Paramagnetic properties of size-controlled squid ink particles dispersed in water

The paramagnetic properties of size-controlled ink particles isolated from the ink sacs of squid were studied by electron spin resonance (ESR). ESR spectra of the large and small ink particles dispersed in water were successfully observed at room temperature. Both the ink particles in aqueous suspensions seemingly indicated similar ESR spectra consisting of a singlet with a slightly asymmetrical signal. The linewidth below saturation was almost the same in both the ink particles, but the linewidth of the small ink particle was obviously broadened with an increase in microwave power. On the other hand, the progressive microwave power saturation revealed a clear difference between the paramagnetic behaviors of the ink particles in aqueous suspensions and in solid states. In comparison with dehydrated samples, the ESR signals of the ink particles dispersed in water showed the inhomogeneous broadening and faster spin-lattice relaxation processes. The fundamental characteristics of size-controlled ink particles would serve as basic information for various applications. (author)