The binding of divalent metal ions to polyelectrolytes in mixed counterion systems. II. Dextransulfate-Mg2+ and dextransulfate-Ca2+ in solutions containing added NaCl or KCl

Measurements of magnesium and calcium ion activities in solutions of the polyelectrolyte dextransulfate, with added sodium chloride or potassium chloride are presented. A two wavelength dye spectrophotometric method is used. Dextransulfate concentrations Cp (expressed as moles sulfate ion/litre) vary between 0.001 and 0.007, total ionic strengths between 0.005 and 0.08 mole/XXX. Divalent metal ion concentrations are varied between 0 and 1.2 Cp. The results for the metal ion activities are expressed in the form of parameters theta2 = C2/Cp (C(2bp) = bound divalent metal ion concentration) and K2 = theta2/(C2-C2b). For each divalent/univalent counterion pair the values obtained for theta2 and K2 as a function of C2,Cp, and ionic strength are compared to predictions of the "two variable theory" developed for these mixed counterion systems by Manning. This comparison shows that the observed decrease in theta2 with increasing ionic strength at fixed C2 and Cp is generally well predicted by the two variable theory. The extent of divalent ion binding at a given C2, Cp, and ionic strength is largest for the Ca/Na counterion combination, and lowest for the Mg/K combination.     

Binding thermodynamics of phosphorylated inhibitors to triosephosphate isomerase and the contribution of electrostatic interactions

Electrostatic interactions have a central role in some biological processes, such as recognition of charged ligands by proteins. We characterized the binding energetics of yeast triosephosphate isomerase (TIM) with phosphorylated inhibitors 2-phosphoglycollate (2PG) and phosphoglycolohydroxamate (PGH). We determined the thermodynamic parameters of the binding process (K_b, ΔG_b, ΔH_b, ΔS_b and ΔC_p) with different concentrations of NaCl, using fluorimetric and calorimetric titrations in the conventional mode of ITC and a novel method, multithermal titration calorimetry (MTC), which enabled us to measure ΔC_p in a single experiment. We ruled out specific interactions of Na⁺ and Cl^- with the native enzyme and did not detect significant linked protonation effects upon the binding of inhibitors. Increasing ionic strength (I) caused K_b, ΔG_b and ΔH_b to become less favorable, while ΔS_b became less unfavorable. From the variation of K_b with I, we determined the electrostatic contribution of TIM−2PG and TIM−PGH to ΔG_b at I = 0.06 M and 25 °C to be 36% and 26%, respectively. The greater affinity of PGH for TIM is due to a more favorable ΔH_b compared to 2PG (by 19-24 kJ mol^-1 at 25 °C). This difference is compatible with PGH establishing up to five more hydrogen bonds with TIM. Both binding ΔC_ps were negative, and less negative with increasing ionic strength. ΔC_ps at I = 0.06 M were much more negative than predicted by surface area models. Water molecules trapped in the interface when ligands bind to protein could explain the highly negative ΔCps. Thermodynamic binding functions for TIM−2PG changed more with ionic strength than those for TIM−PGH. This greater dependence is consistent with linked, but compensated, protonation equilibriums yielding the dianionic species of 2PG that binds to TIM, process that is not required for PGH.     

Bi-ionic potentials of bovine lens capsules and collodion membranes

Concentration dependencies of bi-ionic potentials of well-cleaned bovine lens capsules in vitro, of collodion and of modified collodion membranes were studied. The lens capsules have positively fixed charges, and collodion membranes have negatively fixed charges. As these membranes are partially selectively permeable, both co-ions and counter-ions exist in the membrane. However, many studies on bi-ionic potentials have been limited to systems in which the membrane has extreme ionic selectivity and co-ions are completely excluded from the membrane. Experimental results agreed with theoretical values obtained by assuming the common ion concentration to be constant throughout the membrane for systems such as KCl(C)-membrane (θ>0, or θ<0)-NaCl(C), NaNO₃(C)-membrane (θ>0)-NaCl(C) and CaCl₂(C₁)-membrane (θ>0)-NaCl(C₂) (C₂/C₁ = 2), where C is the bulk concentration. The theoretical reliability of this assumption was checked. When both electrolytes in solution were uni-univalent, the ratio of ionic mobilities of two counter-ions (or two co-ions) in all of these membranes was almost the same as the ratio obtained in bulk solution, while the ratio of ionic mobilities of the counter-ion and the co-ion was almost the same as the ratio obtained in bulk solution for the lens capsule, but different in the case of the collodion and modified collodion membranes.     

