Tautomeric and conformational stabilities of methylphosphonic dicyanide, methoxydicyanophosphine, and their isocyano analogs: an ab initio calculation

The relative energies and structural parameters of the equilibrium forms and the potential functions of internal rotation of methylphosphonic dicyanide, CH₃(=O)(CN)₂, methoxydicyanophosphine, CH₃OP(CN)₂, and their isocyano analogs, CH₃P(=O)(NC)₂ and CH₃OP(NC)₂, have been calculated at the RHF/6-31G* level. The total energy of the more stable oxo forms CH₃P(=O)(CN)₂ and CH₃P(=O)(NC)₂ are 10–20 kcal mol⁻¹ lower than the energies of the aci forms CH₃OP(CN)₂ and CH₃OP(NC)₂. The relative stabilities of the cyano and isocyano isomers are almost the same in the case of the oxo forms, but for the aci forms the energies of the cyano isomers are 8 kcal mol⁻¹ lower than those of the isocyano isomers. The potential curves for internal rotation in the aci forms are characterized by a deep minimum corresponding to the trans arrangement of the methyl group and the lone pair of electrons on the phosphorus atom. Two less pronounced minima are symmetrically situated with respect to relative maximum corresponding to the transition cis form. The potential curves of internal rotation in the oxo form possess three minima corresponding to staggered configurations of the methyl group and phosphorus atom bonds. The energy characteristics and geometrical parameters of the studied molecules are compared with known data for similar compounds.     

Gas phase electron diffraction study of basketene,C10H10

A gas phase electron diffraction study of the cage hydrocarbon, basketene, is reported. A least squares treatment of molecular intensities has been carried out in terms of a geometrically consistent r_α structure. The mean amplitude values and shrinkage corrections have been calculated using the force field parameters estimated from the data on simpler molecules.Structure refinement of the C_2v molecular model yields the following parameter values (bond lengths, r_a, in nm; angles, r_α in degrees): <C₂—C_3, C₄—C₅?_av 0.1609(14); C₃—C₄ 0.1563(6); C₉C₁₀ 0.1360(9); C₁—C₁₀ 0.1511(13); C₁—C₂ 0.1517(9); <C-H>_av. 0.1092(8); <C₃C₄C₇ 88.5(1.0); dihedral angle C₃C₄C₇/C₃C₅C₇ 153.8(1.0). Parenthesized are three times the standard deviation values, 3σ.In addition to the geometric parameters listed, the mean amplitudes for all bonded and C· C nonbonded distances have been determined by the least squares method. All the other amplitudes (C· H and H· H) have been fixed at the values estimated from the spectral data.Comparison of the results obtained with the literature data on similar polycyclic molecules points to the stronger internal strain in the basketene molecule.     

Acoustic thermometric data on blood flow and thermal output in forearm under physical pressure

The influence of blood flow and thermal output on temperature changes in the human forearm under physical pressure is studied by acoustic thermometry. Compression of the shoulder with a tourniquet decreases blood flow, which make it possible to evaluate the thermal output characteristics only. In calculating the depth temperature of the forearm, the thermal conductivity equation was used and blood flow and additional thermal output sources were taken into account. According to the calculations in which the experimental data were used, the peak depth temperature of the forearm at rest is 36°C. Due to thermal output alone (without blood flow), physical pressure increases this temperature to 37°C, and when both factors are considered, the temperature rises to 38°C. The experiments in question have allowed us to test acoustic thermographic method on subjects, which is an important step in adopting acoustic thermography in clinical practice.     

Toxic metal complexes of macrocyclic cyclen molecule – synthesis,structure and complexing properties

Toxic metal (Cd²⁺, Hg²⁺, Pb²⁺, and Ag⁺) complexes with the tetradentate macrocyclic ligand - cyclen (1,4,7,10-tetraazacyclododecane, [12]aneN₄, L) were prepared and studied in the solid state by IR, X-ray diffraction, elemental and thermal analysis. Diffraction results have yielded three molecular structures, [Cd([12]ane-κ⁴N^1,4,7,10)(NO₃)₂)] (1), [Hg([12]ane-κ⁴N^1,4,7,10)(NO₃-κ²O,O`)]NO₃ (2), [Pb₂([12]ane-κ⁴N^1,4,7,10)₂][Pb(NO₃)₆] (3) and one polymeric structure {[Ag₂([12]ane-κ³N^1,4,7)(μ₂-[12]aneN¹⁰)](NO₃)₂?2H₂O)}_n (4) featuring a unique coordination mode not observed before with cyclen as a ligand. The monodentate (1) and chelate (with small bite angle 50.3(3)°, (2) coordination modes of nitrate ligands were confirmed. Stereochemically active 6s² lone pair was suggested in 3 and DFT results confirmed no significant metal–metal covalent bond. The stability constants of the complexes with Cd²⁺ and Pb²⁺ ions were determined by potentiometric methods in aqueous solutions. Additionally, the structures of complexes in solution were observed by ¹H NMR. Both methods confirm similar cyclen complexing properties toward Zn²⁺ biometal and Cd²⁺, Pb²⁺ toxic metals.     

The role of the covalent interaction in the formation of the electronic structure of Au- and Cu-intercalated graphene on Ni(111)

A study is reported of the role played by covalent interaction in the coupling of graphene formed on Ni(111) to the Ni substrate and after intercalation of Au and Cu monolayers underneath the graphene. Covalent interaction of the graphene π states with d states of the underlying metal (Ni, Au, Cu) has been shown to bring about noticeable distortion of the dispersion relations of the graphene electronic π states in the region of crossing with d states, which can be described in terms of avoided-crossing effects and formation of bonding and antibonding d-π states. The overall graphene coupling to a substrate is mediated by the energy and occupation of the hybridized states involved. Because graphene formed directly on the Ni(111) surface has only bonding-type occupied states, the coupling to the substrate is very strong. Interaction with intercalated Au and Cu layers makes occupation of states of the antibonding and bonding types comparable, which translates into a weak resultant overall coupling of graphene to the substrate. As a result, after intercalation of Au atoms, the electronic structure becomes similar to that of quasi-free-standing graphene, with linear dispersion of π states at the K point of the Brillouin zone and the Dirac point localized close to the Fermi level. Intercalation of Cu atoms under the graphene monolayer results, besides generation of covalent interaction, in a slight charge transport, with a partial occupation of the previously unoccupied π* states and the Dirac point shifted by 0.35 eV toward increasing binding energy.