Studies In Physical Chemistry Research Articles

Extractive electrospray ionization mass spectrometry of ionic liquids

The growing role of ionic liquids (ILs) in industry and research is creating an urgent need for the development of analytical methods for the reliable characterization and control of the composition of the ILs. The application of mass spectrometry (MS) to the analysis of ILs is limited by the poor tolerance of classical MS methods toward samples with high salt concentrations and viscosity. Herein, extractive electrospray ionization mass spectrometry (EESI-MS) was applied to directly analyze various room temperature ILs such as 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]) 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), and 1-butylpyridinium tetrafluoroborate ([BuPy][BF4]). The EESI mass spectra of ILs diluted in methanol revealed great similarities to the mass spectra of the same samples assessed by direct infusion ESI-MS. Both cationic (C+) and anionic (A−) IL components could be detected with a high sensitivity from strongly diluted samples (<10−7 M). [CA − H]− or [CA + H]+ signals were observed for certain ILs using EESI-MS, and in good agreement with their classification based on the acid–base theory. With only minor alterations to the experimental setup, analysis of the ILs could be performed without dilution, which allowed a direct observation of the IL aggregates in the gas phase at a speed of >2 samples per min. EESI-MS allows the direct analysis of ILs in a broad concentration range with a high tolerance to chemical contamination. The reported examples suggest the potential for EESI-MS to interrogate large IL assays, which is critical in both fundamental physical chemistry studies and industrial applications.

Protein folding dynamics in the cell.

Protein folding is a remarkably fast unimolecular reaction, spanning microseconds to hours at room temperature. Thus, free energy differences and activation barriers on the free energy landscape of proteins are rather small. This opens up the possibility of living cells modulating their protein's landscapes, providing cells another way to control the function of their proteomes after transcriptional control, translational control, and post-translational modification. In this Feature Article, we discuss advances in physicochemical studies of protein stability and folding inside living cells. We focus in particular on our studies using fast relaxation imaging (FREI). Although the effect of the cell on protein free energy landscapes is only a few kT, the strong cooperativity of many folding and binding processes allows small modulation of the energy and entropy to produce a large population modulation. Lastly, we discuss some biomolecular processes that are particularly likely to be affected by in-cell modulation of the proteome, and thus of interest for quantitative physical chemistry studies.

Retention of differential and integral calculus: a case study of a university student in physical chemistry

This paper reports a study on retention of differential and integral calculus concepts of a second-year student of physical chemistry at a Danish university. The focus was on what knowledge the student retained 14 months after the course and on what effect beliefs about mathematics had on the retention. We argue that if a student can quickly reconstruct the knowledge, given a few hints, this is just as good as retention. The study was conducted using a mixed method approach investigating students’ knowledge in three worlds of mathematics. The results showed that the student had a very low retention of concepts, even after hints. However, after completing the calculus course, the student had successfully used calculus in a physical chemistry study programme. Hence, using calculus in new contexts does not in itself strengthen the original calculus learnt; they appeared as disjoint bodies of knowledge.

Ultrasmall polarization rotation measurements via weak value amplification

• We present a class of weak measurements where the measurer is an angular variable of the system. • Photon-energy qubits are required, which seems to be the first application of this kind of light. • Both weak optical activity and reflection-induced polarization rotation can be amplified. • This protocol can amplify the optical activity signal in nanostructures and biological tissues. We propose a framework to analyze weak measurements based on an angular version of the von Neumann measurement scheme, where the coupling between the system and the meter causes rotation of the measuring variable. We also discuss an experimental application of this theory in which measurements of weak optical activity and reflection-induced polarization rotation could be amplified in nearly two orders of magnitude. It can shed a new light on a great variety of physical chemistry, molecular biology and nanotechnology studies.

Exploring the Nature of the H2 Bond. 1. Using Spreadsheet Calculations To Examine the Valence Bond and Molecular Orbital Methods

A three-part project for students in physical chemistry, computational chemistry, or independent study is described in which they explore applications of valence bond (VB) and molecular orbital–configuration interaction (MO–CI) treatments of H2. Using a scientific spreadsheet, students construct potential-energy (PE) curves for several states of H2 from the kinetic and potential energies, calculated from closed-form analytical expressions of the ten unique integrals arising from the Born–Oppenheimer Hamiltonian. For this project students use hydrogen 1s basis functions that include a screening parameter. From the calculated PE curves, they find the dissociation energy, De, and equilibrium internuclear distance, Re. In part I students use the Heitler–London (VB) form of the wave function to obtain the PE curves. In part II they optimize the value of the screening parameter to improve the results, and in part III they explore the treatment of H2, using both the simple MO wave function and the application of CI, with and without screening parameter optimization, to obtain the PE curves. Students compare their De and Re results with the experimental values. A set of questions, exercises, and a sample spreadsheet are provided as Supporting Information.

