Isotensor Dibaryon in the pp→ppπ^{+}π^{-} Reaction?

Exclusive measurements of the quasifree pp→ppπ^{+}π^{-} reaction have been carried out at WASA@COSY by means of pd collisions at T_{p}=1.2  GeV. Total and differential cross sections have been extracted covering the energy region T_{p}=1.

Spin Dependence of η Meson Production in Proton-Proton Collisions Close to Threshold.

Taking advantage of the high acceptance and axial symmetry of the WASA-at-COSY detector, and the high polarization degree of the proton beam of COSY, the reaction p[over →]p→ppη has been measured close to threshold to explore the analyzing power A_{y}. The angular distribution of A_{y} is determined with the precision improved by more than 1 order of magnitude with respect to previous results, allowing a first accurate comparison with theoretical predictions. The determined analyzing power is consistent with zero for an excess energy of Q=15  MeV, signaling s-wave production with no evidence for higher partial waves.

Phase Locking the Spin Precession in a Storage Ring.

This Letter reports the successful use of feedback from a spin polarization measurement to the revolution frequency of a 0.97  GeV/c bunched and polarized deuteron beam in the Cooler Synchrotron (COSY) storage ring in order to control both the precession rate (≈121  kHz) and the phase of the horizontal polarization component. Real time synchronization with a radio frequency (rf) solenoid made possible the rotation of the polarization out of the horizontal plane, yielding a demonstration of the feedback method to manipulate the polarization.

How to Reach a Thousand-Second in-Plane Polarization Lifetime with 0.97-GeV/c Deuterons in a Storage Ring.

We observe a deuteron beam polarization lifetime near 1000 s in the horizontal plane of a magnetic storage ring (COSY). This long spin coherence time is maintained through a combination of beam bunching, electron cooling, sextupole field corrections, and the suppression of collective effects through beam current limits. This record lifetime is required for a storage ring search for an intrinsic electric dipole moment on the deuteron at a statistical sensitivity level approaching 10^{-29}  e cm.

New Method for a Continuous Determination of the Spin Tune in Storage Rings and Implications for Precision Experiments.

A new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the spin tune-defined as the number of spin precessions per turn-is given by ν(s)=γG (γ is the Lorentz factor, G the gyromagnetic anomaly). At 970  MeV/c, the deuteron spins coherently precess at a frequency of ≈120  kHz in the Cooler Synchrotron COSY.

Competition between Förster resonance energy transfer and electron transfer in stoichiometrically assembled semiconductor quantum dot-fullerene conjugates.

Understanding how semiconductor quantum dots (QDs) engage in photoinduced energy transfer with carbon allotropes is necessary for enhanced performance in solar cells and other optoelectronic devices along with the potential to create new types of (bio)sensors. Here, we systematically investigate energy transfer interactions between C60 fullerenes and four different QDs, composed of CdSe/ZnS (type I) and CdSe/CdS/ZnS (quasi type II), with emission maxima ranging from 530 to 630 nm. C60-pyrrolidine tris-acid was first coupled to the N-terminus of a hexahistidine-terminated peptide via carbodiimide chemistry to yield a C60-labeled peptide (pepC60).

Site-specific cellular delivery of quantum dots with chemoselectively-assembled modular peptides.

Modular peptides displaying both quantum dot bioconjugation motifs and specific subcellular targeting domains were constructed using a chemoselective aniline-catalyzed hydrazone coupling chemistry. Peptides were ratiometrically assembled onto quantum dots to facilitate their specific delivery to either the plasma membrane, endosomes, the cytosol or the mitochondria of target cells.

Abashian-Booth-Crowe effect in basic double-pionic fusion: a new resonance?

