Affinity chromatography techniques based on the immobilisation of peptides exhibiting specific binding activity

A New Advanced Approach: Design and Screening of Affinity Peptide Ligands Using Computer Simulation Techniques

Peptides acquire target affinity based on the combination of residues in their sequences and the conformation formed by their flexible folding, an ability that makes them very attractive biomaterials in therapeutic, diagnostic, and assay fields. With the development of computer technology, computer-aided design and screening of affinity peptides has become a more efficient and faster method. This review summarizes successful cases of computer-aided design and screening of affinity peptide ligands in recent years and lists the computer programs and online servers used in the process. In particular, the characteristics of different design and screening methods are summarized and categorized to help researchers choose between different methods. In addition, experimentally validated sequences are listed, and their applications are described, providing directions for the future development and application of computational peptide screening and design.

Strategy for Conjugating Oligopeptides to Mesoporous Silica Nanoparticles Using Diazirine-Based Heterobifunctional Linkers

Successful strategies for the attachment of oligopeptides to mesoporous silica with pores large enough to load biomolecules should utilize the high surface area of pores to provide an accessible, protective environment. A two-step oligopeptide functionalization strategy is examined here using diazirine-based heterobifunctional linkers. Mesoporous silica nanoparticles (MSNPs) with average pore diameter of ~8 nm and surface area of ~730 m²/g were synthesized and amine-functionalized. Tetrapeptides Gly-Gly-Gly-Gly (GGGG) and Arg-Ser-Ser-Val (RSSV), and a peptide comprised of four copies of RSSV (4RSSV), were covalently attached via their N-terminus to the amine groups on the particle surface by a heterobifunctional linker, sulfo-succinimidyl 6-(4,4′-azipentanamido)hexanoate (sulfo-NHS-LC-diazirine, or SNLD). SNLD consists of an amine-reactive NHS ester group and UV-activable diazirine group, providing precise control over the sequence of attachment steps. Attachment efficiency of RSSV was measured using fluorescein isothiocyanate (FITC)-tagged RSSV (RSSV-FITC). TGA analysis shows similar efficiency (0.29, 0.31 and 0.26 mol peptide/mol amine, respectively) for 4G, RSSV and 4RSSV, suggesting a generalizable method of peptide conjugation. The technique developed here for the conjugation of peptides to MSNPs provides for their attachment in pores and can be translated to selective peptide-based separation and concentration of therapeutics from aqueous process and waste streams.

Establishment of substance P modified affinity chromatography for specific detection and enrichment of Mas-related G protein-coupled receptor X2

Mas-related G protein-coupled receptor X2 (MrgX2) has been identified to be critical in drug-induced pseudo-allergic reactions and allergic diseases. Herein, an affinity high-performance liquid chromatography was established for the specific detection and enrichment of MrgX2. Substance P was used as an affinity ligand and immobilized on a glutaraldehyde-modified amino silica gel. The successful grafting of substance P was characterized by infrared spectroscopy, elemental analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, and nitrogen adsorption and desorption analyzes. The prepared materials were then used as the stationary phase to investigate the retention behavior of MrgX2 recombinant protein on the affinity column. The results obtained with the analytical techniques show the specificity and selectivity of the MrgX2 recombinant protein on the affinity column. The repeatability and reproducibility for the analysis of MrgX2 on the NH₂-Silico@GD@SP column show relative standard deviation (RSD) values lower than the acceptance criteria of 2 and 5% of retention time, and RSD of peak areas < 7%. The RSD value of the results obtained for the control of the activity of the prepared columns respond to the acceptance criteria of 5% and proves that the NH2-Silico@GD@SP column are stable until 48 h. The suitability of the NH₂-Silico@GD@SP column offline SEC system has been tested by using MrgX2 as positive control. The results of this experiment indicate that the offline system may be used to analyze the retention fraction. MrgX2 extracted from human mast cells LAD2 was also verified. An obvious retention can be observed and the natural MrgX2 was concentrated 114.6 times compared with the original complex components by using the affinity column. These results may provide a new approach for the specific detection and enrichment of G-protein-coupled receptors.