Effect of salt on sodium polystyrene sulfonate measured by light scattering

The quasielastic light scattering method was used to study the ionic strength dependence of the mutual diffusion coefficient of sodium polystyrene sulfonate (NaPSS) as a function of NaCl and CaCl₂ concentrations. The results indicate a splitting in the relaxation times that depends on the ratio C_p/C_s, where C_p and C_s are the polyion and added salt concentrations. A universal relationship taking into account Manning's theory of condensation and the Debye screening due to the added salt is proposed to characterize the fast–slow relaxation time transition.     

Effects of Resonant Magnetic Fields on Chick Femoral Development In Vitro

To assess the possibility that specific ionic resonances can influence bone development, 8-day chick femoral rudiments were explanted to lens paper rafts in BGJ_b medium and exposed for 1/2 hr/day to combined 16 or 80 Hz, 2 × 10^?5 T (Tesla) peak sinusoidal and various static magnetic fields tuned to calcium, magnesium, potassium (16 Hz), and combined Ca/Mg (80 Hz) ion cyclotron resonances (CR) for I days. Ca/Mg tuned cultures were also exposed to 24, 4, 1, and 1/2 hr/day regimes to test for dose-response. Tuning for Ca, Mg, or Ca/Mg increased rudiment length and mid-shaft diameter, diaphyseal collar length     

Ion distributions around left- and right-handed DNA and RNA duplexes: a comparative study

The ion atmosphere around nucleic acids is an integral part of their solvated structure. However, detailed aspects of the ionic distribution are difficult to probe experimentally, and comparative studies for different structures of the same sequence are almost non-existent. Here, we have used large-scale molecular dynamics simulations to perform a comparative study of the ion distribution around (5′-CGCGCGCGCGCG-3′)₂ dodecamers in solution in B-DNA, A-RNA, Z-DNA and Z-RNA forms. The CG sequence is very sensitive to ionic strength and it allows the comparison with the rare but important left-handed forms. The ions investigated include Na⁺, K⁺ and Mg^{2 +}, with various concentrations of their chloride salts. Our results quantitatively describe the characteristics of the ionic distributions for different structures at varying ionic strengths, tracing these differences to nucleic acid structure and ion type. Several binding pockets with rather long ion residence times are described, both for the monovalent ions and for the hexahydrated Mg[(H₂O)₆]²⁺ ion. The conformations of these binding pockets include direct binding through desolvated ion bridges in the GpC steps in B-DNA and A-RNA; direct binding to backbone oxygens; binding of Mg[(H₂O)₆]²⁺ to distant phosphates, resulting in acute bending of A-RNA; tight ‘ion traps’ in Z-RNA between C-O2 and the C-O2′ atoms in GpC steps; and others.     

A new radiochemical method to investigate ion binding with polyelectrolytes

A new method for investigating the binding of ions with polyelectrolytes has been developed. This method, based on Donnan equilibrium and an isotope exchange between the electrolyte and polyelectrolyte, can distinguish territorial from specific binding of ions and can determine fractions of ions bound with the polyion. This method can determine ion binding with polyelectrolytes in a wide range of polyelectrolyte concentrations in multicomponent solutions. The method was tested with radioactive tracers 22Na+, 36Cl- and heparin sodium salt. The influence of the ionic strength on the Na+ binding with heparin was investigated at 310 K. In the limit of zero ionic strength, all Na+ ions are bound to heparin, but only 45% of them are exchangeable. Thus Na+ ions can be bound both territorially and specifically. The fraction of bound ions decreases rapidly with increasing ionic strength. The fraction of the specifically bound ions becomes negligible when the ionic strength exceeds 0.01 M, whereas the fraction of territorially bound ions can be neglected at ionic strengths higher than 0.45 M.     