We report on an exclusive and kinematically complete high-statistics measurement of the basic double-pionic fusion reaction pn→dπ(0)π(0) over the full energy region of the ABC effect, a pronounced low-mass enhancement in the ππ-invariant mass spectrum. The measurements, which cover also the transition region to the conventional t-channel ΔΔ process, were performed with the upgraded WASA detector setup at COSY. The data reveal the Abashian-Booth-Crowe effect to be uniquely correlated with a Lorentzian energy dependence in the integral cross section.

The controlled display of biomolecules on nanoparticles: a challenge suited to bioorthogonal chemistry.

Interest in developing diverse nanoparticle (NP)-biological composite materials continues to grow almost unabated. This is motivated primarily by the desire to simultaneously exploit the properties of both NP and biological components in new hybrid devices or materials that can be applied in areas ranging from energy harvesting and nanoscale electronics to biomedical diagnostics. The utility and effectiveness of these composites will be predicated on the ability to assemble these structures with control over NP/biomolecule ratio, biomolecular orientation, biomolecular activity, and the separation distance within the NP-bioconjugate architecture.

Multivalent conjugation of peptides, proteins, and DNA to semiconductor quantum dots.

Semiconductor nanocrystals or quantum dots (QDs) have become well-established as a unique nanoparticle scaffold for bioapplications due to their robust luminescent properties. In order to continue their development and expand this technology, improved methodologies are required for the controllable functionalization and display of biomolecules on QDs. In particular, efficient routes that allow control over ligand loading and spatial orientation, while minimizing or eliminating cross-linking and aggregation are needed.

Self-assembled quantum dot-sensitized multivalent DNA photonic wires.

Combining the inherent scaffolding provided by DNA structure with spatial control over fluorophore positioning allows the creation of DNA-based photonic wires with the capacity to transfer excitation energy over distances greater than 150 Å. We demonstrate hybrid multifluorophore DNA-photonic wires that both self-assemble around semiconductor quantum dots (QDs) and exploit their unique photophysical properties. In this architecture, the QDs function as both central nanoscaffolds and ultraviolet energy harvesting donors that drive Förster resonance energy transfer (FRET) cascades through the DNA wires with emissions that approach the near-infrared.

Quantum dot DNA bioconjugates: attachment chemistry strongly influences the resulting composite architecture.

The unique properties provided by hybrid semiconductor quantum dot (QD) bioconjugates continue to stimulate interest for many applications ranging from biosensing to energy harvesting. Understanding both the structure and function of these composite materials is an important component in their development. Here, we compare the architecture that results from using two common self-assembly chemistries to attach DNA to QDs.

Quantum dot peptide biosensors for monitoring caspase 3 proteolysis and calcium ions.

The nanoscale size and unique optical properties of semiconductor quantum dots (QDs) have made them attractive as central photoluminescent scaffolds for a variety of biosensing platforms. In this report we functionalize QDs with dye-labeled peptides using two different linkage chemistries to yield Förster resonance energy transfer (FRET)-based sensors capable of monitoring either enzymatic activity or ionic presence. The first sensor targets the proteolytic activity of caspase 3, a key downstream effector of apoptosis.

Combining chemoselective ligation with polyhistidine-driven self-assembly for the modular display of biomolecules on quantum dots.

One of the principle hurdles to wider incorporation of semiconductor quantum dots (QDs) in biology is the lack of facile linkage chemistries to create different types of functional QD--bioconjugates. A two-step modular strategy for the presentation of biomolecules on CdSe/ZnS core/shell QDs is described here which utilizes a chemoselective, aniline-catalyzed hydrazone coupling chemistry to append hexahistidine sequences onto peptides and DNA. This specifically provides them the ability to ratiometrically self-assemble to hydrophilic QDs.

Polyvalent display and packing of peptides and proteins on semiconductor quantum dots: predicted versus experimental results.

Quantum dots (QDs) are loaded with a series of peptides and proteins of increasing size, including a <20 residue peptide, myoglobin, mCherry, and maltose binding protein, which together cover a range of masses from <2.2 to approximately 44 kDa. Conjugation to the surface of dihydrolipoic acid-functionalized QDs is facilitated by polyhistidine metal affinity coordination.

