Class groups of quadratic fields of 3-rank at least 2: Effective bounds

In this paper, we give parametric families of both real and complex quadratic number fields whose class group has 3-rank at least 2. As a consequence, we obtain that for all large positive real numbers x, the number of both real and complex quadratic fields whose class group has 3-rank at least 2 and absolute value of the discriminant ?x is >cx1/3, where c is some positive constant.     

On the connected components of the space of line transversals to a family of convex sets

Let ℒ be the space of line transversals to a finite family of pairwise disjoint compact convex sets in ℝ³. We prove that each connected component of ℒ can itself be represented as the space of transversals to some finite family of pairwise disjoint compact convex sets. The research of J. E. Goodman was supported in part by NSF Grant DMS91-22065 and by NSA Grant MDA904-92-H-3069. R. Pollack's research was supported in part by NSF Grant CCR91-22103 and by NSA Grant MDA904-92-H-3075. The research of R. Wenger was supported in part by NSA Grant MDA904-93-H-3026 and by the NSF Regional Geometry Institute (Smith College, July 1993) Grant DMS90-13220.     

FRET Enhancement in Aluminum Zero‐Mode Waveguides

Zero‐mode waveguides (ZMWs) can confine light into attoliter volumes, which enables single molecule fluorescence experiments at physiological micromolar concentrations. Of the fluorescence spectroscopy techniques that can be enhanced by ZMWs, Förster resonance energy transfer (FRET) is one of the most widely used in life sciences. Combining zero‐mode waveguides with FRET provides new opportunities to investigate biochemical structures or follow interaction dynamics at micromolar concentrations with single‐molecule resolution. However, prior to any quantitative FRET analysis on biological samples, it is crucial to establish first the influence of the ZMW on the FRET process. Here, we quantify the FRET rates and efficiencies between individual donor–acceptor fluorophore pairs that diffuse into aluminum zero‐mode waveguides. Aluminum ZMWs are important structures thanks to their commercial availability and the large amount of literature that describe their use for single‐molecule fluorescence spectroscopy. We also compared the results between ZMWs milled in gold and aluminum, and found that although gold has a stronger influence on the decay rates, the lower losses of aluminum in the green spectral region provide larger fluorescence brightness enhancement factors. For both aluminum and gold ZMWs, we observed that the FRET rate scales linearly with the isolated donor decay rate and the local density of optical states. Detailed information about FRET in ZMWs unlocks their application as new devices for enhanced single‐molecule FRET at physiological concentrations.     

Multivariate statistical identification of human bladder carcinomas using ambient ionization imaging mass spectrometry

Diagnosis of human bladder cancer in untreated tissue sections is achieved by using imaging data from desorption electrospray ionization mass spectrometry (DESI-MS) combined with multivariate statistical analysis. We use the distinctive DESI-MS glycerophospholipid (GP) mass spectral profiles to visually characterize and formally classify twenty pairs (40 tissue samples) of human cancerous and adjacent normal bladder tissue samples. The individual ion images derived from the acquired profiles correlate with standard histological hematoxylin and eosin (H&E)-stained serial sections. The profiles allow us to classify the disease status of the tissue samples with high accuracy as judged by reference histological data. To achieve this, the data from the twenty pairs were divided into a training set and a validation set. Spectra from the tumor and normal regions of each of the tissue sections in the training set were used for orthogonal projection to latent structures (O-PLS) treated partial least-square discriminate analysis (PLS-DA). This predictive model was then validated by using the validation set and showed a 5% error rate for classification and a misclassification rate of 12%. It was also used to create synthetic images of the tissue sections showing pixel-by-pixel disease classification of the tissue and these data agreed well with the independent classification that uses histological data by a certified pathologist. This represents the first application of multivariate statistical methods for classification by ambient ionization although these methods have been applied previously to other MS imaging methods. The results are encouraging in terms of the development of a method that could be utilized in a clinical setting through visualization and diagnosis of intact tissue.     

Intercepting Wacker intermediates with arenes: C-H functionalization and dearomatization

An intramolecular cyclization cascade reaction has been developed utilizing a high valent palladium intermediate that generates a carbon-carbon and carbon-oxygen bond in a single transformation. This method provides rapid access to highly functionalized tricyclic scaffolds, including spirocyclic cyclohexadienones. Good yields and mild conditions are reported with high tolerance toward oxygen and water.     

Intra-operative optical diagnostics with vibrational spectroscopy

Established methods for characterization of tissue and diagnostics, for example histochemistry, magnetic resonance imaging (MRI), X-ray tomography, or positron emission tomography (PET), are mostly not suitable for intra-operative use. However, there is a clear need for an intra-operative diagnostics especially to identify the borderline between normal and tumor tissue. Currently, vibrational spectroscopy techniques (both Raman and infrared) complement the standard methods for tissue diagnostics. Vibrational spectroscopy has the potential for intra-operative use, because it can provide a biochemically based profile of tissue in real time and without requiring additional contrast agents, which may perturb the tissue under investigation. In addition, no electric potential needs to be applied, and the measurements are not affected by electromagnetic fields. Currently, promising approaches include Raman fiber techniques and nonlinear Raman spectroscopy. Infrared spectroscopy is also being used to examine freshly resected tissue ex vivo in the operating theater. The immense volume of information contained in Raman and infrared spectra requires multivariate analysis to extract relevant information to distinguish different types of tissue. The promise and limitations of vibrational spectroscopy methods as intra-operative tools are surveyed in this review.     

