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The generation of spin polarization is key in quantum information science and dynamical nuclear polarization. Polarized electron spins with long spin-lattice relaxation times (T1) at room temperature are important for these applications, but have been difficult to achieve. We report the realization of spin-polarized radicals with extremely long T1 at room temperature in a metal-organic framework (MOF) in which azaacene chromophores are densely integrated. Persistent radicals are generated in the MOF by charge separation after photoexcitation. Spin polarization of triplet generated by photoexcitation are successfully transferred to the persistent radicals. Pulse ESR measurements reveal that the T1 of the polarized radical in the MOF is as long as 274 s at room temperature. The achievement of extremely long spin polarization in MOFs with nanopores accessible to guest molecules will be an important cornerstone for future highly sensitive quantum sensing and efficient dynamic nuclear polarization.

In this study, we identified two Mn2+ sites in apo-Photosystem II (PSII) using the pulsed electron–electron double resonance (PELDOR). A Mn2+ ion was bound to apo-PSII on the deactivation of the oxygen-evolving complex. The electron–electron magnetic dipole interaction of the Mn2+ to YD· was estimated to be 2.4 MHz. The site was assigned at the position between His332 and Glu189 in the D1 polypeptide, which is close to the Mn1 site in mature PS II. Using recent structures observed under electron microscopes (EM), the location of the Mn2+ site on photoactivation was reevaluated. The position between Asp170 and Glu189 in the D1 polypeptide is a good candidate for the initial high-affinity site for photoactivation. Based on a comparison with the PELDOR results, the two EM structures were evaluated.

Despite their importance in function, the conformational state of proteins and its changes are often poorly understood, mainly because of the lack of an efficient tool. MurD, a 47-kDa protein enzyme responsible for peptidoglycan biosynthesis, is one of those proteins whose conformational states and changes during their catalytic cycle are not well understood. Although it has been considered that MurD takes a single conformational state in solution as shown by a crystal structure, the solution nuclear magnetic resonance (NMR) study suggested the existence of multiple conformational state of apo MurD in solution. However, the conformational distribution has not been evaluated. In this work, we investigate the conformational states of MurD by the use of electron paramagnetic resonance (EPR), especially intergadolinium distance measurement using double electron-electron resonance (DEER) measurement. The gadolinium ions are fixed on specific positions on MurD via a rigid double-arm paramagnetic lanthanide tag that has been originally developed for paramagnetic NMR. The combined use of NMR and EPR enables accurate interpretation of the DEER distance information to the structural information of MurD. The DEER distance measurement for apo MurD shows a broad distance distribution, whereas the presence of the inhibitor narrows the distance distribution. The results suggest that MurD exists in a wide variety of conformational states in the absence of ligands, whereas binding of the inhibitor eliminates variation in conformational states. The multiple conformational states of MurD were previously implied by NMR experiments, but our DEER data provided structural characterization of the conformational variety of MurD.

Quantum sensing using molecular qubits is expected to provide excellent sensitivity due to the proximity of the sensor to the target analyte. However, many molecular qubits are used at cryogenic temperatures, and how to make molecular qubits respond to specific analytes remains unclear. Here, we propose a new quantum sensor design in which the coherence time changes in response to a variety of analytes at room temperature. We used the photoexcited triplet, which can be initialized at room temperature, as qubits and introduce them to a metal–organic framework that can flexibly change its pore structure in response to guest adsorption. By changing the local molecular density around the triplet qubits by adsorption of a specific analyte, the mobility of the triplet qubit can be changed, and the coherence time can be made responsive.

