Non-statistical assembly of multicomponent [Pd2ABCD] cages.

Self-assembled hosts, inspired by biological receptors and catalysts, show application potential in sustainable synthesis, energy conversion and medicine. Implementing multiple functionalities in the form of distinguishable building blocks, however, is difficult without risking narcissistic self-sorting or a statistical mess. Here we report a systematic series of integratively self-assembled heteroleptic cages in which two square-planar PdII cations are bridged by four different bis-pyridyl ligands, A, B, C and D, via synergistic effects to exclusively form a single isomer-the lantern-shaped cage [Pd2ABCD]. This self-sorting goal-forming just one out of 55 possible structures-is reached under full thermodynamic control and can be realized progressively (by combining progenitors, such as [Pd2A2C2] with [Pd2B2D2]), directly from ligands and PdII cations or by mixing all four corresponding homoleptic cages. The rational design of complex multicomponent assemblies that enables the modular incorporation of diverse chemical moieties will advance their applicability in functional nanosystems.

A Meta-Analysis and Cohort Study of Histopathologic and Clinical Outcomes in ANCA-Negative versus -Positive Vasculitis.

BACKGROUND: ANCA-negative pauci-immune glomerulonephritis (PIGN) represents a rare and often under-studied subgroup of the vasculitides. This study aims to investigate differences in the clinical phenotype, renal histological features, and clinical outcomes of patients with PIGN, with and without serum ANCA positivity. METHODS: A cohort of biopsy-proven PIGN with and without detectable circulating ANCA was constructed from a single center between 2006 and 2016. Primary outcomes compared clinical presentation and histopathological features according to ANCA status, with multivariate Cox regression to compare mortality and ESKD. A systematic review and meta-analysis of the published literature was undertaken. RESULTS: In our cohort of 146 patients, 22% (n=32) had ANCA-negative disease, with a comparatively younger mean age at diagnosis; 51.4 versus 65.6 years (P<0.001). In total, 14 studies, inclusive of our cohort, were eligible for meta-analysis, totaling 301 patients who were ANCA negative. Those with ANCA-negative disease tended to have fewer extrarenal symptoms and a higher frequency of renal-limited disease, but both failed to reach statistical significance (P=0.92 and P=0.07). The risk of ESKD was significantly higher in seronegative disease (RR, 2.28; 95% confidence interval, 1.42 to 3.65; P<0.001), reflecting our experience, with a fivefold increased risk of ESKD in ANCA-negative disease (P<0.001). No significant difference in the chronicity of histopathological findings was seen and the meta-analysis showed no difference in morality (RR, 1.22; 95% confidence interval, 0.63 to 2.38; P=0.55). CONCLUSION: Our findings demonstrate that ANCA-negative PIGN presents in younger patients, with fewer extrarenal manifestations and higher ESKD risk, despite a lack of difference in histopathology. This study provides the impetus for further research into the pathogenesis, treatment response, and duration of immunotherapy in ANCA-negative disease. We suggest that the absence of positive ANCA serology should not discourage treatment and for clinical trials to include patients who are ANCA negative.

Orientational self-sorting in cuboctahedral Pd cages.

Cuboctahedral coordination cages of the general formula [Pd12L24]24+ (L = low-symmetry ligand) were analyzed theoretically and experimentally. With 350 696 potential isomers, the structural space of these assemblies is vast. Orientational self-sorting refers to the preferential formation of particular isomers within the pool of potential structures. Geometric and computational analyses predict the preferred formation of cages with a cis arrangement at the metal centers. This prediction was corroborated experimentally by synthesizing a [Pd12L24]24+ cage with a bridging 3-(4-(pyridin-4-yl)phenyl)pyridine ligand. A crystallographic analysis of this assembly showed exclusive cis coordination of the 3- and the 4-pyridyl donor groups at the Pd2+ ions.

NMR Relaxivities of Paramagnetic, Ultra-High Spin Heterometallic Clusters within Polyoxometalate Matrix as a Function of Solvent and Metal Ion.

