Contribution to the crystal chemistry of lead-antimony sulfosalts: Systematic Pb-versus-Sb crossed substitution in the plagionite homologous series, Pb2N-1(Pb1-xSbx)2(Sb1-xPbx)2Sb6S13+2N

The plagionite homologous series contains four well-defined members with the general formula Pb1+2NSb8S13+2N: fülöppite (N = 1), plagionite (N = 2), heteromorphite (N = 3), and semseyite (N = 4). The crystal structure of several natural and synthetic samples of fülöppite, plagionite, and semseyite have been refined through single-crystal X-ray diffraction, confirming the systematic Pb-versus-Sb crossed substitution observed previously in semseyite and fülöppite. This crossed substitution takes place mainly in two adjacent cation sites in the middle of the constitutive SnS-type layer. The substitution coefficient x appears variable, even for a given species, with the highest values observed in synthetic fülöppite samples. The developed structural formula of the plagionite homologues can be given as Pb2N-1(Pb1-xSbx)2(Sb1-xPbx)2Sb6S13+2N. In the studied samples, x varies between ∼ 0.10 and 0.40. In the ribbons within the SnS-type layer, (Pb=Sb) mixing can be considered the result of the combination, in a variable ratio, of two cation sequences, i.e. (Sb-Sb-Sb)-Pb-Sb-(..), major in plagionite and semseyite, and (Sb-Sb-Sb)-Sb-Pb-(..), major in fülöppite and, probably, in heteromorphite. The published crystal structure of synthetic "Pb-free fülöppite"is revised according to this approach. It would correspond to a Na derivative, with a proposed structural formula of (Na0.5Sb0.5)(Na0.2Sb0.8)2(Na0.3Sb0.7)2Sb6S15, ideally Na1.5Sb9.5S15. In fülöppite, increasing x induces a flattening of the unit cell along c, with a slight volume decrease. Such a general Pb-versus-Sb crossed substitution would attenuate steric distortions in the middle of the SnS-type layer of the plagionite homologous series. Crystallization kinetics seem the main physical factor that controls such an isochemical substitution

Potential antidepressant effects of scutellaria baicalensis, hericium erinaceus and rhodiola rosea

Recent studies focused on the pharmacology and feasibility of herbal compounds as a potential strategy to target a variety of human diseases ranging from metabolic to brain disorders. Accordingly, bioactive ingredients which are found within a variety of herbal compounds are reported to produce both neuroprotective and psychotropic activities which may help to combat mental disorders such as depression, anxiety, sleep disturbances and cognitive alterations. In the present manuscript, we focus on three herbs which appear effective in mitigating anxiety or depression with favourable risk-benefit profiles, namely Scutellaria baicalensis (S. baicalensis), Hericium erinaceus (H. erinaceus) and Rhodiola rosea (R. rosea). These three traditional folk medicinal herbs target the main biochemical events that are implicated in mental disorders, mimicking, to some extent, the mechanisms of action of conventional antidepressants and mood stabilizers with a wide margin of tolerability. In detail, they rescue alterations in neurotransmitter and neuro-endocrine systems, stimulate neurogenesis and the synthesis of neurotrophic factors, and they counteract oxidative stress, mitochondrial dysfunction and inflammation. Albeit the encouraging results that emerge from both experimental and clinical evidence, further studies are needed to confirm and better understand the mental-health promoting, and specifically, the antidepressant effects of these herbs

