Resetting of soil compositions by irrigation in urban watersheds: Evidence from Sr isotope variations in Austin, TX.

Human activities in urban areas disturb the natural landscape upon which they develop, disrupting pedogenic processes and ultimately limiting the ecosystem services urban soils provide. To better understand the impacts on and resiliency of soils in response to urban development, it is essential to understand the processes by which and degree to which soil physical and chemical properties are altered in urban systems. Here, we apply the source-tracing capabilities of Sr isotopes (87Sr/86Sr) to understand the impacts of urban processes on the composition of soils in eight watersheds in Austin, Texas. We evaluate natural and anthropogenic Sr sources in watersheds spanning a wide range of urbanization, comparing soils by variations in their natural (including mineralogy, thickness, soil type, and watershed) and anthropogenic (including irrigation, soil amendments, and fertilization) characteristics. A strong positive correlation between soil thickness and 87Sr/86Sr is observed among unirrigated soils (R2 = 0.83). In contrast, this relationship is not observed among irrigated soils (R2 = 0.004). 95 % of 42 irrigated soil samples have 87Sr/86Sr values approaching or within the range for municipal supply water. These results indicate soil interaction with municipal water through irrigation and/or water infrastructure leakage. Soils irrigated with municipal water have elevated 87Sr/86Sr values relative to unirrigated soils in seven of eight watersheds. We propose that original soil 87Sr/86Sr values are partially to completely reset by irrigation with municipal water via ion exchange processes. Our results demonstrate that in urban systems, Sr isotopes can serve as an environmental tracer to assess the overprint of urbanization on natural soil characteristics. In the Austin region, resetting of natural soil compositions via urban development is extensive, and the continued expansion of urban areas and irrigation systems may affect the ability of soils to retain nutrients, filter contaminants, and provide other ecosystem services that support environmental resilience.

Cationic Amphiphiles Bearing a Diacetylenic Function in the Headgroup: Aggregative Properties and Polymerization.

In the wide panorama of diacetylenic lipids, the photoresponsive conjugated 1,3-diyne function is usually encased into the hydrocarbon chain of the amphiphile at a variable distance from the headgroup. Therefore, the polydiacetylene network obtained by polymerization upon UV irradiation of the corresponding liposomes, exploited as sensing function, is embedded in the hydrophobic region of liposomes. Structurally related cationic diacetylenic amphiphiles featuring the conjugated triple bonds proximate to charged nitrogen were synthesized and evaluated in their ability to polymerize under aggregative conditions. The occurrence of polymerization only in certain aggregating conditions was rationalized by nuclear magnetic resonance (NMR) and Langmuir trough experiments.

Structurally related glucosylated liposomes: Correlation of physicochemical and biological features.

Liposomes functionalized on their surface with carbohydrates (glycoliposomes) represent an optimal approach for targeting of drugs to diseased tissues in vivo, thanks to biocompatibility, low toxicity and easy manufacturing of these lipid nanoparticles. Here we report on the study of liposomes including a novel glycosylated amphiphile and on the comparison of their features with those of glycosylated analogues described previously. Further, the capability of the different glucosylated formulations to interact with three breast cancer cell lines was investigated. Our results show that the hydrophobic portion of the lipid bilayer strongly influences both the properties and the internalization of glycosylated liposomes.

Glucosylated liposomes as drug delivery systems of usnic acid to address bacterial infections.

Because of the increased incidence of infections caused by resistant pathogens, due to the intensive use of antibiotics, there is an urgent need to develop new therapeutic strategies against bacteria, possibly based on non conventional drugs. (+)-Usnic acid is a natural compound that exerts a potent antibacterial activity, however its clinical application is hampered by its scarce solubility in water. Usnic acid was included, by both passive and active loading techniques, in liposomes containing structurally related glucosylated amphiphiles. Liposome formulations were characterized from the physicochemical point of view and their activity against biofilm associated Staphylococcus epidermidis was also evaluated. The inclusion of usnic acid in glucosylated cationic liposomes promotes its penetration in biofilm matrix with a consequent increase of its antimicrobial activity. The effect of both cationic charge and sugar residue seems to be synergistic.