Selectivity and image contrast are always challenging in magnetic resonance imaging (MRI), which are - inter alia - addressed by contrast agents. These compounds still need to be improved, and their relaxation properties, i. e., their paramagnetic relaxation enhancement (PRE), needs to be understood. The main goal is to improve specificity and relaxivities, especially at the high magnetic fields currently exploited not only in material science but also in the medical environment. Longitudinal and transverse relaxivities, r1 and r2 , which correspond to the longitudinal and transverse relaxation rates R1 and R2, normalized to the concentration of the paramagnetic moieties, need to be considered because both contribute to the image contrast. 1 H-relaxivities r1 and r2 of high-spin heterometallic clusters were studied containing lanthanide and transition-metal ions within a polyoxometalate matrix. A wide range of magnetic fields from 0.5 T/20 MHz to 33 T/1.4 GHz was applied. The questions addressed here concern the rotational and diffusion correlation times which determine the relaxivities and are affected by the solvent's viscosity. Moreover, the variation of the lanthanide and transition-metal ions of the clusters provided insights into the sensitivity of PRE with respect to the electron spin properties of the paramagnetic centers as well as cooperative effects between lanthanides and transition metal ions.

Guest-Modulated Circularly Polarized Luminescence by Ligand-to-Ligand Chirality Transfer in Heteroleptic PdII Coordination Cages.

Multicomponent metallo-supramolecular assembly allows the rational combination of different building blocks. Discrete multifunctional hosts with an accessible cavity can be prepared in a non-statistical fashion. We employ our shape-complementary assembly (SCA) method to achieve for the first time integrative self-sorting of heteroleptic PdII cages showing guest-tunable circularly polarized luminescence (CPL). An enantiopure helicene-based ligand (M or P configuration) is coupled with a non-chiral emissive fluorenone-based ligand (A or B) to form a series of Pd2 L2 L'2 assemblies. The modular strategy allows to impart the chiral information of the helicenes to the overall supramolecular system, resulting in CPL from the non-chiral component. Guest binding results in a 4-fold increase of CPL intensity. The principle offers potential to generate libraries of multifunctional materials with applications in molecular recognition, enantioselective photo-redox catalysis and information processing.

Light-Powered Dissipative Assembly of Diazocine Coordination Cages.

Stimuli-responsive coordination cages allow reversible control over guest binding and release, relevant for adaptive receptors, carriers, catalysts, and complex systems. Light serves as an advantageous stimulus, as it can be applied with precise spatial and temporal resolution without producing chemical waste products. We report the first Pd-mediated coordination cage based on ligands embedding a diazocine photoswitch. While the thermodynamically more stable cis-photoisomer sloppily assembles to a mixture of species with general formula [Pdncis-L2n], the less stable trans-isomer yields a defined [Pd2trans-L4] cage that reversibly converts back to the cis-system by irradiation at 530 nm or thermal relaxation. The [Pdncis-L2n] species do not bind a given guest; however, [Pd2trans-L4] is able to encapsulate a bis-sulfonate as long as it is kept assembled, requiring continuous irradiation at 385 nm. In the absence of UV light, thermal relaxation results in back-switching and guest release. Assembly and properties of the system were characterized by a combination of NMR, ion mobility ESI-MS, single-crystal X-ray diffraction, and UV-vis absorption studies.

Chiral Resolution of Spin-Crossover Active Iron(II) [2x2] Grid Complexes.

Chiral magnetic materials are proposed for applications in second-order non-linear optics, magneto-chiral dichroism, among others. Recently, we have reported a set of tetra-nuclear Fe(II) grid complex conformers with general formula C/S-[Fe4 L4 ]8+ (L: 2,6-bis(6-(pyrazol-1-yl)pyridin-2-yl)-1,5-dihydrobenzo[1,2-d : 4,5-d']diimidazole). In the grid complexes, isomerism emerges from tautomerism and conformational isomerism of the ligand L, and the S-type grid complex is chiral, which originates from different non-centrosymmetric spatial organization of the trans type ligand around the Fe(II) center. However, the selective preparation of an enantiomerically pure grid complex in a controlled manner is difficult due to spontaneous self-assembly. To achieve the pre-synthesis programmable resolution of Fe(II) grid complexes, we designed and synthesized two novel intrinsically chiral ligands by appending chiral moieties to the parent ligand. The complexation of these chiral ligands with Fe(II) salt resulted in the formation of enantiomerically pure Fe(II) grid complexes, as unambiguously elucidated by CD and XRD studies. The enantiomeric complexes exhibited similar gradual and half-complete thermal and photo-induced SCO characteristics. The good agreement between the experimentally obtained and calculated CD spectra further supports the enantiomeric purity of the complexes and even the magnetic studies. The chiral resolution of Fe(II)- [2×2] grid complexes reported in this study, for the first time, might enable the fabrication of magneto-chiral molecular devices.

