Partition Equilibrium Constants Research Articles

Moment analysis method for determination of rate constants of solute permeation across interface of spherical molecular aggregates by means of high-performance liquid chromatography

A moment analysis method was developed for the study of solute permeation at the interface of spherical molecular aggregates. At first, new moment equations were developed for determining the partition equilibrium constant (Kp) and permeation rate constants (kin and kout) of solutes from the first absolute (μ1A) and second central (μ2C) moments of elution peaks measured by using high-performance liquid chromatography (HPLC). Then, the method was applied to the analysis of mass transfer phenomena of three solutes, i.e., hydroquinone, resorcinol, and catechol, at the interface of sodium dodecylsulfate (SDS) micelles. HPLC data were measured by using an ODS column and an aqueous phosphate buffer solution (pH = 7.0) as the mobile phase solvent. Pulse response experiments were conducted while changing SDS concentration (5 - 20 mmol dm−3) in the mobile phase under the conditions that the surface of ODS stationary phase was dynamically coated by SDS monomers. In order to demonstrate the effectiveness of the moment analysis method using HPLC, the values of Kp, kin, and kout were determined for the three solutes as 35 - 69, 2.4 × 10−8 - 1.4 × 10−6 m s−1, and 7.0 × 10−10 - 2.1 × 10−8 m s−1, respectively. Their values increase with an increase in the hydrophobicity of the solutes. The method has some advantages for the study of interfacial solute permeation of molecular aggregates. For example, neither immobilization nor chemical modification of both solute molecules and molecular aggregates is required when elution peaks are measured by using HPLC. Interfacial solute permeation takes place in the mobile phase without any chemical reaction or physical action on molecular aggregates. The values of Kp, kin, and kout were analytically determined from those of μ1A and μ2C by using the moment equations. The results of this study must contribute to the dissemination of an opportunity for studying the interfacial solute permeation of molecular aggregates to many researchers because of extremely high versatility of HPLC.

Moment Analysis of Solute Permeation Kinetics at an Interface of Mixed Micelles of Anionic and Nonionic Surfactants

Abstract Solubilization phenomena of neutral solutes into mixed micelles of anionic and nonionic surfactants were studied by means of micellar electrokinetic chromatography (MEKC). MEKC experiments were conducted by using mixed micelles consisting of sodium dodecylsulfate (SDS) and polyoxyethylene sorbitan monolaurate (Tween 20) or monostearate (Tween 60) as pseudo-stationary phases while changing the concentration of SDS-Tween mixed micelles and the molar fraction of Tween 20 or 60 in mixed micelles. Elution peak profiles measured by MEKC were analyzed on the basis of the moment theory to determine the solute partition equilibrium constant (Kp) and the rate constants of solute permeation at the interface of mixed micelles (kin and kout). It seems that the values of Kp, kin, and kout are increased by adding Tween 20 or 60 and that the influence of the addition of Tween 60 on their values is more remarkable than that of Tween 20. It was demonstrated that moment analysis of MEKC data is effective for studying solubilization phenomena of surfactant micelles under the conditions that both immobilization and chemical modification (i.e., fluorescence labeling) of solute and micelles are not required.

A study on the enrichment mechanism of three nitrophenol isomers in environmental water samples by charge transfer supramolecular-mediated hollow fiber liquid-phase microextraction.

To explore the mechanism of extraction and enrichment of three nitrophenol isomers by charge-transfer supramolecular synergistic three-phase microextraction system, a charge transfer supramolecular-mediated hollow fiber liquid-phase microextraction (CTSM-HF-LPME) combined with high-performance liquid chromatography-ultraviolet detector (HPLC-UV) method was established for the determination of real environmental water samples. In this study, the three nitrophenols (NPs) formed charge-transfer supramolecules with electron-rich hollow fibers, which promoted the transport of NPs in the three-phase extraction system and greatly increased the EFs of NPs. The relationships between the EFs of NPs and their solubility, pKa, apparent partition coefficient, equilibrium constant, and structural property parameters were investigated and discussed. At the same time, most of factors affecting the EFs of NPs were investigated and optimized, such as the type of extraction solvent, pH value of sample phase and acceptor phase, extraction time, and stirring speed. Under optimal conditions, the EFs of o-nitrophenol, m-nitrophenol, and p-nitrophenol were 163, 145, and 87, respectively. With good linearity in the range of 5 × 10-7 ~ 1µg/mL, and the limit of detection of 0.1pg/mL, the relative standard deviations of the method precision were lower than 7.4%, and the average recoveries were between 98.6 and 106.4%. This method had good selectivity and sensitivity, satisfactory precision, and accuracy and had been successfully applied to the trace detection of real water samples.

