Amphiphilic nature of polyethylene glycols and their role in medical research

BackgroundPolyethylene glycol (PEG) is a polyether compound which is an excellent candidate to study possible specific interactions of protein-polymer systems at the atomic level. Such studies would be beneficial in obtaining a more thorough understanding of PEG-protein interactions and might help to explain PEG's effects on protein behavior when used as a crowder.Scope of reviewPEGs has been called double edged sword showing assorted effects on the protein due its hydrophilic, hydrophobic and amphiphatic nature. It has been observed that the stabilization of the protein due to PEGs is because of exclusion volume effect (hard core interactions) shown by the higher molecular sizes of the crowder, however there are soft (chemical) interactions also which leads to destabilization of proteins. Most of low molecular size PEGs are noticed to destabilize proteins due to soft interactions.General significanceHere, the core characteristics of the polyethylene glycols that are responsible for the various interactions with proteins and trying to delineate the behaviour of PEGs being ambiguous, are discussed. To conclude its paradox nature being a factual inert molecule or not, many different reports of PEG interactions with various proteins are clubbed together. In addition, owing to low toxicity, high polarity, high water solubility, typically unhydrolysing or undeteriorating characteristics, it has a practical significance in pharmaceutical and cosmetic industries, and in the research field on which this review shall enlighten from earlier to now.     

Positron annihilation lifetime spectroscopy study of polyvinylpyrrolidone-added polyvinylidene fluoride membranes: Investigation of free volume and permeation relationships

Polyvinylidene fluoride (PVDF) membranes were prepared via the phase inversion method from casting solutions containing PVDF, dimethylformamide (DMF), and polyvinylpyrrolidone (PVP) as pore former. PVP was used in the casting solution in a range of 0–5 wt % and extracted. The effect on membranes of using PVP in the casting process was analyzed by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, viscosity, and water permeability techniques. With an increase of PVP from 0 to 5 wt %, the PVDF casting solution viscosities increased from 858 to 1148 cP; the resulting PVDF membrane thickness increased; and the crystallinity of PVDF membranes decreased from 40.0 to 33.3%, which indicates that the addition of PVP inhibits the degree of crystallization in the PVDF membranes. SEM results revealed the shape and size of macropores in the membranes; these macropores changed after PVP addition to the casting solutions. The impact of structural changes on free-volume properties was evaluated using positron annihilation lifetime spectroscopy (PALS) studies. PALS analysis indicated no effect on the average radius (~3.4 Å) of membrane free-volume holes from the addition of PVP to the casting solution. However, the percentage of o-Ps pick-off annihilation intensity, I₃, increased from 1.7 to 5.1% with increased PVP content. Further, increasing the PVP content from 0.5 to 5% resulted in an increased final pure water permeability flux. For instance, the 210 min flux for a 14% PVDF + 0.5% PVP membrane was found to be 3.3 times greater than a control membrane having the same PVDF concentration. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 589–598     

Characterization of photoresists for ArF‐excimer laser lithography using monoenergetic positron beams

The volume and depth distributions of open spaces in photoresist films designed for ArF‐excimer laser light exposure were studied with monoenergetic positron beams. We measured the Doppler broadening spectra of the annihilation radiation and lifetime spectra of positrons for acrylate and cyclic olefin‐co‐maleic anhydride (COMA) polymers spin‐coated onto Si wafers with methyl amyl ketone, cyclohexanone, and propylene glycol methyl ether acetate solvents. The volume of open spaces in both prebaked acrylate and COMA films was estimated to be 0.12 nm³. The volume of open spaces in acrylate films decreased up to 20% by postexposure baking, but no large change was observed for COMA films. The decrease in the open volume was attributed to the removal of large molecules (adamantyl) from flexible main chains after the chemically amplified reaction of acrylate. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 341–346, 2004     

Thermoynamic properties (Hm, CP,m, Vm, κT) of binary mixtures {x1,3-Dioxane + (1−x)Cyclohexane} at 298.15 K

