Magneto-structural studies on a number of doubly end-on cyanate and azide bridged dinuclear nickel(ii) complexes with {N3O} donor Schiff base ligands.

Two new doubly µ 1,1-N3 bridged (1 and 3) and six new doubly µ 1,1-NCO bridged NiII complexes (2, 4-8) with six different N3O donor Schiff base ligands have been synthesized and magneto-structurally characterized. All these neutral complex molecules are isostructural and constitute edge sharing bioctahedral structures. Magnetic studies revealed that all these complexes exhibit ferromagnetic interaction through bridging pseudohalides with ferromagnetic coupling constant J being significantly higher for azide-bridged complexes than that of the cyanate analogues. This is consistent with the literature reported data and also the presence of polarizable π systems and two different N and O donor atoms in cyanate ion, rendering it a poor magnetic coupler in comparison to azide analogues. Although, the magneto-structurally characterized doubly µ 1,1-N3 bridged NiII complexes are abundant, only few such complexes with µ 1,1-bridging NCO- ions are reported in the literature. Remarkably, addition of these six new examples in this ever-growing series of doubly µ 1,1-NCO bridged systems gives us an opportunity to analyse the precise magneto-structural correlation in this system, showing a general trend in which the J value increases with an increase in bridging angles. Therefore, the high degree of structural and magnetic resemblances by inclusion of six new examples in this series is the major achievement of the present work. An elaborate DFT study was performed resulting in magneto-structural correlation showing that nature and value of the J-parameter is defined not only by Ni-Nb-Ni bond angles, but an important role is also played by the Ni1-Ni2-Nb-Xt dihedral angle (Nb and Xt are bridging N and terminal N or O atom of bridging ligands, respectively).

A Carbonate-Templated Decanuclear Mn Nanocage with Two Different Silsesquioxane Ligands.

The mild reaction of the preorganized silsesquioxane precursor with Mn(II) acetate under ambient conditions results in a mixed-valent {MnII6MnIII4} nanocage (SD/Mn10) which is protected by both acyclic trimer [Si3] and cyclic tetramer [Si4]. Serendipitous capture of atmospheric CO2 as a µ5-carbonate anion placed at the center supports the formation of the cluster. The magnetic analysis reveals the strong antiferromagnetic interactions between Mn ions. Moreover, the drop-casting film of SD/Mn10 shows photoelectric activity indicating its great potential as a semiconductor for photoelectric conversion applications.

Carboxylic acid-tuned nickel(ii) clusters: syntheses, structures, solution behaviours and magnetic properties.

Three novel cicada-like nickel(ii) clusters, formulated as [Ni6(bdped)2(mba)6(Hdmpz)2(NO3)2(H2O)2]·4MeCN (SD/Ni6b), [Ni5(bdped)2(tca)6(Hdmpz)(MeOH)2(H2O)]·MeOH (SD/Ni5a) and [Ni4(Hbdped)2(ba)4(Hdmpz)2]·2NO3·2MeCN (SD/Ni4a), were obtained by tuning the auxiliary carboxylic acids, where H2bdped = 1,2-bis-(3,5-dimethylpyrazol-1-yl)-ethane-1,2-diol; Hmba = 2-methylbenzoic acid; Hdmpz = 3,5-dimethyl-1H-pyrazole; Htca = 3-thiophenecarboxylic acid; and Hba = benzoic acid. The structures of SD/Ni6b, SD/Ni5a and SD/Ni4a are built from a central Ni4O4 opened cube, appending two to zero NiNO5 octahedra. The solution behaviours of SD/Ni6b, SD/Ni5a and SD/Ni4a were studied in detail via an ESI-MS technique and their solution stabilities were confirmed. Magnetic analysis indicated the presence of Ising-type anisotropy: D = -13, -10, and -11 cm-1 for SD/Ni6b, SD/Ni5a, and SD/Ni4a, respectively; moreover, dominantly ferromagnetic interactions were found between magnetic centers: J1 = 6.5 cm-1, J2 = -0.44 cm-1 and J1 = 5.9 cm-1, J2 = 2.6 cm-1 for SD/Ni5a and SD/Ni4a, respectively. Besides, the photocurrent signals were observed and they reached the maximum very quickly for these three nickel(ii) clusters and then their current intensities remained almost constant, which provide a possibility to be used for light-harvesting and photo-related catalysis.

