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Magnetic nanomaterials (MNMs) have attracted significant interest in the past few decades because of their unique properties such as superparamagnetism, which results from the influence of thermal energy on a ferromagnetic nanoparticle. In the superparamagnetic size regime, the moments of nanoparticles fluctuate as a result of thermal energy. To understand the fundamental behavior of superparamagnetism and develop relevant potential applications, various preparation routes have been explored to produce MNMs with desired properties and structures. However, some challenges remain for the preparation of well-defined magnetic nanostructures, including exchange-coupled nanomagnets, which are considered as the next generation of advanced magnets. In such a case, effective synthetic methods are required to achieve control over the chemical composition, size, and structure of MNMs. For instance, liquid-phase chemical syntheses, a set of emerging approaches to prepare various magnetic nanostructures, facilitate precise control over the nucleation and specific growth processes of nanomaterials with diverse structures. Among them, the high-temperature organic-phase method is an indispensable one in which the microstructures and physical/chemical properties of MNMs can be tuned by controlling the reaction conditions such as precursor, surfactant, or solvent amounts, reaction temperature or time, reaction atmosphere, etc. In this Account, we present an overview of our progress on the chemical synthesis of various MNMs, including monocomponent nanostructures (e.g., metals, metal alloys, metal oxides/carbides) and multicomponent nanostructures (heterostructures and exchange-coupled nanomagnets). We emphasize the high-temperature organic-phase synthetic method, on which we have been focused over the past decade. Notably, multicomponent nanostructures, obtained by growing or incorporating different functional components together, not only retain the functionalities of each single component but also possess synergic properties that emerge from interfacial coupling, with improved magnetic, optical, or catalytic features. Herein, potential applications of MNMs are covered in three representative areas: biomedicine, catalysis, and environmental purification. Regarding biomedicine, MNMs can detect or target biological entities after being modified with specific biomolecules, and they can be applied to magnetic resonance imaging, imaging-guided drug delivery, and photothermal therapy. Apart from their magnetic features, the catalytic performance of some MNMs resulting from their highly specific chemical components and surface structure will be briefly introduced, highlighting its impact in the methanol oxidation reaction, the oxygen reduction reaction, the oxygen and hydrogen evolution reactions, and the Fischer-Tropsch synthesis. Finally, environmental purification, primarily for water remediation, will be highlighted with two main aspects: the effective capture of bacteria and the removal of adverse ions in wastewater. We hope that this Account will clarify the progress on the controllable preparation of MNMs with specific compositions, sizes, and structures and generate broad interest in the realms of biomedicine and catalysis as well as in environmental issues and other potential applications. [ABSTRACT FROM AUTHOR]

The first (N=N)2- complex of a rare-earth metal with an end-on dinitrogen bridge, {K-(crypt)}2{[(R2N)3Sc]2[μ-η1:η1-N2]} (crypt = 2.2.2-cryptand, R = SiMe3), has been isolated from the reduction of Sc(NR2)3 under dinitrogen at -35 °C and characterized by X-ray crystallography. The structure differs from the characteristic side-on structures previously observed for over 40 crystallographically characterized rare-earth metal (N=N)2- complexes of formula [A2Ln(THF)x]2[μ-η2:η2- N2] (Ln = Sc, Y and lanthanides; x = 0, 1; A = anionic ligand such as amide, cyclopentadienide and aryloxide). The 1.221(3) Å N-N distance and the 1644 cm-1 Raman stretch are consistent with the presence of an (N=N)2-bridge. The observed paramagnetism of the complex by Evans method measurements is consistent with DFT calculations that suggest a triplet (3A2) ground state in D3 symmetry involving two degenerate Sc-N2-Sc bonding orbitals. Upon brief exposure of the orange Sc3+ bridging dinitrogen complex to UV-light, photolysis to form the monomeric Sc2+ complex, [K(crypt)][Sc(NR2)3], was observed. Conversion of the Sc2+ complex to the Sc3+ dinitrogen complex was not observed with this crypt system, but it did occur with the 18-crown-6 (crown) analog which formed {K(crown)}2{[(R2N)3Sc]2[μ-η1:η1 N2]}. This suggests the importance of the alkali metal chelating agent in the reversibility of dinitrogen binding in this scandium system. [ABSTRACT FROM AUTHOR]

Bacteria employ remarkable membrane-bound nanoarrays to sense their environment and direct their swimming. Arrays consist of chemotaxis receptor trimers of dimers that are bridged at their membrane-distal tips by rings of two cytoplasmic proteins, a kinase CheA and a coupling protein CheW. It is not clear how ligand binding to the periplasmic domain of the receptor deactivates the CheA kinase bound to the cytoplasmic tip ~300 Å away, but the mechanism is thought to involve changes in dynamics within the cytoplasmic domain. To test these proposals, we applied solid-state NMR mobility-filtered experiments to functional complexes of the receptor cytoplasmic fragment (U-13C,15N-CF), CheA, and CheW. Assembly of these proteins into native-like, homogeneous arrays is mediated by either vesicle binding or molecular crowding agents, and paramagnetic relaxation enhancement is used to overcome sensitivity challenges in these large complexes. INEPT spectra reveal that a significant fraction of the receptor is dynamic on the nanosecond or shorter time scale, and these dynamics change with signaling state. The mobile regions are identified through a combination of biochemical and NMR approaches (protein truncations and unique chemical shifts). The INEPT spectra are consistent with an asymmetric mobility in the methylation region (N-helix mobility ≫ C-helix mobility) and reveal an increase in the mobility of the N-helix in the kinase-off state. This finding identifies functionally relevant dynamics in the receptor, and suggests that this N-helix segment plays a key role in propagating the signal. [ABSTRACT FROM AUTHOR]

103Rh NMR parameters and the bonding structure of three complexes of [Cp*RhX2]2, where X = Cl, Br, or I, have been studied with the help of natural bond orbitals (NBOs) and natural localized molecular orbitals (NLMOs). The complexes of [Cp*RhX2]2, where X = Cl, Br, or I, have similar bonding structures, with the major difference being in the degree of covalency of the Rh-X bonds. The decomposition of 103Rh NMR shielding into diamagnetic, paramagnetic, and spin-orbit terms shows that normal halogen dependence (NHD) of the 103Rh NMR shift is defined mostly by the paramagnetic term, with the spin-orbit term being significantly smaller. The decomposition of 103Rh shielding into spin-free NBO and NLMO contributions shows that 103Rh shielding is dominated by Rh d-orbital deshielding contributions. We explain the NHD of the 103Rh NMR shift with the increase in the energies of the virtual antibonding Rh-X orbitals along the X = Cl, Br, and I series. [ABSTRACT FROM AUTHOR]

