Amphiphilic block copolymers as flexible membrane materials generating structural and functional mimics of green bacterial antenna complexes.

We describe the ability of a short-chain amphiphilic block copolymer to self-assemble to form an artificial supramolecular light-harvesting system. Specifically, we demonstrate that the 2.5 kDa, poly(ethylene oxide)-block-poly(butadiene) (PEO-b-PBD), exhibits sufficient morphological flexibility as a membrane material and enables generation of mimics of three-dimensional chlorosomes as well as supported membrane bilayers containing energy acceptors. This overall architecture replicates green bacterial light-harvesting function whereby these assemblies exhibit long-range order and three-dimensional morphology similar to native chlorosomes and are capable of energy transfer internally and to external acceptors, located in a supporting biomimetic polymer membrane. Unlike native green bacterial systems that use multiple lipids as a matrix to generate the appropriate environment for chlorosome assembly and function, the described system matrix is comprised entirely of a single polymer amphiphile. This work demonstrates the potential of short-chain amphiphilic block copolymers in generating self-assembled, bio-mimetic membrane architectures, and in doing so, generates scalable, spatial-energetic landscapes for photonic applications. Finally, the results presented provide evidence of minimal requirements to induce chlorosome-like organization and function.

Statistical analysis of microarray data with replicated spots: a case study with synechococcus WH8102.

Until recently microarray experiments often involved relatively few arrays with only a single representation of each gene on each array. A complete genome microarray with multiple spots per gene (spread out spatially across the array) was developed in order to compare the gene expression of a marine cyanobacterium and a knockout mutant strain in a defined artificial seawater medium. Statistical methods were developed for analysis in the special situation of this case study where there is gene replication within an array and where relatively few arrays are used, which can be the case with current array technology. Due in part to the replication within an array, it was possible to detect very small changes in the levels of expression between the wild type and mutant strains. One interesting biological outcome of this experiment is the indication of the extent to which the phosphorus regulatory system of this cyanobacterium affects the expression of multiple genes beyond those strictly involved in phosphorus acquisition.

Raman spectroscopic imaging markers for fatigue-related microdamage in bovine bone.

Raman spectroscopic markers have been determined for fatigue-related microdamage in bovine bone. Microdamage was induced using a cyclic fatigue loading regime. After loading, the specimens were stained en-bloc with basic fuchsin to facilitate damage visualization and differentiate fatigue-induced damage from cracks generated during subsequent histological sectioning. Bone tissue specimens were examined by light microscopy and hyperspectral near-infrared Raman imaging microscopy. Three regions were defined-tissue with no visible damage, tissue with microcracks, and tissue with diffuse damage. Raman transects, lines of 150-200 Raman spectra, were used for initial tissue surveys. Exploratory factor analysis of the transect Raman spectra has identified spectroscopically distinct chemical microstructures of the bone specimens that correlate with damage. In selected regions of damage, full hyperspectral Raman images were obtained with 1.4-microm spatial resolution. In regions of undamaged tissue, the phosphate nu1 band is found at 957 cm(-1), as expected for the carbonated hydroxyapatic bone mineral. However, in regions of visible microdamage, an additional phosphate nu1 band is observed at 963 cm(-1) and interpreted as a more stoichiometric, less carbonated mineral species. Raman imaging confirms the qualitative relationship between the Raman spectral signature of bone mineral and the type of microdamage in bovine bone. Two tentative explanations for the presence of less carbonated phosphate in damaged regions are proposed.

Spatial distribution of phosphate species in mature and newly generated Mammalian bone by hyperspectral Raman imaging.

Hyperspectral Raman images of mineral components of trabecular and cortical bone at 3 µm spatial resolution are presented. Contrast is generated from Raman spectra acquired over the 600-1400 cm-1 Raman shift range. Factor analysis on the ensemble of Raman spectra is used to generate descriptors of mineral components. In trabecular bone independent phosphate (PO4-3) and monohydrogen phosphate (HPO4-2) factors are observed. Phosphate and monohydrogen phosphate gradients extend from trabecular packets into the interior of a rod. The gradients are sharply defined in newly regenerated bone. There, HPO4-2 content maximizes near a trabecular packet and decreases to a minimum value over as little as a 20 µm distance. Incomplete mineralization is clearly visible. In cortical bone, factor analysis yields only a single mineral factor containing both PO4-3 and HPO4-2 signatures and this implies uniform distribution of these ions in the region imaged. Uniform PO4-3 and HPO4-2 distribution is verified by spectral band integration. © 1999 Society of Photo-Optical Instrumentation Engineers.