Pectin in controlled drug delivery – a review

Controlled drug delivery remains a research focus for public health to enhance patient compliance, drug efficiency and reduce the side effects of drugs. Pectin, an edible plant polysaccharide, has been shown to be useful for the construction of drug delivery systems for specific drug delivery. Several pectin derived formulations have been developed in our laboratory and tested in vitro, ex vivo, and in vivo for the ability to deliver bioactive substances for therapeutic purposes in the context of interactions with living tissues. Pectin derivatives carrying primary amine groups were more mucoadhesive and have shown potential in nasal drug delivery and other mucosal drug delivery. Pectin derivatives with highly esterified galacturonic acid residues are more hydrophobic and able to sustain the release of incorporated fragrances for a prolonged duration. Less esterified pectin derivatives are able to penetrate deeper into the skin and may be useful in aromatherapy formulations. Pectin, in combination with zein, a corn protein, forms hydrogel beads. The bound zein restricts bead swelling and retains the porosity of the beads; the pectin networks shield the zein from protease attack. The complex beads are ideal vehicles for colon-specific drug delivery. Studies presented in this paper indicate the flexibility and possibility to tailor pectin macromolecules into a variety of drug delivery systems to meet different clinical requirements. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.     

Gemini-induced columnar jointing in vitreous ice. Cryo-HRSEM as a tool for discovering new colloidal morphologies

A gemini surfactant is able to promote columnar jointing in vitreous ice where long pillars, often of hexagonal cross section, are formed. This jointing is visible by cryo-high-resolution scanning electron microscopy (cryo-HRSEM), in which colloidal suspensions in bulk water are cooled rapidly in liquid ethane, thereby avoiding the potential artifacts with other types of EM. The jointing is proposed to arise from a new type of colloidal morphology where the surfactant self-assembles into hexagonal columns. Evidence for this mechanism comes from a cryo-HRSEM photo of an ice-free hexagonal "skeleton" composed of surfactant. Cryo-HRSEM, a method that is just beginning to realize its potential, would seem to have a promising future in the discovery of additional and as yet unimagined colloidal structures.     

Reactions of triosmium clusters with organic azides; x-ray crystal structures of [Os3(CO)10(NCMe)(N3COPh)], [Os3(μ-H)(CO)10(HN3Ph)], and [Os3(μ-H)2(CO)9(μ3-NPh)]

Organic azides [N₃R] react with [Os₃(CO)₁₁(NCMe)] and with [Os₃(μ-H)₂(CO)₁₀] to form [Os₃(CO)₁₀(NCMe)(N₃COR)] (R  Ph) and [Os₃(μ-H)(CO)₁₀(HN₃R)] (R  Ph, n-Bu, CH₂Ph, cyclo-C₆H₁₁), respectively; the latter may be converted to [Os₃(μ-H)₂(CO)₉(μ₃-NR)] by thermolysis; the molecular structure of the phenyl derivative of each class of compound has been confirmed by x-ray analysis.     

Salvinicins A and B, new neoclerodane diterpenes from Salvia divinorum

[reaction: see text] Two new neoclerodane diterpenes, salvinicins A (4) and B (5), were isolated from the dried leaves of Salvia divinorum. The structures of these compounds were elucidated by spectroscopic techniques, including (1)H and (13)C NMR, NOESY, HMQC, and HMBC. The absolute stereochemistry of these compounds was assigned on the basis of single-crystal X-ray crystallographic analysis of salvinicin A (4) and a 3,4-dichlorobenzoate derivative of salvinorin B.     