Enhanced mechanical performance and biological evaluation of a PLGA coated β-TCP composite scaffold for load-bearing applications

Porous β-tricalcium phosphate (β-TCP) has been used for bone repair and replacement in clinics due to its excellent biocompatibility, osteoconductivity, and biodegradability. However, the application of β-TCP has been limited by its brittleness. Here, we demonstrated that an interconnected porous β-TCP scaffold infiltrated with a thin layer of poly(lactic-co-glycolic acid) (PLGA) polymer showed improved mechanical performance compared to an uncoated β-TCP scaffold while retaining its excellent interconnectivity and biocompatibility. The infiltration of PLGA significantly increased the compressive strength of β-TCP scaffolds from 2.90 to 4.19 MPa, bending strength from 1.46 to 2.41 MPa, and toughness from 0.17 to 1.44 MPa, while retaining an interconnected porous structure with a porosity of 80.65%. These remarkable improvements in the mechanical properties of PLGA-coated β-TCP scaffolds are due to the combination of the systematic coating of struts, interpenetrating structural characteristics, and crack bridging. The in vitro biological evaluation demonstrated that rat bone marrow stromal cells (rBMSCs) adhered well, proliferated, and expressed alkaline phosphatase (ALP) activity on both the PLGA-coated β-TCP and the β-TCP. These results suggest a new strategy for fabricating interconnected macroporous scaffolds with significantly enhanced mechanical strength for potential load-bearing bone tissue regeneration.     

Hole tunneling and hopping in a Ru(bpy)3(2+)-phenothiazine dyad with a bridge derived from oligo-p-phenylene

A molecular dyad was synthesized in which a Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) photosensitizer and a phenothiazine redox partner are bridged by a sequence of tetramethoxybenzene, p-dimethoxybenzene, and p-xylene units. Hole transfer from the oxidized metal complex to the phenothiazine was triggered using a flash-quench technique and investigated by transient absorption spectroscopy. Optical spectroscopic and electrochemical experiments performed on a suitable reference molecule in addition to the above-mentioned dyad lead to the conclusion that hole transfer from Ru(bpy)(3)(3+) to phenothiazine proceeds through a sequence of hopping and tunneling steps: Initial hole hopping from Ru(bpy)(3)(3+) to the easily oxidizable tetramethoxybenzene unit is followed by tunneling through the barrier imposed by the p-dimethoxybenzene and p-xylene spacers. The overall charge transfer proceeds with a time constant of 41 ns, which compares favorably to a time constant of 1835 ns associated with equidistant hole tunneling between the same donor-acceptor couple bridged by three identical p-xylene units. The combined hopping/tunneling sequence thus leads to an acceleration of hole transfer by roughly a factor of 50 when compared to a pure tunneling mechanism.     

Quantum and classical study of surface characterization by three-dimensional helium atom scattering

Exact time-dependent wavepacket calculations of helium atom scattering from model symmetric, chiral, and hexagonal surfaces are presented and compared with their classical counterparts. Analysis of the momentum distribution of the scattered wavepacket provides a convenient method to obtain the resulting energy and angle resolved scattering distributions. The classical distributions are characterized by standard rainbow scattering from corrugated surfaces. It is shown that the classical results are closely related to their quantum counterparts and capture the qualitative features appearing therein. Both the quantum and classical distributions are capable of distinguishing between the structures of the three surfaces.     

Multistage complexation of fluoride ions by a fluorescent triphenylamine bearing three dimesitylboryl groups: controlling intramolecular charge transfer

A propeller-shaped boron-nitrogen compound (NB(3)) with three binding sites for fluoride anions was synthesized and investigated by optical absorption, luminescence, and ((1)H, (11)B, (13)C, (19)F) NMR spectroscopy. Binding of fluoride in dichloromethane solution occurs in three clearly identifiable steps and leads to stepwise blocking of the three initially present nitrogen-to-boron charge transfer pathways. As a consequence, the initially bright blue charge transfer emission is red-shifted and decreases in intensity, until it is quenched completely in presence of large fluoride excess. Fluoride binding constants were determined from global fits to optical absorption and luminescence titration data and were found to be K(a1) = 4 × 10(7) M(-1), K(a2) = 2.5 × 10(6) M(-1), and K(a3) = 3.2 × 10(4) M(-1) in room temperature dichloromethane solution. Complexation of fluoride to a given dimesitylboryl site increases the electron density at the central nitrogen atom of NB(3), and this leads to red shifts of the remaining nitrogen-to-boron charge transfer transitions involving yet unfluorinated dimesitylboryl groups.