Influence of synthesis parameters on the formation of mesoporous SAPOs

The synthesis and characterization of high-quality mesoporous silicoaluminophosphates (SAPOs) with a hexagonally arranged pore structure and a good thermal stability are described. The influence of some important synthesis parameters including temperature, time, and Si content in the synthesis gel was examined. The local environments of Al, P, and Si were investigated using MAS NMR spectroscopy. The acidity of the mesoporous SAPOs was studied and compared with those of aluminosilicate MCM-41 and SAPO-5. Results show that both the synthesis temperature and time have a significant impact on the formation of mesoporous SAPOs, whereas the presence of Si in the synthesis gel has a direct influence on the structure type and the quality of the resulting mesoporous SAPO materials. High-quality mesoporous SAPOs can be synthesized from the synthesis gels with Si/Al ratio smaller than 0.5 in the presence of cationic surfactants in a weakly basic aqueous solution. The mesoporous SAPO materials show interesting acidity properties, possessing both strong and mild sites. (C) 2002 Elsevier Science Inc. All rights reserved.

Synthesis of polymer-montmorillonite nanocomposites by in situ intercalative polymerization

Two polymer-montmorillonite (MMT) nanocomposites have been synthesized by in situ intercalative polymerization. The styrene monomer is intercalated into the interlayer space of organically modified MMT, a layered clay mineral. Upon the intercalation, the complex is subsequently polymerized in the confinement environment of the interlayer space with a free radical initiator, 2,2-azobis isobutyronitrile. The aniline monomer is also intercalated and then polymerized within the interlayer space of sodium- and copper-MMT initiated by ammonium peroxodisulphate and interlayer copper cations respectively. X-ray diffraction indicates that the MMT layers are completely dispersed in the polystyrene matrix and an exfoliated structure has been obtained. The resulting polyaniline-MMT nanocomposites show a highly ordered structure of a single polyaniline layer stacked with the MMT layers. Fourier transform infrared spectra further confirm the intercalation and formation of both polymer-MMT nanocomposites.

Exploring privileged structures: the combinatorial synthesis of cyclic peptides

Head-to-tail cyclic peptides have been reported to bind to multiple, unrelated classes of receptor with high affinity. They may therefore be considered to be privileged structures. This review outlines the strategies by which both macrocyclic cyclic peptides and cyclic dipeptides or diketopiperazines have been synthesised in combinatorial libraries. It also briefly outlines some of the biological applications of these molecules, thereby justifying their inclusion as privileged structures.

Estimation of total body water from bioelectrical impedance analysis in patients with pancreatic cancer - agreement between three methods of prediction

Introduction Bioelectrical impedance analysis (BIA) is a useful field measure to estimate total body water (TBW). No prediction formulae have been developed or validated against a reference method in patients with pancreatic cancer. The aim of this study was to assess the agreement between three prediction equations for the estimation of TBW in cachectic patients with pancreatic cancer. Methods Resistance was measured at frequencies of 50 and 200 kHz in 18 outpatients (10 males and eight females, age 70.2 +/- 11.8 years) with pancreatic cancer from two tertiary Australian hospitals. Three published prediction formulae were used to calculate TBW - TBWs developed in surgical patients, TBWca-uw and TBWca-nw developed in underweight and normal weight patients with end-stage cancer. Results There was no significant difference in the TBW estimated by the three prediction equations - TBWs 32.9 +/- 8.3 L, TBWca-nw 36.3 +/- 7.4 L, TBWca-uw 34.6 +/- 7.6 L. At a population level, there is agreement between prediction of TBW in patients with pancreatic cancer estimated from the three equations. The best combination of low bias and narrow limits of agreement was observed when TBW was estimated from the equation developed in the underweight cancer patients relative to the normal weight cancer patients. When no established BIA prediction equation exists, practitioners should utilize an equation developed in a population with similar critical characteristics such as diagnosis, weight loss, body mass index and/or age. Conclusions Further research is required to determine the accuracy of the BIA prediction technique against a reference method in patients with pancreatic cancer.

A subset-oriented algorithm for minimizing the number of steps required for synthesis of cyclic-peptide libraries

Libraries of cyclic peptides are being synthesized using combinatorial chemistry for high throughput screening in the drug discovery process. This paper describes the min_syn_steps.cpp program (available at http://www.imb.uq.edu.au/groups/smythe/tran), which after inputting a list of cyclic peptides to be synthesized, removes cyclic redundant sequences and calculates synthetic strategies which minimize the synthetic steps as well as the reagent requirements. The synthetic steps and reagent requirements could be minimized by finding common subsets within the sequences for block synthesis. Since a brute-force approach to search for optimum synthetic strategies is impractically large, a subset-orientated approach is utilized here to limit the size of the search. (C) 2002 Elsevier Science Ltd. All rights reserved.

