Chiral templating of self-assembling nanostructures by circularly polarized light

PMCID: PMC4387888.-- et al.The high optical and chemical activity of nanoparticles (NPs) signifies the possibility of converting the spin angular momenta of photons into structural changes in matter. Here, we demonstrate that illumination of dispersions of racemic CdTe NPs with right- (left-)handed circularly polarized light (CPL) induces the formation of right- (left-)handed twisted nanoribbons with an enantiomeric excess exceeding 30%, which is â 1/410 times higher than that of typical CPL-induced reactions. Linearly polarized light or dark conditions led instead to straight nanoribbons. CPL templating of NP assemblies is based on the enantio-selective photoactivation of chiral NPs and clusters, followed by their photooxidation and self-assembly into nanoribbons with specific helicity as a result of chirality-sensitive interactions between the NPs. The ability of NPs to retain the polarization information of incident photons should open pathways for the synthesis of chiral photonic materials and allow a better understanding of the origins of biomolecular homochirality.This material is based on work partially supported by the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under award number #DE-SC0000957, and by ARO MURI W911NF-12-1-0407 ‘Coherent Effects in Hybrid Nanostructures for Lineshape Engineering of Electromagnetic Media’ (N.A.K. and S.L.). We acknowledge support from the NSF under grant ECS-0601345; CBET 0933384; CBET 0932823; and CBET 1036672. Financial support from the Robert A. Welch Foundation (C-1664) is also acknowledged (S.L.). Support from the NIH grant GM085043 (P.Z.) is gratefully acknowledged. The work of P.K. was supported by the NSF DMR grant No. 1309765 and by the ACS PRF grant No. 53062-ND6.Peer Reviewe

REFLECTION OF LABOR MARKET INTERESTS AND EXPECTATIONS IN EDUCATIONAL ORDER FOR CONTEMPORARY SCHOOL

Purpose of the study: The main objective of the study was the analysis of key labor market request content for the secondary education system, the level of employers' expectations compliance and actual learning outcomes, the research of resources and partnership interaction limitations of all interesting subjects in the process of an educational order development. Methodology: The main method was the questionnaire survey of experts (individual entrepreneurs, the heads of industrial and structural divisions) of Moscow (N = 316). The results of the expert survey showed the interest of employers in close cooperation with school in order to reflect the interests of the labor market in the educational order adequately. Results: The most motivated group is a small business, the leaders of the lowest level in the sphere of trade and service, who directly interact with the school graduates in the process of their early start of labor activity. The experts noted the problems in the development of the social competencies among schoolchildren: excessive self-esteem, an excessive level of claims, low level of willingness to work in a team, the lack of such qualities as responsiveness and responsibility. The cooperation between school and employers is limited to traditional sponsorship practices. The interaction of employers and educational institutions is quite fragmentary, it depends on a variety of random factors (personal and situational motives), which does not ensure the stability and the effectiveness of social partnership. Applications of this study: This research can be used for the universities, teachers, and students. Novelty/Originality of this study: In this research, the model of Reflection of Labor Market Interests and Expectations in Educational Order for Contemporary School is presented in a comprehensive and complete manner

Inorganic–organic nanocomposites of CdSe nanocrystals surface-modified with oligo- and poly(fluorene) moieties

We report a facile grafting-from strategy towards the synthesis of inorganic–organic composites of semiconductor nanocrystals and wide-bandgap polymers. Amino-functional fluorenes have been used as co-ligands for CdSe nanocrystals, thus enabling us to design their surface directly during the synthesis. Highly monodisperse, strongly emitting CdSe nanocrystals have been obtained. Subsequently, a straightforward Yamamoto C–C coupling protocol was used to carry out surface polymerisation, hence modifying CdSe nanocrystals with oligo- and poly(fluorene) moieties. Both amino-fluorene capped CdSe nanocrystals and the resulting nanocrystal–polymer composites were characterized in detail by optical and FT-IR spectroscopy, TEM, AFM, and gel permeation chromatography, showing their potential as novel functional inorganic–organic hybrid materials

Efficient energy transfer in layered hybrid organic/inorganic nanocomposites: A dual function of semiconductor nanocrystals

