K4 Elite
K4 Elite
Calculation utilities and reference material for in-vitro laboratory work with research peptides. Everything on this page is a measurement aid; nothing here is a protocol or a dosing recommendation.
Enter the peptide mass stated on the vial, the volume of bacteriostatic water used to reconstitute it, and the amount you need to measure out. The tool returns the resulting solution concentration and the volume to draw, expressed both in millilitres and in units on a U-100 (100 units/mL) syringe.
The milligram figure printed on a lyophilised vial is usually a gross weight. Synthetic peptides are typically isolated as salts — most often trifluoroacetate (TFA) from reverse-phase HPLC purification, sometimes acetate or hydrochloride — and the bound counterions plus residual water are weighed along with the peptide. A certificate of analysis normally reports two separate numbers: net peptide content (the fraction of the gross weight that is actually peptide backbone, commonly 70–90 %, usually determined by amino-acid analysis or nitrogen content) and HPLC purity (the fraction of that peptide material which is the target sequence rather than deletion or truncation products). Multiplying the labelled mass by both gives the true mass of target peptide in the vial.
Skipping this correction is one of the most common sources of silent error in peptide work: two vials with identical labels but different salt forms can differ by 20 % or more in actual peptide mass, which propagates straight into every downstream concentration. Anchoring calculations to the COA figures rather than the label is what makes results reproducible between lots and between laboratories.
In-vitro work is specified in molar terms, not mass terms — receptor occupancy, EC50 and IC50 values in the literature are all molar. Converting a weighed mass to a molarity requires the molecular weight of the compound; molecular weights for catalogue items are listed in the molecular-data table on each product page and in the Peptide Research Library. Where a peptide is supplied as a salt, use the free-base molecular weight together with the net-peptide-corrected mass from the calculator above.
General laboratory handling practice for lyophilised research peptides. Compound-specific guidance on the certificate of analysis or product page always takes precedence — stability varies substantially with sequence, and peptides containing Cys, Met, Trp or N-terminal Gln are more prone to oxidation, deamidation or cyclisation than the table's general case suggests.
| State | Condition | Working window | Notes |
|---|---|---|---|
| Lyophilised powder | −20 °C or below; −80 °C for archival material | Long term | Keep sealed and desiccated, protected from light and moisture. The dry solid is the most stable form — leave material lyophilised until it is actually needed. |
| Reconstituted solution | 2–8 °C, refrigerated, protected from light | Short working window | Hydrolysis, oxidation and adsorption to container surfaces all begin once the peptide is in solution. Bacteriostatic water limits microbial growth but does not stop chemical degradation. |
| Frozen aliquots | −20 °C to −80 °C in single-use volumes | Extended, if undisturbed | Aliquot immediately after reconstitution so that each experiment thaws a fresh tube. Low-binding tubes reduce loss for dilute or hydrophobic sequences. |
| Freeze–thaw | Minimise cycles | — | Each cycle concentrates solutes at the ice interface and drives aggregation and loss of activity. Aliquoting is the direct way to avoid repeat cycles; never refreeze a tube that has been through several. |
| Before opening | Let the vial reach room temperature first | — | Opening a cold vial draws in humid air that condenses on the powder. Introduced moisture accelerates hydrolysis and skews any subsequent gravimetric measurement. |
Primary sources, not aggregators. Each of these is a public, authoritative database maintained by a research institution or established curator — use them to verify compound identity and to read the underlying literature directly.
NIH open chemistry database. Confirm compound identity, CID, molecular formula, exact molecular weight, canonical SMILES and InChIKey before you record a compound in a notebook.
NLM index of biomedical literature. The primary place to check what has actually been published on a sequence, and to separate peer-reviewed findings from secondary summaries.
Registry of interventional and observational studies. Shows which compounds have entered registered human trials, at what phase, with what endpoints, and whether results were posted.
Curated protein sequence and function knowledgebase. Use it to resolve the parent protein of a peptide fragment, verify residue numbering, and pull cross-references to other databases.
Experimentally determined and computed 3D structures. Useful for inspecting receptor–ligand binding modes and for structural context behind a mechanism described in a paper.
Computes physicochemical properties directly from a sequence: theoretical molecular weight, pI, extinction coefficient, instability index and GRAVY. The fastest way to sanity-check a molecular weight before a molarity calculation.
Drug, target and pathway knowledgebase. Helpful for identifying the molecular targets and mechanism of action associated with a compound and for locating the supporting citations.
Reference profiles with mechanisms, study findings, molecular data and citations for each peptide.
Longer-form write-ups of the published literature, with sources linked throughout.
Third-party HPLC and mass-spectrometry documentation — the source of the net content and purity figures used above.
Available research compounds, sizes and pricing, with molecular data on every product page.