β-Hairpins as peptidomimetics of human phosphoprotein-binding domains

Phosphoprotein-binding domains interact with cognate phosphorylated targets ruling several biological processes. The impairment of such interactions is often associated with disease development, namely cancer. The breast cancer susceptibility gene 1 (BRCA1) C-terminal (BRCT) domain is involved in the control of complex signaling networks of the DNA damage response. The capture and identification of BRCT-binding proteins and peptides may be used for the development of new diagnostic tools for diseases with abnormal phosphorylation profiles. Here we show that designed cyclic β-hairpin structures can be used as peptidomimetics of the BRCT domain, with high selectivity in binding to a target phosphorylated peptide. The amino acid residues and spatial constraints involved in the interaction between a phosphorylated peptide (GK14-P) and the BRCT domain were identified and crafted onto a 14-mer β-hairpin template in silico. Several cyclic peptides models were designed and their binding towards the target peptide and other phosphorylated peptides evaluated through virtual screening. Selected cyclic peptides were then synthesized, purified and characterized. The high affinity and selectivity of the lead cyclic peptide towards the target phosphopeptide was confirmed, and the possibility to capture it using affinity chromatography demonstrated. This work paves the way for the development of cyclic β-hairpin peptidomimetics as a novel class of affinity reagents for the highly selective identification and capture of target molecules.

Affinity binding of chicken apolipoprotein A1 to a novel flax orbitide (linusorb)

Bioactive orbitides (linusorbs, LOs) from flaxseed (Linum usitatissimum L.) were ligated through methionine with resin to form an affinity column. The affinity resin was characterized using elemental analysis and the resin bound 70% of its weight in LOs. Chicken serum was passed over the column and washed to remove non-binding materials. The column was eluted with unbound orbitide to competitively release bound protein. A single 28 kDa protein was found in the affinity binding pool. The protein MW and sequence were identical to apolipoprotein A1 (Apo A1), a major serum protein. Its role includes reverse cholesterol transport and cholesterol efflux. The affinity technique allowed convenient and rapid isolation of Apo A1 with a recyclable affinity column. LO binding to a cholesterol carrier molecule might also help us to understand the mechanism of action of LOs in health and the biological activity of flaxseed products.

Bioactive orbitides (linusorbs) from flaxseed (Linum usitatissimum L.) were ligated through methionine with resin to form an affinity column that selectively binds chicken apolipoprotein A1 from chicken serum.

Production of recombinant coagulation factors: Are humans the best host cells?

The main treatment option for Hemophilia A/B patients involves the administration of recombinant coagulation factors on-demand or in a prophylactic approach. Despite the safety and efficacy of this replacement therapy, the development of antibodies against the coagulation factor infused, which neutralize the procoagulant activity, is a severe complication. The production of recombinant coagulation factors in human cell lines is an efficient approach to avoid such complication. Human cell lines can produce recombinant proteins with post translation modifications more similar to their natural counterpart, reducing potential immunogenic reactions. This review provides a brief overview of the most important characteristics of recombinant FVIII and FIX products available on the market and the improvements that have recently been achieved by the production using human cell lines.

Rapid multiple immunoenzyme assay of mycotoxins

Mycotoxins are low molecular weight fungal metabolites that pose a threat as toxic contaminants of food products, thereby necessitating their effective monitoring and control. Microplate ELISA can be used for this purpose, but this method is characteristically time consuming, with a duration extending to several hours. This report proposes a variant of the ELISA method for the detection and quantification of three mycotoxins, ochratoxin A, aflatoxin B1 and zearalenone, in the kinetic regime. The main requirement for the proposed kinetic protocol was to provide a rapid method that combined sensitivity and accuracy. The use of biotin with an extended spacer together with a streptavidin-polyperoxidase conjugate provided high signal levels, despite these interactions occurring under non-equilibrium conditions. Duration of the individual mycotoxin assays was 20 min, whereas the analysis of all three mycotoxins in parallel reached a maximum duration of 25 min. Recovery of at least 95% mycotoxins in water-organic extracts was shown. The developed assays were successfully validated using poultry processing products and corn samples spiked with known quantities of mycotoxins. The detection limits for aflatoxin B1, ochratoxin A and zearalenone in these substances were 0.24, 1.2 and 3 ng/g, respectively.

