Engineering tyrosine-based electron flow pathways in proteins: the case of aplysia myoglobin

Tyrosine residues can act as redox cofactors that provide an electron transfer ("hole-hopping") route that enhances the rate of ferryl heme iron reduction by externally added reductants, for example, ascorbate. Aplysia fasciata myoglobin, having no naturally occurring tyrosines but 15 phenylalanines that can be selectively mutated to tyrosine residues, provides an ideal protein with which to study such through-protein electron transfer pathways and ways to manipulate them. Two surface exposed phenylalanines that are close to the heme have been mutated to tyrosines (F42Y, F98Y). In both of these, the rate of ferryl heme reduction increased by up to 3 orders of magnitude. This result cannot be explained in terms of distance or redox potential change between donor and acceptor but indicates that tyrosines, by virtue of their ability to form radicals, act as redox cofactors in a new pathway. The mechanism is discussed in terms of the Marcus theory and the specific protonation/deprotonation states of the oxoferryl iron and tyrosine. Tyrosine radicals have been observed and quantified by EPR spectroscopy in both mutants, consistent with the proposed mechanism. The location of each radical is unambiguous and allows us to validate theoretical methods that assign radical location on the basis of EPR hyperfine structure. Mutation to tyrosine decreases the lipid peroxidase activity of this myoglobin in the presence of low concentrations of reductant, and the possibility of decreasing the intrinsic toxicity of hemoglobin by introduction of these pathways is discussed.     

Lab-on-a-bubble: synthesis, characterization, and evaluation of buoyant gold nanoparticle-coated silica spheres

This paper describes the development and preparation of a new class of materials for surface-enhanced Raman scattering (SERS) consisting of gold nanoparticles coated onto hollow, buoyant silica microspheres. These materials allow for a new type of molecular assay designated as a lab-on-a-bubble (LoB). LoB materials serve as a convenient platform for the detection of analytes in solution and offer several advantages over traditional colloidal gold and planar SERS substrates, such as the ability to localize and concentrate analytes for detection. An example assay is presented using the LoB method and cyanide detection. Cyanide binds to SERS-active, gold-coated LoBs and is detected directly from the corresponding SERS signal. The abilities of LoBs and a gold colloid to detect cyanide are compared, and in both cases, a detection limit of ~170 ppt was determined. Differences in measurement error using LoBs versus gold colloid are also described, as well as an assay for 5,5'-dithiobis(2-nitrobenzoic acid) that shows the benefit of using LoBs over SERS analyses in colloids, which are often plagued by particle aggregation.     

Surface transfer doping of hydrogen-terminated diamond by C60F48: energy level scheme and doping efficiency

Surface sensitive C1s core level photoelectron spectroscopy was used to examine the electronic properties of C(60)F(48) molecules on the C(100):H surface. An upward band bending of 0.74 eV in response to surface transfer doping by fluorofullerene molecules is measured. Two distinct molecular charge states of C(60)F(48) are identified and their relative concentration determined as a function of coverage. One corresponds to ionized molecules that participate in surface charge transfer and the other to neutral molecules that do not. The position of the lowest unoccupied molecular orbital of neutral C(60)F(48) which is the relevant acceptor level for transfer doping lies initially 0.6 eV below the valence band maximum and shifts upwards in the course of transfer doping by up to 0.43 eV due to a doping induced surface dipole. This upward shift in conjunction with the band bending determines the occupation of the acceptor level and limits the ultimately achievable hole concentration with C(60)F(48) as a surface acceptor to values close to 10(13) cm(-2) as reported in the literature.     

Comparing light-induced colloidal quasicrystals with different rotational symmetries

Quasicrystals are aperiodic structures with long-range orientational order. Unlike crystals, quasicrystals can, in principle, possess any non-crystallographic rotational symmetry. However, only a few of these rotational symmetries have been observed. By using Monte Carlo simulations of colloidal particles in laser interference patterns with quasicrystalline symmetry, we compare the onset of quasicrystalline order for different rotational symmetries in two dimensions. We find that quasicrystals with 5-, 8-, 10-, and 12-fold rotational axes can be induced with lower laser intensities than quasicrystals with other non-crystallographic rotational symmetries. We relate this finding to the number of local symmetry centers in the respective interference patterns.     

