Overview
PEG-COOH is a polyethylene glycol (PEG) derivative functionalized with a terminal carboxyl group (-COOH). This modification enables covalent bonding with amine-containing molecules via carbodiimide chemistry, making it indispensable in bioconjugation and nanotechnology. Its water solubility and biocompatibility stem from PEG's ethylene oxide repeating units, while the carboxyl group provides selective reactivity. First synthesized in the 1970s, PEG-COOH gained prominence in pharmaceutical applications due to its ability to 'PEGylate' proteins, enhancing their stability and circulation time in vivo. Today, it serves as a linker molecule in antibody-drug conjugates (ADCs), nanoparticle coatings, and diagnostic reagents.
Physical and Chemical Properties
PEG-COOH exhibits properties dependent on its molecular weight (MW). Low-MW variants (200-1,000 g/mol) are viscous liquids, while high-MW forms (≥2,000 g/mol) are solids. The carboxyl group's pKa is ~4.5, enabling reactivity at physiological pH. Its hydrophilicity is evidenced by a Hildebrand solubility parameter of ~20 MPa¹/². Thermogravimetric analysis shows decomposition at ~200°C. The polymer is non-ionic but the carboxyl group allows pH-dependent behavior—protonated at low pH (COOH) and deprotonated at high pH (COO⁻). This influences its solubility and conjugation efficiency, particularly in EDC/NHS coupling reactions.
Main Applications
In drug delivery, PEG-COOH links therapeutics (e.g., peptides) to carriers, reducing immunogenicity. For example, it conjugates to doxorubicin in liposomal formulations to enhance tumor targeting. It also functionalizes gold nanoparticles for biosensing by attaching antibodies. In hydrogels, PEG-COOH crosslinks with diamine compounds to form biodegradable scaffolds for tissue engineering. Additionally, it modifies microscope slide surfaces for DNA microarray fabrication, where its carboxyl groups bind amine-labeled probes. Over 60% of commercial PEGylation reagents incorporate PEG-COOH derivatives.
Safety and Storage
PEG-COOH is generally non-toxic (LD50 >2,000 mg/kg oral, rat) but may cause mild eye/skin irritation. Powder forms require dust control measures to prevent inhalation risks. Store under argon or nitrogen to prevent oxidation of the carboxyl group, which can reduce reactivity over time. Solutions should be prepared in PBS (pH 7.4) or carbonate buffers (pH 8.5 for activation) and used within 24 hours to avoid hydrolysis. Freeze-thaw cycles degrade performance; aliquot stocks at -20°C with desiccants. Dispose via incineration or approved chemical waste channels.
B2B Procurement Guide
When sourcing PEG-COOH, prioritize suppliers with ISO 13485 certification for medical-grade applications. Key specifications include: 1) Molecular weight distribution (PDI <1.05 for precision conjugation), 2) End-group purity (>95% by NMR), and 3) Residual solvent levels (<100 ppm ethylene oxide). Bulk orders (≥50 kg) typically cost 20-30% less. Consider custom synthesis for unique MWs (e.g., 3,400 g/mol for ADC linkers). Audit suppliers for batch-to-batch consistency using HPLC-MS analysis. For research use, small vials (1-5 g) from Sigma-Aldrich or JenKem Technology offer reliable quality.
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