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The principal structural defects in graphene multilayers synthesized on the carbon-terminated face of a 4H-SiC (0001) substrate were investigated using the high-resolution transmission electron microscopy. The analyzed systems include a wide variety of defected structures such as edge dislocations, rotational multilayers, and grain boundaries. It was shown that graphene layers are composed of grains of the size of several nanometres or larger; they differ in a relative rotation by large angles, close to 30°. The structure of graphene multilayers results from the synthesis on a SiC (0001) surface, which proceeds via intensive nucleation of new graphene layers that coalesce under various angles creating an immense orientational disorder. Structural defects are associated with a built-in strain resulting from a lattice mismatch between the SiC substrate and the graphene layers. The density functional theory data show that the high-angular disorder of AB stacked bilayers is not restoring the hexagonal symmetry of the lattice. [ABSTRACT FROM AUTHOR]

Different stacking sequences of graphene are investigated using a combination of experimental and theoretical methods. High-resolution transmission electron microscopy (HRTEM) of the stacking sequence of several layers of graphene, formed on the C-terminated 4H-SiC (0001) surface, was used to determine the stacking sequence and the interlayer distances. These data prove that the three metastable multilayer graphene configurations exist: AB, AA, and ABC. In accordance, those three cases were considered theoretically, using density functional theory (DFT) calculations comparing properties of graphene, both free-standing and positioned on the SiC (0001) substrate. Total energies were calculated, the most stable structure was identified, and the electronic band structure was obtained. These results were compared with results obtained for a graphene single layer, having six or three H atoms attached to the carbon ring. It was found that sixfold symmetry leads to linear dispersion relations and threefold symmetry leads to hyperbolic dispersion relations. Thus the type of dispersion relation, i.e., linear versus hyperbolic, is independent of the number of graphene layers or the interlayer coupling but depends on the graphene symmetry. Similarly, it was shown that a linear dispersion relation is obtained in the presence of the SiC substrate, and also for various distances between adjacent carbon layers for AA stacking. [ABSTRACT FROM AUTHOR]

The principal structural defects in graphene layers, synthesized on a carbon-terminated face, i.e., the SiC(OOOÎ) face of a 4W-SiC substrate, are investigated using microscopic methods. Results of high-resolution transmission electron microscopy (HRTEM) reveal their atomic arrangement. The mechanism of such defects' creation, directly related to the underlying crystallographic structure of the SiC substrate, is proposed. The connection between the 4H-SiC(000Î) surface morphology, including the presence of the single atomic steps, the sequence of atomic steps, and also the macrosteps, and the corresponding emergence of planar defective structure (discontinuities of carbon layers and wrinkles), is revealed. It is shown that the disappearance of the multistep island leads to the stress-related creation of wrinkles in the graphene layers. The density functional theory (DFT) calculation results show excess carbon atoms convert a topmost carbon layer to the sp2-bonded configuration, liberating Si atoms in the barrierless process. The DFT results show that the diffusion of carbon atoms is essentially impossible at the C-terminated SiC surface. On the contrary, DFT results prove that diffusion of the silicon atoms is possible on the C-terminated SiC surface at a high temperature close to 1600°C. Because, according to TEM studies, at the carbon-terminated SiC surface, the buffer layer is absent, that creates a channel for effective horizontal diffusion of both silicon atoms under the graphene layer. Ultimately the silicon atoms escape could be facilitated by the channels created at the bending layer defects (wrinkles). The sp2-bonded carbon atoms are incorporated into the growing graphene layers, which contribute to stress in the growing layers, detachment from SiC support, and partial contribution to the creation of wrinkles. These results explain the phenomenon of the growth of thick undulated graphene layers by subsequent creation of the new layer underneath the existing graphene cover and also the creation of the principal defects in graphene at the C-terminated SiC(000Ï) surface. [ABSTRACT FROM AUTHOR]

A nonradiative recombination channel is proposed, which does not vanish at low temperatures. Defect-mediated nonradiative recombination, known as Shockley-Read-Hall (SRH) recombination, is reformulated to accommodate Coulomb attraction between the charged deep defect and the approaching free carrier. It is demonstrated that this effect may cause a considerable increase in the carrier velocity approaching the recombination center. The effect considerably increases the carrier capture rates. It is demonstrated that, in a typical semiconductor device or semiconductor medium, the SRH recombination rate at low temperatures is much higher and cannot be neglected. This effect renders invalid the standard procedure of estimating the radiative recombination rate by measuring the light output in cryogenic temperatures, as a significant nonradiative recombination channel is still present. We also show that SRH is more effective in the case of low-doped semiconductors, as effective screening by mobile carrier density could reduce the effect.