Transient Response of a Continuous Glucose Monitor

Blood glucose is indirectly measured with a subcutaneous continuous glucose monitor (CGM). Glucose within the interstitial space is converted into hydrogen peroxide via an enzymatic reaction with glucose oxidase. Electrochemical oxidation of the hydrogen peroxide produces a faradaic current proportional to the hydrogen peroxide concentration. In vitro CGM experiments during transient operation demonstrate a range of time constants in the current response. A transient model adaptation of the steady model from Gao et al. was prepared. [1] The transient responses to potential and glucose steps were investigated experimentally and numerically.The transient current response of an electrochemical system with coupled homogeneous and heterogeneous reactions yields time constants dependent on the charging of the electrode, rates of homogeneous reactions, and mass transfer of the participating species. For nonlinear homogeneous reactions involving species of varying diffusion coefficients, analytic expression of these time constants is nontrivial and more readily obtained numerically.A transient model was discretized in space and time with finite differences and the Crank-Nicolson method. Numerical solutions of the model were obtained with Newman’s BAND algorithm. [2] The model demonstrates the charging current, faradaic current, and concentration profile responses within the sensor. When the model is perturbed with a potential step, the initial response is characterized by a charging current; whereas, larger time constants are due to both the mass transfer to the electrode through diffusion and homogeneous reactions.Steady, transient, and impedance responses of the CGM were experimentally obtained. Steady-state current was measured as a function of glucose concentration which provided an estimate for the permeability of glucose in the sensor. Current response to a glucose step was obtained, and the short-time behavior was fit with a single time constant. An equivalent circuit, fabricated based on the impedance spectra, demonstrated a potential step response similar to the sensor. The influence of dissolved oxygen concentration on the transient response was also investigated.The model was fit to the experimental current responses by adjusting diffusion and partition coefficients, rate and equilibrium constants, and electrolyte resistance and capacitance. The numerical model shows the short time constant is due to charging of the sensor, and the larger time constants are due to diffusion and enzymatic reactions. The large time constants of the current response are significantly larger than those predicted by a simple Gerischer model.[3,4] The presence of both diffusing and non-diffusing species involved in the homogeneous reactions may give rise to current instabilities and time constants.References Gao, M., Harding, M., Kong, R., & Orazem, M. (2018). Mathematical Model for the Electrochemical Impedance Response of a Continuous Glucose Monitor. Electrochimica Acta, 275. 119-132.Newman, J., & Thomas-Alyea, E. (2004). Electrochemical Systems (3rd ed.). NJ: John Wiley & Sons, Hoboken.Gerischer, H. (1951). Wechselstrompolarisation Von Elektroden Mit Einem Potentialbestimenden Schritt Beim Gleichgewichtspotential. Zeitschrift fur Physikalische Chemie, 198. 286-313.Orazem, M., & Tribollet, B. (2017). Electrochemical Impedance Spectroscopy. Hoboken, NJ: John Wiley & Sons. AcknowledgementThe support of Medtronic Diabetes (Northridge, CA), Mike Miller, program monitor, is gratefully acknowledged.

Kinetic study on solute permeation at the interface of molecular aggregates by partial filling capillary electrophoresis.

Moment analysis method using partial filling CE was developed for the kinetic study on solute permeation at the interface of spherical molecular aggregates. Moment equations for partial filling CE were developed by classifying CE systems into five categories according to the migration velocities of solute and molecular aggregate. The method was applied to the study on the dissolution of electrically neutral solutes into SDS micelles. Elution peaks were measured by partial filling CE while changing the concentration of SDS and the filling ratio of SDS micellar zone to the capillary (ϕM ). Partition equilibrium constants (Kp ) and rate constants of interfacial solute permeation of SDS micelles (kin and kout ) were determined from the first absolute and second central moments of the elution peaks by using the moment equations. Their values were comparable irrespective of ϕM and were almost the same as those previously measured by complete filling CE. The positive correlation of Kp with the hydrophobicity of the solutes was explained in terms of the change in kin and kout . It was demonstrated that the moment analysis method using partial filling CE is effective for studying solute permeation kinetics at the interface of spherical molecular aggregates.

