PEG Size Research Articles

Polymeric Micelles: Nanocarriers for Cancer-Targeted Drug Delivery

Polymeric micelles represent an effective delivery system for poorly water-soluble anticancer drugs. With small size (10-100nm) and hydrophilic shell of PEG, polymeric micelles exhibit prolonged circulation time in the blood and enhanced tumor accumulation. In this review, the importance of rational design was highlighted by summarizing the recent progress on the development of micellar formulations. Emphasis is placed on the new strategies to enhance the drug/carrier interaction for improved drug-loading capacity. In addition, the micelle-forming drug-polymer conjugates are also discussed which have both drug-loading function and antitumor activity.

PEG-stearate coated solid lipid nanoparticles as levothyroxine carriers for oral administration

In this study, poly ethylene glycol 100 stearate (PEG 100-S) was used to prepare coated solid lipid nanoparticles with loading levothyroxine sodium (levo-loaded PEG 100-S-coated SLNs) by microemulsification technique. Evaluation of the release kinetic of prepared colloidal carriers was conducted. The particle size and zeta potential of levo-loaded PEG 100-S-coated SLNs have been measured to be 187.5 nm and −23.0 mV, respectively, using photon correlation spectroscopy (PCS). Drug entrapment efficiency (EE) was calculated to be 99 %. Differential scanning calorimetry indicated that the majority of drug loaded in PEG 100-S-coated SLNs were in amorphous state which could be considered desirable for drug delivery. The purpose of this study was to develop a new nanoparticle system, consisting lipid nanoparticles coated with PEG 100-S. The modification procedure led to a reduction in the zeta potential values, varying from −40.0 to −23.0 mV for the uncoated and PEG-coated SLNs, respectively. Stability results of the nanoparticles in gastric and intestinal media show that the low pH of the gastric medium is responsible for the critical aggregation and degradation of the uncoated lipid nanoparticles. PEG 100-S-coated SLNs were more stable due to their polymer coating layer which prevented aggregation of SLNs. Consequently, it is possible that the PEG surrounds the particles reducing the attachment of enzymes and further degradation of the triglyceride cores. Shape and surface morphology of particles were determined by transition electron microscopy and scanning electron microscopy that revealed spherical shape of nanoparticles. In vitro drug release of PEG 100-S-coated SLNs was characterized using diffusion cell which showed a controlled release for drug.

PEGylation kinetics of recombinant hirudin and its application for the production of PEGylated HV2 species

A critical challenge of PEGylation is the production of the desired PEGylated protein form at a high yield. In this study, a kinetic model was constructed successfully to describe the PEGylation reaction of recombinant hirudin variant-2 (HV2) with monomethoxy-PEG-succinimidyl carbonate (mPEG-SC) by fitting the experimental data. Moreover, PEGylation reaction conditions were investigated using the established model and the corresponding experiments to determine the optimal condition to achieve the mono-PEG-HV2 at the desired yield. The model predictions agreed well with the experimental data. Several important process parameters (maximum theoretical yield of mono-PEG-HV2 (ymax), critical PEG/HV2 molar ratio (mcrit) and reaction time to achieve ymax (tmax)) and their mathematical equations were obtained to determine the optimum reaction conditions. Among reaction conditions affecting the PEGylation rates, pH and temperature displayed little effect on ymax, but ymax increased as PEG size increased. Optimal reaction condition to produce mono-PEG-HV2 was as follows: pH and temperature could vary in a certain range; whereas PEG/HV2 molar ratio should be slightly greater than mcrit and the reaction should be stopped at tmax. The results of this study indicate that the proposed reaction kinetic model can provide a possible mechanism interpretation for real PEGylation reactions and optimize efficiently the PEGylation step.

Different Insight into Amphiphilic PEG-PLA Copolymers: Influence of Macromolecular Architecture on the Micelle Formation and Cellular Uptake

