Stiffer alginate gels deposit more efficiently in microchannel flows

The behavior of crosslinking polymer solutions as they transition from liquid-like to solid-like material in flow determines success or failure in several applications, from 3D printing to oil recovery in the earth's subsurface to a wide variety of biological flows. Dilute polymer solutions flow easily, while concentrated polymers or crosslinked polymer gels can clog pores, nozzles, or channels. We have recently uncovered and described a third regime of flow dynamics in polymers that occurs when crosslinking happens during flow: intermittent flows. In a model system of alginate and calcium meeting at a Y-shaped junction in a microfluidic channel, a persistent and regular pattern of intermittent flow occurs when driven at a constant volume flow rate. At the junction, calcium crosslinks alginate to form an alginate gel, which subsequently deposits on the channel wall. As gel continues to deposit, it obstructs the channel, causing the driving pressure to increase to maintain a constant flow rate. At a critical pressure, corresponding to a critical shear stress, the fluid pulls the gel from the wall, removing the gel from the device and resulting in a clear channel. The gel deposit begins again, and the process then repeats as long as flow continues. Chemical concentrations and flow rate control both the frequency of ablation and the critical shear stress. In this work, we provide an analytical framework to quantitatively describe the intermittent behavior as a result of diffusively driven deposition in a high Peclet number flow where convection dominates. Fitting the experimental data to the model allows estimation of the deposition efficiency, or the fraction of flowing material that sticks to the channel walls. By correlating the results of the model with bulk rheology measurements, we find that deposition efficiency increases with the stiffness of the gel formed in flow.Comment: 11 pages, 5 figure

Homogeneous Gold Catalysis through Relativistic Effects: Addition of Water to Propyne

In the catalytic addition of water to propyne the Au(III) catalyst is not stable under non-relativistic conditions and dissociates into a Au(I) compound and Cl2. This implies that one link in the chain of events in the catalytic cycle is broken and relativity may well be seen as the reason why Au(III) compounds are effective catalysts.Comment: 12 pages, 3 figures, 1 tabl

Polydimethylsiloxane-Embedded Conductive Fabric: Characterization and Application for Realization of Robust Passive and Active Flexible Wearable Antennas

© 2013 IEEE. We present our study on polydimethylsiloxane (PDMS)-embedded conductive fabric, which we propose as a simple yet effective solution to the challenging issue of poor PDMS-metal adhesion, allowing for a relatively easy realization of robust flexible antennas for wearable applications. The method combines the use of conductive fabric as a radiator with PDMS, which acts as the substrate and a protective encapsulation simultaneously. For the first time, a holistic study on the mechanical and electrical properties of the proposed combination of materials is presented thoroughly using a number of fabricated samples. As concept demonstrations, a microstrip patch and a reconfigurable patch antenna are fabricated using the proposed technique to validate the idea. The inclusion of a PDMS-ceramic composite as part of the antenna's substrate, which leads to over 50% reduction in the size compared with a pure PDMS, is also demonstrated to showcase further the versatility of the proposed technique. The fabricated antennas are tested in several wearable scenarios and consistent performance including reconfigurability is obtained even after the antennas are exposed to harsh environments, i.e., extreme bending and machine-washing

Catalysis at the Heart of Success!

Bornscheuer, UT.; Hashmi, ASK.; García Gómez, H.; Rowan, MA. (2017). Catalysis at the Heart of Success!. ChemCatChem. 9(1):6-9. doi:10.1002/cctc.201601553S6991Bornscheuer, U. T. (2015). Biocatalysis: Successfully Crossing Boundaries. Angewandte Chemie International Edition, 55(14), 4372-4373. doi:10.1002/anie.201510042Bornscheuer, U. T. (2015). Biokatalyse: ein erfolgreicher Blick über den Tellerrand. Angewandte Chemie, 128(14), 4446-4447. doi:10.1002/ange.201510042Bornscheuer, U. T. (2009). Combined Success for Efficient Catalysis. ChemCatChem, 1(1), 5-5. doi:10.1002/cctc.200900144Weckhuysen, B. M. (2009). Crossing the Interfaces of Catalysis. ChemCatChem, 1(1), 7-7. doi:10.1002/cctc.200900146Kan, S. B. J., Lewis, R. D., Chen, K., & Arnold, F. H. (2016). Directed evolution of cytochrome c for carbon–silicon bond formation: Bringing silicon to life. Science, 354(6315), 1048-1051. doi:10.1126/science.aah621