mTOR-related cell-clearing systems in epileptic seizures, an update

Recent evidence suggests that autophagy impairment is implicated in the epileptogenic mechanisms downstream of mTOR hyperactivation. This holds true for a variety of genetic and acquired epileptic syndromes besides malformations of cortical development which are classically known as mTORopathies. Autophagy suppression is sufficient to induce epilepsy in experimental models, while rescuing autophagy prevents epileptogenesis, improves behavioral alterations, and provides neuroprotection in seizure-induced neuronal damage. The implication of autophagy in epileptogenesis and maturation phenomena related to seizure activity is supported by evidence indicating that autophagy is involved in the molecular mechanisms which are implicated in epilepsy. In general, mTOR-dependent autophagy regulates the proliferation and migration of inter-/neuronal cortical progenitors, synapse development, vesicular release, synaptic plasticity, and importantly, synaptic clustering of GABAA receptors and subsequent excitatory/inhibitory balance in the brain. Similar to autophagy, the ubiquitin–proteasome system is regulated downstream of mTOR, and it is implicated in epileptogenesis. Thus, mTOR-dependent cell-clearing systems are now taking center stage in the field of epilepsy. In the present review, we discuss such evidence in a variety of seizure-related disorders and models. This is expected to provide a deeper insight into the molecular mechanisms underlying seizure activit

The crystal structure of alstonite, BaCa(CO3)2: An extraordinary example of 'hidden' complex twinning in large single crystals

Alstonite, BaCa(CO3)2, is a mineral described almost two centuries ago. It is widespread in Nature and forms magnificent cm-sized crystals. Notwithstanding, its crystal structure was still unknown. Here, we report the crystal-structure determination of the mineral and discuss it in relationship to other polymorphs of BaCa(CO3)2. Alstonite is trigonal, space group P31m, with unit-cell parameters a = 17.4360(6), c = 6.1295(2) Å, V = 1613.80(9) Å3 and Z = 12. The crystal structure was solved and refined to R1 = 0.0727 on the basis of 4515 reflections with Fo > 4σ(Fo) and 195 refined parameters. Alstonite is formed by the alternation, along c, of Ba-dominant and Ca-dominant layers, separated by CO3 groups parallel to {0001}. The main take-home message is to show that not all structure determinations of minerals/compounds can be solved routinely. Some crystals, even large ones displaying excellent diffraction quality, can be twinned in complex ways, thus making their study a crystallographic challenge

Generalized Fourier Integral Operators on spaces of Colombeau type

Generalized Fourier integral operators (FIOs) acting on Colombeau algebras are defined. This is based on a theory of generalized oscillatory integrals (OIs) whose phase functions as well as amplitudes may be generalized functions of Colombeau type. The mapping properties of these FIOs are studied as the composition with a generalized pseudodifferential operator. Finally, the microlocal Colombeau regularity for OIs and the influence of the FIO action on generalized wave front sets are investigated. This theory of generalized FIOs is motivated by the need of a general framework for partial differential operators with non-smooth coefficients and distributional data

The crystal structure of alstonite, BaCa(CO3)2: an extraordinary example of 'hidden' complex twinning in large single crystals

AbstractAlstonite, BaCa(CO3)2, is a mineral described almost two centuries ago. It is widespread in Nature and forms magnificent cm-sized crystals. Notwithstanding, its crystal structure was still unknown. Here, we report the crystal-structure determination of the mineral and discuss it in relationship to other polymorphs of BaCa(CO3)2. Alstonite is trigonal, space groupP31m, with unit-cell parametersa= 17.4360(6),c= 6.1295(2) Å,V= 1613.80(9) Å3andZ= 12. The crystal structure was solved and refined toR1= 0.0727 on the basis of 4515 reflections withFo> 4σ(Fo) and 195 refined parameters. Alstonite is formed by the alternation, alongc, of Ba-dominant and Ca-dominant layers, separated by CO3groups parallel to {0001}. The main take-home message is to show that not all structure determinations of minerals/compounds can be solved routinely. Some crystals, even large ones displaying excellent diffraction quality, can be twinned in complex ways, thus making their study a crystallographic challenge

Crystal chemistry of sulfates from the apuan alps (Tuscany, Italy). V. Scordariite, K8(Fe3+0.67 0.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11: A new metavoltine-related mineral

