Liquid-phase exfoliation of bismuth telluride iodide (BiTeI): structural and optical properties of single-/few-layer flakes

Bismuth telluride halides (BiTeX) are Rashba-type crystals with several potential applications ranging from spintronics and nonlinear optics to energy. Their layered structures and low cleavage energies allow their production in a two-dimensional form, opening the path to miniaturized device concepts. The possibility to exfoliate bulk BiTeX crystals in the liquid represents a useful tool to formulate a large variety of functional inks for large-scale and cost-effective device manufacturing. Nevertheless, the exfoliation of BiTeI by means of mechanical and electrochemical exfoliation proved to be challenging. In this work, we report the first ultrasonication-assisted liquid-phase exfoliation (LPE) of BiTeI crystals. By screening solvents with different surface tension and Hildebrandt parameters, we maximize the exfoliation efficiency by minimizing the Gibbs free energy of the mixture solvent/BiTeI crystal. The most effective solvents for the BiTeI exfoliation have a surface tension close to 28 mN m(-1) and a Hildebrandt parameter between 19 and 25 MPa0.5. The morphological, structural, and chemical properties of the LPE-produced single-/few-layer BiTeI flakes (average thickness of & SIM;3 nm) are evaluated through microscopic and optical characterizations, confirming their crystallinity. Second-harmonic generation measurements confirm the non-centrosymmetric structure of both bulk and exfoliated materials, revealing a large nonlinear optical response of BiTeI flakes due to the presence of strong quantum confinement effects and the absence of typical phase-matching requirements encountered in bulk nonlinear crystals. We estimated a second-order nonlinearity at 0.8 eV of |chi((2))| & SIM; 1 nm V-1, which is 10 times larger than in bulk BiTeI crystals and is of the same order of magnitude as in other semiconducting monolayers (e.g., MoS2)

Protein Isoaspartate Methyltransferase Prevents Apoptosis Induced by Oxidative Stress in Endothelial Cells: Role of Bcl-Xl Deamidation and Methylation

BACKGROUND:Natural proteins undergo in vivo spontaneous post-biosynthetic deamidation of specific asparagine residues with isoaspartyl formation. Deamidated-isomerized molecules are both structurally and functionally altered. The enzyme isoaspartyl protein carboxyl-O-methyltransferase (PCMT; EC 2.1.1.77) has peculiar substrate specificity towards these deamidated proteins. It catalyzes methyl esterification of the free alpha-carboxyl group at the isoaspartyl site, thus initiating the repair of these abnormal proteins through the conversion of the isopeptide bond into a normal alpha-peptide bond. Deamidation occurs slowly during cellular and molecular aging, being accelerated by physical-chemical stresses brought to the living cells. Previous evidence supports a role of protein deamidation in the acquisition of susceptibility to apoptosis. Aim of this work was to shed a light on the role of PCMT in apoptosis clarifying the relevant mechanism(s). METHODOLOGY/PRINCIPAL FINDINGS:Endothelial cells transiently transfected with various constructs of PCMT, i.e. overexpressing wild type PCMT or negative dominants, were used to investigate the role of protein methylation during apoptosis induced by oxidative stress (H(2)O(2); 0.1-0.5 mM range). Results show that A) Cells overexpressing "wild type" human PCMT were resistant to apoptosis, whereas overexpression of antisense PCMT induces high sensitivity to apoptosis even at low H(2)O(2) concentrations. B) PCMT protective effect is specifically due to its methyltransferase activity rather than to any other non-enzymatic interactions. In fact negative dominants, overexpressing PCMT mutants devoid of catalytic activity do not prevent apoptosis. C) Cells transfected with antisense PCMT, or overexpressing a PCMT mutant, accumulate isoaspartyl-containing damaged proteins upon H(2)O(2) treatment. Proteomics allowed the identification of proteins, which are both PCMT substrates and apoptosis effectors, whose deamidation occurs under oxidative stress conditions leading to programmed cell death. These proteins, including Hsp70, Hsp90, actin, and Bcl-xL, are recognized and methylated by PCMT, according to the general repair mechanism of this methyltransferase. CONCLUSION/SIGNIFICANCE:Apoptosis can be modulated by "on/off" switch partitioning the amount of specific protein effectors, which are either in their active (native) or inactive (deamidated) molecular forms. Deamidated proteins can also be functionally restored through methylation. Bcl-xL provides a case for the role of PCMT in the maintenance of functional stability of this antiapoptotic protein

Cognitive performance of English and Spanish speaking Mexican-American children on the WISC-R and EIWN-R.

