Ortho-phthalaldehyde Assay
Ortho-phthalaldehyde Assay - Related Videos
03:35
Rapid Quantification of Oxidized and Reduced Forms of Glutathione Using Ortho -phthalaldehyde in Cultured Mammalian Cells In Vitro
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Cited by 2 •
2024
Quantification of both oxidized and reduced forms of glutathione (GSSG and GSH, respectively) has been achieved through the use of Ortho-phthalaldehyde (OPA). OPA becomes highly fluorescent once conjugated to GSH but is unable to conjugate GSSG until reduced. Here, we describe a multiparametric assay to quantify both using protein quantification for normalization.
08:43
Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives
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2016
An operationally simple procedure for the synthesis of ortho-trifluoromethoxylated aniline derivatives via a two-step sequence of O-trifluoromethylation of N-aryl-N-hydroxyacetamide followed by thermally induced intramolecular OCF3-migration is reported.
01:14
Directing Effect of Substituents: ortho–para-Directing Groups
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2025
Ortho–para directors are substituent groups attached to the benzene ring and direct the addition of an electrophile to the positions ortho or para to the substituent. All electron-donating groups are considered ortho–para directors. They donate electrons to the ring and make the ring more electron-rich. The ring is therefore susceptible to the addition of electrophiles. Substituents such as amino, hydroxy, or alkoxy, containing lone pairs on the atom adjacent to the ring, donate electrons...
01:24
ortho–para-Directing Deactivators: Halogens
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2023
Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
01:11
ortho–para-Directing Activators: –CH3, –OH, –NH2, –OCH3
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2025
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
FAQs
Alkalinity and the thiol reagent are both necessary because they support formation of the fluorescent isoindole derivative from a primary amine. The amine supplies the reactive group, while the thiol reagent participates in the chemistry that creates the measurable fluorescent product. Omitting either condition prevents the reaction from following the intended assay pathway.
Reaction conditions, reagent composition, and calibration directly control how fluorescence should be interpreted. A change in alkalinity or reagent composition can change formation of the fluorescent derivative, while an inaccurate standard comparison can distort the estimated concentration. Maintaining consistent conditions and calibrating against standards helps distinguish a genuine difference in primary-amine content from a measurement-related change in signal.
The assay responds to free amino acids and amino groups in peptides or proteins, rather than serving as a general measure of all molecular groups. This selectivity makes it useful when amino-group content is the variable of interest. Interpretation should therefore remain tied to primary-amine abundance and changes in the sample, not fluorescence intensity alone.
A typical workflow brings the biochemical sample into alkaline conditions with ortho-phthalaldehyde and the thiol reagent. After the fluorescent isoindole derivative forms, its fluorescence intensity is measured and compared with standards. That comparison produces an estimated concentration. Consistency in reagent composition and reaction conditions is essential because both influence the reported value.
The method is useful for amino acid analysis because free amino acids contain primary amines that can generate the fluorescent product. It also supports protein hydrolysis studies, where samples are examined for amino-group changes. In both applications, fluorescence provides a sensitive readout that can be related to analyte concentration through comparison with standards.
In biochemical samples, the assay can monitor changes in amino-group content rather than merely indicate that a sample is present. This makes it relevant to protein hydrolysis studies and other comparisons in which amino-group abundance changes. Researchers interpret those differences by comparing fluorescence values with standards under consistent assay conditions.