Prediction of Task Performance From Physiological Features of Stress Resilience.

In this paper, we investigate the potential of generic physiological features of stress resilience in predicting air traffic control (ATC) candidates' performance in a highly-stressful low-fidelity ATC simulator scenario. Stress resilience is highlighted as an important occupational factor that influences the performance and well-being of air traffic control officers (ATCO). Poor stress management, besides the lack of skills, can be a direct cause of poor performance under stress, both in the selection process of ATCOs and later in the workplace. 40 ATC candidates, within the final stages of their selection process, underwent a stimulation paradigm for elicitation and assessment of various generic task-unrelated physiological features, related to resting heart rate variability (HRV) and respiratory sinus arrhythmia (RSA), acoustic startle response (ASR) and the physiological allostatic response, which are all recognized as relevant psychophysiological markers of stress resilience. The multimodal approach included analysis of electrocardiography, electromyography, electrodermal activity and respiration. We make advances in computational methodology for assessment of physiological features of stress resilience, and investigate the predictive power of the obtained feature space in a binary classification problem: prediction of high- vs. low-performance on the developed ATC simulator. Our novel approach yields a relatively high 78.16% classification accuracy. These results are discussed in the context of prior work, while considering study limitations and proposing directions for future work.

Copper(II)-Assisted Ligand Fragmentation Leading to Three Families of Metallamacrocycle.

We present an unprecedented copper(II)-assisted organic ligand fragmentation process under basic conditions leading to several ligands within three families of metallamacrocycle, Cu6, Cu8, and Cu16. The sequential multistep reaction include (i) the deprotonation of the starting alcohol, 1,2-bis(3,5-dimethyl-pyrazol-1-yl)ethane-1,2-diol (H2bdped) to its diolate bdped followed by complexation through six bonds (µ6) to three copper atoms in a ring, (ii) the breaking of the ethane-pyrazole C-N bonds by the different solvent alcohols to form 1-(3,5-dimethyl-pyrazol-1-yl)-2-methoxyethane-1,2-diolate (dpmed) or 2-(3,5-dimethyl-pyrazol-1-yl)-2-hydroxyacetate (dpet), while retaining coordination to the copper centers and (iii) the final step to ethane-1,1,2,2-tetraolate, C2H2O44- (et). Importantly, the latter product, only observed on two previous occasions, occupies the core of Cu6 and Cu16 through exceptionally eight coordination bonds (µ8). Its alkyl esters, 2-alkoxyethane-1,1,2-triolate (met, eet, and pet), also occupy the central parts of Cu8 but forming six bonds (µ6) instead. The other product, 3,5-dimethylpyrazolate (dp), acts as peripheral bridges (µ2) but it is not involved in coordination if the starting salt is copper acetate, this may be a consequence of acetate being a better µ2-chelating ligand. In the presence of an oxidizing agent, K2Cr2O7, C2H2O44- (et) is oxidized to oxalate, C2O42- (ox). Thus, an additional µ3-hydroxide and µ4-oxalate in Cu16 widen the complexity of the structures, not to mention the range of coordination geometries of the copper centers, though in the present cases they can be classed in only two types: distorted square-planar and square-pyramid. In addition to single-crystal crystallography, the results from different techniques such as IR, ESI-MS, optical UV-vis, and SQUID magnetometry help in the characterization of these rare metallamacrocycles made from unexpected and in situ generated ligands. We believe the results of the organic transformations are highly relevant to von Liebig's benzil-benzilic acid rearrangement.

Self-assembly of a nonanuclear NiII cluster via atmospheric CO2 fixation: synthesis, structure, collision-induced dissociation mass spectrometry and magnetic property.

