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PubMed2006

Mechanisms, pathways, and dynamics of excited-state energy flow in self-assembled wheel-and-spoke light-harvesting architectures.

Static and time-resolved optical measurements are reported for two cyclic hexameric porphyrin arrays and their self-assembled complexes with guest chromophores. The hexameric hosts contain zinc porphyrins and 0 or 3 free base (Fb) porphyrins (denoted Zn(6) or Zn(3)Fb(3), respectively). The guests are a tripyridyl arene (TP) and a dipyridyl-substituted free base porphyrin (DPFb), each of which coordinates to zinc porphyrins of a host via pyridyl-zinc dative bonding. Each architecture is designed to have an overall gradient of excited-state energies that affords excitation funneling within the host and ultimately to the guest. Collectively, the studies delineate the various pathways, mechanisms, and rate constants of energy flow among the weakly coupled constituents of the host-guest complexes. The pathways include downhill unidirectional energy transfer between adjacent chromophores, bidirectional energy migration between identical chromophores, and energy transfer between nonadjacent chromophores. The energy transfer to the lowest-energy chromophore(s) within the backbone of a hexameric host (Fb porphyrins in Zn(3)Fb(3) or pyridyl-coordinated zinc porphyrins in Zn(6)*TP and Zn(6)*DPFb) proceeds primarily via a through-bond mechanism; the transfer is rapid (approximately 40 ps depending on the array) and essentially quantitative (>or=98%). The energy transfer from a pyridyl-coordinated zinc porphyrin of the host to the Fb porphyrin guest in the Zn(6)*DPFb complex is almost exclusively Förster through-space in nature; this process is much slower ( approximately 1 ns) and has a lower yield (65%). These studies highlight the utility of cyclic architectures for efficient light harvesting and energy transfer to a designated trapping site.

Journal Article↗
PubMed2006

Engineered complex emulsion system: toward modulating the pore length and morphological architecture of mesoporous silicas.

In the complex alkane/P123/TEOS/H2O emulsion system, an emulsion engineering method to modulate pore length and morphological architecture of mesoporous materials has been built. With fine tuning of the synthetic parameters (e.g., the composition of the synthetic mixtures, temperature, stirring, etc.), a series of chemically significant mesostructures (i.e., short-pore SBA-15 materials) with tunable pore length and morphological architecture have been successfully constructed. The effects of alkane solubilizates on pore length and particle morphology are discussed. The resulting short-pore materials would have potential applications in the fields of adsorption/separation of biomolecules and inclusion chemistry of guest species, etc.

Journal Article↗
PubMed2004

Surface behavior of amphiphilic heteroarm star-block copolymers with asymmetric architecture.

We study the surface behavior of the asymmetric amphiphilic heteroarm poly(ethylene oxide) (PEO)/polystyrene (PS) star polymer on solid substrate. These star polymers differ in both architecture (four- and three-arm molecules, PEO-b-PS(3) and PEO-b-PS(2)) and in the length of PS chains (molecular weight from about 10 000 up to 24 000). We observed that, for a given chemical composition with a predominant content of hydrophobic blocks, the compression behavior of the PS domain structure controls the surface behavior and the final morphology of the monolayers. New features of the surface behavior of star-block copolymers are high stretching of the PS arms from the interface and enhanced stability of the circular PS domain structure, even at high compression. We suggest that for asymmetric star-block copolymers both architecture and chemical composition heavily favor the formation of highly curved interfaces and, thus, more stable circular domain structure with stretched PS arms.

Letter↗
PubMed2006

Principles of hierarchical meso- and macropore architectures by liquid crystalline and polymer colloid templating.

