First-principles study of the structural,elastic and electronic properties of SbXI (X=S,Se, Te) crystals

The structural, elastic, elastic anisotropy and electronic properties of ferroelectric SbSI and paraelectric SbSI, SbSeI and SbTeI crystals were computed using the local density approximation with first-principle calculations, based on density functional theory. The independent elastic constants of SbXI compounds were computed and the results reveal that they are mechanically stable. Some polycrystalline quantities such as bulk modulus, shear modulus, acoustic velocities, Young’s modulus, Poisson’s ratio, elastic anisotropy and elastic Debye temperatures of these compounds were derived from computed elastic constants. Energy band structures show that these compounds have an indirect band gap. The electronic charge distribution and partial density of states of SbXI compounds indicate that the Sb-X bond is typically covalent with a strong hybridization as well as Sb-I compounds that have strong ionic character. The results obtained were compared with experimentally measured values and other theoretical data.     

Electronic, ductile, phase transition and mechanical properties of Lu-monopnictides under high pressures

The structural, elastic and electronic properties of lutatium-pnictides (LuN, LuP, LuAs, LuSb, and LuBi) were analyzed by using full-potential linearized augmented plane wave within generalized gradient approximation in the stable rock-salt structure (B1 phase) with space group Fm-3m and high-pressure CsCl structure (B2 phase) with space group Pm-3m. Hubbard-U and spin-orbit coupling were included to predict correctly the semiconducting band gap of LuN. Under compression, these materials undergo first-order structural transitions from B1 to B2 phases at 241, 98, 56.82, 25.2 and 32.3 GPa, respectively. The computed elastic properties show that LuBi is ductile by nature. The electronic structure calculations show that LuN is semiconductor at ambient conditions with an indirect band gap of 1.55 eV while other Lu-pnictides are metallic. It was observed that LuN shows metallization at high pressures. The structural properties, viz, equilibrium lattice constant, bulk modulus and its pressure derivative, transition pressure, equation of state, volume collapse, band gap and elastic moduli, show good agreement with available data.

Melting, glass transition, and apparent heat capacity of α-d-glucose by thermal analysis

The thermal behaviors of α-d-glucose in the melting and glass transition regions were examined utilizing the calorimetric methods of standard differential scanning calorimetry (DSC), standard temperature-modulated differential scanning calorimetry (TMDSC), quasi-isothermal temperature-modulated differential scanning calorimetry (quasi-TMDSC), and thermogravimetric analysis (TGA). The quantitative thermal analyses of experimental data of crystalline and amorphous α-d-glucose were performed based on heat capacities. The total, apparent and reversing heat capacities, and phase transitions were evaluated on heating and cooling. The melting temperature (T_m) of a crystalline carbohydrate such as α-d-glucose, shows a heating rate dependence, with the melting peak shifted to lower temperature for a lower heating rate, and with superheating of around 25 K. The superheating of crystalline α-d-glucose is observed as shifting the melting peak for higher heating rates, above the equilibrium melting temperature due to of the slow melting process. The equilibrium melting temperature and heat of fusion of crystalline α-d-glucose were estimated. Changes of reversing heat capacity evaluated by TMDSC at glass transition (T_g) of amorphous and melting process at T_m of fully crystalline α-d-glucose are similar. In both, the amorphous and crystalline phases, the same origin of heat capacity changes, in the T_g and T_m area, are attributable to molecular rotational motion. Degradation occurs simultaneously with the melting process of the crystalline phase. The stability of crystalline α-d-glucose was examined by TGA and TMDSC in the melting region, with the degradation shown to be resulting from changes of mass with temperature and time. The experimental heat capacities of fully crystalline and amorphous α-d-glucose were analyzed in reference to the solid, vibrational, and liquid heat capacities, which were approximated based on the ATHAS scheme and Data Bank.     