Extensive ab initio density functional theory molecular dynamics calculations were used to evaluate stability conditions for relevant phases of InN. In particular, the p-T conditions of the thermal decomposition of InN and pressure-induced wurtzite-rocksalt solid-solid phase transition were established. The comparison of the simulation results with the available experimental data allowed for a critical evaluation of the capabilities and limitations of the proposed simulation method. It is shown that ab initio molecular dynamics can be used as an efficient tool for simulations of phase transformations of InN, including solid-solid structural transition and thermal decomposition with formation of N 2 molecules. It is of high interest, because InN is an important component of epitaxial quantum structures, but it has not been obtained as a bulk single crystal. This makes it difficult to determine its basic physical properties to develop new applications.

Polarization doping in a GaN-InN system with a graded composition layer was studied using ab initio simulations. The electric charge volume density in the graded concentration part was determined by spatial potential dependence. The emerging graded polarization charge was determined to show that it could be obtained from a polarization difference and the concentration slope. It was shown that the GaN-InN polarization difference is changed by piezoelectric effects. The polarization difference is in agreement with the earlier obtained data despite the relatively narrow bandgap for the simulated system. The hole generation may be applied in the design of blue and green laser and light-emitting diodes.

Intrahepatic cholestasis of pregnancy (ICP) is an important pregnancy liver disorder. The alterations of different enzymes activity in the hepatocytes in the course of liver diseases are reflected in an increase in the activity of the corresponding enzymes in the blood. In present study we assayed the activity of alcohol dehydrogenase (ADH) and its isoenzyme in the serum of patients with ICP. Serum were collected from 100 pregnancies with ICP in the second or third trimester of pregnancy. Serum samples were also taken from 100 healthy pregnant women. The activity of ADH I was measured by spectrofluorometric method, ADH total was measured by photometric method. There was significant increase in the activity of ADH I (2.79 mU/l vs. 1.72 mU/l) and total ADH activity (1103 mU/l vs. 682 mU/l) in the sera of women with ICP compared to the healthy pregnant women. Importantly, the sensitivity and specificity of ADH I for diagnosis of ICP were 85% and 91%, respectively. Area under the Receiver Operating Curve for ADH I in ICP was 0.81. The activity of ADH I in the sera of women with ICP is statistically significantly increased, which may have a diagnostic significance for ICP patients., (© 2022. The Author(s).)

Introduction: Intrahepatic cholestasis of pregnancy (ICP) is the liver disorder in the second or early third trimester of pregnancy. It is characterized by pruritus with increased serum bile acids concentration and other liver function tests. ICP is connected with increased risk of fetal mortality but is unfortunately detected quite late. Therefore, it is important to recognize the disease in its early stages. We aimed to investigate the serum alcohol dehydrogenase (ADH) activity and compare it with the concentration of total bile acid (TBA) in women with ICP., Methods: Serum samples were taken for routine investigation from 80 pregnancies with ICP in the second or third trimester of pregnancy and from 80 healthy pregnant women at the same time of pregnancy. For measurement of class I activity, we used the spectrofluorometric methods. The total ADH activity was measured by the photometric method., Results: The analysis of results shows a statistically significant increase in the activity of ADH I and ADH total (about 60% and 41.3%, respectively). Activity of ADH I correlated well with aminotransferases (alanine ALT and aspartate AST) and total bile acids (TBA) concentration. The total ADH activity was also positively correlated with ALT, AST and total bile acids., Conclusion: We can state that the activity of class I alcohol dehydrogenase isoenzyme in the sera of patients with ICP is increased and seems to be a good indicator of liver cells destruction during this disease and is comparable with the value of other markers.

