Monomolecular condensation of lambda-DNA induced by cobalt hexamine

Measurements of static and dynamic light scattering have been used to distinguish between monomolecular DNA condensation and aggregation of condensed molecules. In low salt, using Co³⁺(NH₃)₆ as the condensing agent, and at λ-DNA concentrations below 0.2 μg/mL, the transition curves for monomolecular condensation and aggregation are well separated for times of 16 h. In these conditions, the intensity of scattered light (90°) and also the diffusion coefficient of the condensed DNA show reasonable values for monomolecular condensation that are independent of DNA concentration and also of Na⁺ Co³⁺(NH₃)₆ concentrations for which monomolecular condensation is complete. At higher Co³⁺(NH₃)₆ concentrations, which produce aggregation (as judged by the intensity of scattered light), the diffusion coefficient decreases sharply. The transition curve for monomolecular condensation is independent of DNA concentration but shows a hysteresis loop. The kinetics of condensation are slow in the forward direction and fast in the reverse direction, indicating that the actual transition curve is measured closely by reversal experiments. Aggregation is blocked kinetically in both the forward and reverse directions when Co³⁺(NH₃)₆ is the condensing agent at low Na⁺ concentrations. When spermine or spermidine is the condensing agent and observations are made at 16 h, it is not possible to separate the transition curves for monomolecular condensation and for aggregation in conditions that are successful with Co³⁺(NH₃)₆. Some interesting properties of monomolecular condensation are noted. (1) The transition is not a two-state reaction, as judged by measurements of the diffusion coefficient through the transition zone. (2) The transition for monomolecular condensation is diffuse. (3) The dimensions of the monomolecular condensates have been calculated from the translational diffusion coefficient for an assumed toroidal shape by the formula derived by Allison and coworkers [(1981) Biopolymers 20 , 469–488]. These dimensions are in reasonable agreement with ones deduced from electron microscopy by Chattoraj and coworkers [(1978) J. Mol. Biol. 121 , 327–337]. (4) The phase diagram relating the Na⁺ to the Co³⁺(NH₃)₆ concentrations needed for condensation has a slope of 0.6 in a log–log plot. According to numerical solutions of Manning's theory for the atmospheric binding of competing cations to DNA, this means that condensation occurs at a late stage in the replacement of Na⁺ by Co³⁺(NH₃)₆ around the DNA. The fraction of DNA phosphate charge neutralized at condensation is computed to be in the neighborhood of 0.9, as found by Wilson and Bloomfield [(1979) Biochemistry 18 , 2192–2196], but to vary with the Na⁺ concentration.     

Inhibition of cation-induced DNA condensation by intercalating dyes

Several intercalating dyes are shown to inhibit the cation-induced condensation of λ-DNA when Co³⁺(NH₃)₆ is the condensing agent. The dyes that have been studied are ethidium, propidium, proflavin, quinacrine, and actinomycin D. Earlier work has shown that intercalating dyes inhibit ψ-DNA condensation. [Lerman, L. S. (1971) Prog. Mol. Subcell. Biol. 2 , 382–391; Cheng, S. & Mohr, S. C. (1975) Biopolymers 14 , 663–674.] Dye-induced decondensation of intramolecularly condensed DNA has been studied by making use of conditions in which Co³⁺(NH₃)₆ produces intramolecular condensation without significant aggregation. Some aggregation is caused, however, during dye-induced decondensation. Dye titration curves of DNA decondensation have been measured by excess light scattering to monitor decondensation and by fluorescence to monitor intercalation. All of the dyes studied act as competing cations in displacing the condensing cation Co³⁺(NH₃)₆ from the DNA. Competition occurs both in and below the transition zone for condensation. The effectiveness of a dye as a competing cation increases with its net positive charge. Before decondensation begins, no intercalated dye can be detected, suggesting that intercalation might be incompatible with the proper helix packing needed for cation-induced DNA condensation. To test this last point, methidium–spermine was synthesized: it contains an intercalating methidium head group combined with a polyamine tail. Methidium–spermine is found to cause λ-DNA condensation, but aggregation accompanies condensation, as has been found earlier for spermine and spermidine. Fluorescence and absorption spectra indicate that the methidium group is intercalated when the DNA is condensed, indicating that intercalation need not be incompatible with DNA condensation. The presence of aggregates among the condensed DNA molecules makes this last conclusion tentative.     

