DETERMINATION OF ROTATIONAL REORIENTATION CORRELATION TIME AND 59Co NUCLEAR QUADRUPOLAR COUPLING CONSTANT OF POLYAMMONIUM MACROCYCLIC COBALTICYANIDE SUPERCOMPLEXES IN DILUTE AQUEOUS SOLUTIONS——An Application of Dynamic Laser Light Scattering Method

Abstract

Abstract:

The correlation time, τ_c, and the nuclear quadrupolar coupling constant (NQCC) of I>1/2 nuclei are important parameters for characterizing local and microdynamic structures of molecules. However, it is often difficult to determine those constants in solution. In this study, τc and NQCC of the ⁵⁹Co nuclei were determined for a series of supercomplexes [12] aneN₄[Co(CN)₆], [18]aneN₆[Co(CN)₆], [24]aneN₈[Co(CN)₆], [16]aneN₄[CoCN)₆], [24]aneN₆[Co(CN)₆] and [32]aneN₈[Co(CN)₆] in dilute solution. The Dynamic Laser Light Scattering (DLLS) method, which is now widely used in macromolecule research, was first applied to determine the hydrodynamic radii (0.4～0.6 nm) of these molecules. Based on the Stokes-Einstein-Debye equation and the measured hydrodynamic radii, the rotational reorientation correlation times τ_c were calculated. τ_c obtained in this study had a range of 3.8～9.5×10^-11s, which arefairly reasonable for molecules with molecular weights of about 300～500. Finally, NQCC of the ⁵⁹Co nuclei in the supercomplexes were determined by combining the τ_c values calculated and the experimentally measured longitudinal relaxation times, T₁, of the ₅₉Co nuclei. The NQCC values obtained ranged from 0.5 to 2.2 MHz, which are considerably lower than those extracted from solid static NMR lineshape (5 to 7 MHz). The difference is probabl
y due to the structural effects originating from the anisotropy of local electric gradient around ⁵⁹Co nucleus in solid.

Key words: ⁵⁹Co NMR, correlation time, nuclear quadrupolar coupling constant, laser light scattering, supercomplex

CLC Number:

O482.53

ZHOU Ping1*, AU-YEUNG Steve C. F.2. DETERMINATION OF ROTATIONAL REORIENTATION CORRELATION TIME AND ⁵⁹Co NUCLEAR QUADRUPOLAR COUPLING CONSTANT OF POLYAMMONIUM MACROCYCLIC COBALTICYANIDE SUPERCOMPLEXES IN DILUTE AQUEOUS SOLUTIONS——An Application of Dynamic Laser Light Scattering Method[J]. Chinese Journal of Magnetic Resonance.

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DETERMINATION OF ROTATIONAL REORIENTATION CORRELATION TIME AND ⁵⁹Co NUCLEAR QUADRUPOLAR COUPLING CONSTANT OF POLYAMMONIUM MACROCYCLIC COBALTICYANIDE SUPERCOMPLEXES IN DILUTE AQUEOUS SOLUTIONS——An Application of Dynamic Laser Light Scattering Method

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