One constrain in the use of micellar carriers as drug delivery systems (DDSs) is their low stability in aqueous solution. In this study "tree-shaped" copolymers of general formula mPEG-(PLA)n (n = 1, 2 or 4; mPEG = poly(ethylene glycol) monomethylether 2K or 5K Da; PLA = atactic or isotactic poly(lactide)) were synthesized to evaluate the architecture and chemical composition effect on the micelles formation and stability. Copolymers with mPEG/PLA ratio of about 1:1 wt/wt were obtained using a "core-first" synthetic route. Dynamic Light Scattering (DLS), Field Emission Scanning Electron Microscopy (FESEM), and Zeta Potential measurements showed that mPEG2K-(PD,LLA)2 copolymer, characterized by mPEG chain of 2000 Da and two blocks of atactic PLA, was able to form monodisperse and stable micelles. To analyze the interaction among micelles and tumor cells, FITC conjugated mPEG-(PLA)n were synthesized. The derived micelles were tested on two, histological different, tumor cell lines: HEK293t and HeLa cells. Fluorescence Activated Cells Sorter (FACS) analysis showed that the FITC conjugated mPEG2K-(PD,LLA)2 copolymer stain tumor cells with high efficiency. Our data demonstrate that both PEG size and PLA structure control the biological interaction between the micelles and biological systems. Moreover, using confocal microscopy analysis, the staining of tumor cells obtained after incubation with mPEG2K-(PD,LLA)2 was shown to be localized inside the tumor cells. Indeed, the mPEG2K-(PD,LLA)2 paclitaxel-loaded micelles mediate a potent antitumor cytotoxicity effect.

Human Ribonuclease with a Pendant Poly(Ethylene Glycol) Inhibits Tumor Growth in Mice

Human pancreatic ribonuclease (RNase 1) is a small secretory protein that catalyzes the cleavage of RNA. This highly cationic enzyme can enter human cells spontaneously but is removed rapidly from circulation by glomerular filtration. Here, this shortcoming is addressed by attaching a poly(ethylene glycol) (PEG) moiety to RNase 1. The pendant has no effect on ribonucleolytic activity but does increase persistence in circulation. The RNase 1-CPEG conjugates inhibit the growth of tumors in a xenograft mouse model of human lung cancer. Both retention in circulation and tumor growth inhibition correlate with the size of the pendant PEG. A weekly dose of the 60-kDa conjugate at 1 μmol/kg inhibited nearly all tumor growth without affecting body weight. Its molecular efficacy is ~5000-fold greater than that of erlotinib, which is a small molecule in clinical use for the treatment of lung cancer. These data demonstrate that the addition of a PEG moiety can enhance the in vivo efficacy of human proteins that act within cells and highlight a simple means of converting an endogenous human enzyme into a cytotoxin with potential clinical utility.

Effect of preparation parameters on the catalytic performance of mesoporous NiO for the oxidative dehydrogenation of propane to propylene

Mesoporous NiO was prepared by the template synthesis method, using polyethylene glycol as a template, Ni(NO3)2·6H2O and Ni(CH3COO)2·4H2O as a nickel source. The major factors that influenced the formation of mesoporous NiO, such as nickel source, calcining temperature and molecular size of PEG, were estimated. As a result, the nickel source and calcination process could determine the crystallizability and organization of mesostructured NiO particles. The molecular size of PEG surfactant is not only relevant to the pore size of mesoporous NiO, but also of effect on the selectivity to propylene. The fine mesoporous NiO could be formed by using Ni(CH3COO)2·4H2O as nickel source and PEG400 as template, and then being calcined at 400–600 °C. The mesoporous NiO catalysts exhibit significant catalytic activities for the oxidative dehydrogenation of propane. The propylene yield of 14 % was obtained at propane conversion of 27 % at 350 °C. Furthermore, the selectivity to propylene can be maintained around 50 % even at 600 °C, indicating the high catalytic stabilities of mesoporous NiO catalysts in the present work. We proposed that a non-stoichiometric oxygen species on the surface is the catalytic active site and the mesoporous structure is the key factor for the high catalytic stabilities in the light of the characteristic results of mesoporous NiO catalysts.

Development of Copper-Catalyzed Azide–Alkyne Cycloaddition for Increased in Vivo Efficacy of Interferon β-1b by Site-Specific PEGylation

