Meaningful understanding of chemistry, among others, includes the ability of an individual to think simultaneously at macroscopic, submicroscopic and symbolic levels, and this presupposes the competence to translate between different types of chemical representations. In this study, we investigated 11th grade Greek students’ and 3rd year undergraduate chemistry students’ ability to translate chemical representations from one level of chemistry (e.g., submicroscopic) into another (e.g., symbolic) concerning the basic chemical concepts: “chemical element”, “chemical compound”, “aqueous solution” and “solid state of matter”, which have already been taught in earlier grades. We followed a mixed method design in which both quantitative and qualitative research instruments were developed and used. These instruments consisted of multiple choice and open-ended questions, which included real pictures (macroscopic), symbolizations and submicroscopic diagrams. Various representations of the three types were given to the students and they were asked to choose or to construct an equivalent one of a different type. Our results showed that the 11th grade students’ ability to move across the three levels of chemistry is very low, while the 3rd year undergraduate chemistry students’ performance is higher but not satisfactory. In addition, the results obtained from the application of “translation questions” between the three levels of chemistry highlighted many students’ alternative conceptions, some of which still persist among the undergraduate students. The students showed lower performance in translations concerning the concepts “chemical compound” and “aqueous solution” than those concerning the concepts “chemical element” and “solid state of matter”. The students also showed the lowest level of performance in translating the submicroscopic representations into the symbolic ones. Generally, our results indicate that translating between different types of chemical representations is a very challenging task, which depends on students’ conceptual understanding.

The development of renin inhibitors for the treatment of hypertension requires highly sensitive substrates to evaluate potency and to characterize the mechanism of tight-binding inhibitors. A series of intramolecularly quenched fluorogenic renin substrates, based on the N-terminal tetradecapeptide sequence of human angiotensinogen (hTDP), was synthesized using a solid-phase technique. Incorporation of the fluorescent amino acid L-Amp [L-2-amino-3-(7-methoxy-4-coumaryl)propionic acid] and the DNP (2,4-dinitrophenyl) group at various positions resulted in >90% quenching efficiency and strong product fluorescence. Shortening the hTDP sequence to an octapeptide from histidine in P5 to histidine in P3' (substrate 3) resulted in an acceptable k(cat)/K(m) (41000 M(-1).s(-1)) and further systematic variation gave substrate 9, DNP-Lys-His-Pro-Phe-His-Leu-Val-Ile-His-L-Amp, with a k(cat)/K(m) value of 350000 M(-1).s(-1) and 94% quenching efficiency. The free side chain of lysine, replacing the isoleucine residue at P6 position in the angiotensinogen sequence, contributed to the increased value for k(cat). The pH dependence of k(cat)/K(m) for renin and substrate 9 showed that the optimal pH is at pH 6-7. It also showed two titrating groups on the acidic side of the pH optimum, and one titrating group with a pK(a) of 7.8 on the alkaline side. The combination of good kinetic and spectroscopic properties resulted in a >20-fold improvement in the sensitivity of renin assay, compared with the commercial substrate Arg-Glu(EDANS)-Ile-His-Pro-Phe-His-Leu-Val-Ile-His-Thr-Lys(DABCYL)-Arg [where EDANS is 5-[(2-aminoethyl)amino]naphthalene-1-sulphonic acid and DABCYL is 4-(4-dimethylaminophenylazo)benzoic acid] (k(cat)/K(m)=268000 M(-1) x s(-1), quenching efficiency <80%). The detection limit in a microplate renin assay was 60 pM, making substrate 9 well suited for the evaluation of inhibitors at picomolar concentrations.