Incorporation of a perfluoroalkylalkane (RFRH) into the phospholipid bilayer of dmpc liposomes results in greater encapsulation stability

Abstract

The incorporation of a linear perfluoroalkylalkane (R_FR_H diblock compound) with a C_nF_2n+1CH=CHC_mH_2m+1 structure into the bilayer of DMPC liposomes results in a decreased permeability of the liposomal membrane for two fluorescent markers, carboxyfluorescein (CF) and calcein, in a buffer and in human serum. Half-leakage times of CF from DMPC and DMPC/C₄F₉CH=CHC₁₀H₂₁ vesicles in Hepes buffer were 55 min and 15 hrs, respectively. For the same two types of vesicles, half-leakage times of calcein in human serum were 30 and 210 s., respectively.     

The volatile Dufour's gland components of the harvester ants Pogonomyrmex rugosus and P. barbatus

The volatile Dufour's gland components of Pogonomyrmex rugosus and P. barbatus have been examined and found to be hydrocarbons. Homologous families of alkanes from this gland consisted of normal hydrocarbons ranging from n-dodecane to n-pentadecane and three types of methyl-branched homologues of the general formula C_nH_2n+1CH(CH₃)C_mH_2m+1, where n is 2, 4, or 5 and the sum of n and m is 10, 11, 12, or 13. The dimethyl-branched hydrocarbons 3,5-dimethyldodecane and 3,4-dimethyltridecane were also observed.     

Studies of the morphology of chromosomes of some selected species

Karyotypes of twelve species from twenty-four localities in southern Moravia and one locality in Slovakia were investigated. Their counts or karyotypic formulae are as follows:Chenopodium foliosum (Moench) Ascherson: K (2n)=18=16 A^m+2 B^sm;Astragalus austriacus Jacq.: K (2n)=16=8 A^m+8 B^sm;Astragalus exscapus L.: K (2n)=16=10 A^m+4 B^sm+2 C^st;Astragalus cicer L.: K (2n)=64;Astragalus onobrychis L.: K (2n=64 and K (2n)=64+1;Vicia dumetorum L.: K (2n=14=10 A^m+4 B^sm;Vicia sylvatica L.: K (2n)=14=2 A^m+10 B^sm+2 C^st;Vicia pisiformis L.: K (2n)=12=8 A^m+4 B^sm;Vicia cassubica L.: K (2n)=12=4 A^m+6 B^sm+2 C^st;Vicia cracca L. (from five localities in southern Moravia): K (2n)=28=4 A^m+12 B^sm+12 C^st and K (2n)=28+1=5 A^m+12 B^sm+12 C^st;Vicia cracca L. (from one locality in Slovakia): K (2n)=14=2 A^m+6 B^sm+6 C^st;Vicia tenuifolia Roth: K (2n)=24=4 A^m+16 B^sm+4 C^st;Serratula lycopifolia (Vill.) Kern.: K (2n)=60.     

Specific Action of Sodium Dodecyl Sulfate on the Sex Factor of Escherichia coli K-12 Hfr Strains

A specific action of sodium dodecyl sulfate (SDS) on the sex (F) factor in the integrated state of Escherichia coli K-12 Hfr H strain is reported. Growth of Hfr cells in Penassay Broth containing SDS results in the elimination of part or all of the F factor, yielding low and nonfertile variants of defective Hfr type and F⁺ cells and also F⁻ derivatives. Appearance of such variants was generally observed after the culture reached stationary phase. The frequencies of F⁻ cells then increased. F⁻ cells were usually isolated as the major population among survivors. Some defective variants of Hfr cells with an intermediate fertility between standard Hfr and F⁺ cells had lost sensitivity toward the male-specific ribonucleic acid phage M12. Other defective Hfr variants with as much or less fertility than standard F⁺ cells had also all lost sensitivity to phage M12. On single-colony isolation, they segregated nonfertile female H cells which, when infected with F, could restore high fertility with oriented transfer of the chromosome the same as that of the original Hfr H. Also, sensitivity to phage M12 was regained. Female H cells were characterized as those lacking fertility but still retaining a small segment of F or sfa locus at the original part of the chromosome, where newly infected F could attach. Similar results were obtained with two other Hfr strains. A possible mechanism of the specific action of SDS is discussed.     

