peptide standards FAQ

Use it only for non-critical preliminary assays where dose precision matters less than proof of concept. The 6% impurity gap means you're delivering 6% less active peptide per milligram than calculated. Acceptable for exploratory work but not for dose-response curves or regulatory submissions. Adjust your dosing calculations to account for lower purity or request a replacement batch if your protocol requires ≥95% purity.

Contact the supplier immediately and request MS verification before reconstituting the peptide. A missing MS certificate means sequence accuracy is unverified. The peptide could contain amino-acid substitutions, deletions, or truncations that render it structurally different from the target compound. Do not proceed with assays until sequence is confirmed. If the supplier cannot provide third-party MS data, the peptide is not research-grade.

Discard the vial and start with a fresh sample. Once contaminated, sterility cannot be restored. Bacterial growth will proliferate even in refrigerated conditions, degrading the peptide through enzymatic cleavage. Using contaminated peptides introduces variables you cannot control or measure. The cost of replacing one vial is negligible compared to the cost of invalidated experiments or distorted data.

Discard immediately and do not administer. Visible aggregation indicates peptide denaturation or microbial contamination, both of which compromise experimental validity. Dihexa should form a clear, colorless solution upon reconstitution with bacteriostatic water. Cloudiness within 48 hours suggests the lyophilized powder was exposed to humidity before reconstitution, causing partial hydrolysis. Cloudiness after seven days indicates bacterial growth despite bacteriostatic water. The vial was contaminated during reconstitution and must be replaced.

Verify peptide integrity before concluding the protocol failed. Request ESI-MS analysis of the remaining peptide solution to confirm molecular weight matches the theoretical Dihexa mass (738.5 Da for the free base). If mass spec shows degradation products or incorrect mass, the issue was peptide quality, not protocol design. If mass spec confirms intact peptide, consider dosing frequency: switch from once-daily to twice-daily administration to maintain steady-state c-Met receptor occupancy, as the peptide's 4–6 hour brain half-life creates trough periods with single daily dosing.

Aliquot the reconstituted solution into single-use amber glass vials immediately after mixing and store at −80°C. Freezing arrests oxidation and deamidation reactions that degrade the peptide in aqueous solution. Thaw each aliquot only once, immediately before administration. Do not refreeze. This approach maintains potency for 90–120 days. Alternatively, store the peptide as lyophilized powder at −20°C and reconstitute fresh aliquots weekly, which eliminates freeze-thaw cycles entirely.

Do not use it. Request replacement with documented cold-chain logs. Lyophilized peptides exposed to temperatures above 30°C for more than four hours undergo partial racemization that HPLC cannot detect but that abolishes biological activity. The visual appearance remains unchanged. White powder. But potency may be reduced by 20–50%. Using degraded peptide introduces a confounding variable that makes null results uninterpretable: you cannot determine whether the protocol failed or the peptide was inactive.

Published EC50 values for Dihexa in neurogenesis assays range from 10 nM to 1 µM depending on the cell model, assay duration, and serum content in the medium. If your EC50 is consistently 5–10× higher than published values using the same cell line, suspect peptide degradation during storage or reconstitution. Prepare a fresh stock from a newly opened vial, reconstitute in DMSO under anhydrous conditions, and run a side-by-side comparison with your existing stock. Also verify that your assay endpoint (BrdU incorporation, Ki67 staining, neurite outgrowth) matches the published protocol. Different endpoints detect different phases of neurogenesis and yield different potency curves.

Purity percentage alone doesn't indicate what the remaining 1–3% contains. A 99% pure peptide with 1% deletion sequences (missing one amino acid) will underperform a 97% pure peptide where the 3% is residual TFA salt (biologically inert but adds mass). Request the full HPLC chromatogram and check for secondary peaks. Any peak above 1% of the main peak area represents a synthesis impurity. Additionally, verify the molecular weight via mass spectrometry matches the theoretical mass for intact Dihexa (559.73 g/mol for the free base). A mass discrepancy of ±14 Da or more suggests structural modification that would impair c-Met binding.

Verify reconstitution solvent compatibility with your assay. DMSO concentrations above 0.5% in culture medium can independently suppress neural progenitor proliferation or induce differentiation, masking Dihexa's HGF-mediated effects. Dilute DMSO stocks to <0.1% final concentration or switch to bacteriostatic water for reconstitution. Second, confirm your c-Met receptor expression in the cell line being used. Dihexa's mechanism requires functional c-Met on neural progenitors, and some immortalised cell lines downregulate receptor expression after extended passage. Running a Western blot for c-Met or an HGF binding assay can rule out receptor absence as the null result cause.

No. Reconstitute only the amount needed for 7–10 days of experiments if using bacteriostatic water (refrigerated at 2–8°C), or prepare a high-concentration DMSO stock (10–50 mM), aliquot into single-use volumes, and store at −20°C. Repeated pipetting from a single vial introduces contamination risk and repeated temperature fluctuations that degrade peptide over time. For large-scale studies requiring 50+ mg total, order multiple smaller vials (5–10 mg each) rather than one 50 mg vial. This preserves the majority of your stock in unopened, lyophilised form until needed.