First-principles theoretical studies enable an electronic and magnetic characterization of the recently synthesized Ni9Te6(PEt3)8C60 ionic material consisting of Ni9Te6(PEt3)8 superatoms and C60. The PEt3 ligands are shown to create an internal coulomb well that lifts the quantum states of the Ni9Te6 cluster, lowering its ionization potential to 3.39 eV thus creating a superalkali motif. The metallic core has a spin magnetic moment of 5.3 μB in agreement with experiment. The clusters are marked by low magnetic anisotropy energy (MAE) of 2.72 meV and a larger intra-exchange coupling exceeding 0.2 eV, indicating that the observed paramagnetic behavior around 10K is due to superparamagnetic relaxations. The magnetic motifs separated by C60 experience a weak superexchange that stabilizes a ferromagnetic ground state as observed around 2 K. The calculated MAE is sensitive to the charged state that could account for the observed change in magnetic transition temperature with size of the ligands or anion. [ABSTRACT FROM AUTHOR]

We demonstrate the ability of Mössbauer spectroscopy to simultaneously investigate Brownian motion and Néel relaxation in ferrofluidic samples. For this purpose, Mössbauer spectra of coated iron oxide nanoparticles with core diameters of 6.0-26.4 nm dissolved in 70 vol % glycerol solution were recorded in the temperature range of 234-287 K and compared to low-temperature spectra without Brownian motion. By comparison to theory, we were able to determine the particle coating thickness and the dynamic viscosity of the fluid from the broadening of the absorption lines (Brownian motion), as well as the state of Néel relaxation. Results from Mössbauer spectroscopy were crosschecked by AC-susceptometry at several temperatures for Brownian motion and in the high-frequency regime (100 Hz-1 MHz) for Néel relaxation. [ABSTRACT FROM AUTHOR]

Paramagnetic endohedral fullerenes are ideal candidates for quantum information processing and high-density data storage due to their protected spins with particularly high stability. Herein, we report a solid spin system based on a paramagnetic metallofullerene Y2@C79N through incarcerating it into the cage-shaped pores of a metal-organic framework (MOF-177). In this kind of guest and host complex, the Y2@C79N molecules inside the pores of MOF crystal show axisymmetric paramagnetic property. It was found that the pores of MOF-177 crystal play an important role in dispersing the Y2@C79N molecules as well as in steering their electron spin. The group of arranged Y2@C79N molecules and their electron spins in MOF crystals are potential quantum bits for quantum information science and data storage. Moreover, this kind of solid spin system can be used as a probe for nanoscale nuclear magnetic resonance or for motion imaging of a single biomolecule. [ABSTRACT FROM AUTHOR]

Spiro-biphenalenyl (SBP) boron radicals constitute an important family of molecules for the preparation of functional organic materials. The building blocks of several SBP-based crystals are p-dimers of these radicals, in which two phenalenyl (PLY) rings face each other and the other two PLYs point away from the superimposed PLYs. The dimers of ethyl-SBP and butyl-SBP undergo a spin transition between a diamagnetic and a paramagnetic state upon heating, while other dimers exhibit paramagnetism at all temperatures. Here, we present a computational study aimed at establishing the driving forces of the spin-transition undergone by ethyl-SBP at ~140 K. The ground state of the p-dimers below 140 K is a singlet state in which the SBP unpaired electrons are partially localized in the superimposed PLYs. Above 140 K, the unpaired electrons are localized in the nonsuperimposed PLYs. These high-temperature structures are exclusively governed by the ground triplet state because the open-shell singlet with the unpaired electrons localized in the nonsuperimposed PLYs does not feature any minimum in the potential energy surface of the system. Furthermore, we show that the electrostatic component of the interaction energy between SBP radicals in the p-dimers is more attractive in the triplet than in the singlet, thereby partially counteracting the bonding and dispersion components, which favor the singlet. This electrostatic stabilization of the triplet state is a key driving force of the spin transition of ethyl-SBP and a key factor explaining the paramagnetic response of the p-dimers of other SBP-based crystals. [ABSTRACT FROM AUTHOR]

Particle and domain sizes strongly influence the properties of materials. Here we present an NMR approach based on paramagnetic relaxation enhancement (PRE) relayed by spin diffusion (SD), which allows us to determine lengths in the nm−μm range. We demonstrate the method on multicomponent organic polymer mixtures by selectively doping one component with a paramagnetic center in order to measure the domain size in a second component. Using this approach we determine domain sizes in ethyl cellulose/hydroxypropyl cellulose film coatings in pharmaceutical controlled release formulations. Here we measure particle sizes ranging from around 50 to 200 nm. [ABSTRACT FROM AUTHOR]

The paramagnetic relaxation timesof the aromatic and β protonsof Tyr59 and His68 residues of the native ubiquitin and of Tyr59 residueof the non-native ubiquitin were determined from an analysis of chemicallyinduced dynamic nuclear polarization (CIDNP) kinetics obtained duringthe photoreaction of the protein and 2,2′-dipyridyl excitedin the triplet state. Using the paramagnetic relaxation times determinedearlier for the radicals of free amino acids as an internal standardand assuming that the hyperfine interaction (HFI) anisotropy is verysimilar for the radicals of free amino acids and the correspondingradicals of amino acid residues in the proteins, we determined parametersthat characterize the intramolecular mobility of different protonsin native and two non-native states of ubiquitin. The latter are denaturedat pH 2 and 57 °C, and the A-state at pH 2 in a 60%/40% methanol/watermixture. The determination of the two parameters of intramolecularmobility (i.e., the correlation time of internal motion, τe, and the order parameter, S2)was only possible by analyzing paramagnetic relaxation data obtainedat two magnetic fields (4.7 and 9.4 T) using nuclear magnetic resonance(NMR) spectrometry. Intramolecular correlation times fall into thesubmicrosecond–microsecond time scale. Longer correlation timesand higher order parameters were found for the less accessible Tyr59residue than for the His68 residue, as well as for the more buriedβ protons than for the aromatic protons for both of the proteinresidues in the native state. For Tyr59, intramolecular mobility increasesfollowing the loss of the tertiary structure of ubiquitin. These findingsstrongly support the reliability of the obtained data. [ABSTRACT FROM AUTHOR]

Adsorption of ceruloplasmin (Cp)at a gold electrode modified withferromagnetic iron nanoparticles encapsulated in carbon (Fe@C Nps)leads to a successful immobilization of the enzyme in its electroactiveform. The proper placement of Cp at the electrode surface on top ofthe nanocapsules containing an iron core allowed a preorientationof the enzyme, hence allowing direct electron transfer between theelectrode and the enzyme. Laser ablation coupled with inductivelycoupled plasma mass spectrometry indicated that Cp was predominantlylocated at the paramagnetic nanoparticles. Scanning electrochemicalmicroscopy measurements in the sample-generation/tip-collection modeproved that Cp was ferrooxidative inactive if it was immobilized onthe bare gold surface and reached the highest activity if it was adsorbedon Fe@C Nps in the presence of a magnetic field. [ABSTRACT FROM AUTHOR]

