Crystalline Modifications Research Articles

Three-Dimensional Carbon Allotropes Comprising Phenyl Rings and Acetylenic Chains in sp+sp(2) Hybrid Networks.

We here identify by ab initio calculations a new type of three-dimensional (3D) carbon allotropes that consist of phenyl rings connected by linear acetylenic chains in sp+sp2 bonding networks. These structures are constructed by inserting acetylenic or diacetylenic bonds into an all sp2-hybridized rhombohedral polybenzene lattice, and the resulting 3D phenylacetylene and phenyldiacetylene nets comprise a 12-atom and 18-atom rhombohedral primitive unit cells in the symmetry, which are characterized as the 3D chiral crystalline modification of 2D graphyne and graphdiyne, respectively. Simulated phonon spectra reveal that these structures are dynamically stable. Electronic band calculations indicate that phenylacetylene is metallic, while phenyldiacetylene is a semiconductor with an indirect band gap of 0.58 eV. The present results establish a new type of carbon phases and offer insights into their outstanding structural and electronic properties.

Synthesis, Characterization, and Photocatalytic Properties of Sulfur- and Carbon-Codoped TiO2 Nanoparticles.

One-step TiO2 nanoparticle synthesis based on the interaction between thiourea and metatitanic acid is applied for sulfur and carbon anatase codoping. The synthesis of the doped TiO2 has been monitored by means of differential thermal analysis and thermogravimetric analysis (DTA-TG), which allows determining the optimal thermal conditions for the process. Electron microscopy showed micrometer-sized (5–15 μm) randomly distributed crystal aggregates, consisting of many 15–40-nm TiO2 nanoparticles. The obtained phase composition and chemical states of the doping elements are analyzed by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared (IR) and Raman spectroscopies, and electron paramagnetic resonance (EPR). XRD displays in both samples (doped and pristine) the existence of only one crystalline phase—the tetragonal modification of TiO2—anatase. Further data assessment by means of Rietveld refinement allowed detection of a slight c lattice parameter and volume increase related to incorporation of the doping elements. XPS demonstrated the presence of carbon and sulfur as doping elements in the material. It was confirmed that carbon is in elemental form and also present in oxygen-containing compounds, which are adsorbed on the particle surface. The binding energy for sulfur electron core shell corresponds to the established data for sulfate compounds, where sulfur is in 6+ oxidation state. The synthesized S- and C-codoped TiO2 showed excellent photocatalytic performance during the degradation of organic dyes (rhodamine B, methylene blue), gas-phase oxidation of ethanol under visible light, and photocatalytic hydrogen generation from ethanol under ultraviolet light.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1353-5) contains supplementary material, which is available to authorized users.

Electron beam induced rapid crystallization of water splitting nanostructures

ABSTRACTTitanium dioxide (TiO2) loaded with gold (Au) as noble metal, acts as an efficient photocatalyst that has been extensively investigated for water splitting processes. In this paper, we report on the microstructure of atomic layer deposited titanium dioxide and the crystallinity modification of the material using energetic electron beam irradiation. A rapid high-energy electron beam induced crystallization of the nanostructures has been observed in-situ inside a High-Resolution Transmission Electron Microscope (HRTEM). The systematic crystallization of the nanomaterial occurring under the electron beam irradiation (300 KV) indicates the transformation of the near amorphous material into a mixture of two nuances of TiO2 polymorphs, namely rutile and anatase. We believe that this transformation will enhance the efficiency of water splitting process, as the mixed phases of rutile and anatase are known to possess better optical properties than the individual polymorphs of TiO2. This finding may be of particular interest in developing appropriate heat treatment methods for these nanostructures dedicated to water splitting to increase their efficiency.

