Pendant Proton-Relays Systematically Tune the Rate and Selectivity of Electrocatalytic Ammonia Generation in a Fe-Porphyrin Based Metal-Organic Framework.

Electrocatalytic nitrite reduction (eNO2RR) is a promising alternative route to produce ammonia (NH3). Until now, several molecular catalysts have shown capability to homogeneously reduce nitrite to NH3, while taking advantage of added secondary-sphere functionalities to direct catalytic performance. Yet, realizing such control over heterogeneous electrocatalytic surfaces remains a challenge. Herein, we demonstrate that heterogenization of a Fe-porphyrin molecular catalyst within a 2D Metal-Organic Framework (MOF), allows efficient eNO2RR to NH3. On top of that, installation of pendant proton relaying moieties proximal to the catalytic site, resulted in significant improvement in catalytic activity and selectivity. Notably, systematic manipulation of NH3 faradaic efficiency (up to 90 %) and partial current (5-fold increase) was achieved by varying the proton relay-to-catalyst molar ratio. Electrochemical and spectroscopic analysis show that the proton relays simultaneously aid in generating and stabilizing of reactive Fe-bound NO intermediate. Thus, this concept offers new molecular tools to tune heterogeneous electrocatalytic systems.

Spectroscopic investigation on shuttlecock-shaped liquid crystalline trimers: Mesomorphic behaviour and its application in optical storage devices.

In this paper, we discuss the synthesis and characterization of 2,3,4-tris[n-((4-(-cyanophenyl)diazenyl)phenoxy)alkyloxy]benzonitrile obtained by coupling 2,3,4-trihydroxy benzonitrile and (E)-4-((4-((n-bromoalkyl)oxy)phenyl)diazenyl)benzonitrile, pertain to shuttlecock shaped liquid crystals. The molecular structure was confirmed by NMR spectroscopic and elemental analyzer. The thermal behavior of the trimers was assessed using a polarizing optical microscope (POM) and differential scanning calorimetry (DSC). The three diazo groups in the trimers enabled us to study the photo-isomerization effect and evaluate their potential applications in optical storage devices. Importantly, we found these trimers easy to synthesize and process, paving the way for cost-effective alternatives to traditional LC materials. We fabricated an optical storage device to study the light effects on shuttlecock-shaped LC trimers, demonstrating that the geometry of the trimers plays a crucial role in determining structure-property relationships.

Regulation of Catalyst Immediate Environment Enables Acidic Electrochemical Benzyl Alcohol Oxidation to Benzaldehyde.

Electrocatalytic alcohol oxidation in acid offers a promising alternative to the kinetically sluggish water oxidation reaction toward low-energy H2 generation. However, electrocatalysts driving active and selective acidic alcohol electrochemical transformation are still scarce. In this work, we demonstrate efficient alcohol-to-aldehyde conversion achieved by reticular chemistry-based modification of the catalyst's immediate environment. Specifically, coating a Bi-based electrocatalyst with a thin layer of metal-organic framework (MOF) substantially improves its performance toward benzyl alcohol electro-oxidation to benzaldehyde in a 0.1 M H2SO4 electrolyte. Detailed analysis reveals that the MOF adlayer influences catalysis by increasing the reactivity of surface hydroxides as well as weakening the catalyst-benzaldehyde binding strength. In turn, low-potential (0.65 V) cathodic H2 evolution was obtained through coupling it with anodic benzyl alcohol electro-oxidation. Consequently, the presented approach could be implemented in a wide range of electrocatalytic oxidation reactions for energy-conversion application.

Local CO2 reservoir layer promotes rapid and selective electrochemical CO2 reduction.

Electrochemical CO2 reduction reaction in aqueous electrolytes is a promising route to produce added-value chemicals and decrease carbon emissions. However, even in Gas-Diffusion Electrode devices, low aqueous CO2 solubility limits catalysis rate and selectivity. Here, we demonstrate that when assembled over a heterogeneous electrocatalyst, a film of nitrile-modified Metal-Organic Framework (MOF) acts as a remarkable CO2-solvation layer that increases its local concentration by ~27-fold compared to bulk electrolyte, reaching 0.82 M. When mounted on a Bi catalyst in a Gas Diffusion Electrode, the MOF drastically improves CO2-to-HCOOH conversion, reaching above 90% selectivity and partial HCOOH currents of 166 mA/cm2 (at -0.9 V vs RHE). The MOF also facilitates catalysis through stabilization of reaction intermediates, as identified by operando infrared spectroscopy and Density Functional Theory. Hence, the presented strategy provides new molecular means to enhance heterogeneous electrochemical CO2 reduction reaction, leading it closer to the requirements for practical implementation.

