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Saturation recovery (SR) electron paramagnetic resonance was used to determine the distance between iron and nitroxyl for spin-labeled metmyoglobin variants in low-spin and high-spin states of the Fe(III). The interspin distances were measured by analyzing the effect of the heme iron on the spin-lattice relaxation rates of the nitroxyl spin label using the modified Bloembergen equation for low-spin species, and an analogue of the Bloembergen equation for high-spin species. Insight simulations of the spin-labeled protein structures also were used to determine the interspin distances. The distances obtained by SR for high-spin and low-spin complexes with 15-20 A interspin distances, for low-spin CN(-) and high-spin formate adducts at distances up to about 30 A, and results from Insight calculations were in good agreement. For variants with 25-30 A interspin distances, the distances obtained by SR for the fluoride adducts were shorter than observed for the CN(-) or formate adducts or predicted by Insight simulations. Of the heme axial ligands examined (CN(-), imidazole, F(-), and formate), CN(-) is the best choice for determination of iron-nitroxyl distances in the range of 15-30 A.

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In this work, we propose a bit-oriented QIA protocol based on special properties of quantum rotation and the public key cryptographic framework. The proposed protocol exhibited good resistance to both forward search and measure-resend attacks, whereby its security performance was directly related to the length of the authentication code. From our analysis, it was demonstrated that the protocol has good performance, in terms of quantum bit efficiency. In addition, the protocol is well-expandable. The developed protocol is resource-efficient and can be also applied in quantum computing networks.

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According to the properties of Hadamard gate and GHZ state, a quantum authentication protocol with transferable information is proposed. This protocol has higher security and integrity. Especially, the direct appearance of the key and the transmitted information is not required for both quantum and classical channels. In addition, the protocol realizes the key update in the process of identity authentication, which can automatically generate the key needed for the next information transmission. We expect that our protocol can be extended to many other quantum communication technologies.