Long-Lived C60 Radical Anion Stabilized Inside an Electron-Deficient Coordination Cage.

Fullerene C60 and its derivatives are widely used in molecular electronics, photovoltaics, and battery materials, because of their exceptional suitability as electron acceptors. In this context, single-electron transfer on C60 generates the C60• - radical anion. However, the short lifetime of free C60• - hampers its investigation and application. In this work, we dramatically stabilize the usually short-lived C60• - species within a self-assembled M2L4 coordination cage consisting of a triptycene-based ligand and Pd(II) cations. The electron-deficient cage strongly binds C60 by providing a curved inner π-surface complementary to the fullerene's globular shape. Cyclic voltammetry revealed a positive potential shift for the first reduction of encapsulated C60, which is indicative of a strong interaction between confined C60• - and the cationic cage. Photochemical one-electron reduction with 1-benzyl-1,4-dihydronicotinamide allows selective and quantitative conversion of the confined C60 molecule in millimolar acetonitrile solution at room temperature. Radical generation was confirmed by nuclear magnetic resonance, electron paramagnetic resonance, ultraviolet-visible-near-infrared spectroscopy and electrospray ionization mass spectrometry. The lifetime of C60• - within the cage was determined to be so large that it could still be detected after one month under an inert atmosphere.

Impact of Ligands on Structural and Optical Properties of Ag29 Nanoclusters.

A ligand exchange strategy has been employed to understand the role of ligands on the structural and optical properties of atomically precise 29 atom silver nanoclusters (NCs). By ligand optimization, ∼44-fold quantum yield (QY) enhancement of Ag29(BDT)12-x(DHLA)x NCs (x = 1-6) was achieved, where BDT and DHLA refer to 1,3-benzene-dithiol and dihydrolipoic acid, respectively. High-resolution mass spectrometry was used to monitor ligand exchange, and structures of the different NCs were obtained through density functional theory (DFT). The DFT results from Ag29(BDT)11(DHLA) NCs were further experimentally verified through collisional cross-section (CCS) analysis using ion mobility mass spectrometry (IM MS). An excellent match in predicted CCS values and optical properties with the respective experimental data led to a likely structure of Ag29(DHLA)12 NCs consisting of an icosahedral core with an Ag16S24 shell. Combining the experimental observation with DFT structural analysis of a series of atomically precise NCs, Ag29-yAuy(BDT)12-x(DHLA)x (where y, x = 0,0; 0,1; 0,12 and 1,12; respectively), it was found that while the metal core is responsible for the origin of photoluminescence (PL), ligands play vital roles in determining their resultant PLQY.

Kinetics of Intercluster Reactions between Atomically Precise Noble Metal Clusters [Ag25(DMBT)18]- and [Au25(PET)18]- in Room Temperature Solutions.