Roles of electrostatic interaction and dispersion in CH···CH,CH···π, and π···π ethylene dimers

The structural, mechanical, electronic, and optical properties of orthorhombic Bi₂S₃ and Bi₂Se₃ compounds have been investigated by means of first principles calculations. The calculated lattice parameters and internal coordinates are in very good agreement with the experimental findings. The elastic constants are obtained, then the secondary results such as bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, anisotropy factor, and Debye temperature of polycrystalline aggregates are derived, and the relevant mechanical properties are also discussed. Furthermore, the band structures and optical properties such as real and imaginary parts of dielectric functions, energy-loss function, the effective number of valance electrons, and the effective optical dielectric constant have been computed. We also calculated some nonlinearities for Bi₂S₃ and Bi₂Se₃ (tensors of elasto-optical coefficients) under pressure.

Inhibition of glucose transport into brain by phlorizin, phloretin and glucose analogues

An indicator dilution technique with ²²Na⁺ as the intravascular marker was used to measure unidirectional transport of d-[6-³H]glucose from blood into the isolated, perfused dog brain. 18 compounds which are structurally related to glucose were tested for their ability to inhibit glucose transport. The data suggest that no single hydroxyl group is absolutely required for glucose transport, but rather that glucose binding to the carrier probably occurs through hydrogen bonding at several sites (hydroxyls on carbons 1, 3, 4 and 6). In addition, α-d-glucose has higher affinity for the carrier than does β-d-glucose.A separate series of experiments demonstrated that phlorizin and phloretin are competitive inhibitors of glucose transport into brain; however, phloretin is partially competitive and inhibits at lower concentrations than does phlorizin. Inhibition by phlorizin and phloretin is mutually competitive, indicating that these compounds compete for binding to the glucose carrier. Comparison with the results reported in the literature for similar studies using the human erythrocyte demonstrates a fundamental similarity between glucose transport systems in the blood-brain barrier and erythrocyte.     

Measuring the microelastic properties of biological material.

We have used the atomic force microscope (AFM) to measure the local rigidity modulus at points on the surface of a section of hydrated cow tibia. These data are obtained either from contrast changes that occur as the contact force is altered, or from force versus distance curves obtained at fixed points. These two methods yield the same values for rigidity modulus (at a given point). At low resolution, the elastic morphology and topography mirror the features seen in optical and electron micrographs. At high resolution we see dramatic variations in elastic properties across distances as small as 50 nm.     

Structural, electronic, and elastic properties of K-As compounds: a first principles study

First-principle calculations are performed to investigate the structural, elastic and electronic properties of K-As compounds (KAs in NaP, LiAs and AuCu-type structures, KAs(2) in MgCu(2)-type structure, K(3)As in Na(3)As, Cu(3)P and Li(3)Bi-type structures, and K(5)As(4) in A(5)B(4)-type structure). The lattice parameters, cohesive energy, formation energy, bulk modulus, and the first derivative of bulk modulus (to fit to the Murnaghan's equation of state) of the considered structures are calculated and reasonable agreement is obtained, and the phase transition pressure is also predicted. The repeated calculations on the electronic band structures and the related partial density of states are also given. The calculated second-order elastic constants based on the stress-strain method and the other related quantities such as Young's modulus, shear modulus, Poisson's ratio, sound velocities, Debye temperature, and shear anisotropy factors for considered structures are presented, and trends are discussed.     

Cryoprotection of red blood cells by 1,3-butanediol and 2,3-butanediol

1,3-Butanediol and 2,3-butanediol have been used in buffered solutions with 20, 30, or 35% (w/w) alcohol to cool erythrocytes to -196 degrees C at different cooling rates between 1 to 3500 degrees C/min, followed by slow or rapid rewarming. 1,3-butanediol shows the same shapes of red blood cell survival curves as 1,2-propanediol. Having nearly the same physical properties, they have comparable effects on cell survival. The classical maximum of survival for intermediate cooling rates and an increase for the highest cooling rates are observed. This increase seems to be correlated with the glass-forming tendency of the solution. After the fastest cooling rates, a warming rate of 5000 degrees C/min is sufficient to avoid cell damage, but a warming rate of 100-200 degrees C/min is not. Yet both of these rates would be insufficient to avoid the intracellular ice crystallization on warming. The damage on warming after fast cooling seems once again to be correlated with the transition from cubic to hexagonal ice. For all our results, 1,3-butanediol is like a "second" 1,2-propanediol and could be useful as a cryoprotectant for preservation by total vitrification. 2,3-Butanediol always gives extremely low survival rates, though it presents good physical properties. The crystallization of its hydrate seems to be lethal on cooling or on rewarming.     