Proton supplier role of binuclear gold complexes in promoting hydrofunctionalisation of nonactivated alkenes

Density functional theory (DFT) was used to investigate PR 3 AuOTf-catalyzed hydrofunctionalisation of nonactivated alkenes using acetic acid and phenol where OTf = triflate (CF 3 SO 3- ). The gold(i) complex itself is found to be unlikely to operate as the π-activator due to its relatively low electrophilicity. Instead, the concurrent coordination of two gold(i) complexes to a nucleophile (PhOH or AcOH) enhances the acidity of the latter\u27s proton and causes the ensuing binuclear complex to serve as a strong proton supplier for activating the alkene π-bonds. Alternatively, the binuclear complex is also susceptible to produce a hidden HOTf. This hidden acid is accessible for hydrofunctionalization to occur but it is not in sufficient concentration to decompose the final product

Facial Analytics Based on a Coordinate Extrapolation System (zFACE) for Morphometric Phenotyping of Developing Zebrafish

Facial development requires a complex and coordinated series of cellular events that, when perturbed, can lead to structural birth defects. A quantitative approach to quickly assess morphological changes could address how genetic or environmental inputs lead to differences in facial shape and promote malformations. Here, we report on a method to rapidly analyze craniofacial development in zebrafish embryos using facial analytics based on a coordinate extrapolation system, termed zFACE. Confocal images capture facial structures and morphometric data are quantified based on anatomical landmarks present during development. The quantitative morphometric data can detect phenotypic variation and inform on changes in facial morphology. We applied this approach to show that loss of smarca4a in developing zebrafish leads to craniofacial anomalies, microcephaly and alterations in brain morphology. These changes are characteristic of Coffin-Siris syndrome, a rare human genetic disorder associated with mutations in SMARCA4. Multivariate analysis of zFACE data facilitated the classification of smarca4a mutants based on changes in specific phenotypic characteristics. Together, zFACE provides a way to rapidly and quantitatively assess the impact of genetic alterations on craniofacial development in zebrafish

Disruption of Fos Causes Craniofacial Anomalies in Developing Zebrafish

Craniofacial development is a complex and tightly regulated process and disruptions can lead to structural birth defects, the most common being nonsyndromic cleft lip and palate (NSCLP). Previously, we identified FOS as a candidate regulator of NSCLP through family-based association studies, yet its specific contributions to oral and palatal formation are poorly understood. This study investigated the role of fos during zebrafish craniofacial development through genetic disruption and knockdown approaches. Fos was expressed in the periderm, olfactory epithelium and other cell populations in the head. Genetic perturbation of fos produced an abnormal craniofacial phenotype with a hypoplastic oral cavity that showed significant changes in midface dimensions by quantitative facial morphometric analysis. Loss and knockdown of fos caused increased cell apoptosis in the head, followed by a significant reduction in cranial neural crest cells (CNCCs) populating the upper and lower jaws. These changes resulted in abnormalities of cartilage, bone and pharyngeal teeth formation. Periderm cells surrounding the oral cavity showed altered morphology and a subset of cells in the upper and lower lip showed disrupted Wnt/β-catenin activation, consistent with modified inductive interactions between mesenchymal and epithelial cells. Taken together, these findings demonstrate that perturbation of fos has detrimental effects on oral epithelial and CNCC-derived tissues suggesting that it plays a critical role in zebrafish craniofacial development and a potential role in NSCLP

Divergent gold-catalysed reactions of cyclopropenylmethyl sulfonamides with tethered heteroaromatics

Cyclopropenylmethyl sulfonamides with tethered heteroaromatics have been demonstrated to undergo divergent gold-catalysed cyclisation reactions. A formal dearomative (4+3) cycloaddition takes place with furan-tethered substrates, yielding densely functionalised 5,7-fused heterocycles related to the bioactive curcusone natural products. Indole-tethered substrates display divergent reactivity giving biologically important tetrahydro-β-carbolines via a Friedel-Crafts mechanism