Introduction to Sodium Deoxycholate (Na-DOC) as an Anionic Surfactant
Sodium deoxycholate (Na-DOC, CAS 302-95-4) is the sodium salt of deoxycholic acid, a naturally occurring secondary bile acid in mammals. It is produced in the intestine through bacterial 7α-dehydroxylation of cholic acid, one of the major primary bile acids synthesized in the liver from cholesterol. As a bile-salt detergent, sodium deoxycholate occupies a unique place among surfactants: unlike classical linear anionics such as sodium dodecyl sulfate (SDS), Na-DOC has a rigid steroidal backbone that creates a “facial amphiphile”—one side of the molecule is decorated with hydroxyl and carboxyl groups (hydrophilic face), while the opposite side presents a hydrophobic, methyl-rich plane.
Let me break the structure down step by step for you to easy to understand.
- The Steroidal (cholane) backbone：the “cholane” skeleton is a rigid four-ring steroid framework — like four fused hexagons/pentagons in a flat plane.
- At the 3-position and 12-position of the steroid ring, Na-DOC has hydroxyl groups pointing toward the same side. These are polar, water-loving handles sticking out of one face of the plate.
- At the end of the side chain (carbon 24), Na-DOC has a carboxyl group (–COOH). In sodium deoxycholate, this is deprotonated (–COO⁻) and paired with Na⁺, making it strongly ionic and water-soluble. This carboxylate is also on the polar face of the molecule, near the hydroxyl groups.
- The “two-faced” polarity (facial amphiphilicity): One face of the steroid plate has all the polar groups (–OH, –COO⁻). The other face is smooth and covered with methyl groups (–CH₃), which are nonpolar and greasy.
The figure represents that sodium deoxycholate (Na-DOC) is not a simple “head-tail” surfactant (like SDS), but instead a “facial amphiphile” — meaning one face (side) of the rigid steroid plate is hydrophilic, while the opposite face is hydrophobic.
Sodium Deoxycholate (Na-DOC) carried by Aladdin
Aladdin catalog | Product name | Grade & Purity |
Sodium deoxycholate | Suitable for manufacturing of diagnostic kits and reagents | |
Sodium deoxycholate | 10mM in DMSO | |
Sodium deoxycholate | ≥98% | |
Sodium deoxycholate | High-purity | |
Sodium deoxycholate | ≥97% |
Sodium Deoxycholate (Na-DOC) — Structure–Property–Performance Table
Category | Parameter / Feature | Value / Data | Structural Basis | How It Connects to Performance |
Core identifiers | Molecular formula / MW/CAS number | C24H39O4Na / 414.56 g·mol⁻¹ /302-95-4 | Steroidal cholane skeleton + Na⁺ carboxylate | Defines dosing, micelle size, and stoichiometric use in buffers. |
Acid–base property | pKa(free acid) | ~6.2 | C-24 carboxyl group | Ionized above pH ~7 → anionic surfactant; |
Amphiphilicity | HLB | ~16 | “Facial amphiphile”: hydroxyl + carboxylate on one side, hydrophobic face opposite | Places SDC in highly hydrophilic detergent range, explaining use in aqueous lysis buffers and protein digestions. |
Micellization | CMC | ~2–6 mM (0.08–0.25% w/v, 25 °C) | Steroid backbone restricts micelle growth → small aggregation number | Ensures micelle formation at low % (0.1–0.5%); reversible solubilization avoids excessive denaturation. |
| Aggregation number | ~3–12 | Flat, rigid steroid plane prevents large spherical packing | Small, dynamic micelles → rapid lipid/protein exchange, ideal for membrane protein solubilization. |
| Micelle mol. wt. | ~1.2–4.9 kDa | Flat, rigid steroid plane | Important for predicting size-exclusion/filtration behavior. |
Solubility | Solubility (H₂O, 20 °C) | ≥ 274–333 g·L⁻¹ | Na⁺salt form stabilizes dissociation; free acid poorly soluble | High solubility allows concentrated stock solutions; pH-sensitive precipitation enables removal by acidification. |
| Solution pH (20 g/L) | ~7.5–9.0 | Carboxylate buffering | Provides self-buffering mild alkalinity; compatible with neutral–slightly basic buffers. |
Colloidal behavior | Mixed micelles | Forms with phospholipids, cholesterol, other surfactants | Facial amphiphilicity drives non-ideal mixing | Enables custom surfactant blends (e.g., RIPA, proteomics workflows). |
| Salt effects | Added NaCl lowers CMC, increases micelle size | Charge-screening of carboxylates | Allows tuning harshness for selective protein solubilization. |
Performance links | Extraction strength | Effective at 0.1–2% (w/v); RIPA uses 0.5% | Micelles disrupt lipid bilayers | Balanced harshness: extracts membrane proteins without over-denaturation. |
| Proteomics cleanup | Acid precipitation or PTS (ethyl acetate extraction) removes >99% SDC | pH-sensitive solubility | MS-compatible after easy surfactant removal. |
