<p><a></a><a></a><a></a><a></a><a></a><a></a><a></a><a></a><a></a><a></a><a>ABSTRACT</a></p>
<p>Phenols
are ubiquitous in our surroundings including biological molecules such as
L-Dopa metabolites, food components, such as whiskey and liquid smoke, etc. This
dissertation describes a new method for detecting phenols, by reaction with
Gibbs reagent to form indophenols, followed by mass spectrometric detection.
Unlike the standard Gibbs reaction which uses a colorimetric approach, the use
of mass spectrometry allows for simultaneous detection of differently
substituted phenols. The procedure is demonstrated to work for a large variety
of phenols without <i>para</i>‐substitution. With <i>para</i>‐substituted
phenols, Gibbs products are still often observed, but the specific product
depends on the substituent. For <i>para</i> groups with high
electronegativity, such as methoxy or halogens, the reaction proceeds by
displacement of the substituent. For groups with lower electronegativity, such
as amino or alkyl groups, Gibbs products are observed that retain the
substituent, indicating that the reaction occurs at the <i>ortho</i> or <i>meta</i> position.
In mixtures of phenols, the relative intensities of the Gibbs products are
proportional to the relative concentrations, and concentrations as low as
1 μmol/L can be detected. The method is applied to the qualitative
analysis of commercial liquid smoke, and it is found that hickory and mesquite
flavors have significantly different phenolic composition.</p>
<p>In the
course of this study, we used this technique to quantify major phenol
derivatives in commercial products such as liquid smoke (catechol, guaiacol and
syringol) and whiskey (<i>o</i>-cresol,
guaiacol and syringol) as the phenol derivatives are a significant part of the
aroma of foodstuffs and alcoholic beverages. For instance, phenolic compounds
are partly responsible for the taste, aroma and the smokiness in Liquid Smokes
and Scotch whiskies. </p>
<p>In the
analysis of Liquid Smokes, we have carried out an analysis of phenols in
commercial liquid smoke by using the reaction with Gibbs reagent followed by
analysis using electrospray ionization mass spectrometry (ESI-MS). This
analysis technique allows us to avoid any separation and/or solvent extraction
steps before MS analysis. With this analysis, we are able to determine and
compare the phenolic compositions of hickory, mesquite, pecan and apple wood
flavors of liquid smoke. </p>
<p>In the analysis of phenols in whiskey, we describe the
detection of the Gibbs products from the phenols in four different commercial
Scotch whiskies by using simple ESI-MS. In addition, by addition of an internal
standard, 5,6,7,8-tetrahydro-1-napthol (THN), concentrations of the major
phenols in the whiskies are readily obtained. With this analysis we are able to
determine and compare the composition of phenols in them and their contribution
in the taste, smokey, and aroma to the whiskies.</p>
<p>Another
important class of phenols are found in biological samples, such as L-Dopa and
its metabolites, which are neurotransmitters and play important roles in living
systems. In this work, we describe the detection of Gibbs products
formed from these neurotransmitters after reaction with Gibbs reagent and
analysis by using simple ESI‐MS. This technique would be an alternative method
for the detection and simultaneous quantification of these neurotransmitters. </p>
<p>Finally,
in the course of this work, we found that the positive Gibbs tests are obtained
for a wide range of <i>para</i>-substituted
phenols, and that, in most cases, substitution occurs by displacement of the <i>para</i>-substituent. In addition, there is
generally an additional unique second-phenol-addition product, which
conveniently can be used from an analytical perspective to distinguish <i>para</i>-substituted phenols from the
unsubstituted versions. In addition to
using the methodology for phenol analysis, we are examining the mechanism of
indophenol formation, particularly with the <i>para</i>-substituted
phenols. </p>
<p>The
importance of peptides to the scientific world is enormous and, therefore,
their structures, properties, and reactivity are exceptionally
well-characterized by mass spectrometry and electrospray ionization. In the
dipeptide work, we have used mass spectrometry to examine the dissociation of
dipeptides of phenylalanine (Phe), containing sulfonated tag as a charge
carrier (Phe*), proline (Pro) to investigate their gas phase dissociation. The
presence of sulfonated tag (SO<sub>3</sub><sup>-</sup>) on the Phe amino acid
serves as the charge carrier such that the dipeptide backbone has a canonical
structure and is not protonated. Phe-Pro dipeptide and their derivatives were
synthesized and analyzed by LCQ-Deca mass spectroscopy to get the fragmentation
mechanism. To confirm that fragmentation path, we also synthesized
dikitopeparazines and oxazolines from all combinations of the dipeptides. All
these analyses were confirmed by isotopic labeling experiments and determination
and optimization of structures were carried out using theoretical calculation.
We have found that the fragmentation of Phe*Pro and ProPhe* dipeptides form
sequence specific b<sub>2</sub> ions. In addition, not only is the ‘mobile
proton’ involved in the dissociation process, but also is the ‘backbone
hydrogen’ is involved in forming b<sub>2</sub> ions. </p>
<p> </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12126420 |
| Date | 28 April 2020 |
| Creators | Sabyasachy Mistry (7360475) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/MASS_SPECTROMETRIC_DETECTION_OF_INDOPHENOLS_FROM_THE_GIBBS_REACTION_FOR_PHENOLS_ANALYSIS/12126420 |
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