Opposite effects of interactions and disorder on the switching properties of the spin transition compound [FeII(L)2][ClO4]2 · C7H8

We report on a detailed analysis of the thermal transition hysteresis loop and the relaxation curves of the recently investigated compound [Fe^II(L)₂][ClO₄]₂ · C₇H₈ [V. Mishra et al., Inorg. Chem. (2008)]. We developed a variant of a previous kinetic cooperative model, modified for including short-range and long-range Gaussian distributions of energy parameters. The resulting set of coupled master equations was solved numerically for the dynamic and the quasi-static case. We have elucidated the various correlations between the distribution widths and the long-range interaction parameter, which basically have opposite effects. It is shown that presence of a steep hysteresis loop may hide a sizable short-range distribution, while the stretched character of the relaxation curves may also hide the presence of strong interactions. We also show that the coherent analysis of the set of relaxation curves at different temperatures does not allow to disentangle properly all the relevant parameters. We discuss these data with respect to the other photomagnetic experiments, T(LIESST) curve and light-induced thermal hysteresis (LITH) loop, and finally we try to address the question of the real nature of the cooperative relaxation process.     

Isostructural dinuclear phenoxo-/acetato-bridged manganese(II), cobalt(II), and zinc(II) complexes with labile sites: kinetics of transesterification of 2-hydroxypropyl-p-nitrophenylphosphate

Using the dinucleating phenol-based ligand 2,6-bis[3-(pyridin-2-yl)pyrazol-1-ylmethyl]-4-methylphenol] (HL(2)), in its deprotonated form, the six new dinuclear complexes [M(II)(2)(L(2))(μ-O(2)CMe)(2)(MeCN)(2)][PF(6)] (M = Mn (2a), Co (3a), Zn (4a)) and [M(II)(2)(L(2))(μ-O(2)CMe)(2)(MeCN)(2)][BPh(4)] (M = Mn (2b), Co (3b), Zn (4b)) have been synthesized. Crystallographic analyses on 2b·2MeCN, 3b·2MeCN, and 4b·2MeCN reveal that these complexes have closely similar μ-phenoxo bis(μ-carboxylato) structures. The physicochemical properties (absorption and ESI-MS spectral data, 2a,b, 3a,b, and 4a,b; (1)H NMR, 4a,b) of the cations of 2a-4a are identical with those of 2b-4b. Each metal ion is terminally coordinated by a pyrazole nitrogen and a pyridyl nitrogen from a 3-(pyridin-2-yl)pyrazole unit and a solvent molecule (MeCN). Thus, each metal center assumes distorted-octahedral M(II)N(3)O(3) coordination. Temperature-dependent magnetic studies on Mn(II) and Co(II) dimers reveal the presence of intramolecular antiferromagnetic (J = -8.5 cm(-1)) for 2b and ferromagnetic exchange coupling (J = +2.51 cm(-1)) for 3b, on the basis of the Hamiltonian H = -JS(1)·S(2). The exchange mechanism is discussed on the basis of magneto-structural parameters (M···M distance). Spectroscopic properties of the complexes have also been investigated. The pH titration and kinetics of phosphatase (transesterification) activity on 2-hydroxypropyl-p-nirophenylphosphate (HPNP) were studied in MeOH/H(2)O (33%, v/v) with 2a-4a, due to solubility reasons. This comparative kinetic study revealed the effect of the metal ion on the rate of hydrolysis of HPNP, which has been compared with what we recently reported for [Ni(II)(2)(L(2))(μ-O(2)CMe)(2)(MeOH)(H(2)O)][ClO(4)] (1a). The efficacy in the order of conversion of substrate to product (p-nitrophenolate ion) follows the order 4a > 3a > 2a > 1a, under identical experimental conditions. Notably, this trend follows the decrease of pK(a) values of M(II)-coordinated water (7.95 ± 0.04 and 8.78 ± 0.03 for 1a, 7.67 ± 0.08 and 8.69 ± 0.06 for 2a, 7.09 ± 0.05 and 8.05 ± 0.06 for 3a, and 6.20 ± 0.04 and 6.80 ± 0.03 for 4a). In this work we demonstrate that the stronger the Lewis acidity (Z(eff)/r) of the metal ion, the more acidic is the M(II)-coordinated water and the greater is the propensity of the metal ion to catalyze hydrolysis of the activated phosphate ester HPNP. Notably, the observed k(2) values (M(-1) s(-1)) for Mn(II) (2a, 0.152), Co(II) (3a, 0.208), and Zn(II) (4a, 0.230) complexes (1a, 0.058; already reported) linearly correlate with Z(eff)/r values of the metal ion. In each case a pseudo-first-order kinetic treatment has been done. Kinetic data analysis of complexes 2a-4a were also done following Michaelis-Menten treatment (catalytic efficiency k(cat)/K(M) values 0.170 M(-1) s(-1) for 2a, 0.194 M(-1) s(-1) for 3a and 0.161 M(-1) s(-1) for 4a; for 1a the value is 0.089 M(-1) s(-1)). Temperature-dependent measurements were done to evaluate kinetic/thermodynamic parameters for the hydrolysis/transesterification of HPNP and yielded comparable activation parameters (E(a) (kJ mol(-1)): 71.00 ± 4.60 (1a; reported), 67.95 ± 5.71 (2a), 62.60 ± 4.46 (3a), 67.80 ± 3.25 (4a)) and enthalpy/entropy of activation values (ΔH(?) (kJ mol(-1)) = 68.00 ± 4.65 (1a; reported), 65.40 ± 5.72 (2a), 60.00 ± 4.47 (3a), 65.29 ± 3.26 (4a); ΔS(?) (J mol(-1) K(-1)) = -109.00 ± 13 (1a; reported), -107.30 ± 16 (2a), -122.54 ± 14 (3a), -104.67 ± 10 (4a)). The E(a) values for all the complexes are comparable, suggesting a closely similar reaction barrier, meaning thereby similar course of reaction. The ΔS(?) values are consistent with an associative process. Positive ΔH(?) values correspond to bond breaking of the activated complex as a result of nucleophilic attack at the phosphorus atom, releasing cyclic phosphate and p-nitrophenolate ion. These data have helped us to propose a common mechanistic pathway: deprotonation of a metal-bound species to form the effective nucleophile, binding of the substrate to the metal center(s), intramolecular nucleophilic attack on the electrophilic phosphorus atom with the release of the leaving group, and possibly regeneration of the catalyst.     

