Enhanced loading of water-soluble actives into bicontinuous cubic phase liquid crystals using cationic surfactants

Over the past few years, bicontinuous cubic phase liquid crystals have been investigated for their applicability to controlled delivery of active ingredients. These liquid crystals have a unique structure of interpenetrating channels of water and lipid that provides compatibility with water-soluble, lipid-soluble, and amphiphilic active ingredients. Actives tend to be stable in the matrix and the structure provides control over their release. However, loading of water-soluble actives is difficult. It is especially problematic for cubic phase liquid crystal dispersions (cubosomes) given the large fraction of bulk water present. The inherent problem reflects the preference of the water-soluble actives to associate with water rather than with the liquid crystals. Ideally, the properties of the liquid crystal can be tailored to enhance the association of the liquid crystal with the active, thereby increasing loading. It is found that the inclusion of surfactant into the liquid crystal can provide this function. This work illustrates the enhanced loading of negatively charged, water-soluble active ketoprofen by the inclusion of positively charged surfactants into the liquid crystal. Loading differences resulting from the inclusion of dioctadecyl dimethyl ammonium chloride (DODMAC) and dioctadecyl ammonium chloride (DOAC) into the liquid crystal demonstrate that the magnitude of the enhancement is dependent on the surfactant concentration and the steric nature of its head group. The upper limit of the enhancement is explored by the inclusion of di(canola ethyl ester) dimethyl ammonium chloride (DEEDAC) formulated to greater than 20 wt% and demonstrates an order-of-magnitude enhancement over previous reports. This work provides a practical demonstration of functionalizing cubic phase liquid crystals and lays the framework for future work.     

Suppression of metastable interference in matrix-assisted laser desorption/ionization (MALDI) spectra in a reflecting time-of-flight mass spectrometer

Metastable interference in matrix-assisted laser desorption/ionization (MALDI) spectra is reduced by modulating the accelerating potential (by <～100 V) on alternate laser shots. Both parent and daughter ions are reflected on every second shot but only daughter ions are reflected on the next shot. The parent-ion spectrum is then obtained by subtraction. In order to ensure the necessary well defined energy distributions, signals with similar intensity (preferably small) are selected by transferring each transient to a computer for examination. This procedure decreases the complexity in reflected spectra (especially spectra of mixtures) in the lower mass range and improves the mass resolution in the intermediate mass range around 10 000 u. Continuous background in reflected spectra is also suppressed by the technique.     

An investigation of the kinetics of the formation of permanganate from divalent manganese using periodic acid as oxidant

1. The rate at which permanganate is produced when divalent manganese is oxidized with potassium periodate has been followed absorptiometrically in sulphuric and nutric acid solutions Under certain conditions the reaction is of the first order with first order autocatalysis. 2. An expression has been derived for the velocity constant, which is used to compare the speed of oxidation in solutions of various acidities at various temperatures. The velocity is a minimum with 1.5 M acid, but increases in either stronger or weaker acid solutions.. An increase in velocity is accompanied by a decrease in the quantity of permanganate produced from a given quantity of divalent manganese. 3. It has been deduced that divalent manganese is only slowly oxidized by periodate unless a catalyst (such as the surfacc of metallic platinum) is present. The natural catalyst for the reaction is quadrivalent manganese, produced at one stage in tlie oxidation. A detailed account of the probable mechanism of the oxidation is suggested, having regard to the thermodynamical properties of the molecules involved. 4. Suitable conditions for an absorptiometric method are recommended. Metallic platinum is useful for reducing the very long induction period found wlien only traces of manganese are present.     

Surface core level shifts on InP(110): Use of Sb overlayers

The surface core level shift of the P2p from a clean InP(110) surface has been studied by use of the Sb overlayer. It is shown that the nonreactive Sb overlayer removes the surface core level shift and does not introduce any other component. The unique possibility to separately characterize the bulk component allows a precise determination of the surface core level shift. We show that the surface P2p core level is shifted to lower binding energy by −0.29 eV, while an opposite and nearly equal in magnitude +0.30 eV shift is established for the In4d.     

On the collision density in recoil hot atom systems. Effect of reactive events

Characteristics of the collisional distribution function for reactive hot atoms in nuclear recoil systems are examined and illustrated for the T + H₂ system both unmoderated and moderated with argon. Reaction induced extrema are evident in the collision density of the unmoderated case. For this system depletion of hot atoms from the collisional distribution function due to reactive events is reflected significantly in the product yields even at high moderation.