A novel nonanuclear nickel(ii) cluster identified as [Ni9(OH)6(CO3)2(ba)8(Hdmpz)6(DMF)2]·EtOH·2DMF (SD/Ni9a, Hba = benzoic acid, Hdmpz = 3,5-dimethyl-1H-pyrazole) is successfully constructed from mixed ligands. The single-crystal X-ray diffraction (SCXRD) structural analysis confirms the composition and reveals the "drum-like" inner core structure surrounded by ba- and DMF. Six Hdmpz ligands in their neutral form further sandwich the "drum" up and down, and is hydrogen bonded with two carbonate anions that are derived from the atmospheric CO2 with the help of Et3N. Electrospray ionization mass spectrometry (ESI-MS) reveals that the SD/Ni9a maintains an intact core in the solution with a slight exchange of outer ligands. Detailed collision-induced dissociation (CID) experiments reveal the collision energy (CE)-promoted ligand loss and exchange between ba- and Hdmpz. Furthermore, the magnetic study shows that there is no interaction between the Ni centers at room temperature, whereas the ferromagnetic coupling between the Ni centers is found with an S = 3 spin ground state of the cluster at low temperature. Moreover, the UV-vis spectrum and the photocurrent response measurements show its good optical properties with an indirect bandgap of about 2.35 eV and fast current response upon visible light irradiation.

Magnetoelectric Coupling Springing Up in Molecular Ferroelectric: [N(C2H5)3CH3][FeCl4].

A molecule-based ferroelectric triethylmethylammonium tetrachloroferrate(III) ([N(C2H5)3CH3][FeCl4]) powder was designed as a multifunctional material exhibiting excellent multiple bistability. Prepared by the slow evaporation method at room temperature, the compound crystallizes in the non-centrosymmetric assembly of hexagonal symmetry (P63mc space group) which undergoes a reversible temperature-triggered phase transition pinpointed at 363 K to the centrosymmetric packing within the P63/mmc space group. Aside from the inseparable role of the symmetry-breaking process smoothly unveiled from the X-ray powder diffraction data, a striking change in the dielectric permittivity observed during the paraelectric-to-ferroelectric phase transition directly discloses the bistable dielectric behavior-an exceptionally high increase in the dielectric permittivity of about 360% at 100 kHz across the heating and cooling cycles is direct proof showing the highly desirable stimuli-responsive electric ordering in this improper ferroelectric architecture. Due to the magnetically modulated physical properties resulting in the coupling of magnetic and electric orderings, the flexible assembly of [N(C2H5)3CH3][FeCl4] could be used to boost the design and development of novel magnetoelectric devices.

An Octanuclear Cobalt Cluster Protected by Macrocyclic Ligand: In Situ Ligand-Transformation-Assisted Assembly and Single-Molecule Magnet Behavior.

Macrocyclic molecules with multiple coordination sites have been widely used as promising ligands to build polynuclear metal clusters; however, cyclic silsesquioxane-based metal clusters are still rare. Herein, we report a new octanuclear Co-silsesquioxane cluster [Co8(OH)2{(MeSiO2)6}2(bpy)2(Obpy)2] (SD/Co8c; SD = SunDi), wherein the Co8 disc-like core is sandwiched by two hexamethylcyclohexasiloxanolate ligands (MeSiO2)6 at two poles and finally encircled by two bpy (bpy = 2,2'-bipyridine) and two Obpy (HObpy = 6-hydroxy-2,2'-bipyridine) ligands at the equatorial region. Interestingly, both MeSi(OMe)3 and bpy undergo in situ transformations to generate hexameric cyclic (MeSiO2)6 and Obpy, respectively. The unusual hydroxylation of bpy and the OH- anion in the center of Co8 core provide additional binding sites to induce the formation of the larger cluster instead of the traditional hexanuclear cluster. The solution stability and fragmentation route in the gas phase were studied by cold-spray ionization and collision-induced dissociation mass spectrometry, respectively. Both results reveal that the Co8 core is quite stable in solution as well as in the gas phase, even with increased collision voltage. Magnetic susceptibility studies of SD/Co8c show the slow magnetization relaxation indicative of single-molecule magnet (SMM) behavior. This work not only presents the multiple in situ ligand-transformation-assisted assembly of polynuclear cobalt cluster but also provides some new insights into the magnetism-structure relationship for SMMs.

A Polyoxochromate Templated 56-Nuclei Silver Nanocluster.

