Simultaneous Estimation of Cinnamaldehyde and Eugenol in Essential Oils and Traditional and Ultrasound-Assisted Extracts of Different Species of Cinnamon Using a Sustainable/Green HPTLC Technique

A wide range of analytical techniques are reported for the determination of cinnamaldehyde (CCHO) and eugenol (EOH) in plant extracts and herbal formulations either alone or in combination. Nevertheless, sustainable/green analytical techniques for the estimation of CCHO and EOH either alone or in combination are scarce in the literature. Accordingly, the present research was carried out to establish a rapid, highly sensitive, and sustainable high-performance thin-layer chromatography (HPTLC) technique for the simultaneous estimation of CCHO and EOH in the traditional and ultrasound-assisted methanolic extracts of Cinnamomum zeylanicum, C. burmannii, and C. cassia and their essential oils. The simultaneous estimation of CCHO and EOH was performed through NP-18 silica gel 60 F254S HPTLC plates. The cyclohexane/ethyl acetate (90:10, v v⁻¹) solvent system was optimized as the mobile phase for the simultaneous estimation of CCHO and EOH. The greenness score of the HPTLC technique was predicted using AGREE software. The entire analysis was carried out at a detection wavelength of 296 nm for CCHO and EOH. The sustainable HPTLC technique was observed as linear in the range 10–2000 ng band⁻¹ for CCHO and EOH. The proposed technique was found to be highly sensitive, rapid, accurate, precise, and robust for the simultaneous estimation of CCHO and EOH. The content of CCHO in traditional methanolic extracts of C. zeylanicum, C. burmannii, and C. cassia was found to be 96.36, 118.49, and 114.18 mg g⁻¹, respectively. However, the content of CCHO in ultrasound-assisted methanolic extracts of C. zeylanicum, C. burmannii, and C. cassia was found to be 111.57, 134.39, and 129.07 mg g⁻¹, respectively. The content of CCHO in essential oils of C. zeylanicum, C. burmannii, and C. cassia was found to be 191.20, 214.24, and 202.09 mg g⁻¹, respectively. The content of EOH in traditional methanolic extracts of C. zeylanicum, C. burmannii, and C. cassia was found to be 73.38, 165.41, and 109.10 mg g⁻¹, respectively. However, the content of EOH in ultrasound-assisted methanolic extracts of C. zeylanicum, C. burmannii, and C. cassia was found to be 87.20, 218.09, and 121.85 mg g⁻¹, respectively. The content of EOH in essential oils of C. zeylanicum, C. burmannii, and C. cassia was found to be 61.26, 79.21, and 69.02 mg g⁻¹, respectively. The amounts of CCHO and EOH were found to be significantly higher in ultrasound-assisted extracts of all species compared to its traditional extraction and hence ultrasound extraction has been proposed as a superior technique for the extraction of CCHO and EOH. The AGREE analytical score of the present analytical technique was predicted as 0.75, suggesting excellent greenness profile of the proposed analytical technique. Based on all these observations and results, the proposed sustainable HPTLC technique can be successfully used for the simultaneous estimation of CCHO and EOH in different plant extracts and herbal products.     

Determination of thiosulfate concentrations by gravimetric analysis: A desirable experiment for chemical education

An electrochemistry-based gravimetric method of analysis for the determination of thiosulfate concentrations in aqueous solutions and its application in chemical education are introduced. Nine standard aqueous thiosulfate solutions with triplicate concentrations of 0.02 M, 0.03 M, and 0.04 M were prepared in 1.0 M hydrochloric acid. The elemental sulfur produced in each sample was recovered by filtration, and the mass of the recovered elemental sulfur and the electrochemically determined equilibrium constant of the reaction at 25°C (K_eq = 3.5) were used to determine the concentration of thiosulfate in each standard solution. The method % Error is 4.9 ± 3.0, which means that the average method % Error is less than 5.0.     

教育经费投入对区域经济增长影响的实证研究

教育经费投入对于提升人力资本,促进经济增长有着无可代替的作用.通过利用改进的柯布道格拉斯生产函数和人力资本理论,运用2005-2011全国其中30个省级面板数据,对不同层次的教育经费投入与区域经济增长之间的关系进行了实证研究.研究结果表明,初等学校的教育经费投入对中国各区域的经济增长均有显著作用,高等职业学校的教育经费投入对东部和西部地区的经济增长作用显著,本科学校的教育经费投入对中部地区经济增长作用显著.     

Student teachers’ types of probing questions in inquiry-based mathematics teaching with and without GeoGebra

Previous studies have produced several typologies of teacher questions in mathematics. Probing questions that ask students to explain are often included in the types of questions. However, only rare studies have created subtypes for probing questions or investigated how questioning differs depending on whether technology is used or not. The aims of this study are to elaborate on different ways of asking students to give explanations in inquiry-based mathematics teaching and to investigate whether questioning in GeoGebra lessons differs from questioning in other lessons. Data was collected by video recording 29 Finnish mathematics student teachers’ lessons in secondary and upper secondary schools. The lesson videos were coded for the student teachers’ probing questions. After this, categories for the types of probing questions were created, which is elaborated in this paper. It was found that the student teachers who used GeoGebra emphasized conceptual probing questions during the explore phase of a lesson slightly more than the other student teachers.     