Influence of inter- and intramolecular H-bonding on the mesomorphic and photoswitching behaviour of (E)-4-((4-(hexyloxy)phenyl)diazenyl)-N-phenyl benzamides.

We report on the synthesis, phase behaviour and photoswitching studies of new azo linked rod-shaped molecules. These novel materials consist of three phenyl rings separated by a diazo, amide linkage with a hexyloxy tail and 2,4-substituents at either end of the phenyl ring. The mesomorphic behaviours, phase transition temperature including the enthalpies were characterized by polarizing optical microscope (POM) and differential scanning calorimetry (DSC). The influence of inter- and intramolecular hydrogen bonding on mesomorphic and photoisomerization was studied. Photoisomerization studies carried out both in the solid and liquid phase show the quick E-Z transition with prolonged thermal back relaxation (Z-E) by using UV-Visible spectroscopy. This interesting behaviour could be attributed to the presence of the hexyloxy tail, lateral electron withdrawing group and the influence of inter- or intramolecular hydrogen bonding. Excellent bright and dark states were accomplished using one of these materials in optical storage device. Further tuning is necessary to employ them for real applications.

Regulatory role of guanosine 3',5'-monophosphate in adrenocorticotropin hormone-induced steroidogenesis.

The relation between steroidogenesis induced by adrenocorticotropic hormone and the concentrations of adenosine 3',5'-monophosphate (cyclic AMP) and guanosine 3',5'-monophosphate (cyclic GMP) was studied at different time intervals in isolated adrenal cells. Submaximal and supramaximal steroidogenic concentrations of the hormone did not cause detectable changes in cyclic AMP during the first 30 minutes, whereas there was an increase in the concentration of cyclic GMP that was accompanied by phosphorylation and steroidogenesis. It is therefore suggested that cyclic GMP, rather than cyclic AMP, is the physiological mediator of adrenocorticotropic hormone-induced adrenal steroidogenesis.

Fast responding robust nematic liquid crystalline gels formed by a monodisperse dipeptide: electro-optic and rheological studies.

Realization of mechanically robust electrically fast responding liquid crystal devices with low operating voltage is one of the current research interests. Here we report a gel system comprising a commercially available nematic liquid crystal material and a new monodisperse dipeptide liquid crystalline organogelator that results in these properties. The gels exhibit nearly 2 orders of magnitude faster switching response than the pure nematic liquid crystal while having 3 orders of magnitude higher zero shear rate viscosity, and with the attractive feature that the switching threshold voltage is hardly altered. Electro-optic and rheological studies of this system are described here.

Distortions in structures of the twist bend nematic phase of a bent-core liquid crystal by the electric field.

The dielectric spectra of the twist bend nematic phase (N_{TB}) of an achiral asymmetric bent-core liquid crystalline compound are studied for determining the various relaxation modes. Dielectric measurements are also carried out under the bias field E up to 8 V/µm. Two molecular and two collective relaxation processes are observed. The orientational order parameters with respect to the local and the main directors determined using molecular modes are used to find the heliconical angle. The results also show that the order parameter with reference to the main director reverses its trend from increasing to decreasing at temperatures of a few degrees above the N_{TB} to N transition. The collective relaxation modes are assigned to (a) distortions of the local director by the electric field at a frequency of ∼100kHz while the periodic helical structure remains unaltered (mode attributed to flexoelectricity); (b) changes in the periodic structure arising from a coupling of the dielectric anisotropy with the electric field at the lowest frequency in the range of 100 Hz-10 kHz. Frequency of the higher frequency collective mode (∼100kHz) depends primarily on the heliconical angle and has anomalous softeninglike behavior at the N-N_{TB} transition. The lowest frequency mode is studied under the bias field E; the modulus of the wave vector gradually vanishes on increasing E (except for an initial behavior, E^{2}<0.1V^{2}/µm^{2}, which is just the opposite). The transition from the twist bend to splay bend structure is observed by a sudden drop in the frequency of this mode, followed by a linear decrease in frequency by increasing E. The results agree with the predictions made from the currently proposed models for a periodically distorted N_{TB} phase.