Most of polyoxometallates (POMs) templated silver nanoclusters recorded so far are polyoxomolybdates and polyoxotungstates; however, as congeneric polyoxochromates, they are rarely observed in silver nanoclusters. Herein, a high-nuclearity polyoxochromate, (CrIII4CrVI8O36)12-, is uncovered in a novel silver nanocluster (SD/Ag56a) as an anion template. The mixed-valent (CrIII4CrVI8O36)12- consists of four edge-sharing CrIIIO6 octahedra and eight CrVIO4 tetrahedra, which are fused together by sharing one or two vertexes. The (CrIII4CrVI8O36)12- is the by far highest nuclearity polyoxochromate and is trapped by outer Ag56 bracelet-like shell coprotected by quaternary ligands including iPrS-, NapCOO- (2-naphthalenecarboxylate), CF3COO-, and CH3CN. The antiferromagnetic property and solution behavior of SD/Ag56a are discussed in detail.

Self-Organization into Preferred Sites by MgII, MnII, and MnIII in Brucite-Structured M19 Cluster.

The search for functional materials, for example those aiming at microelectronics, magnetic recording, and catalysis, often ventures into mixed metal systems to achieve optimization of the properties. Thus, understanding site preference and self-organization is crucial but hard to implement. Herein, we present a system whereby MgII, MnII, and MnIII ions selectively locate exact positions within the Brucite-structured cluster, Mn13Mg6, [MnIII⊂MgII6⊂MnII9MnIII3( L)18(OH)12(N3)6](ClO4)6·12CH3CN, H L = 1-(hydroxymethyl)-3,5-dimethylpyrazolate). The MnIII being small (78 pm) takes up the core position; while 6 MgII (86 pm) are located in the inner ring, and the 9 large MnII (97 pm) and 3 MnIII occupy the outer ring. The factors (a) ionic radii, (b) regularity in coordination geometry, oxophilicity, and softness of MgII compared to MnII, and (c) Jahn-Teller distortion of MnIII may all be implicated synergistically. Electrospray ionization mass spectrometry reveals the M19 disc remains an integral unit when crystals are dissolved, and exchange between Mg and Mn occurs within the disc during its formation. Diamagnetic MgII doping insulates the magnetic exchange between the central MnIII and those in the outer ring, thus giving an overall antiferromagnetic exchange interaction between nearest-neighbors of the outer ring. The work reveals the underlying rule for site-preference of main group metal versus transition metal in disc-like Brucite-structured cluster and provides an elegant new avenue to assemble heterometallic clusters in a stepwise fashion.

Nanocomposites comprised of homogeneously dispersed magnetic iron-oxide nanoparticles and poly(methyl methacrylate).

Nanocomposites with a high, uniform loading of magnetic nanoparticles are very desirable for applications such as electromagnetic shielding and cancer treatment based on magnetically induced hyperthermia. In this study, a simple and scalable route for preparing nanocomposites with a high, uniform loading of magnetic nanoparticles is presented. The magnetic iron-oxide nanoparticles were functionalized with a methacrylate-based monomer that copolymerized in a toluene solution with the methyl methacrylate (MMA) monomer. The resulting suspension of magnetic nanoparticles decorated with poly(methyl methacrylate) (PMMA) chains in toluene were colloidal, even in the presence of a magnetic field gradient. Nanocomposites were precipitated from these suspensions. The transmission electron microscopy investigation of the prepared nanocomposites revealed that the magnetic nanoparticles were homogeneously dispersed in the PMMA matrix, even in amounts up to 53 wt %. The uniform dispersion of the nanoparticles in the PMMA matrix was attributed to the good solvation of the grafted PMMA chains from the magnetic nanoparticles by the PMMA chains of the matrix. The nanocomposites were superparamagnetic and exhibited large values for the saturation magnetization of up to 36 emu/g. Moreover, the nanocomposite with the largest amount of incorporated nanoparticles exhibited relatively large values for the specific power loss when subjected to alternating magnetic fields, giving this material great potential for the magnetically induced hyperthermia-based treatment of cancer.

Two Unprecedented POM-Based Inorganic-Organic Hybrids with Concomitant Heteropolytungstate and Molybdate.