The generation of porous silica with hierarchically organized bimodal mesoporosity of adjustable size and well-defined shape was investigated by using surfactant mixtures and the nanocasting procedure (liquid crystalline templating). A systematic study of combinations of various block copolymers (Pluronics F127, KLE (poly(omega-hydroxypoly(ethylene-co-butylene)-co-poly(ethylene oxide))) and SE (PS-co-PEO)) with smaller surfactants (Pluronics P123, C16mimCl, and CTAB) revealed that hierarchical bimodal mesopore architectures could only be obtained by the usage of block copolymers with a strong hydrophilic-hydrophobic contrast, such as KLE and SE, giving rise to pores between 6 and 22 nm. Furthermore, the ionic liquid (IL) C16mimCl appeared to have advantageous templating properties, resulting in 2-3-nm pores being located between the block copolymer mesopores, whereas phase separation was observed for Pluronics and CTAB as small templates. Thereby, the study provided also general insights into the mixing and co-self-assembly behavior of block copolymers and ionic surfactants in water and confirmed the special templating properties of ILs, as recently proposed. In addition to the bimodal mesoporosity, additional tunable macroporosity was created by the presence of poly(styrene) or poly(methyl methacrylate) spheres, leading to well-defined trimodal hierarchical pore architectures with the small pores being located in the walls of the respective larger pores. As a major improvement, due to the pore hierarchy, these large-pore materials showed relatively large surface areas and pore volumes, and the size of densely packed macropores could even be decreased down to 90 nm. The materials were characterized by electron microscopy, small-angle X-ray scattering, and nitrogen sorption using a proper NLDFT (nonlocal density functional theory) approach for calculations of the pore size distribution in the entire range of micro- and mesopores.

Journal Article↗
PubMed2006

Invertible architectures from amphiphilic polyesters.

We synthesized and characterized novel amphiphilic polyesters with both hydrophilic and hydrophobic functionalities. The polyesters are soluble in organic and aqueous media and reveal the formation of inverse architectures whose behavior could be correlated to their chemical structure. We foresee that the amphiphilic properties of the polyesters reported here are obviously the basis of new architectures both in solution and on the solid surfaces, which could be used in a broad range of applications. The described synthesis of the copolymers is very simple and is based on commercially available products. That makes this approach attractive in various uses.

Journal Article↗
PubMed2005

Metal recognition of septapeptides via polypod molecular architecture.

The understanding of the nature of recognition of inorganic materials by proteins is one of the core elements of and has profound implications in biological materials science and engineering. Using combinatorial display methods, a considerable number of short polypeptides have recently been selected with affinity to engineering materials. During these selections, more than several polypeptides are identified with binding specificity to a chosen inorganic material. Understanding the nature of surface recognition of materials by polypeptides is essential for rational design and biomimetic engineering of these inorganic-binding polypeptides for use as linkers, catalyzers, and growth modifiers in nanotechnology and nanobiotechnology. Although there may not be direct homology among the amino acids constituting the polypeptides, their function may come from conserved molecular architecture. Here we study crystallographic surface recognition of platinum metal-binding septapeptides by conformational analysis. We find that the septapeptides conform into certain molecular architectures containing multiple protrusions (polypods) that spatially match with the crystallographic metal surfaces. While the physical recognition may originate from how well the molecular polypods spatially match a given crystallographic surface, the degree of binding may be due to the reactive groups that form the polypods, e.g., charged or polar groups (e.g., hydroxyl and amine). These results are highly consistent with the experimental binding characteristics of the Pt binders with various degrees of affinities.

Binding Sites↗
PubMed2005

Thermal resistance of nanoscopic liquid-liquid interfaces: dependence on chemistry and molecular architecture.

Systems with nanoscopic features contain a high density of interfaces. Thermal transport in such systems can be governed by the resistance to heat transfer, the Kapitza resistance (RK), at the interface. Although soft interfaces, such as those between immiscible liquids or between a biomolecule and solvent, are ubiquitous, few studies of thermal transport at such interfaces have been reported. Here we characterize the interfacial conductance, 1/RK, of soft interfaces as a function of molecular architecture, chemistry, and the strength of cross-interfacial intermolecular interactions through detailed molecular dynamics simulations. The conductance of various interfaces studied here, for example, water-organic liquid, water-surfactant, surfactant-organic liquid, is relatively high (in the range of 65-370 MW/m2 K) compared to that for solid-liquid interfaces ( approximately 10 MW/m2 K). Interestingly, the dependence of interfacial conductance on the chemistry and molecular architecture cannot be explained solely in terms of either bulk property mismatch or the strength of intermolecular attraction between the two phases. The observed trends can be attributed to a combination of strong cross-interface intermolecular interactions and good thermal coupling via soft vibration modes present at liquid-liquid interfaces.

