High Temperature Ferromagnetism in a GdAg2 Monolayer.

Materials that exhibit ferromagnetism, interfacial stability, and tunability are highly desired for the realization of emerging magnetoelectronic phenomena in heterostructures. Here we present the GdAg2 monolayer alloy, which possesses all such qualities. By combining X-ray absorption, Kerr effect, and angle-resolved photoemission with ab initio calculations, we have investigated the ferromagnetic nature of this class of Gd-based alloys. The Curie temperature can increase from 19 K in GdAu2 to a remarkably high 85 K in GdAg2. We find that the exchange coupling between Gd atoms is barely affected by their full coordination with noble metal atoms, and instead, magnetic coupling is effectively mediated by noble metal-Gd hybrid s,p-d bands. The direct comparison between isostructural GdAu2 and GdAg2 monolayers explains how the higher degree of surface confinement and electron occupation of such hybrid s,p-d bands promote the high Curie temperature in the latter. Finally, the chemical composition and structural robustness of the GdAg2 alloy has been demonstrated by interfacing them with organic semiconductors or magnetic nanodots. These results encourage systematic investigations of rare-earth/noble metal surface alloys and interfaces, in order to exploit them in magnetoelectronic applications.

Self-assembly of bicomponent molecular monolayers: adsorption height changes and their consequences.

Codeposition of two molecular species [copper phtalocyanine (CuPc, donor) and perfluoropentacene (PFP, acceptor)] on noble metal (111) surfaces leads to the self-assembly of an ordered mixed layer with a maximized donor-acceptor contact area. The main driving force behind this arrangement is assumed to be the intermolecular C-H ⋯ F hydrogen-bond interactions. Such interactions would be maximized for a coplanar molecular arrangement. However, precise measurement of molecule-substrate distances in the molecular mixture reveals significantly larger adsorption heights for PFP than for CuPc. Most surprisingly, instead of leveling to increase hydrogen-bond interactions, the height difference is enhanced in the blends as compared to the heights found in single-component CuPc and PFP layers. The increased height of PFP in mixed layers points to an overall reduced interaction with the underlying substrate, and its influence on electronic properties like the interface dipole is investigated through work function measurements.

Tuning the carrier injection barrier of hybrid metal-organic interfaces on rare earth-gold surface compounds.

Magnetic hybrid metal-organic interfaces possess a great potential in areas such as organic spintronics and quantum information processing. However, tuning their carrier injection barriers on-demand is fundamental for the implementation in technological devices. We have prepared hybrid metal-organic interfaces by the adsorption of copper phthalocyanine CuPc on REAu2 surfaces (RE = Gd, Ho and Yb) and studied their growth, electrostatics and electronic structure. CuPc exhibits a long-range commensurability and a vacuum level pinning of the molecular energy levels. We observe a significant effect of the RE valence of the substrate on the carrier injection barrier of the hybrid metal-organic interface. CuPc adsorbed on trivalent RE-based surfaces (HoAu2 and GdAu2) exhibits molecular level energies that may allow injection carriers significantly closer to an ambipolar injection behavior than in the divalent case (YbAu2).

Serotonin 5-HT2A, 5-HT2c and 5-HT1A receptor involvement in the acute effects of psilocybin in mice. In vitro pharmacological profile and modulation of thermoregulation and head-twich response.

