked and joined by means of long Cu-O bonds involving oxygen atoms from the oxalato and the aqua ligands, giving one-dimensional chains with a [4 + 1] square-planar pyramidal and a [4 + 2] octahedral coordination around the metal centre, respectively. Self-assembled process of compound 3 is further driven by an in-plane network of hydrogen bonding interactions to generate a porous 3D structure containing parallel channels filled by guest water molecules. Variable-temperature magnetic susceptibility measurements of all the complexes show the occurrence of antiferromagnetic interactions between the paramagnetic centres. DFT calculations have been performed to check the influence of packing in the stability of the 7H-amino tautomer of 2 and in the complex geometry of 3.

Adenine↗
PubMed2005

Synthesis, structure and spectral and redox properties of new mixed ligand monomeric and dimeric Ru(II) complexes: predominant formation of the "cis-alpha" diastereoisomer and unusual 3MC emission by dimeric complexes.

The tetradentate ligands 1,8-bis(pyrid-2-yl)-3,6-dithiaoctane (pdto) and 1,8-bis(benzimidazol-2-yl)-3,6-dithiaoctane (bbdo) form the complexes [Ru(pdto)(mu-Cl)](2)(ClO(4))(2) 1 and [Ru(bbdo)(mu-Cl)](2)(ClO(4))(2) 2 respectively. The new di-mu-chloro dimers 1 and 2 undergo facile symmetrical bridge cleavage reactions with the diimine ligands 2,2'-bipyridine (bpy) and dipyridylamine (dpa) to form the six-coordinate complexes [Ru(pdto)(bpy)](ClO(4))(2) 3, [Ru(bbdo)(bpy)](ClO(4))(2) 4, [Ru(pdto)(dpa)](ClO(4))(2) 5 and [Ru(bbdo)(dpa)](ClO(4))(2) 6 and with the triimine ligand 2,2':6,2''-terpyridine (terpy) to form the unusual seven-coordinate complexes [Ru(pdto)(terpy)](ClO(4))(2) 7 and [Ru(bbdo)(terpy)](ClO(4))(2) 8. In 1 the dimeric cation [Ru(pdto)(mu-Cl)](2)(2+) is made up of two approximately octahedrally coordinated Ru(II) centers bridged by two chloride ions, which constitute a common edge between the two Ru(II) octahedra. Each ruthenium is coordinated also to two pyridine nitrogen and two thioether sulfur atoms of the tetradentate ligand. The ligand pdto is folded around Ru(II) as a result of the cis-dichloro coordination, which corresponds to a "cis-alpha" configuration [DeltaDelta/LambdaLambda(rac) diastereoisomer] supporting the possibility of some attractive pi-stacking interactions between the parallel py rings at each ruthenium atom. The ruthenium atom in the complex cations 3a and 4 exhibit a distorted octahedral coordination geometry composed of two nitrogen atoms of the bpy and the two thioether sulfur and two py/bzim nitrogen atoms of the pdto/bbdo ligand, which is actually folded around Ru(II) to give a "cis-alpha" isomer. The molecule of complex 5 contains a six-coordinated ruthenium atom chelated by pdto and dpa ligands in the expected distorted octahedral fashion. The (1)H and (13)C NMR spectral data of the complexes throw light on the nature of metal-ligand bonding and the conformations of the chelate rings, which indicates that the dithioether ligands maintain their tendency to fold themselves even in solution. The bis-mu-chloro dimers 1 and 2 show a spin-allowed but Laporte-forbidden t(2g)(6)((1)A(1g))--> t(2g)(5) e(g)(1)((1)T(1g), (1)T(2g)) d-d transition. They also display an intense Ru(II) dpi--> py/bzim (pi*) metal-to-ligand charge transfer (MLCT) transition. The mononuclear complexes 3-8 exhibit dpi-->pi* MLCT transitions in the range 340-450 nm. The binuclear complexes 1 and 2 exhibit a ligand field ((3)MC) luminescence even at room temperature, whereas the mononuclear complexes 3 and 4 show a ligand based radical anion ((3)MLCT) luminescence. The binuclear complexes 1 and 2 undergo two successive oxidation processes corresponding to successive Ru(II)/Ru(III) couples, affording a stable mixed-valence Ru(II)Ru(III) state (K(c): 1, 3.97 x 10(6); 2, 1.10 x 10(6)). The mononuclear complexes 3-7 exhibit only one while 8 shows two quasi-reversible metal-based oxidative processes. The coordinated 'soft' thioether raises the redox potentials significantly by stabilising the 'soft' Ru(II) oxidation state. One or two ligand-based reduction processes were also observed for the mononuclear complexes.

