Fragment fingerprint

Fig. 5. Positive ion LD TOP mass spectra (top trace) blood sample from a patient infected with P. malariae parasites (to be published) and (bottom trace) control sample (uninfected blood). A commercial LD TOF system is used, and both spectra are normalized to the same detector response value. Each trace represents the average of 100 single laser shot spectra, obtained from linear scanning of an individual sample well. The molecular ion (M at mtz 616) and several characteristic fingerprint fragment ions of desorbed heme are denoted in the upper trace.

Fingerprints structural keys identify a molecule - code is highly compact represented in bits ambiguous not convertible to other representations dependent on the fragment library... 

The mass spectrum is a fingerprint for each compound because no two molecules are fragmented and ionized in exactly the same manner on electron-impact ionization. In reporting mass spectra the data are normalized by assigning the most intense peak (denoted as base peak) a value of 100. Other peaks are reported as percentages of the base peak. 

This fragmentation is characteristic for a given substance, similar to a fingerprint, and is referred to as a mass spectrum. 

The fragment ions are characteristic of any given substance in that the way a compound fragments can be regarded as a fingerprint. For the fragment ions to be useful, it is necessary to know how they relate to each other. In other words, it is necessary to understand which fragment should be connected to which others in the overall chemical structure. 

These signals in the NOE spectra therefore in principle make it possible to determine which fingerprint in the COSY spectrum comes from a residue adjacent to the one previously identified. For example, in the case of the lac-repressor fragment the specific Ser residue that was identified from the COSY spectrum was shown in the NOE spectrum to interact with a His residue, which in turn interacted with a Val residue. Comparison with the known amino acid sequence revealed that the tripeptide Ser-His-Val occurred only once, for residues 28-30. 

One of the most common uses of vibrational spectroscopy is as a molecular fingerprinting tool whereby spectral features are assigned to the presence of particular fragments in molecules. These assignments are, however, only... 

Exonuclease An enzyme that cleaves nucleotides from either the 3 or 5 ends of DNA or RNA. Fingerprinting The use of RFLPs or repeat sequence DNA to establish a unique pattern of DNA fragments for an individual. 

The parent ion usually breaks apart into a collection of smaller pieces, many of which are also positively charged. The masses of these fragments provide a chemical fingerprint that indicates how the atoms in a molecule are connected together. A relatively simple example is the mass spectmm of methane, shown in the figure. There are peaks at mass numbers 16, 15, 14, 13, 12, and 1. Nearly all hydrogen atoms have. <4 = 1, and nearly all carbon atoms have A = 12, so these peaks can be identified as CH4 ,... 

High performance spectroscopic methods, like FT-IR and NIR spectrometry and Raman spectroscopy are widely applied to identify non-destructively the specific fingerprint of an extract or check the stability of pure molecules or mixtures by the recognition of different functional groups. Generally, the infrared techniques are more frequently applied in food colorant analysis, as recently reviewed. Mass spectrometry is used as well, either coupled to HPLC for the detection of separated molecules or for the identification of a fingerprint based on fragmentation patterns. ... 

A richer fingerprint description is provided by the Daylight [45, 46] or UNITY (Tripos Inc., St. Louis) fingerprints. These incorporate a much broader range of features, notably including connected bond path fragments up to seven bonds long. 

Figure 2.4. Peptide fingerprinting by MALDI-TOF mass Spectrometry. Proteins are extracted and separated on by 2D gel electrophoresis. A spot of interest is excised from the gel, digested with trypsin, and ionized by MALDI. The precise mass of proteolytic fragments is determined by time-of- flight mass spectrometry. The identity of the protein is determined by comparing the peptide masses with a list of peptide masses generated by a simulated digestion of all of the open reading frames of the organism.

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