The psychedelic 5-HT2A receptor (5HT2AR) agonist psilocybin (or the active metabolite psilocin) has emerged as potential useful drug for various neuropsychiatric diseases, with a rapid onset of therapeutic activity. However, the mechanisms responsible for such effects remain incompletely characterized. We aimed to study in vitro pharmacological profile and in vivo acute mechanism of psilocin/psilocybin. Competition binding studies with psilocin were performed in brain and cell cultures. The role of 5HT2AR, 5-HT2C receptors (5HT2CR) and 5-HT1A receptors (5HT1AR) on the psychosis-like head-twitch response (HTR) and on body temperature in mice after psilocybin administration were evaluated. Psilocin showed similar affinities for 5HT2AR (Ki: 120-173 nM), 5HT2CR (Ki: 79-311 nM) and 5-HT1AR (Ki: 152-146 nM) in human and mice brain. Psilocybin induced a dose-dependent HTR (maximal effect 17.07 ± 1.31 at 1 mg/kg i.p.) that was completely suppressed by the 5HT2AR antagonist MDL11939 (1 mg/kg). Higher doses of psilocybin (3 mg/kg) induced lower HTR (9.00 ± 0.53). The 5HT2CR antagonist SB242084 (0.1 mg/kg) increased HTR exerted by psilocybin (3 mg/kg). Psilocybin significantly raised core body temperature at low dose (0.125 mg/kg) (Emax=0.67 ± 0.15 °C), whereas a significant decrease was induced by doses over 1 mg/kg (Emax = -1.31 ± 0.16 °C). Pre-treatment with the 5HT1AR antagonist WAY100635 reversed the decrease of body temperature after psilocybin (1 mg/kg), causing hyperthermia (Emax = 0.94 ± 0.26 °C). The present work provides key findings on the 5HT2AR, 5-HT2CR and 5HT1AR involvement in the acute central effects of psilocybin. The results may be relevant for understanding the mechanism of action underlying the therapeutic effects and side effects of this psychedelic drug.

Lifshitz transition across the Ag/Cu(111) superlattice band gap tuned by interface doping.

The two-dimensional, free-electron-like band structure of noble metal surfaces can be radically transformed by appropriate nanostructuration. A case example is the triangular dislocation network that characterizes the epitaxial Ag/Cu(111) system, which exhibits a highly featured band topology with a full band gap above E(F) and a hole-pocket-like Fermi surface. Here we show that controlled doping of the Ag/Cu(111) interface with Au allows one to observe a complete Lifshitz transition at 300 K; i.e., the hole pockets fill up, the band gap entirely shifts across E(F), and the Fermi surface becomes electron-pocket-like.

Correction: Influence of 4f filling on electronic and magnetic properties of rare earth-Au surface compounds.

Correction for 'Influence of 4f filling on electronic and magnetic properties of rare earth-Au surface compounds' by L. Fernandez et al., Nanoscale, 2020, 12, 22258-22267, DOI: 10.1039/D0NR04964F.

Rare-earth surface alloying: a new phase for GdAu2.

Surface alloying is a powerful way of varying physical and chemical properties of metals, for a number of applications from catalysis to nuclear and green technologies. Surfaces offer many degrees of freedom, giving rise to new phases that do not have a bulk counterpart. However, the atomic characterization of distinct surface compounds is a major task, which demands powerful experimental and theoretical tools. Here we illustrate the process for the case of a GdAu2 surface phase of extraordinary crystallinity. The combined use of surface-sensitive techniques and state-of-the-art ab initio calculations disentangles its atomic and electronic properties. In particular, the stacking of the surface layers allows for gadolinium's natural ferromagnetic state, at variance with the bulk phase, where frustration leads to antiferromagnetic interlayer coupling.

Copper-phthalocyanine based metal-organic interfaces: the effect of fluorination, the substrate, and its symmetry.

Metal-organic interfaces based on copper-phthalocyanine monolayers are studied in dependence of the metal substrate (Au versus Cu), of its symmetry [hexagonal (111) surfaces versus fourfold (100) surfaces], as well as of the donor or acceptor semiconducting character associated with the nonfluorinated or perfluorinated molecules, respectively. Comparison of the properties of these systematically varied metal-organic interfaces provides new insight into the effect of each of the previously mentioned parameters on the molecule-substrate interactions.

Relationship between non-functional masticatory activity and central dopamine in stressed rats.