The self-assembly between a water-soluble bis-bidentate ligand L18w and Co(II) salts in water affords three high-spin Co(II) products: a dinuclear meso-helicate [Co2(L18w)3]X4; a tetrahedral cage [Co4(L18w)6]X8; and a dodecanuclear truncated-tetrahedral cage [Co12(L18w)18]X24 (X = BF4 or ClO4). All three products were crystallized under different conditions and structurally characterized. In [Co2(L18w)3]X4 all three bridging ligands span a pair of metal ions; in the two larger products, there is a metal ion at each vertex of the Co4 or Co12 polyhedral cage array with a bridging ligand spanning a pair of metal ions along every edge. All three structural types are known: what is unusual here is the presence of all three from the same reaction. The assemblies Co2, Co4, and Co12 are in slow equilibrium (hours/days) in aqueous solution, and this can be conveniently monitored by ¹H NMR spectroscopy because (i) the paramagnetism of Co(II) disperses the signals over a range of ca. 200 ppm and (ii) the different symmetries of the three species give characteristically different numbers of independent ¹H NMR signals, which makes identification easy. From temperature- and concentration-dependent ¹H NMR studies it is clear that increasing temperature and increasing dilution favors fragmentation to give a larger proportion of the smaller assemblies for entropic reasons. High concentrations and low temperature favor the larger assembly despite the unfavorable entropic and electrostatic factors associated with its formation. We suggest that this arises from the hydrophobic effect: reorganization of several smaller complexes into one larger one results in a smaller proportion of the hydrophobic ligand surface being exposed to water, with a larger proportion of the ligand surface protected in the interior of the assembly. In agreement with this, ¹H NMR spectra in a nonaqueous solvent (MeNO2) show formation of only [Co2(L18w)3]X4 because the driving force for reorganization into larger assemblies is now absent. Thus, we can identify the contributions of temperature, concentration, and solvent on the result of the metal/ligand self-assembly process and have determined the speciation behavior of the Co2/Co4/Co12 system in aqueous solution. [ABSTRACT FROM AUTHOR]

Lanthanide(lll) complexes of a cross-bridged cyclam derivative containing two picolinate pendant arms are kinetically inert in very harsh conditions such as 2 M HC1, with no dissociation being observed for at least 5 months. Importantly, the [Ln(dota)]-complexes, which are recognized to be extremely inert, dissociate under these conditions with lifetimes in the range ca. 1 min to 12 h depending upon the Ln3+ ion. X-ray diffraction studies reveal octadentate binding of the ligand to the metal ion in the [Eu(cb-tedpa)]+ complex, while ¹H and 13C NMR experiments in D2O point to the presence of a single diastereoisomer in solution with a very rigid structure. The structure of the complexes in the solid state is retained in solution, as demonstrated by the analysis of the Yb3+-induced paramagnetic shifts. [ABSTRACT FROM AUTHOR]

A new ternary compound NaCu6Se4 was synthesized from the reaction of Cu in a molten sodium polyselenide flux. The compound crystallizes in trigonal space group R3m with a = 4.0465(3) Å and c = 41.493(5) Å. The crystal structure contains flat two-dimensional slabs of 1/∞[Cu6Se4] with a unique structural arrangement, separated by Na cations. The compound contains mixed valency and has a high conductivity of ~3 × 10³ S cm-1 at room temperature, and exhibits increasing conductivity with decreasing temperature, indicating metallic behavior. A small positive thermopower (4-11 μV K-1 from 300 to 500 K) and Hall effect measurements indicate p-type transport with a carrier concentration of ~2.8(3) × 1021 cm-3 and a hole mobility of ~8.75 cm² V-1 s-1 at 300 K. NaCu6Se4 exhibits temperature-independent Pauli paramagnetism. [ABSTRACT FROM AUTHOR]

Bent-core mesogens containing 6-oxoverdazyl radical as the angular central unit exhibit rich polymorphism that includes isotropic—isotropic transition, re-entant isotropic (lre), and a novel 3D tetragonal (Tet) phases. Surprisingly, the paramagnetic Tet phase interacts linearly with applied electric field and exhibits photoinduced ambipolar charge transport (µ ≈ 10-3 cm2 V-1 s-1). Magnetic analysis showed gradual increase of antiferromagnetic interactions upon cooling. [ABSTRACT FROM AUTHOR]

1-Phenyl-3-trifluoromethyl-l,4-dihydrobenzo[e][1,2,4]triazin-4-yl is the first example of a hydrazyl radical that shows a reversible sharp spin transition fully completed within 5(1) K. The nominally first-order transition takes place at ca. 58(2) K and proceeds via subtle changes of intra- and interstack interactions between two similar structural phases. The low-temperature phase (5—60 K) is diamagnetic and has a singlet ground state (2Jexp= -166.8 cm-1, gsolid = 2.0042, ρ = 0.2%) stemming from a multicenter two-electron interaction. The high-temperature phase (60—300 K) is paramagnetic as a result of noninteracting S = 1/2 spins arising from weakly bound dimers. [ABSTRACT FROM AUTHOR]

The study of inorganic crystalline materials by solid-state NMR spectroscopy is often complicated by the low sensitivity of heavy nuclei. However, these materials often contain or can be prepared with paramagnetic dopants without significantly affecting the structure of the crystalline host. Dynamic nuclear polarization (DNP) is generally capable of enhancing NMR signals by transferring the magnetization of unpaired electrons to the nuclei. Therefore, the NMR sensitivity in these paramagnetically doped crystals might be increased by DNP. In this paper we demonstrate the possibility of efficient DNP transfer in polycrystalline samples of [Co(en)3Cl3]2-NaCl-6H20 (en = ethylenediamine, C2H8N2) doped with Cr(lll) in varying concentrations between 0.1 and 3 mol %. We demonstrate that 1H, 13C, and 59Co can be polarized by irradiation of Cr(lll) with 140 GHz microwaves at a magnetic field of 5 T. We further explain our findings on the basis of electron paramagnetic resonance spectroscopy of the Cr(IIl) site and analysis of its temperature-dependent zero-field splitting, as well as the dependence of the DNP enhancement factor on the external magnetic field and microwave power. This first demonstration of DNP transfer from one paramagnetic metal ion to its diamagnetic host metal ion will pave the way for future applications of DNP in paramagnetically doped materials or metalloproteins. [ABSTRACT FROM AUTHOR]