Polyamine-like effects of cobalt(III) hexaammine on various cyclic nucleotide-independent protein phosphokinase reactions

The chemically inert trivalent ion cobalt(III) hexaammine, Co³⁺(NH₃)₆, was found to exert polyamine-like effects in enhancing certain cyclic nucleotide-independent protein kinase reactions catalyzed by nuclear enzyme preparations from rat ventral prostate or liver. At 1 mM, Co³⁺(NH₃)₆ stimulated chromatin- and also non-histone-protein-associated kinase activities with partially dephosphorylated phosvitin as substrate by 38% and 72% respectively, whereas chromatin-associated kinase-catalyzed phosphorylation of lysine-rich histones was not affected under the same conditions. ³²P incorporation (from γ-³²P-ATP) into endogenous protein substrates of chromatin or non-histone protein fractions catalyzed by their erdogencus kinase activity was increased by 47% and 153%, respectively. These effects of Co³⁺(NH₃)₆ were similar to those produced by 1mM spermine. Autoradiographic analysis of endogenous ³²P-labelled nonhistone proteins revealed similar enhancements of the phosphorylation of several of the same proteins, induced by 1mM spermine or 1 mM Co³⁺(NH₃)₆ or 2mM spermidine. The stimulatory actions of polyamines or Co³⁺(NH₃)₆ were not mimicked by raising the ionic strength by addition of comparable concentrations of NaCl. The effects of 1 mM spermine and of 1 mM Co³⁺(NH₃)₆ tested separately were not additive. Phosphorylation of lysine-rich histones by beef heart cyclic AMP-dependent protein kinase was not affected by polyamines or Co³⁺(NH₃)₆ Various findings hint that the enhancement of cyclic nucleotide-independent kinase-catalyzed phosphorylation of certain protein substrates by spermidine, spermine and Co³⁺(NH₃)₆ is primarily due to interaction of these cations with appropriate protein substrates affecting their conformational status. Further, these effects of polyamines may be a reflection of their cationic charge properties rather than being dependent on any particular conformations assumed by the polyamines.     

Structural basis of polyamine-DNA recognition: spermidine and spermine interactions with genomic B-DNAs of different GC content probed by Raman spectroscopy

Four genomic DNAs of differing GC content (Micrococcus luteus, 72% GC; Escherichia coli, 50% GC; calf thymus, 42% GC; Clostridium perfringens, 27% GC) have been employed as targets of interaction by the cationic polyamines spermidine {[H₃N(CH₂)₃NH₂(CH₂)₄NH₃]³⁺} and spermine {[(CH₂)₄(NH₂(CH₂)₃NH₃)₂]⁴⁺}. In solutions containing 60 mM DNA phosphate (~20 mg DNA/ml) and either 1, 5 or 60 mM polyamine, only Raman bands associated with the phosphates exhibit large spectral changes, demonstrating that B-DNA phosphates are the primary targets of interaction. Phosphate perturbations, which are independent of base composition, are consistent with a model of non-specific cation binding in which delocalized polyamines diffuse along DNA while confined by the strong electrostatic potential gradient perpendicular to the helix axis. This finding provides experimental support for models in which polyamine-induced DNA condensation is driven by non-specific electrostatic binding. The Raman spectra also demonstrate that major groove sites (guanine N7 and thymine C5H₃) are less affected than phosphates by polyamine–DNA interactions. Modest dependence of polyamine binding on genome base composition suggests that sequence context plays only a secondary role in recognition. Importantly, the results demonstrate that polyamine binding has a negligible effect on the native B-form secondary structure. The capability of spermidine or spermine to bind and condense genomic B-DNA without disrupting the native structure must be taken into account when considering DNA organization within bacterial nucleoids or cell nuclei.     