Influence of the state of phase of lipid bilayer on the exposure of glucose residues on the surface of liposomes.

The presence of carbohydrate-binding proteins (i.e. lectins) on the surface of various bacterial strains and their overexpression in some tumor tissues makes the use of glycosylated liposomes a promising approach for the specific drug delivery in antibacterial and anti-cancer therapies. However, the functionalization of liposome surface with sugar moieties by glycosylated amphiphiles does not ensure the binding of sugar-coated vesicles with lectins. In fact, the composition and properties of lipid bilayer play a pivotal role in the exposure of sugar residues and in the interaction with lectins. The influence of the length of the hydrophilic spacer that links the sugar to liposome surface and of the presence of saturated or unsaturated phospholipids in the lipid bilayer on the ability of glucosylated liposomes to interact with a model lectin, Concanavalin A, was investigated. Our results demonstrate that both the chain length and the prensece of unsaturation, parameters that strongly affect the fluidity of the lipid bilayer, affect agglutination. In particular, agglutination is favored when liposomes are in the gel phase within a defined range of temperature. Moreover, the obtained results confirm that the length of the PEG spacer, that influences both lipid organization and the exposure of sugar moieties to the bulk, plays a crucial role in liposome/lectin interaction.

Glucosylated pH-sensitive liposomes as potential drug delivery systems.

The inclusion of pH-sensitive components in liposome formulations can allow a more controlled and efficient release in response to low pH typical of some pathological tissues and/or subcellular compartments. On the other hand decorating the surface of liposomes with sugar moieties attributes to lipid vesicles specificity toward lectins, sugar-binding proteins overexpressed in many tumor tissues. A novel multifunctional pH-sensitive glucosylated amphiphile was synthesized and characterized as pure aggregate component and in mixtures with a natural phospholipid. The comparison of the properties of the new glucosylated amphiphile with respect to those of a previously described cationic structural analogue demonstrates that the pH-sensitivity can strongly affect drug release, lipid organization, as well as the exposure of the glucose residues on liposome surface and their ability to interact with Concanavalin A, a plant lectin used as model system.

Role of the hydrophilic spacer of glucosylated amphiphiles included in liposome formulations in the recognition of Concanavalin A.

The functionalization of liposomes with glycosylated amphiphiles is an optimal strategy for targeted drug delivery, leading to enhanced efficacy as well as to reduced side effects of drugs. In fact, the presence of natural or synthetic glycolipids in vesicle formulations might increase their specificity toward lectins, a class of non-enzymatic sugar-binding proteins involved in cellular recognition and adhesion. The capability of a new glucosylated synthetic amphiphile to interact with Concanavalin A (Con A), a plant lectin used as model system, was investigated by a synergic experimental and computational approach, both as pure component and in formulation with a natural phospholipid. The comparison of the affinity with Con A of the new glucosylated amphiphile with respect to that of a previously described structural analogue demonstrates that the hydrophilic spacer length controls the exposure of the glucose residue on liposome surface, and consequently the recognition by the lectin.

Recognition of concanavalin A by cationic glucosylated liposomes.

The specificity of carbohydrate-lectin interaction has been reported as an attractive strategy for drug delivery in cancer therapy because of the high levels of lectins in several human malignancies. A novel cationic glucosylated amphiphile was therefore synthesized, as a model system, to attribute specificity toward d-glucose receptors to liposome formulations. Fluorescence experiments demonstrated that the monomeric glucosylated amphiphile is capable of interacting with fluorescently labeled concanavalin A, a D-glucose specific plant lectin. The interaction of concanavalin A with liposomes composed of a phospholipid and the glucosylated amphiphile was demonstrated by agglutination observed by optical density and dynamic laser light scattering measurements, thus paving the way to the preparation of other glycosilated amphiphiles differing for the length of polyoxyethylenic spacer, the sugar moieties, and/or the length of the hydrophobic chain.