Transport number and current–voltage of a cation exchange membrane equilibrated in aqueous and organic solutions

A physical-chemistry study of a Nafion 117 membrane is undertaken and a correlation between the transport number and current–voltage data of this cation exchange membrane is established. The current–voltage characteristics of the membrane are obtained with the voltamperometric technique, by means of two feed platinised titanium electrodes and two measuring silver–silver chloride electrodes. Previous measurements show that the membrane presents low electrical resistance and weak permselectivity towards the proton in the presence of other metallic cations. However, its chemical modification with the conducting polymer highly improves the proton conduction and gives better selectivity towards the monovalent cation (Na+) against the divalent cation (Zn2+). The effects of the co-ion (anion), charge, solvent and chemical modification are made in evidence by the current–voltage curves. As a result of its pre-concentration near the anionic layer, the divalent cation increases the value of the limiting current density. Besides, the presence of an organic solvent inside the polymeric matrix of the membrane decreases the limiting current density. Different graphical methods are applied to deduce the limiting current density and the derivative method is found to be more reliable.

Possibilities of cloud educational technologies in the study of physical chemistry

Opening of Mathcad Calculation Server (MCS) (http://www.vpu.ru/mas) at the Moscow Power Engineering Institute made it possible to create and implement an interactive reference book of physico-chemical quantities and thermodynamic database (http://twt.mpei.ac.ru/TTHB/1/HBThermValues.html) in the remote access mode in the educational process.Such authoritative electronic databases as, for example, the Database of Iftantermo, NIST Chemistry WebBook allow to obtain individual numbers or arrays of numbers characterizing the properties of substances and systems, but they do not generate functional and graphical relationships, which significantly reduces their educational opportunities. The peculiarity of interactive web-version of physicochemical quantities is its educational orientation: each Mathcad-document specifies by which experimental data the analytical dependence describing change of the investigated function was made, by which relations and how the investigated parameter is calculated, dependence diagrams are given, that allows to observe behavior of the searched quantity and current point on curve.

New mass spectrometry techniques for studying physical chemistry of atmospheric heterogeneous processes

Ambient particles and droplets have a significant effect on climate, visibility and human health. Once formed, they undergo continuous transformations through condensation and evaporation of water, uptake of low-volatility organic molecules and photochemical reactions involving various gaseous and condensed-phase species in the atmosphere. These transformations determine the physical and chemical properties of airborne particles, such as their ability to absorb and scatter solar radiation and nucleate cloud droplets. The complexity, heterogeneity and size of ambient particles make it challenging to understand the kinetics and mechanisms of their formation and chemical transformations. Mass spectrometry (MS) is a powerful analytical technique that enables detailed chemical characterisation of both small and large molecules in complex matrices. This capability makes MS a promising tool for studying chemical transformations of particles and droplets in the atmosphere. This review is focused on new and emerging experimental MS-based approaches for understanding the kinetics and mechanisms of such transformations. Some of the techniques discussed herein are best suited for ambient samples, while the others work best in laboratory applications. However, in combination, they provide a comprehensive arsenal of methods for characterisation of particles and droplets. In addition, we emphasise the role of fundamental physical chemistry studies in the development of new methods for chemical analysis of ambient particles and droplets.

对大学物理化学课程教学的思考&lt;br&gt; Considerations of Physical Chemistry Teaching in Higher Education

物理化学综合运用了数学、物理等基础科学的理论和实验方法来研究化学过程的普遍规律及其与微观结构的关系，是理论性较强的一门学科，是化工、材料、冶金、生物、环境等诸多学科领域研究、发展的基础。对物理化学知识体系的认知和理解对培养学生的科学素养和实践能力至关重要。本文以物理化学的研究内容和发展状况为出发点，从教师自身素养的主动提升和学生科学素养的培养两个方面出发，探讨了我国高等学校物理化学课程教学过程中应注重的问题。 Physical Chemistry studies the changes that matter can undergo and explains the observations on the physical and chemical properties of matter in terms of the principles of physics and the language of mathematics. The principles of physical chemistry are related with many scientific and technologic fields, such as chemical industry, materials science, metallurgy, environtology, life sciences and medicine. Learning and comprehending the knowledge of physical chemistry, therefore, are important for the development of student’s practical ability and scientific competency in higher education. In this paper, we discussed some questions that have to be noticed during physical chemistry teaching in two aspects: the self-improvement of teachers and the education of students.

