Vermiculite-aliphatic amine interactions at the solid/liquid interface: a thermodynamic approach

Polar n-alkylmonoamines of general formula H₃C(CH₂) _n NH₂ (n = 1, 3, 5) interacted with layered silicate vermiculite at the solid/liquid interface. The maximum amount of amine intercalated (N _f ) inside the interlamellar space were 0.62, 0.46, and 0.38 mmol g⁻¹, to give the following order of intercalation ethyl → butyl → hexylamines. The layered vermiculite solid was suspended in deionized water and calorimetrically titrated with this series of amines, to give favorable thermodynamic data, such as exothermic enthalpy, negative Gibbs free energy and positive entropy data.     

EFFECT OF FAR-UV AND NEAR-UV RADIATION ON THE CELL SURFACE CHARGE OF THE PROTOZOAN

Abstract— Cell electrophoresis was used to detect the effect of far-UV or near-UV radiation on the cell surface charge of the pathogenic protozoan Tritrichomonas foerus . Either far-UV or near-UV radiation interfered with the surface charge of T. foetus at fluences which inhibited cell growth by 50%. Both UV-radiations induced a significant decrease on surface charge of T. foetus , as evaluated by measurement of its electrophoretic mobility (EPM). Determinations of EPM of protozoa in solution of low ionic strength indicated that the decrease in the EPM induced by far-UV is much less pronounced than that observed for near-UV or control cells.     

Immobilization of ethylenesulfide on silica surface using acid and base catalysts Adsorption and thermodynamic data

The reaction of cyclic ethylene sulfide with 3-aminopropyltrimethoxysilane resulted in a new silylating agent, which was anchored onto a silica surface via the sol-gel procedure using hydrochloric acid or ammonium hydroxide as acid or base catalysts, respectively. Both organofunctionalized surfaces have the ability to adsorb divalent cations from aqueous nitrate solution. Through calorimetric titrations, the thermodynamic data of cation-basic center interactions were obtained. Exothermic enthalpy values were obtained for all interaction processes. The calculated free Gibbs energy is in agreement with the spontaneity of the reactions and the positive entropy values for all reactions are favorable for these systems.     

Counterion Nature and Alkylammonium Halide Adsorption Thermodynamics

Two surfactants were synthesized by reacting hydrogen halides (hydrogen chloride and hydrogen bromide) with 1-dodecylamine. The resultant cationic surfactants, 1-dodecylammonium chloride (DDAC) and 1-dodecylammonium bromide (DDAB), were characterized by NMR spectrometry and FTIR spectroscopy and data related to their adsorption at the fluid liquid/gas interface were obtained employing bubble surface tensiometry, in pure water and in HCl 0.1 M. Data did not fit well to Langmuir isotherm but Frumkin isotherm did adequately describe to process of adsorption. Adsorption isotherms, as well as data related to critical micelle concentration, CMC, indicated that in HCl 0.1 M, the presence of electrolytes and a common ion to DDAC decreased chloride solvation, changing surface packing and adsorption profile for this surfactant.     

Strategies and results of field emission scanning electron microscopy (FE-SEM) in the study of parasitic protozoa

Field emission scanning electron microscopy (FE-SEM) provides a range of strategies for investigating the structural organization of biological systems, varying from isolated macromolecules to tissue organization and whole organisms. This review covers some of the results so far obtained using FE-SEM observation and various protocols of sample fixation to analyze the structural organization of parasitic protozoa and their interaction with host cells. The employment of FE-SEM can be broadened through the use of gold-labeled molecules or tracers, gradual extraction by detergents, and cleavage techniques. These analyses provide significant contributions to the characterization of these organisms concerning ultrastructure, cytoskeleton, motility and intracellular behavior.     

A morphological and cytochemical study of the interaction between Paracoccidiodes brasiliensis and neutrophils.

Paracoccidioidomycosis is a systemic granulomatous disease caused by the dimorphic fungus Paracoccidioides brasiliensis. It is the most prevalent systemic mycosis of Latin America and 80% of the reported cases are from Brazil. Because of the great number of neutrophils found in the P. brasiliensis granuloma, studies have been done to evaluate the role of these cells during the development of the infection. Scanning and transmission electron microscopy of thin sections showed that the neutrophils ingest yeast cells through a typical phagocytic process with the formation of pseudopodes. The pseudopodes even disrupt the connection established between the mother and the bud cells. Neutrophils also associate to each other, forming a kind of extracellular vacuole where large yeast cells are encapsulated. Cytochemical studies showed that once P. brasiliensis attaches to the neutrophil surface, it triggers a respiratory burst with release of oxygen-derived products. Attachment also triggers neutrophils degranulation, with release of endogenous peroxidase localized in cytoplasmic granules. Together, these processes lead to killing of both ingested and extracellular P. brasiliensis.     

Acidocalcisomes of Phytomonas fran?ai possess distinct morphological characteristics and contain iron.

