De novo design of strand-swapped beta-hairpin hydrogels

De novo designed peptides, capable of undergoing a thermally triggered beta-strand-swapped self-assembly event leading to hydrogel formation were prepared. Strand-swapping peptide 1 (SSP1) incorporates an exchangeable beta-strand domain composed of eight residues appended to a nonexchangeable beta-hairpin domain. CD shows that, at pH 9 and temperatures less than 35 degrees C, this peptide adopts a random coil conformation, rendering it soluble in aqueous solution. On heating to 37 degrees C or greater, SSP1 adopts a beta-hairpin that displays an exchangeable beta-strand region. The exchangeable strand domain participates in swapping with the exchangeable domain of another peptide, affording a strand-swapped dimer. These dimers further assemble into fibrils that define the hydrogel. A second peptide (SSP2) containing an exchangeable strand composed of only four residues was also studied. Microscopy and scattering data show that the length of the exchangeable domain directly influences the fibril nanostructure and can be used as a design element to construct either twisted (SSP1) or nontwisted (SSP2) fibril morphologies. CD, FTIR, and WAXS confirm that both peptides adopt beta-sheet secondary structure when assembled into fibrils. Fibril dimensions, as measured by TEM, AFM, and SANS indicate a fibril diameter of 6.4 nm, a height of 6.0 nm, and a pitch of 50.4 nm for the twisted SSP1 fibrils. The nontwisted SSP2 fibrils are 6.2 nm in diameter and 2.5 nm in height. Oscillatory rheology, used to measure bulk hydrogel rigidity, showed that the gel composed of the nontwisted fibrils is more mechanically rigid (517 Pa at 6 rad/s) than the gel composed of twisted fibrils (367 Pa at 6 rad/s). This work demonstrates that beta-strand-swapping can be used to fabricate biomaterials with tunable fibril nanostructure and bulk hydrogel rheological properties.     

The good,the bad,and the tiny: a review of microflow cytometry

Recent developments in microflow cytometry have concentrated on advancing technology in four main areas: (1) focusing the particles to be analyzed in the microfluidic channel, (2) miniaturization of the fluid-handling components, (3) miniaturization of the optics, and (4) integration and applications development. Strategies for focusing particles in a narrow path as they pass through the detection region include the use of focusing fluids, nozzles, and dielectrophoresis. Strategies for optics range from the use of microscope objectives to polymer waveguides or optical fibers embedded on-chip. While most investigators use off-chip fluidic control, there are a few examples of integrated valves and pumps. To date, demonstrations of applications are primarily used to establish that the microflow systems provide data of the same quality as laboratory systems, but new capabilities-such as automated sample staining-are beginning to emerge. Each of these four areas is discussed in detail in terms of the progress of development, the continuing limitations, and potential future directions for microflow cytometers.     

Intensified biochip system using chemiluminescence for the detection of Bacillus globigii spores

This paper reports the first intensified biochip system for chemiluminescence detection and the feasibility of using this system for the analysis of biological warfare agents is demonstrated. An enzyme-linked immunosorbent assay targeting Bacillus globigii spores, a surrogate species for Bacillus anthracis, using a chemiluminescent alkaline phosphatase substrate is combined with a compact intensified biochip detection system. The enzymatic amplification was found to be an attractive method for detection of low spore concentrations when combined with the intensified biochip device. This system was capable of detecting approximately 1 × 10⁵ Bacillus globigii spores. Moreover, the chemiluminescence method, combined with the self-contained biochip design, allows for a simple, compact system that does not require laser excitation and is readily adaptable to field use. Figure Schematic diagram of the miniature biochip detection system     

Knot homology via derived categories of coherent sheaves II, $\mathfrak{sl}_{m}$ case

Using derived categories of equivariant coherent sheaves we construct a knot homology theory which categorifies the quantum knot polynomial. Our knot homology naturally satisfies the categorified MOY relations and is conjecturally isomorphic to Khovanov–Rozansky homology. Our construction is motivated by the geometric Satake correspondence and is related to Manolescu’s by homological mirror symmetry.     

A photopatternable silicone for biological applications

We show the application of a commercially available photopatternable silicone (PPS) that combines the advantageous features of both PDMS and SU-8 to address a critical bioMEMS materials deficiency. Using PPS, we demonstrate the ability to pattern free-standing mechanically isolated elastomeric structures on a silicon substrate: a feat that is challenging to accomplish using soft lithography-based fabrication. PPS readily integrates with many cell-based bioMEMS since it exhibits low autofluorescence and cells easily attach and proliferate on PPS-coated substrates. Because of its inherent photopatternable properties, PPS is compatible with standard microfabrication processes and easily aligns to complex featured substrates on a wafer scale. By leveraging PPS' unique properties, we demonstrate the design of a simple dielectrophoresis-based bioMEMS device for patterning mammalian cells. The key material properties and integration capabilities explored in this work should present new avenues for exploring silicone microstructures for the design and implementation of increasingly complex bioMEMS architectures.     

Vibrational ground state properties of H(5)(+) and its isotopomers from diffusion Monte Carlo calculations

Diffusion Monte Carlo computations, with and without importance sampling, of the zero-point properties of H(5)(+) and its isotopomers using a recent high accuracy global potential energy surface are presented. The global minimum of the potential possesses C(2v) symmetry, but the calculations predict a D(2d) geometry for zero-point averaged structure of H(5)(+) with one H atom "in the middle" between two HH diatoms. The predicted zero-point geometries of the deuterated forms have H in the middle preferred over D in the middle and for a nonsymmetric arrangement of D atoms the preferred arrangement is one which maximizes the number of D as the triatomic ion. We speculate on the consequences of these preferences in scattering of H(2)+H(3)(+) and isotopomers at low energies, such as those in the interstellar medium.     

Stereocontrolled synthesis of Z-dienes via an unexpected pericyclic cascade rearrangement of 5-amino-2,4-pentadienals

Donor-acceptor dienes known as Zincke aldehydes, which derive readily from the ring-opening reactions of pyridinium salts with secondary amines, undergo a fascinating thermal rearrangement reaction to afford Z-alpha,beta,gamma,delta-unsaturated amides with excellent stereoselectivity. Efficient, stereocontrolled access to Z-trisubstituted alkenes with two different substitution patterns is possible in three steps beginning with the appropriately substituted pyridine derivative. Preliminary studies have shown that both the amide and the monosubstituted alkene termini can be selectively functionalized. Ease of access, generality of scope, and facile product manipulation render this process attractive for the synthesis of complex polyenes.