Binding of Heparin to Metals

Heparin is a major prophylactic and treatment agent for thrombosis. Structurally, this anticoagulant is a polydisperse, highly negatively charged polysaccharide mixture that contains a variable density of sulfate group substituents per molecule. Previous study has shown that heparin molecules have a high affinity for a wide range of metal ions with varying oxidation states. However, reports in literature on binding of heparin to metals have investigated only a small sampling of heparin–metal ion interactions. Since interaction of heparin with fluid phase and cell surface macromolecules in vivo is dependent on the heparin structure when bound in a metal ion complex, a survey of the physical parameters for heparin binding to metals is imperative. Atomic absorption and spectrophotometry experiments were performed for metal quantification, and in this study, the relative values for affinity constants and number of binding sites for heparin binding to several alkaline, alkaline earth, main group, and transition metals in their most common oxidation states are reported. We found an overall trend for heparin–metal affinity to be Mn²⁺ > Cu²⁺ > Ca²⁺ > Zn²⁺ > Co²⁺ > Na⁺ > Mg²⁺ > Fe³⁺ > Ni²⁺ > Al³⁺> Sr²⁺, with the trend in N _b being opposite compared with the K _a.     

Cation binding to beta-casein. A comparison of electrostatic models

The binding of cations of β-casein at pH 6.6 was considered previously. Available for three sodium concentiations, I = 0.04, 0.08, or 0.16 M are: [1] proton releases between I and [2] for each I, as calcium activity is increased, correlated sequences of monomer net charge, proton release, site bound calcium and protein Solvation- Models for ion binding are examined. Critical considerations are the intrinsic binding constants between hydrogen[H], calcium[Ca] and sodium[Na] ions and phosphate[P] and caiboxyIate[C] sites, and the effects of electrostatic interaction between sites as influenced by spatial fixed charge distribution, ionic strength and dielectric constant [D]. Anticipated intrinsic binding constants are k_H,P^o = 3 × 10⁶, k_Ca,P^o = 120, k_Na,P^o = 1, k_H,C^o = 7 × 10⁴ and k_Ca,C^o = 5.6Distributed charge models, either surface or volume, are inadequate since any reasonable monomer size yields fixed charge densities requiring k_H,P^o and k_Ca,C^o which are too low when the maximum in D is 75. Also, with increasing calcium binding, calculated proton release is only 0.4 to 0.5 of that observed.Discrete charge models accept anticipated k^o and yield calculated sequences of calcium binding and proton release which are in good agreement with those observed provided that: (1) using the known amino acid sequence of the phosphate-containing acidic peptide portion of the molecule, pep tide fixed charge is distributed at the lowest I so as to minimize electrostatic free energy; (2) in the region of fixed charge, D is approximately 5; (3) the distances between peptide fixed charges decrease with increasing ionic strength or calcium binding and (4) while protein is in solution, the acidic peptide and the remainder of the molecule are essentially electrostatically independent.     

Sucrose interaction with alkaline earth metal ions. Synthesis,spectroscopic and structural characterization of sucrose adducts with the Mg(II) and Ca(

Crystalline sucrose interacts with hydrous alkaline earth metal ions to give adducts of the type Mg(sucrose)Cl₂.4H₂O, Mg(sucrose)₂Br₂.4H₂O, Ca(sucrose)Cl₂.2H₂O, and Ca(sucrose)₂Br₂.2H₂O. These adducts are characterized by means of elemental analysis, FT-IR spectroscopy. X-ray powder diffraction, and molar conductivity measurements.Due to the marked spectral similarities with those of the structurally known Na(sucrose)Br.2H₂O and other Na-sucrose adducts in the 1:1 metal sugar compounds, the Mg(II) ion is possibly six-coordinate, binding to two sucrose molecules via O(4), O(6) of the first sugar and O(6') of the second molecule and to three H₂O, whereas in the 1:2 metal-sugar adducts, magnesium ion binds to two sugar molecules through O(4), O(6) and to two H₂O, resulting in a six-coordination geometry around the Mg(II) ion. The Ca(II) ion is possibly seven-coordinate in the 1:1 metal-sugar compound, binding to two sucrose molecules through O(4), O(6) of the first and O(6') of the second sugar and to two H₂O molecules as well as to two halide anions, while in the 1:2 metal-sugar adduct it could be bonded to four sugar molecules via O(4), O(6) of the two and O(6') of the other two molecules and to two H₂O, resulting in an eight-coordination geometry around the Ca(II) ion. Upon metal adduct formation, the strong sugar hydrogen bonding network is rearranged to that of the sucrose-OH ... H₂O ... halide ... OH-sucrose system.     

