Homobifunctional reagents are chemical compounds that contain two identical reactive groups. Symmetrical homobifunctional reagents were among the first crosslinkers developed for conjugation of biomolecules. These were typically hydrophobic compounds, and their use – particularly in one-step reactions – often was accompanied with problems such as inactivation and precipitation of the conjugated biomolecules. Greg Hermanson’s comprehensive reference work Bioconjugate Techniques has an entire chapter (Chapter 5) devoted to homobifunctional reagents. Quanta BioDesign, Ltd. recommends and sells this authoritative reference.
Quanta BioDesign’s products are amphiphilic. Therefore, they impart water solubility to molecules to which they are conjugated. Consequently, when used in crosslinking reactions, Bis-dPEG®25-NHS ester will not cause problems such as aggregation, precipitation, and inactivation.
Using Bis-dPEG®25-NHS ester
NHS esters react with free amines such as the ε-amines of lysine. The optimal pH range for NHS esters to react with free amines is 7.0 – 7.5. However, NHS esters can react with free amines with pH as low as 6.0. NHS esters are susceptible to hydrolysis in aqueous media. As the pH increases, the hydrolysis rate of the ester increases.
Thus, we strongly discourage storing Bis-dPEG®25-NHS ester, product number 10968, in water or aqueous buffer. Instead, we recommend that customers make new solutions of the product as needed, use them immediately, and discard unused solutions after use. If customers desire to store the product in solution, we recommend the use of a pure, anhydrous, water-miscible solvent such as dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAC), or N,N-dimethylformamide (DMF). DMSO, DMAC, or DMF can be dried chemically or by storing for a minimum of 24 hours over 3 Å molecular sieves. With DMF, use only fresh solvent as the compound decomposes over time to form free amines that will react with the NHS esters.
Commercial Scale Production of Bis-dPEG®25-NHS ester Is Available
If you need bulk product in a larger package size than our standard sizes, please contact us for a quote. Our commercial capabilities permit us to manufacture this product at any scale that you need.
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Hydrophobic crosslinkers trigger aggregation and precipitation of biomolecules and contribute to problems with non-specific binding. Polymeric PEG crosslinkers eliminate the issues caused by hydrophobic crosslinkers, but they create new, difficult challenges in analyzing and characterizing the crosslinked conjugates.
You can solve all of those problems right now by clicking on the “Add to Cart” button and purchasing Bis-dPEG®25-NHS ester. The monodispersed PEG crosslinker provides water solubility and larger hydrodynamic volume to the conjugate molecules. However, because it is a discrete compound, not a polymer, the analytical challenges caused by dispersed polymers disappear.
Stop using inferior crosslinkers!