Mass spectrum 1 peaks

Figure 2.16 Different ways to represent a mass spectrum peak profile (a), bar graph (b) and table (c)...

Inspection of the UV chromatogram from the LC-ESI MS analysis of the tryptic digest of the protein revealed a peak not present in the digestion of wild-type TTR, at retention time 25.95 min. The [M + H]+ of this variant peptide (m/z 1392.6) was consistent with a 27 Da increment to the normal tryptic peptide T4, 22GSPAINVAVHVFR34. The location of the mutation was confirmed by MALDI MS analysis of the chromatographic fraction collected between retention times 25.0-27.5 min. In the MALDI mass spectrum, peaks at m/z 1365.2 (wild-type T4) and m/z 1392.1 (variant T4) are both present (Fig. 8). This observation confirmed that the mass difference between the variant and the wild type peptides is indeed +27 Da. The only possible amino acid substitution that would give rise to a +27 Da shift in that peptide is Ser23 —> Asn. 

Diagram 2.2 Mass spectrum peak patterns of ions containing chlorine and bromine... 

Figure 14. The chemoenzymatic synthesis of 4-deoxy-4-fluoro-D- ructose and some mass spectrum peaks of the peracetylated derivative. (a) Immobilized pyranose-2-oxidase (c) sodium borohydride reduction. The observed m/e 129, derived from (10), is diagnostic for a 2-ketopyranose.

Comparison of major mass spectrum peaks from diphenylhydrazone 0-acetylated derivatives of glucose (a), glucosone (b) and 4-deoxy-4-fluoro-glucosone (c)... 

Mass spectra of the partial methanolyzed PBA/PBT/PBSe terpolyester (a) experimental FAB mass spectrum (b) simulated mass spectrum. (Peak assigments are reported in Table 7.2.) (Reprinted with permission from Ref. 72, Copyright American Chemical Society.)... 

FIGURE 24.5 Chromatogram (selected part) of red wine spiked with 500 ng/L of 2,4,6-trichloroanisole obtained after SPME extraction and simultaneous scan/SIM acquisition on a GC/MS system (7890A/5975C MSD, Agilent Technologies). (A) Total ion current (TIC) of scan run (rn/z = 33-233) (B) TIC of SIM run (m/z = 195,197,210) (C) ion abundances in SIM mass spectrum. Peak of 2,4,6-trichloroanisole on chromatogram B marked with an arrow. 

The suggested formula of [Ni(L76)] is in conformity with data from IR, H NMR spectra and mass-spectrometry. In particular, as distinct from [Ni(L74)] and [Ni(L75)], whose fragmentation proceeds at the expense of the S-alkylisothiosemi-carbazide fragment and does not involve cleavage of the diamine metallocycle, the [Ni(L76)] mass-spectrum peaks were found corresponding to losses from the pendant diaminobutane uncoordinated function [107]. 

Compound 63 is a white crystalline substance with melting point 157°C and molecular formula C13H24O5. This implies loss of acetone from humulinone. Confirmation is found in the H NMR spectrum. Several possibilities can be proposed, but only structure 63 (Fig. 31) can explain the mass spectrum (peaks at m/z 292, 210 and 167). 

Multivariate data analysis usually starts with generating a set of spectra and the corresponding chemical structures as a result of a spectrum similarity search in a spectrum database. The peak data are transformed into a set of spectral features and the chemical structures are encoded into molecular descriptors [80]. A spectral feature is a property that can be automatically computed from a mass spectrum. Typical spectral features are the peak intensity at a particular mass/charge value, or logarithmic intensity ratios. The goal of transformation of peak data into spectral features is to obtain descriptors of spectral properties that are more suitable than the original peak list data. 

