Precise mass measurement of a double-stranded 500 base-pair (309 kDa) polymerase chain reaction product by negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd.     

Ciliation and lamellae in crystalline polymers

Molecular cilia, the uncrystallized portions of chains already partly attached to polymer crystals, exert a profound influence on the course of polymeric crystallization with ultimate responsibility for the divergence of adjacent lamellae which leads to spherulitic growth. Their effective size and pressure have been measured, in α-polypropylene, from electron microscopic measurements of the separation and maximum curvature of lamellae in row structures. That cilia exist and extend the effective region occupied by a lamella beyond the geometrical confines of its fold surfaces is important for crystallization theory and may well have implications for the connection of lamellae into networks and for gelation.     

Water absorption kinetics in different wettability conditions studied at pore and sample scales in porous media by NMR with portable single-sided and laboratory imaging devices

NMR relaxation time distributions of water (1)H obtained by a portable single-sided surface device have been compared with MRI internal images obtained with a laboratory imaging apparatus on the same biocalcarenite (Lecce Stone) samples during capillary water uptake. The aim of this work was to check the ability of NMR methods to quantitatively follow the absorption phenomenon under different wettability conditions of the internal pore surfaces. Stone wettability changes were obtained by capillary absorption of a chloroform solution of Paraloid PB72, a hydrophobic acrylic resin frequently used to protect monuments and buildings, through one face of each sample. Both relaxation and imaging data have been found in good quantitative agreement each other and with masses of water determined by weighing the samples. In particular the Washburn model of water capillary rise applied to the imaging data allowed us to quantify the sorptivity in both treated and untreated samples. Combining relaxation and imaging data, a synergetic improvement of our understanding of the water absorption kinetics at both pore and sample scales is obtained. Since relaxation data have been taken over the course of time without interrupting the absorption process, simply by keeping the portable device on the surface opposite to the absorption, the results show that the single-sided NMR technique is a powerful tool for in situ evaluation of water-repellent treatments frequently used for consolidation and/or protection of stone artifacts.     

Understanding the mechanism of short-range electron transfer using an immobilized cupredoxin

The hydrophobic patch of azurin (AZ) from Pseudomonas aeruginosa is an important recognition surface for electron transfer (ET) reactions. The influence of changing the size of this region, by mutating the C-terminal copper-binding loop, on the ET reactivity of AZ adsorbed on gold electrodes modified with alkanethiol self-assembled monolayers (SAMs) has been studied. The distance-dependence of ET kinetics measured by cyclic voltammetry using SAMs of variable chain length, demonstrates that the activation barrier for short-range ET is dominated by the dynamics of molecular rearrangements accompanying ET at the AZ-SAM interface. These include internal electric field-dependent low-amplitude protein motions and the reorganization of interfacial water molecules, but not protein reorientation. Interfacial molecular dynamics also control the kinetics of short-range ET for electrostatically and covalently immobilized cytochrome c. This mechanism therefore may be utilized for short-distance ET irrespective of the type of metal center, the surface electrostatic potential, and the nature of the protein-SAM interaction.     

Characterization of the mistura alloy used for Venetian sesino coins: 16th century

The information provided by material investigations on ancient coins is interesting in many respects, as concerns the archaeological and historical research. In this study a set of Venetian sesino coins, minted over a period ranging from 1554 until 1605, have been investigated in order to shed light on some aspects of the so-called mistura (mixture) alloy. The widespread diffusion of these relatively low-value coins of the Venetian Republic, commonly used in commercial transactions in the second half of 16th century, also outside the territories of the Republic, makes them an important proxy to be used in the reconstruction of the political and historical events of the period. The specific issue of the actual composition of the mistura alloy is herewith addressed for the first time, using a combined approach based on X-ray fluorescence and X-ray diffraction nondestructively applied to the analysis of the samples. It turns out that the mistura alloy, traditionally regarded as a Cu-Ag two phase alloy, over the latest period of circulation of the sesino coins, was actually made of copper only, still containing minor concentrations of lead, to be regarded as an impurity of the alloy and not as an intentional addition.     

Über die Invarianten von Linienelementen und die projektive Geometrie der Kurvengewebe

Ohne ZusammenfassungNach einem am 8. Jänner 1941 in Hamburg gehaltenen Vortrag. Mit 3 Figuren im Text