Metabolic regulation and relationship of endogenous protein kinase activity and steroidogenesis in isolated adrenocortical carcinoma cells of the rat.

In the adrenocortical carcinoma cell, in contrast to normal isolated adrenal cells, 10 to 50 muunits of ACTH do not raise the level of adenosine cyclic 3':5'-monophosphate (cyclic AMP), protein kinase activity, and steroidogenesis. This indicates a lesion in the tumor adenylate cyclase system. Two-tenths to 10 mM cyclic AMP and guanosine cyclic 3':5'-monophosphate (cyclic GMP) which stimulate steroidogenesis in a normal cell, activate protein kinase activity in a concentration-response manner without any detectable rise in steroidogenesis in the adrenocortical carcinoma cell. Cycloheximide and actinomycin D do not inhibit the stimulation of the phosphorylation. These results suggest that the tumor cyclic nucleotide-dependent protein kinase activity is unrelated to steroidogenesis and is also not under the transcriptional or translational control steps. Curiously, muM concentrations of cyclic AMP, in contrast to cyclic GMP, stimulate protein kinase activity. In a normal cell, both cyclic AMP and cyclic GMP, in this concentration range, stimulate protein kinase without an increase in steroidogenesis. It is therefore proposed that, in contrast to the normal cell, there is an additional defect in cyclic GMP-dependent protein kinase.

Partial purification and characterization of the defective cyclic adenosine 3':5'-monophosphate binding protein kinase from adrenocortical carcinoma.

Previous studies with isolated adrenocortical carcinoma 494 cells from this laboratory have indicated that the lack of cyclic adenosine 3':5'-monophosphate (cyclic AMP) control in steroidogenesis in the tumor may be due to the defective cyclic AMP-dependent protein kinase enzyme system. This paper describes the partial purification of such an enzyme. Purification was achieved by precipitation of the tumor homogenate with 30 and 45% ammonium sulfate, adsorption on 3% calcium phosphate gel, and chromatography on DEAE-cellulose. Four major protein peaks were isolated. Peak 2 showed cyclic AMP-binding activity and was investigated further for its kinetic properties. In contrast to the cyclic AMP-dependent protein kinase enzyme found in the normal adrenal gland, the enzyme specifically bound cyclic AMP but failed to phosphorylate exogenous histone. It is postulated that lack of the cyclic nucleotide-dependent kinase activity of the protein kinase enzyme may be responsible for the loss of cyclic AMP-regulated corticosterone synthesis in adrenocortical carcinoma cell. It is further shown that the tumor cyclic AMP-binding enzyme undergoes endogenous phosphorylation, which indicates that it has kinase activity but it is independent of cyclic AMP.

Hybrid Perovskite Quantum Nanostructures Synthesized by Electrospray Antisolvent-Solvent Extraction and Intercalation.

Perovskites based on organometal lead halides have attracted great deal of scientific attention recently in the context of solar cells and optoelectronic devices due to their unique and tunable electronic and optical properties. Herein, we show that the use of electrospray technique in conjunction with the antisolvent-solvent extraction leads to novel low-dimensional quantum structures (especially 2-D nanosheets) of CH3NH3PbI3- and CH3NH3PbBr3-based layered perovskites with unusual luminescence properties. We also show that the optical bandgaps and emission characteristics of these colloidal nanomaterials can be tuned over a broad range of visible spectral region by compositional tailoring of mixed-halide (I- and Br-based) perovskites.

Electronic grade and flexible semiconductor film employing oriented attachment of colloidal ligand-free PbS and PbSe nanocrystals at room temperature.