Thiolate end-group regulates ligand arrangement, hydration and affinity for small compounds in monolayer-protected gold nanoparticles

The ability to control the properties of monolayer protected gold nanoparticles (MPNPs) discloses unrevealed features stemming from collective properties of the ligands forming the monolayer and presents opportunities to design new materials. To date, the influence of ligand end-group size and capacity to form hydrogen bonds on structure and hydration of small MPNPs (<5 nm) has been poorly studied. Here, we show that both features determine ligands order, solvent accessibility, capacity to host hydrophobic compounds and interfacial properties of MPNPs. The polarity perceived by a radical probe and its binding constant with the monolayer investigated by electron spin resonance is rationalized by molecular dynamics simulations, which suggest that larger space-filling groups – trimethylammonium, zwitterionic and short polyethylene glycol – favor a radial organization of the thiolates, whereas smaller groups – as sulfonate – promote the formation of bundles. Zwitterionic ligands create a surface network of hydrogen bonds, which affects nanoparticle hydrophobicity and maximize the partition equilibrium constant of the probe. This study discloses the role of the chemistry of the end-group on monolayer features with effects that span from molecular- to nano-scale and opens the door to a shift in the conception of new MPNPs exploiting the end-group as a novel design motif.

Calculation of sulfur removal in ladle furnace unit by means of ionic theory of slags

This article describes issues of sulfur removal in ladle furnace unit. First of all, metal desulfurization in ladle steel treatment units is achieved due to transition of sulfur to the slag phase. Coefficient of partition of sulfur between metal and slag is affected by sulfide capacity of slag, coefficient of activity of sulfur in the metal, oxidation potential of medium and reaction equilibrium constant of partition of sulfur between metal and slag. Temperature of liquid state in the ladle has significant impact on sulfide capacity of slag. Proposed calculation procedure based on provisions of ionic structure of slags allows evaluating a concentration of sulfur in steel on the basis of determination of coefficient of its partition between metal and slag. Optical basicity is suggested as criterion of refining property of slag, it has been shown that the amphoteric oxide Al2O3 is essential to calculation of this indicator. Its impact on sulfide capacity of slag is detected.

Smart drug carrier based on polyurethane material for enhanced and controlled DOX release triggered by redox stimulus

A series of amphiphilic polymer mPEG-PUSS-mPEG were developed by a combination of ring opening polymerization (ROP) and polyaddition reaction and its self-assembled micelles were developed for hydrophobic anticancer drugs delivery. Polymeric critical micellar concentration (CMC) values in aqueous solution were about 2.8–5.5 mg/L. And the partition equilibrium constant (Kv) of pyrene in micellar solutions ranged from 1.52 × 105 to 2.20 × 105. The average sizes of the self-assembled blank and DOX-loaded micelles were 160–180 nm determined by dynamic light scattering (DLS). The morphology of the DOX-loaded micelles was spherical by transmission electron microscopy (TEM) and scanning electron microscopy (SEM).The in vitro drug release behaviors of DOX and PTX from mPEG-PUSS-mPEG micelles were investigated at different simulated conditions. We found that the PTX release was significantly accelerated by redox stimuli compared with DOX-loaded reduction-sensitive PU micelles. The change of the size of this system under different conditions was further evaluated by DLS. DOX-loaded mPEG-PUSS-mPEG micelles in 50% fetal bovine serum (FBS) were evaluated the hemocompatibility. In addition, the self-assembly process of polymers mPEG-PUSS-mPEG in aqueous solution for micellar formation was also investigated by means of dissipative particle dynamics (DPD) simulations.AndCCK-8 assays revealed that the mPEG-PUSS-mPEG materials had low toxicity, but the DOX-loaded micelles showed a high cytotoxicity against HepG2 tumor cells. All results demonstrate that mPEG-PUSS-mPEG self-assembled micelles are a very promising for hydrophobic anticancer drugs delivery.

Moment theory for the analytical determination of rate constants for solute permeation at the interface of spherical molecular aggregates.

Moment equations were developed on the basis of the Einstein equation for diffusion and the random walk model to analytically determine the rate constant for the interfacial solute permeation from a bulk solvent into molecular aggregates (kin ) and the inverse rate constant from the molecular aggregates to the bulk solvent (kout ). The moment equations were in good agreement with those derived in a different manner. To demonstrate their effectiveness in one concrete example, the moment equations were used to analytically determine the values of kin and kout of three electrically neutral solutes, i.e. resorcinol, phenol, and nitrobenzene, from the first absolute (μ1A ) and second central (μ2C ) moments of their elution peaks, as measured by electrokinetic chromatography (EKC), in which the sodium dodecyl sulfate (SDS) micelles were used as a pseudostationary phase. The values of kin and kout should be determined with no chemical modifications and no physical action with the molecular aggregates because they are dynamic systems formed through weak interactions between the components. The moment analysis of the elution peak profiles measured by EKC is effective to unambiguously determine kin , kout , and the partition equilibrium constant (kin /kout ) under appropriate experimental conditions.