In this paper, ab initio calculations are used to determine polarization difference in zinc blende (ZB), hexagonal (H) and wurtzite (WZ) AlN-GaN and GaN-InN superlattices. It is shown that a polarization difference exists between WZ nitride compounds, while for H and ZB lattices the results are consistent with zero polarization difference. It is therefore proven that the difference in Berry phase spontaneous polarization for bulk nitrides (AlN, GaN and InN) obtained by Bernardini et al. and Dreyer et al. was not caused by the different reference phase. These models provided absolute values of the polarization that differed by more than one order of magnitude for the same material, but they provided similar polarization differences between binary compounds, which agree also with our ab initio calculations. In multi-quantum wells (MQWs), the electric fields are generated by the well-barrier polarization difference; hence, the calculated electric fields are similar for the three models, both for GaN/AlN and InN/GaN structures. Including piezoelectric effect, which can account for 50% of the total polarization difference, these theoretical data are in satisfactory agreement with photoluminescence measurements in GaN/AlN MQWs. Therefore, the three models considered above are equivalent in the treatment of III-nitride MQWs and can be equally used for the description of the electric properties of active layers in nitride-based optoelectronic devices.

The dissolution of molecular nitrogen in Ga and Fe was investigated by ab initio calculations and some complementary experiments. It was found that the N bonding inside these solvents is fundamentally different. For Ga, it is between Ga4s and Ga4p and N2p states whereas for Fe this is by N2p to Fe4s , Fe4p and Fe3d states. Accordingly, the energy of dissolution of N2 for arbitrarily chosen starting atomic configurations was 0.535 eV/mol and -0.299 eV/mol for Ga and Fe, respectively. For configurations optimized with molecular dynamics, the difference between the corresponding energy values, 1.107 eV/mol and 0.003 eV/mol, was similarly large. Full thermodynamic analysis of chemical potential was made employing entropy-derived terms in a Debye picture. The entropy-dependent terms were obtained via a normal conditions path to avoid singularity of ideal gas entropy at zero K. Nitrogen solubility as a function of temperature and N2 pressure was evaluated, being much higher for Fe than for Ga. For T=1800 K and p=104 bar, the N concentration in Ga was 3×10-3 at. fr. whereas for Fe, it was 9×10-2 at. fr. in very good agreement with experimental data. It indicates that liquid Fe could be a prospective solvent for GaN crystallization from metallic solutions.

Intrahepatic cholestasis of pregnancy (ICP) is the most common hepatic disorder related to pregnancy in women. It usually develops within the third trimester of pregnancy and presents with pruritus as well as elevated levels of bile acid and/or alanine aminotransferase. Clinical signs quickly resolve after delivery; however, there is a high risk of the disorder recurring in subsequent pregnancies. ICP is associated with an increased risk of perinatal complications (premature birth, respiratory disorders, even stillbirth). Elevated levels of gestational hormones and genetic predispositions are important factors for the development of ICP; among the latter, mutations in hepatobiliary transport proteins (multidrug resistance protein 3-MDR3, bile salt export pump- BSEP) play a major role. Clinical and biochemical symptoms of ICP include pruritus and increased levels of total bile acids (TBA). Serum levels of TBA should be monitored in ICP patients throughout the pregnancy as concentrations above 40 μmol/L, which define that severe ICP isassociated with an increased risk of fetal complications. Therapeutic management is aimed at reducing the clinical symptoms, normalizing maternal biochemistry and preventing complications to the fetus. Pharmacological treatment of intrahepatic cholestasis of pregnancy consists of the administration of ursodeoxycholic acid to lower the levels of TBA and possibly reduce pruritus. If the treatment fails, premature delivery should be considered.

