Claudius D'Silva

The interaction of an antiparasitic peptide active against African Sleeping Sickness with cell membrane models

Zwitterionic peptides with trypanocidal activity are promising lead compounds for the treatment of African Sleeping Sickness, and have motivated research into the design of compounds capable of disrupting the protozoan membrane. In this study, we use the Langmuir monolayer technique to investigate the surface properties of an antiparasitic peptide, namely S-(2,4-dinitrophenyl)glutathione di-2-propyl ester, and its interaction with a model membrane comprising a phospholipid monolayer. The drug formed stable Langmuir monolayers, whose main feature was a phase transition accompanied by a negative surface elasticity. This was attributed to aggregation upon compression due to intermolecular bond associations of the molecules, inferred from surface pressure and surface potential isotherms, Brewster angle microscopy (BAM) images, infrared spectroscopy and dynamic elasticity measurements. When co-spread with dipalmitoyl phosphatidyl choline (DPPC), the drug affected both the surface pressure and the monolayer morphology, even at high surface pressures and with low amounts of the drug. The results were interpreted by assuming a repulsive, cooperative interaction between the drug and DPPC molecules. Such repulsive interaction and the large changes in fluidity arising from drug aggregation may be related to the disruption of the membrane, which is key for the parasite killing property.

Macrocyclic polyether tetralactams. Part IV. Potentiometric evaluation of ion-selective characteristics with alkaline-earth cations

Macrocyclic polyether dioxatetralactams have been evaluated as ion-selective electrodes in poly(vinyl chloride) membranes. The six ionophores studied proved to be very good Ca2+ neutral carriers showing good discrimination against Mg2+ and alkali-metal cations with Nernstian and near-Nernstian responses to these ions in the range 10–5–10–1 mol dm–3. The fixed interference method was used to determine relative selectivity coefficients for all the electrodes. The highest selectivity for calcium relative to potassium, sodium, lithium, zinc and magnesium ions using potassium tetrakis(p-chlorophenyl)borate as a resistance modifier and 2-nitrophenyl octyl ether as a plasticizer was obtained with ionophore 6 which was found to be comparable in performance to the model calcium carrier ETH 129. The ionophores tested exhibited a fast Nernstian response to changes in Ca2+ concentration which was stable to within <200 µV h–1.

The lipid composition of a cell membrane modulates the interaction of an antiparasitic peptide at the air-water interface.

The antiparasitic property of peptides is believed to be associated with their interactions with the protozoan membrane, which calls for research on the identification of membrane sites capable of peptide binding. In this study we investigated the interaction of a lipophilic glutathioine peptide known to be effective against the African Sleeping Sickness (ASS - African Trypanosomiasis) and cell membrane models represented by Langmuir monolayers. It is shown that even small amounts of the peptide affect the monolayers of some phospholipids and other lipids, which points to a significant interaction. The latter did not depend on the electrical charge of the monolayer-forming molecules but the peptide action was particularly distinctive for cholesterol + sphingomyelin monolayers that roughly resemble rafts on a cell membrane. Using in situ polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS), we found that the orientation of the peptide is affected by the phospholipids and dioctadecyldimethylammonium bromide (DODAB), but not in monolayers comprising cholesterol + sphingomyelin. In this mixed monolayer resembling rafts, the peptide still interacts and has some induced order, probably because the peptide molecules are fitted together into a compact monolayer. Therefore, the lipid composition of the monolayer modulates the interaction with the lipophilic glutathioine peptide, and this may have important implications in understanding how the peptide acts on specific sites of the protozoan membrane.

Glutathione Derivatives Active against Trypanosoma brucei rhodesiense and T. brucei brucei In Vitro

ABSTRACT Diesters based on N-benzyloxycarbonyl-S-(2,4-dinitrophenyl) GSH (CBzGSDNP) containing linear alcohols 3 to 9, branched alcohols 10 to 20, or heteroatom linear alcohols 21 to 25, were investigated as in vitro inhibitors of pathogenic parasites. Diesters 3 to 25 were better inhibitors of Trypanosoma brucei rhodesiense than of T. brucei brucei and had low cytotoxicities. The most active compound had a 50% effective dose (ED50) of 0.2 μM. A quantitative structure activity regression equation relating the log (1/ED50) versus the hydrophobicity parameter (log P), Tafts steric parameter (Es), molecular weight (MW), and the WienI descriptor (W) was determined, and the species difference was found to be related to membrane penetration and steric effects.

Hand-held instrumentation for environmental monitoring

A prototype hand-held electroanalytical instrument has been developed for the simultaneous detection and determination of four electroactive ions in solution. The instrument, which can be battery powered, utilizes the technique of anodic linear-scan stripping voltammetry at a mercury thin-film electrode. The instrumentation and its application to the measurement of solution concentrations of cadmium, copper and lead in the range 10–4–10–5 mol dm–3 are described.