Functionalized organosilica microspheres via a novel emulsion-based route

Thiol-functionalized organosilica microspheres were synthesized via a two-step process: (1) acid-catalyzed hydrolysis and condensation of 3-mercaptopropyltrimethoxysilane (MPTMS), followed by (2) base-catalyzed condensation, which led to the rapid formation of emulsion droplets with a narrow size distribution. These droplets continued to condense to form solid microspheres. Solution (29)Si NMR and optical microscopy were applied to study the mechanism of this novel synthetic route. Solid-state (29)Si NMR, SEM, zeta potential titration, and Coulter counter measurements were used to study the bulk and surface properties and to determine the particle size distributions of the final microspheres. Compared to conventional St?ber silica particles, these microspheres were shown to have a lower degree of cross-linking (average degree of condensation, r = 1.25), a larger average size (up to 6 microm), and a higher isoelectric point (pH = 4.4). Confocal microscopy of dye-labeled microspheres showed an even distribution of dye molecules throughout the interior, characteristic of a readily accessible and permeable organosilica network. These findings have implications for the production of functionalized solid supports for use in catalysis and biological applications, such as optically encoded carriers for combinatorial synthesis.     

Optimization of matrix-assisted laser desorption/ionization time-of-flight collision-induced dissociation using poly(ethylene glycol)

Details of the optimization of the collision-induced dissociation (CID) process, using a collision cell on a matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometer, are described using poly(ethylene glycol) 1000 (PEG 1000) as a model analyte. The effects of collision gas identity (helium, air, and argon), as well as collision gas pressure, on the resulting MS/MS data were investigated. With PEG 1000, helium was found to give the best results with respect to signal-to-noise (S/N) ratio. The optimum pressure for each gas was found to be in the range where the precursor ion signal was attenuated to approximately 30-50% for helium and 40-60% for argon. The effect of cation choice (Li, Na, and K) on the CID of PEG was also studied. CID spectra were produced for each, but PEG cationized with lithium was found to produce the spectra with the highest S/N ratio. The MALDI-TOF CID spectra that were generated for PEG were compared with the high-energy and low-energy MS/MS spectra obtained from a sector mass spectrometer and from a triple quadrupole mass spectrometer, respectively. The results observed for PEG confirm that CID on a MALDI-TOF mass spectrometer is a high-energy MS/MS technique.     

Sorption of triethyleneglycol and tetraethyleneglycol by silicalite at fixed water activities

The sorption of tetraethyleneglycol by silicalite-1 and triethyleneglycol by silicalite-1 and a silicalite-1/silicalite-2 intergrowth has been studied at 25°C and at fixed water activities in the range 0.111<a _w<0.902 by an isopiestic method. All of the glycol uptakes are between 0.95 and 1.2 molecules per unit cell and in all cases they are essentially independent of water activity. The water content of the silicalite-1 was more sensitive to water activity and glycol content than was that of the silicalite-1/2 intergrowth.     

The first intermolecular Friedel-Crafts acylation with beta-lactams

The first intermolecular Friedel-Crafts acylation of a variety of aromatic substrates with azetidinones is described. The Friedel-Crafts acylations are performed under very mild conditions, using trifluoromethanesulfonic acid to produce beta-amino aromatic ketones in excellent yields.     

The thiolate anion as a nucleophile Part XII. Reactions of Lead(II) Benzenethiolate

The reactions of various fluoroaromatics, C₆F_6?xH_x, and C₆F₅X (X = C₆F₆, Cl, Me, NO₂, CF₃, COCl, CH₂Br, OMe, and NH₂) with lead(II) benzenethiolate in DMF have been examined. Lead thiolate acted as an excellent source of benzenethiolate anions and displacement of fluorine, chlorine or the nitro group was observed. The new products have been characterized by elemental analysis, and NMR (H?1 and F?19), infrared and mass spectroscopy.     

Thiophene and butadiene-thiolate complexes of molybdenum: observations relevant to the mechanism of hydrodesulfurization

Mo(PMe3)6 reacts with thiophene to give the eta5-thiophene complex (eta5-C4H4S)Mo(PMe3)3 and the eta5-butadiene-thiolate complex (eta5-C4H5S)Mo(PMe3)2(eta2-CH2PMe2), which are the first examples of (i) eta5-thiophene coordination and (ii) C-S cleavage and hydrogenation by a molybdenum compound. Deuterium labeling studies suggest that the hydrogenation of thiophene may involve an alkylidene intermediate, an observation that has ramifications for the mechanisms of hydrodesulfurization.