We have recently reported phospholipid bicelles (bilayered micelles) that have positive anisotropy of the magnetic susceptibility and align with their normals parallel to an external magnetic field ...J. Am. Chem. Soc. 2001, 123, 1537. Improvements have been made via the synthesis of a new phospholipid, 1-dodecanoyl-2-(4-(4-biphenyl)butanoyl)-sn-glycero-3-phosphocholine (DBBPC). Bicelles can be formed by mixing DBBPC with a short-chain phospholipid, 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) in a ratio between 5.1:1 and 6.5:1 in an aqueous medium. The 31P NMR spectra clearly show that these bicelles align with their principal axes parallel to the magnetic field within a wide temperature range. The 31P chemical shifts indicate that the conformation of the polar headgroup in these bicelles may be different from that in common bicelles. The phase behavior of a mixture of DBBPC/DHPC with 6:1 mole ratio was investigated in the temperature range of 10−75 °C using 31P, 2H, and 23Na NMR. At lower temperatures (10−54 °C), the system is dominated by the bicellar phase. At higher temperatures (54−75 °C), isotropic micelles are formed and coexist with the bicelles. The partial alignment of maltotriose in the DBBPC/DHPC system was studied at three temperatures, and the 1H−13C dipolar coupling constants are compared with those obtained for two other bicelle solutions.
Single molecule magnets (SMM) may be considered for the construction of future integrated nanodevices, provided however that some degree of ordering is imparted to these molecules (surfaces ...nanostructuration). Combining such nanoobjects with liquid-crystalline orderings to control their assembly and to potentially address them individually therefore appears as one promising strategy. Four mesomorphic, mixed-valent MnIII 8MnIV 4O12(L x,y,z‑CB)16(H2O)4 SMM, differing in the number of liquid-crystalline promoters, (L x,y,z‑CB), were synthesized, and their self-organizing and magnetic properties were investigated. The influence of the peripheral modifications, and precisely how supramolecular ordering and magnetic properties may be affected by the evolution of the proto-mesogenic cyanobiphenyl-based ligands substitution pattern, was explored. Small-angle X-ray scattering studies revealed that all of the hybridized clusters self-organize into room-temperature bilayer smectic phases, mandated by the specific mesogenic functionalization and that the polymetallic cores are further organized according to a short-range pseudo-2D lattice with hexagonal and/or square symmetry. All mesomorphous hybridized dodecamanganese complexes still behave as SMM: they exhibit blocking of the magnetization at about 2.6 K as evidenced by the occurrence of frequency-dependent out-of-phase ac susceptibility signals as well as an opening of the hysteresis cycle with coercive fields varying between 0.13 and 0.6 T, depending on the surface ligands topology. Comparison of the magnetic properties within this series reveals intricate correlations between the structural features of the mesomorphous molecule magnet (i.e., symmetry of the ligands substitution patterns, molecular conformation, average intercluster distances, and respective inclination) with respect to the relative proportion of slow- and fast-relaxing species and the absolute values of the coercive fields.
Rate constants obtained from total line-shape analysis of 11 temperature-dependent gas-phase NMR spectra of (15N)trifluoroacetamide yielded the following kinetic parameters: ΔG ⧧ 298 = 15.1(0.36) ...kcal mol-1, ΔH ⧧ = 13.3(1.3) kcal mol-1, and ΔS ⧧ = −5.9(4.5) cal mol-1 K-1. Ab initio calculations performed at the MP2 level using the 6-311++G(d,p) basis set calculated ΔG ⧧ 298 = 15.19 kcal mol-1, ΔH ⧧ = 14.35 kcal mol-1, and ΔS ⧧ = −2.82 cal mol-1 K-1 in reasonable agreement with experiment. Hartree−Fock calculations using that basis set were also in reasonable agreement with experiment, yielding ΔG ⧧ 298 = 16.03 kcal mol-1, ΔH ⧧ = 14.35 kcal mol-1, and ΔS ⧧ = −5.62 cal mol-1 K-1. DFT calculations (B3-PW91) using the same basis set gave results that were considerably less accurate.
We have experimentally investigated bonding of the nitrile functional group (R-Ctbd1;N:) on the Ge(100)-2x1 surface with multiple internal reflection infrared spectroscopy. Density functional theory ...calculations are used to help explain trends in the data. Several probe molecules, including acetonitrile, 2-propenenitrile, 3-butenenitrile, and 4-pentenenitrile, were studied to elucidate the factors controlling selectivity and competition on this surface. It is found that acetonitrile does not react on the Ge(100)-2x1 surface at room temperature, a result that can be understood with thermodynamic and kinetic arguments. A 4+2 cycloaddition product through the conjugated pi system and a 2+2 C=C cycloaddition product through the alkene are found to be the dominant surface adducts for the multifunctional molecule 2-propenenitrile. These two surface products are evidenced, respectively, by an extremely intense nu(C=C=N), or ketenimine stretch, at 1954 cm(-)(1) and the nu(Ctbd1;N) stretch near 2210 cm(-)(1). While the non-conjugated molecules 3-butenenitrile and 4-pentenenitrile are not expected to form a 4+2 cycloaddition product, both show vibrational modes near 1954 cm(-)(1). Additional investigation suggests that 3-butenenitrile can isomerize to 2-butenenitrile, a conjugated nitrile, before introduction into the vacuum chamber, explaining the presence of the vibrational modes near 1954 cm(-)(1). Pathways directly involving only the nitrile functional group are thermodynamically unfavorable at room temperature on Ge(100)-2x1, demonstrating that this functional group may prove useful as a vacuum-compatible protecting group.