B30H8, B39H9 2−, B42H10, B48H10, and B72H12: polycyclic aromatic snub hydroboron clusters analogous to polycyclic aromatic hydrocarbons

Calculations performed at the ab initio level using the recently reported planar concentric π-aromatic B₁₈H₆ ²⁺(1) [Chen Q et al. (2011) Phys Chem Chem Phys 13:20620] as a building block suggest the possible existence of a new class of B_3n H _m polycyclic aromatic hydroboron (PAHB) clusters—B₃₀H₈(2), B₃₉H₉ ^2?(3), B₄₂H₁₀(4/5), B₄₈H₁₀(6), and B₇₂H₁₂(7)—which appear to be the inorganic analogs of the corresponding C _n H _m polycyclic aromatic hydrocarbon (PAHC) molecules naphthalene C₁₀H₈, phenalenyl anion C₁₃H₉ ^?, phenanthrene/anthracene C₁₄H₁₀, pyrene C₁₆H₁₀, and coronene C₂₄H₁₂, respectively, in a universal atomic ratio of B:C?=?3:1. Detailed canonical molecular orbital (CMO), adaptive natural density partitioning (AdNDP), and electron localization function (ELF) analyses indicate that, as they are hydrogenated fragments of a boron snub sheet [Zope RR, Baruah T (2010) Chem Phys Lett 501:193], these PAHB clusters are aromatic in nature, and exhibit the formation of islands of both σ- and π-aromaticity. The predicted ionization potentials of PAHB neutrals and electron detachment energies of small PAHB monoanions should permit them to be characterized experimentally in the future. The results obtained in this work expand the domain of planar boron-based clusters to a region well beyond B₂₀, and experimental syntheses of these snub B_3n H _m clusters through partial hydrogenation of the corresponding bare B_3n may open up a new area of boron chemistry parallel to that of PAHCs in carbon chemistry.

Theoretical study on electronic spectra and interaction in [Au3]-L-[Au3] (L = C6F6,Ag+) complexes

The electronic structure and spectroscopic properties of [Au₃(μ-C(OEt) = NC₆H₄CH₃)₃]_n-(C₆F₆)_m and [Au₃(μ-C²,N³-bzim)₃]_n-(Ag⁺)_m were studied at the B3LYP, PBE and TPSS levels. The interaction between the [Au₃] cluster and L (C₆F₆, Ag⁺) was analyzed. Grimme’s dispersion correction is used for those functionals. Weak π-interactions (Au-C₆F₆) were found to be the main contribution short-range stability in the models; while in the models with Ag⁺, an ionic interaction is obtained. The absorption spectra of these models at the PBE level agree with the experimental spectra.     

Mono- and bimetallic gold(I) and silver(I) pentafluoropropionates and related compounds

A series of eight new carboxylate complexes of the general type (L)_nMOC(O)R (L=PMe₃; n=1; M=Ag, Au; R=C₂F₅. L=PPh₃; n=1-3; M=Ag; R=C₂F₅, t-Bu) have been prepared in high yields. Crystal and molecular structures have been determined for three representative examples. The crystal structure of (Ph₃P)AgOC(O)C₂F₅ contains dimers in which the silver atoms are bridged by the carboxylate oxygen atoms. This bridging resembles the structural motif found in silver carboxylates without ligand support. Usage of the smaller phosphine PMe₃ leads to the formation of a polymeric chain structure in (Me₃P)AgOC(O)C₂F₅ with bridging carboxylate anions and short Ag-Ag contacts holding the monomers together. The reaction of (4-Me₂N-C₆H₄)Ph₂ PAuCl with two equivalents of C₂F₅CO₂Ag leads to the formation of a mixed metal product containing both gold and silver. The crystal structure analysis of this compound revealed a tetranuclear complex containing a central dimeric silver pentafluoropropionate unit which is chelated by the (triarylphosphine)gold(I) pentafluoropropionate molecules via Ag-Au metallophilic contacts and Ag-O donor/acceptor interactions.     