Journal Article↗
PubMed2004

Inactivated enzymes as probes of the structure of arabinoxylans as observed by atomic force microscopy.

The complex structures of water-soluble wheat arabinoxylans have been mapped along individual molecules, and within populations, using the visualisation of the binding of inactivated enzymes by atomic force microscopy (AFM). It was demonstrated that site-directed mutagenesis (SDM) can be used to produce inactive enzymes as structural probes. For the SDM mutants AFM has been used to compare the binding of different xylanases to arabinoxylans. Xylanase mutant E386A, derived from the Xyn11A enzyme (Neocallimastrix patriciarium), was shown to bind randomly along arabinoxylan molecules. The xylanase binding was also monitored following Aspergillus niger arabinofuranosidase pre-treatment of samples. It was demonstrated that removal of arabinose side chains significantly altered the binding pattern of the inactivated enzyme. Xylanase mutant E246A, derived from the Xyn10A enzyme (Cellvibrio japonicus), was found to show deviations from random binding to the arabinoxylan chains. It is believed that this is due to the effect of a small residual catalytic activity of the enzyme that alters the binding pattern of the probe. Control procedures were developed and assessed to establish that the interactions between the modified xylanases and the arabinoxylans were specific interactions. The experimental data demonstrates the potential for using inactivated enzymes and AFM to probe the structural heterogeneity of individual polysaccharide molecules.

Carbohydrate Sequence↗
PubMed1994

Evaluating docked complexes with the HINT exponential function and empirical atomic hydrophobicities.

Methods that predict geometries of ligands binding to receptor molecules can facilitate ligand discovery and yield information on the factors governing complementarity. Here, the use of atomic hydrophobicities in evaluating binding modes has been examined with four ligand-receptor complexes of known structure. In each system, hundreds of hypothetical binding orientations were generated with DOCK and evaluated using the HINT (Hydropathic INTeractions) exponential function and atomic hydrophobic constants. In three of the four systems, the experimental binding mode received the best HINT score; in the fourth system, the experimental binding mode scored only slightly lower than a similar, apparently reasonable orientation. The HINT function may be generally useful as a scoring method in molecular docking.

Binding Sites↗
PubMed2003

Self-assembly of drug-polymer complexes: a spontaneous nanoencapsulation process monitored by atomic force microscopy.

Since hydrophilic matrices were proposed for controlled drug delivery, many polymeric excipients have been studied to make drug release fit the desired profiles. It has been pointed out that lambda-carrageenan, a sulfated polymer from algae, can suitably control the release rate of basic drugs from hydrophilic matrices. Furthermore, the relevance of hydrophobic interactions in drug-polymer aqueous systems has already been demonstrated, although no references to morphological features as well as to the kinetics of the interaction complexes formation have been published to date. In this work, we propose a method to monitor the topographical evolution of the interaction between lambda-carrageenan and dexchlorpheniramine maleate, in order to determine how the release profiles can be so easily controlled. For this purpose, solutions of both polymer and drug were prepared at very low concentration. Solutions were mixed and small volumes were taken every hour for over a period of 24 h and subsequently analyzed. The characterization technique used, atomic force microscopy, provides a high resolution, allowing plotting of three-dimensional images of the sample morphology within the nanometric scale. The results demonstrate that lambda-carrageenan is able to nanoencapsulate spontaneously dexchlorpheniramine maleate molecules, which offers the possibility of controlling the release rate of the drug with no need of complex technological processes. Moreover, this work demonstrates the suitability of atomic force microscopy for the specific case of the on-time monitoring of interaction processes that occur in pharmaceutical systems.

Carrageenan↗
PubMed1997

Subtle hydrophobic interactions between the seventh residue of the zinc finger loop and the first base of an HGATAR sequence determine promoter-specific recognition by the Aspergillus nidulans GATA factor AreA.