The new mineral species scordariite, K8(Fe3+0.67 0.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11, was discovered in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. It occurs as pseudo-hexagonal tabular crystals, yellowish to brownish in color, up to 0.5 mm in size. Cleavage is perfect on 0001. It is associated with giacovazzoite, krausite, gypsum, jarosite, alum-(K), and magnanelliite. Electron microprobe analyses give (wt %): SO3 47.31, Al2O3 0.66, Fe2O3 24.68, FeO 0.69, Na2O 0.52, K2O 17.36, H2Ocalc 15.06, total 106.28. The partitioning of Fe between Fe2+ and Fe3+ was based on Mössbauer spectroscopy. On the basis of 67 O atoms per formula unit, the empirical chemical formula is (K7.50Na0.34)Σ7.84(Fe3+6.29Al0.26Fe2+0.20)Σ6.75S12.02O50·17H2O. The ideal end-member formula can be written as K8(Fe3+0.67 0.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11. Scordariite is trigonal, space group R-3, with (hexagonal setting) a = 9.7583(12), c = 53.687(7) Å, V = 4427.4(12) Å3, Z = 3. The main diffraction lines of the observed X-ray powder pattern are [d(in Å), estimated visual intensity]: 8.3, strong; 6.6, medium; 3.777, medium; 3.299, medium; 3.189, medium; 2.884, strong. The crystal structure of scordariite has been refined using X-ray single-crystal data to a final R1 = 0.057 on the basis of 1980 reflections with Fo > 4σ(Fo) and 165 refined parameters. It can be described as a layered structure formed by three kinds of layers. As with other metavoltine-related minerals, scordariite is characterized by the occurrence of the [Fe3+3O(SO4)6(H2O)3]5- heteropolyhedral cluster

Crystal-chemistry of sulfates from the Apuan Alps, Tuscany, Italy. VIII. New data on khademite, Al(SO 4)F(H 2 O) 5

Khademite, ideally Al(SO4)F(H2O)5, from the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy, has been characterised through quantitative electron microprobe analysis, micro-Raman spectroscopy and single-crystal X-ray diffraction. Khademite occurs as colourless to whitish tabular crystals, up to 5 mm. Electron microprobe analysis (in wt.%, average of 20 spot analyses) gave: SO3 35.43, Al2O3 21.27, F 6.92, H2Ocalc 39.73, sum 103.35, -O = F 2.92, total 100.43. On the basis of 10 anions per formula unit, assuming the occurrence of 5 H2O groups and 1 (F+OH) atom per formula unit, its chemical formula can be written as Al0.96S1.02O4[F0.84(OH)0.16]Σ1.00·5H2O. The Raman spectrum of khademite is characterised by the occurrence of vibrational modes of SO4 groups and by broad and strong bands due to the O-H stretching modes. Khademite is orthorhombic, space group Pcab, with unit-cell parameters a = 11.1713(2), b = 13.0432(3), c = 10.8815(2) Å, V = 1585.54(5) Å3 and Z = 8. The crystal structure refinement converged to R1 = 0.0293 on the basis of 2359 unique reflections with Fo > 4σ(Fo) and 152 refined parameters. The crystal structure of khademite is characterised by the alternation, along b, of two distinct kinds of {010} layers, one formed by [001] rows of isolated Al-centred octahedra, connected to each other through H bonds, and the other showing isolated SO4 groups. Along b, oxygen atoms belonging to SO4 groups act as acceptor of H bonds from H2O groups coordinating Al atoms. The new data improved the description of the H bonds in khademite and led us to discuss about the possible existence of its (OH)-analogue, rostite. In addition, Raman spectroscopic data were collected on the same crystal used for the crystal-chemical characterisation, allowing a comparison with previous results

Fractionation of a three-particle mixture by Brownian sieving hydrodynamic chromatography

Particles ranging in size from a few nanometers (exosomes or viruses) to a few micrometers (bacteria or red blood cells) can be sorted using a size-based separation process. One of the simplest techniques is provided by hydrodynamic chromatography (HDC) which typically requires long channels to achieve adequate resolution. A new separation mechanism based on a Brownian sieving effect coupled with HDC has recently been proposed to overcome these limitations. An efficiency improvement of up to 2000 % has been predicted for a two-size mixture. The aim of this work is to study and optimize a modified geometry useful for obtaining the simultaneous separation of a three-size diluted suspension. The results suggest a significant performance improvement, up to 3000 %, over the standard HDC