Structure, energetics and reactions of metal cation complexes of dipeptides in the gas phase

Structure, energetics and reactions of ions in the gas phase can be revealed by mass spectrometry techniques coupled to ions activation methods. Ions can gain enough energy for dissociation by absorbing IR light photons introduced by an IR laser to the mass spectrometer. Also collisions with a neutral molecule can increase the internal energy of ions and provide the dissociation threshold energy. Infrared multiple photon dissociation (IRMPD) or sustained off-resonance irradiation collision-induced dissociation (SORI-CID) methods are combined with Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometers where ions can be held at low pressures for a long time. The outcome of ion activation techniques especially when it is compared to the computational methods results is of great importance since it provides useful information about the structure, thermochemistry and reactivity of ions of interest. In this work structure, energetics and reactivity of metal cation complexes with dipeptides are investigated. Effect of metal cation size and charge as well as microsolvation on the structure of these complexes has been studied. Structures of bare and hydrated Na and Ca complexes with isomeric dipeptides AlaGly and GlyAla are characterized by means of IRMPD spectroscopy and computational methods. At the second step unimolecular dissociation reactions of singly charged and doubly charged multimetallic complexes of alkaline earth metal cations with GlyGly are examined by CID method. Also structural features of these complexes are revealed by comparing their IRMPD spectra with calculated IR spectra of possible structures. At last the unimolecular dissociation reactions of Mn complexes are studied. IRMPD spectroscopy along with computational methods is also employed for structural elucidation of Mn complexes. In addition the ion-molecule reactions of Mn complexes with CO and water are explored in the low pressures obtained in the ICR cell.

Design construction and testing of a heat loop for study of fouling and its interrelationship to corrosion in heat exchanger tubes

A heat loop suitable for the study of thermal fouling and its relationship to corrosion processes was designed, constructed and tested. The design adopted was an improvement over those used by such investigators as Hopkins and the Heat Transfer Research Institute in that very low levels of fouling could be detected accurately, the heat transfer surface could be readily removed for examination and the chemistry of the environment could be carefully monitored and controlled. In addition, an indirect method of electrical heating of the heat transfer surface was employed to eliminate magnetic and electric effects which result when direct resistance heating is employed to a test section. The testing of the loop was done using a 316 stainless steel test section and a suspension of ferric oxide and water in an attempt to duplicate the results obtained by Hopkins. Two types of thermal ·fouling resistance versus time curves were obtained . (i) Asymptotic type fouling curve, similar to the fouling behaviour described by Kern and Seaton and other investigators, was the most frequent type of fouling curve obtained. Thermal fouling occurred at a steadily decreasing rate before reaching a final asymptotic value. (ii) If an asymptotically fouled tube was cooled with rapid cir- ·culation for periods up to eight hours at zero heat flux, and heating restarted, fouling recommenced at a high linear rate. The fouling results obtained were observed to be similar and 1n agreement with the fouling behaviour reported previously by Hopkins and it was possible to duplicate quite closely the previous results . This supports the contention of Hopkins that the fouling results obtained were due to a crevice corrosion process and not an artifact of that heat loop which might have caused electrical and magnetic effects influencing the fouling. The effects of Reynolds number and heat flux on the asymptotic fouling resistance have been determined. A single experiment to study the effect of oxygen concentration has been carried out. The ferric oxide concentration for most of the fouling trials was standardized at 2400 ppM and the range of Reynolds number and heat flux for the study was 11000-29500 and 89-121 KW/M², respectively.