A change of a universally conserved leucine to valine in the DNA-binding domain of the GATA factor AreA results in inability to activate some AreA-dependent promoters, including that of the uapA gene encoding a specific urate-xanthine permease. Some other AreA-dependent promoters become able to function more efficiently than in the wild-type context. A methionine in the same position results in a less extreme, but opposite effect. Suppressors of the AreA(Val) mutation mapping in the uapA promoter show that the nature of the base in the first position of an HGATAR (where H stands for A, T or C) sequence determines the relative affinity of the promoter for the wild-type and mutant forms of AreA. In vitro binding studies of wild-type and mutant AreA proteins are completely consistent with the phenotypes in vivo. Molecular models of the wild-type and mutant AreA-DNA complexes derived from the atomic coordinates of the GATA-1-AGATAA complex account both for the phenotypes observed in vivo and the binding differences observed in vitro. Our work extends the consensus of physiologically relevant binding sites from WGATAR to HGATAR, and provides a rationale for the almost universal evolutionary conservation of leucine at the seventh position of the Zn finger of GATA factors. This work shows inter alia that the sequence CGATAGagAGATAA, comprising two almost adjacent AreA-binding sites, is sufficient to ensure activation of transcription of the uapA gene.

Aspergillus nidulans↗
PubMed2002

Living polymerization of ethylene catalyzed by titanium complexes having fluorine-containing phenoxy-imine chelate ligands.

Seven titanium complexes bearing fluorine-containing phenoxy-imine chelate ligands, TiCl(2)[eta(2)-1-[C(H)=NR]-2-O-3-(t)Bu-C(6)H(3)](2) [R = 2,3,4,5,6-pentafluorophenyl (1), R = 2,4,6-trifluorophenyl (2), R = 2,6-difluorophenyl (3), R = 2-fluorophenyl (4), R = 3,4,5-trifluorophenyl (5), R = 3,5-difluorophenyl (6), R = 4-fluorophenyl (7)], were synthesized from the lithium salt of the requisite ligand and TiCl(4) in good yields (22%-76%). X-ray analysis revealed that the complexes 1 and 3 adopt a distorted octahedral structure in which the two phenoxy oxygens are situated in the trans-position while the two imine nitrogens and the two chlorine atoms are located cis to one another, the same spatial disposition as that for the corresponding nonfluorinated complex. Although the Ti-O, Ti-N, and Ti-Cl bond distances for complexes 1 and 3 are very similar to those for the nonfluorinated complex, the bond angles between the ligands (e.g., O-Ti-O, N-Ti-N, and Cl-Ti-Cl) and the Ti-N-C-C torsion angles involving the phenyl on the imine nitrogen are different from those for the nonfluorinated complex, as a result of the introduction of fluorine atoms. Complex 1/methylalumoxane (MAO) catalyst system promoted living ethylene polymerization to produce high molecular weight polyethylenes (M(n) > 400 000) with extremely narrow polydispersities (M(w)/M(n) < 1.20). Very high activities (TOF > 20 000 min(-1) atm(-1)) were observed that are comparable to those of Cp(2)ZrCl(2)/MAO at high polymerization temperatures (25, 50 degrees C). Complexes 2-4, which have a fluorine atom adjacent to the imine nitrogen, behaved as living ethylene polymerization catalysts at 50 degrees C, whereas complexes 5-7, possessing no fluorine adjacent to the imine nitrogen, produced polyethylenes having M(w)/M(n) values of ca. 2 with beta-hydrogen transfer as the main termination pathway. These results together with DFT calculations suggested that the presence of a fluorine atom adjacent to the imine nitrogen is a requirement for the high-temperature living polymerization, and the fluorine of the active species for ethylene polymerization interacts with a beta-hydrogen of a polymer chain, resulting in the prevention of beta-hydrogen transfer. This catalyst system was used for the synthesis of a number of unique block copolymers such as polyethylene-b-poly(ethylene-co-propylene) diblock copolymer and polyethylene-b-poly(ethylene-co-propylene)-b-syndiotactic polypropylene triblock copolymer from ethylene and propylene.

Journal Article↗
PubMed2006

Validity of phase space theory for atom-diatom insertion reactions.

