When orthotoludine reagent is added to water and if free chohine is present, what colour will be produced?
**Core Concept:**
The question is about the reaction between orthotoludine reagent (also known as Griess reagent) and free sulfhydryl compounds (thiols), particularly hydrogen sulfide (H2S) which can be found in water samples. The reagent produces a colored complex that can indicate the presence of free sulfhydryl groups.
**Why the Correct Answer is Right:**
Orthotoludine reagent is a mixture of dithionitrobenzene and sulfanilic acid, which reacts with free sulfhydryl (SH) compounds, like hydrogen sulfide (H2S), to form a colored complex. The reaction is as follows:
H2S + DTNB (5,5'-Dithiobis(2-nitrobenzoic acid)) → 5-thio-2-nitrobenzoic acid (TNB) + H+
**Why Each Wrong Option is Incorrect:**
Option A, B, and C are incorrect because they do not represent the correct reaction between orthotoludine reagent and free sulfhydryl compounds.
**Clinical Pearl:**
Understanding the role of free sulfhydryl compounds, such as hydrogen sulfide (H2S), in various physiological and pathological processes is crucial for medical professionals. For example, H2S is a signaling molecule involved in various physiological functions, including regulation of blood pressure, neurotransmission, and inflammation. However, excessive H2S levels can contribute to pathological conditions, such as neurodegenerative diseases and atherosclerosis. By correctly identifying the color produced by orthotoludine reagent, medical students can evaluate the presence of free sulfhydryl groups in biological samples and interpret the results for diagnostic or therapeutic purposes.
**Correct Answer:**
The correct answer is D. Orthotoludine reagent forms a colored complex with free sulfhydryl compounds, like hydrogen sulfide (H2S), producing a purple color.
**Explanation:**
When orthotoludine reagent reacts with hydrogen sulfide (H2S), the following reaction occurs:
H2S + DTNB → 5-thio-2-nitrobenzoic acid (TNB) + H+
The purple color indicates the presence of free sulfhydryl groups, specifically hydrogen sulfide (H2S), in the sample. This reaction is essential for medical professionals to understand and interpret the results for diagnostic or therapeutic purposes.