Comparative Study of the Condensation of Chicken Erythrocyte and Calf Thymus Chromatins by Di- and Multivalent Cations

Abstract

The condensation of chicken erythrocyte (CE) and calf thymus (CT) chromatins upon addition of di- and multivalent cations has been studied using turbidityJulprecipitation and electric dichroism measurements. For all the cations investigated (Mg²⁺, Tb³⁺, Co(NH₃)₆ ³⁺, spermidine Spd²⁺ and spermine Sp⁴⁺) condensation of CE chromatin occurred before the onset of aggregation, while aggregation of CT chromatin started before condensation with all cations except Mg²⁺ and Tb³⁺. Precipitation of CE chromatin required lower di- and multivalent cations concentrations than CT chromatin. The electric dichroism data for both chromatins, at low ionic strength in the absence of di- or multivalent cations, indicated that the nucleoprotein molecules were not totally decondensed but that a “precondensed” state was already present. A positive electric dichroism was observed for the most condensed chromatin fibers, in agreement with the “cross-linker” models. Tb³⁺ led to less compact condensed particles as judged from the electric dichroism observations, but electron microscopy revealed that “30 nm fibers” were formed. Very little aggregation was produced by Tb³⁺. On the contrary, spermine produced very large networks of condensed molecules, but large spheroidal particles were also observed. The condensation of CE chromatin happened without changes of solution conductivity upon cation salt addition, regardless of the condensing cation, indicating a cooperative uptake of the ions during this process.     

A molecular dynamics simulation study of polyamine– and sodium–DNA. Interplay between polyamine binding and DNA structure

Four different molecular dynamics (MD) simulations have been performed for infinitely long ordered DNA molecules with different counterions, namely the two natural polyamines spermidine(3+) (Spd³⁺) and putrescine(2+) (Put²⁺), the synthetic polyamine diaminopropane(2+) (DAP²⁺), and the simple monovalent cation Na⁺. All systems comprised a periodical hexagonal cell with three identical DNA decamers, 15 water molecules per nucleotide, and counterions balancing the DNA charge. The simulation setup mimics the DNA state in oriented DNA fibers, previously studied using NMR and other experimental methods. In this paper the interplay between polyamine binding and local DNA structure is analyzed by investigating how and if the minor groove width of DNA depends on the presence and dynamics of the counterions. The results of the MD simulations reveal principal differences in the polyamine–DNA interactions between the natural [spermine(4+), Spd³⁺, Put²⁺] and the synthetic (DAP²⁺) polyamines.Abbreviations DAP diaminopropane - DDD Drew–Dickerson dodecamer - MD molecular dynamics - Put putrescine - RDF radial distribution function - Spd spermidine - Spm spermine     

Compacting effect of BBR3464, a new-generation trisplatinum anticancer agent,on DNA

BBR3464 is a trinuclear platinum compound of formula [{trans-PtCl(NH₃)₂}₂-μ-trans-Pt(NH₃)₂{NH₂(CH₂)₆NH₂}₂]⁴⁺. It is a new-generation platinum chemotherapeutic agent that exhibits cytotoxicity at ten to thousand times lower dose limit compared to the well-known platinum drug cisplatin, in cisplatin-sensitive as well as in cisplatin-resistant cells. DNA is thought to be the primary cellular target of BBR3464. In this work, we have applied high-resolution atomic force microscopy (AFM) for the first time, to obtain direct information on BBR3464-induced structural changes of DNA. It is found that the DNA molecules get compacted after treatment with BBR3464, for the drug:DNA molar ratio and the drug treatment period of 0.01 and 48 h, respectively. These values of molar ratio and incubation period have been obtained previously, as a result of biochemical optimization studies carried out for achieving maximum drug effects. The DNA structural changes, as observed in AFM topographs, have been correlated to the bulk level spectroscopic information. A remark on the significance of BBR3464-induced DNA compaction with respect to the available AFM reports on DNA modification by cisplatin has been made.     