Despite the growingtechnological interest of polydopamine (dopaminemelanin)-based coatings for a broad variety of applications, the factorsgoverning particle size, shape, and electronic properties of thisbioinspired multifunctional material have remained little understood.Herein, we report a detailed characterization of polydopamine growth,particle morphology, and paramagnetic properties as a function ofdopamine concentration and nature of the buffer (pH 8.5). DynamicLight Scattering data revealed an increase in the hydrodynamic radii(Rh) of melanin particles with increasingdopamine concentration in all buffers examined, especially in phosphatebuffer. Conversely, a marked inhibition of particle growth was apparentin Tris buffer, with Rhremaining as lowas <100 nm during polymerization of 0.5 mM dopamine. Small angleneutron scattering data suggested formation of bidimensional structuresin phosphate or bicarbonate buffers, while apparently three-dimensionalfractal objects prevailed in Tris buffer. Finally, electron paramagneticresonance spectra revealed a broader signal amplitude with a peculiarpower saturation decay profile for polydopamine samples prepared inTris buffer, denoting more homogeneous paramagnetic centers with respectto similar samples obtained in phosphate and bicarbonate buffers.Overall, these results disclose Tris buffer as an efficient modulatorof polydopamine buildup and properties for the rational control andfine-tuning of melanin aggregate size, morphology, and free radicalbehavior. [ABSTRACT FROM AUTHOR]

The endohedral fullerene once erroneously identified as Sc3@C82 was recently shown to be Sc3C2@Ih-C80, the first example of an open-shell cluster metallofullerene. We herein report that benzyl bromide (1) reacts with Sc3C2@Ih-C80 via a regioselective radical addition that affords only one isomer of the adduct Sc3C2@Ih-C80 (CH2C6H5) (2) in high yield. An X-ray crystallographic study of 2 demonstrated that the benzyl moiety is singly bonded to the fullerene cage, which eliminates the paramagnetism of the endohedral in agreement with the ESR results. Interestingly, X-ray results further reveal that the 3-fold disordered Sc3C2 cluster adopts two different configurations inside the cage. These configurations represent the so-called “planar” form and the computationally predicted, but not crystallographically characterized, “trifoliate” form. It is noteworthy that this is the first crystallographic observation of the “trifoliate” form for the Sc3C2 cluster. In contrast, crystallographic investigation of a Sc3C2@Ih-C80/Ni(OEP) cocrystal, in which the endohedral persists in an open-shell structure with paramagnetism, indicates that only the former form occurs in pristine Sc3C2@Ih-C80. These results demonstrate that the cluster configuration in EMFs is highly sensitive to the electronic structure, which is tunable by exohedral modification. In addition, the electrochemical behavior of Sc3C2@Ih-C80 has been markedly changed by the radical addition, but the absorption spectra of the pristine and the derivative are both featureless. These results suggest that the unpaired electron of Sc3C2@Ih-C80 is buried in the Sc3C2 cluster and does not affect the electronic configuration of the cage. [ABSTRACT FROM AUTHOR]

Electrocrystallization of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) in the presence of the tris(chloranilato)ferrate(III) [Fe(Cl2An)3]3- paramagnetic chiral anion in different stoichiometric ratios and solvent mixtures afforded three different hybrid systems formulated as [BEDT-TTF]3[Fe(Cl2An)3]·3CH2Cl2·H2O (1), δ-[BEDT-TTF]5[Fe(Cl2An)3]·4H2O (2), and ɑ?-[BEDT-TTF]18[Fe(Cl2An)3]3·3CH2Cl2·6H2O (3). Compound 1 presents an unusual structure without the typical alternating organic and inorganic layers, whereas compounds 2 and 3 show a segregated organic-inorganic crystal structure where layers formed by Λ and δ enantiomers of the paramagnetic complex, together with dicationic BEDT-TTF dimers, alternate with layers where the donor molecules are arranged in the δ (2) and ɑ? (3) packing motifs. Compound 1 behaves as a semiconductor with a much lower conductivity due to the not-layered structure and strong dimerization between the fully oxidized donors, whereas 2 and 3 show semiconducting behaviors with high room-temperature conductivities of ca. 2 S cm-1 and 8 S cm-1, respectively. The magnetic properties are dominated by the paramagnetic S = 5/2 [Fe(Cl2An)3]3- anions whose high-spin character is confirmed by electron paramagnetic resonance and magnetic susceptibility measurements. The correlation between crystal structure and conductivity behavior was studied by means of tight-binding band structure calculations, which support the observed conducting properties. [ABSTRACT FROM AUTHOR]

A massive interest has been generated lately by the improvement of solid-state magic-angle spinning (MAS) NMR methods for the study of a broad range of paramagnetic organic and inorganic materials. The open-shell cations at the origin of this paramagnetism can be metals, transition metals, or rare-earth elements. Actinide-bearing compounds and their 5f unpaired electrons remain elusive in this intensive research area due to their well-known high radiotoxicity. A dedicated effort enabling the handling of these highly radioactive materials now allows their analysis using high-resolution MAS NMR (>55 kHz). Here, the study of the local structure of a series of actinide dioxides, namely, ThO2, UO2, NpO2, PuO2, and AmO2, using solid-state 17O MAS NMR is reported. An important increase of the spectral resolution is found due to the removal of the dipolar broadening proving the efficiency of this technique for structural analysis. The NMR parameters in these systems with numerous and unpaired 5f electrons were interpreted using an empirical approach. Single-ion model calculations were performed for the first time to determine the z component of electron spin on each of the actinide atoms, which is proportional to the shifts. A similar variation thereof was observed only for the heavier actinides of this study. [ABSTRACT FROM AUTHOR]

A computational experiment investigating the 1H and 13C nuclear magnetic resonance (NMR) chemical shifts of molecules with unpaired electrons has been developed and implemented. This experiment is appropriate for an upper-level undergraduate laboratory course in computational, physical, or inorganic chemistry. The chemical shift range for paramagnetic systems differs substantially from the well-known range of diamagnetic compounds. Students carried out density functional theory calculations of the chemical shifts of an organic radical and a related closed-shell system. This simple exercise illustrated that a single unpaired electron may result in dramatically different chemical shifts. Organometallic systems were also considered. The chemical shifts of the closed shell molecule ferrocene were compared to those of vanadocene and nickelocene, which afford three and two unpaired electrons, respectively. A natural bonding orbital (NBO) analysis was employed to study the electronic structure of NiCp2. [ABSTRACT FROM AUTHOR]

Measurementsof specific interactions between proteins are challenging.In redox systems, interactions involve surfaces near the attachmentsites of cofactors engaged in interprotein electron transfer (ET).Here we analyzed binding of cytochrome c2to cytochrome bc1by measuring paramagneticrelaxation enhancement (PRE) of spin label (SL) attached to cytochrome c2. PRE was exclusively induced by the iron atomof heme c1of cytochrome bc1, which guaranteed that only the configurations withSL to heme c1distances up to ∼30Å were detected. Changes in PRE were used to qualitatively andquantitatively characterize the binding. Our data suggest that atlow ionic strength and under an excess of cytochrome c2over cytochrome bc1, severalcytochrome c2molecules gather near thebinding domain forming a “cloud” of molecules. Whenthe cytochrome bc1concentration increases,the cloud disperses to populate additional available binding domains.An increase in ionic strength weakens the attractive forces and theaverage distance between cytochrome c2and cytochrome bc1increases. The spatialarrangement of the protein complex at various ionic strengths is different.Above 150 mM NaCl the lifetime of the complexes becomes so short thatthey are undetectable. All together the results indicate that cytochrome c2molecules, over the range of salt concentrationencompassing physiological ionic strength, do not form stable, long-livedcomplexes but rather constantly collide with the surface of cytochrome bc1and ET takes place coincidentally with oneof these collisions. [ABSTRACT FROM AUTHOR]