The term "peptoids" was introduced decades ago to describe peptide analogues that exhibit better physicochemical and pharmacokinetic properties than peptides. Oligo(N-substituted glycine) (oligo-NSG) was previously proposed as a peptoid due to its high proteolytic resistance and membrane permeability. However, oligo-NSG is conformationally flexible, and ensuring a defined shape in water is difficult. This conformational flexibility severely limits the biological application of oligo-NSG. Here, we propose oligo(N-substituted alanine) (oligo-NSA) as a peptoid that forms a defined shape in water. The synthetic method established in this study enabled the first isolation and conformational study of optically pure oligo-NSA. Computational simulations, crystallographic studies, and spectroscopic analysis demonstrated the well-defined extended shape of oligo-NSA realized by backbone steric effects. This new class of peptoid achieves the constrained conformation without any assistance of N-substituents and serves as a scaffold for displaying functional groups in well-defined three-dimensional space in water, which leads to effective biomolecular recognition.

In this study, we identified two Mn

Despite their importance in function, the conformational state of proteins and its changes are often poorly understood, mainly because of the lack of an efficient tool. MurD, a 47-kDa protein enzyme responsible for peptidoglycan biosynthesis, is one of those proteins whose conformational states and changes during their catalytic cycle are not well understood. Although it has been considered that MurD takes a single conformational state in solution as shown by a crystal structure, the solution nuclear magnetic resonance (NMR) study suggested the existence of multiple conformational state of apo MurD in solution. However, the conformational distribution has not been evaluated. In this work, we investigate the conformational states of MurD by the use of electron paramagnetic resonance (EPR), especially intergadolinium distance measurement using double electron-electron resonance (DEER) measurement. The gadolinium ions are fixed on specific positions on MurD via a rigid double-arm paramagnetic lanthanide tag that has been originally developed for paramagnetic NMR. The combined use of NMR and EPR enables accurate interpretation of the DEER distance information to the structural information of MurD. The DEER distance measurement for apo MurD shows a broad distance distribution, whereas the presence of the inhibitor narrows the distance distribution. The results suggest that MurD exists in a wide variety of conformational states in the absence of ligands, whereas binding of the inhibitor eliminates variation in conformational states. The multiple conformational states of MurD were previously implied by NMR experiments, but our DEER data provided structural characterization of the conformational variety of MurD.

The utilization of near-infrared light is an important objective for the high-efficiency utilization of solar energy. Here, we describe a new class of a near-infrared light-induced electron transfer system using a distorted phthalocyanine as a photosensitizer. We revealed that the appropriate modification of distorted phthalocyanine affords a near-infrared absorbing dye with high photostability and long excitation lifetime, and a near-infrared light-induced electron transfer system was successfully established using the dye. The mechanistic investigation clarified that the electron transfer system works via a dynamic quenching mechanism. The system generated a long-lived anion radical species of the dye upon near-infrared light irradiation (>750 nm).

The electronic structure of manganese (Mn) cluster in photosystem II was investigated by electron paramagnetic resonance (EPR) spectroscopy. In order to determine the spin density distribution in magnetically coupled Mn in the S2 state Mn cluster, pulsed electron-electron double resonance (PELDOR) measurement was performed. The local environment of the Mn cluster was investigated by electron-nuclear double resonance (ENDOR). Using spin projections determined by PELDOR, ENDOR signals were assigned to the water molecules ligated to the Mn cluster. The location of a high-affinity Mn2+ site in apo-photosystem II, which is the initial site of photoactivation of the Mn cluster, was determined by PELDOR.

To understand the electronic states on the boundary region between the commensurate antiferromagnetic (II) phase and the incommensurate spin-density-wave phase in the generalized phase diagram for one-dimensional organic conductors, we performed antiferromagnetic resonance (AFMR) and nuclear magnetic resonance (NMR) measurements for ${(\mathrm{TMTTF})}_{2}\mathrm{Br}$. The angular dependence of the AFMR fields at 1.5 K is different from that at 4.8 K, and the temperature dependence of the two AFMR modes is enhanced below 5 K. Furthermore, $^{2}\mathrm{D}$(Deuterium)-NMR measurements were performed for deuterated ${(\mathrm{TMTTF}\text{\ensuremath{-}}{d}_{12})}_{2}\mathrm{Br}$ to investigate charge distribution by quadrupole splitting at low temperatures. We found that the $^{2}\mathrm{D}$-NMR spectrum changes at 4 K in the antiferromagnetic phase. Successive phase transition and a possible magnetic structure are discussed.

