The certification of SRM 1546 – Meat Homogenate, a new reference material for nutrients in a high protein, high fat matrix

In response to reference material needs expressed by the food industry and government regulators, the National Institute of Standards and Technology (NIST) has developed a new Standard Reference Material (SRM) consisting of a canned meat product with certified and reference values for a large number of constituents. SRM 1546 Meat Homogenate consists of a mixture of finely ground pork and chicken prepared and canned by a commercial process. NIST determined the concentration levels of cholesterol, sodium, calcium, iron, and seven fatty acids in this SRM using well defined methods and procedures. These analytes as well as 34 other constituents or properties were determined in an interlaboratory comparison exercise involving 21 laboratories, most of which are associated with the National Food Processors Association (NFPA) Food Industry Analytical Chemists Subcommittee (FIACS). From statistical analysis of the data, NIST assigned certified concentrations for the eleven analytes measured at NIST and reference concentrations for the proximates, six additional fatty acids, seven minerals, and seven water-soluble vitamins. Information values without uncertainties are provided for the concentrations of six additional constituents for which the uncertainties could not adequately be assessed. SRM 1546 will provide laboratories with a means to evaluate the accuracy of the methods they use to assign nutrient levels to processed meats and similar products. Received: 11 October 2000 / Revised: 15 December 2000 / Accepted: 21 December 2000     

Macromolecular pair correlation functions from fluorescence depolarization experiments

Depolarization of fluorescence resulting from the transport of electronic excitations in chromophore-containing polymers is investigated as a technique for detecting deviations from ideal-chain statistics. An approximate expression for the fluorescence anisotropy that depends only on the pair correlation function of chromophore labels is presented. This approximation is shown to be accurate for particular cases of long-range correlations, short-range correlations, and no correlations among chromophore positions. The formalism allows fluorescence depolarization experiments to be used as a probe of macromolecular pair correlation functions.     

Applications of Mössbauer spectroscopy in the geochemistry of sedimentary rocks

A set of pure iron-rich minerals characteristic of common fine-grained sedimentary rocks has been prepared and their Mössbauer spectra obtained. These include pyrite, carbonates and silicates. Six marine mudrocks were then chosen from a large set for which complete chemical data were available. It proved possible to reproduce mudrock spectra by addition of the pure mineral spectra in proportions indicated by the chemical analyses. Unfortunately, however, overlap of Fe(III) in dioctahedral silicates with Fe(II) in pyrite prevents reliable deconvolution of mudrock spectra to obtain quantitative estimates of component concentrations. Useful information about Fe(II) in other minerals can still be obtained. Mössbauer spectroscopy would appear to have great promise for the study of early reactions in non-marine sediments which are usually low in sulphur. Mineral products are either X-ray amorphous or extremely fine-grained mixtures and very difficult to study by other means.     

Non-Linear realization of supersymmetry algebra from supersymmetric constraint

We discuss spontaneous symmetry breaking of global supersymmetry for a single scalar superfield in an arbitrary Kähler manifold. We show that when the curvature of the manifold goes to infinity (or, equivalently, the masses of the scalar partners of the goldstino go to infinity) a non-linear realization of supersymmetry is obtained. The model can be described, in perfect analogy to the ordinary σ-models, by means of a supersymmetric constraint on the superfield Φ, of the form Φ²=0. The non-linear realization we obtain is different from that of Volkov and Akulov. The differences among the two realizations are discussed.     

EXTENDING CIRCULAR DICHROISM SPECTRA INTO THE VACUUM UV AND ITS APPLICATION TO PROTEINS

Circular dichroism (CD) spectra measured into the vacuum UV region provide information necessary for this technique to fulfill its potential. In the case of proteins, CD spectra measured to 184 nm or below can be analyzed for secondary structure: generalized inverses make such analyses particularly simple. Generalized inverses for α-helix, anti-parallel β-sheet, parallel β-sheet, β-turn, and "other" structures are given in tabular form. When the dot product of each inverse is taken with the digitized spectrum of a protein, the amount of corresponding secondary structure is predicted. However, protein CD spectra truncated above 184 nm give too little information to give reliable analyses. Furthermore, adding constraints only complicates this problem because unreliable analyses now appear good.     

Molybdenum/cobalt/sulfur clusters: Models and precursors for hydrodesulfurization (HDS) catalysts

Sulfido clusters which incorporate molybdenum and a late transition metal, e.g. iron, cobalt or nickel, are readily prepared by the reactions of Cp₂Mo₂S₄, Cp₂Mo₂S₂(SR)₂ or Cp₂Mo₂(CO)₂(SR)₂ with Fe₂(CO)₉, Co₂(CO)₈, Ni(CO)₄, Cp₂Ni, etc. The homogeneous reactions of the cluster Cp₂Mo₂Co₂S₃(CO)₄ with thiols, thiophene, and phosphines are reviewed, as are some reactions of the clusters with metal oxide surfaces to produce heterogeneous catalysts for CO hydrogenation or hydrodesulfurization.