Background/aim: The liver of pregnant women undergoes physiological and pathological changes and the changes in liver enzyme activity and release reflect changes in serum enzymatic activity. We aimed to assess the activity of alcohol dehydrogenase (ADH) isoenzymes, and aldehyde dehydrogenase (ALDH) in the sera of women with intrahepatic cholestasis of pregnancy (ICP), the most common pregnancy-related liver disease., Patients and Methods: Serum samples were taken from 40 women with ICP in the second or third trimester of pregnancy. Serum samples were also obtained from 40 healthy pregnant women at the same time of pregnancy and 40 healthy non-pregnant women. Class I and II of ADH and ALDH activity was measured by a spectrofluorometric method. Class III, IV ADH and total ADH activity was measured by photometric methods., Results: The total ADH activity was significantly higher in women with ICP than in healthy pregnant and non-pregnant women (about 42%). The median total activity of ADH was 1067 mU/l in women with ICP, 628 mU/l in healthy pregnant and 605 mU/l in non-pregnant women. A statistically significant increase in class I ADH isoenzymes was found in the sera of pregnant women with ICP. The median activity of this class in the ICP group increased about 62% and 80% in comparison to the healthy pregnant women and non-pregnant women, respectively., Conclusion: The activity of class I ADH isoenzymes in the sera of women with ICP is statistically significantly increased and may have a diagnostic significance., (Copyright© 2020, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Background/aim: Human pancreas parenchyma contains various alcohol dehydrogenase (ADH) isoenzymes and also possesses aldehyde dehydrogenase (ALDH) activity. The altered activities of ADH and ALDH in damaged pancreatic tissue in the course of pancreatitis are reflected in the human serum. The aim of this study was to investigate a potential role of ADH and ALDH as markers for acute (AP) and chronic pancreatitis (CP)., Patients and Methods: Serum samples were collected for routine biochemical investigations from 75 patients suffering from acute pancreatitis and 70 patients with chronic pancreatitis. Fluorometric methods were used to measure the activity of class I and II ADH and ALDH activity. The total ADH activity and activity of class III and IV isoenzymes were measured by a photometric method., Results: There was a significant increase in the activity of ADH III isoenzyme (15.06 mU/l and 14.62 mU/l vs. 11.82 mU/l; p<0.001) and total ADH activity (764 mU/l and 735 mU/l vs. 568 mU/l) in the sera of patients with acute pancreatitis or chronic pancreatitis compared to the control. The diagnostic sensitivity for ADH III was about 84%, specificity was 92 %, positive and negative predictive values were 93% and 87% respectively in acute pancreatitis. Area under the Receiver Operating Curve (ROC) curve for ADH III in AP and CP was 0.88 and 0.86 respectively., Conclusion: ADH III has a potential role as a marker of acute and chronic pancreatitis., (Copyright© 2018, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Background: Autoimmune hepatitis (AIH) is a progressive inflammatory hepatopathy and an important cause of end-stage liver. The liver cells' destruction is reflected by increased activity of different enzymes in the serum. These enzymes include alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), which play a significant role in the metabolism of many biological substances and exist mainly in the liver. In this study we investigated the activity of alcohol dehydrogenase and its isoenzymes and the total activity of ALDH in the sera of patients with autoimmune hepatitis., Methods: Serum samples were taken for routine biochemical investigation from 32 patients with autoimmune hepatitis and from 40 healthy subjects. Class I and II of ADH and ALDH activity was measured by the spectrofluorometric method. For measurement of class III ADH and total ADH activity we employed the photometric methods., Results: The activity of the class I ADH isoenzyme was significantly higher in the sera of patients with autoimmune hepatitis. The median activity of this isoenzyme in the patients group was approximately 63% (3.94 mU/L) higher than the control level (1.46 mU/L). For this reason, the total ADH activity was also significantly increased. The activities of other ADH isoenzymes and ALDH tested were unchanged., Conclusions: The activity of total ADH and class I isoenzymes in the sera of patients with autoimmune hepatitis is increased, and it seems to be caused by the release of alcohol dehydrogenase from damaged liver cells.

In yeast and mammals, prohibitins (PHBs) are considered as structural proteins that form a scaffold-like structure for interacting with a set of proteins involved in various processes occurring in the mitochondria. The role of PHB in plant mitochondria is poorly understood. In the study, the model organism Arabidopsis thaliana was used to identify the possible roles of type-II PHBs (homologs of yeast Phb2p) in plant mitochondria. The obtained results suggest that the plant PHB complex participates in the assembly of multisubunit complexes; namely, respiratory complex I and enzymatic complexes carrying lipoic acid as a cofactor (pyruvate dehydrogenase, 2-oxoglutarate dehydrogenase and glycine decarboxylase). PHBs physically interact with subunits of these complexes. Knockout of two Arabidopsis type-II prohibitins (AtPHB2 and AtPHB6) results in a decreased abundance of these complexes along with a reduction in mitochondrial acyl carrier proteins. Also, the absence of AtPHB2 and AtPHB6 influences the expression of the mitochondrial genome and leads to the activation of alternative respiratory pathways, namely alternative oxidase and external NADH-dependent alternative dehydrogenases.