Gadolinium asa probe of the alkaline earth and ATP-metal binding sites in pyruvate kinase

The rare earth gadolinium forms a binary enzyme-metal complex with muscle pyruvate kinase which enhances the water proton relaxation rate (?_b = 12 ± 2). Analysis of a Scatchard plot of the binding data indicates 3.7 ± 0.5 gadolinium binding sites with K_d = 26 ± 10 μM per protein of 237,000 daltons. The transition metal ion, manganese, is displaced from the enzyme by the rare earths, gadolinium, neodymium, thulium, and lanthanum as well as the alkaline earths, magnesium and calcium suggesting all of these metal ions bind to the same site on the protein. Upon addition of ATP to a solution of gadolinium and enzyme a decrease in enhancement is observed which is consistent with the formation of a metal bridge complex. Because of the low dissociation constant for the Gd-ATP complex (0.1 μm) it is possible to directly measure the dissociation of the Gd-ATP complex from the ternary enzyme-Gd-ATP complex, K₂ = 13 μM ± 4 μM. However, a ternary complex of phospho-enolpyruvate-Gd-enzyme is not detected by water proton relaxation rate enhancement measurements which leads to speculation that the ionic radius of gadolinium (0.94 Å) is so large that it results in a distortion of the phosphoenolypyruvate binding site on pyruvate kinase thus preventing phosphoenolpyruvate binding.     

Hydrothermal synthesis and structural investigation of silver magnesium complex of benzenehexacarboxylic acid (mellitic acid), Ag2Mg2[C6(COO)6] · 8H2O with two-dimensional layered structure

Crystal and molecular structure of silver magnesium mellitate, Ag₂Mg₂[C₆(COO)₆] · 8H₂O, was synthesized hydrothermally and characterized by X-ray structure analysis. The complex crystallizes in the monoclinic system, space group P2/n, with unit cell dimensions of a=7.4347(2), b=9.9858(2), c=14.4248(3) Å, β=99.2429(5)°, V=1055.01(4) ų, and Z=2. The structure was solved and refined to R=0.036 (R_w=0.045) for 1707 independent reflections [I_o>2σ(I_o)]. The Ag cations are coordinated by six carboxylic oxygen atoms of mellitate anions with composition of [C₆(COO)₆]⁶⁻ on the (1 0 1) plane; each mellitate anion linking three neighboring Ag distorted trigonal prisms produces a two-dimensional layered structure parallel to (1 0 1). The Mg cations, which are coordinated by four water molecules and two carboxylic oxygen atoms, are intercalated between the two-dimensional layer stacks. The carboxylate group coordinated to Mg and Ag cations serve as a tridentate ligand in that structure. The number of water molecules incorporated into the mellitate compound is controlled mainly by ionic radii of metal cation in the structure. Furthermore, the ionic radii of metal cations in the mellitate compound play an essential role in arrangement of mellitate anions in the structure, whether as a one-dimensional infinite chain, a two-dimensional layered structure, or a three-dimensional framework structure.     

Synthesis,FT-IR and 1H NMR studies of alkali and alkaline earth metal complexes with guanosine

The synthesis of complexes of Li(I), K(I), Mg(II), Ca(II) and Ba(II) with guanosine in basic non aqueous solutions is described. The complexes were of two types: (1) complexes having the general formula, M(Guo)_nX_m·YH₂O·ZC₂H₅OH, where M = Mg(II), Ca(II), Ba(II) and Li(I), n = 1,2,4, X = Cl^?, Br^?, NO₃^?, ClO₄^? and OH^?, m = 1,2, Y = 0?6 and X = 0?2, and (2) complexes with the general formula, M(GuoH-1)(OH)_n^?1·YH₂O, where M = K(I), Ca(Il) and Ba(II), GuoH-1 =Ionized guanosine at N₁, n = 1,2 and Y = 1?3. The complexes are characterized by their proton nuclear magnetic resonance (¹H NMR) and Fourier transform infrared (FT-IR) spectra. The FT-IR and ¹H NMR data of the non ionized nucleoside complexes suggest that the metal binding is through the N₇-site of guanine and that the anion (X) is hydrogen bonded to N₁H and NH₂ groups. In the N₁-ionized guanosine complexes the metal binding is via the O₆^? of guanine. All the complexes formed exhibited a transition of the sugar conformation from C₂′-endo/anti in the free nucleoside to C₃′-endo/anti in the metal complexes.     

