THE PREPARATION AND STABILITY OF COLLOIDAL METAL DISPERSIONS PREPARED BY A TWO-PHASE NON-AQUEOUS ROUTE

Stable suspensions of small metal Au, Ru, PI, Pd, Rh, Co and Nl particles dispersed in n-heptane and n-dodecane have been prepared using a novel two-phase system, Involving the formation of the particles In a methanolic phase and subsequent phase transfer of the panicles to the alkane medium. The dispersions consisted of small particles having diameters In the range of 8-30 nm (the gold sols were very polydlsperse having average diameters of ca.34 nm). The phase transfer of the particles and their subsequent colloid stability were effected by the presence of dissolved dispersant in the hydrocarbon phase (either Oloa 1200 or Hypermer LP 8). In the case of Oloa 1200, a widely-used polylsobutylene succinimide automotive engine dispersant, It Is proposed that the amlne groups adsorb strongly to the acidic surface o1 the particles, and the 70-carbon polyisobutylene chains extend Into the hydrocarbon medium sufficiently to maintain the separation of adjacent particles by steric and possibly also by electrical repulsion.     

On the construction of equiangular frames from graphs

We give details of the 1-1 correspondence between equiangular frames of n vectors for and graphs with n vertices. This has been studied recently for tight equiangular frames because of applications to signal processing and quantum information theory. The nontight examples given here (which correspond to graphs with more than 2 eigenvalues) have the potential for similar applications, e.g., the frame corresponding to the 5-cycle graph is the unique Grassmannian frame of 5 vectors in openR³. Further, the associated canonical tight frames have a small number of angles in many cases.     

Sequential fractionation with concurrent chemical and toxicological characterization of the combustion products of chlorogenic acid

Chlorogenic acid is the most abundant polyphenol found in the tobacco plant. The biological effects of its combustion products remain largely unknown. In this study, chlorogenic acid was burned at 640 °C for 2 min and the particulate matter of the smoke was collected onto Cambridge filter pads followed by selective extraction in five different solvents. Various fractions of the chlorogenic acid combustion products were tested for induction of micronuclei in V79 Chinese hamster fibroblast cells. Over 40 compounds were identified in the dimethyl sulfoxide (DMSO) extract by high-performance liquid chromatography coupled to electrospray time-of-flight mass spectrometry (HPLC/TOF-MS). The DMSO extract was then fractionated into three major fractions by preparative LC. The fraction inducing the highest degree of toxicity was further separated into four sub-fractions. The sub-fraction responsible for the most toxic response was determined to contain catechol as its major component. The overall reproducibility of the combustion, the extraction procedure and the chemical characterization of the compounds responsible for the toxicity in the chlorogenic acid smoke were evaluated by LC/TOF-MS.     

Characterisation of Ripening and Pressure-Induced Changes in Tomato Pericarp Using NMR Relaxometry

A combination of two-dimensional nuclear magnetic resonance (NMR) relaxometry and optical microscopy is used to investigate the effects of ripening and high-pressure treatment on tomato pericarp tissue. It is shown that the relaxation times of the vacuolar water increase during the early stages of ripening even when there is no visible change and that this could be the basis of a useful on-line sensor for sorting tomatoes. The membrane rupturing and biopolymer denaturation associated with high-pressure treatments are also reflected in the NMR relaxation spectra.     

Multidimensional NMR cross-correlation relaxation study of carrot phloem and xylem. Part I: Peak assignment

We report, for the first time, a detailed analysis of the complicated two-dimensional (2-D) nuclear magnetic resonance relaxation spectra of the xylem and phloem of carrots. By combining chemical extraction with different 2-D pulse sequences attempts are made to assign relaxation peaks to cell components, including compartmentalized water, pectins, starch, proteins and hemicelluloses. In a separate report, we use these assignments to interpret the effects of thermal and high-pressure processing (M. E. Furfaro, N. Marigheto, G. K. Moates, K. Cross, M. L. Parker, K. W. Waldron, B. P. Hills: Appl. Magn. Reson. 35, 537–547, 2009).     

Minimally supported error representations and approximation by the constants

Summary. Distribution theory is used to construct minimally supported Peano kernel type representations for linear functionals such as the error in multivariate Hermite interpolation. The simplest case is that of representing the error in approximation to f by the constant polynomial f(a) in terms of integrals of the first order derivatives of f. This is discussed in detail. Here it is shown that suprisingly there exist many representations which are not minimally supported, and involve the integration of first order derivatives over multidimensional regions. The distance of smooth functions from the constants in the uniform norm is estimated using our representations for the error. Received June 30, 1997 / Revised version received April 6, 1999 / Published online February 17, 2000     

Comparison of two glutaraldehyde immobilization techniques for solid-phase tryptic peptide mapping of human hemoglobin by capillary zone electrophoresis and mass spectrometry

Stabilization of proteolytic enzymes, especially by immobilization, is of considerable interest because of their potential applications in medicine and the chemical and pharmaceutical industries. We report here a detailed comparison of two procedures for trypsin immobilization using the same homobifunctional agent, glutaraldehyde, for the purpose of peptide mapping. These methods include covalent coupling either to controlled pore glass (solid support) or via a cross-linking reaction (without any solid support). The immobilized trypsin preparations were characterized by the determination of immobilization efficiency, which ranged from 68 to > 95%, and measurement of apparent kinetic parameters toward a synthetic peptide-like substrate. Batch digestions of whole denaturated human normal adult hemoglobin (HbA) were performed to obtain peptide maps by capillary zone electrophoresis (CZE). Migration time reproducibility of the CZE maps was excellent, with a mean relative standard deviation of 1.5%. Moreover, the two immobilized enzyme preparations showed excellent reproducibility for repeated digestions. Matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry was also used for peptide mass mapping of denaturated HbA digested using the two immobilized trypsin preparations. Even though the two immobilized trypsin preparations do not behave identically, similar sequence coverages of 57% and 61% (for the two HbA chains merged) were achieved for the support-based and cross-linked trypsin preparations, respectively.     

Structure and electronic properties of monoclinic Nb12O29

Monoclinic Nb₁₂O₂₉ is metallic and antiferromagnet despite possessing a low number of unpaired electrons. The origin of its magnetic ordering is described, which is due to a charge ordering transition, localising half of the unpaired electrons onto a specific crystallographic site within its (4×3) block structure, causing the formation of a one-dimensional chain of spins.     

Drift compression of an intense neutralized ion beam

Longitudinal compression of a velocity-tailored, intense neutralized beam at 300 keV, 25 mA has been demonstrated. The compression takes place in a 1-2 m drift section filled with plasma to provide space-charge neutralization. An induction cell produces a head-to-tail velocity ramp that longitudinally compresses the neutralized beam, enhancing the beam peak current by a factor of 50 and producing a pulse duration of about 3 ns. This measurement has been confirmed independently with two different diagnostic systems.