Solid Lipid Nanoparticles (SLNs): Preparation and Properties of Calix[4]resorcinarene Derived Systems.

Solid Lipid Nanoparticles (SLNs) have been prepared fromc-2,c-8,c-14,c-20-tetraundecyl-4,6,10,12,16,18,22,24-octahydroxyresorc[4]areneas colloidal suspensions. Photon Correlation Spectroscopy studies revealed aparticle hydrodynamic diameter of 150 nm. Non-contact mode Atomic ForceMicroscopy allows observation of the particles as slightly flattened sphericalobjects of 236 (±40) nm diameter and 145 (±40) nm height. Thestudy of the preparation parameters showed that shear force does not affectthe hydrodynamic size of the SLNs. In contrast, the viscosity and the pH ofthe aqueous phase, the amphiphile concentration in the organic phase and thevolume of organic phase used, all lead to variation in the size of the particles.In term of post preparation parameters only the ionic strength has been shownto affect significantly the particle size; while the pH of the storing solution,microwave, ultrasonic and thermal treatments do not. Short and long-termstability studies have been performed to measure the effect of the ionic strengthon the stability of the particles. The use of carbohydrate cryoprotectants does notallow re-dispersion of the colloidal suspension after freeze-drying.     

Monitoring the packet gap of real-time packet traffic

Real-time packet traffic is characterized by a strict deadline on the end-to-end time delay and an upper bound on the information loss. Due to the high correlation among consecutive packets, the individual packet loss does not well characterize the performance of real-time packet sessions. An additional measure of packet loss is necessary to adequately assess the quality of each real-time connection. The additional measure considered here is the average number of consecutively lost packets, also called the average packet gap. We derive a closed form for the average packet gap for the multiclassG/G/m/B queueing system in equilibrium and show that it only depends on the loss behavior of two consecutive packets. This result considerably simplifies the monitoring process of real-time packet traffic sessions. If the packet loss process is markovian, the consecutive packet loss has a geometric distribution.     

Efficient synthesis of 2- and 3-substituted-2,3-dihydro [1,4]dioxino[2,3-b]pyridine derivatives

A versatile new approach for the synthesis in three steps of 2-substituted-2,3-dihydro[1,4]dioxino[2,3-b]pyridines B via a Smiles rearrangement using easily available reagents is described. A study illustrating the influence of experimental conditions on the progress of the reaction is reported.     

Synthesis of 2-substituted-2,3- dihydro-1,4-dioxino[2,3-b]pyridine derivatives

[reaction--see text] A variety of 2-substituted-2,3-dihydro-1,4-dioxino[2,3-b]pyridines B have been synthesized from the readily available 2-nitro-3-oxiranylmethoxypyridine 1 via a Smiles rearrangement. We demonstrate how variations of reaction conditions affect the product distribution of A and B.     

Application of personal microcomputers in the analytical laboratory--I: Potentiometric analysis

A novel general-purpose interface-controller unit has been designed and applied in potentiometric analysis. The unit is operated by a personal microcomputer programmed in BASIC. The interface-controller permits direct reading of specific ion-electrodes and can activate, under program control, laboratory instruments such as motor-driven burettes. The interface-controller is expendable to 16 analogue input channels, 16 binary (logic) input lines and 16 control relays but requires only one microcomputer I/O port (a total of 9 I/O lines) to handle all operations. Analogue to digital conversion is realized by counting, with the microcomputer, the output frequency of an analogue-to-frequency converter. This inexpensive method is effective in rejecting interfering signals such as power-line interference. The system has been applied in potentiometric titration analysis for determining the apparent dissociation constants of carbonic acid in sea-water and Dead Sea brines, and for ammonia determination with a gas-sensing electrode.     

Detection of chiral perturbations in ferroelectric liquid crystals induced by an atropisomeric biphenyl dopant

The atropisomeric dopant 2,2',6,6'-tetramethyl-3,3'-dinitro-4,4'-bis[(4-nonyloxybenzoyl)oxy]biphenyl (1) induces a ferroelectric SmC phase when doped into the SmC liquid crystal hosts 2-(4-butyloxyphenyl)-5-octyloxypyrimidine (PhP1) and (+/-)-4-[(4-methylhexyl)oxy]phenyl 4-decyloxybenzoate (PhB). The propensity of dopant 1 to induce a spontaneous polarization (polarization power) is much higher in PhP1 than in PhB (1555 nC/cm(2) vs <35 nC/cm(2)), which is attributed to a greater propensity of 1 to undergo chirality transfer via core-core interactions with PhP1. In previous work, we postulated that a chiral perturbation exerted by 1 in PhP1 amplifies the polarization power of the dopant by causing a chiral distortion of the mean field potential (binding site) constraining the dopant in the SmC host, as described by the Chirality Transfer Feedback (CTF) model. To test the validity of the CTF model, and to provide a more direct assessment of the chiral perturbation exerted by dopant 1 on surrounding host molecules, we measured the effect of 1 on the polarization power of other chiral dopants acting as probes. In one series of experiments, (S,S)-5-(2,3-difluorooctyl)-2-(4-octylphenyl)pyridine (MDW950) and (S)-4-(1-methylheptyloxy)phenyl 4-decyloxybenzoate (4), which mimic the structures of PhP1 and PhB, were used as probes. In another series of experiments, the atropisomeric dopant 2,2',3,3',6,6'-hexamethyl-4,4'-bis[(4-nonyloxybenzoyl)oxy]biphenyl (2) was used as probe in PhP1. The results of the probe experiments suggest that dopant 1 exerts a much stronger chiral perturbation in PhP1 than in PhB. More significantly, the results of experiments using 2 as probe show that the chiral perturbation exerted by 1 can amplify the polarization power of another atropisomeric dopant, thus providing the first experimental evidence of the CTF effect.