Enthalpy-driven micellization of oligocarbonate-fluorene end-functionalized Poly(ethylene glycol)

A fluorescent pyrene probe method was applied to measure the critical micelle concentration (CMC) of oligocarbonate-fluorene end-functionalized poly(ethylene glycol) (FmE445Fm) triblock copolymers in water. The CMC decreases with lower temperature and higher values of the hydrophobic block length, m. When analyzed by a closed-assembly micelle model, the estimated energetic parameters find a negative ΔH°mic and small positive ΔS°mic suggestive of enthalpy-driven micellization, which differs from entropy-driven oxyethylene/oxybutylene triblock copolymers and octaethylene glycol-n-alkyl ethers. The enthalpy-driven micellization of FmE445Fm may result from the limited hydration of individual hydrophobic F blocks that leads to few hydrogen-bonded waters released during F block association. The π-π stacking oligocarbonate-fluorene system also observed enthalpy-entropy compensation when compared to a series of published data on diblock and triblock copolymer systems. An anomalously low partition equilibrium constant for m = 15.3 implies a tightly-packed core that excludes pyrene intercalation into the fluorene core. This is discussed along with the possible limited applicability to estimate the CMC and potential model drug molecule insertions into the intercalated micelle core.

High temperature partition function – a key role of ro-vibrational coupling and inflection points

ABSTRACTA breakdown of the normal modes (harmonic) approximation for partition function and equilibrium constant that occur with increasing temperature is reported. That breakdown happens when thermal energy of the molecule reaches regions of potential energy curve/surface where it inflects and , as a result, it cannot be approximated with the harmonic potential. This inflection point effect is shown now on the example of H+H+2 H++H2 reaction. A key role of ro-vibrational coupling is revealed. Additionally, equilibrium constant of H+H+2 H++H2 reaction is calculated with a new methodology composed of TI/PIMC method combined with rigid rotor harmonic approximation. Finally, breakdown of harmonic approximation is shown for two-dimensional model.

Micellar liquid chromatography of terephthalic acid impurities

The production of terephthalic acid (TPA) by oxidation of p-xylene is an important industrial process because high purity TPA is required for the synthesis of polyethylene terephthalate, the primary polymer used to make plastic beverage bottles. Few separation methods have been published that aim to separate TPA from eight major aromatic acid impurities. This work describes a “green” micellar liquid chromatography (MLC) method using a C18 column (100×2.1mm, 3.5μm), an acidic 1% sodium dodecyl sulfate (SDS) mobile phase, and a simple step flow rate gradient to separate TPA and eight impurities in less than 20min. The resulting chromatogram shows excellent peak shape and baseline resolution of all nine acids, in which there are two sets of isomers. Partition coefficients and equilibrium constants have been calculated for the two sets of isomers by plotting the reciprocal of the retention factor versus micelle concentration. Quantitation of the nine analytes in an actual industrial TPA sample is possible. Limits of detection for all nine acids range from 0.180 to 1.53ppm (2.16–19.3 pmoles) and limits of quantitation range from 0.549 to 3.45ppm (6.48–43.0 pmoles). In addition, the method was tested on two other reversed phase C18 columns of similar dimensions and particle diameter from different companies. Neither column showed quite the same peak resolution as the original column, however slight modifications to the mobile phase could improve the separation.

Physico-chemical profiling of semisynthetic opioids

Species-specific acid–base and partition equilibrium constants were experimentally determined for the therapeutically important semisynthetic opioid receptor agonist hydromorphone, dihydromorphine, and mixed agonist-antagonist nalorphine and nalbuphine. The acid–base microequilibria were characterized by combining pH-potentiometry and deductive methods using synthesized auxiliary compounds. Independent of the pH, there are approximately 4.8 times as many zwitterionic microspecies than non-charged ones in nalbuphine solutions, while for nalorphine it is the non-charged form that predominates by the same ratio. The non-charged microspecies is the dominant one also in the case of hydromorphone, although its concentration exceeds only 1.3 times that of its zwitterionic protonation isomer. The pH-independent partition coefficients of the individual microspecies were determined by a combination of experimentally measured, pH-dependent, conditional distribution constants and a custom-tailored evaluation method, using highly similar auxiliary compounds. The pH-independent contribution of the zwitterionic microspecies to the distribution constant is 1380, 1070, 3160 and 72,440 times smaller than that of the inherently more lipophilic non-charged one for hydromorphone, dihydromorphine, nalbuphine and nalorphine, respectively.