Journal Article↗
PubMed2000

Architecture of the thin filament-Z-line junction: lessons from nebulette and nebulin homologies.

Nebulette and nebulin are homologous proteins associated with the Z-lines of cardiac and skeletal muscle sarcomeres. Although these proteins share 70% sequence homology and an identical domain layout, nebulette is one-tenth the size of nebulin. To define structurally important features of these proteins in terms of the Z-line architecture, we have analyzed the primary structure of nebulette and nebulin from a variety of species and developmental stages. Alignment of the 35 residue nebulin-like modules from both proteins demonstrates that the individual modules share 30-90% homology across the six proteins analyzed. In addition, this analysis demonstrates a number of areas in which the identity across the six proteins is as high as 75%. These areas may be important signals for Z-line assembly and function in the striated muscles. Significantly, most of the areas of high identity also coincide with consensus phosphorylation sites. To evaluate if nebulette, like nebulin, exhibits tissue-specific and developmental specific polymorphism, a series of immunoblot assays were performed. These data demonstrate that nebulettes from different portions of the heart are the same size. Comparison of nebulette from embryonic and adult cardiac muscle also demonstrates that this protein does not appear to vary in size with developmental stage. Consistent with the large number of consensus phosphorylation sites identified in the nebulette primary structure, we find that nebulette is phosphorylated in the cardiac muscle at serine and threonine residues. These data and sequence analyses are discussed in terms of current models for Z-line architecture.

Actin Cytoskeleton↗
PubMed2001

The genetic architecture of odor-guided behavior in Drosophila melanogaster.

The avoidance response to repellent odorants in Drosophila melanogaster, a response essential for survival, provides an advantageous model for studies on the genetic architecture of behavior. Transposon tagging in a highly inbred strain of flies in combination with a rapid and simple statistical behavioral assay enables the identification of not only large phenotypic effects, but also small aberrations from wild-type avoidance behavior. The recent completion of the sequence of the Drosophila genome facilitates the molecular characterization of transposon-tagged genes and correlation between gene expression and behavior in smell-impaired (smi) mutant lines. Quantitative genetic analyses of a collection of smi lines in a coisogenic background revealed an extensive network of epistatic interactions among genes that shape the olfactory avoidance response. The identification and functional characterization of proteins encoded by smi genes that form part of the olfactory subgenome and correlation of polymorphisms in these genes with variation in odor-guided behavior in natural populations will advance our understanding of the genetic architecture of chemosensory behavior.

Animals↗
PubMed2001

Shift changes, updates, and the on-call architecture in space shuttle mission control.

In domains such as nuclear power, industrial process control, and space shuttle mission control, there is increased interest in reducing personnel during nominal operations. An essential element in maintaining safe operations in high risk environments with this 'on-call' organizational architecture is to understand how to bring called-in practitioners up to speed quickly during escalating situations. Targeted field observations were conducted to investigate what it means to update a supervisory controller on the status of a continuous, anomaly-driven process in a complex, distributed environment. Sixteen shift changes, or handovers, at the NASA Johnson Space Center were observed during the STS-76 Space Shuttle mission. The findings from this observational study highlight the importance of prior knowledge in the updates and demonstrate how missing updates can leave flight controllers vulnerable to being unprepared. Implications for mitigating risk in the transition to 'on-call' architectures are discussed.

Communication↗
PubMed2002

Temporal changes in colonic vascular architecture and inflammatory mediator levels in animal models of colitis.

This study investigated the temporal relationship between inflammatory mediator production and colonic vascular architecture in rabbit and rat trinitrobenzene sulfonic acid (TNBS) models of colitis. In both species significant colonic damage and loss of mucosal integrity occurred over time. In the rabbit there was a significant increase in TxB2 levels in the muscularis propria and mucosa at 1, 6, and 48 hr after TNBS, with a significant elevation in PGE2 production in the muscularis propria at 48 hr. However, elevated mediator levels were not associated with measurable changes in vascular architecture. In contrast, significant changes in the numbers and diameters of colonic blood vessels were observed in the rat, in the absence of significant elevations in TxB2 or PGE2 levels. These data suggest that the role of lipid mediators in acute colitis is species-dependent and, although there are corresponding gross and microscopic changes in both models, these occur through disparate mechanisms.