Phase space theory (PST) is applied to the calculation of state-resolved integral and differential cross sections for the complex-forming atom-diatom insertion reactions A + H(2) --> AH(2) --> AH + H with A = C((1)D), S((1)D), O((1)D), and N((2)D). In the asymptotic channels, vibration motion is quantized while rotation and translation motions are treated classically. The approach is compared to exact quantum scattering calculations and quantum statistical models. Given the simplicity of PST, the agreement with the previous much more refined treatments is very satisfying. Although PST is a well-established theory, this work is, to our knowledge, the first such systematic comparison of its predictions with accurate quantum scattering and quantum statistical calculations.

Journal Article↗
PubMed2005

Atomic and electronic structure of mixed and partial dislocations in GaN.

Here we present a detailed study of mixed dislocations in GaN, in which the complexities of the atomic arrangement in the cores have been imaged directly for the first time using an aberration corrected scanning transmission electron microscope. In addition to being present as a full-core structure, the mixed dislocation is observed to dissociate into partial dislocations separated by a stacking fault only a few unit cells in length. The generation of this stacking fault appears to be impurity driven and its presence is consistent with theoretical predictions for dislocation dissociation in materials with hexagonal crystal symmetry.

Journal Article↗
PubMed2006

RNA polymerase and an activator form discrete subcomplexes in a transcription initiation complex.

Using high-resolution atomic force microscopy (AFM) we show that in a ternary complex of an activator protein, FIS, and RNA polymerase containing the sigma(70) specificity factor at the Escherichia coli tyrT promoter the polymerase and the activator form discrete, but connected, subcomplexes in close proximity. This is the first time that a ternary complex between an activator, a sigma(70) polymerase holoenzyme and promoter DNA has been visualised. Individually FIS and RNA polymerase wrap approximately 80 and 150 bp of promoter DNA, respectively. We suggest that the architecture of the ternary complex provides a general paradigm for the facilitation of direct, but weak, interactions between polymerase and an activator.

DNA↗
PubMed2001

Saccharinate as a versatile polyfunctional ligand. Four distinct coordination modes, misdirected valence, and a dominant aggregate structure from a single reaction system.

The reaction system consisting of copper, saccharinate, and the auxiliary ligands H(2)O, PPh(3), and NH(3) produces a sequence of compounds in which saccharinate is coordinated to copper in four distinct manners. The complex trans-[Cu(sacch)(2)(H(2)O)(4)] (2) (produced by thermal dehydration of trans-[Cu(sacch)(2)(H(2)O)(4)].2H(2)O (1)) reacts with triphenylphosphine in CH(2)Cl(2) to produce any or all of three Cu(I) complexes, depending upon conditions. The three Cu(I) compounds are Cu(sacch)(PPh(3))(3) (3), in which saccharinate binds to copper through the carbonyl group of the ligand, Cu(sacch)(PPh(3))(2) (4), in which sacch binds to Cu through its charge-bearing nitrogen atom; and [Cu(sacch)(PPh(3))](2) (5), a dinuclear complex in which saccharinate bridges two Cu centers through its imidate nitrogen and carbonyl oxygen atoms. Complexes 3-5 can be isolated individually, although in solution they exist in a complex equilibrium which has been examined by NMR spectroscopy. Each of the three Cu(I) products reacts with NH(3) in CH(2)Cl(2) solution to produce trans-[Cu(sacch)(2)(NH(3))(4)] (6), an unstable Cu(II) complex that exhibits misdirected valence at the Cu-N(sacch) bond. Complex 6 evolves spontaneously to [Cu(sacch)(NH(3))(4)](sacch).H(2)O (7), which in the solid state is dominated by a supramolecular aggregate of two formula units, linked by hydrogen bonding in which the water molecule plays a central role. Alternative pathways exist to several of the products. The X-ray crystal structure analyses of 3-7 are reported and establish the coordination modes of saccharinate, the misdirected valence in 6, and the supramolecular aggregation in 7. The structure analysis of 7 by single-crystal neutron diffraction is reported and together with the previously reported neutron structure analysis of 1 establishes the substitution of the auxiliary ligand H(2)O by NH(3) in the Cu(II) products.

Journal Article↗