Acidocalcisomes are acidic calcium storage compartments described initially in trypanosomatid and apicomplexan parasites, and recently found in other unicellular eukaryotes. The aim of this study was to identify the presence of acidocalcisomes in the plant trypanosomatid Phytomonas fran?ai. Electron-dense organelles of P. fran?ai were shown to contain large amounts of oxygen, sodium, magnesium, phosphorus, potassium, calcium, iron, and zinc as determined by X-ray microanalysis, either in situ or when purified using iodixanol gradient centrifugation or by elemental mapping. The presence of iron is not common in other acidocalcisomes. In situ, but not when purified, these organelles showed an elongated shape differing from previously described acidocalcisomes. However, these organelles also possessed a vacuolar H+-pyrophosphatase (V-H+-PPase) as determined by biochemical methods and by immunofluorescence microscopy using antibodies against the enzyme. Together, these results suggest that the electron-dense organelles of P. fran?ai are homologous to the acidocalcisomes described in other trypanosomatids, although with distinct morphology and elemental content.     

Visualization of the flagellar surface of protists by atomic force microscopy

In many cells, motility is mediated by flagellar beating. Protist parasites are capable of highly coordinated motility which contributes to their pathogenicity in mammalian hosts. Understanding the structural aspects of the flagellum may be important to the identification of novel targets for therapeutic intervention. Our group used atomic force microscopy (AFM) to examine the ultrastructure of Trypanosoma cruzi, obtaining valuable information on the organisation of the flagellar sub-structure. AFM images revealed novel flagellar components such as the presence of periodically-spaced protrusions organised along a flagellar furrow and oriented through the major flagellar axis between the axoneme and the paraflagellar rod. The nature and functional role of this structure are still unknown, although the hypothesis that the furrow might physically separate the two distinct domains of the flagellar membrane that comprise the surface of the axoneme and the paraflagellar rod (PFR) has been raised. To test whether the furrow was present or not only in PFR-bearing flagella, different protists containing or lacking the PFR, were analysed by AFM. Analysis of T. cruzi, Trypanosoma brucei and Herpetomonas megaseliae, which present distinct PFRs, showed similar and equivalent furrows along the main axis of their flagella, whereas Crithidia deanei, Giardia lamblia and Tritrichomonas foetus (in which the PFR is reduced or absent) lacked a furrow. Our results strongly suggest that the flagellar furrow is a characteristic feature of PFR-containing flagella and opens new perspectives for its functional role in the definition of sub-domains on the flagellar membrane.     

A chiral porous metal-organic framework for highly sensitive and enantioselective fluorescence sensing of amino alcohols

A highly porous and fluorescent metal-organic framework (MOF), 1, was built from a chiral tetracarboxylate bridging ligand derived from 1,1'-bi-2-naphthol (BINOL) and a cadmium carboxylate infinite-chain secondary building unit. The fluorescence of 1 can be effectively quenched by amino alcohols via H-bonding with the binaphthol moieties decorating the MOF, leading to a remarkable chiral sensor for amino alcohols with greatly enhanced sensitivity and enantioselectivity over BINOL-based homogeneous systems. The higher detection sensitivity of 1 is due to a preconcentration effect by which the analytes are absorbed and concentrated inside the MOF channels, whereas the higher enantioselectivity of 1 is believed to result from enhanced chiral discrimination owing to the cavity confinement effect and the conformational rigidity of the BINOL groups in the framework. 1 was quenched by four chiral amino alcohols with unprecedentedly high Stern-Volmer constants of 490-31200 M(-1) and enantioselectivity ratios of 1.17-3.12.     

Design,Synthesis and Antiparasitic Evaluation of Click Phospholipids

A library of seventeen novel ether phospholipid analogues, containing 5-membered heterocyclic rings (1,2,3-triazolyl, isoxazolyl, 1,3,4-oxadiazolyl and 1,2,4-oxadiazolyl) in the lipid portion were designed and synthesized aiming to identify optimised miltefosine analogues. The compounds were evaluated for their in vitro antiparasitic activity against Leishmania infantum and Leishmania donovani intracellular amastigotes, against Trypanosoma brucei brucei and against different developmental stages of Trypanosoma cruzi. The nature of the substituents of the heterocyclic ring (tail) and the oligomethylene spacer between the head group and the heterocyclic ring was found to affect the activity and toxicity of these compounds leading to a significantly improved understanding of their structure–activity relationships. The early ADMET profile of the new derivatives did not reveal major liabilities for the potent compounds. The 1,2,3-triazole derivative 27 substituted by a decyl tail, an undecyl spacer and a choline head group exhibited broad spectrum antiparasitic activity. It possessed low micromolar activity against the intracellular amastigotes of two L. infantum strains and T. cruzi Y strain epimastigotes, intracellular amastigotes and trypomastigotes, while its cytotoxicity concentration (CC₅₀) against THP-1 macrophages ranged between 50 and 100 μM. Altogether, our work paves the way for the development of improved ether phospholipid derivatives to control neglected tropical diseases.