The amino add analysis of all peptide chains on the resins indicated a ratio of Pro Val 6.6 6.0 (calcd. 6 6). The peptides were then cleaved from the resin with 30% HBr in acetic acid and chromatogra phed on sephadex LH-20 in 0.001 M HCl. 335 mg dodecapeptide was isolated. Hydrolysis followed by quantitative amino acid analysis gave a ratio of Pro Val - 6.0 5.6 (calcd. 6 6). Cycll2ation in DMF with Woodward s reagent K (see scheme below) yielded after purification 138 mg of needles of the desired cyc-lododecapeptide with one equiv of acetic add. The compound yielded a yellow adduct with potassium picrate, and here an analytically more acceptable ratio Pro Val of 1.03 1.00 (calcd. 1 1) was found. The mass spectrum contained a molecular ion peak. No other spectral measurements (lack of ORD, NMR) have been reported. For a thirty-six step synthesis in which each step may cause side-reaaions the characterization of the final product should, of course, be more elaborate. 

During the course of biochemical studies (138). the mass spectrum of 2-acetamidothiazole was recorded its main peaks are the molecular ion (m/e= 142, relative intensity = 26%) and fragments 100 (100), 58 (2. 5), and 43 (39). For 2-acetamido-5-bromothiazole the main peak results again from the loss of C2H2O by the molecular ion. 2-AcetyIacet-amido-4-methylthiazole (2S) exhibits significant loss of from the... 

The base peak in the mass spectrum of the LM free metal-ligand ion and the fragmentation patterns of this parent ion are of particuliar significance since they illustrate the effect of coordination upon the properties of the thiazole ligand. The free thiazole fragments upon electron impact by two major routes (Scheme 86 also cf. Section II. 6). 

FIGURE 13 40 The mass spectrum of benzene The peak at miz = 78 corresponds to the CgHg molecular ion... 

The mass spectrum of benzene is relatively simple and illustrates some of the mfor matron that mass spectrometry provides The most intense peak m the mass spectrum is called the base peak and is assigned a relative intensity of 100 Ion abundances are pro portional to peak intensities and are reported as intensities relative to the base peak The base peak m the mass spectrum of benzene corresponds to the molecular ion (M" ) at miz = 78... 

There is a small peak one mass unit higher than M m the mass spectrum of ben zene What is the origin of this peak d What we see m Figure 13 40 as a single mass spectrum is actually a superposition of the spectra of three isotopically distinct benzenes Most of the benzene molecules contain only and H and have a molecular mass of 78 Smaller proportions of benzene molecules contain m place of one of the atoms or m place of one of the protons Both these species have a molecular mass of 79... 

Not only the molecular ion peak but all the peaks m the mass spectrum of benzene are accompanied by a smaller peak one mass unit higher Indeed because all organic com pounds contain carbon and most contain hydrogen similar isotopic clusters will appear m the mass spectra of all organic compounds... 

The peak at m/z 77 m the mass spectrum of chlorobenzene m Figure 13 41 is attributed to this fragmentation Because there is no peak of significant intensity two atomic mass units higher we know that the cation responsible for the peak at m/z 77 cannot contain chlorine... 

Some classes of compounds are so prone to fragmentation that the molecular ion peak IS very weak The base peak m most unbranched alkanes for example is m/z 43 which IS followed by peaks of decreasing intensity at m/z values of 57 71 85 and so on These peaks correspond to cleavage of each possible carbon-carbon bond m the mol ecule This pattern is evident m the mass spectrum of decane depicted m Figure 13 42 The points of cleavage are indicated m the following diagram... 

FIGURE 13 42 The mass spectrum of decane The peak for the molecular ion is extremely small The most prominent peaks arise by fragmentation... 

FIGURE 13 43 The mass spectrum of propylbenzene The most intense peak is... 

Three of the most intense peaks in the mass spectrum of ] 2 methyl 2 butanol appear at m/z 59 70 and 73 Explain the origin of these peaks J... 

The most intense peaks in the mass spectrum of an alcohol correspond to the ton formed according to carbon-carbon cleavage of the type shown ... 

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