Preparation, optimization and application of affinity absorbent with a polysaccharide YCP as the ligand

YCP, an α-glucan from the mycelium of marine filamentous fungus Phoma herbarum YS4108, has great antitumor potential via enhancement of host immune through Toll-like receptor (TLR) 2 and TLR4 signaling. In the current study, YCP was coupled to EAH Sepharose 4B agarose beads to prepare the YCP-Sepharose affinity absorbent using 1-cyano-4-dimethylaminopyridinium tetrafluoroborate (CDAP) as the activating agent. An orthogonal experiment L9 (3)(4) was applied to optimize the coupling procedure, giving the optimal parameters as follows: molar ratio of CDAP to YCP of 1:2, CDAP-activation time of 5 min, gel volume of 0.1 mL, and gel-incubation time of 72 h, respectively. Scanning electron microscopy analysis indicated successfully preparation of YCP immobilized sepharose beads, while these beads essentially maintained biological properties of free YCP since they can interact with TLR2 and TLR4 specifically at comparable level. Collectively, our findings provide an alternative approach to immobilize carbohydrate-based molecules for studying the carbohydrate-protein interaction.

Recombinant protein purification using complementary peptides as affinity tags

Affinity tags have become highly popular tools for purifying recombinant proteins from crude extracts by affinity chromatography. Besides, short peptides are excellent ligands for affinity chromatography, as they are not likely to cause an immune response in case of leakage into the product, they are more stable than antibodies to elution and cleaning conditions and they usually have very acceptable selectivity. Hydropathically complementary peptides designed de novo show enough selectivity to be used successfully as peptide ligands for protein purification from crude extracts. Recognition specificity and selectivity in the interaction between the complementary peptide pair His-Leu-Leu-Phe-Pro-Ile-Ile-Ile-Ala-Ala-Ser-Leu and Lys-Asn-Tyr-Pro-Lys-Lys-Lys-Met-Glu-Lys-Arg-Phe have been demonstrated by other authors. In this work, we designed a recombinant protein purification method using a peptide affinity tag that binds to a peptide-binding partner immobilized on a chromatographic matrix. The enhanced green fluorescent protein expressed (EGFP) in Escherichia coli was used as the model. The peptide Gly-Gly-Gly-His-Leu-Leu-Phe-Pro-Ile-Ile-Ile-Ala-Ala-Ser-Leu was synthesized by solid phase using the Fmoc chemistry and immobilized in NHS-Sepharose (PC-Sepharose). Gly residues were added as a spacer arm at the N terminus. The EGFP was expressed either with the fusion tag Lys-Asn-Tyr-Pro-Lys-Lys-Lys-Met-Glu-Lys-Arg-Phe on the C terminus (EGFP-CPTag) or without any fusion tag. After cell disruption, the extract was directly applied to the PC-Sepharose column equilibrated with 20mM sodium phosphate buffer, pH 7.0. The adsorbed EGFP-CPTag was then eluted with 1M Tris. The yield was 98% and the purification factor 4.6. By contrast, EGFP without tag pass through without interacting with the PC-Sepharose column. The method designed can be applied for the purification of other recombinant proteins.

Affinity chromatography based on a combinatorial strategy for rerythropoietin purification

Small peptides containing fewer than 10 amino acids are promising ligand candidates with which to build affinity chromatographic systems for industrial protein purification. The application of combinatorial peptide synthesis strategies greatly facilitates the discovery of suitable ligands for any given protein of interest. Here we sought to identify peptide ligands with affinity for recombinant human erythropoietin (rhEPO), which is used for the treatment of anemia. A combinatorial library containing the octapeptides X-X-X-Phe-X-X-Ala-Gly, where X = Ala, Asp, Glu, Phe, His, Leu, Asn, Pro, Ser, or Thr, was synthesized on HMBA-ChemMatrix resin by the divide-couple-recombine method. For the library screening, rhEPO was coupled to either Texas Red or biotin. Fluorescent beads or beads showing a positive reaction with streptavidin-peroxidase were isolated. After cleavage, peptides were sequenced by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Fifty-seven beads showed a positive reaction. Peptides showing more consensuses were synthesized, and their affinity to rhEPO was assessed using a plasma resonance biosensor. Dissociation constant values in the range of 1-18 μM were obtained. The best two peptides were immobilized on Sepharose, and the resultant chromatographic matrixes showed affinity for rhEPO with dissociation constant values between 1.8 and 2.7 μM. Chinese hamster ovary (CHO) cell culture supernatant was spiked with rhEPO, and the artificial mixture was loaded on Peptide-Sepharose columns. The rhEPO was recovered in the elution fraction with a yield of 90% and a purity of 95% and 97% for P1-Sepharose and P2-Sepharose, respectively.