Recent advances in ZnO nanostructure as a gas-sensing element for an acetone sensor: a short review

Air pollution is a severe concern globally as it disturbs the health conditions of living beings and the environment because of the discharge of acetone molecules. Metal oxide semiconductor (MOS) nanomaterials are crucial for developing efficient sensors because of their outstanding chemical and physical properties, empowering the inclusive developments in gas sensor productivity. This review presents the ZnO nanostructure state of the art and notable growth, and their structural, morphological, electronic, optical, and acetone-sensing properties. The key parameters, such as response, gas detection limit, sensitivity, reproducibility, response and recovery time, selectivity, and stability of the acetone sensor, have been discussed. Furthermore, gas-sensing mechanism models based on MOS for acetone sensing are reported and discussed. Finally, future possibilities and challenges for MOS (ZnO)-based gas sensors for acetone detection have also been explored.     

Leghemoglobin. Low temperature optical spectra of acid and alkaline forms of leghemoglobin(IV). Configuration of the heme.

Leghemoglobin(IV), the derivative of leghemoglobin at the formal oxidation state IV, when cooled to liquid nitrogen temperature exhibits radically different spectra at acid and alkaline pH. The acid and alkaline forms are freely interconvertible. The optical spectrum of the acid form is closely similar to optical spectra of the red higher oxidation states of horseradish and cytochrome c peroxidases, showing that the configuration of the heme iron is the same throughout this family of compounds. That configuration is believed to be Fe(IV) in a porphyrin environment. The optical spectrum of the alkaline form of leghemoglobin(IV) recalls that of alkaline low spin ferric leghemoglobin. Near infrared spectra of leghemoglobin(IV), myoglobin(IV), and the higher oxidation states of the peroxidases are featureless to 1300 nm, suggesting a common structural feature. The acid form of leghemoglobin(IV), seen in fluid buffer as a transient species at pH 5 or less, is conveniently generated by cooling a solution of the more stable alkaline form in borate buffer to liquid nitrogen temperature. At this temperature borate buffers become acid.     

Role of Molecular Electronic Properties of Some Novel Antimalarial Cyclic Peroxy Ketals in Relation to Potency and Potential Toxicity

Calculated molecular electronicproperties of 20 recently reported cyclic peroxy ketals have been rationalized with their in vitro antimalarial activity with the overall goal to guide the design for safer and effective peroxide-containing antimalarial agents. Stereoelectronicproperties were calculated on the optimized geometry of each compound using the ab initio 3-21G* quantum chemical basis set. Potency appears to be related to electronic properties rather than structural properties such as bond lengths and bond angles though an aliphatic cyclic ring seems to be a structural requirement for potent activity. Electronic properties such as differences in molecular polarity, in electrostatic potential profiles about the peroxide bond and the aromatic ring, in peroxide bond strength, and in the LUMO orbital energy of the molecules are all associated with potency. The three-dimensionalisopotential profile beyondthe van der Waals surface at –10 kcal/mol for the more potent analogs has a distinct large negative potential region by the aromatic ring extending to the methoxy moiety, suggesting a site for initial recognition interaction with the receptor away from the peroxide bond. The HOMO and LUMO isodensity surfaces for all molecules are located on the aromatic ring. The peroxide bond strength of the compounds is around 100 kcal/mol greater than the peroxide-containing clinically used antimalarial artemisinin compounds. In addition, density of the peroxy ketals also appears related to potent activity. The above features of the cyclic peroxy ketals are consistent with these compounds being less potent than the artemisinin compounds, but at the same time are less likely to be as neurotoxic as the artemisinins.     