Analysis of cooperativity and ion effects in the interaction of quinacrine with DNA

The interaction of quinacrine with calf thymus DNA was monitored at several different ionic strengths using spectrophotometric and equilibrium dialysis techniques. The binding results can be explained, assuming each base pair is a potential binding site, using a model containing two negative cooperative effects: (1) ligand exclusion at binding sites adjacent to a filled binding site and (2) ligand–ligand negative cooperativity at adjacent filled binding sites. The logarithm of the observed equilibrium constant (K_obs) determined by this model varies linearily with log[Na⁺], as predicted by the ion condensation theory for polyelectrolytes. When the log K_obs plot is correlated for sodium release by DNA in the intercalation conformational change, the predicted number of ion pairs between the ligand and DNA is approximately two, as expected for the quinacrine dication. Even though K_obs depends strongly on ionic strength, the ligand negative cooperativity parameter ω was found to be indpendent of ionic strength within experimental error. This finding is also in agreement with the ion condensation theory, which predicts a relatively constant amount of condensed counterion on the DNA double helix over this ionic strength range. Drugs would, therefore, experience a relatively constant ionic environment when complexed to DNA even though the ionic conditions of the solvent could change considerably.     

Heat capacity effects of water molecules and ions at a protein-DNA interface

The interaction of the TATA-box binding protein from the thermophilic and halophilic archaea Pyrococcus woesei (PwTBP) with an oligonucleotide containing a specific binding site is stable over a very broad range of temperatures and ionic strengths, and is consequently an outstanding system for characterising general features of protein-DNA thermodynamics. In common with other specific protein-DNA recognition events, the PwTBP-TATA box interaction is accompanied by a large negative change in heat capacity (ΔC_p) arising from the total change in solvation that occurs upon binding, which in this case involves a net uptake of cations. Contrary to previous hypotheses, we find no overall effect of ionic strength on this heat capacity change. We investigate the local contributions of site-specific ion and water binding to the overall change in heat capacity by means of a series of site-directed mutations of PwTBP. We find that although changes in the local ion binding capacity affect the enthalpic and entropic contributions to the free energy of the interaction, they do not affect the change in heat capacity. In contrast, we find remarkably large heat capacity effects arising from two particular symmetry-related mutations. The great magnitude of these effects is not explicable in terms of current semi-empirical models of heat capacity change. Previously reported X-ray crystal structures show that these mutated residues are at the centre of an evolutionarily conserved network of water-mediated hydrogen bonds between the protein and the DNA backbone. Consequently, we conclude that, in addition to water molecules buried in the protein-DNA interface that have been previously shown to influence heat capacity, bridging water molecules in a highly polar surface environment can also contribute substantially to negative heat capacity change on formation of a protein-DNA complex.     

Purification of three γ-chains with different molecular weights from normal human plasma fibrinogen

Three forms of the normal human plasma fibrinogen γ-chain which differ in molecular weight have been purified. Plasma fibrinogen was separated by ion exchange chromatography on DEAE-Sephacel into three populations of molecules, each with a unique γ-chain composition. Following reduction and S-carboxymethylation, the fibrinogen polypeptide chains in each chromatographic peak were separated by ion exchange chromatography on DEAE-Sephacel and identified following sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The Aα, Bβ and smallest γ-chain (γ₅₀) eluted at progressively higher ionic strengths, but the elution positions of Aα, Bβ and γ₅₀ chains were identifcal for fibrinogen from each of the three different chromatographic fractions. The unique γ chain of fibrinogen in the second chromatographic peak (γ₅₅) eluted at an ionic strength higher than that of the γ₅₀ chain, while the largest γ-chain (γ_57.5), which was contained only in the third chromatographic peak of fibrinogen, eluted at the highest ionic strength. The higher ionic strengths needed to elute fibrinogen in the second and third peaks was paralleled by the higher ionic strengths needed to elute the γ-chains unique to them, suggesting that the γ-chain composition of the three fibrinogen fractions accounted for their differential binding to the ion exchange resin. Following desialation with neuraminidase, the differences in electrophoretic mobilities between the three γ-chain forms was maintained, indicating that differential migration on SDS-polyacrylamide gel electrophoresis was not due to variation in sialic acid content.     

Binding changes and apparent pK a shifts of bromthymol blue as tools for mitochondrial reactions

The passive interaction of bromthymol blue and other anionic and neutral dyes with mitochondria and particles is accompanied by an increase of the apparent pK_a, is enhanced at higher ionic strengths, is slightly inhibited by neutral dyes, is high only for the acidic, un-ionized form, and is independent of the presence of the sulfonic side chain. The pH dependence for the binding of the dyes follows the ionization of the chromophoric group: the pK of binding, defined as the pH for 50% binding, is identical with the apparent pK_a of the dye.     

