The influence and utility of varying field strength for the separation of tryptic peptides by ion mobility-mass spectrometry

The influence of field strength on the separation of tryptic peptides by drift tube-based ion mobility-mass spectrometry is reported. Operating the ion mobility drift tube at elevated field strengths (expressed in V cm(-1) torr(-1)) reduces separation times and increases ion transmission efficiencies. Several accounts in the literature suggest that performing ion mobility separation at elevated field strength can change the selectivity of ion separation. To evaluate the field strength dependant selectivity of ion mobility separation, we examined a data set of 65 singly charged tryptic peptide ion signals (mass range 500-2500 m/z) at six different field strengths and four different drift gas compositions (He, N2, Ar, and CH4). Our results clearly illustrate that changing the field strength from low field (15 V cm(-1) torr(-1)) to high field (66 V cm(-1) torr(-1)) does not significantly alter the selectivity or peak capacity of IM-MS. The implications of these results are discussed in the context of separation methodologies that rely on the field strength dependence of ion mobility for separation selectivity, e.g., high-field asymmetric ion mobility spectrometry (FAIMS).     

Synthesis and spectral analysis of (±)-cis-N-[1-(2-hydroxy-2-phenyl-ethyl)-3-methyl-4-piperidyl]-N-phenylpropanamide and (±)-cis-N-[1-(2-hydroxy-1-phenylethyl)-3-methyl-4-piperidyl]-N-phenylpropanamide

Treatment of (±)-cis-N-(3-methyl-4-piperidyl)-N-phenylpropanamide (2) with styrene oxide (1) yielded a mixture of (±)-cis-N-[1-(2-hydroxy-2-phenylethyl)-3-methyl-4-piperidyl]-N-phenylpropanamide (3) and (±)-cis-N-[1-(2-hydroxy-1-phenylethyl)-3-methyl-4-piperidyl]-N-phenylpropanamide (4) . The structure of compound 3 was confirmed by an unambiguous synthesis via (±)-cis-N-[1-(2-oxo-2-phenylethyl)-3-methyl-4-piperidyl]-N-phenylpropanamide (6) . The proton and carbon-13 resonances of compounds 3 and 4 were assigned with the aid of two-dimensional heteronuclear correlation experiments.     

Simulation of titration curves indicated with two indicator electrodes (biamperometry)

A rigorous method to simulate titration curves with indication using two indicator electrodes (biamperometry) is presented. Computer simulations can be carried out for reversible as well as for irreversible systems. The different parameters like the area of the individual electrodes, applied potential difference, heterogeneous rate constant, and the kinetic parameter were varied and investigated as to their influence upon the shape of the titration curves. The theoretically derived effects match with the effects obtained by experiment. Considering the effects described here, it is possible to tailor the shape of the titration curve by the experimental conditions for specific applications in order to get an optimum shape at the end point of the titration.     

A tandem Jackson network with feedback to the first node

AnN-node tandem queueing network with Bernoulli feedback to the end of the queue of thefirst node is considered. We first revisit the single-nodeM/G/1 queue with Bernoulli feedback, and derive a formula forEL(n), the expected queue length seen by a customer at his nth feedback. We show that, asn becomes large,EL(n) tends to /(l ), being the effective traffic intensity. We then treat the entire queueing network and calculate the mean value ofS, the total sojourn time of a customer in theN-node system. Based on these results we study the problem ofoptimally ordering the nodes so as to minimize ES. We show that this is a special case of a general sequencing problem and derive sufficient conditions for an optimal ordering. A few extensions of the serial queueing model are also analyzed. We conclude with an appendix in which we derive an explicit formula for the correlation coefficient between the number of customers seen by an arbitrary arrival to anM/G/1 queue, and the number of customers he leaves behind him upon departure. For theM/M/1 queue this coefficient simply equals the traffic intensity .     

Finite Euclidean graphs over rings

We consider graphs attached to , where , for an odd prime , using an analogue of the Euclidean distance. These graphs are shown to be mostly non-Ramanujan, in contrast to the case of Euclidean graphs over finite fields.

     

Metallic thin film growth on vicinal Cu substrates

In this study we have investigated the heteroepitaxial growth of nickel and silver on vicinal copper substrates. Nickel was deposited onto a (211) substrate. The low lattice mismatch between copper and nickel of 2.5% enables epitaxial bidimensional growth in the substrate's orientation, where the strain can be accommodated in the overlaying film. On the contrary, copper and silver have a much larger mismatch of about 13% which usually cannot be accommodated in the film. In general, Ag is known to form alloys or to induce faceting on a stepped Cu surfaces. Here, silver was deposited onto a Cu(311) facet covered with a monatomic layer of NaCl. For the first time we show that Ag can be grown as ultrathin film in the substrates's orientation on a stepped surface using NaCl as a novel surfactant material.