Chemical Concepts Research Articles

Nuclear quantum and H/D isotope effects on aromaticity: path integral molecular dynamics study.

Aromaticity is an important concept in organic chemistry, and thus, many theoretical and experimental studies have been conducted so far. However, the majority of theoretical studies have concentrated on the aromaticity of the stationary point structures. Herein, the influence of nuclear quantum fluctuation (nuclear quantum effects: NQEs) and thermal fluctuation on the aromaticity of benzene have been analyzed by path integral molecular dynamics (PIMD) simulation. The PIMD simulations revealed that the NQEs affected not only the C-H bonds but also the C-C bonds. The HOMA and NICS calculations demonstrated that the aromaticity decreased due to the NQEs of carbon atoms, attributed to an increase in the contribution from specific vibrational modes strongly correlated with benzene's aromaticity.

A New Exploration of the Preparation of Polyacrylic Acid by Free Radical Polymerization Based on the Concept of Green Chemistry

A New Exploration of the Preparation of Polyacrylic Acid by Free Radical Polymerization Based on the Concept of Green Chemistry

Strengthened, thermoreversible and conductive rubber with dual dynamic networks for strain sensors

Conductive composites have great potential in the field of strain sensors, which can be endowed with thermoreversible properties and excellent mechanical properties through the construction of dual dynamic networks structure inside the material, and compounded with the concept of green chemistry.

Origin of the Felkin-Anh(-Eisenstein) model: a quantitative rationalization of a seminal concept.

Quantum chemical calculations were carried out to quantitatively understand the origin of the Felkin-Anh(-Eisenstein) model, widely used to rationalize the π-facial stereoselectivity in the nucleophilic addition reaction to carbonyl groups directly attached to a stereogenic center. To this end, the possible approaches of cyanide to both (S)-2-phenylpropanal and (S)-3-phenylbutan-2-one have been explored in detail. With the help of the activation strain model of reactivity and the energy decomposition analysis method, it is found that the preference for the Felkin-Anh addition is mainly dictated by steric factors which manifest in a less destabilizing strain-energy rather than, as traditionally considered, in a lower Pauli repulsion. In addition, other factors such as the more favorable electrostatic interactions also contribute to the preferred approach of the nucleophile. Our work, therefore, provides a different, more complete rationalization, based on quantitative analyses, of the origin of this seminal and highly useful concept in organic chemistry.

Atividade saneante de nanopartículas de prata sintetizadas com produtos naturais sobre superfícies da indústria de laticínio

ABSTRACT: Surface contamination by pathogenic and deteriorating microorganisms is a constant concern in the food industry. Therefore, in this study we evaluated the antimicrobial activity of silver nanoparticles (AgNPs), produced using the essential oil of Lippia origanoides Kunth and ethanolic extract of Hymenaea martiana Hayne, against bacteria used in milk processing. For this, AgNPs were synthesized and their antimicrobial activity was evaluated for minimum inhibitory and bactericidal concentrations, time-kill, interference on the biofilm, and application on the surfaces of different materials. AgNPs showed bacteriostatic and bactericidal activity against Staphylococcus aureus (ATCC 25923), Staphylococcus aureus (ATCC 33591), Escherichia coli (ATCC 25922), Salmonella enterica subsp. enterica serovar Choleraesuis (ATCC 10708), Listeria monocytogenes, Escherichia coli, Salmonella spp.,andPseudomonas aeruginosa,and interfered with biofilm formation more than with consolidated biofilms. A 1hour period was sufficient to reduce the bacterial cells, whereas a Minimum Duration for Killing (MDK) of 99% was reached after approximately 30 min. AgNPs were effective against bacteria attached to stainless steel and polyethylene, but ineffective on tile surfaces. Thus, owing to the growing microbial resistance and the need to develop new products based on the concepts of green chemistry, these AgNPs are presented as a new possibility for cleaning processes in the food industry.