Interplay of ion binding and attraction in DNA condensed by multivalent cations

We have measured forces generated by multivalent cation-induced DNA condensation using single-molecule magnetic tweezers. In the presence of cobalt hexammine, spermidine, or spermine, stretched DNA exhibits an abrupt configurational change from extended to condensed. This occurs at a well-defined condensation force that is nearly equal to the condensation free energy per unit length. The multivalent cation concentration dependence for this condensation force gives the apparent number of multivalent cations that bind DNA upon condensation. The measurements show that the lower critical concentration for cobalt hexammine as compared to spermidine is due to a difference in ion binding, not a difference in the electrostatic energy of the condensed state as previously thought. We also show that the resolubilization of condensed DNA can be described using a traditional Manning–Oosawa cation adsorption model, provided that cation–anion pairing at high electrolyte concentrations is taken into account. Neither overcharging nor significant alterations in the condensed state are required to describe the resolubilization of condensed DNA. The same model also describes the spermidine³⁺/Na⁺ phase diagram measured previously.     

The phosphate clamp: sequence selective nucleic acid binding profiles and conformational induction of endonuclease inhibition by cationic Triplatin complexes

The substitution-inert polynuclear platinum(II) complex (PPC) series, [{trans-Pt(NH₃)₂(NH₂(CH₂)_nNH₃)}₂-μ-(trans-Pt(NH₃)₂(NH₂(CH₂)_nNH₂)₂}](NO₃)₈, where n = 5 (AH78P), 6 (AH78 TriplatinNC) and 7 (AH78H), are potent non-covalent DNA binding agents where nucleic acid recognition is achieved through use of the ‘phosphate clamp'' where the square-planar tetra-am(m)ine Pt(II) coordination units all form bidentate N–O–N complexes through hydrogen bonding with phosphate oxygens. The modular nature of PPC–DNA interactions results in high affinity for calf thymus DNA (K_app ∼5 × 10⁷ M⁻¹). The phosphate clamp–DNA interactions result in condensation of superhelical and B-DNA, displacement of intercalated ethidium bromide and facilitate cooperative binding of Hoechst 33258 at the minor groove. The effect of linker chain length on DNA conformational changes was examined and the pentane-bridged complex, AH78P, was optimal for condensing DNA with results in the nanomolar region. Analysis of binding affinity and conformational changes for sequence-specific oligonucleotides by ITC, dialysis, ICP-MS, CD and 2D-¹H NMR experiments indicate that two limiting modes of phosphate clamp binding can be distinguished through their conformational changes and strongly suggest that DNA condensation is driven by minor-groove spanning. Triplatin-DNA binding prevents endonuclease activity by type II restriction enzymes BamHI, EcoRI and SalI, and inhibition was confirmed through the development of an on-chip microfluidic protocol.     

Reactions of pentaammineruthenium complexes with 1,2- and 1,4-dicyanobenzene and cyanobenzamides: evidences of neighboring group participation