Experimental and theoretical study on the structure and electronic spectra of imiquimod and its synthetic intermediates

Crystal structure of the imiquimod has been determined by single crystal X-ray analysis, imiquimod crystallizes in orthorhombic space group P2(1)2(1)2(1) and the molecules are linked along the c axis by the strong N-H ... N hydrogen bonds. A density functional theory (DFT) study on the electronic properties of imiquimod and its synthetic intermediates has been performed at B3LYP/6-31G* level, while taking solvent effects into account. Both the single configuration interaction (CIS) method and the time-dependent DFT (TDDFT) approaches have been used to calculate the electronic absorption spectra, and there is a good agreement between the calculated and experimental UV-visible absorption spectra. The fluorescence emission spectra of these three compounds in solution have also been measured, the relatively low fluorescence intensity is attributed to a chlorine-modulated heavy atom effect that enhances intersystem crossing between excited singlet and triplet states, and the relatively high fluorescence intensity of imiquimod results from an extended pi-conjugated system which enhances S(1)-->S(0) radiant transition.     

Interactions of anilinoacridines with nucleic acids: effects of substituent modifications on DNA-binding properties

Spectroscopic methods are used to probe the interactions of several anilinoacridine analogues with calf thymus DNA over a wide range of temperatures and sodium chloride concentrations. The structurally similar compounds m-AMSA, AMSA (both active as antitumor agents), and o-AMSA (inactive as an antitumor agent) have been widely studied in their abilities to bind DNA in an intercalative manner. Recent studies from this laboratory reveal distinct differences in the thermodynamic binding mechanisms between m-AMSA and o-AMSA (Wadkins & Graves, 1989), with the m-AMSA-DNA interaction being an enthalpy-driven process while the binding of o-AMSA to DNA is characterized by more positive entropy values. To further examine the physical chemical properties associated with these compounds and their correlation with antitumor activities, an in-depth investigation into the thermodynamic parameters of these compounds and structurally related anilinoacridine analogues was performed. These studies demonstrate that substituent type and position on the aniline ring of the anilinoacridines greatly influences both the affinities of these drugs in binding to DNA and dictates whether the DNA binding is an enthalpy- or entropy-driven process. The differences in thermodynamic mechanisms of binding between the two isomers along with molecular modeling studies reveal the electronic and/or steric factors resulting from the positioning of the methoxy substituent group on the anilino ring directs the DNA-binding properties through orientation of the methanesulfonamido group at the 1' position of the aniline ring. The orientation of this substituent group may result in favorable contacts through hydrogen bonding with neighboring base pairs and ultimately influence the biological effectiveness as an antitumor agent.     

Spatial symmetries in vestibular projections to the uvula-nodulus

The discharge of secondary vestibular neurons relays the activity of the vestibular endorgans, occasioned by movements in three-dimensional physical space. At a slightly higher level of analysis, the discharge of each secondary vestibular neuron participates in a multifiber projection or pathway from primary afferents via the secondary neurons to another neuronal population. The logical organization of this projection determines whether characteristics of physical space are retained or lost. The logical structure of physical space is standardly expressed in terms of the mathematics of group theory. The logical organization of a projection can be compared to that of physical space by evaluating its symmetry group. The direct projection from the semicircular canal nerves via the vestibular nuclei to neck motor neurons has a full three-dimensional symmetry group, allowing it to maintain a three-dimensional coordinate frame. However, a projection may embed only a subgroup of the symmetry group of physical space, which incompletely mirrors the properties of physical space. The major visual and vestibular projections in the rabbit via the inferior olive to the uvula-nodulus carry three degrees of freedom—rotations about one vertical and two horizontal axes—but do not have full three dimensional symmetry. Instead, the vestibulo-olivo-nodular projection has symmetries corresponding to a product of two-dimensional vestibular and one-dimensional optokinetic spaces. This combination of projection symmetries provides the foundation for distinguishing horizontal from vertical rotations within a three dimensional space. In this study, we evaluate the symmetry group given by the physiological organization of the vestibulo-olivo-nodular projection. Although it acts on the same sets of elements and mirrors the rotations that occur in physical space, the physiological transformation group is distinct from the spatial group. We identify symmetries as products of physiological and spatial transformations. The symmetry group shapes the information the projection conveys to the uvula-nodulus; this shaping may depend on a physiological choice of generators, in the same way that function depends on the physiological choice of coordinates. We discuss the implications of the symmetry group for uvula-nodulus function, evolution, and functions of the vestibular system in general.     

