Peg System Research Articles

Co-nonsolvency effect of thermosensitive N-isopropylacrylamide nanometer-sized gel particles in water–PEG systems

Nanometer-sized N-isopropylacrylamide (NIPA) gel particles were prepared by precipitation polymerization, and their thermosensitive swelling behaviors in water–poly(ethylene glycol) (PEG) (MW = 200, 400) systems were investigated using photon correlation spectroscopy (PCS). The volume transition temperature decreased with increasing PEG concentration, and a completely unexpected swelling behavior was observed at high PEG concentrations. The cloud points of poly(N-isopropylacrylamide) (PNIPA) in water–PEG systems were also determined by thermo-optical analysis (TOA) in order to compare the volume transition temperatures of gel particles with the phase transition temperatures of linear PNIPA in given solvent mixtures. A lattice-based molecular thermodynamic framework was employed to calculate interaction parameters from binary liquid–liquid equilibria (LLE), and those parameters were then applied directly to describe the co-nonsolvency effects of the ternary solutions. By combining the molecular thermodynamic model for the mixing contribution with the Flory–Rehner (FR) model for the elasticity contribution, the reentrant swelling equilibria at various temperatures were calculated. Using only one adjustable parameter, we were able to describe the swelling behaviors at high temperature regions (above the LCST). Lastly, the predicted results were compared to PEG (MW = 200, 1000) selectivity data inside NIPA gel, and were found to be in good agreement with the proposed model without further adjustable parameters.

Phase behavior of rifampicin in cholesterol-based liquid crystals and polyethylene glycol

The phase behavior of rifampicin in cholesteryl-based carbonate esters (CCEs), cholesterol and polyethylene glycol4000 (PEG4000) was determined to evaluate their potential in the formulation of dry powder inhalation dosage forms. To guide the identification of the most suitable liquid crystalline system for the solubilization of rifampicin, the dielectric constants were evaluated. Thereafter, the phase behavior of various mixtures were characterized by polarized light microscope (PLM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Among the mixed-carrier systems, the cholesteryl cetyl carbonate (CCC) and PEG4000 system at 1:1mole ratios yielded a homogeneous mixture with relatively high rifampicin content. This result was consistent with the prediction based on the dielectric constants. The phase diagram contained a eutectic point at CCC:PEG4000 (1:1) and 50°C. Finally, the rifampicin drug was successfully incorporated into CCC and PEG system at a 1:6:6mole ratio. Such a system would be amenable for oral inhalation.

Long-Term Outcomes of Pegged and Unpegged Bioceramic Orbital Implants

To evaluate the long-term outcomes of pegged and unpegged bioceramic orbital implants. A retrospective analysis of 101 cases of evisceration, enucleation, or secondary implant surgery with placement of a bioceramic porous implant was conducted. Type of surgery, existence of a peg, peg system used, time of pegging, problems encountered before and after pegging, treatment methods, and final status were recorded. Evisceration was performed on 74, enucleation on 16, and secondary implant surgery on 11 patients. The patients were observed for a mean of 68.4 months (3 months-12 years). Fifty-three of the 101 patients were pegged. Patients were pegged at a mean of 9.3 months (6-23 months). Hydroxyapatite-coated, titanium-sleeved, titanium pegs were used in 43 patients, and titanium peg and sleeve system was used in 10 patients. Major complications were exposure and infection. Three patients presented with early exposure and late exposure developed in 14 of pegged and 4 of unpegged patients. The difference in late-exposure rates between pegged and unpegged group was statistically significant (p < 0.05). Implant infection developed in 9 of the pegged and in 1 of the unpegged patients. Implant exposure was noted in 6 of these 10 patients with infection. The difference in infection rates between the pegged and unpegged patients was statistically significant (p < 0.05). In 2 of the pegged patients, removal of bioceramic implant was required and after resolution of infection, another type of porous implant was implanted and repegged. The peg system was removed in 6 patients for the management of either exposure, infection, extrusion, hypermobility of sleeve, or peg falling out. Four patients were repegged. The time period between peg insertion and development of complications ranged from 15 days to 10 years. 86.8% of pegged patients were free of major complications and satisfied with the result at the last follow-up visit. Despite potential complications that can occur as late as 10 years, bioceramic porous implants yield satisfactory long-term results. Existence of a peg system appears to play a role in the increased rate of late-onset complications. Further investigations on new and safer pegging systems should be conducted.

