Stable Arrangement Research Articles

Numerical study of the defect adamantine compound CuGaGeSe4

ABSTRACTThe electronic structure, elastic and optical properties of the defect adamantine compound CuGaGeSe4 in structure are systematically investigated using first-principles calculations. Through detailed calculation and comparison, we obtain three independent atomic arrangements and predict the most stable atomic arrangement according to the lattice constants and enthalpy formation energies. The elastic constants are calculated, which can be used to predict the axial thermal expansion coefficients accurately. The optical properties of compound CuGaGeSe4, including the dielectric function, refractive index and absorption spectrum, are depicted for a more intuitive understanding. Our calculated zero-frequency limits ϵ1(0) and n(0) are very close to the other theoretical values, which proves that our calculations are reliable.

Surface-driven first-step events of nanoscale self-assembly for molecular peptide fibers: An experimental and theoretical study.

New experimental results are reported on the self-assembling behavior of EAK16-II, the first discovered ionic self-complementary peptide, incubated at ultralow concentration (10-6 M) at neutral pH onto differently charged surfaces. It is found that strongly negatively charged surfaces promote the self-assembly of flat, micrometer-long mono-molecular fibers of side-on assembled sequences, lying onto a continuous monolayer of flat-on EAK16-II molecules. These results suggest that the monomolecular EAK16-II self-assembly is driven by the peculiar matching condition between peptide and surface electrostatic properties. Molecular Mechanics simulations of the basic bimolecular interactions confirmed the experimental inferences, showing that the flat-on state is the most stable arrangement for two interacting EAK16-II sequences onto strongly negatively charged surfaces, where indeed EAK16-II β-sheet conformation is stabilized, while the weak electrostatic interactions with mildly charged substrates promote an "entangled" EAK16-II geometry. Molecular Dynamics simulations further showed that the mobility and diffusional freedom of the peptides from the surfaces are ruled by the relative strength of peptide-surface electrostatic interactions, so that desorption probability for the peptide sequences is negligible from strongly-charged surfaces and high from mildly-charged surfaces. Furthermore, it has been found that an oligopeptide sequence lying onto two flat-on EAK16-II molecules, gains a remarkable lateral mobility, while remaining weakly bound to the surface, thus allowing the further molecular self-alignment responsible for the micrometer-long fiber formation. The reported results pave the way to the understanding and control of the subtle peptide-surface structural motifs matching enabling the formation of micrometer-long, but nanometer-wide monomolecular fibers.

Experimental comparative study of solvent effects on the structure of two sulfonated resorcinarenes

The conformational behaviours of two samples of sulfonated resorcin[4]arene, tetrasodium 5,11,17,23-tetrakissulfonatemethylen-2,8,14,20-tetra(butyl)resorcinarene and tetrasodium 5,11,17,23-tetrakissulfonatemethylen-2,8,14,20-tetra(2(methylthio)ethyl)resorcin[4]arene were studied in deuterated dimethylsulfoxide ((CD3)2SO), deuterated methyl alcohol (MeOD), and deuterium oxide (D2O). Our NMR analysis was based on the assignment of 1H and 13C signals of the molecules in the three solvents. In this way, different behaviours of the molecules were revealed in these solvents. In (CD3)2SO, it was possible to define stable crown conformational arrangements for both solutes, whereas in D2O, a greater conformational freedom was enabled by the signals of the methylene bridge and the aromatic region, and it was shown that sulfonated resorcinarene still had some conformational mobility at low temperatures. 13C NMR data confirmed the presence of two conformers in the aqueous solution. In the MeOD solution, one of these solutes exhibited two conformational forms, while for the other, only one conformational isomer was observed. Comparison of the behaviours of these two sulfonated resorcin[4]arenes allowed for seeing how the effect of the substituent on the lower rim played an important role in the stability of the conformers, and the study of the thermodynamic properties in water allowed for interpreting these results in terms of the interactions in solution.

Epitaxial growth of ReS2(001) thin film via deposited-Re sulfurization

In this paper, we present the formation of large-size rhenium disulfide (ReS2) films via the sulfurization of Re films deposited on sapphire substrates. The effects of sulfurization temperature and pressure on the crystal quality were investigated. A [001]-oriented single crystal of ReS2 films with 6 × 10 mm2 area was realized. By sulfurizing Re films at 1100 °C, ReS2 films with well-defined sharp interfaces to c-plane sapphire substrates could be formed. Below and above the sulfurization temperature of 1100 °C, incomplete sulfurization and film degradation were observed. The twofold symmetry of the monocrystalline in-plane structure composed of Re–Re bonds along with Re–S bonds pointed to a distorted 1T structure, indicating that this structure is the most stable atomic arrangement for ReS2. For a S/Re compositional ratio equal to or slightly lower than 2.0, characteristic Raman vibrational modes with the narrowest line widths were observed. The typical absorption peak of ReS2 can be detected at 1.5 eV.

