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Publication costs assisted by the IBM CorporationThe refractive indices, density, and diamagnetic susceptibility are reported as a function of temperature for three materials that exhibit nematic liquid crystalline phases in the vicinity of room temperature.The temperature dependence of the nematic order parameter is essentially identical for the three materials. The applicability of models used in the computation of polarization fields of anisotropic molecules is evaluated.

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The double Mn2+ complex of concanavalin A with bound saccharide (SMMPL) was examined by electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements. A room temperature X-band (9 GHz) EPR spectrum of SMMPL revealed a relatively weak, broad resonance in contrast to the spectrum with a six-line hyperfine-split pattern observed for the mononuclear, high-spin Mn2+ complex found in Ca2+-Mn2+-concanavalin A with saccharide present (SCMPL). The EPR spectrum of SMMPL at 77 K, however, consisted of a series of overlapping patterns of 11 hyperfine-split lines near g = 2.0 with members of each pattern separated by 47 G, half the value of the hyperfine splitting of SCMPL. These 11-line patterns are preserved at Q-band (35 GHz), indicating that the manganese ions in SMMPL form a spin-coupled, binuclear center. As expected for an exchange-coupled system, the EPR signal of SMMPL at 77 K saturates at a higher microwave power than those for SCMPL or Mn2+ aquoion. There is also a marked loss of EPR signal intensity for SMMPL between 4.2 and 1.4 K, which supports the view that the pair of manganese ions is exchanged-coupled. The temperature dependence of both the magnetic susceptibility and the low-temperature EPR spectral intensity can be explained by a model in which the two high-spin Mn2+ ions of SMMPL are antierromagnetically exchanged-coupled with an isotropic coupling constant J = 1.8 cm-1 (for the spin Hamiltonian Hex = JS1.S2). Zero-field splitting D' was estimated to be 375 G from the EPR spectrum.(ABSTRACT TRUNCATED AT 250 WORDS)

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