The efficiency of energy transfer in hybrid organic/inorganic nanocomposites based on conjugated polymers and semiconductor nanocrystals is strongly dependent on both the energy transfer rate and the rate of the nonradiative recombination of the polymer. We demonstrate that the polymer nonradiative recombination can be reduced by the suppression of exciton diffusion via proper morphology engineering of a hybrid structure. In the layer-by-layer assembled nanocomposite of a conjugated polymer and CdTe nanocrystals the latter have a dual role: first, they are efficient exciton acceptors and, second, they reduce nonradiative recombination in the polymer by suppressing exciton diffusion across the layers.Fil: Lutich, Andrey A.. Ludwig Maximilians Universitat; AlemaniaFil: Pöschl, Andreas. Ludwig Maximilians Universitat; AlemaniaFil: Jiang, Guoxin. Ludwig Maximilians Universitat; AlemaniaFil: Stefani, Fernando Daniel. Ludwig Maximilians Universitat; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Susha, Andrei S.. City University of Hong Kong; ChinaFil: Rogach, Andrey L.. City University of Hong Kong; ChinaFil: Feldmann, Jochen. Ludwig Maximilians Universitat; Alemani

CdTe Quantum Dot/Dye Hybrid System as Photosensitizer for Photodynamic Therapy

We have studied the photodynamic properties of novel CdTe quantum dots—methylene blue hybrid photosensitizer. Absorption spectroscopy, photoluminescence spectroscopy, and fluorescence lifetime imaging of this system reveal efficient charge transfer between nanocrystals and the methylene blue dye. Near-infrared photoluminescence measurements provide evidence for an increased efficiency of singlet oxygen production by the methylene blue dye. In vitro studies on the growth of HepG2 and HeLa cancerous cells were also performed, they point toward an improvement in the cell kill efficiency for the methylene blue-semiconductor nanocrystals hybrid system

Effect of growth temperature on the structural, optical and luminescence properties of cadmium telluride nanoparticles

Cadmium telluride (CdTe) has been successfully prepared by a simple wet chemical process at different reaction temperatures. Temperature is one parameter that thermodynamically plays an important role in controlling the growth rate, morphology, size and size distribution of the as-prepared nanoparticles (NPs). Effect of this parameter was investigated on the growth, structural and optical properties of CdTe NPs. It was observed that the Powder X-ray diffraction (XRD) pattern for samples prepared at 50 °C had many impurities from unreacted precursors while those prepared at > 100 °C displayed polycrystalline NPs. The XRD results revealed that the structure of the CdTe NPs was cubic with the planes (111), (220), (311) being the main observed peaks. The crystallite sizes obtained from Scherrer formula increased with the increase in growth temperature (2.86–3.62 nm grown at 50–200 °C respectively). The scanning electron microscopy micrographs showed that the morphology of the nanoparticles possessed spherical-shaped particles over the entire surface. This was further confirmed by high resolution transmission electron microscopy micrographs which also displayed increase in the particle size with an increase in the growth temperature. In the optic study, the photoluminescence (PL) spectra displayed a red shift (540–560 nm) in emission as growth temperature increased from 50 to 200 °C. The highest PL peak intensity was realized at a growth temperature of 150 °C. Absorption band maxima were observed to shift towards longer wavelength for higher growth temperatures. The optical band gap decreased with increase in the growth temperature from 2.67 to 2.08 eV for 50–200 °C respectively

Effect of chemical composition on luminescence of thiol-stabilized CdTe nanocrystals

Judicious selection of the amount of surfactant during synthesis enables a drastic increase in the photoluminescence efficiency of aqueous CdTe nanocrystals (NCs) stabilized by thioglycolic acid (TGA). Elemental determination of the NCs was undertaken to identify the origin of this effect. The molar ratio of (Te + S) to Cd approached unity when the optimum amount of TGA was used during synthesis, whereas the number of S atoms originating from TGA molecules in one NC (2.6 nm of diameter) remained unchanged at 90 ± 3. This indicates that the core lattice composition at the beginning of synthesis, rather than the surface conditions, affects the photoluminescence efficiency of the NCs even after prolonged refluxing

Trust in distance learning during the COVID-19 pandemic: Evaluation of the quality of education of students and teachers of Russian universities