Two novel POM-based inorganic-organic hybrids, [Cu6II(2,2'-bipy)6(Mo6O22)(SiW12O40)]n (1), and {[Cu6II(ppz)6(H2O)5(MoO4)(SiW12O40)]·4H2O}n (2) (2,2'-bipy = 2,2'-bipyridine, Hppz = 3-(pyrid-2-yl)pyrazole), have been constructed from heteropolytungstates and molybdates. Two compounds have been identified by single crystal X-ray diffraction, elemental analysis, and FT-IR. Compound 1 shows a 1D (one-dimensional) chain structure constructed from classical Keggin heteropolytungstate [SiW12O40]4- clusters and [Cu6(2,2'-bipy)6] modified isopolymolybdates [Mo6O22]8-. Compound 2 also represents a 1D chain-like motif built from classical Keggin heteropolytungstate [SiW12O40]4- clusters and [Cu8(ppz)6(H2O)5] modified molybdates MoO42-. Compound 1 represents the first example of POM-based inorganic-organic hybrid with mixed heteropolytungstates and isopolymolybdates. ESI-MS (electrospray ionization mass spectrometry) technique was employed to reveal the species and their evolutions in the hydrothermal reaction, whereby trivacant [SiW9] building block gradually transforms to classical Keggin [SiW12] during assembly process. Furthermore, the electrocatalytic and magnetic properties were discussed in details.

pH-Controlled assembly of two novel Dawson-sandwiched clusters involving the in situ reorganization of trivacant α-[P2W15O56](12-) into divacant α-[P2W16O57](8.).

Modified classical trivacant Wells-Dawson α-[P2W15O56](12-) and the assembly of related sandwiched transition metal clusters are of interest, but surprisingly few reports of these materials exist because of the sensitivity of α-[P2W15O56](12-) to the assembly environment. Herein, we describe the pH-controlled assembly of two novel Dawson-sandwiched clusters, (H2bpz)6[Co2(P2W16O57)2]·22H2O (1, bpz = 3,3',5,5'-tetramethyl-4,4'-bipyrazole) and (H2bpz)6[Co3H2(P2W16O57)(P2W15O56)(H2O)]·12H2O (2), involving the in situ transformation of α-[P2W15O56](12-). Both clusters were characterized by X-ray single-crystal diffraction, FT-IR spectroscopy, UV-Visible spectroscopy, thermogravimetric analysis, powder X-ray diffraction, and elemental analyses. X-ray crystallography showed that both heteropolytungstates become divacant α-[P2W16O57](8-) and symmetrically encapsulate two edge-shared CoO6 octahedra in the interior in 1, while only one divacant α-[P2W16O57](8-) is observed in 2, which combined with another trivacant α-[P2W15O56](12-) to asymmetrically clamp three edge-shared CoO6 octahedra. The α-[P2W16O57](8-) heteropolytungstate should be generated in situ from α-[P2W15O56](12-)via self-decomposition equilibria in solution. Their electrochemical behaviors reveal characteristic multi-electron redox processes related to W(VI) centers. The electrocatalytic reduction performances toward nitrite, hydrogen peroxide, chlorate, bromate and iodate were fully measured and discussed; among these species, both clusters exhibit the best electrocatalytic activity towards the reduction of bromate. Magnetic measurements indicate weak ferromagnetic exchange interactions between Co atoms sandwiched by vacant polyoxometalates.

Bacterial chemotaxis and entropy production.

Entropy production is calculated for bacterial chemotaxis in the case of a migrating band of bacteria in a capillary tube. It is found that the speed of the migrating band is a decreasing function of the starting concentration of the metabolizable attractant. The experimentally found dependence of speed on the starting concentration of galactose, glucose and oxygen is fitted with power-law functions. It is found that the corresponding exponents lie within the theoretically predicted interval. The effect of the reproduction of bacteria on band speed is considered, too. The acceleration of the band is predicted due to the reproduction rate of bacteria. The relationship between chemotaxis, the maximum entropy production principle and the formation of self-organizing structure is discussed.

Mathematical modeling of the myosin light chain kinase activation.

The mathematical model presented here describes the interactions among Ca2+, calmodulin (CaM), and myosin light chain kinase (MLCK) and consists of a kinetic scheme taking into account 7 reactions instead of 12 as proposed previously. We derive a system of 5 nonlinear ordinary differential equations. Solving it yields the prediction of active MLCK as a function of [Ca2+] whereby the active MLCK is defined to be proportional to the Ca4CaM.MLCK complex concentration. The model predictions are compared with other theoretical and experimental predictions of active MLCK as well as with the results of our previously proposed complex model.