Design, synthesis and screening of antisense peptide based combinatorial peptide libraries towards an aromatic region of SARS-CoV

A combination of high-performance affinity chromatography and antisense peptide based combinatorial peptide libraries was used to screen a potential inhibitor for SARS-CoV. An aromatic-amino acid-rich region within the transmembrane domain at the C terminal of spike (S) protein identified as a membrane-active region was chosen as the target sense peptide (SP) and immobilized as affinity ligand. Four antisense peptides were designed based on the degeneracy of genetic codes. One of them was screened as the lead peptide to construct the extended peptide libraries (EPL). The library screening was carried out at pH 5.5 so as to mimic the low-pH milieu required by virus fusion. After five cycles of screening, a dodecapeptide KKKKYRNIRRPG (DP) was identified to possess the highest binding affinity to the immobilized sense peptide. The dissociation constant of the complex between the DP and the SP was 5.64 x 10(-7) M in a physiological condition. The recognition between the DP and recombinant SARS S protein was demonstrated by ELISA assay to be in a saturable way. The competitive inhibition of the sense peptide in the competitive ELISA reveals the affinity binding between the DP and SARS S protein is specific and directed towards the target SP of the S protein. The results indicate this preferred polypeptide can be used as a lead compound of potent inhibitor of SARS-CoV. The mechanism study suggests the specific recognition between the DP and the target peptide was due to sequence-dependent and multi-modal affinity interaction.

Identification of protein-binding peptides by direct matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis of peptide beads selected from the screening of one bead–one peptide combinatorial libraries

A fast and inexpensive strategy for the identification of peptide ligands by direct matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) analysis of peptide beads screened from one bead-one peptide combinatorial libraries is herein described. Streptavidin was used as the model protein. A combinatorial library of 6561 peptides was synthesized on ChemMatrix resin by the divide-couple-recombine method. 4-Hydroxymethylbenzoic acid was used as the linker and five residues of Gly were incorporated at the C termini to increase the final peptide molecular weight. Positive control peptides with the HPQ motif and negative control peptides without the HPQ motif evidenced that the linker and the five residues of Gly have neither impaired the specific binding nor facilitated unspecific binding. After screening the library, positive beads were isolated and washed with 8M guanidine hydrochloride. The beads were sliced into two or four pieces, deposited onto the stainless steel MALDI sample plate, and treated with ammonia vapor to release the peptides. In addition, 26 beads picked at random from the library were subjected to the same treatment. All samples were analyzed by MALDI-TOF-MS and the peptides were unambiguously identified with very good reproducibility between the bead pieces, thus evidencing the good homogeneity of the bead. All sequences obtained from the screening contained HPQ.

Leveraging protein purification strategies in proteomics

The proteomic studies, although, tend to be analytical in nature, yet many strategies of preparative protein purification can be usefully employed in such studies. This review points out the importance of purification techniques which are capable of dealing with samples which are suspensions rather than clear solution, e.g. aqueous two phase partitioning, three phase partitioning, expanded bed chromatography, etc. The review also outlines the potential of non-chromatographic techniques in dealing with fractionation of proteomes. Separation protocols which can deal with post-translationally modified (PTM) proteins are also considered.

Rational design of affinity peptide ligand by flexible docking simulation

Rational design of affinity peptide ligands of proteins by flexible docking simulation is performed using the SYBYL program package. This approach involves the use of experimental data to verify a scoring function that can be used to assess the affinity of a peptide for its target protein. The enzyme-linked immunosorbent assay (ELISA) data of several peptides displayed on phage surfaces for insulin and lysozyme, respectively, reported in literature are used for the purpose. It is found that the absolute values of the Dscore calculated from the docking correspond well to the ELISA data that relate to the affinity between the peptides and the target molecule. So, the Dscore function is used to assess the affinity of docked peptides in a pentapeptide library designed on the basis of protein (alpha-amylase) structure. As a result, a pentapeptide with a high Dscore value is selected and a hexapeptide (FHENWS) is built by linking serine to its C-terminal to lengthen the peptide. Molecular surface analysis with the MOLCAD program reveals that electrostatic interactions (including hydrogen bonds) and Van der Waals forces contribute to the affinity of the hexapeptide for alpha-amylase. Chromatographic experiments with the immobilized peptide have given further evidence for this observation. Adsorption isotherm described by the Langmuir equation indicates that the apparent binding constant of alpha-amylase to the immobilized hexapeptide was 2.5x10(5)L/mol. Finally, high affinity and specificity of the affinity adsorbent is exemplified by the purification of alpha-amylase from crude fermentation broth of Bacillus subtilis.

