Simple RF design for human functional and morphological cardiac imaging at 7 tesla

Morphological and functional cardiac MRI can potentially benefit greatly from the recent advent of commercial high-field (7 tesla and above) MRI systems. However, conventional hardware configurations at lower field using a body-coil for homogeneous transmission are not available at these field strengths. Sophisticated multiple-transmit-channel systems have been shown to be able to image the human heart at 7 tesla but such systems are currently not widely available. In this paper, we empirically optimize the design of a simple quadrature coil for cardiac imaging at 7 tesla. The size, geometry, and position have been chosen to produce a B₁ field with no tissue-induced signal voids within the heart. Standard navigator echoes for gating were adapted for operation at the heart/lung interface, directly along the head–foot direction. Using this setup, conventional and high-resolution cine functional imaging have been successfully performed, as has morphological imaging of the right coronary artery.     

Symbiotic relationship between brain structure and dynamics

Background  

Brain structure and dynamics are interdependent through processes such as activity-dependent neuroplasticity. In this study, we aim to theoretically examine this interdependence in a model of spontaneous cortical activity. To this end, we simulate spontaneous brain dynamics on structural connectivity networks, using coupled nonlinear maps. On slow time scales structural connectivity is gradually adjusted towards the resulting functional patterns via an unsupervised, activity-dependent rewiring rule. The present model has been previously shown to generate cortical-like, modular small-world structural topology from initially random connectivity. We provide further biophysical justification for this model and quantitatively characterize the relationship between structure, function and dynamics that accompanies the ensuing self-organization.     

Tracing glycoprotein structures: electrospray ionization tandem mass spectrometric analysis of sugar-peptide adducts

Owing to the diversity of carbohydrate structures and their significance for the function of many biopolymers, structural analysis of various carbohydrate-related compounds is of great importance. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) was used to establish the fragmentation behaviour of a range of sugar-peptide adducts as model compounds of widespread glycoprotein structures. The compounds used in this study were chosen to provide correlation of distinct fragment ions with specific structural differences, namely position and type of carbohydrate-peptide bond and structure of the sugar moiety. All compounds show N- and C-terminal sequence ions along with losses of up to three water molecules. Fructose-related Amadori compounds exhibit M + 78 modified N-terminal peptide fragment ions. Fragmentation of glucose-peptide esters is characterized by the sugar ring fragmentation. Additionally, under the ESI-MS conditions applied, the esters studied undergo intramolecular reaction giving cyclic sugar-peptide structures that can be traced by the presence of N-terminal peptide M + 42 adducts. Detailed analysis of cyclic fructose-related compound comprising structural features of both studied groups revealed a rich fragmentation pattern derived from amino acid residues and water molecules losses from [M - 2H(2)O + H](+) ion. Also, some interesting differences were found with respect to the nature of carbohydrate moieties.     

Use of dilithio-tosylmethyl isocyanide in the synthesis of oxazoles and imidazoles

Dilithio-tosylmethyl isocyanide ($\text{2}$) reacts with the carbonyl of unsaturated esters to form oxazoles, unlike tosylmethyl isocyano monoanion which gives pyrroles by reaction with the conjugated carbon-carbon double bonds. Reaction of $\text{2}$ with carbon-nitrogen multiple bonds leads to imidazoles, an example of which is the one-step synthesis of imidazo[5,1-a]isoquinoline from isoquinoline. From $\text{2}$ and pyridine-N-oxide or pyridazine-N-oxide unsaturated ring opened products are obtained.     

Hydrophilic elastomers for microcontact printing of polar inks

A moderately hydrophilic, thermoplastic elastomer (poly(ether-ester)) was investigated as a stamp material for microcontact printing of a polar ink: pentaerythritol-tetrakis-(3-mercaptopropionate). Stamps with a relief structure were produced from this polymer by hot embossing, and a comparison was made with conventional poly(dimethylsiloxane) (PDMS) and oxygen-plasma-treated PDMS. It is shown that the hydrophilic stamps can be used for the repetitive printing (without re-inking) of at least 10 consecutive patterns, which preserve their etch resistance, and this in rather sharp contrast to conventional and oxygen plasma-treated PDMS stamps. It is argued that these enhanced printing characteristics of the hydrophilic stamps originate from an improved wetting and solubility of polar inks in the hydrophilic stamp.     