Triphenylene Substituted Pyrene Derivative: Synthesis and Single Molecule Investigation

A novel donor–acceptor material based on pyrene derivative with two substituted triphenylenes (Py-TP2) is synthesized via the Sonogashira coupling reaction. The structure and physical chemistry properties of the target molecule have been discussed, ranging from the traditional 1H NMR and high-resolution mass spectroscopy (HRMS), over UV and PL spectra, and to the surface science research. The results revealed that the Py-TP2 molecule shows a narrowed energy gap between LUMO–HOMO and a bathochromic shift of 27 nm in the solid state as compared to that in solution, which is important for its practical applications in optoeletronic devices. Moreover, combined with DFT calculations, our STM results clearly show that the Py-TP2 molecule assembled into a stable long-ranged zigzag structure on HOPG surface. The interesting results in this contribution will boost the physical chemistry study of other functional materials under such methods.

Study of physical chemistry on biosorption of zinc by using Chlorella pyrenoidosa

Discharge of heavy metals from metal processing industries is known to have adverse effects on the environment. Biosorption of heavy metals by metabolically inactive biomass of microbial organisms is an innovative and alternative technology for removal of these pollutants from aqueous solution. Presence of heavy metals in the aquatic system is posing serious problems. Zinc has been used in many industries and removal of Zn ions from waste water is significant. Biosorption is one of the economic methods used for removal of heavy metals. In the present study, the biomass obtained from the dried Chlorella pyrenoidosa was used for evaluating the biosorption characteristics of Zn ions in aqueous solutions. Batch adsorption experiments were performed with this material and it was found that the amount of metal ions adsorbed increased with the increase in the initial metal ion concentration. In this study effect of agitation time, initial metal ion concentration, temperature, pH and biomass dosage were studied. Maximum metal uptake (qmax) observed at pH 5 was 101.11 mg/g. The biosorption followed both Langmuir and Freundlich isotherm model. The adsorption equilibrium was reached in about 1 h. The kinetic of biosorption followed the second-border rate. The biomass could be regenerated using 0.1 M HNO3. A positive value of ΔH° indicated the endothermic nature of the process. A negative value of the free energy (ΔG°) indicated the spontaneous nature of the adsorption process. A positive value of ΔS° showed increased randomness at solid-liquid interface during the adsorption of heavy metals, it also suggests some structural changes in the adsorbate and the adsorbent. FTIR Spectrums of Chlorella pyrenoidosa revealed the presence of hydroxyl, amino, carboxylic and carbonyl groups. The scanning electron micrograph clearly revealed the surface texture and morphology of the biosorbent.

催化表面物理化学的模型体系研究

Surface physical chemistry studies of catalysts aim to understand the surface structure-activity relation and the reaction mechanism of heterogeneous catalytic reaction at the molecular level for the improvement and design of efficient catalysts. It is difficult to unambiguously correlate the catalytic activity with the structure for powder catalyst because of its structural complexity and un-uniformity. Therefore, model catalysts with uniform and well-defined structures have been always employed for the surface physical chemistry studies of catalysts. In this paper, I review the research concept and the recent progress that has been achieved in surface physical chemistry studies of model systems for heterogeneous catalysis in my research group. We have innovated model catalysts from the traditional single crystals/single crystal thin films to nanocrystals with uniform and well-defined structures for the surface physical chemistry studies for targeted heterogeneous catalytic system. Our research concept might achieve the fundamental understanding of the surface structure-activity relation and the reaction mechanism of the practical heterogeneous catalytic reaction at the molecular level.

Study of physical chemistry on biosorption of zinc by using Chlorella pyrenoidosa