In humans, diurnal tooth-clenching and other oral stereotyped behaviour are associated with stress/anxiety. In rodents, gnawing/biting of objects is observed during exposure to stress. Both nigrostriatal and mesocortical dopaminergic systems are involved in the development of this coping behaviour. To clarify the relationship between central dopaminergic activity and stress-induced parafunctional masticatory behaviour, using microdialysis in vivo, we assessed the changes in extracellular dopamine concentrations in both prefrontal cortex and striatum of rats subjected to a mild tail pinch. The animals were divided into two groups according to the degree of non-functional masticatory activity (NFMA) displayed during exposure to tail pinch. In prefrontal cortex, rats which displayed severe NFMA showed a greater increase in extracellular dopamine concentration in relation to basal values (Emax=184±26%) than those which did not display this coping behaviour (Emax=139± 23%) (F(NFMA) [1,86]=3·97; P<0·05) (n=17). A positive association was also found between cortical dopamine maximal value from baseline and the degree of NFMA displayed (r=0·36; P<0·05) (n=17). There were no significant differences in the tail-pinch-induced striatal dopamine increase between both groups of rats (Emax=130±10%) (n=17). These results provide further evidence in support of prefrontal dopamine playing a relevant role in the expression of stress-induced masticatory coping behaviour.

Influence of 4f filling on electronic and magnetic properties of rare earth-Au surface compounds.

One-atom-thick rare-earth/noble metal (RE-NM) compounds are attractive materials to investigate two-dimensional magnetism, since they are easy to synthesize into a common RE-NM2 structure with high crystal perfection. Here we perform a comparative study of the GdAu2, HoAu2, and YbAu2 monolayer compounds grown on Au(111). We find the same atomic lattice quality and moiré superlattice periodicity in the three cases, but different electronic properties and magnetism. The YbAu2 monolayer reveals the characteristic electronic signatures of a mixed-valence configuration in the Yb atom. In contrast, GdAu2 and HoAu2 show the trivalent character of the rare-earth and ferromagnetic transitions below 22 K. Yet, the GdAu2 monolayer has an in-plane magnetic easy-axis, versus the out-of-plane one in HoAu2. The electronic bands of the two trivalent compounds are very similar, while the divalent YbAu2 monolayer exhibits different band features. In the latter, a strong 4f-5d hybridization is manifested in neatly resolved avoided crossings near the Fermi level. First principles theory points to a residual presence of empty 4f states, explaining the fluctuating valence of Yb in the YbAu2 monolayer.

Self-assembly of heterogeneous supramolecular structures with uniaxial anisotropy.

Uniaxial anisotropy in two-dimensional self-assembled supramolecular structures is achieved by the coadsorption of two different linear molecules with complementary amine and imide functionalization. The two-dimensional monolayer is defined by a one-dimensional stack of binary chains, which can be forced to line up along steps in vicinal surfaces. The competing driving forces in the self-organization process are discussed in light of the structures observed during single molecule adsorption and coadsorption on flat and vicinal surfaces and the corresponding theoretical calculations.

Cu-Zn-superoxide dismutase activity in Moniezia expansa: inhibition by pyrimidine derivatives.

Copper-zinc, cyanide-sensitive superoxide dismutase (Cu-Zn-SOD) was detected in homogenates of Moniezia expansa. The enzyme was purified by a sequence of multiple differential centrifugations, ammonium sulphate precipitation, ion-exchange and G-75 Sephadex column chromatography. The final enzyme preparation had a specific activity of 623.00 +/- 9.97U per mg protein and, after isolation, a single-staining band on acrylamide-SDS gels was detected which coincided with enzyme activity. The inhibitory activities of several benzimidazoles and several novel pyrimidine derivatives were determined on purified extracts of the M. expansa Cu-Zn-SOD. The results indicated that the percentage inhibition of Cu-Zn-SOD by some pyrimidine derivatives (6-amino-1, 3-dimethyl-5-nitroso-uracil, 6-amino-5-methyl-5-nitroso-uracil and 5-amino-uracil) was markedly higher than inhibition with the benzimidazoles.

Cellular distribution, purification and electrophoretic properties of malate dehydrogenase in Trichuris ovis and inhibition by benzimidazoles and pyrimidine derivatives.