Fluid Mechanical Matching of H-ATP Synthase Subunit c-Ring with Lipid Membranes Revealed by H Solid-State NMR

The F₁F_o-ATP synthase utilizes the transmembrane H⁺ gradient for the synthesis of ATP. F_o subunit c-ring plays a key role in transporting H⁺ through F_o in the membrane. We investigated the interactions of Escherichia coli subunit c with dimyristoylphosphatidylcholine (DMPC-d₅₄) at lipid/protein ratios of 50:1 and 20:1 by means of ²H-solid-state NMR. In the liquid-crystalline state of DMPC, the ²H-NMR moment values and the order parameter (S_CD) profile were little affected by the presence of subunit c, suggesting that the bilayer thickness in the liquid-crystalline state is matched to the transmembrane hydrophobic surface of subunit c. On the other hand, hydrophobic mismatch of subunit c with the lipid bilayer was observed in the gel state of DMPC. Moreover, the viscoelasticity represented by a square-law function of the ²H-NMR relaxation was also little influenced by subunit c in the fluid phase, in contrast with flexible nonionic detergents or rigid additives. Thus, the hydrophobic matching of the lipid bilayer to subunit c involves at least two factors, the hydrophobic length and the fluid mechanical property. These findings may be important for the torque generation in the rotary catalytic mechanism of the F₁F_o-ATPse molecular motor.     

Chromosome morphology of the czechoslovak species of the genusScorzonera

Karyotypic formulae of theScorzonera L. species are as follows:S. purpurea L.: K (2n)=14=8 A^m+6 B^sm and K (2n)=14+1=9 A^m+6 B^sm;S. austriaca Willd.: K (2n)=14=6 A^m+6 B^sm+2 C^st;S. humilis L.: K (2n)=14=12 A^m+2 B^sm;S. parviflora Jacq.: K (2n)=14=10 A^m+4 B^sm;S. hispanica L.: K (2n)=12 A^m+2 B^sm. The results of the study of the karyotypes of the generaScorzonera L.,Tragopogon L. andPodospermum DC. are summarized.     

Ionic metallomesogens derived from silver(I) bis-amine complexes: Structure and mesogenic behavior

Complexes [Ag(NH₂R)₂]X, (X = NO₃, R = -C₆H₄-C_nH_2n+1-p, -C₆H₄-O-C_nH_2n+1-p, -CH₂-C₆H₄-O-C_nH_2n+1-p, n = 6, 8, 10, 12, 14; X = BF₄, R = -CH₂-C₆H₄-O-C_nH_2n+1-p, n = 6, 8, 10, 12, 14; X = OAc, R = -CH₂-C₆H₄-O-C₁₀H₂₁-p; X = CF₃SO₃, R = -CH₂-C₆H₄-O-C₁₀H₂₁-p) have been prepared. They all show S_A mesophases corresponding to two kinds of structures, already present in the solid state. The alkylaniline and alkoxyaniline derivatives adopt a bilayered structure where the cation has an extended centrosymmetric conformation. The benzylamine derivatives contain U-shaped cations giving rise to a bilayered structure which allows microsegregation of the organic part of the molecule from the inorganic Ag?(anion) part. Some degree of interdigitation of the terminal chains is observed for all the complexes with aryl containing ligands.     

Kinetics of the reactions involving CF2 and CF in a pure tetrafluoromethane plasma: II. Production and loss of CF2 and CF in the processes of fluorocarbon polymerization

Mechanisms for the production and loss of CF₂ and CF radicals in a glow discharge in pure CF₄ are investigated by the time-resolved laser-induced fluorescence method. The fluorocarbon polymerization processes are shown to contribute significantly to the production of radicals both in the plasma volume and on the surface of the discharge tube. The effective frequencies of both the volume and surface processes of radical production and loss are determined. An analysis of these frequencies allowed us to study the polymerization mechanism in a CF₄ plasma at a high relative concentration of F atoms and low ion energy. It is shown that, at elevated pressures, when the density of C_xF_y polymer particles in the plasma volume becomes comparable with the density of simple fluorocarbon radicals, the electron-impact dissociation of these particles is the main channel for the production of CF₂ and CF radicals. Another source of CF₂ and CF radicals is related to the reactions of C_nF_2m+1 unsaturated fluorocarbon particles both in the plasma volume and on the surface of a fluorocarbon film arising on the discharge tube wall. The C_xF_y fluorocarbon polymer particles form both in the discharge volume and on the fluorocarbon filmsurface also in the course of the film destruction. At lowered pressures, the main channel for the production of CF₂ and CF is the direct electron-impact dissociation of CF₄ molecules, whereas the loss of these radicals at the tube wall is the main loss channel. The probabilities of the heterogeneous losses of CF₂ and CF radicals on the heavily fluorinated surface of the fluorocarbon film at low ion energies are determined. Under these conditions, the surface recombination of the Fch chemisorbed fluorine atoms and CF _x ^ph physisorbed radicals with the production of an activated complex is shown to be the most probable mechanism for the heterogeneous losses of CF₂ and CF. The approximate activation energies for the production of F_ch · CF ₂ ^ph and F_ch · CF^ph surface complexes are found to be 750±70 K and 1030±100 K, respectively.     