Electronic grade semiconductor films have been obtained via the sintering of solution processed PbS and PbSe nanocrystals at room temperature. Prior attempts to achieve similar films required the sintering of nanocrystals at higher temperatures (>350 °C), which inhibits the processing of such films on a flexible polymer substrate, and it is also expensive. We reduced the sintering temperature by employing two important strategies: (i) use of ligand-free nanocrystals and (ii) oriented attachment of nanocrystals. Colloidal ligand-free PbS and PbSe nanocrystals were synthesized at 70 °C with high yield (∼70%). However, these nanocrystals start to agglomerate with time in formamide, and upon the removal of the solvation energy, nanocrystals undergo oriented attachment, forming larger elongated crystals. PbS and PbSe nanocrystal films made on both glass and flexible substrates at room temperature exhibit Ohmic behavior with optimum DC conductivities of 0.03 S m(-1) and 0.08 S m(-1), respectively. Mild annealing of the films at 150 °C increases the conductivity values to 1.1 S m(-1) and 137 S m(-1) for PbS and PbSe nanocrystal films, respectively. AC impedance was measured to distinguish the contributions from grain and grain boundaries to the charge transport mechanism. Charge transport properties remain similar after the repeated bending of the film on a flexible polymer substrate. Reasonably high thermoelectric Seebeck coefficients of 600 µV K(-1) and 335 µV K(-1) for PbS and PbSe nanocrystal pellets, respectively, were obtained at room temperature.

Altered phosphoinositide-specific phospholipase C and adenylyl cyclase in brain cortical membranes of cats with GM1 and GM2 gangliosidosis.

Phosphoinositide-specific phospholipase C and adenylyl cyclase were studied in brain cortical membranes from cats with GM1 and GM2 gangliosidosis. In contrast to brain cortical membranes from unaffected control cats, phospholipase C acting against exogenously supplied phosphoinositide substrates did not respond to stimulation by GTP gamma S, carbachol or fluoroaluminate in cortical membranes of cats with gangliosidosis. However, the enzyme was activated by calcium in membranes from affected cats to the same extent as in membranes from control cats. Basal adenylyl cyclase activity was increased 3-fold in cortical membranes of cats with GM1 and GM2 gangliosidosis, compared with unaffected sibling controls. Fluoroaluminate was equally effective in stimulating adenylyl cyclase in controls and in membranes of affected and normal cats. In addition, GppNHp was able to inhibit the forskolin-activated enzyme both in membranes from cats with gangliosidosis and sibling controls. These data suggest that the activation of phosphoinositide-specific phospholipase C in brain membranes by guanine nucleotide binding proteins is markedly impaired in GM1 and GM2 gangliosidoses.

Effect of thyroid hormone on the synthesis of sialosyl galactosylceramide (GM4) in myelinogenic cultures of cells dissociated from embryonic mouse brain.

A sialyltransferase, which catalyzes the biosynthesis of the myelin-associated sialosyl galactosylceramide (GM4) from galactocerebroside and cytidine-5'-monophospho-N-acetylneuraminic acid, has been detected in primary reaggregating, surface adhering cultures of cells dissociated from embryonic mouse brain. The ontogenetic profile of this enzyme in culture mimics its in vivo developmental pattern in that its activity could be detected only after 28 days in vitro and reached peak values around 48 days in vitro. Between 48 to 75 days in culture (oldest age studied) only a very slow increase in activity is observed. Unlike other myelin marker enzymes whose activities appear at an earlier time in development, the gene expression of the sialyltransferase responds relatively slowly to stimulation by triiodothyronine. However, if exposed to hypothyroid conditions at an early developmental age before the enzyme activity is expressed, little or no activity appears in latter stages of development.

Methylmercury inhibits the in vitro uptake of the glutathione precursor, cystine, in astrocytes, but not in neurons.