Encapsulation of an integrated thin-film multi-electrode sensor using photocurable poly(styrene)

The direct photolithographic structuring of poly(styrene) by bi-functional azides has been elaborated and applied to the encapsulation of a disposable thin-film three-electrode device. Effective dielectric encapsulation has been shown with a polystyrene layer only 10 μm thick when chemically bonded to the sensor surface. This process may be generally amenable to the encapsulation of a wide variety of other types of sensors and electronic devices.

BIBRACCHIAL DIAZATETRALACTAMS. SIDE-CHAIN EFFECTS ON CATION BINDING AND IONOPHORIC PROPERTIES

The formation constants in THF solutions of calcium complexes diazatetralactams bearing two side-chains were found in the range 4.6 < log βML < 8.2 and follow the substituent sequence Boc < Me ∼ CH2CO2Me < CH2CONMe2 < CH2Py. This side-chain effect was again observed in liquid–liquid extraction studies either with calcium or zinc picrates. Efficient zinc extraction constitutes the main difference with the dioxatetralactam series. The metallic ion transport across a chloroformic membrane studied with the pyridine derivative agrees well with extraction data. Specific ionophoric properties were evidenced with ion-selective electrodes.

Antimicrobial effects of N-benzyloxycarbonyl-S-(2,4-dinitrophenyl) glutathione diesters against chloroquinine sensitive (NF54) and resistant (K1) strains of Plasmodium falciparum

N-Benzyloxycarbony-S-(2,4-dinitrophenyl)glutathione diesters have been investigated for antimalarial activity against chloroquinine sensitive (NF54) and resistant (K1) strains of P. falciparum. Both strains appear equally susceptible to inhibition by compounds 1-4, with an IC50 ∼ 4.92-6.97 μM, consistent with the target of these compounds being the PfMRP transporter. Against the NF54 strain, diester derivatives containing ethyl side chains showed lower in vitro activity than those with methyl side chains 1-4, IC50 ∼ 5.7-6.97 μM with the exception of compound 5 (IC50 > 25 μM). The cytotoxicity of compounds with log P ∼ 3.9-5.8 were lower against the murine L6 cell line than compounds with a higher log P > 5.8 that were toxic. Overall the cytotoxicity of compounds 1-7 were lower against KB cells than against the L6 cell line with the exception of compound 4, which showed a higher relative toxicity.

Antiprotozoal glutathione derivatives with flagellar membrane binding activity against T. brucei rhodesiense.

A new series of N-substituted S-(2,4-dinitrophenyl)glutathione dibutyl diesters were synthesized to improve in vitro anti-protozoal activity against the pathogenic parasites Trypanosoma brucei rhodesiense, Trypanosoma cruzi and Leishmania donovani. The results obtained indicate that N-substituents enhance the inhibitory properties of glutathione diesters whilst showing reduced toxicity against KB cells as in the cases of compounds 5, 9, 10, 16, 18 and 19. We suggest that the interaction of N-substituted S-(2,4-dinitrophenyl) glutathione dibutyl diesters with T. b. brucei occurs mainly by weak hydrophobic interactions such as London and van der Waals forces. A QSAR study indicated that the inhibitory activity of the peptide is associated negatively with the average number of C atoms, NC and positively to SZX, the ZX shadow a geometric descriptor related to molecular size and orientation of the compound. HPLC-UV studies in conjunction with optical microscopy indicate that the observed selectivity of inhibition of these compounds against bloodstream form T. b. brucei parasites in comparison to L. donovani under the same conditions is due to intracellular uptake via endocytosis in the flagellar pocket.

Waterproofness Results for the Surface Treatment of Heavy-Duty Leather for Adhesion Enhancement

This article presents further work undertaken in respect to the use of specific primers for adhesion on leather surfaces. This research focused on the use of photoreactive reagents and silane networks as primers and investigated their roles in seam strength and resistance against water ingress. A specific waterproof test was undertaken on treated samples in accordance with EN ISO 5403:2002. Samples treated with 4-(2,2′-iminodiethanol)-3-nitrophenylazide (azide 4) when primed only on one side of the test panel showed good resistance to water ingress. Samples treated with 3,5-dihydroxyphenyl-4-azidobenzoate (azide 7) or 3-(2-aminoethylamino)propyltriethoxysilane (AEAPES) on both sides of the test panels resulted in a seam that did not fail. However, double side treatment with these reagents generated a thicker glue line than single side treatment, which might present practical problems in terms of the flexibility of the resultant assembly during its life cycle.