Effects of lipopolysaccharide-induced inflammation on expression of growth-associated genes by corticospinal neurons

Background  

Inflammation around cell bodies of primary sensory neurons and retinal ganglion cells enhances expression of neuronal growth-associated genes and stimulates axonal regeneration. We have asked if inflammation would have similar effects on corticospinal neurons, which normally show little response to spinal cord injury. Lipopolysaccharide (LPS) was applied onto the pial surface of the motor cortex of adult rats with or without concomitant injury of the corticospinal tract at C4. Inflammation around corticospinal tract cell bodies in the motor cortex was assessed by immunohistochemistry for OX42 (a microglia and macrophage marker). Expression of growth-associated genes c-jun, ATF3, SCG10 and GAP-43 was investigated by immunohistochemistry or in situ hybridisation.     

Environmentally benign approach towards C–S cross-coupling reaction by organo-copper(II) complex

Molecular Diversity - C–S cross-coupling reaction in water giving an excellent yield of the desired C–S coupled product by using a newly developed...     

Graphene Oxide as an Enhancer of Fluorescence

Solvent‐dependent switching of graphene oxide (GO) as fluorescence quencher or enhancer was observed. In some solvents, GO increases the fluorescence yield of a hydrophilic molecule 7‐(diethylamino)‐coumarin‐3‐carboxylic acid (7‐DCA), and in some solvents GO act as a quencher of fluorescence.     

Kinetics and mechanism of acid and base hydrolysis ofcis-chloro-(benzotriazole)bis(ethylenediamine)cobalt(III) andcis-chloro-(N-methylbenzotriazole)bis(ethylenediamine)cobalt(III) cations

Summary The kinetics of acid hydrolysis ofcis-[CoCl(btzH)(en)₂]²⁺ andcis-[CoCl(btzMe)(en)₂]²⁺ complexes (where btzH = benzotriazole, btzMe =N-methylbenzotriazole and en = ethylenediamine) have been investigated in HClO₄ at ionic strength 1 = 0.25 mol dm^–3 in the 30–40° range. In the 1.0 x 10^–1 to 1.0 X 10^–3 mol dm^–3 acid strength range, the rate of aquation of the [CoCl(btzH)(en)₂]²⁺ cation follows the relationship:-d ln[complex]/dt = k₁ + k₂K_NH[^H+]^–1, where k₁ and k₂ are aquation rate constants of the acid independent and acid dependent steps respectively, and K_NH is the acid dissociation constant of the coordinated benzotriazole.cis-[CoCl(btzMe)-(en)₂]²⁺ undergoes acid independent hydrolysis presumably due to the absence of a labile N-H proton. The base hydrolysis could be followed for thecis-[CoCl(btzMe)(en)₂]²⁺ complex only by measuring hydrolysis rates at 0°.     

Non-linear behaviour of electron acoustic wave dynamics in a magnetized plasma with non-thermal hot electrons

Non-linear dynamical behaviour of electron acoustic waves (EAWs) is studied in a magnetized non-thermal plasma (containing inertial cold electrons, inertialess hot electrons following non-thermal distribution function, and static ions) via a fluid dynamical approach. A linear dispersion relation is derived and the propagation of two possible modes and their evolution are studied through the different plasma configuration parameters, such as non-thermality and external magnetic field strength. In a non-linear perturbation regime, a reductive perturbation technique is employed to derive the non-linear evolution equation and the analysis is executed for travelling plane waves in terms of a non-linear dynamical system to enlighten the numerous aspects of the phase space dynamics. The results of numerical simulation predict the existence of a wide class of non-linear structures, namely solitonic, periodic, quasiperiodic, and chaotic depending upon different controlling plasma parameters. Also, Poincaré return map analysis confirms these non-linear structures of the EAWs.     

Probabilistic Inductive Classes of Graphs

A unifying framework—probabilistic inductive classes of graphs (PICGs)—is defined by imposing a probability space on the rules and their left elements from the standard notion of inductive class of graphs. The rules can model the processes creating real-world social networks, such as spread of knowledge, dynamics of acquaintanceships or sexual contacts, and emergence of clusters. We demonstrate the characteristics of PICGs by casting some well-known models of growing networks in this framework. Results regarding expected size and order are derived. For PICG models of connected and 2-connected graphs order, size and asymptotic degree distribution are presented. The approaches used represent analytic alternative to computer simulation, which is mostly used to obtain the properties of evolving graphs.     

Rational design of a new class of polycyclic organic bases bearing two superbasic sites and their applications in the CO2 capture and activation process

A new type of polycyclic organic superbases is reported with very high proton affinities in the gas phase and the pK(a) upto 45.8 units in acetonitrile. They have exhibited the 2nd pK(a) upto 44.4 units, which is the highest 2nd pK(a) reported till date. These organic superbases can be useful in the fixation of CO(2) released from different industrial sources.