Synthetic ion transporters: pore formation in bilayers via coupled activity of non-spanning cobalt-cage amphiphiles.

Three amphiphilic cobalt-cage congeners bearing a diaza-crown bridge and varying alkyl chains (1:2:3; n = 12, 16, 18) have been assessed for their ion transport across planar lipid bilayer membranes. In symmetrical electrolyte solutions, a range of ion transport activity is provoked: 1 disrupts painted (fluid) bilayers in a detergent-like mode of action; 2 forms conducting "pores" in folded (rigid) membranes with long open lifetimes (>2 min) while 3 requires the larger auxiliary solvent volume and lower lateral stress of painted membranes to effect ion transport via long-lived pores. Hill analysis of the conductance variation with monomer concentration yields coefficients (2:3; n = 2.3, 1.9) in support of dimeric (n = 2) membrane-active structures, for which the derived "pore" radii are correlated with charge-density of the transported cations and their affinity for the crown moiety. A toroidal-pore model is invoked to account for the flux of guest ions through planar bilayer membranes without a fast-diffusing intermediary or direct membrane-spanning structure.

Synthesis and Bioactivity of a Cyclopolypeptide from Caribbean Marine Sponge.

Synthesis of a natural proline-rich cyclopolypeptide - rolloamide A was carried out by coupling of tri- and tetrapeptide units Boc-Phe-Pro-Val-OMe and Boc-Pro-Leu-Pro-Ile-OMe after proper deprotection at carboxyl and amino terminals using carbodiimide chemistry in alkaline environment followed by cyclization of linear heptapeptide segment in the presence of base. The structure of synthesized peptide was confirmed by spectral techniques including FTIR, 1H NMR, 13C NMR, MS analyses. Newly synthesized peptide was subjected to biological screening against pathogenic microbes and earthworms. Cyclopeptide 8 possessed promising activity against pathogenic fungi Candida albicans (ZOI: 24 mm, MIC: 6 µg/mL) and Gram-negative bacteria Pseudomonas aeruginosa (ZOI: 27 mm, MIC: 6 µg/mL) and Klebsiella pneumoniae (ZOI: 23 mm, MIC: 12.5 µg/mL), in comparison to reference drugs - griseofulvin (ZOI: 20 mm, MIC: 6 µg/mL) and ciprofloxacin (ZOI: 25 mm, MIC: 6 µg/mL/ZOI: 20 mm, MIC: 12.5 µg/mL). Also, newly synthesized heptacyclopeptide exhibited potent anthelmintic activity against earthworms Megascoplex konkanensis, Pontoscotex corethruses, and Eudrilus species (MPT/MDT ratio - 8.22-16.02/10.06-17.59 min), in comparison to standard drugs - mebendazole (MPT/MDT ratio - 10.52-18.02/12.57-19.49 min) and piperazine citrate (MPT/MDT ratio - 12.38-19.17/13.44-22.17 min).

DPPC monolayer response to non-spanning cobalt-cage metallosurfactants: Electrostatic complex formation.

A novel series of amphiphilic cobalt-cage derivatives (ACCD), bearing a diaza-crown bridge and varying alkyl chains, facilitate ion transport across biomembrane models via self-aggregation. In this study, compression isotherm analyses and atomic force microscopy (AFM) were used to assess the interactions of these amphiphiles with Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC) in order to elucidate electrostatic and steric contributions to ion transport. The stability and compressibility of DPPC monolayers are disrupted by ACCD molecules with short (C12) alkyl chains. These top-heavy amphiphiles (large cone angles) create voids at the interface of the hydrophobic/aqueous layer leading to monolayer expansion and packing efficiency of the aliphatic chains is disrupted. Long-tailed analogues (C16, C18) are cohesively integrated into DPPC monolayers due to their smaller cone angles at the interfacial region and increased hydrocarbon compatibility in the hydrophobic region. Thermodynamic data indicate the formation of electrostatic complexes between DPPC and longer-tailed amphiphiles consistent with AFM observations of aggregate structures at the corresponding concentrations.