The kinetics of intercluster metal atom exchange reactions between solvated [Ag25(DMBT)18]- and [Au25(PET)18]- (DMBT and PET are 2,4-dimethylbenzenethiol and 2-phenylethanethiol, respectively, both C8H10S) were probed by electrospray ionization mass spectrometry and computer-based modeling. Anion mass spectra and collision induced dissociation (CID) measurements show that both cluster monomers and dimers are involved in the reactions. We have modeled the corresponding kinetics assuming a reaction mechanism in which metal atom exchange occurs through transient dimers. Our kinetic model contains three types of generic reactions: dimerization of monomers, metal atom exchange in the transient dimers, and dissociation of the dimers to monomers. There are correspondingly 377 discrete species connected by in total 1302 reactions (i.e., dimerization, dissociation and atom exchange reactions) leading to the entire series of monomeric and dimeric products [AgmAu25-m]- (m = 1-24) and [AgmAu50-m]2- (m = 0-50), respectively. The rate constants of the corresponding reactions were fitted to the experimental data, and good agreement was obtained with exchange rate constants which scale with the probability of finding a silver or gold atom in the respective monomeric subunit of the dimer, i.e., reflecting an entropic driving force for alloying. Allowing the dimerization rate constant to scale with increasing gold composition of the respective reactants improves the agreement further. The rate constants obtained are physically plausible, thus strongly supporting dimer-mediated metal atom exchange in this intercluster reaction system.

Coal-Tar Dye-based Coordination Cages and Helicates.

A strategy to implement four members of the classic coal-tar dye family, Michler's ketone, methylene blue, rhodamine B, and crystal violet, into [Pd2 L4 ] self-assemblies is introduced. Chromophores were incorporated into bis-monodentate ligands using piperazine linkers that allow to retain the auxochromic dialkyl amine functionalities required for intense colors deep in the visible spectrum. Upon palladium coordination, ligands with pyridine donors form lantern-shaped dinuclear cages while quinoline donors lead to strongly twisted [Pd2 L4 ] helicates in solution. In one case, single crystal X-ray diffraction revealed rearrangement to a [Pd3 L6 ] ring structure in the solid state. For nine examined derivatives, showing colors from yellow to deep violet, CD spectroscopy discloses different degrees of chiral induction by an enantiomerically pure guest. Ion mobility mass spectrometry allows to distinguish two binding modes. Self-assemblies based on this new ligand class promise application in chiroptical recognition, photo-redox catalysis and optical materials.

Structural insights into metal-metalloid glasses from mass spectrometry.

Despite being studied for nearly 50 years, smallest chemically stable moieties in the metallic glass (MG) could not be found experimentally. Herein, we demonstrate a novel experimental approach based on electrochemical etching of amorphous alloys in inert solvent (acetonitrile) in the presence of a high voltage (1 kV) followed by detection of the ions using electrolytic spray ionization mass spectrometry (ESI MS). The experiment shows stable signals corresponding to Pd, PdSi and PdSi2 ions, which emerges due to the electrochemical etching of the Pd80Si20 metallic glass electrode. These fragments are observed from the controlled dissolution of the Pd80Si20 melt-spun ribbon (MSR) electrode. Annealed electrode releases different fragments in the same experimental condition. These specific species are expected to be the smallest and most stable chemical units from the metallic glass which survived the chemical dissolution and complexation (with acetonitrile) process. Theoretically, these units can be produced from the cluster based models for the MG. Similar treatment on Pd40Ni40P20 MSR resulted several complex peaks consisting of Pd, Ni and P in various combinations suggesting this can be adopted for any metal-metalloid glass.

Linear Size Contraction of Ligand Protected Ag29 Clusters by Substituting Ag with Cu.

There are only a few examples of atomically precise, ligand protected, bimetallic coinage metal clusters in which molecular structure remains essentially unchanged over a wide composition range starting from the corresponding homometallic species. Such model systems are particularly useful to study the dynamics of alloy formation on the nanoscale. Here we demonstrate the unusual reactivity of solvated metalloid-superatom Ag29(BDT)12(PPh3)4 (BDT = 1,3 benzenedithiol) clusters toward semiconducting Cu12S6(DPPPT)4 (DPPPT = bis(diphenylphosphino)pentane) clusters as an efficient way to exchange multiple copper atoms into the atomically precise silver clusters without changing overall the structure type. Concentration-dependent UV-vis absorption and online mass spectrometry shows that 14 Cu atoms can be exchanged into the silver cluster. Beyond the 14 Cu atom exchange, the cluster degrades to smaller thiolates. Information on cluster structures is obtained from high-resolution ion mobility mass spectrometry, which shows a linear decrease in collision cross section (CCS) with each Ag/Cu exchanged. Several isomeric structures are calculated by density functional theory (DFT), and their calculated collision cross sections are used to identify the most stable isomers for each Ag/Cu exchange product. Ag/Cu exchange is essentially limited to the cluster surface/shell. The core appears not to be involved.