Metastable ion formation and disparate charge separation in the gas-phase dissection of protein assemblies studied by orthogonal time-of-flight mass spectrometry

The dissection of specific and nonspecific protein complexes in the gas phase is studied by collisionally activated decomposition. In particular, the gas phase dissection of multiple protonated homodimeric Human Galectin I, E. Coli Glyoxalase I, horse heart cytochrome c, and Hen egg Lysozyme have been investigated. Both the Human Galectin I and E. Coli Glyoxalase I enzymes are biologically active as a dimer, exhibiting molecular weights of approximately 30 kDa. Cytochrome c and Lysozyme are monomers, but may aggregate to some extent at high protein concentrations. The gas phase dissociation of these multiple protonated dimer assemblies does lead to the formation of monomers. The charge distribution over the two concomitant monomers following the dissociation of these multiple protonated dimers is found to be highly dissimilar. There is no evident correlation between the solution phase stability of the dimeric proteins and their gas-phase dissociation pattern. Additionally, in the collisionally activated decomposition spectra diffuse ion signals are observed, which are attributed to monomer ions formed via slow decay of the collisionally activated dimer ions inside the reflectron time-of-flight. Although, the formation of these diffuse metastable ions may complicate the interpretation of collisionally activated decomposition mass spectra, especially when studying noncovalent protein complexes, a simple mathematical equation may be used to reveal their origin and pathway of formation.     

Characterization of a phosphorylated peptide and peptoid and peptoid-peptide hybrids by mass spectrometry

Nano-electrospray tandem mass spectrometry (nano-ES-MS/MS) was used to record collision-induced dissociation (CID) spectra of a set of peptoid-peptide hybrids and the complete peptoid derived from the phosphopeptide Ac-pTyr-Glu-Thr-Leu-NH(2) (1). The presence of B and Y'-type fragment ions in the tandem mass spectra of the protonated molecular ions [M + H](+) allowed confirmation of sequence similar to mass spectrometric sequence analysis in peptides. In the isomeric peptoid compounds studied, one or several amino acid residues were replaced by peptoid residues (N-substituted glycine residues), which resulted in characteristic tandem mass spectra with differently increased relative abundances of Y'-and B-type fragment ions. The increment of a particular Y'-ion was directly correlated to the position of a peptoid residue present. In addition to these increased peak intensities, other characteristic peaks were also observed compared with the spectrum of reference peptide 1. When a peptoid phosphotyrosine was incorporated, the presence of this residue was apparent from the occurrence of a relatively intense peak at m/z 187 representing the positively charged side-chain of phosphotyrosine, which was almost absent in the spectrum of the reference peptide 1. Since the threonine side-chain had to be translated into the homo peptoid analog this substitution was apparent from the presence of [M + H](+) and fragment ions 14 mass units higher than observed in the spectrum of the reference phosphopeptide 1. The presence of an NLeu peptoid residue could be confirmed by the specific fragmentation of the immonium ion showing an intense peak in its tandem mass spectrum at m/z 57, which results from the loss of an neutral imine molecule leading to a positively charged [C(4)H(9)](+) ion. By means of these mass spectrometric characteristics, all isomeric peptoid compounds could be distinguished from each other and characterized. The methods used appear to be very useful in future studies of peptoids and peptoid-peptide hybrids.     

Liquid chromatography with atmospheric pressure chemical ionization and electrospray ionization mass spectrometry of flavonoids with triple-quadrupole and ion-trap instruments

With 15 flavonoids as test compounds, the analytical performance of four modes of LC-MS, multiple MS (MSn) and tandem MS operation (atmospheric pressure chemical ionization (APCI), electrospray ionization, positive and negative ionization) was compared for two mass spectrometers, a triple-quadrupole and an ion-trap instrument. Two organic modifiers, methanol and acetonitrile, and two buffers, ammonium acetate and ammonium formate, were used. In general, the use of APCI in the negative ion mode gave the best response, with the signal intensities and the mass-spectral characteristics not differing significantly between the two instruments. The best results were obtained when methanol-ammonium formate (pH 4.0) was used as LC eluent. Under optimum conditions full-scan limits of detection of 0.1-30 mg/l were achieved in the negative APCI mode. Here it needs to be emphasized that up to 2-order response differences were found both between analytes and between modes of ionization. This implies that one should be very cautious when interpreting data on the screening of real-life samples. The main fragmentations observed in the MSn spectra on the ion-trap, or the tandem MS spectra on the triple-quadrupole were generally the same. The advantage of the former approach is the added possibility to ascertain precursor-->product ion relationships.     

Reexamination of the heat capacities obtained by flow microcalorimetry. Recommendation for the use of a chemical standard

A series of measurements with aqueous electrolyte and nonelectrolyte solutions indicates that there is a small systematic difference between the heat capacities per unit volume determined with a Picker flow microcalorimeter and the original prototype. Through various tests and comparisons, it is, concluded that the commercial instrument gives results closer to the true values. Most of the previous data obtained in our laboratory have been corrected and expressed relative to aqueous NaCl at 25°C taken as a standard.On leave of absence from the Free University of Amsterdam, Amsterdam, The Netherlands