Characterizing metalloendonuclease mixed metal complexes by global kinetic analysis

To test the role of a secondary metal ion in a two metal ion metallonuclease mechanism, some groups have introduced a nonsupportive metal ion [usually Ca(II)] in cleavage reactions. Stimulation of Mg(II)- or Mn(II)-supported activity has been taken as evidence that the second metal ion is regulatory. However, this activity has yet to be dissected to determine what processes and species contribute to this observation. Here, we test global kinetic analysis as an approach to this problem. Taking advantage of the various binding and cleavage constants established for PvuII endonuclease, we apply cleavage data obtained under a range of Mg(II) and Ca(II) concentrations to a number of kinetic models which specify A and B sites for both metal ions and various active species. The data are best fit and simulated with models which feature Ca(II) being held more strongly in the B (or secondary) site. This mixed metal enzyme species is the only one which forms appreciably and exhibits a cleavage rate constant similar to that observed when there is only one Mg(II) per active site (approximately 0.01 s^?1). Thus, in the case of PvuII endonuclease, Ca(II) does not stimulate cleavage. However, a simulated increase in activity at moderate Ca(II) concentrations can be rationalized with a cleavage rate constant for the mixed species similar to that when two Mg(II) ions are present in the active site. This provides an important insight into the underlying basis for the Ca(II)-stimulated activity observed for some metallonucleases that is not accessible by any other means.     

Homo- and heteronuclear complexes based on arene ruthenium complexes bearing bis(diphenylphosphinomethyl)phenylphosphine (dpmp)

Reactions of [(p-cymene)RuCl₂]₂ (1a) with dpmp ((Ph₂PCH₂)₂PPh) in the absence or presence of KPF₆ afforded the ionic complexes [{(p-cymene)RuCl₂}(dpmp-P¹,P³;P²){RuCl(p-cymene)}](X) (2a₁: X=Cl; 2a₂: X=PF₆). A (p-cymene)RuCl moiety constructs a 6-membered ring coordinated by two terminal P atoms of the dpmp ligand and another one binds to a central P atom of the ligand. Reactions of [(C₆Me₆)RuCl₂]₂ (1b) with an excess of dpmp in the presence of KPF₆ gave a 4-membered complex [(C₆Me₆)RuCl(dpmp-P¹,P²)](PF₆) (3b), chelated by a terminal and a central P atom and another terminal atom is free. Use of Ag(OTf) instead of KPF₆ gave [{(C₆Me₆)RuCl₂(dpmp)Ag} ₂](OTf)₂ (5b) that the Ag atoms were coordinated by a terminal and a central P atom of each dpmp ligand. Reaction with an equivalent of dpmp in the presence of KPF₆ gave [{(C₆Me₆)RuCl}(dpmp-P¹,P²;P³){(C₆Me₆)RuCl₂}](PF₆) 4b. Complex has a structure that the (C₆Me₆)RuCl₂ moiety coordinated to the free P atom of 3b. Complex 3b was treated with MCl₂(cod) (M=Pd, Pt), [Pd(MesNC)₄](PF₆)₂ (MesNC=2,4,6-Me₃C₆H₂NC) or [Pt₂(XylNC)₆](PF₆)₂ (XylNC=2,6-Me₂C₆H₃NC), generating [{(C₆Me₆)RuCl(dpmp)}₂MCl₂](PF₆)₂ (8b: M=Pd; 9b: M=Pt), [{(C₆Me₆)RuCl(dpmp)}₂{Pt(MesNC)₂}](PF₆)₄ (10b) and [{(C₆Me₆)RuCl(dpmp)}₂{Pt₂(XylNC)₄}](PF₆)₄ (11b), respectively. Complex 3b reacted readily with [Cp*MCl₂]₂ (M=Rh, Ir) or AuCl(SC₄H₈), affording the corresponding hetero-binuclear complexes [{(C₆Me₆)RuCl}(dpmp-P¹,P²;P³)(MCl₂Cp^*](PF₆) (6b: M=Rh; 7b: M=Ir) and [{(C₆Me₆)RuCl}(dpmp-P¹,P²;P³)(AuCl)](PF₆) (12b). These complexes have two chiral centers. Some complexes were separated as two diastereomers by successive recrystallization. The structures of 3b, 5b, 6b, 8b and 12b were confirmed by X-ray analyses.