The development of protein conjugate therapeutics requires control over the site of modification to allow for reproducible generation of a product with the desired potency, pharmacokinetic, and safety profile. Placement of a single nonnatural amino acid at the desired modification site of a recombinant protein, followed by a bioorthogonal reaction, can provide complete control. To this end, we describe the development of copper-catalyzed azide-alkyne cycloaddition (CuAAC, a click chemistry reaction) for site-specific PEGylation of interferon β-1b (IFNb) containing azidohomoalanine (Aha) at the N-terminus. Reaction conditions were optimized using various propargyl-activated PEGs, tris(benzyltriazolylmethyl)amine (TBTA), copper sulfate, and dithiothreitol (DTT) in the presence of SDS. The requirement for air in order to advance the redox potential of the reaction was investigated. The addition of unreactive PEG diol reduced the required molar ratio to 2:1 PEG-alkyne to IFNb. The resultant method produced high conversion of Aha-containing IFNb to the single desired product. PEG-IFNbs with 10, 20, 30, and 40 kDa linear or 40 kDa branched PEGs were produced with these methods and compared. Increasing PEG size yielded decreasing in vitro antiviral activities along with concomitant increases in elimination half-life, AUC, and bioavailability when administered in rats or monkeys. A Daudi tumor xenograft model provided comparative evaluation of these combined effects, wherein a 40 kDa branched PEG-IFNb was much more effective than conjugates with smaller PEGs or unPEGylated IFNb at preventing tumor growth in spite of dosing with fewer units and lesser frequency. The results demonstrate the capability of site-specific nonnatural amino acid incorporation to generate novel biomolecule conjugates with increased in vivo efficacy.

PEGylation of a proprotein convertase peptide inhibitor for vaginal route of drug delivery: In vitro bioactivity, stability and in vivo pharmacokinetics

Uterine proprotein convertase (PC) 6 is critical for embryo implantation in mice and women. It is also one of the PC family members that play a vital role in HIV infectivity. We hypothesized that inhibiting PC6 in the female reproductive tract (vagina, cervix and uterus), may protect women from both pregnancy and HIV infection. One key requirement to prove this concept in an animal model is a vaginally deliverable PC6 inhibitor. Nona-d-arginine (Poly R) is a potent peptide PC inhibitor and is able to inhibit HIV in cell culture. We modified Poly R by PEGylation with different strategies and determined their biochemical properties in vitro and in vivo. PEGylation at the C-terminus, regardless of the PEG size (30kDa or 1239Da) did not compromise the inhibitory potency of Poly R. In contrast, PEGylation at both termini (1239Da) dramatically reduced its inhibitory activity. Poly R and C-PEGylated Poly Rs also showed equal potency in inhibiting a PC6-dependent cellular process critical for embryo implantation. Poly R and the equipotent C-PEGylated Poly Rs were further tested for their serum stability in vitro and pharmacokinetics in vivo following vaginal administration in mice. All Poly Rs were equally stable in mouse serum in vitro for 24h; C-PEGylated Poly Rs showed enhanced vaginal absorption and penetration across the vaginal mucosa/epithelium. This is the first report that C-terminal PEGylation significantly enhances the therapeutic properties of Poly R for vaginal drug delivery. Our findings also provide important insights into future design of Poly R derivatives.

Synthesis and characterization of a novel poly(ester-urethane) containing short lactate sequences and PEG moieties

A novel poly(ester-urethane) with tailor-made structure was prepared by using lactic acid (LA) as starting material through a combination of two facile common reactions. First, a diol was prepared via the esterification between LA and poly(ethylene glycol) (PEG) with low molecular weight. Subsequently, the poly(ester-urethane) was synthesized through the addition polymerization of the LA-based diol and toluene 2,4-diisocyanate with 1,4-butanediol as chain extender. The structure, morphology, and properties of intermediate and the poly(ester-urethane) were analyzed with Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, gel permeation chromatography (GPC), X-ray diffraction, differential scanning calorimetry, polarizing optical microscopy, and thermogravimetric analysis. The results indicated that the intermediate was a diol of conjugating quite short lactate sequences with PEG oligomer, and the structure of the poly(ester-urethane) was as expected. The thermal transition, thermal decomposition temperature, and crystallinity of the polymer samples depended on the molecular size of PEG. In vitro degradation property of the poly(ester-urethane) also relied on the molecular weight of PEG. The weight loss percentages varied from 11 to 36% after 12-days immersing in phosphate-buffer saline at 37°C. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Microcalorimetric Study of the Adsorption of PEGylated Lysozyme and PEG on a Mildly Hydrophobic Resin: Influence of Ammonium Sulfate

Adsorption of native as well as mono-, di-, and tri-PEGylated lysozyme on Toyopearl PPG-600M, a mildly hydrophobic resin is studied by isothermal titration calorimetry and by independent adsorption equilibrium measurements in sodium phosphate buffer at pH 7.0 and 25 °C. For PEGylation two different PEG sizes are used (5 and 10 kDa) which leads to six different forms of PEGylated lysozyme all of which are systematically studied. Additionally, the adsorption of five pure PEGs is explored. The ammonium sulfate concentration is varied from 600 to 1200 mM. The molar enthalpy of adsorption Δh(p)(ads) is determined from the calorimetric and the adsorption equilibrium data. It is found to be endothermic in all experiments. The comparison of the adsorption of different PEGylated forms shows that the adsorption of PEGylated lysozyme is driven by the adsorption of the PEG chain. The results provide insight into the adsorption mechanisms of polymer-modified proteins on hydrophobic chromatographic resins.

