Corrigendum to: Physicochemical insights of irradiation-enhanced hydroxyl radical generation from ZnO nanoparticles.

[This corrects the article DOI: 10.1039/c5tx00384a.].

Initializing 214 Pure 14-Qubit Entangled Nuclear Spin States in a Hyperpolarized Molecular Solid.

Quantum entanglement has been realized on a variety of physical platforms such as quantum dots, trapped atomic ions, and superconductors. Here we introduce specific molecular solids as promising alternative platforms. Our model system is triplet pentacene in a host single crystal at level anticrossing (LAC) conditions. First, a laser pulse generates the triplet state and initiates entanglement between an electron spin and 14 hyperfine coupled proton spins (quantum bits or qubits). This gives rise to large nuclear spin polarization. Subsequently, a resonant high-power microwave (mw) pulse disentangles the electron spin from the nuclear spins. Simultaneously, high-dimensional multiqubit entanglement is formed among the proton spins. We verified the initialization of 214 pure 14-qubit entangled nuclear spin states with an average degree of entanglement of Eav = 0.77 ± 0.03. These results pave the way for large-scale quantum information processing with more than 10 000 multiqubit entangled states corresponding to computational (Hilbert) space dimensions of dim >1053.

A new series of heteronuclear metal strings, MRhRh(dpa)4Cl2 and MRhRhM(dpa)4X2, from the reactions of Rh2(dpa)4 with metal ions of group 7 to group 12.

We report the syntheses, structures, magnetic and electrochemical properties of MRhRh metal cores helically wrapped by four dpa- (2,2'-dipyridylamide) ligands. We successfully synthesized the precursor Rh2(dpa)4 (1) in high yield and characterized its structure including its oxidized form (1+) which facilitated the syntheses of this series of metal springs. By the reactions of (1) and the metal ions of group 7 to group 12 (M = Mn(2), Fe(3), Co(4), Ni(5), Cu(6), Pd(8), Pt(9), Ru(10), Ir(11) and Rh(12)), ten MRh2(dpa)4Cl2 complexes were successfully isolated. Note that Cd(7) can only be obtained by the one-pot method. The yield of Rh3(dpa)4Cl2 (12) is also improved by this stepwise method. The oxidized complexes [MRh2(dpa)4Cl2](PF6) (M: Ni(5+), Ru(10+), Ir(11+)) are also synthesized for the studies of electronic structures and magnetic properties. The X-ray diffraction technique is applied to characterize all of their structures. The results of these structural, magnetic, and electrochemical studies provide us with in-depth knowledge and comprehensive insight into metal-metal bonds and interactions for this new series of metal strings. In particular, four metal-metal bonds with short distances are found: Pd-Rh (2.372(13) Å), Pt-Rh (2.385(7) Å), Ru-Rh (2.33(3) Å), and Ir-Rh (2.373(5) Å). The remaining ones show no evidence of covalent metal bonds judging from their metal-metal distances, magnetic behaviour, and redox couples in electrochemical analysis. Besides, two unique tetranuclear MRhRhM(dpa)4X2 (M: Cu+(13) and Ag+(14)) complexes with a Rh2(dpa)4 framework are developed. Four metals are aligned linearly. This coordination mode of metal strings provides a unique synthetic route for constructing longer metal chains from a smaller number of dentate ligands.

Giant Zeeman Splitting for Monolayer Nanosheets at Room Temperature.

Giant Zeeman splitting and zero-field splitting (ZFS) are observed in 2D nanosheets that have monolayers of atomic thickness. In this study, single-crystalline CdSe(ethylenediamine)0.5 and Mn2+-doped nanosheets are synthesized via a solvothermal process. Tunable amounts of Mn2+(0.5-8.0%) are introduced, resulting in lattice contraction as well as phosphorescence from five unpaired electrons. The exciton dynamics are dominated by spin-related electronic transitions (4T1 → 6A1) with long lifetimes (20.5, 132, and 295 µs). Temperature-varied EPR spectroscopy with spectral simulation reveals large ZFS (D = 3850 MHz) due to axial distortion of substituted Mn2+ (S = 5/2). In the magnetic circular dichroism (MCD) measurements, we observed giant Zeeman splitting with large effective g values (up to 231 ± 21), which implies huge sp-d exchange interactions in 2D monolayer regimes, leading to diluted magnetic semiconductor (DMS) materials.