Maintenance of adequate intracellular glutathione (GSH) levels is vital for intracellular defense against oxidative damage. The toxic effects of methylmercury (MeHg) are attributable, at least in part, to elevated levels of reactive oxygen species, and thus decreases in GSH synthesis may increase methylmercury toxicity. Astrocytes have recently been proposed to play an essential role in providing GSH precursors to neurons. Therefore, cystine transport, a prerequisite to GSH production, was characterized in cultured astrocytes and neurons, and the effects of methylmercury on this transport were assessed. Astrocytes and neurons both possessed temperature dependent transport systems for cystine. Astrocytes accumulated cystine by Na+-independent (X(C)-) and -dependent (X(AG)-) systems while neurons used exclusively Na+-independent systems. Inhibition of the X(AG)- transport system decreased cystine transport in astrocytes to levels equivalent to those in sodium-depleted conditions, suggesting that cystine is carried by a glutamate/aspartate transporter in astrocytes. Inhibition of the multifunction ectoenzyme/amino acid transporter gamma-glutamyltranspeptidase (GGT) decreased cystine transport in both neurons and astrocytes. Inhibition of System X(C)- with quisqualate also decreased cystine uptake in both astrocytes and neurons. These data demonstrate that cultured astrocytes accumulate cystine via three independent mechanisms, System X(AG)-, System X(C)-, and GGT, while cultured hippocampal neurons use System X(C)- and GGT exclusively. Inhibition of cystine uptake in astrocytes by methylmercury appears to be due to actions on the System X(AG)- transporter.

Dibutyryl cyclic AMP-induced changes in neuron-astroglia interactions and fibronectin immunocytochemistry in dissociated rat cerebellar cultures.

In mixed primary embryonic CNS cultures flat astroglia grow exclusively underneath the initially formed neuronal network. This invasive under-growth results in neuronal detachment and degeneration. The present study sought to find out whether or not morphological differentiation of astroglia, from flat to process-bearing cells, could alter astroglial-neuronal growth relationships in rat cerebellar cultures. Morphological differentiation of astroglia was induced by treatment with dibutyryl cyclic AMP. The results demonstrate that in contrast to flat astroglia, large stellate astroglia can grow over the neurite bundles, and that in these dibutyryl cyclic AMP-treated cultures neurons can persist. Immunocytochemical studies show that the extracellular matrix protein fibronectin is present in these cultures and appears to be associated with flat astroglia rather than with stellate astroglia. The study indicates that in the presence of dibutyryl cyclic AMP transformed stellate astroglia interact differently with neurons and with the growth substratum as compared with flat astroglia.

The uptake of cysteine in cultured primary astrocytes and neurons.

One of the vitally important functions of glutathione (GSH) is to adequately protect cells against toxic chemicals, reactive oxygen metabolites and free radical species. The amino acid, cysteine, is the key rate-limiting substrate for the biosynthesis of GSH, and the maintenance of adequate intracellular GSH levels is dependent upon the extracellular availability and transport of cysteine into cells. In the present study, primary cultures of astrocytes and neurons were employed to characterize cysteine transport systems. Both astrocytes and neurons used Na(+)-dependent systems as the major route for cysteine uptake (80-90% of total), while Na(+)-independent uptake represented a minor component of total transport (10-20% of total). Among the Na(+)-dependent systems, X(AG(-)) was the major contributor (approx. 80-90%) for cysteine uptake in both neurons and astrocytes, with a minor contribution from the ASC transport system (Na(+)-dependent neutral amino acid transport system for alanine, serine, and cysteine). In the Na(+)-independent transport systems (10-20% of total cysteine transport), multifunctional ectoenzyme/amino acid transporter gamma-glutamyltranspeptidase (GGT), and the neutral amino acid L-system contributed approximately equally towards cysteine uptake, in both neurons and astrocytes. The present studies demonstrate that astrocytes and neurons accumulate cysteine by both Na(+)-dependent and Na(+)-independent uptake systems, with major uptake occurring through the X(AG(-)) system and minor uptake via the ASC, GGT and L-systems.

Methylmercury inhibits cysteine uptake in cultured primary astrocytes, but not in neurons.