Novel ruthenium(II) diamine complexes

The complex cations [Ru(C₇H₁₆N₂)(C₁₀H₁₄)Cl]⁺, [Ru(C₇H₁₆N₂)(C₆H₆)Cl]⁺, [Ru(C₉H₁₈N₂)(C₆H₆)Cl]⁺, [Ru(C₉H₁₈N₂)(C₁₀H₁₄)Cl]⁺ and [Ru(C₁₄H₁₆N₂)(C₁₀H₁₄)Cl]⁺ have been synthesised from the reaction between the ruthenium-arene complexes [with C₆H₆ (benzene) or C₁₀H₁₄ (p-cymene)] and the respective chiral diamines [C₇H₁₆N₂=(S)-(−)-2-aminomethyl-1-ethylpyrrolidine, C₉H₁₈N₂=(S)-(+)-2-(pyrrolidinylmethyl)-pyrrolidine, or C₁₄H₁₆N₂=(1R,2R)-(+)-1,2-diphenylethylenediamine], isolated and characterised as chloride salts using single-crystal X-ray diffraction. All complexes were fully characterised by elemental analysis, mass spectrometry, ¹³C and ¹H NMR, and also found to exhibit catalytic activity in the transfer hydrogenation of acetophenone to 1-phenylethanol at 50 °C (enantiomeric excesses range from ca. 25% to 60%, and conversions from ca. 30% to 50%).     

Biologically active bisquaternary ammonium chlorides: physico–chemical properties of long chain amphiphiles and their evaluation as non-viral vectors for gene delivery

The biological properties of bisquaternary ammonium salts, which are derivatives of N,N-bisdimethyl-1,2-ethanediamine (bis-C_nBEC), of general formula /C_nH_2n+1OOCCH₂(CH₃)₂N⁺CH₂CH₂N⁺(CH₃)₂CH₂COOC_nH_2n+1/2Cl⁻, were investigated (n=10, 12, 14). The interaction with model membrane was studied by differential scanning calorimetry experiments, and the apparent adiabatic molar compressibility of their solution as a function of concentration was obtained by sound velocity measurements. Their biological activities were assayed by Electrophoresis Mobility Shift, MTT proliferation, and transient transfection. All the investigated compounds interact with the DNA and are able to transfect DNA, when they are coformulated with DOPE, with an efficiency significantly greater than that of a standard commercial transfection reagent. Bis-C₁₄BEC is the only molecule able to deliver DNA inside the cells without a helper lipid, as shown by EGFP expression, albeit with a low efficiency in comparison with a standard commercial transfection reagent. This may be due to a slightly different interaction of bis-C₁₄BEC from bis-C₁₀BEC and bis-C₁₂BEC with phospholipid bilayers. Bis-C₁₀BEC and bis-C₁₂BEC show a slight fluidising effect, while bis-C₁₄BEC increases stability of both the gel and the rippled gel phases.     

Disubstituted diaryl diselenides inhibit δ-ALA-D and Na+, K+-ATPase activities in rat brain homogenates in vitro

Toxicological and pharmacological studies demonstrated that the introduction of functional groups into the aromatic ring of diphenyl diselenide alter its effect. The aim of this study was to evaluate the in vitro effect of m-trifluoromethyl-diphenyl diselenide (m-CF₃–C₆H₄Se)₂, p-chloro-diphenyl diselenide (p-Cl–C₆H₄Se)₂ and p-methoxyl-diphenyl diselenide (p-CH₃O–C₆H₄Se)₂ on δ-aminolevulinate dehydratase (δ-ALA-D) and Na⁺, K⁺-ATPase activities in rat brain homogenates. Diselenides inhibited δ-ALA-D activity (IC₅₀ 4–6 μM [concentration inhibiting 50%]), and dithiothreitol (DTT) restored the enzyme activity. ZnCl₂ (100 μM) did not restore δ-ALA-D inhibition caused by (p-Cl–C₆H₄Se)₂ and (m-CF₃–C₆H₄Se)₂. Na⁺, K⁺-ATPase activity was more sensitive to (p-Cl–C₆H₄Se)₂ and (m-CF₃–C₆H₄Se)₂ (IC₅₀ 6 μM) than (p-CH₃O–C₆H₄Se)₂ and (PhSe)₂ (IC₅₀ 45 and 31 μM, respectively). DTT restored the activity of Na⁺, K⁺-ATPase inhibited by diselenides. The effect of diselenides on Na⁺/K⁺-ATPase is dependent on their substitutions in the aromatic ring. The mechanism through which diselenides inhibit δ-ALA-D and Na⁺, K⁺-ATPase activities involves the oxidation of thiol groups.     