Background: Chloroplasts were formed by uptake of cyanobacteria into eukaryotic cells ca. 1.6 billion years ago. During evolution most of the cyanobacterial genes were transferred from the chloroplast to the nuclear genome. The rbcX gene, encoding an assembly chaperone required for Rubisco biosynthesis in cyanobacteria, was duplicated. Here we demonstrate that homologous eukaryotic chaperones (AtRbcX1 and AtRbcX2) demonstrate different affinities for the C-terminus of Rubisco large subunit and determine their crystal structures., Methods: Three-dimensional structures of AtRbcX1 and AtRbcX2 were resolved by the molecular replacement method. Equilibrium binding constants of the C-terminal RbcL peptide by AtRbcX proteins were determined by spectrofluorimetric titration. The binding mode of RbcX-RbcL was predicted using molecular dynamic simulation., Results: We provide crystal structures of both chaperones from Arabidopsis thaliana providing the first structural insight into Rubisco assembly chaperones form higher plants. Despite the low sequence homology of eukaryotic and cyanobacterial Rubisco chaperones the eukaryotic counterparts exhibit surprisingly high similarity of the overall fold to previously determined prokaryotic structures. Modeling studies demonstrate that the overall mode of the binding of RbcL peptide is conserved among these proteins. As such, the evolution of RbcX chaperones is another example of maintaining conserved structural features despite significant drift in the primary amino acid sequence., General Significance: The presented results are the approach to elucidate the role of RbcX proteins in Rubisco assembly in higher plants., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Recombination via short repeats in plant mitochondrial genomes results in sublimons--DNA molecules with a copy number much lower compared to the main mitochondrial genome. Coexistence of stoichiometrically different mitotypes, called heteroplasmy, plays an important evolutionary role, since sublimons occasionally replace the main genome resulting in a new plant phenotype. It is not clear, how frequency of recombination and sublimon production is regulated and how it is related to changes in the quantity of the main genome and sublimons. We analyzed the accumulation of two recombining main genome sequences and two resulting sublimons in apical meristems, undifferentiated tissues and leaves of different age of Phaseolus vulgaris. Copy numbers of the main genome sequences varied greatly depending on tissue type and organ age while accumulation of sublimons remained much more stable. Although the overall accumulation of plant mtDNA decreased with the leaf age, the quantity of sublimons increased relative to the main genome indicating a higher frequency of recombination via the short 314 bp repeat. Recombination was symmetrical in young developing leaves while in senescent tissues it shifted towards asymmetric events resulting in overrepresentation of one product. We propose that during plant lifetime replication and recombination frequencies change oppositely sustaining heteroplasmic compositions of the genome, which are favorable for inheritance and maintenance of complex plant mtDNA.

In the present work, we carried out density functional calculations of struvite--the main component of the so-called infectious urinary stones--to study its structural and elastic properties. Using a local density approximation and a generalised gradient approximation, we calculated the equilibrium structural parameters and elastic constants C(ijkl). At present, there is no experimental data for these elastic constants C (ijkl) for comparison. Besides the elastic constants, we also present the calculated macroscopic mechanical parameters, namely the bulk modulus (K), the shear modulus (G) and Young's modulus (E). The values of these moduli are found to be in good agreement with available experimental data. Our results imply that the mechanical stability of struvite is limited by the shear modulus, G. The study also explores the energy-band structure to understand the obtained values of the elastic constants.