Bark extractives as sources of carbon-efficient functional precursors and materials

<p>Biomass residues generated in forest operations represent an abundant and renewable resource in need for valorization. Bark is becoming increasingly relevant, not only in the bioproducts sector, but also in the context of the circular bioeconomy, which is placing emphasis on underutilized residues and waste. Among these, tree bark is one of the largest forestry by-products, accessible at a megaton scale but so far mostly utilized for its solid fuel value. Bark valorization should include the isolation of valuable natural compounds that add functionalities to a variety of bioproducts. This is the subject of this review, which considers bark extractives prospects, under the biorefinery concept, placing attention on extractives' chemical profiles and properties. We introduce the most recent pathways reported for bark fractionation and the opportunities to achieve new materials by using the concepts of supramolecular chemistry, leading to special assemblies. We show that value-added chemicals and materials are possible and expected to become most relevant in efforts aimed at maximizing bark utilization.</p>

Exploring diversity: student's (un-)productive use of resonance in organic chemistry tasks through the lens of the coordination class theory

Resonance is a crucial concept in Organic Chemistry that enables both deriving chemical properties from molecular structures and predicting reactions by considering electron density distribution. Despite its importance for problem-solving and learning success, learners encounter various difficulties with this concept. Although prior research suggests that learners struggle to reason about resonance in problem-solving tasks, existing studies are often limited to singular contexts. Given that task approaches and reasoning are context-dependent, little is known about how learners use resonance across task contexts and which characteristics underlie productive concept use. To this end, a qualitative interview study was conducted, in which undergraduate chemistry students (N = 21), all beginners of Organic Chemistry, solved three organic case comparison tasks requiring the consideration of resonance. Through the analytical lens of the coordination class theory, we analysed the extent to which students used their representations of resonance structures, their task approaches, and the variety of resonance-related resource activation and connection in problem-solving across three different contexts. The results show that students’ use of resonance is diverse across the contexts. It can be characterized by a complex interplay of multiple factors reflecting the multifold processes when considering resonance. However, some essential characteristics of productive concept use in problem-solving (e.g., the activation of resources across different granularity levels) could be deduced. Implications for supporting learners’ use of resonance in problem-solving are discussed.

Application of a white and green spectrofluorimetric approach for facile quantification of amlodipine, a hypotensive drug, in batch materials, dosage forms, and biological fluids; content homogeneity testing.

The suggested study adheres to a particular protocol to ensure that the process is environmentally friendly and sustainable. It is worth mentioning that several tools have been adopted as prospective measures of the method greenness. Fortunately, the established analytical method is identified as white by the white analytical chemistry (WAC) concept, which uses the red/ green/blue color scheme (RGB 12 tool) to combine ecological and functional factors for the first time in studying of the cited drug. Amlodipine (AMD), a cardiovascular treating agent, belongs to the dihydropyridine class of oral calcium channel-blocking agents. This article presents a novel, simple, green, one-pot-processed, fast, and ultrasensitive fluorimetric approach for monitoring and assessment of AMD using molecular-size-dependent fluorescence augmentation of the light scattering-driven signal of eosin, a biological stain at a wavelength of 415 nm. This enhancement was directly proportional to the size of the produced complex. The linearity range was from 30 to 900 ng mL-1 , with corresponding sensitivity limits (detection and quantitation levels) of 9.2 and 28 ng mL-1 , respectively. The planned approach was also successfully used to track AMD content in bulk, dosage forms, and bio-fluids (human plasma and urine). The developed method's eco-friendliness was established by different eco-rating metric tools.