Recent applications of affinity interactions in capillary electrophoresis

Systems biology depends on a comprehensive assignment and characterization of the interactions of proteins and polypeptides (functional proteomics) and of other classes of biomolecules in a given organism. High‐capacity screening methods are in place for ligand capture and interaction screening, but a detailed dynamic characterization of molecular interactions under physiological conditions in efficiently separated mixtures with minimal sample consumption is presently provided only by electrophoretic interaction analysis in capillaries, affinity CE (ACE). This has been realized in different fields of biology and analytical chemistry, and the resulting advances and uses of ACE during the last 2.5 years are covered in this review. Dealing with anything from small divalent metal ions to large supramolecular assemblies, the applications of ACE span from low‐affinity binding of broad specificity being exploited in optimizing selectivity, e.g., in enantiomer analysis to miniaturized affinity technologies, e.g., for fast processing immunoassay. Also, approaches that provide detailed quantitative characterization of analyte–ligand interaction for drug, immunoassay, and aptamer development are increasingly important, but various approaches to ACE are more and more generally applied in biological research. In addition, the present overview emphasizes that distinct challenges regarding sensitivity, parallel processing, information‐rich detection, interfacing with MS, analyte recovery, and preparative capabilities remain. This will be addressed by future technological improvements that will ensure continuing new applications of ACE in the years to come.

Immobilised peptide displaying phages as affinity ligands

An affinity purification procedure for the direct purification of lactoferrin from defatted (skimmed) milk has been developed. The procedure is based on using selected phage clones expressing a peptide with high binding affinity for lactoferrin which were covalently coupled to macroporous poly(dimethylacrylamide) monolithic column. Large pore size (10-100 microm) of macroporous poly(dimethylacrylamide) makes it possible to couple long (1 microm) phage particles as ligands without any risk of blocking the monolithic column. Bound lactoferrin was eluted using 1M NaCl with a purity of >95%. The technique presents a good alternative to conventional immunoaffinity chromatography for purification of a protein of interest from complex samples due to (i) the robustness of the system in terms of recovery and ligand leakage and (ii) economical aspect in terms of low ligand cost.

Affinity chromatography matures as bioinformatic and combinatorial tools develop

Affinity chromatography has the reputation of a more expensive and less robust than other types of liquid chromatography. Furthermore, the technique is considered to stand a modest chance of large-scale purification of proteinaceous pharmaceuticals. This perception is changing because of the pressure for quality protein therapeutics, and the realization that higher returns can be expected when ensuring fewer purification steps and increased product recovery. These developments necessitated a rethinking of the protein purification processes and restored the interest for affinity chromatography. This liquid chromatography technique is designed to offer high specificity, being able to safely guide protein manufactures to successfully cope with the aforementioned challenges. Affinity ligands are distinguished into synthetic and biological. These can be generated by rational design or selected from ligand libraries. Synthetic ligands are generated by three methods. The rational method features the functional approach and the structural template approach. The combinatorial method relies on the selection of ligands from a library of synthetic ligands synthesized randomly. The combined method employs both methods, that is, the ligand is selected from an intentionally biased library based on a rationally designed ligand. Biological ligands are selected by employing high-throughput biological techniques, e.g. phage- and ribosome-display for peptide and microprotein ligands, in addition to SELEX for oligonucleotide ligands. Synthetic mimodyes and chimaeric dye-ligands are usually designed by rational approaches and comprise a chloro-triazinlyl scaffold. The latter substituted with various amino acids, carbocyclic, and heterocyclic groups, generates libraries from which synthetic ligands can be selected. A 'lead' compound may help to generating a 'focused' or 'biased' library. This can be designed by various approaches, e.g.: (i) using a natural ligand-protein complex as a template; (ii) applying the principle of complementarity to exposed residues of the protein structure; and (iii) mimicking directly a natural biological recognition interaction. Affinity ligands, based on the peptide structure, can be peptides, peptide-mimetic derivatives (<30 monomers) and microproteins (e.g. 25-200 monomers). Microprotein ligands are selected from biological libraries constructed of variegated protein domains, e.g. minibody, Kunitz, tendamist, cellulose-binding domain, scFv, Cytb562, zinc-finger, SpA-analogue (Z-domain).