Structure and magnetic properties of a novel heteroheptanuclear metal string complex [Ni3Ru2Ni2(µ7-teptra)4(NCS)2](PF6).

We report the synthesis of a novel heteroheptanuclear metal string complex (HMSC) [Ni3Ru2Ni2(µ7-teptra)4(NCS)2](PF6) 1 supported by tetra-pyridyl-tri-amine (H3teptra) ligands. We employed X-ray diffraction and other spectroscopic techniques to characterize the complex. The observed remarkably short Ru-Ru distance of 2.2499(3) Å for 1 is indicative of a unique metal-metal interaction in the mixed-valence [Ru2]5+ (S = 3/2) unit. The complex exhibits a relatively high magnetic moment value of 4.55 B.M. at 4 K, which increases rapidly to 6.00 B.M. at 30 K and remains at 6.11 B.M. from 50 to 300 K as shown by SQUID measurements, indicating a high spin (S≥ 3/2) system which is further supported by the analyses of EPR spectra at low temperatures. These magnetic behaviors can be ascribed to the result of spin-exchange interactions among multi-spin centers.

Manganese Telluride Carbonyl Complexes: Facile Syntheses and Exotic Properties-Reversible Transformations, Hydrogen Generation, Paramagnetic, and Semiconducting Properties.

A novel family of five Mn-Te-CO complexes was prepared via facile syntheses: mono spirocyclic [Mn4Te(CO)16]2- (1), four-membered Mn2Te2 ring-type [Mn2Te2(CO)8]2- (2), hydride-containing square pyramidal [HMn3Te2(CO)9]2- (3), and dumbbell-shaped [Mn6Te6(CO)18]4- (4) and [Mn6Te10(CO)18]4- (5). Electron-precise complexes 4 and 5 exhibit unusual paramagnetism arising from two types of Mn atoms in different oxidation states, as determined by X-ray photoelectron spectroscopy, electron paramagnetic resonance, and density functional theory (DFT) calculations. The structural transformations from small-sized Mn4Te 1 and Mn2Te2 2 to the largest Mn6Te10 5 were controllable, the off/on magnetic-switched transformation between HMn3Te2 3 and 5 was reversible, and the magnetic transformation between Mn6Te6 4 and 5 was observed. Interestingly, the reversible dehydridation and hydridation between the HMn3Te2-based cluster 3 and [Mn3Te2(CO)9]- were successfully accomplished, in which the release of a high yield of H2 was detected by gas chromatography. In addition, upon the addition of CO, cluster 3 first forms a carbonyl-inserted intermediate [HMn3Te2(CO)10]2- (3'), detected by the high resolution ESI-MS, which is readily transformed to a dimeric dihydrido cluster [{HMn3Te2(CO)10}2]2- (6) with the introduction of O2. These low- to high-nuclearity complexes exhibit rich redox properties with semiconducting behavior in solids, possessing low but tunable energy gaps (1.06-1.62 eV) due to efficient electron transport via nonclassical C-H···O(carbonyl) interactions. The structural nature, reversible structural transformations, controllable on/off magnetic switches, electron communication networks, and associated chemical properties for hydrogen generation are discussed in detail and supported by DFT calculations, density of states, band structures, and noncovalent interaction analyses.

Structures and paramagnetism of five heterometallic pentanuclear metal strings containing as many as four different metals: NiPtCo2Pd(tpda)4Cl2.

Five heterometallic pentanuclear metal strings were prepared by stepwise synthesis from two to three and four kinds of metals aligned in one chain. In particular, NiPtCo2Pd(tpda)4Cl2 (5) possesses four different metals, and the SQUID measurement shows that Ni2+ is the only magnetically active center. Besides, the shortest Co(ii)-Co(ii) single bond (2.105(9) Å), so far, is reported.

The synthesis and magnetic properties of a linear mixed-valence [Ni3]5+ in an anthyridine tri-nickel complex.

A novel trinuclear complex [Ni3(µ3-dbay)4Cl2]I3 (1) with a mixed-valence state was prepared by reacting the tridentate ligand 1,13,14-triaza-dibenz[a,j]anthracene (dibenzanthyridine = dbay) with anhydrous NiCl2 and sodium tetraphenylborate. The title compound provides the first example of a trinuclear nickel-anthyridine-based string complex in which the metal framework of complex 1 consists of NiII-NiI-NiII. X-ray crystallography, magnetic susceptibility and detailed EPR measurements were performed to characterize the structure and magnetic properties of this unique complex.