Widening university participation in learning using students’ contextualised storytelling in general chemistry

Many students find introductory general chemistry courses difficult because they feel alienated by traditional approaches to teaching and learning. This can become particularly problematic in laboratory sessions where students simply follow processes and procedures that students can view as being mundane and lacking creativity. Contextualised storytelling offers a novel pedagogical approach to help students connect and make sense of chemistry ideas in the context of their own life experiences. The current study implemented the CLEAR (chemistry learning via experiential academic reflection) approach to contextualised storytelling as a sequence of four assignments across a laboratory course for first-year students. The research explored students’ experiences writing contextualised stories to make sense of and learn chemistry. Using hermeneutics as a methodology, the data collected included participants’ written contextualised stories, semi-structured interview recordings, and field notes. While the CLEAR approach differs from other approaches to storytelling in chemistry education, the current study suggests that CLEAR can make positive contributions to student learning. The findings showed that, although many students initially resisted or felt confused by the new approach, CLEAR helped students see the connection and relevance of chemistry concepts to their lives. Students also recognized the importance of self-directed learning while writing their CLEAR stories, which suggests that CLEAR engaged students in learning that was active and organic. Furthermore, writing CLEAR stories supported students in talking to people about scientific concepts they learned in class, which suggests that writing the CLEAR stories: (a) helped students find the relevancy of the ideas to the degree that they felt they could share the ideas in their own words outside of class and (b) increased students’ interest in the course and what they were learning to the degree that they wanted to share it. Implementing CLEAR as multiple assignments across the course appears important and valuable because students refined their thinking and writing skills through iteration within and across CLEAR stories.

The evolution of an assignment: how a Writing-to-Learn assignment's design shapes organic chemistry students’ elaborations on reaction mechanisms

Asking students to explain why phenomena occur at a molecular level is vital to increasing their understanding of chemistry concepts. One way to elicit students’ mechanistic reasoning and guide construction of knowledge is through Writing-to-Learn (WTL), which is a promising approach for students in organic chemistry courses. In the design of WTL assignments, rhetorical aspects provide an authentic context by designating a role, genre, and audience for students. This context can support students’ learning, but, if the rhetorical aspects misalign with the learning objectives of the assignment, they can hinder students’ ability to achieve these objectives. In this project, we designed a WTL assignment about a base-free Wittig reaction, which we implemented in an organic chemistry laboratory course. Here, we explore how changes in the rhetorical aspects of this assignment can influence the way students explain two different comparisons of reaction mechanisms. We consider how students use explicit and implicit properties and how the use of these features compares within the context of the reaction. Results indicate that, when the rhetorical aspects align with the learning objectives of the assignment, students provide more productive elaborations that use both explicit and implicit properties. This is supported by both the analysis of students’ writing and students’ feedback about the assignments.

Resources for reasoning of chemistry concepts: multimodal molecular geometry

Central to conceptual understanding of STEM disciplines is visuospatial processing. Despite its acknowledged role in assuring learners’ success, less is known about the underlying reasoning students must employ when solving 3-D problems and the ways in which gaining an understanding of this can inform formative assessment and learning in STEM education. Chemists must utilise their spatial understanding when visualising 3-D structures and processes from 2-D representations and so this exploratory practitioner-researcher study sought to identify the ways in which secondary school chemistry students reason when explaining their predictions about molecular geometry, and how the use of certain modalities was linked to assessed accuracy. Coding of students’ verbal and written responses to the research task revealed that students employed multiple reasoning strategies and conceptual resources to facilitate use of analytical heuristics and imagistic reasoning. Analysis of students’ verbal responses and spontaneous gestures provided insight into the extent of imagistic vs. analytical reasoning and the finer-grained conditions which promoted their use. Importantly, it was observed that despite being instructed on the use of VSEPR theory to find analytical solutions, some students exhibited preference for alternative reasoning strategies drawing upon imagistic reasoning; showing more nuanced and varying degrees of accuracy through their verbal responses and representations gestured in 3D space. This work has pedagogical implications as use of specific reasoning strategies and the identification of key conceptual resources is not readily promoted as classroom practice for learning or assessment. This study therefore raises questions and contributes to the evidence base for attending to learners’ visuospatial thinking, as revealed through the multiple modalities they may use to assist and communicate their understanding, and highlights the significance of this to formative assessment in Chemistry and STEM Education.