Synthesis and characterization of new zeolite materials obtained from fly ash for heavy metals removal in advanced wastewater treatment

Waste management and water quality are two of the main problems that humanity faces nowadays. Increased urbanization and industrialization lead to excessive release of wastes into the environment, including fly ash resulted from coal combustion. Fly ash reuse in developing low cost, efficient adsorbents of zeolite-type could support wastewater treatment according to the concept wastes for waste treatment. The ashes converted in zeolite materials were collected from two Combined Heat and Power Plants (CET Brasov and DEVA) from Romania. The zeolite materials were characterized by AFM, XRD, FT-IR, SEM, BET and surface energy measurements to outline the crystalline and morphology modifications. The zeolite-type substrates were obtained by using the fly ashes modified through hydrothermal processes using a low concentration of NaOH, and were further used for heavy metals removal (Cd2+, Ni2+, Cu2+, Zn2+, Pb2+) from synthetic solutions with mono-, bi-, and five-cations. In order to obtain maximum efficiency during the heavy metals removal of the adsorption conditions (contact time, optimum amount of substrate and initial concentration) were optimized. These parameters were further used in the thermodynamic and kinetic modelling of the adsorption processes. Correlated with the surface structure, composition and morphology, the kinetic adsorption mechanisms and the substrate capacities are further discussed.

Crystallinity and crystalline phase orientation of poly(1,4-cis-isoprene) fromHevea brasiliensisandTaraxacum kok-saghyz

Crystallization is studied for poly(isoprene-1,4-cis) from Hevea brasiliensis (natural rubber [NR]) and from taraxacum kok-saghyz, mainly by collecting wide-angle X-ray diffraction patterns after processing and stretching. Although rubber samples before stretching are generally fully amorphous, crystallization can be induced in NR samples by processing at room temperature under moderate pressure. This phenomenon is possibly associated with nucleation by saturated fatty acid components. For rubber samples being fully amorphous in the undeformed state, strain-induced crystallization occurs only at high strain ratios (α > 4), leading to high degrees of crystalline phase orientation (fc > 0.9 for α = 5). Rubber samples presenting some crystallinity already in the unstretched state, on the contrary, reach much lower degrees of axial orientation, even for high strain ratios (fc < 0.7 for α = 5). These differences in crystallinity and in crystalline phase orientations produce large differences in stress–strain behavior of the rubber. By room temperature processing, the considered NR samples can also develop an unreported disordered crystalline modification, with low intensity of 120 and 121 reflections. This disordered crystalline modification, which is also maintained after axial stretching procedures, can rationalized by a structural disorder along the b axis, possibly associated with statistical sequences of A+TA− or A−T A+ conformations for poly(isoprene-1,4-cis) chains. Copyright © 2016 John Wiley & Sons, Ltd.

About different packing states of alkyl groups in comb-like polymers with rigid backbones.

We report a comparative X-ray diffraction study on three series of comb-like polymers with rigid backbones and layered morphologies [regio-regular poly(3-alkyl thiophenes), alkoxylated polyesters, alkoxylated polyphenylenevinylenes] highlighting the importance of the volume per methylene unit VCH2 in alkyl nanodomains for the overall packing state. We demonstrate that there is a large (≈30%) variation in the VCH2 values for different polymer series and packing states but no significant change in VCH2 depending on the length of the alkyl side groups. This calls into question commonly used structural models which are based only on tilting and interdigitation of ideally stretched alkyl side groups. We argue that a linear dependence of the layer spacings with side chain length can also be explained by a constant VCH2 value and unchanged main chain packing. The potential importance of side chain packing for the occurrence of different (liquid-) crystalline modifications in various polymer series and possible interrelations between main and side chain packings are discussed.

Aggregation of α-crystallins in kynurenic acid-sensitized UVA photolysis under anaerobic conditions.

The reactions of photoexcited kynurenic acid (KNA) with bovine α-crystallins under anaerobic conditions proceed via the electron transfer from tryptophan (Trp) and tyrosine (Tyr) residues to the triplet KNA molecules. The subsequent radical reactions lead to the protein aggregation and insolubilization. The absorption of the photolyzed proteins at 335 nm as well as their total fluorescence significantly increases, while the tryptophan-related fluorescence decreases. It has been established that the alterations of the protein optical properties are related to the modifications of Trp residues. Intrinsic lens antioxidants ascorbate (Asc) and glutathione (GSH) that are present in the human lens at the millimolar level effectively block the formation of the observed light-induced protein modifications. The protective effect of Asc was attributed to its ability to quench highly reactive triplet states, while the role of GSH, most likely, corresponds to the reduction of photochemically formed radicals into a diamagnetic state. The results obtained disclose the possible mechanism of UVA-induced modifications of the lens crystallins, leading to the formation of cataract, and the role of major lens antioxidants Asc and GSH in the protection of the lens proteins.