Formation of β-Cyclodextrin inclusion compound with doxycycline: A theoretical approach

Recently, the inclusion compound formed by doxycycline and modified CD was investigated. In the inclusion compound, the unstable site of doxycycline was protected by the hydrophobic CD cavity. However, the guest arrangement inside CD cavity has not identified. In some situations, the correlation between protons of the guest and host in a 2D-ROESY experiment can be compatible with head and tail spatial arrangements. In the present work, the most stable guest spatial arrangement for the inclusion of doxycycline into β-CD was evaluated at B97-D/6-311++(2d,p) level of theory. For sake of comparison, tetracycline inclusion compound was also studied.

Shared Residence After Separation: A Review and New Findings from the Netherlands

In 2009 the Dutch legislator introduced a law that sought to encourage shared residence. We summarize key findings on shared residence from prior work in the Netherlands, and present new data. Previous research showed that shared residence has increased steadily in recent decades. Our recent estimates revealed that shared residence increased from nearly 20% in 2008 (prereform) to 28% in 2010 (postreform). Official court data showed a decline again to a little over 20% in 2013. We also found shared residence to be less a stable arrangement than mother or father residence. Consistent with earlier studies, parents with shared residence were found to be well‐resourced parents with little conflict and few personal problems. These parents were also more likely to maintain this arrangement, but the instability of shared residence also appeared to be related to practical circumstances and to children's needs. Earlier findings on the consequences of shared residence for child and parent well‐being were mixed, but suggest positive effects.

On the interaction of cyanoformaldehyde with HNO, HF, HCl, H2O, and CH3OH: A preference for orthogonal structures

The potential energy surfaces of the complexes of cyanoformaldehyde, (formyl cyanide, HCOCN), with HNO, HF, HCl, H2O, and CH3OH have been investigated theoretically at the MP2 and CCSD(T) levels using several extended basis sets. Twenty-two low-lying minima have been detected, seven for HCOCN-HNO, three for each of the HCOCN-HF and HCOCN-HCl dimers, four for HCOCN-H2O and five for the HCOCN-CH3OH complex. The two most stable HCOCN-HNO complexes have non-planar structures as do the most stable arrangements of HCOCN-H2O and HCOCN-CH3OH. The vibrational frequency shifts typical for formyl groups engaged in hydrogen bonding, red shifts of CO stretches and blue shifts of CH stretches, occur in most of the dimers. Similarly, in almost all HCOCN-HNO complexes, the NH stretching frequencies are also blue-shifted. However, in case of the two most stable HCOCN-HNO complexes, red shifts of harmonic NH stretches are calculated. Inclusion of anharmonic contributions reduces these red shifts substantially and in one case converts the red shift to a blue shift. Conventional red shifts of XH (X=F, Cl, O) stretching frequencies and blue shifts for formyl CH stretches are calculated for the complexes with HF, HCl, H2O, and CH3OH.

Ab Initio Studies of Ultrathin Ionic Liquid Films on Au (111) Surface

Room-temperature ionic liquids (RTILs) as alternative electrolytes are of great interest to electrochemical energy storage devices, such as supercapacitors. A key to understanding the performance of these systems is to know the ion arrangement near the electrode surface and the ion-electrode interaction. In this work, we will present our ab initio studies of a few layers of 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (EMMIM TFSI) ionic liquid on gold (111) surface, a system that was recently studied in a novel experiment using low-energy electron and photoemission electron microscopy (LEEM/PEEM). [1] Our work probes different ion arrangements on Au (111) and the corresponding work function change. We further investigate the most stable ion arrangement at different electrode charge densities and identify their out-of-plane layering structure. The dynamics of the ions with reordering and drifting under electric field can be inferred as well. We then use our findings to explain the observed changes in electron reflectivity/photoemission yield in LEEM/PEEM. Together, our results provide important understanding towards the structures and responses of ionic liquids on an electrified metal surface. This research was carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under contract DE-SC0012704. [1] Wattaka Sitaputra, Dario Stacchiola, James F. Wishart, Feng Wang, and Jerzy T. Sadowsk, In situ Probing of Ion Ordering at Electrified Ionic Liquid/Au Interface, Adv. Mater. DOI:10.1002/adma.201606357

