Mass Spec of Derivatized (TBDMS) Proline and Isoleucine

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In summary, mass spectrometry is an analytical technique that uses an electric or magnetic field to separate and detect molecules based on their mass-to-charge ratio. TBDMS is commonly used in mass spectrometry to improve the volatility and stability of molecules, such as proline and isoleucine. Derivatization in mass spectrometry can lead to better detection, identification, and structural analysis of molecules. Applications of mass spectrometry of derivatized TBDMS proline and isoleucine include protein and peptide analysis, metabolomics, drug discovery, and clinical research on amino acid metabolism and disease biomarkers.
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pearbear21
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Hi all,

NOTE: Images attached if things get confusing.

I'm trying to work out the identity of some of the major mass spec peaks found for proline and isoleucine after derivativization with tert-butyl dimethyl silane. I know that TBDMS is added to the OH side of the carboxylic acids of each amino acid, and that it adds to the NH2 of isoleucine, though I'm not certain if it would attach to the NH of the fused ring found in proline via some ring opening mechanism or not.

I assume if the ring did open, the NH would remain connected to the carbon alpha to the carboxyl group and that an alkyl chain would be left extending from this carbon. Does this sound reasonable?

My issue with isoleucine is not in the derivatization chemistry, but in the fragmentations enacted by mass spec. My mass-histogram shows major species of the following weights: 302, 274, 200, and 147, all with small isotopic peaks adjacent to them. The fully derivatized species weighs 359 and each TBDMS group weighs 115. It's pretty common for one of the tert-butyl methyls to fragment leaving a radical cation behind. I know that sometimes the tert butyl group is completely removed leaving the Si as the radical cation, as well.

It is also possible that only one derivative group is added, rather than two, which would lead to varying weights. I still can't reconcile some of the weights I've listed and I've tried mapping all possible fragmentation products. Is it possible for a methyl to be cleaved from the Si and a methyl cleaved from the tert-butyl, leaving two radicals which then form a double bond between the Si and the former tert carbon of the tert-butyl group?

Check out my guesses so far for isoleucine and see what you think. I'm at a loss. I guess if this gets a good response I'll then try to work through the proline fragmentations. Note that a radical dot should be added to each cation in my images.

Any help would be greatly appreciated!
 

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Hi there,

Firstly, I commend you for your thorough analysis and approach to understanding the mass spec peaks for proline and isoleucine after derivatization with tert-butyl dimethyl silane. It is clear that you have a good understanding of the chemistry involved and have put a lot of effort into mapping out the possible fragmentations and their corresponding weights.

Regarding your question about the possibility of a methyl being cleaved from the Si and a methyl cleaved from the tert-butyl group, leading to the formation of a double bond between the Si and the former tert carbon of the tert-butyl group – this is indeed possible. In fact, this type of fragmentation is known as McLafferty rearrangement and is commonly observed in mass spectrometry.

In terms of your mass-histogram for isoleucine, the major peaks at 302, 274, 200, and 147 are likely due to the following fragmentations:

- 302: This could be the fully derivatized isoleucine molecule with one TBDMS group attached to the NH2 group and one TBDMS group attached to the OH group.
- 274: This could be the fully derivatized isoleucine molecule with one TBDMS group attached to the NH2 group and two TBDMS groups attached to the OH group. This fragment would have lost the tert-butyl group from the OH group, leading to a radical cation at m/z 274.
- 200: This could be the fully derivatized isoleucine molecule with two TBDMS groups attached to the NH2 group and one TBDMS group attached to the OH group. This fragment would have lost the tert-butyl group from the NH2 group, leading to a radical cation at m/z 200.
- 147: This could be the fully derivatized isoleucine molecule with two TBDMS groups attached to the NH2 group and two TBDMS groups attached to the OH group. This fragment would have lost both tert-butyl groups, leading to a radical cation at m/z 147.

It is also possible that some of the peaks you are seeing are due to the loss of a TBDMS group from the fully derivatized molecule, as you mentioned. This could explain the smaller peaks adjacent to the major ones.

I hope this helps in your analysis and understanding of the mass spec peaks for isoleucine after derivatization with TBDMS.
 

1. What is mass spectrometry (MS) and how does it work?

Mass spectrometry is an analytical technique used to identify and quantify molecules based on their mass-to-charge ratio. It works by ionizing molecules and then separating and detecting them based on their mass-to-charge ratio using an electric or magnetic field.

2. Why is TBDMS used for derivatization of proline and isoleucine in mass spectrometry?

TBDMS (tert-butyldimethylsilyl) is a commonly used derivatizing agent in mass spectrometry because it can improve the volatility and stability of amino acids, such as proline and isoleucine. This allows for better detection and quantification of these molecules in MS analysis.

3. What are the benefits of derivatization in mass spectrometry?

Derivatization can improve the ionization and fragmentation efficiency of molecules, leading to better detection and identification in MS analysis. It can also increase the volatility and stability of molecules, making them easier to analyze and reducing the risk of degradation during sample preparation.

4. How does TBDMS derivatization affect the mass spectrum of proline and isoleucine?

TBDMS derivatization adds a specific mass to the molecule, which can be used to identify and quantify these amino acids in mass spectrometry. It also changes the fragmentation pattern of the molecule, providing additional information for identification and structural analysis.

5. What are some common applications of mass spec of derivatized TBDMS proline and isoleucine?

Mass spectrometry of derivatized proline and isoleucine is commonly used in the analysis of proteins and peptides, as well as in metabolomics and drug discovery. It can also be used in clinical research to study amino acid metabolism and biomarkers in diseases.

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