Phase separation in crowded micro-spheroids: DNA–PEG system

Living cells are characterized as micro-vesicles encapsulating highly crowded macromolecular media, including DNA. To probe the intrinsic property of such crowded systems in a micro-closed environment, we observed a mixture of DNA and hydrophilic polymer, PEG within an aqueous micro-spheroid. It was found that the mixture causes phase-segregation by depositing DNA near the spheroid surface, whereas corresponding bulk solution sustains isotropic phase. After the phase segregation, DNA molecules in the condensed phase exhibit time evolution to an ordered state. This surface-mediated segregation is discussed in terms of the depletion effect under micro-confinement.

Synthesis of cationic polyacrylamide by aqueous two‐phase polymerization in poly(ethylene glycol) chloride solution

AbstractAqueous two‐phase copolymerization of acrylamide(AM) and acryloyloxyethyl trimethyl ammonium chloride (DAC) was performed in poly(ethylene glycol) (PEG) solution and in PEG chloride(Cl‐PEG) solution, respectively. Series of cationic polyacrylamide(CPAM) aqueous dispersion were prepared using potassium persulfate (KPS) as initiator. The effect of total amount of monomers, the dosage of initiator, the content of dispersant, the mass ratio of AM to DAC, and the temperature on the conversion, molecular weight, cationic degree, and stability of aqueous dispersion were studied in detail. It is found that the increase of initiator and reaction temperature resulted in the increase of the final conversion, whereas the increase of DAC and PEG concentration resulted in the decrease of the final conversion. The optimum reaction conditions of synthesis were as follows: (1) PEG‐H2O system: PEG 7.5 g, AM 8 g, DAC 2 g, KPS 0.05 g, H2O 100 mL, 70°C. In this process conditions, the molecular weight of CPAM was 3.21 × 106, the cationic degree of CPAM was 24.4%, the storage stability of the aqueous dispersion was over 3 months. (2) Cl‐PEG‐H2O system: Cl‐PEG 7.5 g, AM 8 g, DAC 2 g, KPS 0.05 g, H2O 100 mL, 65°C. In this process conditions, the molecular weight was 3.68 × 106, the cationic degree was 23.3%, and the storage stability of the aqueous dispersion was over 6 months. In general, the stability of CPAM aqueous dispersion in Cl‐PEG system is much better than in PEG system. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Partitioning studies of l-glutaminase production by Bacillus cereus MTCC 1305 in different PEG–salt/dextran

Partitioning studies of l-glutaminase production by Bacillus cereus MTCC 1305 was carried out in different PEG–salt/PEG–dextran system. The partitioning value of l-glutaminase increased with increasing molecular weight of PEG from 2000–4000kDa and decreased with higher molecular weight of 6000kDa. Phase system of PEG 4000 (8.5%)/dextran T500 (9.5%) was selected for the extractive fermentative production of l-glutaminase on the basis maximum partition coefficient (1.31). The production of l-glutaminase was found higher in top phase of ATPS (2.09U/ml) than control media (1.42U/ml). Overall production of l-glutaminase (1.83U/ml) was found lower than top phase (2.09U/ml) in ATPS system. The growth profile with short lag phase and higher cell concentration was obtained for ATPS. The partition coefficient of l-glutaminase increased with increase of system pH and temperature and optimum production was obtained at pH 7.5 and temperature 30°C in top phase of PEG 4000/dextran T500 system.

