H-Leu-Lys-OH.2TFA is the bis(trifluoroacetate) salt of L-leucyl-L-lysine. The supplied structure shows the expected Leu-Lys peptide bond, a free N-terminal amino group on leucine, a free epsilon-amino group on lysine, and two trifluoroacetic acid components associated with the dipeptide.

The two basic amines explain why a 2TFA form is chemically reasonable. For quantitative work, however, the salt form must be treated as part of the material identity: free H-Leu-Lys-OH and H-Leu-Lys-OH.2TFA have different formula weights and therefore give different peptide-content values when weighed on a gross-mass basis.

Product Information

Why the 2TFA Assignment Matters

H-Leu-Lys-OH contains two readily protonatable amino groups: the N-terminal alpha amine and the lysine epsilon amine. The supplied structure includes two TFA components, supporting the bis-TFA designation. We consider this counterion assignment important for any experiment that uses gravimetric concentration, elemental composition or peptide-content calculations.

Free Peptide vs Bis-TFA Salt

Free L-leucyl-L-lysine has formula C12H25N3O3 and molecular weight 259.35 g/mol. Adding two equivalents of trifluoroacetic acid gives the overall composition C16H27F6N3O7 and a calculated formula weight of 487.40 g/mol. The counterions contribute almost half of the gross mass, so concentration calculations should specify whether they are based on total salt mass or free-peptide content.

Sequence and Structural Identity

The structure corresponds to H-Leu-Lys-OH, with leucine at the N-terminus and lysine at the C-terminus. This sequence direction is important because H-Lys-Leu-OH is a different dipeptide even though the same two amino-acid residues are present. For lot release, LC-MS confirms molecular identity while sequence assignment and stereochemistry should remain consistent with the product structure and COA.

TFA Counterions in Peptide Workflows

TFA salts are common in peptide chemistry after acidic cleavage or purification. Counterion content can influence solution pH, ionic strength and apparent peptide concentration. If a project requires a different counterion, a defined salt exchange, or a longer Leu-Lys-containing sequence, these requirements can be specified through our custom peptide synthesis and purification service.

Procurement and QC Considerations

For AS4107, confirm the Leu-Lys sequence, L/L stereochemistry, peptide purity, two-TFA designation and lot-specific peptide content. We recommend keeping gross salt mass separate from free-peptide-equivalent calculations in protocols and analytical records. Water and residual solvent can further affect assay-by-weight, so the COA remains the appropriate source for lot-specific quantitative specifications.

Product Documents

A Safety Data Sheet (SDS / MSDS) is available for this product to support laboratory handling, storage and safety assessment.

MSDS_H-Leu-Lys-OH-2TFA_AS4107

Certificates of Analysis (COAs) are batch-specific. Please contact us to request the COA for your product, and we will provide it by email.

Frequently Asked Questions

Why does H-Leu-Lys-OH form a 2TFA salt?

The dipeptide contains a free N-terminal amino group and a lysine side-chain amino group. The supplied structure shows two TFA components associated with these basic sites.

What molecular weight should be used for the exact 2TFA composition?

The calculated molecular weight is 487.40 g/mol for C12H25N3O3 · 2(C2HF3O2).

Is 1 mg of the bis-TFA salt equal to 1 mg of free Leu-Lys?

No. The TFA counterions contribute to the gross mass. For quantitative assays, use the lot-specific peptide content or calculate on a free-peptide-equivalent basis when appropriate.

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