Bladder schistosomiasis

Giardia intestinalis, the causative agent of giardiasis, has complex cytoskeleton organization with structures involved in motility, adhesion, cell division, and cell differentiation. Microtubules are key components of the cytoskeleton and are the main elements of the ventral disc, median body, funis, in addition to four pairs of flagella. These cytoskeletal elements are basically stable microtubule arrangements. Although tubulins are the main proteins of these elements, molecular and biochemical analyses of Giardia trophozoites have revealed the presence of several new and not yet characterized proteins in these structures, which may contribute to their nanoarchitecture (mainly in the ventral disc). Despite these findings, morphological data are still required for understanding the organization and biogenesis of the cytoskeletal structures. In the study of this complex and specialized network of filaments in Giardia, two distinct and complementary approaches have been used in recent years: (a) transmission electron microscopy tomography of conventionally processed as well as cryo-fixed samples and (b) high-resolution scanning electron microscopy and helium ion microscopy in combination with new plasma membrane extraction protocols. In this review we include the most recent studies that have allowed better understanding of new Giardia components and their association with other filamentous structures of this parasite, thus providing new insights in the role of the cytoskeletal structures and their function in Giardia trophozoites.

Beyond icosahedral symmetry in packings of proteins in spherical shells

The formation of quasi-spherical cages from protein building blocks is a remarkable self-assembly process in many natural systems, where a small number of elementary building blocks are assembled to build a highly symmetric icosahedral cage. In turn, this has inspired synthetic biologists to design de novo protein cages. We use simple models, on multiple scales, to investigate the self-assembly of a spherical cage, focusing on the regularity of the packing of protein-like objects on the surface. Using building blocks, which are able to pack with icosahedral symmetry, we examine how stable these highly symmetric structures are to perturbations that may arise from the interplay between flexibility of the interacting blocks and entropic effects. We find that, in the presence of those perturbations, icosahedral packing is not the most stable arrangement for a wide range of parameters; rather disordered structures are found to be the most stable. Our results suggest that (i) many designed, or even natural, protein cages may not be regular in the presence of those perturbations and (ii) optimizing those flexibilities can be a possible design strategy to obtain regular synthetic cages with full control over their surface properties.

Minority (dis)advantage in population games

We identify a novel ‘cultural red king effect’ that, in many cases, results in stable arrangements which are to the detriment of minority groups. In particular, we show inequalities disadvantaging minority groups can naturally arise under an adaptive process when minority and majority members must routinely determine how to divide resources amongst themselves. We contend that these results show how inequalities disadvantaging minorities can likely arise by dint of their relative size and need not be a result of either explicit nor implicit prejudices, nor due to intrinsic differences between minority and majority members.

When equity matters for marital stability: Comparing German and U.S. couples.

Comparing West Germany and the United States, we analyze the association between equity - in terms of the relative gender division of paid and unpaid work hours - and the risk of marriage dissolution. Our aim is to identify under what conditions equity influences couple stability. We apply event-history analysis to marriage histories using data from the German Socio-Economic Panel for Western Germany and the Panel Study of Income Dynamics for the United States for the period 1986 to 2009. For the United States, we find that deviation from equity is particularly destabilizing when the wife under-benefits, and when both partners' paid work hours are similar. In West Germany, equity is less salient. Instead we find that the male breadwinner model remains the single most stable arrangement.

An insight into the molecular mechanism of the temporary enhancement effect of isopulegol decanoate on the skin

Chemical enhancers are widely used to facilitate drug permeation in transdermal drug delivery system (TDDS) and the effect of chemical enhancers is desired to be temporary. Though temporary enhancement effect of chemical enhancers has been widely discussed, there is still a lack of knowledge about the molecular mechanism of temporary enhancement effect. Using the skin permeation of flurbiprofen as a probe, the temporary enhancement effect of isopulegol decanoate (ISO-10) was evaluated with in vitro permeation experiment and confocal laser scanning microscopy (CLSM). In addition, molecular mechanism of skin recovery was explored with skin retention of ISO-10, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), molecular dynamic (MD) simulation and transepidermal water loss (TEWL). Temporary enhancement effect of ISO-10 was observed by the permeation of flurbiprofen after the treatment of 180min. Furthermore, temporary enhancement effect of ISO-10 on the diffusion of intercellular lipid in the stratum cornuem (SC) was observed by ATR-FTIR, molecular dynamic (MD) simulation. The SC barrier function recovered with the existence of ISO-10 in the lipid bilayer as indicated by the retention study and TEWL. In conclusion, the lipid bilayer accepted the enhancer as a new component to form a new stable arrangement, resulted the recovery of the skin barrier function. This work processed a novel mechanism of the recovery of skin barrier function after the addition of chemical enhancers.