Animals↗
PubMed2003

A multiagent architecture for developing medical information retrieval agents.

Information that is available on the world wide web (WWW) is already more vast than can be comprehensibly studied by individuals and this quantity is increasing at a staggering pace. The quality of service delivered by physicians is dependent on the availability of current information. The agent paradigm offers a means for enabling physicians to filter information and retrieve only information that is relevant to current patient treatments. As with many specialized domains, agent-based information retrieval in medical domains must satisfy several domain-dependent constraints. A multiple agent architecture is developed and described in detail to efficiently provide agent-based information retrieval from the WWW and other explicit information resources. A simulation of the proposed multiple agent architecture shows a 97% decrease in information overload and an 85% increase in information relevancy over existing meta-search tools (with even larger gains over standard search engines).

Artificial Intelligence↗
PubMed1999

Muscular architecture and manometric image of gastroesophageal barrier in the rat.

The two components of the gastroesophageal barrier, the sphincter and the crural sling, closely overlap in humans, whereas they are widely separated in the rat. This investigation correlates the anatomical components of the barrier and their manometric counterparts in this animal. Sphincteric and crural sling pressures were measured in four quadrants in 23 rats. Muscle thickness was measured at nine levels of the gastroesophageal junction in the same quadrants in 12 rats and the muscular architecture of the region was studied in 10 fresh specimens. The manometric sphincteric component is stronger on the right side where the thickest muscle fibers anchor to the anterior and posterior borders of a mucosal ridge that almost surround the cardia. Conversely, the sling pressure is highest towards the left where the muscular bundles straddle the esophagus. In conclusion, there is a close correspondence between the manometric image and the muscular architecture of the components of the gastroesophageal barrier in the rat. The anatomical arrangement of U-shaped muscular bundles oriented in opposite directions creates a particularly powerful antireflux mechanism.

Animals↗
PubMed2004

Plant vascular architecture and within-plant spatial patterns in resource quality following herbivory.

In this study, we used plant vascular architecture as a framework from which to predict induced changes in resource quality for Lema trilinea feeding on the host plant Solanum dulcamara at both low and high levels of herbivory. The systemic patterns of allocation of dye from a capillary tube inserted onto the petiole of the first true leaf and sections of the stem were used to establish the degree of vascular connectivity among different leaf positions. Induced changes in the activity of two defensive proteins, proteinase inhibitor (PI) and polyphenol oxidase (PPO), as well as larval L. trilinea performance, were measured in weakly or strongly connected leaves on plants with the first leaf damaged or undamaged by adult L. trilinea. At high levels of herbivory, larval performance decreased on the sixth leaf, which has strong vascular connections to the first leaf, yet increased on the fifth leaf, which has weak vascular connections to the first leaf. PPO activity increased in both the fifth and sixth leaf, while PI activity decreased in the fifth leaf although remaining unchanged in the sixth leaf. At low levels of herbivory, a decrease in larval performance was observed in the sixth leaf, but no change occurred in the weakly connected fifth leaf. Hence, plant vascular architecture clearly predicted within-plant changes in resource quality following only small amounts of herbivore damage.

Animals↗
PubMed2003

Degeneration and regeneration of neuromuscular junction architecture in rat skeletal muscle fibers damaged by bupivacaine hydrochloride.