Formation of structure in Au, Cu and Ni nanoclusters: MD simulations

The molecular dynamics method with the modified tight-binding (TB-SMA) potential has been used to study structure formation in gold nanoparticles 1.6-5.0 nm in diameter. The formation of the internal structure of gold nanoclusters is studied in terms of canonical ensembles. The stability boundaries of various crystalline isomers are analyzed. The obtained dependences are compared with the corresponding data obtained for copper and nickel nanoparticles. The structure formation during solidification is found to be characterized by a clear effect of the particle size on the stability of a crystalline modification.

Interaction of βA3-Crystallin with Deamidated Mutants of αA- and αB-Crystallins.

Interaction among crystallins is required for the maintenance of lens transparency. Deamidation is one of the most common post-translational modifications in crystallins, which results in incorrect interaction and leads to aggregate formation. Various studies have established interaction among the α- and β-crystallins. Here, we investigated the effects of the deamidation of αA- and αB-crystallins on their interaction with βA3-crystallin using surface plasmon resonance (SPR) and fluorescence lifetime imaging microscopy-fluorescence resonance energy transfer (FLIM-FRET) methods. SPR analysis confirmed adherence of WT αA- and WT αB-crystallins and their deamidated mutants with βA3-crystallin. The deamidated mutants of αA–crystallin (αA N101D and αA N123D) displayed lower adherence propensity for βA3-crystallin relative to the binding affinity shown by WT αA-crystallin. Among αB-crystallin mutants, αB N78D displayed higher adherence propensity whereas αB N146D mutant showed slightly lower binding affinity for βA3-crystallin relative to that shown by WT αB-crystallin. Under the in vivo condition (FLIM-FRET), both αA-deamidated mutants (αA N101D and αA N123D) exhibited strong interaction with βA3-crystallin (32±4% and 36±4% FRET efficiencies, respectively) compared to WT αA-crystallin (18±4%). Similarly, the αB N78D and αB N146D mutants showed strong interaction (36±4% and 22±4% FRET efficiencies, respectively) with βA3-crystallin compared to 18±4% FRET efficiency of WT αB-crystallin. Further, FLIM-FRET analysis of the C-terminal domain (CTE), N-terminal domain (NTD), and core domain (CD) of αA- and αB-crystallins with βA3-crystallin suggested that interaction sites most likely reside in the αA CTE and αB NTD regions, respectively, as these domains showed the highest FRET efficiencies. Overall, results suggest that similar to WT αA- and WTαB-crystallins, the deamidated mutants showed strong interactionfor βA3-crystallin. Variable in vitro and in vivo interactions are most likely due to the mutant’s large size oligomers, reduced hydrophobicity, and altered structures. Together, the results suggest that deamidation of α-crystallin may facilitate greater interaction and the formation of large oligomers with other crystallins, and this may contribute to the cataractogenic mechanism.

Doped sol–gel films vs. powders TiO2: On the positive effect induced by the presence of a substrate

SiO2 and Ag–SiO2 doped TiO2 films and powders have been produced using a controlled sol–gel process. The dopant has been introduced using an alkoxysilane-functionalized ligand, with or without complexed silver ions. The influence of dopants on physico-chemical properties of the catalysts is studied by XRD, TEM–EDX, DRUV–vis analyses in the case of powders, while GIXRD, XPS, profilometry, UV–vis absorption analyses have been used for thin films. The photocatalytic activity has been evaluated from the degradation of methylene blue under UV-A light in the presence of the different catalysts over a period of 24h. The detailed comparison between powders and films highlights a surprising positive effect in the case of films due to the presence of the substrate. In the case of photocatalytic powders, the presence of SiO2 or Ag–SiO2 into the TiO2 matrix has a detrimental effect on the photocatalytic activity while the opposite tendency is observed in the case of films, with best activities obtained with Ag–SiO2 doping. Different factors, in particular crystallinity modification between powders and films, have been studied to explain these opposite behaviors. In the case of powders, crystallization is hindered by SiO2 and Ag particles incorporation into the TiO2 matrix, leading to a decrease of the photocatalytic activity. In the case of thin films, probably because of the presence of a substrate, crystallization is not influenced by the presence of SiO2 and Ag particles. Therefore, the latter ones can fully play their role of electron traps leading to an enhanced photocatalytic activity.

