Surface cleaning and sample carrier for complementary high-resolution imaging techniques

Nowadays, high-resolution imaging techniques are extensively applied in a complementary way to gain insights into complex phenomena. For a truly complementary analytical approach, a common sample carrier is required that is suitable for the different preparation methods necessary for each analytical technique. This sample carrier should be capable of accommodating diverse analytes and maintaining their pristine composition and arrangement during deposition and preparation. In this work, a new type of sample carrier consisting of a silicon wafer with a hydrophilic polymer coating was developed. The robustness of the polymer coating toward solvents was strengthened by cross-linking and stoving. Furthermore, a new method of UV-ozone cleaning was developed that enhances the adhesion of the polymer coating to the wafer and ensures reproducible surface-properties of the resulting sample carrier. The hydrophilicity of the sample carrier was recovered applying the new method of UV-ozone cleaning, while avoiding UV-induced damages to the polymer. Noncontact 3D optical profilometry and contact angle measurements were used to monitor the hydrophilicity of the coating. The hydrophilicity of the polymer coating ensures its spongelike behavior so that upon the deposition of an analyte suspension, the solvent and solutes are separated from the analyte by absorption into the polymer. This feature is essential to limit the coffee-ring effect and preserve the native identity of an analyte upon deposition. The suitability of the sample carrier for various sample types was tested using nanoparticles from suspension, bacterial cells, and tissue sections. To assess the homogeneity of the analyte distribution and preservation of sample integrity, optical and scanning electron microscopy, helium ion microscopy, laser ablation inductively coupled plasma mass spectrometry, and time-of-flight secondary ion mass spectrometry were used. This demonstrates the broad applicability of the newly developed sample carrier and its value for complementary imaging. © 2020 Author(s)

The reactions of thymine and thymidine with ozone

The ozonolysis of thymine and thymidine has been investigated by a product study complemented by kinetic studies using spectrophotometry, conductometry and stopped-flow with optical and conductometric detection. Material balance has been obtained. Ozonolysis of thymine (k = 3.4 x 10(4) dm(3) mol(-1) s(-1)) leads to the formation of the acidic (pK(a) = 4) hydroperoxide 1-hydroperoxymethylene-3-(2-oxopropanoyl)urea 5 (similar to34%), neutral hydroperoxides (possibly mainly 1- hydroperoxyhydroxymethyl-3-(2-oxopropanoyl)urea 6, total similar to41%) and H2O2 (25%, with corresponding formation of 1-formyl-5-hydroxy-5-methylhydantoin 11). The organic hydroperoxides decay (similar to1.1 x 10(-3) s(-1) at 20 degreesC, 1.3 x 10(-4) s(-1) at 3 degreesC) releasing formic acid (formation of 5-hydroperoxy-5-methylhydantoin 18) and also to some extent H2O2 (and 11). After 100 min, the formic acid yield is 75%. Upon treatment at high pH, it increases to 100%. Reduction of the organic hydroperoxides with bis(2- hydroxyethyl)sulfide (k = 50 dm(3) mol(-1) s(-1)) leads to 11 whose subsequent treatment with base yields 5-hydroxy-5- methylhydantoin 13 in 100% yield. It is suggested that the Criegee ozonide formed upon reaction with ozone at the C(5)- C(6) double bond opens heterolytically in two directions with subsequent opening of the C(5)-C( 6) bond. In the preferred route (75%), the positive charge resides at C(6). Deprotonation at N(1) gives rise to 5, while its reaction with water yields 6. Loss of formic acid yields 5-hydroperoxy-5- methylhydantoin 18. Reduction of 5 and 6 with the sulfide yields 11. In the minor route (25%), the positive charge remains at C(5) followed by a reaction with water. The resulting alpha-hydroxy hydroperoxide rapidly loses H2O2 (formation of 11). In basic solution, singlet dioxygen is formed (8%). The concomitant product, 5,6-dihydroxy-5,6-dihydrothymine has been detected. In the ozonolysis of thymidine, the rapid formation of conductance (k = 0.55 s(-1)) is due to the release of acetic acid (18%). In this reaction a short-lived hydroperoxide is destroyed. As a consequence of this, 25 s after ozonolysis the total hydroperoxide yield is only 78% (including 8% H2O2). The products corresponding to acetic acid are suggested to be CO2 and N-(2-deoxy-beta-D-erythropentofuranosyl)formylurea 22. A number of organic hydroperoxides have been detected by HPLC by post-column derivatisation with iodide. An acidic hydroperoxide such as 5 in the case of thymine is not among the products. Upon sulfide reduction, the organic hydroperoxides yield mainly (43-50%) N-1-(2-deoxy-beta-D-erythropentofuranosyl)-5-hydroxy- 5-methylhydantoin 23. The reasons for some striking differences in the ozonolyses of thymine and thymidine are discussed

How fast is the reaction of hydrated electrons with graphene oxide in aqueous dispersions?

Understanding the mechanism of the reduction of graphene oxide (GO) is a key-question in graphene related materials science. Here, we investigate the kinetics of the reaction of radiolytically generated hydrated electrons with GO in water. The electron transfer proceeds on the ns time scale and not on the ps time scale, as recently reported by Gengler et al. (Nat. Commun., 2013, 4, 2560)