The increasing interest in the functional versatility of glycan epitopes in cellular glycoconjugates calls for developing sensitive methods to define carbohydrate conformation in solution and to characterize protein-carbohydrate interactions. Measurements of pseudocontact shifts in the presence of a paramagnetic cation can provide such information. In this work, the energetically privileged conformation of a disaccharide (lactose as test case) was experimentally inferred by using a synthetic carbohydrate conjugate bearing a lanthanide binding tag. In addition, the binding of lactose to a biomedically relevant receptor (the human adhesion/growthregulatory lectin ga]ectin-3) and its consequences in structural terms were defined, using Dy3+, Tb3+, and Tm3+. The described approach, complementing the previously tested protein tagging as a way to exploit paramagnetism, enables to detect binding, even weak interactions, and to characterize in detail topological aspects useful for physiological ligands and mimetics in drug design. [ABSTRACT FROM AUTHOR]

The article discusses the relevant advances in the field of polydopamine and its derivative materials. Topics discussed include an overview of the physicochemical properties of polydopamine which includes paramagnetism, chemical reactivity and adhesive property, polymerization mechanism and polydopamine-derived hybrid materials like polydopamine capsules, hydrogels and synthetic membranes. It concludes the use of polydopamine in the field of research.

Opticalpumping of spin polarization can produce almost completespin order but its application is restricted to select atomic gasesand condensed matter systems. Here, we theoretically investigate anovel route to nuclear spin hyperpolarization in arbitrary fluidsin which target molecules are exposed to polarized paramagnetic centerslocated near the surface of a host material. We find that adsorbednuclear spins relax to positive or negative polarization dependingon the average paramagnetic center depth and nanoscale surface topology.For the particular case of optically pumped nitrogen-vacancy centersin diamond, we calculate strong nuclear spin polarization at moderatemagnetic fields provided the crystal surface is engineered with surfaceroughness in the few-nanometer range. The equilibrium nuclear spintemperature depends only weakly on the correlation time describingthe molecular adsorption dynamics and is robust in the presence ofother, unpolarized paramagnetic centers. These features could be exploitedto polarize flowing liquids or gases, as we illustrate numericallyfor the model case of a fluid brought in contact with an opticallypumped diamond nanostructure. [ABSTRACT FROM AUTHOR]

Single crystals of YbOs2Al10 and LuOs2Al10 were grown for the first time using an aluminum self-flux method. The compounds crystallized into a cagelike structure in space group Cmcm, similar to the prototype compound YbFe2Al10. YbOs2All0 exhibited a mixed-valent nature, as determined by magnetic susceptibility measurements over a wide temperature range from 2 to 900 K, in which the inter-configuration--fluctuation model revealed a broad peak around 400 K. In contrast, LuOs2Al10 displayed Pauli-like paramagnetic behavior over the same temperature range. Both compounds were metallic in nature between 2 and 300 K. The electronic specific heat coefficient of 21.3(2) mJ mol-l K-2 for YbOs2Al10 was determined to be larger than that for LuOs2Al10 [8.9(1) mJ mol-1 K-2], reflecting the mixed-valent nature of the former. First-principles calculations predicted the presence of a mixed-valent state in YbOs2Al10, in agreement with the experimental observations. The novel compound YbOs2Al10 elucidates the evolution of the mixed-valent nature of the Yb-based ternary transition metal aluminides from the 3d to 5d elements. [ABSTRACT FROM AUTHOR]

A comprehensive study of actinide cation paramagnetism in acidic aqueous solution has been completed in perchlorate media. Employing the Evans method, all the readily accessible actinide cations have been studied using our specially outfitted NMR spectrometer equipped for use with radioactive samples. The effective magnetic moments observed, ranging from 0 to 13 μB, differ from the isoelectronic lanthanides, previous solid actinide studies, and older solution studies. Actinide (IV) and (V) ions show less paramagnetic character, while some actinide (III) ions exhibit greater paramagnetic behavior than predicted from free-ion calculation. Temperature dependence of actinide magnetic susceptibilities from 5 to 80 °C are in good agreement with a Curie-like law except for U(VI), which appears to be temperature-independent. Diamagnetic behavior of Th(IV) exhibits a very low temperature dependence of the magnetic susceptibility. Some explanations for the observations are offered, and the 5f electron behavior is compared to the 4f analogues. [ABSTRACT FROM AUTHOR]

The use of pulsed electron spin resonance (ESR) to measure interspin distance distributions has advanced biophysical research. The three major techniques that use pulsed ESR are relaxation rate based distance measurements, double quantum coherence (DQC), and double electron electron resonance (DEER). Among these methods, the DEER technique has become particularly popular largely because it is easy to implement on commercial instruments and because programs are available to analyze experimental data. [ABSTRACT FROM AUTHOR]

Fullerenes are carbon cages assembled from fused hexagons andpentagons that have closed networks and conjugated π systems. The curve of the fullerene structure requires that the constituent carbon atoms take on a pyramidal shape and produces extra strain energy. However, the highly symmetrical geometry of the fullerene decreases the surface tension in these structures, so highly symmetrical fullerenes are usually very stable. For example, C60with icosahedral symmetry (Ih) is the most stable fullerene molecule. However, another highly symmetrical fullerene, Ih-C80, is extremely unstable. The reason for this difference is the open-shell electronic structure of Ih-C80, which has a 4-fold degenerate HOMO occupied by only two electrons. Predictably, once the degenerate HOMO of Ih-C80accepts six more electrons, it forms a closed-shell electronic structure similar to Ih-C60and with comparable stability. Because the hollow structure of fullerenes can encapsulate metal atoms and those internal metals can transfer electrons to the fullerene cage, the encapsulation of metal clusters may provide an ideal technique for the stabilization of the Ih-C80fullerenes. [ABSTRACT FROM AUTHOR]

Ligands containing linked dipicolylamine (dpa) and bipyridine sites have been explored as platforms for the synthesis of heterometallic complexes containing the paramagnetic metals Cu2+ and Co2+. IR and EPR studies on the bimetallic complexes and simplified model compounds support dpa-selective binding by both of these metals. The IR spectra have also been compared to those of diamagnetic Rh+, Zn2+, and Pd2+ complexes whose metal binding sites had been independently determined through NMR techniques. The binding preferences have been used to control selective metalation in the synthesis of heterometallic Pt/Cu, Pd/Cu, and Rh/Cu complexes. [ABSTRACT FROM AUTHOR]