Synthesis, Characterization, Electrochemistry, Photoluminescence and Magnetic Properties of a Dinuclear Erbium(III)-Containing Monolacunary Dawson-Type Tungstophosphate: [{Er(H2O)(CH3COO)(P2W17O61)}2]16.

Reaction of the trilacunary Wells-Dawson anion {α-P2W15O56}12- with ErIII ion in a 1 M LiOAc/HOAc buffer (pH 4.8) solution produces a dinuclear erbium(III) substituted sandwich-type structure [{Er(H2O)(CH3COO)(P2W17O61)}2]16- (1). The isolated compound was structurally characterized using single crystal and powder X-ray diffraction, FTIR spectroscopy, mass spectrometry and thermogravimetric analysis. The electrochemical, electrocatalytic, photoluminescence and magnetic properties of 1 were investigated.

Nonenzymatic Glucose Sensing Using Ni60Nb40 Nanoglass.

Despite being researched for nearly five decades, chemical application of metallic glass is scarcely explored. Here we show electrochemical nonenzymatic glucose-sensing ability of nickel-niobium (Ni60Nb40) amorphous alloys in alkaline medium. Three different Ni60Nb40 systems with the same elemental composition, but varying microstructures are created following different synthetic routes and tested for their glucose-sensing performance. Among melt-spun ribbon, nanoglass, and amorphous-crystalline nanocomposite materials, nanoglass showed the best performance in terms of high anodic current density, sensitivity (20 mA cm-2 mM-1), limit of detection (100 nM glucose), stability, reproducibility (above 5000 cycles), and sensing accuracy among nonenzymatic glucose sensors involving amorphous alloys. When annealed under vacuum, only the heat-treated nanoglass retained a similar electrochemical-sensing property, while the other materials failed to yield desired results. In nanoglass, a network of glassy interfaces, compared to melt-spun ribbon, is plausibly responsible for the enhanced sensitivity.

Ultrafast Intersystem Crossing in Isolated Ag29(BDT)123- Probed by Time-Resolved Pump-Probe Photoelectron Spectroscopy.

The photophysics of the isolated trianion Ag29(BDT)123- (BDT = benzenedithiolate), a ligand-protected cluster comprising BDT-based ligands, terminating a shell of silver thiolates and a core of silver atoms, was studied in the gas phase by femtosecond time-resolved, pump-probe photoelectron spectroscopy. UV excitation at 490 nm populates one or more singlet excited states with significant charge transfer (CT) character in which electron density is shifted from shell to core. These CT states relax on an average time scale of several hundred femtoseconds by charge recombination to yield either the vibrationally excited singlet ground state (internal conversion) or a long-lived triplet (intersystem crossing). Our study is the first ultrafast spectroscopic probe of a ligand-protected coinage metal cluster in isolation. In the future, it will be interesting to study how cluster size, overall charge state, or heteroatom doping can be used to tune the corresponding relaxation dynamics in the absence of solvent.

Covalent cucurbit[7]uril-dye conjugates for sensing in aqueous saline media and biofluids.

Non-covalent chemosensing ensembles of cucurbit[n]urils (CBn) have been widely used in proof-of-concept sensing applications, but they are prone to disintegrate in saline media, e.g. biological fluids. We show here that covalent cucurbit[7]uril-indicator dye conjugates are buffer- (10× PBS buffer) and saline-stable (up to 1.4 M NaCl) and allow for selective sensing of Parkinson's drug amantadine in human urine and saliva, where the analogous non-covalent CB7⊃dye complex is dysfunctional. The in-depth analysis of the covalent host-dye conjugates in the gas-phase, and deionized versus saline aqueous media revealed interesting structural, thermodynamic and kinetic effects that are of general interest for the design of CBn-based supramolecular chemosensors and systems. This work also introduces a novel high-affinity indicator dye for CB7 through which fundamental limitations of indicator displacement assays (IDA) were exposed, namely an impractical slow equilibration time. Unlike non-covalent CBn⊃dye reporter pairs, the conjugate chemosensors can also operate through a SN2-type guest-dye exchange mechanism, which shortens assay times and opens new avenues for tailoring analyte-selectivity.