What's in a word? Student beliefs and understanding about green chemistry

For the past decade, the College of Chemistry at UC Berkeley has iteratively redesigned general chemistry laboratory courses to introduce students to green chemistry concepts, while simultaneously using green chemistry as a relevant context to learn chemistry. To investigate the effectiveness of this curriculum we developed approaches to investigate student understanding of green chemistry. We adapted a constructivist educational framework to iteratively design fixed and free response items appropriate for large enrollment courses that probe student knowledge of green chemistry concepts and practices. Two free response items were designed to probe students’ ability to define green chemistry and make green chemistry decisions in the context of a case study. A set of fixed response items were designed to probe particular aspects of green chemistry knowledge that were included in the course. Together, we used these items to characterize (1) changes in student understanding of green chemistry and (2) how prior “green” knowledge impacts student learning of new green chemistry principles in the general chemistry laboratory course. Analysis of student responses indicated that, on average, students demonstrated increased green chemistry understanding after completing this green chemistry aligned laboratory course. Students were able to integrate more normative green chemistry principles in their answers and began to indicate awareness of complex interconnected systems. Because the items focused on assessing student knowledge of green chemistry, rather than their self-assessment of knowledge, they provided valuable insight regarding students’ prior green chemistry knowledge that will be used to develop future versions of the curriculum.

Identifying the critical features of resonance: instructors’ intentions for the teaching and learning of resonance in General Chemistry I and Organic Chemistry I

Resonance is a fundamental chemistry concept first introduced to students in General Chemistry I (GCI), reintroduced in Organic Chemistry I (OCI), and then utilized throughout other higher-level chemistry courses. Student difficulties with resonance are well documented. Instruction is one potential source of student difficulties. What instructors choose to expose students to and how they choose to expose students to concepts related to resonance is influenced by instructors’ intentions for learning. As a first step in understanding and addressing the difficulties students encounter when learning about resonance, we qualitatively examined what instructors intend for their students to understand about and do with resonance in the courses in which it is first introduced, GCI and OCI. The instructors we interviewed identified eleven critical features of resonance that they deemed important for students to learn about. We found that GCI and OCI instructors in this study identified many of the same critical features of resonance. However, there were differences in what they expected students to know about and do with those critical features. GCI and OCI instructors also identified critical features unique to their courses. Overall, while discussing the critical features, the instructors tended to emphasize an operational versus conceptual understanding of resonance, which may partially explain students’ focus on using resonance instead of understanding it, as has been reported previously in the literature. The instructor-identified critical features presented herein have important implications for teaching and learning, as instructors’ perceptions determine what they expose their students to during instruction and ultimately influence what students have the possibility to learn about resonance.

Implementing team-based learning in a large environmental chemistry course and its impact on student learning and perceptions

Team-based learning (TBL) is an instructional strategy where students participate in a set of activities including, applying course concepts to real-life case studies in instructor-selected teams. Here, we describe how TBL has been incorporated into a 3rd year, large, environmental chemistry course and investigate the benefits of using this strategy. A combination of pre/post survey and coursework data were analyzed to understand: (1) What were student perceptions of TBL? (2) How did using TBL to deliver content influence student learning, measured by exam performance? (3) How did students’ team skills evolve? Post-survey results indicate that students perceived TBL as enhancing their interest in course content, creating real-world connections, and most helpful for achieving practical critical thinking skills. Student performance on TBL-related final exam items was significantly better (Mean = 73%, SD = 21%) than non TBL-related final exam items, (Mean = 65%, SD = 21%), despite the level of complexity being similar between the two categories. The pre/post survey results indicate that, as compared to the start of term, students reported being significantly more comfortable expressing opinions in group meetings (t(78) = 4.25, p < 0.001, Cohen's d = 0.48), and leading group discussions (t(78) = 3.11, p = 0.003, Cohen's d = 0.35), by the end of the term. The one-minute reflections (completed following the first and fifth TBL activities) indicated that there was a 14% increase (77% vs. 91%) in the number of students reporting on collective team decision making. This study demonstrates the wide-ranging positive impacts of TBL to student learning in a large Environmental Chemistry course all while enhancing active learning and applying chemistry concepts to relevant and real-life case studies.