Problematic topics in first-year mathematics: lecturer and student views

In this paper we report on the outcomes of two surveys carried out in higher education institutions of Ireland; one of students attending first-year undergraduate non-specialist mathematics modules and another of their lecturers. The surveys aimed to identify the topics that these students found difficult, whether they had most difficulty with the concepts or procedures involved in the topics, and the resources they used to overcome these difficulties. In this paper we focus on the mathematical concepts and procedures that students found most difficult. While there was agreement between students and lecturers on certain problematic topics, this was not uniform across all topics, and students rated their conceptual understanding higher than their ability to do questions, in contrast to lecturers’ opinions.     

Pre-service teachers' free and structured mathematical problem posing

This exploratory study examined how pre-service teachers (PSTs) pose mathematical problems for free and structured mathematical problem-posing conditions. It was hypothesized that PSTs would pose more complex mathematical problems under structured posing conditions, with increasing levels of complexity, than PSTs would pose under free posing conditions, because the structured posing condition would guide PSTs to more closely consider the mathematical relationships in a posing situation. Sixty-five PSTs – 61 participating in a written assessment and 4 participating in task-based interviews – responded to problem-posing tasks under free or structured posing conditions. Two-way independent samples t-tests and chi-square tests were used to test the hypothesis, along with a qualitative analysis of the task-based interviews. We found that while the task format had limited impact on the complexity of problems posed, PSTs in the structured-posing condition may have more closely attended to the mathematical concepts in each task, and may have also impacted their process of posing problems than those in the free posing condition.     

Prospective and current secondary mathematics teachers’ criteria for evaluating mathematical cognitive technologies

As technology becomes more ubiquitous in the mathematics classroom, teachers are being asked to incorporate it into their lessons more than ever before. The amount of resources available online is staggering and teachers need to be able to analyse and identify resources that would be most appropriate and effective with their students. This study examines the criteria prospective and current secondary mathematics teachers use and value most when evaluating mathematical cognitive technologies (MCTs). Results indicate all groups of participants developed criteria focused on how well an MCT represents the mathematics, student interaction and engagement with the MCT, and whether the MCT was user-friendly. However, none of their criteria focused on how well an MCT would reflect students’ solution strategies or illuminate their thinking. In addition, there were some differences between the criteria created by participants with and without teaching experience, specifically the types of supports available in an MCT. Implications for mathematics teacher educators are discussed.     

Glycerol as an Efficient Medium for the Petasis Borono–Mannich Reaction

The multicomponent Petasis borono–Mannich (PBM) reaction is a useful tool for the preparation of complex molecules in a single step from boronic acids, aldehydes/ketones, and amines. Here, we describe the use of glycerol in the PBM reaction of salicylaldehydes or 2-pyridinecarbaldehyde with several boronic acids and secondary amines. From these readily available starting materials, alkylaminophenols, 2-substituted pyridines, and 2H-chromenes were prepared in reasonable to good yields. Glycerol was compared with other solvents, and in some cases, it provided the reaction product in higher yield. Crude glycerol, as generated by the biodiesel industry, was evaluated and found to be a suitable solvent for the PBM reaction, successfully expanding the potential use of this industry by-product. Based on density functional theory (DFT) calculations and the obtained experimental results, the involvement of glycerol-derived boronic esters in the reaction mechanism is suggested to be competitive with the free boronic acid pathway. Similar Gibbs free energies for the aryl migration from the boronate species to the iminium were determined for both mechanisms.     

Enzymatic Halogenation of Tryptophan on a Gram Scale

Halogenated arenes are important building blocks in medicinal and agrochemistry. Chemical electrophilic aromatic halogenation requires molecular halogen, whereas FAD‐dependent halogenases form halogenated arenes with high regioselectivity while only halide salts and O₂ are required. This reaction proceeds at room temperature in aqueous media. However, enzymatic halogenation is considered inefficient, mainly because halogenases are not stable. Thus, the preparative application remained elusive. We were able to show that the long‐term stability and, hence, the preparative efficiency of the tryptophan‐7‐halogenase RebH can be significantly improved by immobilization together with the other enzymes required for cofactor regeneration. We established a facile scalable method suitable for the halogenation of tryptophan and its derivatives on a gram scale using a solid, multifunctional, and recyclable biocatalyst; this immobilization strategy might also be applicable for other FAD‐dependent halogenases.     

Chlorine‐Free Red‐Burning Pyrotechnics

The development of a red, chlorine‐free pyrotechnic illuminant of high luminosity and spectral purity was investigated. Red‐light emission based solely on transient SrOH_(g) has been achieved by using either 5‐amino‐1H‐tetrazole or hexamine to deoxidize the combustion flame of a Mg/Sr(NO₃)₂/Epon‐binder composition and reduce the amount of both condensed and gaseous SrO, which emits undesirable orange‐red light. The new formulations were found to possess high thermal onset temperatures. Avoiding chlorine in these formulations eliminates the risk of the formation of PCBs, PCDDs, and PCDFs. This finding, hence, will have a great impact on both military pyrotechnics and commercial firework sectors.