Influence of Fire Mosaics, Habitat Characteristics and Cattle Disturbance on Mammals in Fire-Prone Savanna Landscapes of the Northern Kimberley.

Patch mosaic burning, in which fire is used to produce a mosaic of habitat patches representative of a range of fire histories ('pyrodiversity'), has been widely advocated to promote greater biodiversity. However, the details of desired fire mosaics for prescribed burning programs are often unspecified. Threatened small to medium-sized mammals (35 g to 5.5 kg) in the fire-prone tropical savannas of Australia appear to be particularly fire-sensitive. Consequently, a clear understanding of which properties of fire mosaics are most instrumental in influencing savanna mammal populations is critical. Here we use mammal capture data, remotely sensed fire information (i.e. time since last fire, fire frequency, frequency of late dry season fires, diversity of post-fire ages in 3 km radius, and spatial extent of recently burnt, intermediate and long unburnt habitat) and structural habitat attributes (including an index of cattle disturbance) to examine which characteristics of fire mosaics most influence mammals in the north-west Kimberley. We used general linear models to examine the relationship between fire mosaic and habitat attributes on total mammal abundance and richness, and the abundance of the most commonly detected species. Strong negative associations of mammal abundance and richness with frequency of late dry season fires, the spatial extent of recently burnt habitat (post-fire age <1 year within 3 km radius) and level of cattle disturbance were observed. Shrub cover was positively related to both mammal abundance and richness, and availability of rock crevices, ground vegetation cover and spatial extent of ≥4 years unburnt habitat were all positively associated with at least some of the mammal species modelled. We found little support for diversity of post-fire age classes in the models. Our results indicate that both a high frequency of intense late dry season fires and extensive, recently burnt vegetation are likely to be detrimental to mammals in the north Kimberley. A managed fire mosaic that reduces large scale and intense fires, including the retention of ≥4 years unburnt patches, will clearly benefit savanna mammals. We also highlighted the importance of fire mosaics that retain sufficient shelter for mammals. Along with fire, it is clear that grazing by introduced herbivores also needs to be reduced so that habitat quality is maintained.

Mammals of Australia's tropical savannas: a conceptual model of assemblage structure and regulatory factors in the Kimberley region.

We construct a state-and-transition model for mammals in tropical savannas in northern Australia to synthesize ecological knowledge and understand mammalian declines. We aimed to validate the existence of alternative mammal assemblage states similar to those in arid Australian grasslands, and to speculate on transition triggers. Based on the arid grassland model, we hypothesized that assemblages are partitioned across rainfall gradients and between substrates. We also predicted that assemblages typical of arid regions in boom periods would be prevalent in savannas with higher and more regular rainfall. Data from eight mammal surveys from the Kimberley region, Western Australia (1994 to 2011) were collated. Survey sites were partitioned across rainfall zones and habitats. Data allowed us to identify three assemblage states: State 0:--low numbers of mammals, State II:--dominated by omnivorous rodents and State III:--dominated by rodents and larger marsupials. Unlike arid grasslands, assemblage dominance by insectivorous dasyurids (State I) did not occur in savannas. Mammal assemblages were partitioned across rainfall zones and between substrates as predicted, but-unlike arid regions-were not related strongly to yearly rainfall. Mammal assemblage composition showed high regional stability, probably related to high annual rainfall and predictable wet season resource pulses. As a consequence, we speculate that perpetually booming assemblages in savannas allow top-down control of the ecosystem, with suppression of introduced cats by the dingo, the region's top predator. Under conditions of low or erratic productivity, imposed increasingly by intense fire regimes and introduced herbivore grazing, dingoes may not limit impacts of cats on native mammals. These interacting factors may explain contemporary declines of savanna mammals as well as historical declines in arid Australia. The cat-ecosystem productivity hypothesis raised here differs from the already-articulated cat-habitat structure hypothesis for mammal declines, and we suggest approaches for explicit testing of transition triggers for competing hypotheses.