Characterization and evaluation of β-glucan formulations as injectable implants for protein and peptide delivery

Context: Injectable implants are biodegradable, syringeable formulations that are injected as liquids, but form a gel inside the body due to a change in pH, ions or temperature.Objective: To investigate the effect of polymer concentration, pH, ions and temperature on the gel formation of β-glucan, a natural cell-wall polysaccharide derived from barley, with particular emphasis on two-phase system formation after addition of dextran or PEG.Materials and methods: Oscillation viscometry was used to evaluate the gel character by measuring flow index (N), storage (G′) and loss (G″) moduli. Two-phase systems were further characterized for hardness and syringeability using a texture analyzer. Finally, in vitro release characteristics were determined using Franz diffusion cells.Results: Oscillation viscometry revealed that only addition of dextran or PEG resulted in distinct gel formation. This was seen by a decrease in N after polymer addition. Moreover, hardness (in g) of the gels increased significantly (p < 0.001) from 3.65 ± 0.43 to 34.30 ± 8.90 (dextran) and 805.80 ± 5.30 (PEG) 24 h after polymer addition. In vitro release profiles showed significantly (p < 0.05) reduced AUC0–8 h, k and percentage of drug released from two-phase systems compared to β-glucan dispersions, with the PEG system resulting in the lowest amount released over 8 h (15.1 ± 1.6%).Discussion: The unfavorable mixing enthalpy and higher water affinity of PEG resulted in the formation of a dense β-glucan gel.Conclusion: 1.5% (w/w) β-glucan combined with PEG at a ratio of 1:3 seemed to be the most promising injectable formulation with respect to fastest gel formation, increased hardness and sustained release.

Separation of Proteins by Aqueous Two-phase Extraction System Combined with Liquid Chromatography

Abstract A method was developed for the enrichment and separation of proteins by an aqueous two-phase extraction system (ATPS) of PEG/(NH4)2SO4 combined with high-performance liquid chromatography (HPLC). The effects of the type and the concentration of inorganic salts, PEG molecular weight, pH value, temperature and NaCl on the formation of two phases and partition of cytochrome c, lysozyme, trypsin, bovine serum albumin and myoglobin were investigated, respectively. The results showed that five proteins were enriched mainly in bottom phase in 15% PEG-4000/10% (NH4)2SO4 at room temperature and pH from 3.5 to 9.0. High-abundance proteins in serum were also distributed in two phases and the bottom phase had larger amount under the same conditions, which could be extracted and separated by optimized ATPS. The proteins were collected on the basis of their retention time in HPLC, and could be removed from serum samples.

PURIFICAÇÃO DA ENZIMA BROMELINA PRESENTE NO CURAUÁ (Ananas erectifolius L.B. SMITH) VARIEDADE ROXA, POR SISTEMA BIFÁSICO AQUOSO PEG 4000/FOSFATO DE POTÁSSIO

Curaua (Ananas erectifolius LB Smith) is a typical plant of northern and central-western Brazil. It produces a highly strong fiber with applications in several areas, mainly in the automotive industry. Belonging to the family of Bromeliaceae, it contains significant levels of bromelain, a group of proteolysis’ enzymes with application in several areas such as in the food, pharmaceutical and cosmetics industries. In this work we evaluated the purification of the enzyme present in the leaves of Curaua by means of an aqueous two-phase system PEG 4000/Potassium phosphate. The enzyme had its activity measured in each phase by the Biuret method. The purification factor (PF) was obtained in order to optimize the conditions for purification of the bromelain. It was used 03 pH 7.0, 8.0 and 9.0 values, varying the proportional composition in between the polymeric and the saline phases (tie-lines). It was used the purple variety of Curaua. The results showed that PEG system 4000/ potassium phosphate polymer with a higher concentration and at pH 7.0 produced better results in enzyme purification.