Molecular dynamics study of changes in physico-chemical properties of DMPC lipid bilayers by addition of nonionic surfactant C12E10

Changes in physico-chemical properties of dimyristoyl phosphatidylcholine (DMPC) lipid bilayers caused by the addition of 9.4 mol% nonionic surfactant decaoxyethylene monododecyl ethers (C₁₂E₁₀) have been investigated by molecular dynamics calculations. In spite of addition of single chain C₁₂E₁₀, the lipid bilayers showed an increase of membrane area. Isothermal area compressibility, which is a measure of membrane softness in lateral direction, also increased by 50% for DMPC/C₁₂E₁₀ mixed bilayers. Furthermore, the order parameter of C–H vector for DMPC acyl tails decreased. We found that these changes are caused by the hydrophilic head groups of C₁₂E₁₀ which are located near the glycerol backbone of the DMPC molecules and have bulky random coil conformation without any preferential ordered structures.     

First principles calculations of the electronic and chemical properties of graphene,graphane, and graphene oxide

The electrical and chemical properties of graphene (C₂₄H₁₂), graphane (C₂₄H₂₄) and graphene oxide (C₅₄H₁₇+O+(OH)₃+COOH) were studied through the density functional theory (DFT) at level of Local Density Approximation (LDA) using a model C_nH_m like. The optimized geometry, energy gap and chemical reactivity for the proposed carbon 2D models are reported. It was found that while the graphene and graphane structures have semiconductor behavior, the graphene oxide behaves as semi-metal. However, a transition from semi-mental to semiconductor is predicted if the carboxyl group (COOH) is removed from such structure. The chemically active sites are analyzed on the basis of the electrophilic Fukui functions for each structure.     

Phase transition behavior of single phosphatidylcholine bilayers on a solid spherical support studied by DSC, NMR and FT-IR

For the first time, the chain melting transition from the gel phase to the liquid crystalline phase of a single DPPC bilayer on a solid, spherical support (silica beads) is observed by differential scanning calorimetry (DSC). This transition is remarkably cooperative, exhibits a transition temperature T_m which is 2°C lower than usually found for DPPC multilamellar vesicles and its excess enthalpy is about 25% less than in DPPC multilayers. 31P- and 2H-NMR data as well as FT-IR data provide evidence that despite the highly asymmetric characteristic of the model system, the whole single bilayer undergoes the transition at T_m, i.e., there is no decoupling of the two monolayer leaflets at the main phase transition. Furthermore, our results show that the formation of the ripple (P_β') phase is inhibited in single bilayers on a solid support. This result confirms a conclusion which we reached previously on the basis of neutron scattering data obtained on planar supported bilayers. The most likely reason for this inhibition as well as for the above mentioned thermodynamic differences between multilamellar vesicles and supported membranes is a significantly higher lateral stress in the latter. Moreover, the exchange of lipids between two populations of spherical supported vesicles (DMPC and chain perdeuterated DMPC) is studied by DSC. It is shown that this exchange process is symmetric and its half-time is a factor of 3-4 higher than observed for small sonicated DMPC vesicles.     