Experimental test of a new technique to overcome spin-depolarizing resonances.

We recently tested a new spin resonance crossing technique, Kondratenko Crossing (KC), by sweeping an rf-solenoid's frequency through an rf-induced spin resonance with both the KC and traditional fast crossing (FC) patterns. Using both rf bunched and unbunched 1.85 GeV/c polarized deuterons stored in COSY, we varied the parameters of both crossing patterns.

Polyvalent display of heme on hepatitis B virus capsid protein through coordination to hexahistidine tags.

The addition of a hexahistidine tag to the N terminus of the hepatitis B capsid protein gives rise to a self-assembled particle with 80 sites of high local density of histidine side chains. Iron protoporphyrin IX has been found to bind tightly at each of these sites, making a polyvalent system of well-defined spacing between metalloporphyrin complexes. The spectroscopic and redox properties of the resulting particle are consistent with the presence of 80 site-isolated bis(histidine)-bound heme centers, comprising a polyvalent b-type cytochrome mimic.

Experimental verification of predicted beam-polarization oscillations near a spin resonance.

The Chao matrix formalism allows analytic calculations of a beam's polarization behavior inside a spin resonance. We recently tested its prediction of polarization oscillations occurring in a stored beam of polarized particles near a spin resonance. Using a 1.

Unnatural amino acid incorporation into virus-like particles.

Virus-like particles composed of hepatitis B virus (HBV) or bacteriophage Qbeta capsid proteins have been labeled with azide- or alkyne-containing unnatural amino acids by expression in a methionine auxotrophic strain of E. coli. The substitution does not affect the ability of the particles to self-assemble into icosahedral structures indistinguishable from native forms.

Plasma clearance of bacteriophage Qbeta particles as a function of surface charge.

Self-assembled protein capsids have gained attention as a promising class of nanoparticles for biomedical applications due to their monodisperse nature and versatile genetic and chemical tailorability. To determine the plasma clearance and tissue distribution in mice of the versatile capsid of bacteriophage Qbeta, the particles were decorated with gadolinium complexes using the CuI-mediated azide-alkyne cycloaddition reaction. Interior surface labeling was engineered by the introduction of an azide-containing unnatural amino acid into the coat protein for the first time.

Precision study of the eta3He system using the dp--> 3Heeta reaction.

The differential and total cross sections for the dp--> 3Heeta reaction have been measured in a high precision high statistics COSY-ANKE experiment near threshold using a continuous beam energy ramp up to an excess energy Q of 11.3 MeV with essentially 100% acceptance. The kinematics allowed the mean value of Q to be determined to about 9 keV.

Bio-distribution, toxicity and pathology of cowpea mosaic virus nanoparticles in vivo.

Virus-based nanoparticles (VNPs) from a variety of sources are being developed for biomedical and nanotechnology applications that include tissue targeting and drug delivery. However, the fate of most of those particles in vivo has not been investigated. Cowpea mosaic virus (CPMV), a plant comovirus, has been found to be amenable to the attachment of a variety of molecules to its coat protein, as well as to modification of the coat protein sequence by genetic means.

Viral MRI contrast agents: coordination of Gd by native virions and attachment of Gd complexes by azide-alkyne cycloaddition.

Icosahedral virus particles decorated with a Gd(DOTA) analogue by Cu-mediated azide-alkyne cycloaddition (CuAAC) and/or with Gd(3+) ions by coordination to the viral nucleoprotein show increased T(1) relaxivity relative to free Gd(DOTA) complexes in solution.

Measurement of the analyzing power in p-->d-->(p p)n with a fast forward 1S0 proton pair.

A measurement of the analyzing power A(y) of the p-->d--> (p p) + n reaction was carried out at the ANKE spectrometer at COSY at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy E(pp) < 3 MeV.