The maintenance of adequate intracellular glutathione (GSH) concentrations is dependent on the availability and transport of the rate-limiting substrate, cysteine. A suggested mechanism of methylmercury (MeHg) neurotoxicity in brain involves the formation of oxygen radicals, and a decrease in intracellular levels of GSH. Recently, we have characterized various cysteine transport systems (both Na(+)-dependent and -independent) in cerebrocortical astrocytes and hippocampal neurons. The present study was carried out to investigate the effect of MeHg on cysteine uptake in both astrocytes and neurons, and to determine whether cysteine transport is differentially affected in the two cell types by MeHg treatment. Sixty-minute pretreatment with MeHg caused significant concentration-dependent inhibition in cysteine uptake in astrocytes, but not in neurons. As most of the cysteine transport is Na(+)-dependent (80-90% of total), additional studies focused on MeHg's effect on the Na(+)-dependent cysteine transporters X(AG(-)) and ASC. An additive inhibitory effect on cysteine uptake was observed in astrocytes treated with MeHg (5 microM) plus sub-maximal inhibitory concentrations (0.1 and 0.5 mM) of threo-beta-hydroxy-aspartate (THA), a specific inhibitor of the Na(+)-dependent transporter, X(AG(-)), compared to astrocytes treated with MeHg (P<0.001) or THA alone (P<0.05). There was no additive effect of MeHg and maximal inhibitory concentrations of THA (1.0 and 5.0 mM) on astrocytic cysteine uptake inhibition. Additional studies examined the sensitivity of the Na(+)-dependent ASC transport system to MeHg treatment. Maximal inhibitory concentration of L-serine (10 mM) alone had a rather modest inhibitory effect on cysteine uptake, and when applied in the presence of MeHg there was no additive effect. These results suggest that the inhibition of cysteine uptake by MeHg in astrocytes occurs through specific inhibition of both the X(AG(-)) as well as the ASC transport system.

Estrogen modulates the inducible expression of platelet-derived growth factor mRNA by monocyte/macrophages.

We examined the effects of estrogen, 12-O-tetradecanoylphorbol 13 acetate (TPA), and lipopolysaccharide (LPS) on the gene expression of platelet-derived growth factor (PDGF) by the monocyte/macrophage cell line, THP-1. THP-1 cells were exposed to TPA for 48 or 96 hours to induce differentiation. Some were treated with LPS in the last 3 hours and/or ethinyl estradiol (estrogen) (10(-9) M) in the last 20 hours. Total cellular RNA was isolated and cDNA was synthesized and then coamplified (with an internal control, beta-actin, product size 1126 bp) using polymerase chain reaction (PCR) and a set of primers for PDGF-A (product size 225 bp), PDGF-B (217 bp), or PDGF beta-receptor (PDGF-R) (228 bp). The products were separated on an agarose gel and the ratios of radioactivity incorporated into PDGF PCR products to beta-actin products were used to assess the relative changes in the levels of PDGF mRNA abundance in response to various inducers. TPA induced the expression of PDGF-A mRNA, whereas LPS had no effect. Treatment of TPA-stimulated cells with estrogen caused a 61% and 190% increase in PDGF-A mRNA (p < 0.05) at 48 and 96 hours, respectively. Addition of estrogen to cells treated with both TPA and LPS did not cause any significant change in the amounts of the transcripts. In contrast to PDGF-A mRNA, attempts to visualize and estimate PDGF-B and PDGF-R mRNA were unsuccessful. This was probably due to low levels of these transcripts in THP-1 cells. The results indicate that estrogen modulates PDGF-A gene expression by monocyte/macrophages and suggest that estrogen may influence atherogenesis at the vascular level.

Investigations on myelinogenesis in vitro: I. The occurrence of endogenous protein kinase and its role in the phosphorylation of myelin basic proteins in "myelin-like membranes" isolated from cerebral cell cultures.

The presence of a protein kinase capable of phosphorylating endogenous as well as exogenously added myelin basic proteins has been demonstrated in a myelin-like membrane fraction isolated from reaggregating and surface adhering, primary cultures of cells dissociated from embryonic mouse brain. Only the large and small components of myelin basic proteins were found to be phosphorylated when myelin-like membrane fraction was incubated with [gamma-32P]ATP. The protein kinase endogenous to the myelin-like membrane fraction was mainly of the cyclic AMP independent type. There was very little cyclic AMP dependent or cyclic GMP dependent protein kinase activities in this myelin-like fraction. Although the myelin basic proteins were the only endogenous proteins phosphorylated, protein kinase of the myelin-like membrane was capable of catalyzing the phosphorylation of exogenous substrates, such as histones.