Inverted chemical force microscopy: following interfacial reactions on the nanometer scale

Atomic force microscopy (AFM) with chemical specificity using chemically modified AFM probes, so-called chemical force microscopy, was applied to study surface chemical reactions on the nanometer scale. To overcome the typical limitations of conventional AFM in following reactions in real-time, i.e. slow data acquisition, as well as thermal and instrumental drifts, we have introduced a new approach, named inverted chemical force microscopy (iCFM). In iCFM the reactants are immobilized on the AFM tip rather than on the substrate. The chemical reactions take place at the surface of the tip and are probed in real-time by force-displacement measurements on an inert octadecanethiol-covered Au substrate. The reactions studied were the hydrolysis and aminolysis of 11,11^′-dithiobis(N-hydroxysuccinimidylundecanoate) (NHS-C₁₀). By iCFM intermolecular interactions and hence reaction kinetics can be quantitatively studied on the level of ∼10-100 molecules. In particular, our iCFM data showed that the aminolysis reaction with n-butylamine on SAMs of NHS-C₁₀ is a spatially heterogeneous reaction. In addition, information about the defect density of reactive SAMs was obtained.     

Journeys to the Westersingel Natuurkunde Laboratorium

Hyperfine Interactions - Both Ag and Fe are mutually immiscible elements and this feature made it possible to produce nano-scaled multilayer laminates. Super-laminates of [Ag/Fe]10,000 layers and...     

Correlation Functions and Boundary Conditions in Rational Conformal Field Theory and Three-Dimensional Topology

We give a general construction of correlation functions in rational conformal field theory on a possibly nonorientable surface with boundary in terms of three-dimensional topological field theory. The construction applies to any modular category in the sense of Turaev. It is proved that these correlation functions obey modular invariance and factorization rules. Structure constants are calculated and expressed in terms of the data of the modular category.     

Synthesis,Crystal Structure Determination from X‐Ray Powder Diffractometry and Vibrational Spectroscopic Properties of Mg[N(CN)2]2 · 4 H2O

Magnesium dicyanamide tetrahydrate Mg[N(CN)₂]₂ · 4 H₂O was synthesized by aqueous ion exchange starting from Na[N(CN)₂] and Mg(NO₃)₂ · 6 H₂O. The crystal structure was solved and refined on the basis of powder X‐ray diffraction data (P2₁/c, Z = 2, a = 737.50(2), b = 732.17(1), c = 971.67(2) pm, β = 98.074(1)°, wR_p = 0.059, R_p = 0.046, R_F = 0.075). In the crystal there are neutral complexes [Mg[N(CN)₂]₂(H₂O)₄] which are only connected via hydrogen bonds. Above 40 °C the tetrahydrate decomposes into anhydrous Mg[N(CN)₂]₂.     

Mathematical theory of radiation

In this paper we present an informal review of our recent work whose goal is to develop a mathematical theory of the physical phenomenon of emission and absorption of radiation by systems of nonrelativistic matter such as atoms and molecules. Dedicated to Larry Horwitz on the occasion of his 65th birthday. Research supported by DFS 288 and by NSF Phy 90-10433A02. Research supported by SNF. Research supported by NSERC Grant NA 7901.     

Passive Runge–Kutta Methods—Properties, Parametric Representation, and Order Conditions

In this paper, a new class of Runge–Kutta methods is introduced. Some basic properties of this subgroup of algebraically stable methods are presented and a complete parametric representation is given. Necessary and sufficient order conditions for lower order methods as well as sufficient order conditions for higher order methods are derived yielding a significantly reduced number of conditions when compared with general Runge–Kutta methods. Design examples conclude this paper.     

Spectrophotometric determination of olanzapine by its oxidation with N-bromosuccinimide and cerium(IV)sulfate.

Three simple spectrophotometric methods have been described for the assay of olanzapine in its pure and pharmaceutical formulations. The direct method (A) is based on the drug oxidation with excess of N-bromosuccinimide in acidic medium and the two indirect methods (B and C) are based on the oxidation of the drug with excess of N-bromosuccinimide and cerium(IV)sulfate, followed by the reaction of the unconsumed oxidants with celestine blue. The calibration graphs were linear over the range 10 - 120 microg mL(-1) (method A), 0.5 - 6.0 microg mL(-1) (method B) and 0.6 - 3.0 microg mL(-1) (method C). After validation, the proposed methods were successfully applied to assay of olanzapine in its commercial tablets with mean percentage recoveries of 101.23 +/- 0.10, 96 +/- 0.10 and 94 +/- 0.04%. The mechanism of olanzapine oxidation with N-bromosuccinimide was also proposed.