MALDI mass spectra

Fullerenes are spontaneously attracted to porphyrins and metalloporphyrins. The palladium-linked m-pyridyl dimer (shown in Figure 42) has a high binding constant in solution. Addition of C60 or C70 to solutions of these palladium-linked bis-porphyrins gave complexes that were chromatographically distinct from their individual components. This indication of tight binding was also seen in MALDI mass spectra.517... 

This work was funded under a Laboratory Directed Research and Development (LDRD) grant administered by Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for the US Department of Energy. We acknowledge the help of April Getty with 13C NMR and Catherine Petersen with MALDI Mass Spectra. Keith Peterson assisted in reactor support and Tom Wietsma in analytical support. Finally we appreciate the help of Jim White and Dennis Miller for helpful discussions. 

While this chapter has described two examples of our efforts in bacterial strain identification, a number of other groups have contributed to this research area. It remains to be seen whether mathematical algorithms such as the modified correlation approach described herein are always more effective for strain assignments than the simple use of distinctive biomarker peaks. Nilsson reported MALDI mass spectra of Helicobacter pylori with three different matrices and solvent conditions.59 She showed that some strains of this bacteria yield rather similar mass spectra while others are quite different. Nevertheless, each strain appears to exhibit some unique peaks that might be used for distinguishing strains. 

Jacobs, A. Dahlman, O. Enhancement of the quality of MALDI mass spectra of highly acidic oligosaccharides by using a Nafion-coated probe. Anal. Chem. 2001, 73,405 110. 

Figure 14.2 MALDI mass spectra of three different species of Pseudomonas.

An example of the microorganism differentiation power achievable with the protein profiling approach is illustrated using the MALDI mass spectra of Escherichia coli and Cryptosporidium parvum (Figure 14.3). Clear... 

Figure 14.3 MALDI mass spectra of E. coli (top) and Cryptosporidium parvum (bottom).

Liao, P.-C. Allison, J. Dissecting MALDI Mass Spectra. J. Mass Spectrom. 1995, 30, 763-766. 

Fig. 2a,b. Comparison of MALDI mass spectra for [G-6]-OH and a narrow molecular weight distribution poly(ethylene glycol), PD=1.05... 

A schematic of the basic principles of a matrix-assisted laser desorption/ion source is shown in Figure 2.35. By the interaction of a focused laser beam with short pulses and a suitable matrix, the energy of the photons is transferred to the matrix molecules. In MALDI mostly pulsed UV (e.g., nitrogen, X = 337 nm, pulse duration 3-10 ns), but also IR lasers (e.g., Er YAG, X = 2.94 (xm or C02, X = 10.6(xm with a higher pulse duration of up to 600 ns) are used. The MALDI mass spectra obtained during soft ionization by UV and IR lasers are identical. The energy density... 

Record MALDI mass spectra in positive ion mode. Look for proton, sodium, and potassium adduct ions in the range mJz 250 to 1000. Fragment ions caused by the loss of carbohydrate moieties are typical and can be diagnostic. 

FIGURE 7.44 MALDI mass spectra from on-CD analysis of the phosphopeptide-con-taining sample, (a) Peptide mass spectrum after concentration/desalting. A database search showed that the sample contained bovine protein disulfide isomerase. (b) Phosphopeptide enrichment by IMAC. Two phosphopeptides at m/z 964 and 2027 were recognized (c) Phosphopeptide enrichment followed by enzymatic on-column dephosphorylation using alkaline phosphatase. Two phosphopeptides at m/z 884 and 1947 were recognized from the mass shifts of 80 Da from (B), which were resulted from dephosphorylation [794]. Reprinted with permission from the American Chemical Society. 

Norris J, Cornett D, Mobley J, Andersson M, Seeley E, Chaurand P, Caprioli R (2007) Processing MALDI mass spectra to improve mass spectral direct tissue analysis. Int J Mass Spectrom 260 212-221. doi 10.1016/j.ijms.2006.10.005... 

Definitive location of all guest molecules inside the cavity is somewhat ambiguous owing to inexact stoichiometry and disorder. However, the (+)-MALDI mass spectra of II indicate that each individual capsule encloses different mixtures of water and acetone. In particular, two peaks implicated the presence of 24 entrapped water molecules that occupy axial coordination sites orientated toward the center of the cavity. 

The wide application of newly developed advanced Surface MALDI MS methods, such as laser desorption ionization (LDI), surface-enhanced laser desorption ionization (SELDI), direct ionization on silicon surface (DIOS), etc. have two shortcomings. First, problems with MALDI-TOF MS sample preparation for nano-sized systems have not been completely worked out. Second, the reliability and reproducibility of experimental data concerning similar bio-active systems is lacking. Sometimes molecular, associative and fragment ions cannot, be observed in the MALDI mass spectra. We are currently working on overcoming these difficulties with some encouraging results.13,14... 

Another mutant for the tobacco mosaic virus (TMV Asp77Arg) (Fig. 4), was identified using the same approach. MALDI mass spectra of the digests of the capsid protein were identical except for the fragment occurring at 2051.4 Da in the wild type and 2091.8 Da in the mutant. The mass of the peptide for the wild... 

MALDI mass spectra were acquired on a Broker Reflex mass spectrometer equipped with a 337 nm nitrogen laser and a multiple sample stage source. The spectra were acquired in linear mode, represent the sum of 20 laser shots, and are un-smoothed. All ions were desorbed at a laser power just above threshold, at an ion extraction voltage of 30 kV. The matrix used was a saturated solution of 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid, Aldrich Chemicals) in a 1 1 water/acetonitrile solution. Low-mass matrix ions were deflected by the application of a voltage pulse. 

The mass accuracy of LSIMS for measurement of the unresolved isotopic cluster is typically within 100 p.p.m. of the calculated average [M+H]+ mass. The accuracy of the observed masses listed in Tables I and II for the MALDI mass spectra benefited from the use of a reflectron instrument which generally reduced the deviation observed between spectra measured under different experimental conditions (e.g. different matrix or laser power) from 1000 p.p.m. to 300 p.p.m. Reflecting this level of mass accuracy we present the MALDI measurements with only 4 significant figures, compared with 5 significant figures for the LSIMS measurements. 

Table I. Observed masses in the LSIMS and MALDI mass spectra of fractions of C. striatus...

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