The binding site of the extrinsic protein PsbP in plant photosystem II was mapped by pulsed electron-electron double resonance, using mutant spinach PsbP (Pro20Cys, Ser82Cys, Ala111Cys, and Ala186Cys) labeled with 4-maleimido-TEMPO (MSL) spin label. The distances between the spin label and the Tyr160 neutral radical (YD ) in PsbD, the D2 subunit of plant photosystem II, were 50.8 ± 3.5 A, 54.9 ± 4.0 A, 57.8 ± 4.9 A, and 58.4 ± 14.1 A, respectively. The geometry inferred from these distances was fitted to the PsbP crystal structure (PDB: 4RTI ) to obtain the coordinates of YD relative to PsbP. These coordinates were then fitted under boundary conditions to the structure of cyanobacterial photosystem II (PDB: 4UB6 ), by rotating on Euler angles centered at fixed YD coordinates. The result proposed two models which show possible acidic amino acid residues in CP43, CP47 and D2 that can bind the basic amino acids Arg48, Lys143, and Lys160 in PsbP.

Conjugated covalent networks Although graphene and related materials are two-dimensional (2D) fully conjugated networks, similar covalent organic frameworks (COFs) could offer tailored electronic and magnetic properties. Jin et al. synthesized a fully π-conjugated COF through condensation reactions of tetrakis(4-formylphenyl)pyrene and 1,4-phenylenediacetonitrile. The reactions were reversible, which provides the self-healing needed to form a crystalline material of stacked, π-bonded 2D sheets. Chemical oxidation of this semiconductor with iodine greatly enhanced its conductivity, and the radicals formed on the pyrene centers imparted a high spin density and paramagnetism. Science , this issue p. 673

Photosynthetic water splitting is catalyzed by a Mn(4)CaO(5) cluster in photosystem II, whose structure was recently determined at a resolution of 1.9Å [Umena, Y. et al. 2011, Nature, 473:55-60]. To determine the electronic structure of the Mn(4)CaO(5) cluster, pulsed electron-electron double resonance (PELDOR) measurements were performed for the tyrosine residue Y(D)() and S(2) state signals with non-oriented and oriented photosystem II (PS II) samples. Based on these measurements, the spin density distributions were calculated by comparing with the experimental results. The best fitting parameters were obtained with a model in which Mn1 has a large positive projection, Mn3 has a small positive projection, and Mn2 and Mn4 have negative projections (the numbering of Mni (i=1-4) is based on the crystal structure at a 1.9Å resolution), which yielded spin projections of 1.97, -1.20, 1.19 and -0.96 for Mn1-4 ions. The results show that the Mn1 ion, which is coordinated by H332, D342 and E189, has a valence of Mn(III) in the S(2) state. The sign of the exchange interactions J(13) is positive, and the other signs are negative.

We synthesized a two-dimensional (2D) crystalline covalent organic framework (sp

The location of the high-affinity Mn(2+) site in apo-photosystem (PS) II was investigated by pulsed EPR. The electron-electron magnetic dipole interaction of 1.7 MHz between the YD(•) radical and Mn(2+) ion was observed using the pulsed electron-electron double resonance (PELDOR) technique, and the Mn(2+) ion was bound to one apo-PS II in the absence and presence of Ca(2+). PELDOR signals were calculated using the previously determined spin distribution on the YD(•) radical and its known position in the crystal structure, assuming that the specific Mn(2+) site was located in the oxygen evolving complex. The results show that the high-affinity Mn(2+) site is located at the position denoted by Mn4(A) in the native crystal structure. The Mn(2+) is coordinated with axial ligands Asp170 and Glu333 in the D1 polypeptide.