I. Overview
H2N-PEG7-OH is a polyethylene glycol derivative with specific terminal functional groups. Its name directly describes its chemical structure:

H2N- : The amino group at one end
PEG7: A polyethylene glycol chain composed of 7 ethylene glycol repeating units
-OH: The hydroxyl group at the other end
Therefore, it is a heterogeneous biffunctional crosslinking agent, meaning it has two distinct ends that can undergo chemical reactions separately. This makes it an ideal "bridge" or "spacer arm" for connecting different molecules (for example, one molecule with a carboxyl group and another with an amino group).


II. Chemical Structural Formula
Its linear chemical structure can be expressed as:
H₂N-CH₂CH₂-O-(CH₂CH₂-O)₆-CH₂CH₂-OH
Or more concisely expressed as:
NH₂-PEG₇-OH
Here, PEG₇ represents seven -ch ₂CH₂O- repeating units.

Molecular weight: Approximately 365.4 g/mol


III. Main Features and Advantages

Heterogeneous bifunctionality
Amino groups are usually positively charged under physiological conditions and can react with activated ester, carboxyl, carbonyl and other groups to form amide bonds or other stable connections.
Hydroxyl groups are relatively inactive but can be activated under specific conditions, forming ester bonds with carboxyl groups or reacting with other hydroxyl groups.

Excellent solubility
The PEG chain has strong hydrophilicity, which makes H2N-PEG7-OH have excellent solubility in water, buffers and many organic solvents, greatly facilitating its application in biochemical reactions.

Steric hindrance shielding and extended half-life:
When drugs, peptides or proteins are linked to PEG chains, the PEG chains can form a "hydrated layer" around the molecules, effectively shielding against attacks from large molecules such as proteases, thereby enhancing stability.
The modified molecules have an increased size, reducing renal filtration and thereby prolonging their circulating half-life in the body.

Reduce immunogenicity
Pegylation can mask the antigenic determinants on the surface of biomolecules (such as therapeutic antibodies and enzymes), thereby reducing their immunogenicity and lowering the risk of antibody production.

Flexible spacer arm
A 7-unit PEG chain provides a sufficiently long and flexible spatial distance. This helps the two connected molecules maintain their respective activities, especially when one of the molecules needs to interact with a target located deep within the binding pocket.


IV. Main Application Fields
H2N-PEG7-OH is widely used in bioconjugated chemistry and materials science, mainly including:

Peg-ylation modification
Protein/peptide peG-ylation: By reacting the amino terminal with the carboxyl group on the protein, or by reacting the amino group on the protein with its activated carboxyl group, the protein is modified by peg-ylation to improve its pharmacokinetic properties.
Peg-ization of small molecule drugs: Linking small molecule drugs with PEG chains to improve their water solubility and bioavailability.

Biological conjugation and crosslinking
As a crosslinking agent, it connects a molecule with a carboxyl group to another molecule with an amino group. For instance, linking biotin to antibodies, or linking fluorescent dyes to oligonucleotides.

Material surface functionalization
It is fixed on the surface of materials with active groups (such as silica, gold nanoparticles, polymer microspheres) through its hydroxyl end, endowing the surface with free amino groups. These amino groups can be further linked to targeted molecules, fluorescent probes or other functional molecules for the preparation of biosensors, drug delivery carriers, etc.

Synthesis of dendrimers and polymers:
As a building block, it is used to synthesize more complex polymer materials with precise structures.


V. Precautions for Use
Storage: It should be sealed and stored in a dry and cool place (usually -20°C is recommended). Due to its hygroscopicity, it will absorb moisture when exposed to the air, which may lead to side reactions such as carbonation of amino groups.
Reactivity: Amino groups are prone to oxidation in the air, and reactions usually need to be carried out under the protection of inert gas.
Functional group protection: In multi-step synthesis, if it is necessary to retain the activity of the amino group, it may be necessary to use a protecting group to protect the amino group, and then remove the protection after the reaction at the other end is completed.


VI. Summary
H2N-PEG7-OH is a very important and commonly used heterogeneous bifunctional PEG crosslinking agent. It plays an indispensable role in fields such as drug development, bioconjugation chemistry, nanotechnology and materials science, thanks to its unique structure with an amino group at one end and a hydroxyl group at the other, good water solubility, biocompatibility and the ability to serve as a flexible spacer arm. It is a powerful tool for researchers to construct complex biological conjugates and functionalized materials.