Discharge of heavy metals from metal processing industries is known to have adverse effects on the environment. Biosorption of heavy metals by metabolically inactive biomass of microbial organisms is an innovative and alternative technology for removal of these pollutants from aqueous solution. Presence of heavy metals in the aquatic system is posing serious problems and zinc has been used in many industrials and removal of Zn ions from waste waters is significant. Biosorption is one of the economic methods that is used for removal of heavy metals. In the present study, the biomass generated from the dried Chlorella pyronoidsa was used for evaluating the biosorption characteristics of Zn ions in aqueous solutions. Batch adsorption experiments were performed on these leaves and it was found that the amount of metal ions adsorbed increased with the increase in the initial metal ion concentration. In this study effect of agitation time, initial metal ion concentration, temperature, pH and biomass dosage were studied. Maximum metal uptake was observed at pH = 5. Maximum metal uptake (qmax) was 101.11 mg/g. The biosorption followed both Langmuir and Freundlich isotherm model. The adsorption equilibrium was reached in about 1 h. The kinetic of biosorption followed the second – order rate. The biomass could be regenerated using 0.1 M HNO3. A positive value of ∆H° indicated the endothermic nature of the process. A negative value of the free energy (∆G°) indicated the spontaneous nature of the adsorption process. A positive value of ∆S° showed increased randomness at solid–liquid interface during the adsorption of heavy metals, it also suggests some structural changes in the adsorbate and the adsorbent.Fourier transform infrared (FTIR) spectrums of C. pyrenoidosa revealed the presence of hydroxyl, amino, carboxylic and carbonyl groups. The scanning electron micrograph (SEM) clearly revealed the surface texture and morphology of the biosorbent. Key words: Biosorption, Chlorella pyronoidosa, Zn, isotherm models, kinetic.

Use of Simple Kinetic and Reaction-Order Measurements for the Evaluation of the Mechanism of Surfactant–Liposome Interactions

Surfactant-liposome interactions have been previously studied through different methods and techniques. We present here a classical physical chemistry study on liposome solutions added to destabilizing agents at concentrations well above the solubilization concentration, which enable us to draw useful and interesting conclusions about the mechanism of surfactant-induced liposomal breakdown by simply exploiting the kinetics and the reaction order of the liposomal content release. In such excess of surfactant, the mechanism of surfactant-induced rupture of the liposomes has been demonstrated to be different from that proposed for low surfactant concentrations. Thus, depending on the surfactant concentration, two prevailing processes have been evidenced: (i) a cooperative mechanism that implies the assembly of a critical number of surfactant molecules to trigger the formation of a channel and therefore the release of the liposomal content and (ii) a mechanism driven by direct interaction of the surfactant molecules with the lipids that causes the complete solubilization of the liposomes. The former mechanism occurs at low surfactant concentrations, whereas the latter occurs at higher concentrations and above the CMC of the surfactants. The effect of different guests embedded into the liposomal bilayer on the mechanism of surfactant-induced liposomal breakdown has been compared by using the second-order rate constants measured for the liposome breakdown process.

Regiospecific synthesis of quercetin O-β- d-glucosylated and O-β- d-glucuronidated isomers

Quercetin, the polyphenolic compound, which has the highest daily intake, is well known for its protective effects against aging diseases and has received a lot of attention for this reason. Both quercetin 3- O-β- d-glucuronide and quercetin 3′- O-β- d-glucuronide are human metabolites, which, together with their regioisomers, are required for biological as well as physical chemistry studies. We present here a novel synthetic route based on the sequential and selective protections of the hydroxyl functions of quercetin allowing selective glycosylation, followed by TEMPO-mediated oxidation to the glucuronide. This methodology enabled us to synthesize the five O-β- d-glucosides and four O-β- d-glucuronides of quercetin, including the major human metabolite, quercetin 3- O-β- d-glucuronide.

Molecular Behavior in Small Spaces

The study of physical organic chemistry in solution is a mature science, over a century old, but over the last 10 years or so, reversible encapsulation has changed the way researchers view molecular interactions. It is now clear that the behavior of molecules in dilute solution is really quite different from their behavior in capsules. Molecules isolated from bulk media in spaces barely large enough to accommodate them and a few neighbors show new phenomena: their activities resemble those of molecules inside biochemical structures--pockets of enzymes, interiors of chaperones, or the inner space of the ribosome--rather than conventional behavior in solution. In this Account, we recount the behavior of molecules in these small spaces with emphasis on structures and reactivities that have not been, and perhaps cannot be, seen in conventional solution chemistry. The capsules self-assemble through a variety of forces, including hydrogen bonds, metal-ligand interactions, and hydrophobic effects. Their lifetimes range from milliseconds to hours, long enough for NMR spectroscopy to reveal what is going on inside. We describe one particular capsule, the elongated shape of which gives rise to many of the effects and unique phenomena. Molecular guests that are congruent to the space of the host can be tightly packed inside and show reduced mobilities such as rotation and translation within the capsule. These mobilities depend strongly on what else is encapsulated with them. We also relate how asymmetric spaces can be created inside the capsule by using a chiral guest. In contrast to the situation in dilute solution, where rapid exchange of solute partners and free molecular motion average out the steric and magnetic effects of chirality, the long lifetimes of the encounters in the capsules magnify the effects of an asymmetric environment. The capsule remains achiral, but the remaining space is chiral, and coencapsulated molecules respond in an amplified way. We probe the various regions of the capsule with guests of different shape. Primary acetylenes, the narrowest of functional groups, can access the tapered ends of the capsule that exclude functions as small as methyl groups. The shape of the capsule also has consequences for aromatic guests, gently bending some and straightening out others. Flexible structures such as normal alkanes can be compressed to fit within the capsule and conform to its shape. We obtain a measure of the internal pressure caused by the compressed guests by determining its effect on the motion of the capsule's components. These forces can also drive a spring-loaded device under the control of external acids and bases. We show that spacer elements can be added to give self-assembled capsules of increased complexity, with 15 or more molecules spontaneously coming together in the assembly. In addition, we analyze the behavior of gases, including the breakdown of ideal gas behavior, inside these capsules. The versatility of these capsule structures points to possible applications as nanoscale reaction chambers. The exploration of these confined spaces and of the molecules within them continues to open new frontiers.