Site specific oxidation of amino acid residues in rat lens γ-crystallin induced by low-dose γ-irradiation

Although cataracts are a well-known age-related disease, the mechanism of their formation is not well understood. It is currently thought that eye lens proteins become abnormally aggregated, initially causing clumping that scatters the light and interferes with focusing on the retina, and ultimately resulting in a cataract. The abnormal aggregation of lens proteins is considered to be triggered by various post-translational modifications, such as oxidation, deamidation, truncation and isomerization, that occur during the aging process. Such modifications, which are also generated by free radical and reactive oxygen species derived from γ-irradiation, decrease crystallin solubility and lens transparency, and ultimately lead to the development of a cataract. In this study, we irradiated young rat lenses with low-dose γ-rays and extracted the water-soluble and insoluble protein fractions. The water-soluble and water-insoluble lens proteins were digested with trypsin, and the resulting peptides were analyzed by LC-MS. Specific oxidation sites of methionine, cysteine and tryptophan in rat water-soluble and -insoluble γE and γF-crystallin were determined by one-shot analysis. The oxidation sites in rat γE and γF-crystallin resemble those previously identified in γC and γD-crystallin from human age-related cataracts. Our study on modifications of crystallins induced by ionizing irradiation may provide useful information relevant to human senile cataract formation.

Structural mechanisms of the Ih–II and II → Ic transitions between the crystalline phases of aqueous ice

Structural mechanisms are proposed for experimentally observed phase transitions between crystalline modifications of aqueous ice, Ih and II, as well as II and Ic. It is known that the Ih–II transition occurs with the conservation of large structural units (hexagonal channels) common for these ices. It is shown that the Ih → II transition may occur with the conservation of 5/6 of all hydrogen bonds in crystal, including all hydrogen bonds in the retained channels (3/4 of the total number of bonds in crystal) and 1/3 of the bonds between these channels (1/12 of the total number). The transformation of other hydrogen bonds between the retained channels leads to the occurrence of proton order in ice II. A structural mechanism is proposed to explain the transformation of single crystals of ice Ih either into single crystals of ice II or into crystalline twins of ice II with c axes rotated by 180° with respect to each other, which is often observed at the Ih → II transition. It is established that up to 7/12 of all hydrogen bonds are retained at the irreversible cooperative II → Ic transition.

Deamidation of N76 in human γS-crystallin promotes dimer formation

BackgroundCataract formation is often attributed to the build-up of post-translational modifications in the crystallin proteins of the eye lens. One such modification, the deamidation of N76 in human γS-crystallin to D76, is highly correlated with age-related cataract (Hooi et al. Invest. Ophthalmol. Vis. Sci. 53 (2012) 3554–3561). In the current work, this modification has been extensively characterised in vitro. MethodsBiophysical characterisation was performed on wild type and N76D γS-crystallins using turbidity measurements to monitor aggregation, intrinsic fluorescence and circular dichroism spectroscopy to determine the folded state and NMR spectroscopy for identifying local changes in structure. Protein mass was determined using SEC–MALLS and analytical ultracentrifugation methods. ResultsRelative to the wild type protein, deamidation at N76 in γS-crystallin causes an increase in the thermal stability and resistance to thermally induced aggregation alongside a decrease in stability to denaturants, a propensity to aggregate rapidly once destabilised and a tendency to form a dimer. We ascribe the apparent increase in thermal stability upon deamidation to the formation of dimer which prevents the unfolding of the inherently less stable monomer. ConclusionsDeamidation causes a decrease in stability of γS-crystallin but this is offset by an increased tendency for dimer formation. General significanceDeamidation at N76 in human γS-crystallin likely has a combinatorial effect with other post-translational crystallin modifications to induce age-related cataract. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.