An ensemble-based approach is presented to explore the conformational space sampled by a multidomain protein showing moderate interdomain dynamics in terms of translational and rotational motions. The strategy was applied on a complex of calmodulin (CaM) with the IQ-recognition motif from the voltage-gated calcium channel Cav1.2 (IQ), which adopts three different interdomain orientations in the crystal. The N60D mutant of calmodulin was used to collect pseudocontact shifts and paramagnetically induced residual dipolar couplings for six different lanthanide ions. Then, starting from the crystal structure, pools of conformations were generated by free MD. We found the three crystal conformations in solution, but four additional MD-derived conformations had to be included into the ensemble to fulfill all the paramagnetic data and cross-validate optimally against unused paramagnetic data. Alternative approaches led to similar ensembles. Our "ensemble" approach is a simple and efficient tool to probe and describe the interdomain dynamics and represents a general method that can be used to provide a proper ensemble description of multidomain proteins. [ABSTRACT FROM AUTHOR]

The electrochemistry of the {RhNO}8complexes [Rh(PCPtBu)(NO)][BF4] (1), [Rh(PCPtBuCH2)(NO)][BF4] (2), and Rh(PCPtBu)(NO)Cl (3) was studied. Both four-coordinate complexes 1橷 2笘扮a reversible reduction within the CH2Cl2solventwindow. Nevertheless, the chemical or electrochemical reduction of 1橷 2 CH2Cl2led to the formation of thefive-coordinate {RhNO}8complexes 3and Rh(PCPtBuCH2)(NO)Cl (4),respectively, through chloride abstraction from CH2Cl2by the one-electron-reduced {RhNO}9species [Rh(PCPtBu)(NO)]•(1•) and [Rh(PCPtBuCH2)(NO)]•(2•), as has been observed for many other17-electron paramagnetic complexes. The new complex 4was fully characterized by multinuclear NMR techniques, IR, X-raydiffraction, CV, UV–vis, and elemental analysis. On the otherhand, the five-coordinate complexes 3and 4show only one irreversible oxidation in CH2Cl2and two irreversible reductions in THF. The {RhNO}9complex 1•could be obtained quantitativelyby one-electron reduction of 1숫 cobaltocene in nonchlorinated solvents and was characterizedby IR, EPR, and 1H NMR in solution. Activation of carbon–halogenbonds by complex 1•wasobserved by studying the reactivity of 1•with some aryl halides, giving in all cases the {RhNO}8Rh(PCPtBu)(NO)X (X = Cl–, 3, or X = I–, 6) asthe only rhodium complex, while a complex with coordination of thearyl moiety was not observed as a stable final product in any case.The fate of the aryl organic radicals could be determined in somecases. In addition, DFT calculations were performed to elucidate theelectronic structure of 1•and to support the observed reactivity. [ABSTRACT FROM AUTHOR]

Theparamagnetic behavior of 18-electron cyclopentadienylnickel(II)complexes of the [CpNi(μ-Br)]2type with two unpairedelectrons per metal ion has been investigated by 1H and 13C NMR spectroscopy of [Cp‴Ni(μ-Br)]2(1; Cp‴ = 1,3,4-tBu3C5H2), [3CpNi(μ-Br)]2(2; 3Cp = 1,3,4-iPr3C5H2), and [4CpNi(μ-Br)]2(3; 4Cp = 2,3,4,5-iPr4C5H). The tri-tert-butylcyclopentadienylderivative 1crystallizes in the triclinic space group P1̅ and has been investigated by X-ray crystallography.Solid-state magnetic susceptibility measurements of 3revealed an effective magnetic moment at room temperature of 4.04μB, confirming the presence of two d8nickel(II)ions. While antiferromagnetic coupling via the bromo bridges is weak(J= −2.4 cm–1), zero-fieldsplitting is substantial (D= +48.2 cm–1). NMR spectra of complexes 1–3showsignals with half-widths up to 3600 Hz within a spectral window exceeding500 ppm (1H) or 2200 ppm (13C). An analysisof the spectra gave insight into the spin delocalization, the equilibriumorientation of the iPr substituents, and the presenceof different conformers of compound 3.Paramagnetic behaviorhas also been observed for the Cp* derivative [Cp*Ni(μ-Br)]2(Cp* = C5Me5) by 1H NMRspectroscopy. The presence of two unpaired electrons is discussedin terms of the weak ligand field originating from the combined interactionof poorly π accepting alkylcyclopentadienyl and π donatingbromo ligands with the nickel(II) center. [ABSTRACT FROM AUTHOR]

The reaction of N-methydiethanolamine (mdeaH2), benzoic acid, FeCl3, and Ln(NO3)3·6H2O or LnCl3·xH2O yields a series of decanuclear coordination clusters, [Ln3Fe7(μ4-O)2(μ3-OH)2(mdea)7(μ-benzoate)4(N3)6]·4MeCN·H2O, where Ln = GdIII (1) or TbIII (2), and [Er3Fe7(μ4-O)2(μ3-OH)2(mdea)7(μ-benzoate)4(N3)5(MeOH)]Cl·7.5H2O·11.5MeOH (3). The isostructural compounds 1-3 all crystallize isotypically in the triclinic space group P1 with Z = 2, as does the previously reported dysprosium analogue 4. Six of the FeIII ions are pseudooctahedrally coordinated, whereas the seventh has a trigonal-bipyramidal coordination geometry. Temperature-dependent direct-current magnetic susceptibility studies indicate that intracluster antiferromagnetic interactions are dominant in 1-3. The frequency-dependent out-of-phase (Χn) alternating-current susceptibility reveals that 2 undergoes a slow relaxation of its magnetization, presumably resulting from anisotropy of the TbIII ions. Between 30 and 295 K, the 57Fe Mössbauer spectra reveal paramagnetic behavior with six partially resolved quadrupole doublets, one for the trigonal-bipyramidal FeIII site and five for the six pseudooctahedral FeIII sites. The Mössbauer spectra of 2 and 3 obtained between 3 and 30 K are consistent with the presence of FeIII intracluster antiferromagnetic coupling with slow magnetic relaxation relative to the Larmor precession time. Further, the observed changes in the effective magnetic field values in the spectra measured at 3 K with increasing applied field are consistent with the effect of the local spin polarization along the applied magnetic field direction, a behavior reminiscent of antiparallel spin-coupled iron molecular paramagnetic systems. [ABSTRACT FROM AUTHOR]

Pseudocontact shifts (PCS) contain a wealth of geometric information, which makes paramagnetic NMR one of the best methods for accurate geometric determinations in solution. It is well-known that PCS are intrinsically linked to Fermi contact (FC) shifts, and die separation of the two terms is achieved through linearization methods, which heavily rely on (a) isostructurality (even concerning a labile axial site) and (b) die validity of Bleaney's constants. Recently we proposed a method that circumvents both assumptions in the case of axially symmetric complexes, and presendy we generalize it to lower symmetry. Our metiiod is model-free and thus does not rely on any structural hypothesis. Our results compare very well with recendy published data obtained through an accurate ab initio approach. [ABSTRACT FROM AUTHOR]