The purpose of this study was to do a comparative analysis of the Wechsler Intelligence Scale for Children-Revised (WISC-R), a test of intelligence which is frequently used with Mexican American students, and its Spanish translation the Escala de Inteligencia Wechsler Para Ninos-Revisada (EIWN-R). The WISC-R was administered in English to 109 bilingual English proficient Mexican American students, and the EIWN-R was administered in Spanish to 109 other than English proficient or monolingual Spanish speakers. Language proficiency was determined according to students scores on the Language Assessment Scales (LAS). The groups were matched by sex, school and grade. Students tested were students who were referred for testing because of academic difficulties or students placed in Special Education classes who are required to be re-evaluated every three years. Using Confirmatory factor analysis, the first objective was to determine if the factor structures underlying the EIWN-R and the WISC-R are equivalent to the factor structure of the WISC-R normative population. The correlation matrices of both groups were compared to the correlation matrix of the normative population. Factor structures of the WISC-R and the normative population were found to be statistically different, while the factor structures of the EIWN-R and the normative group were not found to be different. The second objective was to determine if the subtest means of the WISC-R and EIWN-R were significantly different. To determine this, the subtest means of both groups were subjected to MANOVA. Significant differences between subtest means were found on four of the subtests. A MANOVA was also utilized for the third objective which set out to determine if significant differences in performance are present in the EIWN-R between those students who are placed in Special Education programs and those students who are not placed. So as not to confound the results, the EMR population was removed from the sample. Significant differences in the placed and the non-placed groups were found on eight of the eleven subtests. Implications of research findings are discussed as well as future trends regarding the assessment of language minority students

Development and validation of a university students’ progression in learning quantum mechanics through exploratory factor analysis and Rasch analysis

We report an empirical study on the development and validation of a learning progression (LP) in quantum mechanics (QM) at university level. Drawing on research results about students’ reasoning in QM, we designed a hypothetical LP (HLP) consisting of three Big Ideas: Measurement, A toms and Electrons, Wave function. We then developed ten Ordered-Multiple-Choice (OMC) items to assess the construct validity and hierarchy of HLP levels. We administered the questionnaire to 244 students attending the Bachelor in Physics, divided into three groups under different instruction conditions: no course, introductory course, introductory and upper-level course. An additional group of 43 non-physics students, who attended an introductory QM course, was also involved to inspect the role of physics background knowledge . We used exploratory factor analysis and Rasch analysis to analyse collected data. The results provided evidence for the revision of the HLP around only two Big Ideas – Atomic description and measurement; Wave function and its properties in the measurement process – which roughly match the topics covered in the introductory and upper-level courses, respectively. However, the hierarchy of hypothesised levels was substantially confirmed. Implications of our findings for the teaching of QM, and the improvement of the revised LP are also discussed

Kidney micro-organoids in suspension culture as a scalable source of human pluripotent stem cell-derived kidney cells

Kidney organoids have potential uses in disease modelling, drug screening and regenerative medicine. However, novel cost-effective techniques are needed to enable scaled-up production of kidney cell types We describe here a modified suspension culture method for the generation of kidney micro-organoids from human pluripotent stem cells. Optimisation of differentiation conditions allowed the formation of micro-organoids, each containing six to ten nephrons that were surrounded by endothelial and stromal populations. Single cell transcriptional profiling confirmed the presence and transcriptional equivalence of all anticipated renal cell types consistent with a previous organoid culture method. This suspension culture micro-organoid methodology resulted in a three- to fourfold increase in final cell yield compared with static culture, thereby representing an economical approach to the production of kidney cells for various biological applications