Comparison of modified supports on the base of glycoprotein interaction studies and of adsorption investigations

The features of matrices, suitable for affinity chromatography, have been extensively investigated and got subject for several reviews. But these investigations show, that there is still a lack in adsorbent characterization and a demand of comparative investigations of adsorbents, based on different materials with a range of different surface functionalities. In this work the performance of self-prepared silica and cellulose-based adsorbents were compared with commercially available polymeric supports. A model system was chosen comprising the lectins concanavalin A (ConA) and wheat germ agglutinin (WGA), which were covalently attached to the support matrices, combining the selectivity of the lectin-sugar interaction with the chemical and mechanical properties of the support that influence the efficacy of the prepared adsorbent. The verification of the different supports provides information about tayloring carbohydrate specific lectin adsorbents. The characterization outlines the main features of the different adsorbents and takes into account the properties of the pure supports. It encompasses immobilization kinetics and isotherms as well as the description of the binding capacity of the adsorbents by depicting adsorption isotherms. The separation performances were also investigated in terms of glycoprotein purification factors and recoveries. Further, detailed information about binding of GOD to immobilized ConA are obtained.

Probing affinity via capillary electrophoresis: advances in 2003–2004

This review addresses recent advances in capillary electrophoresis of biological-based molecular interaction from a broader perspective, based on applications reported during the period 2003-2004. These capillary electrophoresis-based studies of molecular interactions include affinity capillary electrophoresis, electrokinetic chromatography, and free zone electrophoresis. The review is written as a general synopsis of applications and does not cover the theory or protocol involved in the implementation of the analyses.

A novel matrix for high performance affinity chromatography and its application in the purification of antithrombin III

Viscose fiber, a regenerated cellulose, was evaluated for using as a novel matrix for high performance affinity chromatography. With a one-step activation with epichlorohydrin, heparin can be readily covalently attached to the matrix. This heparin-viscose fiber material was used for purifying antithrombin III (AT III) from human plasma. The purity of the AT III from this one-step purification is 93% as measured by SDS-PAGE and the protein recovery yield is about 90%. This column is highly specific as described by the dissociation constant of the complex of immobilized heparin and AT III, which was 2.83 x 10(-5)mol/L. And more important, this viscose fiber material demonstrated its excellent mechanical property that allows the flow rate to reach up to 900 cm/h or more.

Screening of inhibitors for influenza A virus using high-performance affinity chromatography and combinatorial peptide libraries

The affinity inhibitor of fusion peptide of influenza A virus has been studied using a combination of high-performance affinity chromatography (HPAC) and combinatorial peptide libraries. Fusion peptide (FP) (1-11) of influenza A virus was used as the affinity ligand and immobilized onto the poly(glycidyl methacrylate) (PGMA) beads. Positional scanning peptide libraries based on antisense peptide strategy and extended peptide libraries were designed and synthesized. The screening was carried out at acidic pH (5.5) in order to imitate the environment of virus fusion. A hendecapeptide FHRKKGRGKHK was identified to have a strong affinity to the FP (1-11). The dissociation constant of the complex of the hendecapeptide and the FP (1-11) is 3.10 x 10(-6) mol l(-1) in a physiological buffer condition. The polypeptide has a fairly inhibitory effect on three different strains of influenza A virus H1N1 subtype.

Interaction-Controlled HPLC for Block Copolymer Analysis and Separation

An interaction-controlled HPLC technique has been developed to analyze homopolymer precursors in block copolymer systems that are not easily identified by size exclusion chromatography (SEC) and to obtain block copolymers that are homopolymer-free and compositionally narrower than the as-synthesized ones. We demonstrate that a "single peak" in SEC does not necessarily mean that the block copolymers are free of homopolymers (due to limitations in the SEC analysis of block copolymers) and propose to employ the interaction-controlled HPLC strategy for rigorous analysis and purification of block copolymers in terms of their chemical heterogeneity.