DNA Encapsulation of Ten Silver Atoms Produces a Bright, Modulatable, Near Infrared-Emitting Cluster

Photostability, inherent fluorescence brightness, and optical modulation of fluorescence are key attributes distinguishing silver nanoclusters as fluorophores. DNA plays a central role both by protecting the clusters in aqueous environments and by directing their formation. Herein, we characterize a new near infrared-emitting cluster with excitation and emission maxima at 750 and 810 nm, respectively that is stabilized within C(3)AC(3)AC(3)TC(3)A. Following chromatographic resolution of the near infrared species, a stoichiometry of 10 Ag/oligonucleotide was determined. Combined with excellent photostability, the cluster's 30% fluorescence quantum yield and 180,000 M(-1)cm(-1) extinction coefficient give it a fluorescence brightness that significantly improves on that of the organic dye Cy7. Fluorescence correlation analysis shows an optically accessible dark state that can be directly depopulated with longer wavelength co-illumination. The coupled increase in total fluorescence demonstrates that enhanced sensitivity can be realized through Synchronously Amplified Fluorescence Image Recovery (SAFIRe), which further differentiates this new fluorophore.     

Structural and Spectroscopic Characterization of Mer-[RhBr3(Me2pzH)3] (Me2pzH?=?3, 5-Dimethylpyrazole); Interpreting the Results with Density Functional Theory Calculations

Abstract  

Mer-RhBr₃(Me₂pzH)₃ (Me₂pzH = 3,5-dimethylpyrazole) (monoclinic, P2₁/n, a = 8.3300 (5) Å, b = 16.2889 (9) Å, c = 15.9299 (11) Å, α = 90°, β = 100.217 (5)°, γ = 90°; V = 2,127.2 (2) ų; Z = 4) has been characterized by X-ray diffraction, ¹H and ¹³C nuclear magnetic resonance spectroscopy, infrared spectroscopy, and electronic absorption spectroscopy, and modeled by density functional theory (DFT) and time-dependent density functional theory (TDDFT). Mer-RhBr₃(Me₂pzH)₃ is an octahedral complex with a HOMO → LUMO transition at 486 nm. The DFT and TDDFT calculations predicted mer-RhBr₃(Me₂pzH)₃ to be an octahedral complex with a HOMO → LUMO transition at 540 nm.     

Role of thermodynamics in the shape transformation of embedded metal nanoparticles induced by swift heavy-ion irradiation

Swift heavy-ion irradiation of elemental metal nanoparticles (NPs) embedded in amorphous SiO(2) induces a spherical to rodlike shape transformation with the direction of NP elongation aligned to that of the incident ion. Large, once-spherical NPs become progressively more rodlike while small NPs below a critical diameter do not elongate but dissolve in the matrix. We examine this shape transformation for ten metals under a common irradiation condition to achieve mechanistic insight into the transformation process. Subtle differences are apparent including the saturation of the elongated NP width at a minimum sustainable, metal-specific value. Elongated NPs of lesser width are unstable and subject to vaporization. Furthermore, we demonstrate the elongation process is governed by the formation of a molten ion-track in amorphous SiO(2) such that upon saturation the elongated NP width never exceeds the molten ion-track diameter.     

Chirped area coupled resonator optical waveguide gyroscope

We study the transmission of an optical field through a rotating coupled resonator optical waveguide (CROW) in which the size of the ring resonators changes from one ring to the next. We focus on symmetric integer wavelength chirps of the circumference of the rings relative to the central ring in the array. The transfer matrix method is used to obtain the transmission as a function of the inertial rotation rate Ω resulting from the Sagnac effect. Chirping increases the slope of the oscillations in the transmission as a function of Ω, which can be exploited to further enhance the rotation sensitivity beyond that of a CROW with uniform resonators.     

Lipopolysaccharide-induced inflammation attenuates taste progenitor cell proliferation and shortens the life span of taste bud cells

Background  

The mammalian taste bud, a complex collection of taste sensory cells, supporting cells, and immature basal cells, is the structural unit for detecting taste stimuli in the oral cavity. Even though the cells of the taste bud undergo constant turnover, the structural homeostasis of the bud is maintained by balancing cell proliferation and cell death. Compared with nongustatory lingual epithelial cells, taste cells express higher levels of several inflammatory receptors and signalling proteins. Whether inflammation, an underlying condition in some diseases associated with taste disorders, interferes with taste cell renewal and turnover is unknown. Here we report the effects of lipopolysaccharide (LPS)-induced inflammation on taste progenitor cell proliferation and taste bud cell turnover in mouse taste tissues.     

Helix Induction by Dirhodium: Access to Biocompatible Metallopeptides with Defined Secondary Structure

The use of carboxylate side chains to induce peptide helicity upon binding to dirhodium centers is examined through experimental and computational approaches. Dirhodium binding efficiently stabilizes α helicity or induces α helicity in otherwise unstructured peptides for peptides that contain carboxylate side chains with i, i+4 spacing. Helix induction is furthermore possible for sequences with i, i+3 carboxylate spacing, though in this case the length of the side chains is crucial: ligating to longer glutamate side chains is strongly helix inducing, whereas ligating the shorter aspartate side chains destabilizes the helical structure. Further studies demonstrate that a dirhodium metallopeptide complex persists for hours in cellular media and exhibits low toxicity toward mammalian cells, enabling exploitation of these metallopeptides for biological applications.