PLA–PEG copolymers micronization by supercritical assisted atomization

Supercritical assisted atomization (SAA) under reduced pressure was used to produce microparticles with defined spherical morphology, controlled particle size and distribution of PEG–PLA copolymers. These compounds, because of their low glass transition temperature are difficult to process using other techniques.Different architectures were tested to optimize PEG–PLA copolymers from the point of view of SAA processability and their pharmaceutical application. Synthesis and micronization of copolymers with relative content of PEG:PLA of 1:4 (w/w) and 1:8 (w/w) and with atactic or stereoregular (isotactic) PLA arms were performed and the architectures of linear copolymers (l, PEG(PLA)), branched of first generation (G1, PEG(PLA)2) and branched of second generation (G2, PEG(PLA)4), characterized by one, two and four PLA arms respectively, were tested.Well defined particles of the linear copolymer PEG–PLA, with isotactic PLA chain, were obtained with a mean particle size of 0.25–0.45μm, for both PEG:PLA ratios. G2 branched copolymer were successfully micronized in the case of 1:8 PEG:PLA ratio with isotactic PLA blocks and spherical particles with a mean particle size of about 0.3μm were obtained. On the contrary, the G1 copolymers with isotactic PLA arms formed coalescing microparticles when processed by SAA. Copolymers with atactic PLA arms, independently on the architecture, were not successfully processable.SAA process did not modify the structure of the starting copolymers, as shown by 1H NMR and GPC analyses. The microparticles obtained showed a lower degree of crystallinity compared to the untreated materials, as confirmed by XRPD and DSC analyses. The G2 branched 1:8 PEG:PLA copolymer, because of the structure and the size of the obtained particles, can be considered the most promising for the controlled release of a drug.

Insulin complexes with PEGylated basic oligopeptides

Biodegradable oligolysine and oligoarginine-type homopeptides functionalized with PEG of two different molecular weights interact with insulin, at physiological pH, affording complexes studied by dynamic light scattering, ζ-potential, circular dichroism, FTIR spectroscopy, and isothermal titration calorimetry (ITC). High levels of insulin complexation efficiencies (>99.5%) were determined for all derivatives. FTIR spectra suggest that the positively charged homo-oligopeptide derivatives interact with B chain C-terminus of insulin leading to the formation of nanoparticles than can be traced even at low oligopeptide/insulin molar ratios. The ITC profiles are complex, displaying significant endothermic and exothermic contributions. Oligoarginine-type derivatives exhibit the strongest interactions, while PEGylation of either oligopeptide with the high molecular weight chains significantly affects the ITC profiles and leads to larger enthalpy changes. This may be attributed to PEG-induced aggregation of insulin due to the depletion attraction effect leading to the formation of stable nanocomplexes. Stabilization of complexed insulin against enzymatic degradation by trypsin and α-chymotrypsin is observed especially for the high molecular weight PEGylated arginine-based derivative. Insulin release rates in simulated intestinal fluid are controlled by the length of PEG chains and the presence of arginine end-groups. Released insulin retains its secondary structure as established by circular dichroism spectroscopy.

Pharmacokinetic, Biodistribution, and Biophysical Profiles of TNF Nanobodies Conjugated to Linear or Branched Poly(ethylene glycol)

Covalent attachment of poly(ethylene glycol) (PEG) to therapeutic proteins has been used to prolong in vivo exposure of therapeutic proteins. We have examined pharmacokinetic, biodistribution, and biophysical profiles of three different tumor necrosis factor alpha (TNF) Nanobody-40 kDa PEG conjugates: linear 1 × 40 KDa, branched 2 × 20 kDa, and 4 × 10 kDa conjugates. In accord with earlier reports, the superior PK profile was observed for the branched versus linear PEG conjugates, while all three conjugates had similar potency in a cell-based assay. Our results also indicate that (i) a superior PK profile of branched versus linear PEGs is likely to hold across species, (ii) for a given PEG size, the extent of PEG branching affects the PK profile, and (iii) tissue penetration may differ between linear and branched PEG conjugates in a tissue-specific manner. Biophysical analysis (R(g)/R(h) ratio) demonstrated that among the three protein-PEG conjugates the linear PEG conjugate had the most extended time-average conformation and the most exposed surface charges. We hypothesized that these biophysical characteristics of the linear PEG conjugate accounts for relatively less optimal masking of sites involved in elimination of the PEGylated Nanobodies (e.g., intracellular uptake and proteolysis), leading to lower in vivo exposure compared to the branched PEG conjugates. However, additional studies are needed to test this hypothesis.