Mono- and binuclear Pd(II) complexes with 2-(5,6-dimethyl-4-oxo-3,4-dihydrothieno[2,3-d]pyrimidin-2-yl)-N-phenylhydrazinecarbothioamide: Synthesis, crystal structure and spectroscopic characterization

Two novel Pd2+ mononuclear [Pd(HL)PPh3Cl]·nDMF (1) (n = 1, 2) and binuclear [Pd2(L)2(PPh3)2]·SPPh3·3DMF (2) complexes have been synthesized by reaction of [Pd(PPh3)2Cl2] with 2-(5,6-dimethyl-4-oxo-3,4-dihydrothieno[2,3-d]pyrimidin-2-yl)-N-phenylhydrazinecarbothioamide and characterized by single-crystal X-ray diffraction. Complex 1 has been additionally characterized by 1H NMR, IR and UV–Vis spectroscopy. For the complex 1, two crystalline polymorphic modifications have been found: monoclinic (1a) and more stable triclinic (1b) one, which crystal structure differs by different crystal packing and number of lattice solvent molecules. In both polymorphs, the ligand molecules are coordinated as monoanion in thiol tautomeric form with transferring of thiosemicarbazide proton to nitrogen atom of thienopyrimidine moiety. In the case of complex 2, additional deprotonation of thienopyrimidine nitrogen atom leads to coordination of the ligand as dianion. The crystal structure of 2 also contains one molecule of triphenylphosphine sulfide formed by side reaction. In both complexes “soft” phosphorus atoms of triphenylphosphine molecules are coordinated in trans-positions to more “hard” nitrogen atoms.

Fabrication of hierarchically crystallographic morphologies in isotactic polypropylene

ABSTRACTThe hierarchically crystallographic morphologies were fabricated in isotactic polypropylene (iPP) by controlling the stratified distribution of the nucleating agents. The α‐ and β‐nucleating agents were chosen for preparing the different crystalline modifications. The transcrystals and spherulites were found in the stratified distribution samples by polar optical microscopy (POM) and scanning electron microscope (SEM). The transcrystals grew from the surfaces of the nucleating agents filled layers and occupied most space of the pure iPP layers. The crystalline modifications and crystallinity were analyzed by X‐ray diffraction (XRD) and differential scanning calorimeter (DSC) analysis. The mechanical and thermal degradation properties of these samples with hierarchically crystallographic morphologies were investigated by tensile testing machine and thermogravimetric analysis (TGA) respectively, and showed better than that of the samples with single crystallographic morphology (spherulites). © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42703.

Structure and optical properties of thin poly(p-xylylene) – Silver nanocomposite films prepared by low-temperature vapor deposition polymerization

In this study, variable-temperature grazing-incidence X-ray diffraction, transmission electron and scanning force microscopy were employed to address the semicrystalline structure and surface morphology of thin poly(p-xylylene) – silver nanocomposite films with Ag concentrations up to 12 vol.%. It was observed that the dominant crystalline modification of poly(p-xylylene) in the studied films is α-form, which is in contrast to thick poly(p-xylylene) films deposited at liquid nitrogen temperature where β-form prevails. The films exhibit planar texture that can be further enhanced on annealing. The optical properties of the films were studied by UV–vis and IR-spectroscopy. It was found that the samples display surface plasmon resonance, with the peak wavelength in the range of 435–445 nm. The peak positions undergo a redshift upon a long-term storage under ambient conditions. The IR-spectroscopy reveals the bands, which can be assigned to the vibrations of oxygen-containing groups, with intensity increasing with silver content.