The spectral (UV-Vis and IR) and electrochemical behavior of the nitrile bonded complexes [Ru(NH₃)₅L]²⁺ (L = 1,4-dicyanobenzene (1,4-dcb), 1,2-dicyanobenzene (1,2-dcb)), [Ru(NH₃)₅(NHC(OH)-bz-4-CN)]³⁺, [Ru(NH₃)₅(NHC(O)-bz-2-CN)]²⁺ and [Ru(NH₃)₅(NH(C)NHC(O)bz)]³⁺ (NH(C)NHC(O)-bz = 3-imino-1-oxo-isoindoline) are described. Oxidation of [Ru(NH₃)₅L]²⁺, at 0 ? pH ? 6, is followed by hydrolysis of the coordinated nitrile to give amide complexes in which the amide is through the nitrogen, with pH-dependent rate constants. The estimated values of the rate constant of hydrolysis (k_obs) at 25 °C are 2.9 × 10⁻³ s⁻¹ for [Ru(NH₃)₅(1,4-dcb)]³⁺ and 5.6 × 10⁻³ s⁻¹ for [Ru(NH₃)₅(1,2-dcb)]³⁺ at pH 4.65. Reduction of [Ru(NH₃)₅(NHC(O)-bz-4-CN)]²⁺ and [Ru(NH₃)₅(NHC(O)-bz-2-CN)]²⁺ is followed by two reactions, one is an aquation forming [Ru(NH₃)₅(OH₂)]²⁺ and free ligand, and the other an intramolecular linkage isomerization forming [Ru(NH₃)₅(NC-bz-4-NH₂C(O))]²⁺ and [Ru(NH₃)₅(NC-bz-2-NH₂C(O))]²⁺. The oxidized1,2-cyanobenzamide complex [Ru(NH₃)₅(NHC(OH)-bz-2-CN)]³⁺ undergoes an amide to nitrile intramolecular linkage isomerization, followed by a cyclization reaction resulting in [Ru(NH₃)₅(NH-(C)(HN-C(O)-2-bz))]³⁺ ((NH-(C)(HN-C(O)-2-bz)) = 3-imino-1-oxo-isoindoline bonded through the exocyclic nitrogen) (pK_a = 4.3). The rates of these reactions, which occur with neighboring group participation, increase with acidity. The reduced form, [Ru(NH₃)₅(NH-(C)(HN-C(O)-2-bz))]²⁺, is relatively substitution inert.     

Reversal of antizyme-induced inhibition of ornithine decarboxylase by cations in barley seedlings

Ornithine decarboxylase (ODC) forms a stable complex with its antizyme (Az), a non-competitive protein inhibitor of ODC. The complex formation of ODC with Az occurs very rapidly and is dissociated by high salt concentrations e.g., 10% ammonium sulfate. When ODC and Az were mixed in the presence of increasing concentrations of Mg²⁺, a relief of ODC inhibition by Az was obtained. Complete relief of inhibition occurred at 2.0 mM of MgCl₂. Other bivalent cations Ca²⁺, Ba²⁺, Co²⁺, Mn²⁺, Zn²⁺ as well as the monocations Na⁺ and K⁺ caused similar effect. The polyamines putrescine, spermidine and spermine also caused relief of the in vitro inhibition of ODC by Az. Therefore, the in vivo inactivation of ODC by forming the ODC-Az complex is dependent on the intracellular amounts of salt and polyamines.     

Na<Superscript>+</Superscript>,K<Superscript>+</Superscript>-ATPase Activity in the Posterior Gills of the Blue Crab, <Emphasis Type="Italic">Callinectes ornatus</Emphasis> (Decapoda,Brachyura): Modulation of ATP Hydrolysis by the Biogenic Amines Spermidine and Spermine

We investigated the effect of the exogenous polyamines spermine, spermidine and putrescine on modulation by ATP, K⁺, Na⁺, NH₄ ⁺ and Mg²⁺ and on inhibition by ouabain of posterior gill microsomal Na⁺,K⁺-ATPase activity in the blue crab, Callinectes ornatus, acclimated to a dilute medium (21‰ salinity). This is the first kinetic demonstration of competition between spermine and spermidine for the cation sites of a crustacean Na⁺,K⁺-ATPase. Polyamine inhibition is enhanced at low cation concentrations: spermidine almost completely inhibited total ATPase activity, while spermine inhibition attained 58%; putrescine had a negligible effect on Na⁺,K⁺-ATPase activity. Spermine and spermidine affected both V and K for ATP hydrolysis but did not affect ouabain-insensitive ATPase activity. ATP hydrolysis in the absence of spermine and spermidine obeyed Michaelis–Menten behavior, in contrast to the cooperative kinetics seen for both polyamines. Modulation of V and K by K⁺, Na⁺, NH₄ ⁺ and Mg²⁺ varied considerably in the presence of spermine and spermidine. These findings suggest that polyamine inhibition of Na⁺,K⁺-ATPase activity may be of physiological relevance to crustaceans that occupy habitats of variable salinity.     