Introduction. The widespread transition of higher education institutions to distance learning during the COVID-19 pandemic contributed to a decrease in education quality ratings. These trends, against the background of forecasts of an increase in the share of “distance learning” in the educational process, may initiate an increase in social tension, as well as a decrease in the level of trust in the activities of authorities that do not fully ensure the maintenance of the quality of education in the new conditions. Aim. The aim of the article was to assess the quality of education in the context of distance learning, to analyse the consequences of the transformation of the practices of interaction between a teacher and a student. Methodology and research methods. An all-Russian comprehensive sociological study was conducted using the following methods: questionnaires and focus groups. The first wave of the study was a survey of students of higher educational institutions of economic orientation from 14 regions of the Russian Federation (the sample population was 6,500 students). During the second wave, the following projects were implemented: 1) a survey of students of economic universities from 17 regions of the Russian Federation (sample population = 7600); 2) a survey of teachers of the Financial University (sample population = 520); 3) focus groups with students. Results and scientific novelty. The results obtained allow the authors to draw the following conclusions: the remote format of classes during the quarantine restrictions did not cause a sharp drop in the quality of education. Meanwhile, students’ preferences demonstrate a commitment to the traditional form of education. The factors that shape the readiness of students for distance education (course of study, budget/contract form, direction of training) are identified. The main problem is related to the lack of face-to-face communication, which is interpreted by the authors not so much as an objective limitation of the remote format of work, but as a subjective unavailability, low adaptation of pedagogical and communicative practices to remote online interaction. The study showed the strengthening of the role of informal network interactions that ensure the filling of the information vacuum in conditions of uncertainty, the formation of trust. Practical significance. The research results and conclusions can be used for further theoretical and practical developments in this area, and can also become the basis for the preparation of methodological recommendations to reduce the negative consequences of the introduction of distance learning and improve the quality of education in the new environment.Введение. Повсеместный переход высших учебных заведений на дистанционное обучение в период пандемии способствовал снижению оценок качества образования. Данные тенденции на фоне прогнозов увеличения доли «дистанта» в образовательном процессе могут инициировать рост социальной напряженности, а также снижение уровня доверия к деятельности органов власти, которые не в полной мере обеспечивают поддержание качества образования в новых условиях. Цель статьи заключалась в оценке качества образования в условиях дистанционного обучения, анализе последствий трансформации практик взаимодействия педагога и студента. Методология и методы. Проведено всероссийское комплексное социологическое исследование с применением следующих методов: анкетирование и фокус-группы. Первая волна исследования представляла собой опрос студентов высших учебных заведений экономической направленности из 14 регионов Российской Федерации (выборочная совокупность составила 6 500 обучающихся). В период второй волны были реализованы: 1) опрос студентов вузов экономической направленности из 17 регионов Российской Федерации (выборочная совокупность = 7 600); 2) опрос преподавателей Финансового университета (выборочная совокупность = 520); 3) фокус-группы со студентами. Результаты и научная новизна. Полученные результаты позволяют сделать следующие выводы: дистанционный формат проведения занятий в период карантинных ограничений не вызвал резкого падения оценок качества образования. Но при этом студенты демонстрируют приверженность к традиционной форме обучения. Выявлены факторы, формирующие удовлетворенность студентов дистанционным обучением (курс обучения, бюджетная/контрактная форма, направление подготовки). Основная проблема связана с недостатком очного общения, что интерпретируется авторами не столько как объективное ограничение дистанционного формата работы, сколько как субъективная неготовность, низкая адаптация педагогических и коммуникативных практик к удаленному онлайн взаимодействию. Исследование показало усиление роли неформальных сетевых взаимодействий, обеспечивающих заполнение информационного вакуума в условиях неопределенности, формирование доверияПрактическая значимость. Полученные результаты и сделанные на их основе выводы могут быть использованы для дальнейших теоретических и практических разработок в данной сфере, а также могут стать основой для подготовки методических рекомендаций по снижению негативных последствий внедрения дистанционного обучения и повышению качества образования в новых условиях.The current research was carried out based on the results of studies carried out at the expense of budgetary funds under the state assignment of the Financial University under the Government of the Russian Federation.Исследование выполнено по результатам исследований, выполненных за счет бюджетных средств по государственному заданию Финансового университета при Правительстве РФ