Structural, electrical and luminescent properties of ZnO:Li films fabricated by screen‐printing method on sapphire substrate

AbstractUndoped and Li‐doped ZnO thick films were fabricated by a screen‐printing technique on sapphire substrate. The effect of sintering temperature (TS = 800, 900 and 1000 °C) and Li content ([Li] = 0.003, 0.03 and 0.3 wt%) on the photoluminescence (PL), electrical and structural properties of the films was investigated. The X‐ray diffraction shows that all the films are polycrystalline with a wurtzite structure. It is found that both high sintering temperature and low Li content favour formation of the low‐resistive films with an enhanced UV emission. The high Li content stimulates an appearance of semi‐insulating behaviour of the films and deteriorated PL properties. It is shown that the effect of Li‐doping on light‐emitting properties of the films consists mainly in the modification of the film crystallinity and the engineering of the concentration of intrinsic defects. (© 2015 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Laser Induced Porosity and Crystallinity Modification of a Bioactive Glass Coating on Titanium Substrates

Functionally graded bioactive glass coatings on bioinert metallic substrates were produced by using continuous-wave (CW) laser irradiation. The aim is to achieve strong adhesion on the substrates and high bioactivity on the top surface of a coating material for load-bearing implants in biomedical applications. The morphology and microstructure of the bioactive glass from the laser coating process were investigated as functions of processing parameters. Laser sintering mechanisms were discussed with respect to the resulting morphology and microstructure. It has been shown that double layer laser coating results in a dense bond coat layer and a porous top coat layer with lower degree of crystallinity than an enameling coating sample. The dense bond coat strongly attached to the titanium substrate with a 10 μm wide mixed interfacial layer. A highly bioactive porous structure of the top coat layer is beneficial for early formation of a bone-bonding hydroxycarbonate apatite (HCA) layer. The numerical model developed in this work also allows for prediction of porosity and crystallinity in top coat layers of bioactive glass developed through laser induced sintering and crystallization.

Competitive precipitation of amorphous and crystalline silicon nitride in ferrite: Interaction between structure, morphology, and stress relaxation

We present a detailed analysis based on both experimental and modeling approaches of the unique silicon nitride precipitation sequence recently observed in ferritic Fe–Si alloys upon nitriding. At 570°C, silicon nitride forms as an amorphous phase of size-dependent cuboidal morphology which results from the symmetry of matrix crystal structure. These amorphous precipitates are stable over remarkably long treatment durations. However, we demonstrate here that it is possible to trigger a transition to the precipitation of a crystalline modification of Si3N4 by switching to a denitriding medium at the same temperature. This change in structure is associated with a change from the cube-like morphology to a hexagonal prism shape. This unique phenomenon, driven by a classical nucleation and growth process, can be explained by the shift of stress-relief mechanism related to the change of atmosphere. The plentiful availability of nitrogen atoms during nitriding allows a strong relaxation of the precipitation-induced stress, which is energetically more favorable to the amorphous phase. Upon annealing in a low nitrogen activity medium, nitrogen in solid solution diffuses outward and no longer relieves the precipitation-induced stress. In that configuration, the crystalline modification of Si3N4 becomes more stable owing to its lower associated stress. It precipitates in a hexagonal prism shape, which is the equilibrium shape dictated by the crystal symmetries of both the matrix and the precipitates.

Tuning loading and release by modification of micelle core crystallinity and preparation

Controlling and tuning the loading and release of incorporated drugs are vital parts of the advancement of drug delivery systems. Micelle systems that use core crystallinity to tune the loaded amount of hydrophobic molecules as well as their released amount were therefore developed. The conductive and electroactive aniline pentamer was incorporated into poly(ethylene glycol)–poly(ε‐caprolactone) (PEG–PCL) micelles with semi‐crystalline cores and poly(ethylene glycol)–poly(ε‐decalactone) (PEG–PεDL) micelles with amorphous cores. The difference in core crystallinity of the two micelle systems gave rise to highly different loading capacities and release rates. The loading capacity was strongly dependent on the core crystallinity, and the amorphous PEG–PεDL micelles had almost twice as high loading capacity as the semi‐crystalline PEG–PCL micelles. In addition, the loading capacity was highly influenced by the loading procedure. The dependence on core crystallinity was also evident for the release of the aniline pentamer. The release occurred faster for the PEG–PεDL micelles with amorphous cores compared with the PEG–PCL micelles with semi‐crystalline cores. The use of just these two systems gave us the ability to tune the released amount and rate, and a combination of these systems can enable access to a wide range of release profiles, thereby being available to a variety of drug delivery applications. © 2015 The Authors. Polymers for Advanced Technologies Published by John Wiley &amp; Sons Ltd.