Detection of superhumps in the cataclysmic variable V378 Peg (PG 2337+300)

The cataclysmic variable V378 Peg is known since 15 years. Although V378 Peg is a rather bright star (14 mag), it underwent no detailed study. We performed photometric observations of V378 Peg during 75 h with the goal to detect periodic brightness variations. The obtained light-curves clearly showed changes with a period of about 3 h. The Fourier analysis reveals that this oscillation occurs with a period of 3.238 h and a semiamplitude of 0.07 mag. Although the detected oscillation possesses certain coherence, it appears to have a slightly unstable period or phase. Therefore, the detected period cannot be the orbital period of the V378 Peg system. Because such instability is typical of superhumps, we must consider the detected oscillation as superhumps. Furthermore, V378 Peg shows no outbursts and has to be a nova-like variable rather than a dwarf nova. Hence, the detected superhumps have to be regarded as permanent superhumps. Because superhump periods in cataclysmic variables are close to orbital periods, we can find the place of V378 Peg in the orbital period distribution of cataclysmic variables. V378 Peg is a permanent superhump system above the upper edge of the 2–3 h period gap in the orbital period distribution.

Methacrylate polymer layers bearing poly(ethylene oxide) and phosphorylcholine side chains as non-fouling surfaces: In vitro interactions with plasma proteins and platelets

Two methacrylate monomers, oligo(ethylene glycol) methyl ether methacrylate (OEGMA; MW = 300 g mol −1, poly(ethylene glycol) (PEG) side chains of average length n = 4.5) and 2-methacryloyloxyethyl phosphorylcholine (MPC; MW = 295 g mol −1), were grafted from silicon wafer surfaces via surface-initiated atom transfer radical polymerization. The grafted surfaces were used as model PEG and phosphorylcholine surface systems to allow comparison of the effectiveness of these two motifs in the prevention of plasma protein adsorption and platelet adhesion. It was found that at high graft density fibrinogen adsorption from plasma on the poly(MPC) and poly(OEGMA) surfaces for a given graft chain length was comparable and extremely low. At low graft density, poly(OEGMA) was slightly more effective than poly(MPC) in resisting fibrinogen adsorption from plasma. Flowing whole blood experiments showed that at low graft density the poly(OEGMA) surfaces were more resistant to fibrinogen adsorption and platelet adhesion than the poly(MPC) surfaces. At high graft density, both the poly(MPC) and poly(OEGMA) surfaces were highly resistant to fibrinogen and platelets. Immunoblots of proteins eluted from the surfaces after contact with human plasma were probed with antibodies against a range of proteins, including the contact phase clotting factors, fibrinogen, albumin, complement C3, IgG, vitronectin and apolipoprotein A-I. The blot responses were weak on the poly(MPC) and poly(OEGMA) surfaces at low graft density and zero at high graft density, again indicating strongly protein resistant properties for these surfaces. Since the side chains of the poly(OEGMA) are about 50% greater in size than those of poly(MPC), the difference in protein resistance between the poly(MPC) and poly(OEGMA) surfaces at low graft density may be due to the difference in surface coverage of the two graft types.

ASIAN MONETARY UNIT (AMU) AS A SURVEILLANCE INDICATORS FOR REGIONAL MONETARY COOPERATION

Ogawa and Shimizu (2005) proposed an Asian Monetary Unit (AMU), which is a common currency basket composed of ASEAN plus three Asian currencies, and AMU Deviation Indicators (AMU DIs), which indicates deviations of each Asian currency in terms of the AMU compared to the benchmark rate. In this paper, we use daily and monthly data of AMU and AMU DIs to examine their usefulness as a surveillance indicator for monetary cooperation in Asia. We find that an AMU peg system stabilizes the trade-weighted exchange rates within Asia and that AMU DIs warn of misalignments of and between Asia currencies.