PEGylation for drug delivery to ischemic myocardium: Pharmacokinetics and cardiac distribution of poly(ethylene glycol)s in mice with normal and ischemic myocardium

PEGylation now plays an important role in drug delivery and is considered as the method of choice for improving the pharmacokinetics and stability of parenteral agents. However, its application in treating cardiac diseases is still limited. To guide the design of PEGylation for drug delivery to ischemic myocardium, the effects of the molecular weight of PEG and the myocardial ischemic conditions on PEG levels in plasma and myocardium were studied in this work following intravenous administration of fluorescein isothiocyanate-labeled 20- and 40-kDa mPEGs to mice with normal and ischemic myocardium. The results show that myocardial ischemia caused some consistent changes in pharmacokinetic parameters of mPEGs. Due to the enhanced permeability and retention (EPR) effect caused by ischemia, the distribution of 20- and 40-kDa mPEGs in ischemic hearts was approximately 1.47- and 1.92-fold higher than that in normal hearts, respectively. Under the same heart condition (either normal or ischemic), the cardiac AUC0.5–24hs of the two mPEGs were comparable, although their plasma AUCs differed by nearly 4-fold; however, a smoother cardiac level-time profile was achieved by 40-kDa mPEG. This study addressed the relative importance of the EPR effect of ischemic zones and the molecular size of PEG in cardiac drug delivery, which is believed to be helpful for macromolecular drug design.

Purification of a PEGylated single chain Fv

In this manuscript we describe the two-step purification of a mono-PEGylated anti-epidermal growth factor receptor (EGFR) single-chain Fv. A weak cation exchanger was used for capture. Elution using arginine suppressed protein aggregation and allowed a very good resolution with purity and product-recovery was above 90%. Free PEG was removed completely. The use of hydrophobic interaction chromatography (HIC) increased purity to 98%. Increasing the size of PEG from 5 to 30kDa increased retention on HIC and reduced it on cation exchangers. Bioactivity of PEGylated scFv was confirmed by 125I based cell tests. Proteins modified with 5kDa PEG showed higher bioactivity than proteins modified with larger PEGs. The combination of cation exchange and HIC provides a rational and effective basis for PEGylated scFv purification.

A General Model for Solute Effects: How to Predict the Effect of Any Solute on Any Process

Small solutes affect protein and nucleic acid processes because of favorable or unfavorable chemical interactions of the solute with the biopolymer surface exposed or buried in the process. Large solutes also exclude volume and affect processes where biopolymer molecularity and/or shape changes. Here, we develop an analysis to separate and interpret or predict excluded volume and chemical effects of a flexible coil polymer on a process. We report a study of the concentration-dependent effects of the full series from monomeric to polymeric PEG on intramolecular hairpin and intermolecular duplex formation by 12-nucleotide DNA strands. We find that chemical effects of PEG on these processes increase in proportion to the product of the amount of DNA surface exposed on melting and the amount of PEG surface that is accessible to this DNA, and these effects are completely described by two interaction terms that quantify the interactions between this DNA surface and PEG end and interior groups. We find that excluded volume effects, once separated from these chemical effects, are quantitatively described by the analytical theory of Hermans, which predicts the excluded volume between a flexible polymer and a rigid molecule. From this analysis, we show that at constant concentration of PEG monomer, increasing PEG size increases the excluded volume effect but decreases the chemical interaction effect, because in a large PEG coil a smaller fraction of the monomers are accessible to the DNA. Volume exclusion by PEG has a much larger effect on intermolecular duplex formation than on intramolecular hairpin formation.