Ion Competition in Condensed DNA Arrays in the Attractive Regime

Physical origin of DNA condensation by multivalent cations remains unsettled. Here, we report quantitative studies of how one DNA-condensing ion (Cobalt³⁺ Hexammine, or Co³⁺Hex) and one nonDNA-condensing ion (Mg²⁺) compete within the interstitial space in spontaneously condensed DNA arrays. As the ion concentrations in the bath solution are systematically varied, the ion contents and DNA-DNA spacings of the DNA arrays are determined by atomic emission spectroscopy and x-ray diffraction, respectively. To gain quantitative insights, we first compare the experimentally determined ion contents with predictions from exact numerical calculations based on nonlinear Poisson-Boltzmann equations. Such calculations are shown to significantly underestimate the number of Co³⁺Hex ions, consistent with the deficiencies of nonlinear Poisson-Boltzmann approaches in describing multivalent cations. Upon increasing the concentration of Mg²⁺, the Co³⁺Hex-condensed DNA array expands and eventually redissolves as a result of ion competition weakening DNA-DNA attraction. Although the DNA-DNA spacing depends on both Mg²⁺ and Co³⁺Hex concentrations in the bath solution, it is observed that the spacing is largely determined by a single parameter of the DNA array, the fraction of DNA charges neutralized by Co³⁺Hex. It is also observed that only ∼20% DNA charge neutralization by Co³⁺Hex is necessary for spontaneous DNA condensation. We then show that the bath ion conditions can be reduced to one variable with a simplistic ion binding model, which is able to describe the variations of both ion contents and DNA-DNA spacings reasonably well. Finally, we discuss the implications on the nature of interstitial ions and cation-mediated DNA-DNA interactions.     

Ion Competition in Condensed DNA Arrays in the Attractive Regime

Physical origin of DNA condensation by multivalent cations remains unsettled. Here, we report quantitative studies of how one DNA-condensing ion (Cobalt³⁺ Hexammine, or Co³⁺Hex) and one nonDNA-condensing ion (Mg²⁺) compete within the interstitial space in spontaneously condensed DNA arrays. As the ion concentrations in the bath solution are systematically varied, the ion contents and DNA-DNA spacings of the DNA arrays are determined by atomic emission spectroscopy and x-ray diffraction, respectively. To gain quantitative insights, we first compare the experimentally determined ion contents with predictions from exact numerical calculations based on nonlinear Poisson-Boltzmann equations. Such calculations are shown to significantly underestimate the number of Co³⁺Hex ions, consistent with the deficiencies of nonlinear Poisson-Boltzmann approaches in describing multivalent cations. Upon increasing the concentration of Mg²⁺, the Co³⁺Hex-condensed DNA array expands and eventually redissolves as a result of ion competition weakening DNA-DNA attraction. Although the DNA-DNA spacing depends on both Mg²⁺ and Co³⁺Hex concentrations in the bath solution, it is observed that the spacing is largely determined by a single parameter of the DNA array, the fraction of DNA charges neutralized by Co³⁺Hex. It is also observed that only ∼20% DNA charge neutralization by Co³⁺Hex is necessary for spontaneous DNA condensation. We then show that the bath ion conditions can be reduced to one variable with a simplistic ion binding model, which is able to describe the variations of both ion contents and DNA-DNA spacings reasonably well. Finally, we discuss the implications on the nature of interstitial ions and cation-mediated DNA-DNA interactions.     