Partition functions and equilibrium constants for diatomic molecules and atoms of astrophysical interest

Partition functions and dissociation equilibrium constants are presented for 291 diatomic molecules for temperatures in the range from near absolute zero to 10 000 K, thus providing data for many diatomic molecules of astrophysical interest at low temperature. The calculations are based on molecular spectroscopic data from the book of Huber & Herzberg (1979, Constants of Diatomic Molecules) with significant improvements from the literature, especially updated data for ground states of many of the most important molecules by Irikura (2007, J. Phys. Chem. Ref. Data, 36, 389). Dissociation energies are collated from compilations of experimental and theoretical values. Partition functions for 284 species of atoms for all elements from H to U are also presented based on data collected at NIST. The calculated data are expected to be useful for modelling a range of low density astrophysical environments, especially star-forming regions, protoplanetary disks, the interstellar medium, and planetary and cool stellar atmospheres. The input data, which will be made available electronically, also provides a possible foundation for future improvement by the community.

Species-specific lipophilicity of morphine antagonists

Complete sets of microscopic acid–base and partition equilibrium constants were experimentally determined for therapeutically important morphine derivatives, including the widely used antagonists naloxone and naltrexone. The acid–base microequilibria were characterized by combining pH-potentiometry and deductive methods using synthesized auxiliary compounds. Microscopic protonation equilibria show that approximately three times as many zwitterionic microspecies than non-charged ones exist in oxymorphone and naltrexone solutions. On the other hand, the non-charged microspecies is the dominant one in the case of naloxone, although its concentration is only 1.34 times higher than that of its zwitterionic protonation isomer. Partition coefficients of the individual microspecies were determined by a combination of experimentally measured distribution constants and deductive methods. The contribution ratio of the non-charged versus zwitterionic species to the overall lipophilicity is quantified and depicted in terms of species-specific lipophilicities over the entire pH range for each compound. Our lipophilicity values allowed the molecular interpretation of the classical pharmacologic observation that naloxone has a faster onset for antagonist activity, and a concomitant shorter duration of action.

Preparation of methoxy poly (ethyleneglycol)-b-poly (ε-caprolactone-co-L-lactide) and characterization as biodegradable micelles

To compare methoxy poly (ethylene glycol) (MPEG)-b-poly (e-caprolactone) (M7C10L0) and MPEG-b-poly (L-lactide) (M7C0L10), we performed block copolymerization of e-caprolactone (CL) and L-lactide (LA) to synthesize block copolymers composed of MPEG-b-poly (e-caprolactone-co-L-lactide) (MxCyLz). The obtained MxCyLz, M7C10L0, and M7C0L10 had molecular weights close to the theoretical values calculated from the CL and/or LA to MPEG molar ratios and exhibited monomodal gel permeation chromatography (GPC) curves. The micellar characterization of MxCyLz block copolymers in an aqueous phase was carried out by using NMR, dynamic light scattering (DLS), and fluorescence techniques. The diameters of micelles, measured by DLS, were 30–370 nm. The critical micelle concentration (CMC) and partition equilibrium constant (K v) depended on the block lengths and compositions of block copolymers. The degradation of the MxCyLz block copolymers mainly depends on both the length of hydrophilic MPEG segments and the proportion of the CL and LA in the hydrophobic segments present in their structure. We confirmed that MxCyLz block copolymers formed biodegradable micelles suitable for biomedical applications.

ExoMol line lists – III. An improved hot rotation-vibration line list for HCN and HNC

A revised rotation-vibration line list for the combined hydrogen cyanide (HCN) / hydrogen isocyanide (HNC) system is presented. The line list uses {\it ab initio} transition intensities calculated previously (Harris et al., ApJ, 2002, 578, 657) and extensive datasets of recently measured experimental energy levels (Mellau, J. Chem. Phys. and J. Mol. Spectrosc. 2010-2011). The resulting line list has significantly more accurate wavelengths than previous ones for these systems. An improved value for the separation between HCN and HNC is adopted leading to an approximately 25%\ lower predicted thermal population of HNC as a function of temperature in the key 2000 to 3000 K region. Temperature-dependent partition functions and equilibrium constants are presented. The line lists are validated by comparison with laboratory spectra and are presented in full as supplementary data to the article and at \url{www.exomol.com}.