Remote actuation of hydrogel nanocomposites: Heating analysis, modeling, and simulations

AbstractRecently, there has been increasing interest in remote heating of polymer nanocomposites for applications such as actuators, microfluidic valves, drug delivery devices, and hyperthermia treatment of cancer. In this study, magnetic hydrogel nanocomposites of poly(ethylene glycol) (PEG) with varying amounts of iron oxide nanoparticle loadings were synthesized. The nanocomposites were remotely heated using an alternating magnetic field (AMF) at three different AMF amplitudes, and the resultant temperatures were recorded. The rate of the temperature rise and the steady state temperatures were analyzed with a heat transfer model, and a correlation of heat generation per unit mass with the nanoparticle loadings was established for different AMF amplitudes. The temperature rise data of a PEG system with different swelling properties were found to be accurately predicted by the model. Furthermore, the correlations were used to simulate the temperatures of the nanocomposite and the surrounding tissue for potential hyperthermia cancer treatment applications. © 2010 American Institute of Chemical Engineers AIChE J, 2011

The role of financial development in exchange rate regime choices

We make the first attempt in the literature to empirically investigate the role of financial development in the choice of exchange rate regimes. Using a binary choice model, we first show that financially less developed countries are more likely to adopt a fixed exchange rate. To further examine the impact of financial development on the conditional probability of exiting from an existing pegged system to a flexible one, we then employ hazard-based duration analysis. We find strong evidence that countries with higher levels of financial development are more likely to exit a pegged system, and, interestingly, financial development only matters to orderly exits but not disorderly exits. Our results are robust to controlling for endogeneity and sample selection.

Pegging the Porous Orbital Implant

Hydroxyapatite (HA) orbital implants are commonly used for the anophthalmic socket. With a HA implant, if motility is not satisfactory then a peg system can be surgically placed in attempts to improve motility. The authors report the technique and results of 83 patients who received motility peg placement over an 8-year period by a single surgeon. Retrospective chart review of all patients with previous enucleation with either primary or secondary insertion of a HA implant who received a motility peg by a single oculoplastic surgeon between January 1999 and February 2007. Eighty-three patients underwent placement of a titanium peg and sleeve during the study period. Complications seen in the follow-up period included discharge, pyogenic granuloma, and others. Infection was experienced in 1 case. Fourteen patients (17%) required further surgical management due to complications. The largely positive results of this moderately sized case series validates the efficacy of pegging a hydroxyapatite orbital implant with minor risk of serious complications; this may have been due to a combination of factors including an experienced surgeon and adequate follow-up. As a procedure that can be completed in a hospital or minor surgical suite with sedation, it remains a viable option for many patients.

POSITIONED AGENTS IN ECO-GRAMMAR SYSTEMS

Positioned eco-grammar systems (PEG systems, for short) were introduced in [9]. Motivation of introducing positioned eco-grammar systems is an attempt to describe interplay between evolving environment and community of agents living in this environment whereas we focus on the positions of agents in the environment. PEG systems bring a new view to investigating interplay between community of agents and environment. Our approach allows to study local changes in evolving environment caused by agents moreover the position of the agent is strictly given by special symbol and we are able to predict its behavior and control the evolution of environment as well. In this paper we compare generative power of the PEG systems with three types of pure (regulated) grammars.

Asian Monetary Unit and Monetary Cooperation in Asia

Regional monetary and financial cooperation in Asia has been discussed for years. To move towards a coordinated exchange rate policy, Ogawa and Shimizu (2005) proposed both an Asian Monetary Unit (AMU), which is a common currency basket computed as a weighted average of the thirteen ASEAN 3 currencies, and AMU Deviation Indicators (AMU DIs), which indicates the deviation of each Asian currency in terms of the AMU compared with the benchmark rate. The AMU and the AMU DIs are considered both as surveillance measures under the Chiang Mai Initiative and as benchmarks for coordinated exchange rate policies among Asian countries. In this paper, the authors show that monitoring the AMU and the AMU DIs plays an important role in the regional surveillance process under the Chiang Mai Initiative. By using daily and monthly data of AMU and AMU DIs for the period from January 2000 to June 2010 which are available from the website of the Research Institute of Economy, Trade, and Industry (RIETI), they examine their usefulness as a surveillance indicator. Our studies of AMU and AMU DIs confirm the following: first, an AMU peg system stabilizes the nominal effective exchange rate (NEER) of each Asian country. Second, the AMU and the AMU DIs could signal overvaluation or undervaluation for each of the Asian currencies. Third, trade imbalances within the region have been growing as the AMU DIs have been widening. Fourth, the AMU DIs could predict huge capital inflows and outflows for each Asian country. The above findings support the usefulness of using the AMU and the AMU DIs as surveillance indicators for monetary cooperation in Asia.