Fluoride-mediated synthesis of TON and MFI zeolites using 1-butyl-3-methylimidazolium as structure-directing agent

In this work, 1-butyl-3-methylimidazolium (1B3MI) cation has been employed as a structure-directing agent for the synthesis of pure silica and Ti-containing zeolites in fluoride media. The 1B3MI OSDA exhibited distinct phase selectivity depending on the synthesis conditions, and particularly the concentration of the synthesis gel. Thus, under more diluted conditions (H2O/SiO2 = 14), the 1B3MI cation yielded pure silica TON zeolite with high crystallinity. Attempts to obtain Ti-containing zeolites, however, failed at this diluted condition even after 15 days of synthesis. In contrast, highly crystalline Ti-MFI was the only phase obtained upon reducing the H2O/SiO2 molar ratio from 14 to 7. The presence of Ti in the MFI zeolite framework was confirmed by both infrared and DRS UV-vis spectroscopies. The presence of intact OSDA molecules within the micropores was inferred from elemental analysis and 13C CP-MAS NMR spectroscopy. On the other hand, thermogravimetric analyses showed a different packing of the 1B3MI cation in the pure silica TON and Ti-MFI samples. Moreover, the environments for Si and F species in the as-made materials were investigated by means of 29Si and 19F MAS NMR, respectively. Finally, molecular simulations showed that the most stable arrangement of the 1B3MI cations involves the location of the imidazolium rings on the channel intersections and of the butyl chains on the sinusoidal channels.

Electrospray‐Ionisation Mass‐Spectrometric (ESI‐MS) Investigation of Beryllium Hydrolysis in Acidic Solutions of Beryllium Sulfate

The speciation and hydrolysis of beryllium ions in an aqueous solution of its sulfate salt have been studied over a pH range of 2.5–6.0 by using electrospray ionisation mass spectrometry (ESI‐MS). Ions observed by ESI‐MS revealed that the highly charged beryllium hydroxido species in solution were preserved into the gas phase by pairing with the sulfate ion. The pH‐dependent hydrolytic tendencies of the Be2+ cation presented as an ESI‐MS speciation diagram were in good agreement with previous speciation data, suggesting the ability of ESI‐MS to be developed as a quick, sensitive and safe screening technique to observe beryllium speciation with ligands of interest at low concentrations. Collision‐induced dissociation patterns further supported the trimer [Be3(OH)3]3+ as the most stable beryllium hydroxide species arrangement while the pronounced association of the beryllium cation and sulfato ligand yielded additional beryllium cluster arrangements such as {Be3(µ3‐O)} clusters and mixed sulfato/hydroxido species such as [Be3O(HSO4)3]+.

The structure of Cu(II) and Hg(II) complexes of bispyrenyl azine revisited.

Azine ligands show preference for the antiperiplanar conformation, but their 2:2 ligand-metal complexes can exhibit a central N4M2 core in the most stable chair arrangement, as in the case of the model lithium complex, with the ligand displaying a synclinal conformation that is not stable in the free ligand. According to DFT calculations, complexation of Cu2+ with bis(1-pyrenyl)azine (1) affords a C2-symmetric [1·Cu2+]2 species with a planar central N4Cu2 core exhibiting a weak cuprophilic interaction. The pendant pyrenyl substituents are brought close and parallel to each other, therefore accounting for the π-stacking that is responsible for excimer fluorescence. In case of Hg2+, complexation by the same ligand affords a C2-symmetric complex with an essentially linear N-Hg-C coordination environment at every metal center and without intermetallic interaction. T-Stacking interactions between pyrenyl groups explain the overall rigidity required for enhancement of fluorescence. Graphical abstract The structures of 2:2 complexes of Hg(II) and Cu(II) with bispyrenyl azine are reported.