Molar excess enthalpies H_m^E, isobaric heat capacities C_P,m^E, volumes V_m^E and isothermal compressibilities κT^E for the 1,3-dioxane(3DX) + cyclohexane mixture were measured at 298.15 K, in order to compare to those of the 1,4-dioxane(4DX) + cyclohexane mixture. H_m^E is endothermic and the maximum value about 1.5 kJ mol⁻¹ at x ≈ 0.45, and lower than that of the 4DX mixture by about 80 J mol⁻¹. V_m^E is positive over the whole concentration and the maximum value is about 0.85 cm³ mol⁻¹ at x ≈ 0.45, and lower than that of the 4DX mixture. The above results suggest the energetic unstabilization, resulting in the volume expansion in the mixture. C_P,m^E shows the characteristic W-shaped concentration dependence, which has maximum at x ≈ 0.45 and two minima at x ≈ 0.1 and 0.9. The maximum C_P,m^E value for 3DX mixture shifts toward the positive side, compared to that of 4DX mixture. κT^E were estimated from speeds of sound, densities, thermal expansion coefficients and isobaric heat capacities of the pure component liquids and the mixtures. The κT^E result shows the positive concentration dependence over the whole composition range. The 3DX mixture has the similar thermodynamic properties to the 4DX mixture, despite that 4DX is the nonpolar solvent and 3DX is the dipolar liquid. this means that there exists the local dipolar interaction between 4DX molecules, and the prevalence of “microheterogeneity” in the both mixtures.     

Thermodynamics of mixtures formed by polycyclic aromatic hydrocarbons with long chain alkanes

Thermodynamic properties of polycyclic aromatic hydrocarbons (PAH) and long chain alkanes determine the phase behaviour of heavy petroleum fractions. Studying thermodynamic excess functions of these systems is difficult and consequently experimental data available in the literature are scarce. Enthalpies of mixing of 13 PAH-alkane systems at temperature above the melting point of both components are reported in this paper. Morever, 13 solid-liquid equilibria of the same family of systems are presented. Experimental results were correlated using S.S.F. model (Rogalski and Malanowski, 1977). Several regularities observed in the liquid-solid phase diagrams of the systems studied are discussed     

Time sensitive functionals of marked Cox processes

This paper continues studies on a multivariate marked Cox process C_t observed upon some random epochs τ={τ₁,τ₂,…} initiated in [J. Math. Anal. Appl. 293 (2004) 1-13]. The goal is to connect the continuous time parameter process C_t with C_τ for which closed-form transforms were presented in that paper. This work does not only restore some or much of the information on C_t lost due to its limited observation, but it also manages to scrutinize the behavior of C_τ around the first passage time of C_τ (that takes place upon one of the observation epochs τ) within some random time intervals. Again, analytically tractable formulas for functionals of C_τ are derived.     

制导光缆线包光附加损耗分析与计算

为了求得制导光缆线包的光附加损耗，首先对光缆缠绕时引起的光纤应进行研讨，然后分析微弯应变谱密度，推计计算光附加损耗的公式。计算机模拟验证了计算结果的实用性。     

国产航空有机玻璃(PMMA)的压缩应力-应变行为研究——Ⅱ.力学性能特征参数分析

讨论从加卸载循环的应力-应变表征曲线提取得到的各材料力学性能,尤其是关于屈服和塑性变形的特征参数。包括加卸载弹性模量E_L~T,E_u~T;屈服点的表征参数:屈服应力σ_s~T,屈服应变ε_s~N,屈服应变能U_s;热激活塑性变形的表征参数:活化体积V_τ和活化能ΔH。讨论这些参数对温度和应变率的依赖关系,寻求由这些特征参数作表述,或是存在于这些参数之间的经验关系或规律。     

Excitation of Complicated Shapes in Three Dimensions

We experimentally verified a recently proposed technique for the excitation of a complicated three-dimensional profile (CARVE,completelyarbitraryregionalvolumeexcitation). CARVE is based on a generalized DANTE RF pulse sequence and a synchronous string of gradient steps. Provided there is no limitation in the number of pulses, CARVE can generate an excitation profile of any shape with any resolution. However, hardware limitations and sample properties restrict the number of RF pulses and gradient steps and, thus, limit attainable resolution of the excitation profile. We theoretically and experimentally showed that spatial resolution can be increased by distributing a long sequence among several CARVE experiments and summing up their signals. This is particularly important for three-dimensional excitation profiles where ann-fold increase in resolution requires ann³-fold increase of the number of events in the sequence. The potential use of three-dimensional CARVE might be in spectroscopic imaging where the excitation profile can be tailored to match the shape of a selected organ or body part.