Lab guides

Fundamentals

• What is a peptide?

  A peptide is a short chain of amino acids joined by amide bonds. This guide explains how peptides are built, named, modified, made and classified, and how they differ from proteins.

• Lyophilization explained

  Lyophilization, or freeze-drying, removes water from a frozen peptide solution by sublimation, producing a dry, stable powder. This guide covers freezing, primary and secondary drying, cake appearance, residual moisture and handling dried material.

• Solid-phase peptide synthesis

  Solid-phase peptide synthesis builds a peptide one residue at a time on a resin support. This guide covers Merrifield's method, Fmoc and Boc strategies, coupling and cleavage, and the impurities that synthesis produces.

• Amino acid reference for peptide research

  A reference to the 20 standard amino acids, with three-letter and one-letter codes, side-chain chemistry and groupings, plus the non-standard residues most often found in research peptides, such as Aib, norleucine, D-isomers, pyroglutamate and ornithine.

• Peptide nomenclature and modifications

  How peptide sequences and modifications are written: one-letter and three-letter codes, the N-to-C convention, terminal groups such as Ac- and -NH2, cyclic and disulfide notation, D-residue prefixes, salt forms and the INCI names used for cosmetic peptides.

• Lipidation and half-life extension

  Native peptides are cleared from circulation quickly. This guide explains the main strategies used to extend their persistence: fatty acid side chains and albumin binding, PEGylation, Fc fusion and albumin fusion, and the Drug Affinity Complex approach.

• Cyclic peptides and disulfide bonds

  Cyclization constrains a peptide's shape and can increase stability and receptor selectivity. This guide compares disulfide bridges, lactam bridges and head-to-tail cyclization, with examples such as oxytocin, PT-141, melanotan II and setmelanotide.

• D-amino acids and retro-inverso peptides

  D-amino acids are mirror images of the natural L-forms. This guide explains chirality in peptides, why D-substitutions resist proteases, how retro-inverso peptides such as FOXO4-DRI are designed, and how D-content is analyzed.

• How to read preclinical peptide research

  Much peptide research comes from cell and animal studies. This guide explains levels of evidence, why in-vitro and animal findings often fail to translate to people, why cross-species dose comparisons are unreliable, and how replication and publication bias shape a literature.

• Compounding: 503A vs 503B

  US pharmacy compounding is regulated under sections 503A and 503B of the Federal Food, Drug, and Cosmetic Act. This guide explains each pathway, the bulk drug substances lists, FDA's interim categories, the PCAC's role and how compounding differs from research-use-only sales.

Quality and testing

• How to read a peptide certificate of analysis

  A certificate of analysis summarizes the tests run on one lot of peptide. This guide walks through each section of a typical COA, what the numbers mean, and the red flags that suggest the document cannot be relied on.

• Purity vs net peptide content

  HPLC purity and net peptide content answer different questions about a peptide powder. This guide explains what each measures, how they are determined, and how to use them together when preparing solutions of known concentration.

• HPLC and mass spectrometry explained

  HPLC and mass spectrometry are the two core analytical methods for peptides. This guide explains how reversed-phase HPLC separates peptides, how ESI and MALDI mass spectrometry confirm identity, and how LC-MS combines them.

• Endotoxin testing for peptides

  Endotoxins are lipopolysaccharides from Gram-negative bacteria that can distort cell-based and animal experiments. This guide covers LAL gel-clot, turbidimetric and chromogenic methods, recombinant factor C, endotoxin units and how to read results.

• Counter-ions: TFA vs acetate

  Synthetic peptides are supplied as salts, most often with trifluoroacetate or acetate counter-ions. This guide explains where counter-ions come from, how they affect net peptide content and experiments, and how salt exchange works.

• Copper content in GHK-Cu

  GHK-Cu is a complex of the tripeptide glycyl-histidyl-lysine with copper(II). This guide covers copper binding and stoichiometry, what the blue colour indicates, how copper is measured by ICP-MS, ICP-OES and colorimetric methods, and why free copper matters in assays.

• Peptide quantification methods

  How the amount of peptide in a powder or solution is determined: gravimetric weighing, UV absorbance at 280, 214 and 205 nm, amino acid analysis, nitrogen determination and quantitative NMR, and why BCA and Bradford protein assays are unreliable for short peptides.

Handling and storage

• Peptide storage and stability

  Peptides degrade through oxidation, deamidation, aspartimide formation, hydrolysis and aggregation. This guide explains each pathway, which sequences are most at risk, and lab practices for storing lyophilized powder and solutions.

• Reconstitution for lab use

  How to dissolve lyophilized peptides for in-vitro work: predicting solubility from charge and hydrophobicity, choosing between sterile water, bacteriostatic water, dilute acetic acid and DMSO, mixing gently, aliquoting and calculating stock concentrations.

• Predicting peptide solubility from the sequence

  How net charge, isoelectric point, hydrophobicity and secondary-structure tendency predict whether a peptide will dissolve, and how to use those estimates to choose solvents and pH for in-vitro stock solutions.

• Peptide aggregation

  Peptides can self-associate into oligomers, amorphous precipitates, gels or amyloid-like fibrils. This guide explains what drives aggregation, how it is detected, how it distorts experiments and the lab practices that reduce it.

• Sterile filtration of peptide solutions

  Sterile filtration through 0.22 µm membranes removes bacteria from peptide solutions for in-vitro work. This guide covers pore size ratings, membrane materials such as PES and PVDF, adsorption losses, what filtration does not remove and good laboratory practice.