We evaluated the degeneration and regeneration of neuromuscular junctions (NMJs) on the extensor digitorum longus muscle of Fischer 344 rats between 4 h and 3 weeks after bupivacaine hydrochloride (BPVC) injection, which induces muscle fiber necrosis, using histochemical staining by acetylcholine esterase (AchE)-silver and electron microscopy. Degeneration of muscle fibers and NMJs was observed 4 h after BPVC injection. One week after BPVC injection, some terminal axons were almost completely retracted, and the level of basal lamina-associated AchE in some NMJ regions had gradually disappeared. At that time, the depression contained a few, mostly pit-like or elongated oval invaginations: the incipient junctional folds and some NMJs did not have any secondary junctional fold. By 2 weeks after the BPVC injection, secondary junctional folds began to develop: however, the number of secondary junctional folds was clearly less than that in normal NMJs. At 3 weeks when regeneration of muscle fibers was well advanced, the staining for AchE at the end-plates became stronger and better-defined. The volume density of mitochondria in the terminal area of the terminal significantly decreased upon BPVC-induced destruction of the NMJ, and the density reached the lowest value 24 h after BPVC injection. Significant changes in the ultrastructural features of the architecture of NMJs occurred in skeletal muscle fibers damaged by BPVC during both the degeneration and regeneration processes. The changes in the ultrastructural and morphological features of the NMJ architecture during the regeneration of degenerated muscle fibers resembled those that occur during the differentiation of normal muscle fibers.

Animals↗
PubMed2006

Further evidence that the SNARC effect is processed along a dual-route architecture: Evidence from the lateralized readiness potential.

In a binary response setting, it has been frequently observed that small numbers are reacted to faster with the left hand and large numbers with the right hand (i. e., the SNARC-effect) which reflects the spatial left-right orientation of the mental number line (Dehaene, Bossini, & Giraux, 1993). In line with the work of Keus and Schwarz (in press), we investigated the locus of the conflict in the SNARC effect in a parity judgment task with the Arabic numerals 1, 2, 8, or 9. Differences between compatible (left-hand response to 1 or 2 and right-hand response to 8 and 9) and incompatible SNARC conditions (left-hand response to 8 or 9 and right-hand response to 1 or 2) were observed in the lateralized readiness potential (LRP) but not in the peak latency of the P300. In accordance with Keus and colleagues (Keus, Jenks, & Schwarz, 2005), we argue that the locus of the conflict is situated at intermediate response-related stages. However, instead of adopting a single-route processing architecture, a dual route account is proposed as the underlying processing architecture explaining the SNARC effect.

Adult↗
PubMed2000

Superadditive effects of multiple lesions in a connectionist architecture: implications for the neuropsychology of optic aphasia.

Neuropsychological disorders have traditionally been understood in terms of a focal lesion to a single component of a cognitive architecture. Optic aphasia (OA) defies explanation in this way. In OA, naming of visual stimuli is impaired in the absence of general visual agnosia or anomia. OA has been explained by positing multiple semantic systems or multiple functional pathways to visual naming. M. J. Farah (1990) instead sketched a parsimonious account based on multiple lesions--to pathways mapping visual input to semantic and semantics to naming responses--and the assumption that the effects of the lesions are superadditive. The authors demonstrate superadditive effects of damage in a connectionist architecture and model other phenomena associated with OA. Multiple lesions with superadditivity provide a novel class of explanations for neuropsychological deficits that previously seemed to imply the existence of highly specialized processing components.

Aphasia↗
PubMed1989

Three-dimensional architecture of the calcium channel/foot structure of sarcoplasmic reticulum.

The calcium channel responsible for the release of Ca2+ from the sarcoplasmic reticulum of skeletal muscle during excitation-contraction coupling has recently been identified and purified. The isolated calcium channel has been identified morphologically with the 'foot' structures which are associated with the junctional face membrane of the terminal cisternae of sarcoplasmic reticulum. In situ, the foot structure extends across the gap of the triad junction from the terminal cisternae of the reticulum to the transverse tubule. We describe here the three-dimensional architecture (3.7 nm resolution) of the calcium channel/foot structure from fast-twitch rabbit skeletal muscle, which we determined from electron micrographs of isolated, non-crystalline structures that had been tilted in the electron microscope. The reconstruction reveals two different faces and an internal structure in which stain accumulates at several interconnected locations, which could empty into the junctional gap of the triad junction. The detailed architecture of the channel complex is relevant to understanding both the physical path followed by calcium ions during excitation-contraction coupling and the association of the terminal cisternae and the transverse tubules in the triad junction.

Animals↗