Mesolamellar thiogermanates [CnH2n + 1NH3]4Ge4S10

The mesostructured lamellar phases with the general formula [C_nH_2n + 1NH₃]₄Ge₄S₁₀ (n = 12, 14, 16, 18) were synthesized by metathesis of alkyl ammonium chloride surfactants and Na₄Ge₄S₁₀ in aqueous medium. The crystal structures of the phases with n = 12 and 14 were determined by single-crystal X-ray diffraction; [C₁₂H₁₃NH₃]₄Ge₄S₁₀ crystallizes in monoclinic C2/c space group (a = 16.149(3), b = 46.576(9) c = 9.147(2) Å, β = 97.13(3)° and Z = 4) and [C₁₄H₂₉NH₃]₄Ge₄S₁₀ in the triclinic space group (a = 9.1280(6), b = 16.1992(1), c = 26.971(2) Å, α =73.370(1)°, β = 88.307(1)°, γ = 82.825(1)° and Z = 2). These compounds possess layers of adamantane [Ge₄S₁₀]⁴⁻ anions separated by layers of deeply interpenetrated long chain alkylammonium molecules. Strong hydrogen bonding is observed between the terminal sulfur atoms of the [Ge₄S₁₀]⁴⁻ clusters and H atoms of the NH₃ groups of the surfactant molecules. Spectroscopic and thermal characterization of these compounds is reported.     

Role of Cl− in Electrogenic H+ Secretion by Cortical Distal Tubule

The presence of an electrogenic H⁺-ATPase has been described in the late distal tubule, a segment which contains intercalated cells. The present paper studies the electrogenicity of this transport mechanism, which has been demonstrated in turtle bladder and in cortical collecting duct. Transepithelial PD (V _t ) was measured by means of Ling-Gerard microelectrodes in late distal tubule of rat renal cortex during in vivo microperfusion. The tubules were perfused with electrolyte solutions to which 2 × 10⁻⁷ m bafilomycin or 4.6 × 10⁻⁸ m concanamycin were added. No significant increase in lumen-negative V _t upon perfusion with these inhibitors as compared to control, was observed as well as when 10⁻³ m amiloride, 10⁻⁵ m benzamil or 3 mm Ba²⁺ were perfused alone or in combination. The effect of an inhibition of electrogenic H⁺ secretion, i.e., increase in lumen-negative V _t by 2–4 mV, was observed only when Cl⁻ channels were blocked by 10⁻⁵ m 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB). This blocker also reduced the rate of bicarbonate reabsorption in this segment from 1.21 ± 0.14 (n= 8) to 0.62 ± 0.03 (8) nmol.cm⁻².sec⁻¹ as determined by stationary microperfusion and pH measurement by ion-exchange resin microelectrodes. These results indicate that: (i) the participation of the vacuolar H⁺ ATPase in the establishment of cortical late distal tubule V _t is minor in physiological conditions, but can be demonstrated after blocking Cl⁻ channels, thus suggesting a shunting effect of this anion; and, (ii) the rate of H⁺ secretion in this segment is reduced by a Cl⁻ channel blocker, supporting coupling of H⁺-ATPase with Cl⁻ transport. Received: 6 July 1996/Revised: 27 December 1996     

Bis(heptalene) “submarine” metal dimer sandwich compounds (C12H10)2M2 (M = Ti, V, Cr, Mn, Fe, Co, Ni)

The bis(heptalene)dimetal complexes (C₁₂H₁₀)₂M₂ of the first row transition metals from Ti to Ni are predicted by density functional theory to exhibit “submarine” sandwich structures with a pair of metal atoms sandwiched between the two heptalene rings. For the early transition metal derivatives (C₁₂H₁₀)₂M₂ (M = V, Cr) there are two types of such structures. In one structural type the metals are sandwiched between two heptahapto heptalene rings with metal-metal distances (3.5–3.8 Å) too long for direct metal-metal bonding. The other type of (C₁₂H₁₀)₂M₂ (M = V, Cr, Mn) structure has a pair of bonded metal atoms sandwiched between a fully bonded heptalene ligand and a heptalene ligand bonded to the metals only through an eight-carbon heptafulvene subunit, leaving an uncomplexed cis-1,3-diene unit. The formal metal-metal bond orders in these latter structures are 3, 2, and 1 for M = V, Cr, and Mn with predicted bond lengths of 2.5, 2.7, and 2.8 Å, respectively. For (C₁₂H₁₀)₂Fe₂ a singlet structure with each iron atom sandwiched between a hexahapto and a tetrahapto heptalene ring is energetically preferred over an alternate structure with ferrocene-like iron atoms sandwiched between two pentahapto heptalene rings. Partial bonding of each heptalene ring to the metal atoms occurs in the late transition metal derivatives (C₁₂H₁₀)₂M₂ (M = Co, Ni). This leads to an unsymmetrical structure for the cobalt derivative and a structure for the nickel derivative with each nickel atom sandwiched between a trihapto ligand and a tetrahapto ligand.