Optical and electronic coupling of the redox copper Azurin on ITO-coated quartz substrate

We have investigated the hybrid system constituted by the redox copper protein Azurin integrated with the semiconductor indium tin oxide (ITO) coated on quartz substrate. The system appears to be a good candidate for bio-sensing and bio-optoelectronics applications, especially due to the coupling between the optical and electron transfer features of Azurin with the conductive properties and optical transparency of ITO. The optical, morphological and electrical properties of the system have been investigated by combining optical absorption and transmission, steady-state fluorescence, resonance Raman spectroscopy and scanning probe microscopies. We found that Azurin molecules are firmly anchored on ITO and retain their structural and optical features underlying the physiological electron transfer activity. Scanning tunnelling spectroscopy evidenced a good electric coupling between the protein molecules and the substrate and a concomitant modulation of the ITO semiconductor properties upon deposition of Azurin. Some interplay between the conduction and valence bands of ITO and the electronic levels of Azurin is therefore suggested. These results are of a significant relevance in the perspective of developing bio-nanodevices able to process both optical and electrical signals, in conjugation also with the biorecognition capability of the protein molecules.     

Gas chromatography—mass spectrometry of metabolites in hemodialysis fluid

An analytical method has been developed for the separation and identification of several metabolites in used hemodialysis fluid obtained during the treatment of a uremic patient on the artificial kidney. The procedure involves ion exchange, evaporation, and trimethylsilylation; the derivatized components were studied by combined gas chromatography—mass spectrometry.Twelve compounds were satisfactorily resolved; six were conclusively identified from mass spectral data. The identified components include phosphoric acid, glucopyranurono(6→1)-lactone, citric acid, d-gluconic acid-5-lactone, α-d-glucose, and β-d-glucose. A seventh component was tentatively identified as mannonic acid.     

Elastic-plastic finite elements analysis of transient and residual stresses in ceramo-metal restorations

Transient and residual stresses occurring in partially fixed dental prostheses after the firing process can be calculated with elastic or elastic-plastic finite element analyses (FEA). In this study, firstly, the mechanical and thermal properties at various temperatures of the materials used in a porcelain fused metal (PFM) system were obtained by experimental and literature studies. The effects of viscoelastic and viscoplastic behaviours of the dental porcelain at the elevated temperatures were reflected onto its elastic properties. The equivalent heat transfer coefficients were determined experimentally by measuring temperatures and the results were supplied as input to the 3D finite elements analysis. It has been observed that the maximum stresses occur within a short time period after cooling begins and that stresses decrease during the cooling process and remain at a constant value at the end of cooling; these are the thermal residual stresses.     

Hydroxycoumarins as selective MAO-B inhibitors

A series of 3-aryl-4-hydroxycoumarin derivatives was synthesized with the aim to find out the structural features for the MAO inhibitory activity and selectivity. Methoxy and/or chloro substituents were introduced in the 3-phenyl ring, whereas the position 6 in the coumarin moiety was not substituted or substituted with a methyl group or a chloro atom due to their different electronic, steric and/or lipophilic properties. Most of the synthesized compounds presented MAO-B inhibitory activity. The presence of methoxy and chloro groups, respectively in the para and meta positions of the 3-phenyl ring, have an important influence on the inhibitory activity. Moreover, the presence of a chloro atom in the six position of the moiety (compound 7) improved the inhibitor activity as well as its selectivity against MAO-B compared with iproniazide, used as reference compound. Docking experiments were carried out to understand which are the most energetically preferred orientations adopted by compounds 5, 6 and 7 inside the MAO-B binding pocket.