Ligand effects on the structure, mixed-valence sites and magnetic properties of novel pentanickel string complexes.

We report the syntheses, characterization, electronic structures and magnetic properties of four redox pairs of novel nickel-extended metal-atom chain (EMAC) complexes containing pyridine-, naphthyridine- and sulfonyl-containing ligands (H2Tspnda and H2Mspnda) (1-2 and 5-6). We further study the corresponding phenyl-substituted ligands (H2Tsphpnda and H2Msphpnda) (3-4 and 7-8) to examine the details of ligand effects. The X-ray structure of one-electron-reduced [Ni5]9+ complexes shows shorter Ni-Ni bond distances (2.2646(6) for 1, 2.2943(7) for 3, 2.2436(11) for 5 and 2.2322(8) Å for 7) in comparison with an average Ni-Ni distance of 2.3187(8) Å for these complexes, indicative of a partial metal-metal bond interaction in the mixed-valence [Ni2]3+ (S = 3/2) unit. The most striking result is that the [Ni2]3+ site migrates from Ni(1)-Ni(2) to Ni(2)-Ni(3) when we replace the p-tolyl-sulfonyl group with methyl-sulfonyl group. These complexes present a rare example of the effect of crystal packing on the symmetric molecular structure yielding unsymmetric electronic distribution. Cyclic voltammetry measurements show four reversible redox waves and display the lower potentials of the [Ni5]9+ complexes. These unusual lower potentials facilitate one-electron oxidation of these four complexes to [Ni5]10+-core forms. We applied the magnetic susceptibility and EPR measurements to examine the magnetic properties of these four [Ni5]9+-core pentanickel complexes and study the bonding nature of these mixed-valence [Ni2]3+ units. Indeed, the results of EPR measurements reflect the migration of the mixed-valence site and the change of symmetry. Surprisingly, the oxidized [Ni5]10+ counterparts behave differently: complex 2 exhibits an antiferromagnetic interaction with J = -13.59 cm-1 between the two terminal Ni ions, while the others (4, 6 and 8) display diamagnetic properties as all of the Ni2+ ions are in low-spin (S = 0) states. These three complexes, to the best of our knowledge, are the first examples of all Ni2+ ions in a null spin configuration for pentanickel chains. Even though the structures of these complexes are similar to each other, their corresponding electronic structure and oxidized products show drastic changes in their magnetic properties and bonding nature. These differences of the properties and bonding nature of these pentanickel complexes are attributed to the ligand effects.

Destabilizing Character of a π-Conjugated Boron Center in Bisphenol Radicals.

Although boron-containing radicals are promising materials for molecular electronic devices, the electronic effect of the σ-donating yet π-accepting boron center on the stability of open-shell species has been less discussed. In this work, the role of a tricoordinate boron center in π-conjugated radicals was explored through electron paramagnetic resonance measurement of several boron-linked bisphenol radicals and diradicals. Replacing the bridging methine fragment of a neutral Galvinoxyl radical with an arylboryl group led to the corresponding boron-linked radical anion that requires excessive steric protection at the boron center to be persistent in solution. Experimental and theoretical investigations revealed that the introduction of boron would diminish the quinoidal character of the phenoxyl radical and increase both the electrophilicity and nucleophilicity of the open-shell species. Therefore, it is important to consider the steric protection of the boron center in boron-containing π-conjugated organic radicals.

1,2-Migration of N-Diarylboryl Imidazol-2-ylidene through Intermolecular Radical Process.

1,2-Boryl migration of N-boryl N-heterocyclic carbene to 2-boryl imidazole is proposed to proceed through generation and recombination of two radical intermediates, namely, a neutral diarylboron radical and a N-heterocyclic carbene radical. Crossover experiments suggest that these two radical species are stable enough to escape solvent cages and recombine intermolecularly. The presence of radical intermediates is further supported by spin trapping experiments. Besides, the coordination of Li+ cation is found to be critical for the stability of the NHC radical.

A Structurally Characterized Nonheme Cobalt-Hydroperoxo Complex Derived from Its Superoxo Intermediate via Hydrogen Atom Abstraction.