| Microbiological selectivity | 1–5 g·L⁻¹ in DCA/XLD media inhibits Gram-positives | Bile-salt mimicry | Selective growth medium component; suppresses sensitive flora. |
Applications and Laboratory Considerations of Sodium Deoxycholate (Na-DOC)
Application | Typical Use / Data | Key Laboratory Considerations |
Cell lysis / protein extraction | 0.5% (w/v) in RIPA buffer with NP-40 + SDS | Below CMC (~2–6 mM) = ineffective; excessive levels denature proteins. Balance needed for efficient yet gentle extraction. |
Proteomics digestion workflows | 0.1–2% Na-DOC enhances trypsin activity and solubilizes hydrophobic proteins | Acidification (pH ≤ 5.5) precipitates DOC — useful for removal |
Phase-Transfer Surfactant (PTS) protocols | Na-DOC + lauroylsarcosinate; ethyl acetate extraction removes >99% detergent post-digestion | Requires strict pH control and handling of organic solvents; improper phase separation risks peptide loss. |
Microbiological selective media (DCA, XLD, etc.) | 1–5g·L⁻¹ Na-DOC inhibits Gram-positives, allows enteric Gram-negatives | Too little → weak selectivity; |
Endotoxin removal (Detoxi-Gel, etc.) | Strips lipopolysaccharides (LPS) from affinity columns | Overexposure may strip or destabilize sensitive proteins along with LPS. |
Virology / lipid disruption | Micelles disrupt enveloped viruses, extract lipids | Strong detergent action risks damaging membrane proteins or losing functional complexes. |
General handling / storage | Highly soluble (≥ 274–333 g·L⁻¹ in H2O, 20 °C); stable stocks at 4 °C | GHS07 hazard (H302, H315, H319): harmful if swallowed, irritant. Use gloves, goggles, fume hood. Avoid Mn²⁺ contamination. |
Sodium Deoxycholate (Na-DOC) vs. Sodium Cholate (Na-Cholate)
Feature | Sodium Deoxycholate (Na-DOC) | Sodium Cholate (Na-Cholate) | Key Difference & Impact |
Parent acid | Deoxycholic acid (secondary bile acid) | Cholic acid (primary bile acid) | Deoxycholic acid is formed by bacterial 7α-dehydroxylation of cholic acid in the gut. |
Hydroxyl groups | Two hydroxyls: 3α, 12α | Three hydroxyls: 3α, 7α, 12α | Extra hydroxyl group in cholic acid makes it more hydrophilic. |
Hydrophobicity | More hydrophobic (fewer OH groups) | More hydrophilic (extra OH group) | Na-DOC is a stronger membrane disruptor; Na-Cholate is milder. |
CMC | ~2–6 mM (higher, less stable micelles) | ~5–15 mM (varies, slightly higher depending on conditions) | Both high compared to SDS, but Na-DOC forms slightly larger, more effective micelles. |
Micelle aggregation number | Low (~3–12) | Similar but slightly smaller due to higher hydrophilicity | Na-DOC tends to interact more strongly with lipids. |
Applications | Protein extraction (RIPA), proteomics (phase-transfer surfactant), microbiological selective agent | Gentler solubilization of membrane proteins, stabilizing bile salt transport studies, crystallization additives | Choice depends on balance between solubilization vs. preservation. |
Physiological role | Major secondary bile salt in humans; aids in lipid digestion, but also associated with cytotoxicity in excess | Major primary bile salt in liver secretion; central to fat digestion and absorption | Reflects metabolic stage: Na-Cholate is liver-synthesized, Na-DOC is gut-modified. |
References:
1. Sigma-Aldrich (Merck). Sodium deoxycholate, ≥97% (titration), CAS 302-95-4, Product Information Sheet. Merck KGaA; 2024. Available from: https://www.sigmaaldrich.com
2. Thermo Fisher Scientific. Sodium deoxycholate, Product Datasheet. Thermo Fisher; 2024. Available from: https://www.thermofisher.com
3. RSC Advances. Effect of additives on sodium deoxycholate micellization. RSC Adv. 2016;6(94):91903–91912.
4. He L, Diedrich J, Chu Y, Yates JR. Extracting accurate precursor information for tandem mass spectra by rawconverter. Anal Chem. 2015;87(22):11361–11367.
5. Masuda T, Tomita M, Ishihama Y. Phase transfer surfactant-aided trypsin digestion for membrane proteome analysis. J Proteome Res. 2008;7(2):731–740.
6. Hara T, Takahashi N, Yoshimura Y, et al. Sodium deoxycholate-assisted tryptic digestion combined with phase transfer surfactant extraction for enhanced proteome analysis. Proteomics. 2013;13(5):876–882.
7. Atlas RM. Handbook of Microbiological Media. 4th ed. CRC Press; 2010. (for DCA and bile salt agar formulations).
8. Levine M. Differentiation of enteric bacteria on deoxycholate agar. J Bacteriol. 1918;3(5):401–420.
9. Thermo Fisher Scientific. Detoxi-Gel Endotoxin Removing Columns, Protocol and Applications. Thermo Fisher; 2024.
10. Small DM. The physical chemistry of cholanic acids. J Lipid Res. 1968;9(3):297–318.
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