Maja Elmgren

Electron transfer between cellobiose dehydrogenase and graphite electrodes

Abstract Electron transfer between the enzyme cellobiose dehydrogenase (CDH) and a flavin adenine dinucleotide (FAD) containing a catalytic active fragment of CDH (FAD-fragment) and a graphite electrode, respectively, was established. The current response in the presence of the enzyme substrate for graphite electrodes with CDH or the FAD-fragment adsorbed on the freshly polished graphite surface were compared with that of electrodes where CDH or the FAD-fragment were crosslinked in a redox polymer at the electrode surface. The initial slope, dj d[S] s = 0 , where j is the current density and [S]s = 0 the zero substrate concentration, was taken as a measure of the substrate response. For the electrodes with enzymes adsorbed directly on the surface, dj d[S] s = 0 , was a factor of 3 lower than for electrodes prepared with the polymer mixture. The redox polymer based electrodes, with CDH and with FAD-fragment, both showed a high and close to equal substrate response. In contrast the surface adsorbed CDH gave a much higher substrate response than the FAD-fragment.

Cellobiose oxidase crosslinked in a redox polymer matrix at an electrode surface—a new biosensor

The properties of an enzyme electrode, based on cellobiose oxidase, CBO, crosslinked in a redox polymer (poly[(vinylpyridine)Os(bpy)2Cl2+3+]/polyamine) matrix on a rotating disk electrode were studied. Effects on the steady state cellobiose response of pH, temperature, rotation rate and film thickness were investigated. The percentage of accessible redox couples remained constant, regardless of film thickness up to at least 2.5 μm, indicating full access to the outermost layer of the enzyme—polymer matrix. The apparent Michaelis constant K′m increased with increasing film thickness, owing to depletion of substrate in the film. The turnover number k′2 decreased with increasing film thickness, indicating reaction limitation due to charge propagation through the film. Extrapolated to an infinitesimal film, the kinetic constants of the electrode mirror the enzyme kinetics in solution. The Arrhenius activation energy was determined to be 42 kJ mol−1 for the thickest electrode and 34 kJ mol−1 for the thinnest. The electrode is suited as a sensor for cellobiose, lactose and maltose as well as for cellotriose and corresponding oligosaccharides up to a degree of polymerization of at least six.

Charge propagation through a redox polymer film containing enzymes—effects of enzyme loading, pH and supporting electrolyte

Abstract Charge propagation through a redox polmer film (poly[(vinylpyridine)Os(bpy) 2 Cl 2+/3+ ]/polyamine) containing the enzymes glucose oxidase and cellobiose oxidase was studied using potential-step chronocoulometry and cyclic voltammetry. The results were correlated with substrate response measurements made using the electrodes as amperometric biosensors. To explore the effect of enzyme loading, a series of electrodes were made with varying polymer-to-enzyme ratios but constant film thickness. The apparent charge-transport diffusion coefficient D E drastically decreased with decreasing amount of polymer, i.e. increasing amounts of enzymes. Thus it is evident that values of D E from pure redox polymers cannot be used to describe charge propagation in enzyme electrodes. The pH dependence of charge propagation is more pronounced for electrodes with the pure polymer than for electrodes with a mixture of enzymes and polymer. For all electrodes D E increased with decreasing pH below pH 5. A change of supporting electrolyte, giving a marked effect on the enzyme electrode response, does not alter charge propagation through the film. This shows that the effect is derived from the enzyme action only.

Electrochemical properties of an amphiphilic viologen in differently charged micelles

The electrochemical properties of N-tetradecyl-N′-methylviologen (TMV) in differently charged micelles were studied with a glassy carbon electrode using electrochemical techniques. The redox potential varied depending on the charge of the surrounding surfactants. When the viologen was situated in cationic micelles the redox potential for the 2+/1+ reaction was more positive than when situated in negatively charged micelles. The non-ionic micelles destabilised the 2+-state most showing the highest redox potentials. From studies of several different cationic micelles it was concluded that the most important parameter for the redox potential was the surface charge density. A calculation based on a simple model confirmed this. Other interactions also influenced the stability of the redox states. Adsorption, desorption and reorganisation of the surfactants at the electrode surface caused capacitive currents. To control the nonfaradaic current, differential pulse voltammetry (DPV) was used in addition to cyclic voltammetry.

Photoelectrochemical etching of polycrystalline TiO2 thin film electrodes

Abstract The photoelectrochemical etching of polycrystalliine TiO 2 thin film electrodes prepared by thermal oxidation of electropolished titanium metal has been studied using various electrochemical and photoelectrochemical techniques. The results reveal the influence of the polycrystalline structure and the presence of defect sites on the photocurrent and recombination of photogenerated charge carriers. The presence of a gradient in dopant density and a highly oxidized low-doped top layer was concluded. Photoelectrochemical etching of the TiO 2 electrodes causes deterioration of the photoelectrochemical response, contrary to the improvement achieved on mechanically polished TiO 2 single crystals. This suggests a well ordered lattice structure of the areas subject to PEC etching.