High levels of malate dehydrogenase were found in Trichuris ovis. Two molecular forms of the enzyme, of different cellular location and electrophoretic pattern, were isolated and purified. The activity of soluble malate dehydrogenase was greater than that of mitochondrial malate dehydrogenase. Both forms also displayed different electrophoretic profiles in comparison with purified extracts from goat (Capra hircus) liver. Substrate concentration directly affected enzyme activity. Host and parasite malate dehydrogenase activity were both inhibited by a series of benzimidazoles and pyrimidine-derived compounds, some of which markedly reduced parasite enzyme activity, but not host enzyme activity. Percentage inhibition by some pyrimidine derivatives was greater than that produced by benzimidazoles.

Electrophoretic analysis of gene-enzyme systems in Chabertia ovina.

In Chaberia ovina species an electrophoretic study of 15 loci of the following enzymes has been conducted: glucose phosphate isomerase, mannose phosphate isomerase, glucose-6-phosphate dehydrogenase, glutamate-oxaloacetate transaminase, superoxide dismutase, isocitrate dehydrogenase, hexokinase, adenylate kinase, malate dehydrogenase, malic enzyme, carbonic anhydrase and 6-phosphogluconate dehydrogenase. The genetic variability has been relatively high, with 40% polymorphism values noted, an 0.10 mean heterozygosity observed and an 0.17 mean heterozygosity expected. The greater part of the allele frequencies were not in Hardy-Weinberg equilibrium.

Behavioral, neurochemical and morphological changes induced by the overexpression of munc18-1a in brain of mice: relevance to schizophrenia.

Overexpression of the mammalian homolog of the unc-18 gene (munc18-1) has been described in the brain of subjects with schizophrenia. Munc18-1 protein is involved in membrane fusion processes, exocytosis and neurotransmitter release. A transgenic mouse strain that overexpresses the protein isoform munc18-1a in the brain was characterized. This animal displays several schizophrenia-related behaviors, supersensitivity to hallucinogenic drugs and deficits in prepulse inhibition that reverse after antipsychotic treatment. Relevant brain areas (that is, cortex and striatum) exhibit reduced expression of dopamine D(1) receptors and dopamine transporters together with enhanced amphetamine-induced in vivo dopamine release. Magnetic resonance imaging demonstrates decreased gray matter volume in the transgenic animal. In conclusion, the mouse overexpressing brain munc18-1a represents a new valid animal model that resembles functional and structural abnormalities in patients with schizophrenia. The animal could provide valuable insights into phenotypic aspects of this psychiatric disorder.

Understanding Periodic Dislocations in 2D Supramolecular Crystals: The PFP/Ag(111) Interface.

In-plane dislocation networks arise in both inorganic and organic films as a way of relieving the elastic strain that builds up at the substrate interface. In molecule/surface systems, supramolecular interactions are weak and more complex (compared to the atomic bonds in inorganic films), and their interplay with molecule-substrate interactions is very subtle, making it difficult to single out the driving force for a nanoscale dislocation pattern. On the basis of a combined experimental and theoretical work, we here show that periodic dislocations in a molecular PFP film are mainly driven by the optimization of molecule-substrate interactions. Compared to inorganic networks however, it implies a much lower energy imbalance, allowing a thermally induced transition from a low-energy strain dislocation pattern to a high-energy incommensurate moiré.

Lateral engineering of surface states - towards surface-state nanoelectronics.

Patterned metal surfaces can host electron quantum waves that display interference phenomena over distances of a few nanometres, thus providing excellent information carriers for future atomic-scale devices. Here we demonstrate that collimation and waveguiding of surface electrons can be realized in silver-induced strain dislocation networks on Cu(111) surfaces, as a conceptual proof-of-principle of surface-state nanoelectronics (SSNE). The Ag/Cu(111) system exhibits featured surface bands with gaps at the Fermi energy, which are basic requirements for a potential SSNE material. We establish a solid analogy between the behavior of surface-state electrons and surface plasmons in patterned metal surfaces, thus facilitating the transfer of existing knowledge on plasmonic structures to the new scenario presented by engineered electronic surface-state nanostructures, with the advantage of a 1000-fold reduction in wavelength and geometrical parameters.