Bubbling O2 into a THF solution of CoII(BDPP) (1) at -90 °C generates an O2 adduct, Co(BDPP)(O2) (3). The resonance Raman and EPR investigations reveal that 3 contains a low spin cobalt(III) ion bound to a superoxo ligand. Significantly, at -90 °C, 3 can react with 2,2,6,6-tetramethyl-1-hydroxypiperidine (TEMPOH) to form a structurally characterized cobalt(III)-hydroperoxo complex, CoIII(BDPP)(OOH) (4) and TEMPO•. Our findings show that cobalt(III)-superoxo species are capable of performing hydrogen atom abstraction processes. Such a stepwise O2-activating process helps to rationalize cobalt-catalyzed aerobic oxidations and sheds light on the possible mechanism of action for Co-bleomycin.

Physicochemical insights of irradiation-enhanced hydroxyl radical generation from ZnO nanoparticles.

The widespread use of zinc oxide nanoparticles (ZnO NPs) has raised environmental and human health concerns owing to their significant cytotoxicity. Although their cytotoxic effects have been associated with reactive oxygen species (ROS), the physicochemical mechanism underlying this phenomenon remains poorly understood. In this study, the physicochemical properties of ZnO NPs were systematically investigated in relation to their effect on ROS generation. Factors that were found to affect hydroxyl radical (˙OH) generation included: NP concentration, irradiation, NP hydrodynamic size, localized pH, ionic strength, NP zeta-potential, and dissolved oxygen levels. The mechanism by which ˙OH was generated under alkaline conditions was found to obey first-order reaction kinetics that followed the conversion of OH- anions and dissolved O2 to ˙OH. Based on these findings, we propose that ZnO NP cytotoxicity involves ˙OH adsorption to the nanoparticle surface, creating a highly localized source of ROS capable of potentiating oxidative damage to cellular structures. This hypothesis was evaluated with time-resolved intracellular calcium [Ca] i imaging that irradiated ZnO NPs triggered cytoplasmic calcium influxes and facilitated nuclear degradation. Together these findings present a novel physicochemical mechanism for ˙OH generation from ZnO NPs with significant implications for nanoparticle cytotoxicity and their relation to human health.

Redox chemistry of a hydroxyphenyl-substituted borane.

Chemical reduction of a hydroxyphenyl-substituted borane triggers a sequential electron- and intramolecular hydrogen-atom-transfer process to afford a hydridoborate phenoxide dianion. On the other hand, hydrogen-atom abstraction of the borane leads to the isolation of a neutral borylated phenoxyl radical, which can be transformed to the corresponding benzoquinone borataalkene derivative by reduction with cobaltocene.

Roles of free radicals in type 1 phototherapeutic agents: aromatic amines, sulfenamides, and sulfenates.

Detailed analyses of the electron spin resonance (ESR) spectra, cell viability, and DNA degradation studies are presented for the photolyzed Type I phototherapeutic agents: aromatic amines, sulfenamides, and sulfenates. The ESR studies provided evidence that copious free radicals can be generated from these N-H, N-S, and S-O containing compounds upon photoirradiation with UV/visible light. The analyses of spectral data allowed us to identify the free radical species. The cell viability studies showed that these agents after exposure to light exert cytotoxicity to kill cancer cells (U937 leukemia cell lines HTC11, KB, and HT29 cell lines) in a dosage- and time-dependent manner. We examined a possible pathway of cell death via DNA degradation by a plasmid cleavage assay for several compounds. The effects of photosensitization with benzophenone in the presence of oxygen were examined. The studies indicate that planar tricyclic amines and sulfenamides tend to form π-electron delocalized aminyl radicals, whereas nonplanar ones tend to yield nitroxide radicals resulting from the recombination of aminyl radicals with oxygen. The ESR studies coupled with the results of cell viability measurements and DNA degradation reveal that planar N-centered radicals can provide higher potency in cell death and allow us to provide some insights on the reaction mechanisms. We also found the formation of azatropylium cations possessing high aromaticity derived from azepines can facilitate secondary electron transfer to form toxic O2(•-) radicals, which can further exert oxidative stress and cause cell death.

Protection of HeLa cells against ROS stress by CuZnSOD mimic system.