Covariational reasoning and mathematical narratives: investigating students’ understanding of graphs in chemical kinetics

Graphical representations are an important tool used to model abstract processes in fields such as chemistry. Successful interpretation of a graph involves a combination of mathematical expertise and discipline-specific content to reason about the relationship between the variables and to describe the phenomena represented. In this work, we studied students’ graphical reasoning as they responded to a chemical kinetics prompt. Qualitative data was collected and analyzed for a sample of 70 students through the use of an assessment involving short-answer test items administered in a first-year, non-majors chemistry course at a Swedish university. The student responses were translated from Swedish to English and subsequently coded to analyze the chemical and mathematical ideas students attributed to the graph. Mathematical reasoning and ideas related to covariation were analyzed using graphical forms and the shape thinking perspective of graphical reasoning. Student responses were further analyzed by focusing on the extent to which they integrated chemistry and mathematics. This was accomplished by conceptualizing modeling as discussing mathematical narratives, characterizing how students described the “story” communicated by the graph. Analysis provided insight into students’ understanding of mathematical models of chemical processes.

Life and work in academia

T he significance of higher education for individuals and society as well as its size and complexity justify that research on higher education is recognised and developed. In this special issue, we focus on academic citizenship and academic work. Life and work in academia has mostly been described in terms of teaching and research, personalised by academic staff (Boyer, Altbach, & Whitelaw, 1994). These core activities are related to historically developed missions of the university embedded invalues like academic freedom and professional autonomy. Another distinction focuses on the difference between the core and the support system developed to enable teaching, research and public outreach. Academics may very well be engaged in one or several of the university missions and involved in both core activities and support systems. Consequently, there are potentially many complex relations within universities as well as in the interplay between the university and different sectors of society. Still a large number of activities integral to academic life are often left out and to some degree they appear as less visible aspects of the academic culture. Many of these activities can be related to those duties (Kennedy, 1997), responsibilities or virtues of academic faculty that Bruce Macfarlane (2007) includes in academic citizenship. Academics perform services with differing status to several overlapping communities public, discipline-based/professional, institutional, collegial and student community (cf Gordon & Whitchurch, 2010). With massification, marketisation and managerialism, higher education institutions face new situations that challenge academic work and our understanding of it. Even though research on academic work has increased, it is still rather restricted. In an extensive literature review, edited by Kehm and Teichler (2013), several dimensions structuring the academic profession were identified: blurred boundaries of professional identities and the emergence of hybrid professionals overlapping academic and administrative tasks and functions; decommissioning of the academic profession since the 1990s; tensions between academic and managerial values in a context of changing governance of higher education; challenges faced by the traditional structure of academic career paths (Henningsson, Jörnesten, & Geschwind, in press); internationalisation of academic markets and careers; challenges in terms of quality, societal relevance and research excellence calling for new forms of academic work and collaboration with external stakeholders (cf. Fumasoli, Goastellec, & Kehm, 2015). In this special issue of Nordic Journal of Studies in Educational Policy, several aspects of stability and change within academia are elaborated on by scholars from various disciplines, scientific fields and institutions from three Nordic countries. Consequently, a number of theoretical perspectives, methodologies and data are being employed. At the same time, there are similarities between the Nordic countries, even beyond European agreements. All Nordic countries are small and open, highly dependent on exchange with the world outside, not least in higher education. They offer free education and all have a high percentage of the population in doctoral education (Elmgren, Forsberg, Lindberg-Sand, & Sonesson, 2016). Furthermore, the Nordic welfare states have in common a tradition of the state as a ‘guardian angel’ of national higher education institutions a situation some regard as challenged today by changed relations between the national state and higher education (cf Nybom, 2007). The Nordic societies are also among the most equal in the world. In sum, these similarities between the Nordic countries lay a foundation for mutual understanding, while the openness makes studies relevant also to the outside. Topics and themes represented in the articles comprise academic values, governance and collegiality, the formation of the scholar, professionalisation, formalisation processes, peer review and socialisation. This variety reflects the landscape of higher education research in general, often described as a multidisciplinary field with no obvious domain within any of the established disciplines (Forsberg & Geschwind, 2016; Teichler, 1992; Tight, 2013). Kerstin Sahlin and Ulla Eriksson-Zetterquist discuss governance ideals and practices in their article Collegiality in Modern Universities, in which possibilities and limitations of bureaucracy, management and collegiality are illustrated and compared. In the vivacious debate on collegiality, they have noted an absence of clarification of the concept, leading to less stringent argumentation. They contribute with a principled discussion on what collegiality is, since collegiality might be undermined, not just through influence of new public management but also through undeveloped reflections on collegiality itself. Furthermore, they discuss how collegiality can be maintained and supported, and argue that collegiality cannot remain unchanged and also needs to be complemented by various modes of governance. Efficiency has been an important argument for introducing elements of new public management in academia; however, while the consequences of that have been

International Comparisons of Tertiary Chemistry Education: A Best-Practice Approach for Development and Quality Enhancement

There are many reasons chemistry education varies among nations and institutions: cultural traditions, societal expectations, socio-economic factors, and educational resources, to name just a few. At the university level there is also a dependence on the earlier educational system, as well as the research profile of the particular institution. In an increasingly globalized world, however, graduate mobility across international boundaries is more relevant than ever. In order to promote high quality chemistry education, comparisons and communication at both national and international levels are important for designing or improving programs. Such comparisons can raise the awareness of what to change and what to hold on to.