The Curtin−Hammett Principle in Mass Spectrometry

The Curtin-Hammett principle (CHP) is an important concept in physical organic chemistry and is often utilized in the investigation of reaction mechanisms. Two reactants, A and B, in rapid equilibrium, react to form products P(A) and P(B) with rates k(A) and k(B), respectively. If the reaction is under kinetic control and the rate of equilibration between the two reactants is much faster than the reactions to form products, then the branching ratio of products P(A) and P(B) depends solely on the difference in barrier heights for the two product channels. The CHP is based on the fact that the ratio of products formed is not determined by the reactant population ratio. However, the CHP also applies to studies in other areas of chemistry, including mass spectrometry. This Account describes work from our groups in which the results must be interpreted in light of the CHP. These studies illustrate two important implications of the CHP. First, they demonstrate how product distributions cannot be used to assess reactant structure in mechanistic studies in Curtin-Hammett systems. A recent investigation of the structure of hydroxysiliconate anions demonstrated that it was not possible to distinguish between the possible reactant ion structures. A second important implication of the CHP is that the structure of the reactant does not affect the product branching ratio and therefore does not need to be a consideration if the CHP applies. We address this aspect of the discussion through kinetic method studies of the acidities of amino acids and proton affinities of bifunctional compounds. Recently reported mass spectrometric studies illustrate how the CHP puts limitations on what conclusions can be drawn from product distribution studies but also allows experimental methods, such as the kinetic method, to be carried out for complicated systems without having to know all the details of the reactant ion structures. These studies show that although the CHP is most commonly applied in mechanistic studies in physical organic chemistry, it also applies to other areas of chemistry, including mass spectrometry. Although the CHP in some cases limits the conclusions that can be drawn from an experimental study, its proper application can often be used to greatly simplify very complicated chemical systems. Therefore, it is important in mass spectrometry, and indeed, in all areas of chemistry, to recognize those systems in which the CHP should and should not apply.

Introduction to the Molecular Recognition and Self-Assembly Special Feature

Molecular recognition is a mature branch of chemical science, and why shouldn't it be? Decades of studies in physical organic chemistry have defined and evaluated the weak intermolecular forces involved when 2 molecules encounter each other. Every bimolecular reaction, whether it occurs in the gas phase, dilute solution, or an enzyme's interior, begins with a recognition event. It is an apt time to explore recognition in a larger context, that of multicomponent assemblies, and this special issue of 14 contributions is a beginning.

Use of a multimedia DVD for Physical Chemistry: analysis of its effectiveness for teaching content and applications to current research and its impact on student views of physical chemistry

In this study, a new multimedia learning tool for physical chemistry was implemented in a class setting, and students’ attitudes and learning gains examined. The Physical Chemistry in Practice (PCIP) DVD contains multimedia modules that provide an in-depth description of the research of eight different scientists. Each module contains a documentary style video program of the researcher and their laboratory, HTML-based background information about the topic, problems for students to work on, and links to related information. The DVD was implemented in a physical chemistry laboratory course where students worked through a module on surface- enhanced Raman spectroscopy (SERS). Data was collected in the form of pre- and post-tests of content knowledge and surveys about attitudes and academic career choices. Students showed statistically significant learning gains after using the DVD and showed an increase in their recognition of the applications of physical chemistry to real problems. Students also showed an increased interest in further study of physical chemistry. [Chem. Educ. Res. Pract., 2007, 8 (3), 308- 326.]

Physical chemistry study on the Ore-forming process of the hetaoping Pb–Zn-polymetallic deposit, baoshan county, yunnan province, China

Physical chemistry study on the Ore-forming process of the hetaoping Pb–Zn-polymetallic deposit, baoshan county, yunnan province, China