Photoswitchable calcium sensor: ‘On’–‘Off’ sensing in cells or with microstructured optical fibers

Calcium is a ubiquitous intracellular signaling ion that plays a critical role in the modulation of fundamental cellular processes. A detailed study of these processes requires selective and reversible sensing of Ca2+ and an ability to quantify and monitor concentration changes in a biological setting. Three new, rationally designed, synthesized and photoswitchable spiropyran-based reversible sensors for Ca2+ are reported. Sensor 1a is highly selective for Ca2+ with an improved profile relative to the other two analogues, 1b and 1c. Formation of the merocyanine–Ca2+ complex is proportional to an increase in Ca2+ released from HEK293 cells on stimulation with ionomycin. The photophysical processes surrounding the binding of Ca2+ to compound 1a were further explored using computational methods based on density functional theory (DFT). The ability of sensor 1a to bind Ca2+ and photoswitch reversibly was also characterized using silica suspended-core microstructured optical fiber (SCF). These SCF experiments (with 100 nM Ca2+) represent a first step toward developing photoswitchable, minimally invasive and highly sensitive Ca2+ sensing platforms for use in a biological setting.Sabrina Heng, Adrian M. Mak, Roman Kostecki, Xiaozhou Zhang Jinxin Pei, Daniel B.Stubing, Heike Ebendorff-Heidepriem, Andrew D.Abel

Fire drives phylogenetic clustering in Mediterranean Basin woody plant communities

8 páginas, 2 tablas, 2 figuras.1. Many Mediterranean plant species persist after fire because their seeds are protected from the heat of the fire (e.g. hard-coated seeds, serotinous cones), thus permitting rapid post-fire recruitment. For simplicity, this trait will hereafter be called P and its two possible phenotypes P+ (seeder) and P– (non-seeder). 2. Because P+ appears in a narrow taxonomic spectrum and confers persistence under high fire frequencies, we test the extent to which communities with different fire histories have different phenotypic and phylogenetic structures. Specifically, we compare coastal vegetation growing in a warm and dry Mediterranean climate subject to high fire frequency (HiFi vegetation) with montane vegetation subject to a subhumid climate where fires are rare (LowFi) under the hypothesis that P+ species will be over-represented in HiFi communities, thus producing phenotypic and phylogenetic clustering. 3. Trait conservatism on P is evaluated by testing the presence of a phylogenetic signal, phenotypic clustering is tested by correlating co-occurrence and phenotypic distance matrices, and the phylogenetic structure is evaluated by testing whether the phylogenetic distances between species in each community are different from those expected by chance. 4. The results suggest that: (a) P is a strongly conserved trait; (b) co-occurring species have similar P phenotypes (phenotypic clustering); and (c) the phylogenetic structure in HiFi vegetation is significantly clustered while LowFi vegetation tends to be overdispersed. 5.Synthesis: Fire is a strong driving force in assembling HiFi communities while other forces, such as competitive interactions, are the main assembly mechanisms in LowFi communities. This result supports the role of recurrent disturbances as filters driving phylogenetic community structure.We thank C. Webb and S. Kembel for their help in the use of the Phylocom software and P. García-Fayos and G. Segarra-Moragues for helpful comments on the local flora. P. Clarke, P. Vesk and C. Romero provided valuable comments on the manuscript and J. A. Pascual produced the map for Fig. 1. This work has been partially financed by the Spanish Government project PERSIST (CGL2006-07126/BOS). CEAM is supported by Generalitat Valenciana and Bancaixa.Peer reviewe

Dual sensor for Cd(II) and Ca(II): selective nanoliter-scale sensing of metal ions

The first selective, dual sensor for Ca²⁺ and Cd²⁺ capable of detection at 100 pM concentrations was designed and synthesized. The experimental observations made for the MC-cation complexes and the selectivity of compounds 1 and 2 with Ca²⁺ and Cd²⁺ ions were further explored using density functional theory. A first step toward a nanoliter-scale dip sensor for the dual sensing of Ca²⁺ and Cd²⁺ was demonstrated using microstructured optical fiber as the sensing platform which is important for ion sensing in confined spaces such as the medium surrounding cell clusters. In addition, this system displays picomolar sensitivity for these ions, with an added ability to reproducibly turn ion-binding on/off.Sabrina Heng, Adrian M. Mak, Daniel B. Stubing, Tanya M. Monro, and Andrew D. Abel

Who appropriates centrality rents? The role of institutions in regulating social networks in the global Islamic finance industry

This study explains and tests the effects of country-level institutions on the distribution of centrality rents between two sets of actors in an interorganizational network. Building on the literature on corporate elites, we propose that a cohesive elite following organizational logics other than profit-maximization diverts centrality rents and induces costs on firms, and that macro institutions act as external governance mechanisms to shape this relationship. We develop our theory in the emerging Islamic finance industry, where “Shariah scholars” connect firms and constitute a religious corporate elite. While central scholars in this network create legitimacy for firms, they also shirk and cause information leakage, suggesting a negative centrality-performance relationship for the firms. Country-level institutions such as government regulation and democracy, we argue, ameliorate these effects by influencing this religious elite’s institutional logic and restraining their actions, while institutions developed from within the industry strengthen the power of the elite. Testing our theory in a network of 367 scholars and 396 institutions over 31 countries using multi-level methods, we indeed find a negative centrality-performance relationship that is ameliorated by stronger government regulation but exacerbated by better-developed industry-specific institutions, as well as a negative relationship between democratic and regulatory institutions and centrality