Insights on molecular structure and micro-properties of alkali-activated slag materials: A reactive molecular dynamics study

The material design of the alkali activated slag (AAS) contributes to the development of the sustainable “Green Building Materials” for the recycle of industrial waste and energy reservation of cement materials production. A computational simulation technique based on reactive molecular dynamics proposed a new view of molecular structure for the main hydrate, C-A-S-H gel, in AAS. In this paper, structure, dynamics and mechanical properties of C-A-S-H gel have been investigated. The proposed C-A-S-H model exhibits heterogeneity layered features with ordered and stable atomistic arrangement in the calcium sheets and disordered chemical connections in the interlayer region. Structurally, Al atoms bridge the neighboring oxygen atoms in the defective silicate chains, contributing to the polymerization of the C-A-S-H gel. The increase of Al or Si can significantly enhance the mean silicate chain length of the structure, and the introduction of Al atoms in the interlayer region can improve the mechanical properties of the C-A-S-H gel. Therefore, the mean chain length can be taken as important parameter to guide the high performance AAS materials design.

Complexation and Electronic Communication between Corannulene-Based Buckybowls and a Curved Truxene-TTF Donor.

The association behavior of an electron-donating, bowl-shaped, truxene-based tetrathiafulvalene (truxTTF) with two corannulene-based fullerene fragments, C32 H12 and C38 H14 , is investigated in several solvents. Formation of 1:1 complexes is followed by absorption titrations and complemented by density functional theory (DFT) calculations. The binding constants are in the range log Ka =2.9-3.5. DFT calculations reveal that the most stable arrangement is the conformation in which the 1,3-dithiole ring of truxTTF is placed inside the concave cavity of the corannulene derivative. This arrangement is confirmed experimentally by NMR measurements, and implies that a combination of π-π and CH-π interactions is the driving force for association. Time-dependent DFT calculations reproduce the experimental UV/Vis titrations and provide a detailed understanding of the spectral changes observed. Femtosecond transient absorption studies reveal the processes occurring after photoexcitation of either C32 H12 or C38 H14 and their supramolecular associates with truxTTF. In the case of truxTTF⋅C38 H14 , photoexcitation yields the charge-separated state truxTTF.+ ⋅C38 H14.- with a lifetime of approximately 160 ps.

Fluorescence Evidences for Non-Homogeneity and Residual Structure of Denatured States

About 30 % of human proteins do not fold into a stable 3D arrangement of secondary structure elements, but stay predominantly unfolded -similar to proteins under highly denaturing conditions. These proteins are involved in many cell signaling processes. Their characterization poses a great challenge for current experimental methods as they consist of an ensemble of rapidly interconverting conformations. Intense debate exists on the possibility that they show, to certain extent, residual structure, which might facilitate folding or enhance ligand binding. To study the unfolded state conformational heterogeneity using Forster resonance energy transfer (FRET), we used the lysozyme from the phage T4 (T4L) in denaturing conditions as a model system. We built an elastic network model that spans T4L's topology in order to evaluate local and global conformational changes by combining ensemble (ensemble time-resolved fluorescence lifetime and anisotropy) and single-molecule spectroscopic (multiparameter fluorescence detection, photon distribution analysis, (filtered) fluorescence correlation spectroscopy) methods. Through extensive comparison of models, we identified regions with apparent residual structure under highly denaturing conditions, which might serve as folding nuclei; and additionally we showed that chemically denatured T4L is not a random coil as previously thought. By using obtained distance restraints we determined that denatured T4L shows a native-like mean structure, albeit larger in size compared to the native state. We demonstrate here the necessity of careful data interpretation, but also the potential of a multidimensional approach to characterize an ensemble of states, which can be applied generally to unstructured or denatured proteins.

Historical Perspectives on Precarious Work: The Cases of Egypt and India under British Imperialism

<p>The concept of precarious work is used by social scientists to describe work that is “uncertain, unpredictable, and risky from the point of view of the worker” (Kalleberg, 2009: 2). This paper argues that such work can take a variety of forms, beyond those seen in the transition from the stable post-WWII era to the neo-liberal era in the West. Egypt and India offer instructive case studies. Industrialisation (or lack thereof) in Egypt and India has been thoroughly documented by others. The purpose of this paper is to argue that these developments can be seen as the emergence of precarious, industrial working arrangements. This framework is useful for demonstrating that precarious work has come along with industrial development in a range of countries during different time periods. In this light, the stable employment arrangements characteristic of the post-war West were an anomaly. The global economic and social history of industrialisation is characterised by precarious working arrangements, as seen in colonial-era Egypt and India.</p>