Recent research in fast magic angle spinning (MAS) methods has drasticallyimproved the resolution and sensitivity of NMR spectroscopy of biomolecules and materials in solids. In this Account, we summarize recent and ongoing developments in this area by presenting 13C and 1H solid-state NMR (SSNMR) studies on paramagnetic systems and biomolecules under fast MAS from our laboratories. [ABSTRACT FROM AUTHOR]

Metal ions are ubiquitous in biochemical and cellular processes. Since many metal ions are paramagnetic due to the presence of unpaired electrons, paramagnetic molecules are an important class of targets for research in structural biology and related fields. Today, NMR spectroscopy plays a central role in the investigation of the structure and chemical properties of paramagnetic metalloproteins, linking the observed paramagnetic phenomena directly to electronic and molecular structure. [ABSTRACT FROM AUTHOR]

Many structures of the proteins and protein assemblies that play central roles in fundamental biological processes and disease pathogenesis are not readily accessible via the conventional techniques of single-crystal X-ray diffraction and solution-state nuclear magnetic resonance (NMR). On the other hand, many of these challenging biological systems are suitable targets for atomic-level structural and dynamic analysis by magic-angle spinning (MAS) solid-state NMR spectroscopy, a technique that has far less stringent limitations on the molecular size and crystalline state. [ABSTRACT FROM AUTHOR]

Sensing and imaging paramagneticspecies under physiological conditionsis a key technology in chemical and biochemical analytics, cell biology,and medical sciences. At submicrometer length scales, nitrogen-vacancy(NV) centers in diamond offer atom-sized probes for magnetic fields.We show that spin relaxation of an ensemble NV sensor allows sensingof adsorbed and freely diffusing manganese(II) ions and adsorbed ferritin.Sensitivities approach 175 Mn ions and 10 ferritin proteins per diffractionlimited spot under ambient conditions. [ABSTRACT FROM AUTHOR]

Themagnetic metal-bridged fullerene dimer {Co(Ph3P)(C6H5CN)}2(μ2-η2,η2-C60)2was synthesizedfor the first time and studied by X-ray crystallography and magneticsusceptibility methods. The dimers, in which two fullerene C60cages are η2-bonded through two Co0atoms(S= 1/2), have a triplet (S= 1) state and transfer to a diamagnetic singlet (S= 0) ground state below 50 K (J/kB= −28.6 K). The theoretical calculationsshow that C60can work as an efficient spin coupler betweenparamagnetic metals. [ABSTRACT FROM AUTHOR]

Malaria is a serious disease that threatens the public health, especially in developing countries. Various methods have been developed to separate malaria-infected red blood cells (i-RBCs) from blood samples for clinical diagnosis and biological and epidemiological research. In this study, we propose a simple and label-free method for separating not only late-stage but also early-stage i-RBCs on the basis of their paramagnetic characteristics due to the malaria byproduct, hemozoin, by using a magnetic field gradient. A polydimethylsiloxane (PDMS) microfluidic channel was fabricated and integrated with a ferromagnetic wire fixed on a glass slide. To evaluate the performance of the microfluidic device containing the ferromagnetic wire, lateral displacement of NaNO2-treated RBCs, which also have paramagnetic characteristics, was observed at various flow rates. The results showed excellent agreement with theoretically predicted values. The same device was applied to separate i-RBCs. Late-stage i-RBCs (trophozoites and schizonts), which contain optically visible black dots, were separated with a recovery rate of approximately 98.3%. In addition, using an optimal flow rate, early-stage (ring-stage) i-RBCs, which had been difficult to separate because of their low paramagnetic characteristics, were successfully separated with a recovery rate of 73%. The present technique, using permanent magnets and ferromagnetic wire in a microchannel, can effectively separate i-RBCs in various developmental stages so that it could provide a potential tool for studying the invasion mechanism of the malarial parasite, as well as performing antimalarial drug assays. [ABSTRACT FROM AUTHOR]

Reported are the synthesis, crystal structure, electronic structure, and magnetic properties of a series of zinc-rich ternary phases with formulas RE2Zn5Tt (RE = La-Nd; Tt = Sn and Pb). The structures of these compounds have been established by single-crystal and powder X-ray diffraction. They crystallize in the orthorhombic space group Cmcm (No. 63, LaRhSn2 structure type, Pearson symbol oC32). The most prominent structural feature is the trigonal-planar coordination of the Sn(Pb) atoms; the latter interconnect layers of Zn atoms to comprise a complex [Zn5Tt] polyanionic framework. The structural relationships between the structure of the title compounds and the EuIn4, La3Al11, and YIrGe2 structure types are highlighted. Temperature-dependent DC magnetization measurements indicate Pauli-like paramagnetism for La2Zn5Sn, while Ce2Zn5Sn, Pr2Zn5Sn, and Nd2Zn5Sn display Curie-Weiss behavior in the high-temperature regime. At cryogenic temperatures, the magnetic responses of Ce2Zn5Sn, Pr2Zn5Sn, and Nd2Zn5Sn appear to deviate from the Curie-Weiss law; however, no magnetic orderings could be observed down to 5 K. Theoretical considerations of the electronic structure on the basis of the tight-binding linear muffin-tin orbital (TB-LMTO-ASA) method are also presented and discussed. [ABSTRACT FROM AUTHOR]

We report an organo-paramagnetic switch consisting of a linked bis(viologen) dication diradical that can be cycled reversibly between diamagnetic and paramagnetic states via noncovalent guest–host chemistry with cucurbit[7]uril (CB[7]) in room-temperature water. Computations suggest that the nature of the interaction between the viologen cation radical units is that of a pi dimer (pimer). Molecules with switchable magnetic properties have possible applications in spintronics, data storage devices, chemical sensors, building blocks for materials with switchable bulk magnetic properties, as well as magnetic resonance probes for biological applications. [ABSTRACT FROM AUTHOR]

Hybridnanoarchitectures are among the most promising nanotechnology-enabledmaterials for biomedical applications. Interfacing of nanoparticleswith active materials gives rise to the structures with unique multiplefunctionality. Superparamagnetic iron oxide nanoparticles particlesSPION are widely employed in the biology and in developing of advancedmedical technologies. Polymeric micelles offer the advantage of multifunctionalcarriers which can serve as delivery vehicles carrying nanoparticles,hydrophobic chemotherapeutics and other functional materials and molecules.Stimuli-responsive polymers are especially attractive since theirproperties can be modulated in a controlled manner. Here we reporton multifunctional thermo-responsive poly(N-isopropylacrylamide-co-acrylamide)-block-poly(ε-caprolactone)random block copolymer micelles as magnetic hyperthermia-mediatedpayload release and imaging agents. The combination of copolymers,nanoparticles and doxorubicin drug was tailored the way that the loadedmicelles were cable to respond to magnetic heating at physiologically-relevanttemperatures. A surface functionalization of the micelles with theintegrin β4 antibody and consequent interfacing of the resultingnanobio hybrid with squamous head and neck carcinoma cells which isknown to specifically over-express the A9 antigen resulted in concentrationof the micelles on the surface of cells. No inherent cytotoxicitywas detected for the magnetic micelles without external stimuli application.Furthermore, SPION-loaded micelles demonstrate significant MRI contrastenhancement abilities. [ABSTRACT FROM AUTHOR]