Surface-active phospholipid in total hip arthroplasty

This is the first report of surface-active phospholipid as the boundary lubricant in total hip arthroplasty. Aspirate and rinsings from the bearing surfaces of 25 revision operations and one primary surgery were analyzed from 3 weeks to 26 years postoperatively. All samples contained substantial amounts of surface-active phospholipids ranging from 14 to 4186 μg. These findings indicate that synoviocytes continue producing the lubricant in significant quantities after arthroplasty surgery independent of the type of joint replacement and its fixation. Surface-active phospholipid was found on all bearing surfaces analyzed including polyethylene, stainless steel, chrome cobalt, alumina, zirconia, and titanium.

Synthesis, antiprotozoal and antibacterial activity of nitro- and halogeno-substituted benzimidazole derivatives

Two series of benzimidazole derivatives were sythesised. The first one was based on 5,6-dinitrobenzimidazole, the second one comprises 2-thioalkyl- and thioaryl-substituted modified benzimidazoles. Antibacterial and antiprotozoal. activity of the newly obtained compounds was studied. Some thioalkyl derivatives showed remarkable activity against nosocomial strains of Stenotrophomonas malthophilia, and an activity comparable to that of metronidazole against Gram-positive and Gram-negative bacteria. Of the tested compounds, 5,6-dichloro-2-(4-nitrobenzylthio)-benzimidazole showed the most distinct antiprotozoal activity.

The synthesis and structure of an n-terminal dodecanoic acid conjugate of a-conotoxin MII

The alpha-conotoxin MII is a 16 amino acid long peptide toxin isolated from the marine snail, Conus magus. This toxin has been found to be a highly selective and potent inhibitor of neuronal nicotinic acetylcholine receptors of the subtype alpha3beta2. To improve the bioavailability of this peptide, we have coupled to the N-terminus of conotoxin MII, 2-amino-D,L-dodecanoic acid (Laa) creating a lipidic linear peptide which was then successfully oxidised to produce the correctly folded conotoxin MII construct.

Regioselective synthesis of antiparallel loops on a macrocyclic scaffold constrained by oxazoles and thiazoles

[GRAPHICS] The regioselective syntheses and structures are reported for two tris-macrocylic compounds, each possessing two antiparallel loops on a macrocyclic scaffold constrained by two oxazoles and two thiazoles. NMR solution structures show the loops projecting from the same face of the macrocycle. Such molecules are shown to be prototypes for mimicking multiple loops of proteins.

Synthesis and structural analysis of the N-terminal domain of the thyroid hormone-binding protein transthyretin

Transthyretin (TTR) is a 55 kDa protein responsible for the transport of thyroid hormones and retinol in human serum. Misfolded forms of the protein are implicated in the amyloid diseases familial amyloidotic polyneuropathy and senile systemic amyloidosis. Its folding properties and stabilization by ligands are of current interest due to their importance in understanding and combating these diseases. To assist in such studies we developed a method for the solid phase synthesis of the monomeric unit of a TTR analogue and its folding to form a functional 55 kDa tetramer. The monomeric unit of the protein was chemically synthesized in three parts, comprising amino acid residues 151, 5499 and 102127, and ligated using chemoselective thioether ligation chemistry. The synthetic protein was folded and assembled to a tetrameric structure in the presence of the TTRs native ligand, thyroxine, as shown by gel filtration chromatography, native gel electrophoresis, TTR antibody recognition and thyroid hormone binding. In the current study the solution structure of the first of these fragment peptides, TTR(151) is examined to determine its intrinsic propensity to form beta-sheet structure, potentially involved in amyloid fibril formation by TTR. Despite the presence of extensive beta-structure in the native form of the protein, the Nterminal fragment adopts an essentially random coil conformation in solution.

A suite of novel allenes from Australian melolonthine scarab beetles. Structure, synthesis, and stereochemistry

A suite of allenic hydrocarbons, previously unknown as a molecular class from insects, has been characterized from several Australian melolonthine scarab beetles. The allenes are represented by the formula CH3(CH2)nCH=.=CH(CH2)(7)CH3 with n being 11-15, 17 and 19, and thus, all have Delta(9,10)-unsaturation. These structures have been confirmed by syntheses and comparisons of spectral and chromatographic properties with those of the natural components. The enantiomers of (+/-)-Delta(9,10)-tricosadiene and Delta(9,10)-pentacosadiene were separable on a modified beta-cyclodextrin column (gas chromatography), and the natural Delta(9,10)-tricosadiene (n = 11) and Delta(9,10)-pentacosadiene (n = 13) were shown to be of >85% ee. Syntheses of nonracemic allenes of known predominating chirality were acquired using both organotin chemistry and sulfonylhydrazine intermediates, and comparisons then demonstrated that the natural allenes were predominantly (R)-configured.

Insect chemistry and chirality

Examination of the chemistry of a number of Australian insect species provided examples of unusual structures and encouraged determinations of their absolute stereochemistry by stereocontrolled syntheses and chromatographic comparisons. Inter alia, studies with the fruit-spotting bug (Amblypelta nitida), certain parasitic wasps (Biosteres sp.), the aposematic shield bug (Cantao parentum), and various species of scarab grubs are summarized. The determination of enantiomeric excesses (ee's) for component epoxides, lactones, spiroacetals, and allenes are described. Stereochemical and related aspects of the biosynthesis of spiroacetals in certain fruit-fly species (Bactrocerae sp.) are also presented.