A new copper zinc complex (CZpbi), [(bipyridinyl)2Cu-µ-pbi-Zn(pbi)](ClO4)2, pbi = 2-(2-pyridyl)-benzimidazole, was synthesized to mimic copper zinc superoxide dismutase (CuZnSOD). CZpbi was then encapsulated onto a dye (fluorescein isothiocyanate, FITC) functionalized mesoporous silica nanoparticles (MSN) where MSN serves as a nanofactory platform for delivering the catalytic action of the center copper complex. We examined the inhibition of oxidative damage of HeLa cells in the presence of paraquat (PQ, 1,1'-dimethyl-4,4'-bipyridylium dichloride, an oxidative stressor). We further studied the cell viability and cell cycle process under the influence of paraquat stress in the presence of the SOD-mimic FITC-MSN-CZpbi material by flow cytometry and western blot test. We found the nano-sized FITC-MSN is an excellent nano-carrier for delivering the mimic SOD complexes to HeLa cells. Here the reactants are already inside the cell and the result is a promotion of cell function. We present the methodology of encapsulating bio-inspired SOD-mimic in FITC-MSN to achieve a better drug delivery vehicle and catalytic (detoxification) activity. The potency and the stability of SOD-mimic FITC-MSN-CZpbi may provide a new avenue in the future development of artificial antioxidant enzymes.

Strong metal-support interactions between gold nanoparticles and ZnO nanorods in CO oxidation.

The catalytic performances of supported gold nanoparticles depend critically on the nature of support. Here, we report the first evidence of strong metal-support interactions (SMSI) between gold nanoparticles and ZnO nanorods based on results of structural and spectroscopic characterization. The catalyst shows encapsulation of gold nanoparticles by ZnO and the electron transfer between gold and the support. Detailed characterizations of the interaction between Au nanoparticles and ZnO were done with transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR), and FTIR study of adsorbed CO. The significance of the SMSI effect is further investigated by probing the efficiency of CO oxidation over the Au/ZnO-nanorod. In contrast to the classical reductive SMSI in the TiO(2) supported group VIII metals which appears after high temperature reduction in H(2) with electron transfer from the support to metals, the oxidative SMSI in Au/ZnO-nanorod system gives oxygen-induced burial and electron transfer from gold to support. In CO oxidation, we found that the oxidative SMSI state is associated with positively charged gold nanoparticles with strong effect on its catalytic activity before and after encapsulation. The oxidative SMSI can be reversed by hydrogen treatment to induce AuZn alloy formation, de-encapsulation, and electron transfer from support to Au. Our discovery of the SMSI effects in Au/ZnO nanorods gives new understandings of the interaction between gold and support and provides new way to control the interaction between gold and the support as well as catalytic activity.

Type 1 Phototherapeutic Agents. 2. Cancer Cell Viability and ESR Studies of Tricyclic Diarylamines.

Type 1 phototherapeutic agents based on diarylamines were assessed for free radical generation and evaluated in vitro for cell death efficacy in the U937 leukemia cancer cell line. All of the compounds were found to produce copious free radicals upon photoexcitation with UV-A and/or UV-B light, as determined by electron spin resonance (ESR) spectroscopy. Among the diarylamines, the most potent compounds were acridan (4) and 9-phenylacridan (5), with IC50 values of 0.68 µM and 0.17 µM, respectively.

Type 1 phototherapeutic agents, part I: preparation and cancer cell viability studies of novel photolabile sulfenamides.

Novel type 1 phototherapeutic agents based on compounds containing S-N bonds (sulfenamides) were synthesized, assessed for free radical generation, and evaluated in vitro for cell death efficacy in four cancer cell lines (U937, HTC11, KB, and HT29). All of the compounds were found to produce copious free radicals upon photoexcitation with UV-A and/or UV-B light, as determined by electron spin resonance spectroscopy. Among the sulfenamides, the most potent compounds were derived from dibenzazepine 7b and dihydroacridine 8b as determined in all of the four cancer cell lines.

Quantum oscillations and polarization of nuclear spins in photoexcited triplet states.

The unique physical properties of photoexcited triplet states have been explored in numerous spectroscopic studies employing electron paramagnetic resonance (EPR). So far, however, no quantum interference effects were found in these systems in the presence of a magnetic field. In this study, we report the successful EPR detection of nuclear quantum oscillations in an organic triplet state subject to an external magnetic field. The observed quantum coherences can be rationalized using an analytical theory. Analysis suggests that the nuclear spins are actively involved in the intersystem crossing process. The novel mechanism also acts as a source of oscillatory nuclear spin polarization that gives rise to large signal enhancement in nuclear magnetic resonance (NMR). This opens new perspectives for the analysis of chemically induced dynamic nuclear polarization in mechanistic studies of photoactive proteins.