¹H NMR measurements are reported for D20 solutions of paramagnetic complex [ER(H20)(EDTA4-]- (I) for temperature interval 273-319 K. Diamagnetic complex [LU(H20)(EDTA4-)]- (II) was used as an NMR reference compound. The spectra obtained have been analyzed using a band-shape analysis technique in the framework of dynamic NMR (DNMR) taking into account the temperature dependence of lanthanide-induced shifts. Intramolecular dynamics in I was assigned to the interconversion of δ-ƛE-ƍƍƍƍ and δ-ƛE-ƍƍƍƍ conformers with estimated activation free energy δG‡(298 K) = 50 ± 4 kj/mol. The methodology of paramagnetic 4f-element probe applications on the example of Er3+ for the study of free-energy changes in chemical exchange processes, as well as the advantages of this method in comparison with DNMR studies of diamagnetic substances, is discussed. In accordance with the literature reviewed, the fulfilled experimental study is the first example of intramolecular dynamics determination for erbium complexes. An additional advantage of the investigation is in the approach proposed which extends the range of measurement of the NMR rate constants for paramagnetic 4f-element complexes compared to diamagnetic ones. Coordination compounds investigated represent a new type of thermometric NMR sensors and lanthanide paramagnetic probes for in situ temperature control in solutions. [ABSTRACT FROM AUTHOR]

The host--guest chemistry of the octanuclear cubic coordination cage [Co8L12]16+ (where L is a bridging ligand containing two chelating pyrazolyl-pyridine units connected to a central naphthalene-l,S-diy] spacer via methylene "hinges") has been investigated in detail by *H NMR spectroscopy. The cage encloses a cavity of volume of ca. 400 Å3, which is accessible through 4 Á diameter portals in the centers of the cube faces. The paramagnetism of the cage eliminates overlap of NMR signals by dispersing them over a range of ca. 200 ppm, making changes of specific signals easy to observe, and also results in large complexation-induced shifts of bound guests. The cage, in CD3CN solution, acts as a remarkably size- and shape-selective host for small organic guests such as coumarin (K = 78 M-1) and other bicyclic molecules of comparable size and shape such as isoquinolíne-N-oxide (K = 2100 M-1). Binding arises from two independent recognition elements, which have been separately quantified. These are (i) a polar component arising from interaction of the H-bond accepting O atom of the guest with a convergent group of CH protons inside the cavity that he close to a/ac tris-chelate metal center and are therefore in a region of high electrostatic potential; and (ii) an additional component arising from the second aromatic ring (aromatic/van der Waals interactions with the interior surface of the cage and/or solvophobic interactions). The strength of the first component varies linearly with the H-bond-accepting ability of the guest; the second component is fixed at approximately 10 kj mol-1. We have also used ¹H--¹H exchange spectroscopy (EXSY) experiments to analyze semiquantitatively two distinct dynamic processes, viz. movement of the guest into and out of the cavity and tumbling of the guest inside the host cavity. Depending on the size of the guest and the position of substituents, the rates of these processes can vary substantially, and the rates of processes that afford observable cross-peaks in EXSY spectra (e.g., between free and bound guest in some cases; between different conformers of a specific host-guest complex in others) can be narrowed down to a specific time window. Overall, the paramagnetism of the host cage has allowed an exceptionally detailed analysis of the kinetics and thermodynamics of its host--guest behavior. [ABSTRACT FROM AUTHOR]

A novel cancer-cells-triggered controlled-release gadolinium-dopedluminescent and mesoporous strontium hydroxyapatite nanorods (designatedas Gd:SrHap nanorods) system using cell-type-specific aptamers ascaps has been constructed. Aptamers behave as a dual-functional moleculethat acts as not only a lid but also a targeted molecular that canbe used in an effective way for therapeutically special cancer cells.After incubated with cancer cells, for example, MCF-7 cells, the doxorubicin-loadedand aptamer-capped Gd:SrHap nanorods (designated as Gd:SrHap-Dox-aptamer)can be internalized into MCF-7 cells, resulting in the pore openingand drug releasing. Furthermore, the high biocompatibility and biodegradabilityGd:SrHap nanorods with blue autofluorescence and paramagnetism couldserve as a good contrast agent of targeting fluorescence and magneticresonance imaging. We envision that this Gd:SrHap system could playa significant role in developing new generations of site-selective,controlled-release delivery and interactive sensory nanodevices. [ABSTRACT FROM AUTHOR]

The structures of paramagnetic copper complexes, theproducts ofphotolysis of tetrachlorocuprates of quaternary ammonium in frozensolvents, earlier denoted as 1-Cuand 2-Cu, were established on the basis of comparison of experimental andtheoretical UV–vis spectra. UV–vis spectra of photolysisproducts were registered at 77–116 K. Comparison with the EPRdata in this temperature range allowed to assign photolysis productsbands in the vis spectrum either to 1-Cuor to 2-Cu.Model structures for 1-Cuand 2-Cuwere proposed. TD-DFT calculated spectra of model compounds alongwith CuCl42–anion are in excellent agreementwith the experiment. The comparison of UV–vis and EPR dataand results of TD-DFT calculations evidence that 1-Cuand 2-Cuare paramagnetic organochlorocuprates(II)with general formulas Cu(II)Cl2R and Cu(II)Cl3R, respectively, where R is (−C6H12)N+(C6H13)3. [ABSTRACT FROM AUTHOR]

We present a time-saving strategy for acquiring 3D magicanglespinning NMR spectra for chemical shift assignments in proteins andprotein assemblies in the solid state. By simultaneous applicationof nonuniform sampling (NUS) and paramagnetic-relaxation-assistedcondensed data collection (PACC), we can attain 16-fold time reductionin the 3D experiments without sacrificing the signal-to-noise ratioor the resolution. We demonstrate that with appropriate concentrationof paramagnetic dopant introduced into the sample the overwhelmingmajority of chemical shifts are not perturbed, with the exceptionof a limited number of shifts corresponding to residues located atthe surface of the protein, which exhibit small perturbations. Thisapproach enables multidimensional MAS spectroscopy in samples of intrinsicallylow sensitivity and/or high spectral congestion where traditionalexperiments fail, and is especially beneficial for structural anddynamics studies of large proteins and protein assemblies. [ABSTRACT FROM AUTHOR]