On efficient stopping times

This paper is devoted to efficient sequential estimation in stochastic processes whose corresponding sufficient statistics are processes with stationary independent increments. It is proved that a stopping time is efficient if and only if it represents a time of the first attaining of a hyperplane., which cannot ‘be passed’, in the sense which is made precise below. The problem of determining the explicit form of the hyperplanes which cannot ‘be passed’ is also discussed.     

Host/Guest Interactions and NMR Spectroscopy. A Computer Program for Association Constant Determination

A computer program is presented for the computation of association constants for host/guest compounds based on experimental data obtained from the NMR spectra of samples with different host/guest ratios of known concentration.     

Encapsulation and release by star‐shaped block copolymers as unimolecular nanocontainers

A five‐arm star‐shaped poly(ethylene oxide) (PEO) with terminal bromide groups was used as a macroinitiator for the atom transfer radical polymerization of tert‐butyl acrylate (tBA), resulting in five‐arm star‐shaped poly(ethylene oxide)‐block‐poly(tert‐butyl acrylate) block copolymers. The polymerization proceeded in a controlled way using a copper(I)bromide/pentamethyl diethylenetriamine catalytic system in acetonitrile as solvent. The hydrolysis of the tBA blocks of the amphiphilic star‐shaped PEO‐b‐PtBA block copolymer resulted in dihydrophilic star structures. The encapsulation of the star‐block copolymers and their release properties in acid environment have been followed by UV‐spectroscopy and color changes, using the dye methyl orange as a hydrophilic guest molecule. Characterization of the structures has been done by ¹H NMR, size exclusion chromatography, MALDI‐TOF, and differential scanning calorimetry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 650–660, 2008     

Macrotricyclic host molecules with basket shaped cavities

The syntheses of several macrotricyclic hexalactams (1–3) and of a corresponding hexalactone (4) are described in detail for the first time. The molecules have a basket shaped skeleton and contain a non-collapsible cavity, the size and shape of which is varied by use of spacer groups. Compounds1–3 selectively form crystalline adducts with ethanol as guest; the macrotricyclic hexaester4 does not. Evidence for an interaction of1 with ethanol was obtained by exchange experiments with perdeuteroethanol. Complexation experiments in solution did not show significant host/guest interactions with the guest chosen.     

Crystal and molecular structure of the inclusion compound between 1,1′-binaphthyl-2,2′-dicarboxylic acid and acetylacetone (1∶1)

The lattice type crystalline inclusion compound of 1,1-binaphthyl-2,2-dicarboxylic acid (BNDA) with acetylacetone (AcAc) 11 has been investigated by single crystal X-ray diffraction. AcAc is present as the enolic tautomer, stabilized by a notably short intramolecular hydrogen bond. This H-bond closes a six-membered ring with delocalization of the system of conjugated double bonds. In the crystal the AcAc molecules are incorporated into channels, delimited by bulky binaphyl moieties, in a hydrogen-bonded framework of BNDA, and they do not show any disorder. The strictly stoichiometric host:guest ratio seems to be enforced by packing forces only.     

Crystal structure and thermal analysis of an inclusion compound of a chiral sexipedal host with 1,4-dioxane

The crystal structure of the 16 inclusion compound of the chiral host, hexakis[3-o-chlorophenyl)-3-(phenyl-3-hydroxy-1-propynyl]benzene with 1,4-dioxane shows that both O–H...O and C–H...O hydrogen bonds are used to bind the guests.     

Ein neues makrobicyclisches Wirtmolekül-Synthese und ANS-Komplexierung

The synthesis of the new host molecule1b is described. Its complexation properties towards 1,8-ANS as a guest are reported. Compared to the monomacrocyclic host molecules2c and2e, the complex stabilities of1b with ANS as a guest are particularly higher, suggesting that the macrobicyclic host forms a better fitting niche to allow the nestling of guest molecules in solution.

     

Combinations of natural and synthetic inclusion compounds and their thermal stability

Inclusion compounds do not belong to the group of simple compounds. They consist of molecules of the host and guest components. Some of them form supermolecules and exhibit super-molecular properties.Combinations of inclusion compounds as even more complicated systems need more methods to be used for their identification. Thermoanalytical study enables to study the sorption during their formation and the progressive liberation of their individual components and parts. Many layered silicates, phosphates and other similar synthetic and natural compounds enclosing or adsorbing cyclodextrins, pharmaceuticals, aromatics, various agrochemicals and inorganics are analysed from the view of their formation and properties.