On the notion of strong correlation in electronic structure theory.

Strong correlation has been said to have many faces, and appears to have many synonyms of questionable suitability. In this work we aim not to define the term once and for all, but to highlight one possibility that is both rigorously defined and physically transparent, and remains so in reference to molecules and quantum lattice models. We survey both molecular examples - hydrogen systems (Hn, n = 2, 4, 6), Be2, H-He-H, and benzene - and the half-filled Hubbard model over a range of correlation regimes. Various quantities are examined including the extent of spin symmetry breaking in correlated single-reference wave functions, energetic ratios inspired by the Hubbard model and the Virial theorem, and metrics derived from the one- and two-electron reduced density matrices (RDMs). The trace and the square norm of the cumulant of the two-electron reduced density matrix capture what may well be defined as strong correlation. Accordingly, strong correlation is understood as a statistical dependence between two electrons, and is distinct from the concepts of "correlation energy" and more general than entanglement quantities that require a partitioning of a quantum system into distinguishable subspaces. This work enables us to build a bridge between a rigorous and quantifiable regime of strong electron correlation and more familiar chemical concepts such as anti-aromaticity in the context of Baird's rule.

Linking chemical concepts of enzymatic function in the introductory biology lab

Linking chemical concepts of enzymatic function in the introductory biology lab

Дидактикалық ойындар арқылы оқушылардың химия пәніне қызығушылығын арттыру

Currently, awakening students` interest in the subject is a problem of achieving results in the learning process. In the era of rapid development of information communication, gaming activity is of great importance for motor activity distracting them from gadgets and computers. The article considers the problem of increasing the cognitive outlook and interest of students in the subject of chemistry with the effective use of gaming technologies. The effectiveness of conducting a lesson with the help of gaming technologies lies in the fact that students easily study the topic and become more motivated for the lesson. Gaming technologies create a fun and creative atmosphere in the classroom. The article presents the didactic games in more detail, and an overview of some types of games was conducted. Theoretical and empirical, quantitative, and qualitative methods were used in the implementation of the research work. Control and experimental groups were selected and lessons were conducted using the traditional method and game technology. To determine the level of interest of students, a questionnaire method was used. In the lesson conducted based on traditional methods and didactic games, an increase in interest and understanding of the topic studies by students of the experimental group was found. During the task, the greatest activity and the motivation to understand chemical concepts and phenomena of the experimental group was observed compared with the control group. Didactic games allowed students to increase their interest in the subject, and describe concepts and phenomena in the process of completing the task. The game, combining mind and activity contributed to the easier and faster achievement of learning goals and the formation of personal qualities.

High-pressure stabilization of open-shell bromine fluorides.

Halogen fluorides are textbook examples of how fundamental chemical concepts, such as molecular orbital theory or the valence-shell electron-repulsion (VSEPR) model, can be used to understand the geometry and properties of compounds. However, it is still an open question whether these notions are applicable to matter subject to high pressure (>1 GPa). In an attempt to gain insight into this phenomenon, we present a computational study on the phase transitions and reactivity of bromine fluorides at pressures of up to 100 GPa (≈106 atm). We predict that at a moderately high pressure of 15 GPa, the bonding preference in the Br/F system should change considerably with BrF3 becoming thermodynamically unstable and two novel compounds emerging as stable species: BrF2 and BrF6. Calculations indicate that both these compounds contain radical molecules while being non-metallic. We propose a synthetic route for obtaining BrF2 which does not require the use of highly reactive elemental fluorine. Finally, we show how molecular orbital diagrams and the VSEPR model can be used to explain the properties of compressed bromine fluorides.