X-ray diffraction studies on cation-collapsed DNA

The polyamines spermidine, spermine and putrescine are now known to induce tertiary collapse of DNA. In this collapsed state DNA assumes a compact toroidal conformation. However, the structural details of DNA in these compact particles and the forces that stabilize the collapsed state are not clear. We show here that the structural arrangement of DNA in this tertiary conformation is determined by the chemical structure of the agent used to collapse. We have used aliphatic triamines (NH₃⁺-(CH₂)₃-NH₂⁺-(CH₂)_n-NH₃⁺ with n = 3, 4, 5 and 8) and diamines (NH₃⁺-(CH₂)_x-NH₃⁺ with x = 2, 3, 4 and 6) to collapse DNA. We find that the Bragg spacing and the calculated interhelical spacing for a hexagonal packing model vary systematically with the length of the methylene bridge. We also find that the ionic strength of the solution has no effect on the Bragg spacing. This observation suggests that the arrangement of DNA strands in the complexes is determined by the structure of the polycation, and argues against suggestions that the structure of the collapsed state is maintained by the balance of long-range electrostatic repulsive and attractive forces. Instead we propose that DNA helices form a hexagonal array with counterions in the interstices between the helices resulting in a stable three-dimensional phase with high structural order. Arguments are presented favoring such a model in terms of stabilizing and destabilizing thermodynamic forces.     

Hydrothermal synthesis and structure of an open framework Co0.7Zn1.3(PO4)2(NH3-CH2CH2NH3) and Co6.2(OH)4(PO4)4Zn1.80, a new adamite type phase

The hydrothermal reaction of cobalt(II)oxalate di-hydrate, zinc oxide, and triethyl-orthophosphate, using 1,2-diaminoethane as structure directing template in water, produced two major crystal phases in almost equal amount: the purple crystals of [NH₃-CH₂CH₂NH₃][Co_0.7Zn_1.3(PO₄)₂] (1) and the red burgundy crystals of Co_6.2(OH)₄(PO₄)₄Zn_1.80 (2), a new adamite type phase. The structure of [NH₃-CH₂CH₂NH₃] [Co_0.7Zn_1.3(PO₄)₂] (1) exhibits a 3D open framework built from PO₄ and (Co/Zn)O₄ tetrahedra, and (Co/Zn)O₅ trigonal bipyramids, forming two major channels, an 8-membered ring channel and a 16-membered ring channel, that host the ethanediammonium ions. The Co_6.2(OH)₄(PO₄)₄Zn_1.80 (2) is isomorphous with adamite-type M₂(OH)XO₄ structure, with a condensed vertex and edge sharing network of (Co/Zn)O₅, and distorted CoO₆, and PO₄ subunits. The cobalt preference for higher coordination numbers is displayed in this structure, where the octahedral sites are wholly occupied by cobalt. Thermal analysis confirmed that these compounds display high thermal stability.     

Collapse of DNA caused by trivalent cations: pH and ionic specificity effects

A comparison of the condensation of T4 phage DNA by spermidine and Co(NH₃) at pH values between 5.1 and 10.2 has been made using quasielastic light scattering to determine translational diffusion coefficients and Stokes radii. Co(NH₃) is more effective than spermidine in causing condensation at all pH, indicating that the differences observed in previous work were not due to pH effects, as might have been inferred from recent theories of intermolecular forces. The DNA particles collapsed with Co(NH₃) are smaller than those obtained with spermidine. The hydrodynamic radius of spermide-collapsed structures decreases slightly with increasing pH, while the size of the Co(NH₃)collapsed structures is almost independent of pH. These results confirm that there are specific ion effects in DNA condensation by oligocations, in addition to the dominant general polyelectrolyte effects.