Form I of Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) is composed of eight large (RbcL) and eight small (RbcS) subunits. Assembly of these subunits into a functional holoenzyme requires the assistance of additional assembly factors. One such factor is RbcX, which has been demonstrated to act as a chaperone in the assembly of most cyanobacterial Rubisco complexes expressed in heterologous system established in Escherichia coli cells. Analysis of Arabidopsis thaliana genomic sequence revealed the presence of two genes encoding putative homologues of cyanobacterial RbcX protein: AtRbcX1 (At4G04330) and AtRbcX2 (At5G19855). In general, both RbcX homologues seem to have the same function which is chaperone activity during Rubisco biogenesis. However, detailed analysis revealed slight differences between them. AtRbcX2 is localized in the stromal fraction of chloroplasts whereas AtRbcX1 was found in the insoluble fraction corresponding with thylakoid membranes. Search for putative "partners" using mass spectrometry analysis suggested that apart from binding to RbcL, AtRbcX1 may also interact with β subunit of chloroplast ATP synthase. Quantitative RT-PCR analysis of AtRbcX1 and AtRbcX2 expression under various stress conditions indicated that AtRbcX2 is transcribed at a relatively stable level, while the transcription level of AtRbcX1 varies significantly. In addition, we present the attempts to elucidate the secondary structure of AtRbcX proteins using CD spectroscopy. Presented results are the first known approach to elucidate the role of RbcX proteins in Rubisco assembly in higher plants.

ATP-dependent proteases from three families have been identified experimentally in Arabidopsis mitochondria: four FtsH proteases (AtFtsH3, AtFtsH4, AtFtsH10, and AtFtsH11), two Lon proteases (AtLon1 and AtLon4), and one Clp protease (AtClpP2 with regulatory subunit AtClpX). In this review we discuss their submitochondrial localization, expression profiles and proposed functions, with special emphasis on their impact on plant growth and development. The best characterized plant mitochondrial ATP-dependent proteases are AtLon1 and AtFtsH4. It has been proposed that AtLon1 is necessary for proper mitochondrial biogenesis during seedling establishment, whereas AtFtsH4 is involved in maintaining mitochondrial homeostasis late in rosette development under short-day photoperiod., (Copyright © 2010 Elsevier B.V. All rights reserved.)

We identify and characterize two matrix (m)-AAA proteases (AtFtsH3 and AtFtsH10) present in the mitochondria of Arabidopsis thaliana. AtFtsH3 is the predominant protease in leaves of wild type plants. Both proteases assemble with prohibitins (PHBs) into high molecular weight complexes (approximately 2 MDa), similarly to their yeast counterparts. A smaller PHB complex (approximately 1 MDa), without the m-AAA proteases, was also detected. Unlike in yeast, stable prohibitin-independent high molecular weight assemblies of m-AAA proteases could not be identified in A. thaliana. AtFtsH3 and AtFtsH10 form at least two types of m-AAA-PHB complexes in wild type plants. The one type contains PHBs and AtFtsH3, and the second one is composed of PHBs and both AtFtsH3 and AtFtsH10. Complexes composed of PHBs and AtFtsH10 were found in an Arabidopsis mutant lacking AtFtsH3 (ftsh3). Thus, both AtFtsH3 and AtFtsH10 may form hetero- and homo-oligomeric complexes with prohibitins. The increased level of AtFtsH10 observed in ftsh3 suggests that functions of the homo- and hetero-oligomeric complexes containing AtFtsH3 can be at least partially substituted by AtFtsH10 homo-oligomers. The steady-state level of the AtFtsH10 transcripts did not change in ftsh3 compared with wild type plants, but we found that almost twice more of the AtFtsH10 transcripts were associated with polysomes in ftsh3. Based on this result, we assume that the AtFtsH10 protein is synthesized at a higher rate in the ftsh3 mutant. Our results provide the first data on the composition of m-AAA and PHB complexes in plant mitochondria and suggest that the abundance of m-AAA proteases is regulated not only at the transcriptional but also at the translational level.

First-principles calculations of the phonon dispersion relations and the phonon density of states for ZnO polymorphs: wurtzite, zinc-blende, rocksalt structures, and as yet the experimentally undiscovered CsCl structure, are presented. All the phases were exposed to pressures ranging from 0 to 20 GPa. The pressure-temperature phase diagram of ZnO was constructed and compared to experimental data, where available.