Green Chemistry: Approach to Improve the Performance of Grade 11 STEM Students in Chemical Equilibrium

Most science activities and programs provide emphasis on saving the environment. The Green Chemistry approach matches this effort to enhance students’ understanding of chemical concepts at the same time promote the value of responsible stewardship by applying principles that reduce or eliminate the use or generation of hazardous substances in the design of laboratory activities. This study focused on the use of Green Chemistry to improve the performance of Grade 11 students in Chemistry particularly on the topic on chemical equilibrium. This action research employed the experimental design where the 205 Grade 11 STEM students enrolled during the second semester of the school year 2019-2020 were exposed to two Green Chemistry laboratory activities in chemical equilibrium. The pretest and posttest data were analyzed using appropriate statistical measures namely: highest possible score, highest score obtained, lowest score obtained, mean, mean percentage score, median and standard deviation. The level of performance of the Grade 11 STEM students were further described as high, average or low. Paired samples t-test analysis of students’ pretest and posttest assessments was carried out at 0.05 level of significance. The results of the pretest revealed an “average” level of performance among the Grade 11 STEM students. Higher scores are evident during the posttest showing a “high” level of performance. The effectiveness of the Green Chemistry approach was further established by comparing the performance of the Grade 11 students in the pretest and posttest. Their posttest scores were significantly higher than their pretest scores. The results suggest that the green chemistry approach is effective in improving the students’ performance in Chemistry specifically in their understanding of one of the most complex topics which is chemical equilibrium. Prior to the intervention, most students held misconceptions about chemical equilibrium. However, after using the green chemistry approach, they gave logical explanations about systems in equilibrium and how they were affected by external stresses. The Green Chemistry hands-on activities helped the students to improve their performance in chemistry by reinforcing the development of students’ concepts in chemical equilibrium while taking measures to save the environment. It is recommended that the green chemistry teaching approach be adopted by other chemistry teachers in Urdaneta City Division. Similar approach can also be used in teaching other science concepts. The study shows that the Green Chemistry approach greatly improved the Grade 11 STEM students’ understanding of Chemical Equilibrium. Pre-test scores averaged 7.81 with no high performers, while post-test scores rose to 15.15, with 63.4% of students achieving high performance. A paired t-test confirmed a significant improvement (p < .05), proving the effectiveness of Green Chemistry in teaching complex topics. Additionally, the approach promoted environmental awareness, making it a valuable teaching method for broader use in science education.

The impact of co-design-based formative assessment practices on preservice science teachers’ understanding of chemical concepts in a general chemistry laboratory course

Recently, scholars have suggested a co-design collaboration with instructors and students to effectively implement formative assessment (FA) practices because it ensures a high-quality design that considers users’ needs, values, and goals in a specific learning context. This study examines the effect of co-designed FA practices, in which preservice science teachers (PSTs) are co-designers of FA practices, on promoting their conceptual understanding of chemistry topics in a first-year undergraduate chemistry laboratory course. Sixteen randomly selected PSTs participated in the study for two consecutive semesters. At the end of the first semester, a co-design of the FA practices was developed collaboratively with the PSTs upon the approach of conjecture mapping. Then, the second semester was devoted to examining the impact of the co-design-based FA environment on overcoming the PSTs’ alternative conceptions regarding selected four chemistry laboratory topics: thermochemistry, chemical kinetics, chemical equilibrium, acids and bases. This study employed a conversion mixed research design. To evaluate the co-design-based FA practices, PSTs’ alternative conceptions were identified through pre- and post-laboratory concept maps. The results obtained from both qualitative and quantitative data analyses showed that implementing the co-designed FA practices had a significant impact on overcoming most of the alternative conceptions held by the PSTs in all topics of laboratory investigations. This study strongly implies the inclusion of undergraduate students as active co-participants of the iterative reasoning process of the FA design to promote their understanding of chemical concepts in laboratory courses.