Vapor-liquid equilibrium properties of sodium n-heptyl sulfonate in Water and in aqueous solutions of poly(ethylene glycol) at different temperatures

The vapor-liquid equilibria properties of sodium n-heptyl sulfonate (C7SO3Na) in pure water and in aqueous poly(ethylene glycol) (PEG) solutions were determined at different temperatures below and above the critical micelle concentration (CMC). Vapor-liquid equilibrium data such as water activity, vapor pressure, osmotic coefficient, activity coefficient and Gibbs free energies were obtained through isopiestic method. The concentration dependence of all investigated thermodynamic properties exhibit a change in slope at the concentration in which micelles are formed. It was found that the vapor pressure depression for a ternary aqueous C7SO3Na + PEG system is more than the sum of those for the corresponding binary solutions and, at higher temperatures, the higher concentration of PEG is in equilibrium with a certain concentration of surfactant.

A comprehensive photometric study of the Algol-type eclipsing binary: BG Pegasi

This study presents new photometric observations of classical Algol type binary BG Peg with a δ Scuti component. The light curve modeling was provided with the physical parameters of the component stars in the BG Peg system for the first time. After modeling light curves in B and V filters, the eclipse and proximity effects were removed from the light curve to analyze intrinsic variations caused by the hotter component of the system. Frequency analysis of the residuals light represents the multi-mode pulsation of the more massive component of the BG Peg system at periods of 0.039 and 0.047 days. Two frequencies could be associated with non-radial ( l = 2) modes. The total amplitude of the pulsational variability in the V light curve was found to be about 0.045 mag. The long-term orbital period variation of the system was also investigated for the first time. The O– C analysis indicates periodic variation superimposed on a downward parabola. The secular period variation means that the orbital period of the system is decreasing at a rate of −5.5 seconds per century, probably due to the magnetic activity of the cooler component. The tilted sinusoidal O– C variation may be caused by the gravitational effect of an unseen component around the system.

Monetary targeting for price stability in Bangladesh: How stable is its money demand function and the linkage between money supply growth and inflation?

Since the mid-1980s Bangladesh has implemented a loose form of monetary targeting under two exchange-rate régimes: a pegged system until May 2003 and a ‘managed floating’ exchange-rate system. Under both régimes, broad money has been used as an intermediate target to maintain price stability, which implies as the ultimate goal a relatively low and stable rate of inflation. Inflation in this country has, however, remained moderately high and volatile, especially during the 1970s under the pegged exchange-rate system. With the apparent ineffectiveness of the monetary-targeting system in achieving price stability, even following the 2003 ‘managed float’ of the currency, there has been some suggestion that it should be replaced by, say, inflation targeting. This paper forms an element of a fuller study of the issue. It investigates the behaviour of broad money demand in Bangladesh using annual data over the period 1973–2008. Empirical results suggest that an open-economy broad money demand function has remained stable in Bangladesh since the early 2000s. Empirical results also suggest the existence of a causal relationship between money supply growth and inflation. The paper concludes that, although monetary targeting remains appropriate for Bangladesh, its implementation can be made more effective in stabilising the price level if the Bangladesh Bank enhances its control over the money supply by eschewing nominal exchange-rate stabilisation through foreign exchange market interventions.