Electron Spin Resonance Spectroscopic Study of Size-Controlled Ink Particles Isolated from Sepia officinalis

Abstract

The paramagnetic properties of size-controlled ink particles isolated from the ink sacs of Sepia officinalis were studied by electron spin resonance (ESR) spectroscopy. Both the size-controlled ink particles and synthetic melanins seemingly yielded similar ESR spectra consisting of a singlet with a slightly asymmetrical signal. However, the progressive microwave power saturation revealed a clear difference between their paramagnetic behaviors. In comparison with synthetic melanins, the ESR spectra of the ink particles readily reached saturation, indicating a long spin–lattice relaxation time. On the other hand, the ESR linewidth depended on particle size. This implies that the particle size is related to the distance between paramagnetic species in the particles. Hence, it is reasonable that the large ink particle has the weakest spin–spin interaction among these samples. The employment of the size-controlled ink particles enabled us to determine precisely the paramagnetic parameters of Sepia inks.

Paramagnetic Properties of Size-Controlled Squid Ink Particles Dispersed in Water

“…6) A similar T 2 value was also found in dehydrated ink particles. 12) The spin-lattice relaxation time T 1 of the small ink particle was slightly shorter than that of the large ink particle. However, an important point to emphasize is that the T 1 values of both the ink particles dispersed in water were one digit smaller than those of dehydrated ink particles.…”

“…However, an important point to emphasize is that the T 1 values of both the ink particles dispersed in water were one digit smaller than those of dehydrated ink particles. 12)…”

“…This behavior is observed in dehydrated ink particles, because a coat of residual protein fragments in the ink particles may serve as a barrier that prevents the magnetic interaction between the oxygen and the organic free radical in the ink particles. 12) The drying process used to prepare dehydrated samples evaporated only water from the aqueous suspensions of the ink particles isolated from the ink sacs, but the residual protein fragments or amino acids in aqueous suspensions might have remained with the ink particles. It is thought that these remains covered the surface of the ink particles.…”

“…Indeed, the inhomogeneous broadening is also found in synthetic melanins in solid states. 12) Sarna and Sealy have reported that the removal of protein has no marked effect on the ability of a natural melanin to generate free radicals. 17) The generation of free radicals is a property of the melanin polymer rather than any associated protein.…”

“…11) A recent report revealed the correlation between particle sizes and their paramagnetic properties. 12) However, ESR studies of the ink particles have been restricted to their solid state. To provide basic information for various technological applications, it is essential to reveal paramagnetic properties of the sizecontrolled ink particles dispersed in water.…”