Syntheses, Crystal Structure, Electrocatalytic, and Magnetic Properties of the Monolanthanide-Containing Germanotungstates [Ln(H2O) n GeW11O39]5- (Ln = Dy, Er, n = 4,3).

Two monolanthanide-containing polyanions based on monolacunary Keggin germanotungstates [Ln(H2O) n GeW11O39]5- (Ln = Dy, Er, n = 4,3) have been synthesized in simple one-pot synthetic procedure and compositionally characterized in solid state by single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, and elemental analysis. Electronic absorption and emission spectra of the title compounds in solution were also studied. The [DyIII(H2O)4GeW11O39]5- Keggin POM exhibits a slow relaxation of magnetization. The cyclic voltammetry measurements and mass spectrometry were carried out to check the stability of the compounds in solution. Both polyanions prove efficient in the electrocatalytic reduction of nitrite. To our knowledge, this observation establishes the first example of electrocatalysis of nitrite reduction by all inorganic monolanthanide-containing germanotungstates family.

Combination of pulsed laser ablation and inert gas condensation for the synthesis of nanostructured nanocrystalline, amorphous and composite materials.

A new instrument combining pulsed laser ablation and inert gas condensation for the production of nanopowders is presented. It is shown that various nanostructured materials, such as regular metallic, semiconducting, insulating materials, complex high entropy alloys, amorphous alloys, composites and oxides can be synthesized. The unique variability of the experimental set-up is possible due to the reproducible control of laser power (pulse energy and repetition rate), laser ablation pattern on the target, and experimental conditions during the inert gas condensation, all of which can be controlled and optimized independently. Microstructure analysis of the as-prepared composite and amorphous Ni60Nb40 nanopowders establishes the instrument's ability for the synthesis of materials with unique compositions and atomic structure. It is further shown that small variations of the synthesis parameters can influence materials properties of the final product, in terms of particle size, composition and properties. As an example, the laser power has been used to control the magnetic properties of amorphous Ni60Nb40 nanopowders. A few selected examples of the manifold possibilities of the new synthesis apparatus are presented in this report together with detailed structural characterization of the produced nanopowders.

Metal-Ligand Interface in the Chemical Reactions of Ligand-Protected Noble Metal Clusters.

We discuss the role of the metal-ligand (M-L) interfaces in the chemistry of ligand-protected, atomically precise noble metal clusters, a new and expanding family of nanosystems, in solution as well as in the gas phase. A few possible mechanisms by which the structure and dynamics of M-L interfaces could trigger intercluster exchange reactions are presented first. How interparticle chemistry can be a potential mechanism of Ostwald ripening, a well-known particle coarsening process, is also discussed. The reaction of Ag59(2,5-DCBT)32 (DCBT = dichlorobenzenethiol) with 2,4-DCBT leading to the formation of Ag44(2,4-DCBT)30 is presented, demonstrating the influence of the ligand structure in ligand-induced chemical transformations of clusters. We also discuss the structural isomerism of clusters such as Ag44(SR)30 (-SR = alkyl/aryl thiolate) in the gas phase wherein the occurrence of isomerism is attributed to the structural rearrangements in the M-L bonding network. Interfacial bonding between Au25(SR)18 clusters leading to the formation of cluster dimers and trimers is also discussed. Finally, we show that the desorption of phosphine and hydride ligands on a silver cluster, [Ag18(TPP)10H16]2+ (TPP = triphenylphosphine) in the gas phase, leads to the formation of a naked silver cluster of precise nuclearity, such as Ag17+. We demonstrate that the nature of the M-L interfaces, i.e., the oxidation state of metal atoms, structure of the ligand, M-L bonding network, and so forth, plays a key role in the chemical reactivity of clusters. The structure, dynamics, and chemical reactivity of nanosystems in general are to be explored together to obtain new insights into their emerging science.