Mass spectrometry tetramers

Reports of depolymerization studies carried out by Semiyen and co-workers at the University of York, UK, typically used much longer reaction times (24-72 h) for the depolymerization of PET [27], This group also reported that the titanates were ineffective catalysts for depolymerization, but it is not known whether measures to prevent titanate hydrolysis were taken. The York group also reported that the relative proportions of cyclic oligomers (trimer, tetramer, etc.) altered as the dilution ratio was changed. Similar results were seen with PBT. They have also reported fast-atom bombardment mass spectrometry (FAB-MS), LC-MS, GPC and X-ray crystallography data. The most recent work reports characterization of the cyclic oligomers from six ester and ether ester systems [29],... 

We first confirmed the formation of these macrocycles in the polymerization of THF by using coupled gas chromatography/mass spectrometry ( 2). Macrocyclic ethers containing up to 8 THF units could be separated and identified by this method (23). The two predominant macrocyclic species found in THF polymerization mixtures are a cyclic tetramer and a cyclic pentamer. In analogy to the "crown ether" nomenclature, we proposed the name 20-crown-4 for the cyclic tetramer and 25-crown-5 for the cyclic pentamer (22). 

The gas-phase structure of f-BuLi has also been probed by McLean and coworkers using photo ionization mass spectrometry". At room temperature, they detected only tetramers and determined the ionization potential of (f-BuLi)4 to be 6.2 eV. Other ions were detected above 8 eV with general formulae R Li4+(n = 1-3) and RLi2+(R = f-Bu). Both R3Li4+ and RLi2 had also been observed by Brown and coworkers in the H spectra of f-BuLi vapor, while R2Li4 and RLi4+ had not . 

Plavsic, Srzic and Klasinc performed a detailed electron impact mass spectrometric investigation of alkyllithium compounds . They have concluded that MeLi, /-PrLi, 5-BuLi and r-BuLi consist of tetrameric clusters only, while n-PrLi, n-BuLi and i-BuLi form mixtures of tetramers and hexamers, in the gas phase. Fast atom bombardment (FAB) mass spectrometry was used by Abdul-Sada, Greenway and Seddon to show that the extent of aggregation of f-BuLi is tetrameric while n-BuLi is hexameric (Table 1). Nevertheless, for both alkyllithium compounds the ion corresponding to (RLi)Li+ is the most abundant in the spectrum, as also shown in other studies of alkyllithium vapor. 

EF-1 was analyzed by spectrophotometer IH and 13C NMR (Bmker AC 200, 200MHz) using as solvent chloroform (CDCI3) and methanol (CD3OD) deuterated at a ratio of 9 1 to tetrame-thylsilane (TMS) as internal reference standard. An aliquot of EF-1 (5 mg) was methylated with diazomethane and subjected to mass spectrometry (MS Agilent Technologies). The spectral data obtained were compared with the literature [Oliveira et al, 2006]. 

Mass spectrometry was used to confirm the existence of [Me4Zn4(OR )4] tetramers (R = Me, Et, i-Pr, f-Bu) in the vapor phase All compounds showed [Me3Zn4 (OROa] ions in the El mass spectra. The MS detection of ionic aggregates having more than four monomeric RZnOR units has also been reported. ... 

Characterization of noncovalent bonding of the proteins can also be done using MS. For example MALDI MS has been used in measurement of the molecular mass of the noncovalendy linked tetramer of glucose isomerase, a complex consisting of identical monomers of 43.1 kDa each. MALDI-TOFF peptide mass fingerprinting combined with electrospray tandem mass spectrometry can efficiently solve many complicated peptide protein analysis problems. 

Two-dimensional NMR studies and mass spectrometry identified the isomers as being the cyclic tetramer 6 and the [2]catenane 7 consisting of two interlocked cyclic dimers. Later X-ray crystal structures confirmed these results [16, 17],... 

Schwartz, B. L., Light-Wahl, K. J., and Smith, R. D. (1994). Observation of noncovalent complexes in the Avidin tetramer by electrospray ionization mass spectrometry. J. Am. Soc. Mass Spectrom. 5, 201-204. 

Self-assembly of monopyrazolylporphyrins by hydrogen bonding has been examined by Ikeda and coworkers [144]. IR spectral measurements of the pyrazole NH stretches indicate that self-aggregates hydrogen bond at concentrations above 10 M. The identities of cyclic dimer 61 and tetramer 62 are confirmed by electrospray ionization mass spectrometry (ESI). H NMR titrations in CDCI3 give association constants of 39 M and 9.3 x 10 M for 61 and 62, respectively. No electron transfer studies on these systems have yet been undertaken. 

AK Vrkic, RAJ O Hair, S Foote, GE Reid. Fragmentation reactions of all 64 pro-tonated trirner oligonucleotides and 16 mixed base tetramer oligonucleotides via tandem mass spectrometry in an ion trap. IntJ Mass Spectrom 194 145—164,2000. 

The most abundant species in the equilibrium vapor over condensed metals are generally atoms as shown by Knudsen effusion mass spectrometry. The relative abundance of the homonuclear diatomic molecules was determined to be between 10 and 10 percent if they are detectable. Exceptions are bismuth and antimony. The dimer partial pressure over liquid bismuth at temperatures below 1000 K exceeds that of the monomer [83, 164, 165]. The tetramer is the most abundant species over liquid antimony [85]. Other polyatomic homonuclear species have so far been observed under equilibrium conditions for some of the alkali metals, as well as the group Ib, IVb, and Vb metals. Particularly large polymers up to 667 and Sn7 were detected for germanium [84,166,167] and tin [168],... 

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