Influence of atmospheric turbulence on states of light carrying orbital angular momentum

We have experimentally studied the degradation of mode purity for light beams carrying orbital angular momentum (OAM) propagating through simulated atmospheric turbulence. The turbulence is modeled as a randomly varying phase aberration, which obeys statistics postulated by Kolmogorov turbulence theory. We introduce this simulated turbulence through the use of a phase-only spatial light modulator. Once the turbulence is introduced, the degradation in mode quality results in crosstalk between OAM modes. We study this crosstalk in OAM for 11 modes, showing that turbulence uniformly degrades the purity of all the modes within this range, irrespective of mode number.     

Synthesis of trans-azoalkane ligands RNNR by dehalogenation of N,N-dihaloalkylamines,RNCl2

N,N-Dihaloalkylamines, RNCl₂, are dehalogenated by organometallic sodium or lithium salts to give trans-azoalkanes, RNNR, and their corresponding metal complexes.     

Some vicinal dioximes as gravimetric reagents

A series of 3,3-substituted indane-1,2-dionedioximes has been synthesized and their reactions with transition metals have been investigated. From the results obtained it is suggested that the selectivity of such dioximes, as gravimetric reagents, is not a function of the dioxime grouping but is due to metal-metal bonding in the complex.     

Standing cones and lying cones

Summary It can be demonstrated in reconstructive surgery when using a fusiform excision that as the ratio of its lengthL to widthW is increased, the probability of a satisfactory closure is also increased. It is found that there is a minimum value ofL/W for a given area of skin beyond which small standing cones appear at the ends of the excision on closure. This indicates that there is a maximum value of the angle, included at the ends of the excision by its two sides, that can be closed satisfactorily. In other surgical procedures not only standing cones may form but also lying cones when the prodecure involves opening an angle instead of closing it.The phenomena of these standing and lying cones in human skin subject to reconstructive surgery are shown to be dependent on the characteristics of the tissue in uniaxial compression. It can be demonstrated that there is a critical value of this compression before the skin in vivo buckles into a ridge or cone.A semi empirical procedure is outlined that allows the surgeon to predict the maximum excisional angles which may be closed or opened without causing the formation of standing or lying cones.

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Zusammenfassung Es wird gezeigt, daß in der Wiederherstellungschirurgie bei Benutzung spindelförmiger Exzisionen mit Steigerung des Verhältnisses Länge L/DurchmesserW die Wahrscheinlichkeit eines zufriedenstellenden Verschlusses erhöht wird. Die Ergebnisse zeigen, daß es einen Minimalwert für das VerhältnisL/W bei einem vorgegebenen Hautbereich gibt, bei dessen Unterschreitung an den Enden der Exzision bei Verschluß kleine stehende Kegel auftreten. Das läßt den Schluß zu, daß es ein Maximum für den Winkel gibt, der am Ende der Exzision durch deren beide Seiten gebildet wird, welcher noch zufriedenstellend verschlossen werden kann. Bei anderen chirurgischen Verfahren können sich nicht nur stehende, sondern auch liegende Kegel bilden, wenn bei dem Verfahren ein Winkel geöffnet statt geschlossen werden muß.Die Erscheinung dieser stehenden und liegenden Kegel in menschlicher Haut, die der Wiederherstellungschirurgie ausgesetzt ist, ist, wie die Untersuchungen zeigen, abhängig von den Eigenschaften des Gewebes bei einachsiger Kompression. Für diese Kompression wird ein kritischer Wert abgeleitet, ehe sich die Haut in vivo zu einem Grat oder Kegel verzieht.Es wird ein halbempirisches Verfahren entwickelt, mit dessen Hilfe der Chirurg den maximalen Exzisionswinkel vorherzusagen vermag, der ohne die Bildung von stehenden oder liegenden Kegeln geschlossen werden kann.

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Paper presented to the British Society of Rheology Conference on Rheology in Medicine and Pharmacy, London, April 14–16, 1970.