Detection of Hg(II) amidst several heavy and toxic metal ions after their selective separation by chromatography: rationalization of separation factors in terms of Density Functional (hardness) Index

Ascending paper chromatography of Hg+2 has been performed with mixed acids as developing mobile phase. Effects of temperature, concentration, and composition of the mobile phase on Rf values have been investigated. Hg+2 has been selectively separated from several synthetic binary and multicomponent mixtures containing the toxic and heavy metal ions. Often these metal ions remain associated with it in its ores and alloy samples. Hg+2 in trace level has been separated and detected from blood serum containing the congeners Zn+2, Cd+2, Pb+2, Bi+3, Th+4, Tl+3, and Cu+2. On the basis of the difference in the migration of the spots on the paper, twenty difficult separations have been achieved. Several thermodynamic parameters, ΔG, ΔH, and ΔS have been determined by differential variation of radii of the spot with respect to temperature utilizing the thermodynamic relationship. The partition equilibrium constant was also determined. Metal ions were detected by borohydride reduction on the paper strip. Separation factors have been correlated in terms of DesityFunctional (corrected hardness, η∗) Index. From η∗, hydrated radii of the metal ions have been determined. A plausible mechanism for the differential migration of diverse metal ions has been suggested.

Synthesis and Physicochemical Characterization of Amphiphilic Triblock Copolymer Brush Containing pH-Sensitive Linkage for Oral Drug Delivery

A novel and well-defined pH-sensitive amphiphilic triblock copolymer brush poly(lactide)-b-poly(methacrylic acid)-b-poly(poly(ethylene glycol) methyl ether monomethacrylate) (PLA-b-PMAA-b-PPEGMA) and its self-assembled micelles were developed for oral administration of hydrophobic drugs. The copolymer and its precursors were synthesized by the combination of activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) and ring-opening polymerization (ROP) techniques. The molecular structures and characteristics were confirmed by GPC, (1)H NMR, and FT-IR. The critical micelle concentration (CMC) values of PLA-b-PMAA-b-PPEGMA in aqueous medium varied from 1.4 to 2.6 mg/L, and the partition equilibrium constant (K(v)) of pyrene in micellar solutions ranged from 2.873 × 10(5) to 3.312 × 10(5). The average sizes of the self-assembled blank and drug-loaded micelles were 140-250 nm determined by DLS in aqueous solution. The morphology of the micelles was found to be spherical by SEM. Nifedipine (NFD), a poorly water-soluble drug, was selected as the model drug and wrapped into the core of micelles via dialysis method. The in vitro release behavior of NFD from the micelles was pH-dependent. In simulated gastric fluid (SGF, pH 1.2), the cumulative release percent of NFD was relative low, while in simulated intestinal fluid (SIF, pH 7.4), more than 96% was released within 24 h. All the results showed that the pH-sensitive PLA-b-PMAA-b-PPEGMA micelle may be a prospective candidate as oral drug delivery carrier for hydrophobic drugs with controlled release behavior.

Synthesis and Micellar Behavior of Novel Amphiphilic Poly[bis(trifluoroethoxy)phosphazene]-co-poly[(dimethylamino)ethyl methacrylate] Block Copolymers

A number of amphiphilic diblock copolymers based on poly[bis(trifluoroethoxy)phosphazene] (TFE) as the hydrophobic block and poly[(dimethylamino)ethyl methacrylate] (PDMAEMA) as the hydrophilic block were developed. The TFE block was synthesized first by the controlled living cationic polymerization of a phosphoranimine, followed by replacement of all the chlorine atoms using sodium trifluoroethoxide. To allow for the growth of the PDMAEMA block, 3-azidopropyl-2-bromo-2-methylpropanoate, an atom transfer radical polymerization (ATRP) initiator, was grafted onto the end-cap of the TFE block via the “click” reaction followed by the ATRP of 2-(dimethylamino)ethyl methacrylate (DMAEMA). Once synthesized, micelles were formed by a standard method, and their characteristics were examined using fluorescence techniques, dynamic light scattering, and transmission electron microscopy. The critical micelle concentrations of the diblock copolymers as determined by fluorescence techniques using pyrene as a hydrophobic probe were between 3.47 and 9.55 mg/L, with the partition equilibrium constant of pyrene in these micelles ranging from 0.12 × 105 to 1.52 × 105. The diameters measured by dynamic light scattering were 100–142 nm at 25 °C with a narrow distribution, which were also confirmed by transmission electron microscopy.