Understanding materials with dimensions down to few nanometers is of major importance for fundamental science as well as prospective applications. Structural transformation and phononconfinement effects in the nanodiamonds (NDs) have been theoretically predicted below 3 nm size. Here we investigate the effect of size on the surface chemistry, microscopic structure, and Raman scattering of high-pressure high-temperature (HPHT) and detonation nanodiamonds (DNDs) down to 2-3 nm. The surface and size of NDs are controlled by annealing in air and ultracentrifugation resulting in three ND fractions. Particle size distribution (PSD) of the fractions is analyzed by combining dynamic light scattering (DLS), analytical ultracentrifugation (AUC), small angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) as complementary techniques. Based on the obtained PSD we identify size-dependent and synthesis-dependent differences of NDs properties. In particular, interpretation of Raman scattering on NDs is revisited. Comprehensive comparison of detonation 3 and pure monocrystalline HPHT NDs reveals effects of diamond core size and defects, chemical and temperature (in)stability as well as limitations of current phonon confinement models. In addition, low-frequency Raman scattering in the 20 -200 cm -1 range is experimentally observed.The size dependence of this signal for both HPHT NDs and DNDs suggests that it may correspond to confined acoustic vibrational, "breathing-like" modes of NDs.

Using density functional methods, the initial reaction steps of limonene ozonolysis have been investigated with a focus on primary ozonide formation and its decomposition to Criegee intermediates and carbonyl compounds. The ozonide formation is highly exothermic, and the decomposition channels have similar free energies of activation, ΔG(‡), indicating that there is no primary pathway for ozonide decomposition. Assuming that ozonide formation is the rate limiting step, the theoretical rate coefficient, k = 1.6 × 10(-16) molecule(-1) cm(3) s(-1), evaluated at the CCSD(T)/6-31G(d,p)//BHandHLYP/cc-pvdz level and 298.15 K for d-limonene is in good agreement with the experimental value, k(exp) = 3.3 × 10(-16) molecule(-1) cm(3) s(-1). The theoretical Arrhenius expression is also in good agreement with experimental results.

From the pH‐dependence of the transverse relaxation‐time T2 of protons in 17O‐enriched water we have determined the rate constants k1 und k2 of the two proton‐exchange processes (I) and (II)magnified imagein the temperature range from +5°C to +60°C. – Modified Bloch equations including exchange between the different states of the proton‐septett are used to fit the experimental data yielding directly the rate constants k1 and k2. Classical and quantum mechanical relations connecting the limiting ionic equivalent conductivities λH+ and λOH− with the rate constants k1 and k2 are discussed.

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Differential pulse voltammetry with a glassy carbon electrode was used for the determination of trace amounts of 4-nitroaniline in Britton-Robinson buffer at pH 2.0 as an optimal base electrolyte. 4-Nitroaniline can be determined by differential pulse voltammetry directly using either its electrochemical oxidation or reduction. The calibration curve was measured for both reactions in the same concentration range from 2 to 100 lmol dm -3 . The calculated limits of detection and quantification are 0.2 and 0.7 lmol dm -3 (RSD 6.62 % and R 2 = 0.9906 for n = 5) for cathodic reduction and 0.3 and 1.0 lmol dm -3 (RSD 7.62 % and R 2 = 0.9995 for n = 5) for anodic oxidation. Graphical abstract