Raising Awareness of the Myth of the “Unaffected Hand” in Childhood Hemiplegia

Background and aims: The term ‘hemiplegia’ implies a unilateral deficit, yet several studies have demonstrated abnormal limb control ipsilateral to the brain lesion. This is under-recognised by clinicians and has implications for function and therapy. We documented deficits in the “unaffected” hand in children with hemiplegia using a dexterity test developed by our group for use in children with motor disorders. Methods: Participants: 33 children (4-11y) with hemiplegia (18 male; 19 left hemiplegia); 66 age, sex and handedness matched controls. Assessment: Adapted 9-hole pegboard test (2 adjacent boards; 3 peg sizes; electronically timed). Analysis: ANOVA (between-group factors group (hemiplegia/control), age (4-5, 6-7, 8-11), sex, dominant hand) performed separately for each peg size. Results: Some hemiplegic children with radiologically confirmed unilateral lesions had prolonged pegboard completion times whereas others scored similarly to controls (Figure: filled symbols - hemiplegia). For all peg sizes, main effects of group (p< 0.001) and age (p< 0.001) were significant but sex and dominant hand were not. There was a significant interaction between group and age (p< 0.005), with smaller difference in group means in the oldest age-group. This deserves exploration with a longitudinal study. Figure Conclusion: The “unaffected” hand in children with hemiplegia is less dextrous than the dominant hand of controls. Therapy to improve function of the more-affected hand should be designed to achieve optimal outcomes bilaterally.

Aldehyde PEGylation Kinetics: A Standard Protein versus a Pharmaceutically Relevant Single Chain Variable Fragment

The mPEG-aldehyde PEGylation with two different PEG sizes and two proteins was experimentally determined with respect to yield, conversion, and selectivity. The kinetic behavior of these PEGylation reactions was simulated using a numerically solved set of differential equations. We show that the assumption of an inactivation of mPEG-aldehyde is crucial for the simulation of the overall PEGylation and that the inactivation is pH-dependent. We further demonstrate that ideal PEGylation parameters such as pH, temperature, reaction time, and protein concentration need to be chosen carefully depending on the protein and PEG size. In terms of selectivity and yield, we show that the reaction should be stopped before the highest mono-PEG concentration is reached. Moreover, room temperature and a slightly acidic pH of approximately 6 are good starting points. In conclusion, selectivity can be optimized choosing a shorter reaction time and a reduced reaction temperature.

Porphyrin-Cross-Linked Hydrogel for Fluorescence-Guided Monitoring and Surgical Resection

We demonstrate that porphyrins can be used as efficient cross-linkers to generate a new class of hydrogels with enabling optical properties. Tetracarboxylic acid porphyrins reacted with PEG diamines to form a condensation polyamide in a range of appropriate conditions, with respect to reaction time, diisopropylethylamine initiator concentration, porphyrin-to-PEG ratio, porphyrin concentration, and PEG size. The network structure of the hydrogel maintained a porphyrin spacing that prevented excessive fluorescence self-quenching despite high porphyrin density. The near-infrared properties readily enabled low background, noninvasive fluorescence monitoring of the implanted hydrogel in vivo, as well as its image-guided surgical removal in real time using a low-cost fluorescence camera prototype. Emission could be tuned by incorporating copper metalloporphyrins into the network. The approach of creating hydrogels using cross-linking porphyrin comonomers creates opportunities for new polymer designs with strong optical character.

Separation of preferential interaction and excluded volume effects on DNA duplex and hairpin stability.

Small solutes affect protein and nucleic acid processes because of favorable or unfavorable chemical interactions of the solute with the biopolymer surface exposed or buried in the process. Large solutes also exclude volume and affect processes where biopolymer molecularity and/or shape changes. Here, we develop an analysis to separate and interpret or predict excluded volume and chemical effects of a flexible coil polymer on a process. We report a study of the concentration-dependent effects of the full series from monomeric to polymeric PEG on intramolecular hairpin and intermolecular duplex formation by 12-nucleotide DNA strands. We find that chemical effects of PEG on these processes increase in proportion to the product of the amount of DNA surface exposed on melting and the amount of PEG surface that is accessible to this DNA, and these effects are completely described by two interaction terms that quantify the interactions between this DNA surface and PEG end and interior groups. We find that excluded volume effects, once separated from these chemical effects, are quantitatively described by the analytical theory of Hermans, which predicts the excluded volume between a flexible polymer and a rigid molecule. From this analysis, we show that at constant concentration of PEG monomer, increasing PEG size increases the excluded volume effect but decreases the chemical interaction effect, because in a large PEG coil a smaller fraction of the monomers are accessible to the DNA. Volume exclusion by PEG has a much larger effect on intermolecular duplex formation than on intramolecular hairpin formation.