Comparison of column properties in reversed-phase chromatography: monolithic, cholesterolic and mixed bonded stationary phases

A commercial Chromolith C18 column and two new stationary phases with mixed ligands bonded on the Kromasil silica gel support, SG-MIX and SG-Chol, were characterized using simple tests based on the retention of non-polar, basic and acidic compounds. Polar and methylene selectivity tests in acetonitrile-water and methanol-water mobile phases revealed lower hydrophobicities of the SG-MIX and SG-Chol columns in comparison to the Chromolith column. The columns were further characterized using new test criteria - gradient oligomer capacity and isomeric selectivity and peak symmetry of naphthalene di-sulphonic acids in aqueous mobile phases. The cholesterolic column shows greater gradient oligomer selectivity for the separation of oligoethylene glycol samples than the SG-MIX and the Chromolith columns. Increased retention and peak tailing, but decreased isomeric selectivity for naphthalene-di-sulphonic acids was observed with the SG-MIX column, because of interactions with various polar bonded groups.     

Convenient multigram synthesis of monodisperse oligo(ethylene glycols): effective reaction monitoring by infrared spectroscopy using an attenuated total reflection fibre optic probe

A convenient approach for the synthesis of monodisperse oligo(ethylene glycols) up to 12 units is described. A novel cleavage protocol replacing laborious hydrogenolysis is introduced to achieve a fast, inexpensive and widely applicable procedure. In addition to the synthetic part, Fourier transform infrared (FTIR) spectroscopy using a fibre optic attenuated total reflection (ATR) sensor was applied to monitor the formation of sensitive key intermediates, resulting in optimized reaction times. By applying this in-line technique, the possibility of real-time analysis under inert conditions was impressively demonstrated.     

Ungewöhnliche Phasendiagramme der Polyethylenglykole 6000 und 4000 mit Harnstoff

The binary systems of urea with polyethylene glycols 6000 and 4000 show inclusion compounds with higher melting points than the two components (m.p. 143 and 142.5°C resp.). From the melt unstable forms crystallize beside the stable crystal modifications. These have also been identified by FTIR microscopy and X-ray powder diffractometry. The phase diagrams are uncommon in so far as the inclusion compounds do not form eutectics but monotectics with both components. The inclusion compounds of the two polyethylene glycols with urea are isomorphous and form a series of mixed crystals following the Roozeboom I type of diagram.     

Empirical equations of state for adsorption layer: Alkylthiopolyoxyethylene glycols

Surface tension isotherms ofn-alkylthiopolyoxyerhylene glycols:n-C _x H_2x+1S(CH₂CH₂O) _y H, wherex=5 to 8,y=3 or 4, were approximated with orthogonal polynomials to get good quality values of surface pressure (II) and molar area of the adsorbed layer (). The modified Volmer (*(–₀)=Z*R*T) van der Waals and virial equations of state were used to correlate and in terms of real two-dimensional gas. The combination of Volmer and van der Waals equations of state made it possible to determine the interaction energy, , which was prescribed to cohesion of hydrophobic chains in the adsorption layer. The value of for the amphiphiles in question was in the range 0.97–1.91R*T and the average contribution per methylene group was ca. 0.21R*T.The Lennard-Jones potentials calculated from second virial coefficient were of the same range as , but no clear relation was found between their values and number of structure elements of the alkylthiopolyoxyethlene glycols.Presented during 7th International Conference: Surface and Colloid Science, July 7–13, 1991, Compiegne, France     

Viscosity B coefficients of polyethyleneglycols in water

The viscosity B coefficients of polyethylene glycols (M=62–1000) are determined at 25 °C. The B coefficient increases non-linearly with the number of ethyleneoxide (EO) units. The increase of the B coefficient per EO(0.111 dm³/mole) is less than the B value for two methylene groups (0.160 dm³/mole). This is discussed in terms of changes in the configurations of polyethylene glycols with long EO chains.Molecular size is the major factor that contributes to B at shorter chains, but solvation (hydration) becomes dominant as the number of ethyleneoxide groups increases. The hydration parameter,(gH₂O/g ethyleneglycol), shows a linear dependence on B at low mass followed by a non-linear increase at high molecular mass and the viscosity C coefficient accounts for the solute-solute interactions.Symbols absolute viscosity - _d absolute viscosity of dispersion medium - _r relative viscosity - _sp specific viscosity - ¦ _o ¦ intrinsic viscosity at infinite dilution - ¦ _c ¦ intrinsic viscosity as a function of solute concentration - partial specific volume - volume fraction - hydration (weight of H₂O hydrating 1 g of polyethylene glycol) - _c hydration as a function of solute concentration - K shape function - K _c shape function as a function of solute concentration     

水＋甲酰胺＋环己烷＋二乙二醇丁醚拟三元系的三临界现象

用改进的体积法研究了拟三元体系水＋甲酰胺＋环己烷＋二乙二醇丁醚的三临界现象. 以水+甲酰胺作为拟“纯组分”，通过控制甲酰胺在拟“纯组分”中的质量分数w，逐渐向三临界点逼近，当w从0增加到0.206时，三相区范围ΔT从1.500 ℃减小到0.228 ℃. 由实验数据得到体系的临界质量分数w=0.286±0.003，临界温度为（54.8±0.7） ℃. 实验发现平均温度下三相区三角形的水-油边与三角坐标中的水-油边几乎平行，而且三相区三角形水-油边的边长及其对应的高与ΔT的指数关系符合三临界的经典理论.     

Synthesis and characterization of functionalized amphiphilic polymers for utilization as surfactants

Eight novel PEG-based amphiphilic block copolymers having self-assembling properties has been reported in the present study. The polymers have been synthesized by reacting Poly(ethylene glycols) (PEGs) of different molecular weights viz. 600, 1000, 1500 and 2000 and dimethyl-5-hydroxyisophthalate in presence of concentrated H₂SO₄ as catalyst in solventless condition at 80–90°C and further alkylating the resulting polymers by attaching octyl and hexadecanyl chains to phenolic hydroxyl group. The resulting functionalized amphiphilic polymers have been characterized by ¹H and ¹³C-NMR spectroscopy. These polymers, when dissolved in water, aggregate to form micelles, giving sizes ranging from 13.00 to 87.24 nm as determined by Dynamic Light Scattering (DLS) instrument. The molecular weights have been also calculated from the DLS and are in the range 3.5×10⁴ to 1.8×10⁶ KDa (Kilo Daltons). Critical Micelle Concentrations (CMC) of the synthesized polymers was determined using electrical conductivity meter with values in the range of 105 to 138 mg L^?1 (milligrams per litre).     

Mechanism for enhancing dispersion of Co3O4 nanoparticles in Co/SiO2 Fischer–Tropsch synthesis catalyst by adding glycol to impregnating solution: a quick‐XAFS study

In situ Co K‐edge quick‐EXAFS (QEXAFS) coupled with temperature‐programmed oxidation as well as ex situ XAFS was applied to investigating the mechanism for enhancing the dispersion of Co₃O₄ nanoparticles in a calcined Co/SiO₂ Fischer–Tropsch synthesis catalyst prepared by adding triethylene glycol (TEG) to a Co(NO₃)₂.6H₂O impregnating solution. Ex situ Co K‐edge XAFS indicated that, regardless of whether the catalysts were prepared with or without using TEG, the hexaaqua Co (II) complex was formed in impregnated samples which then underwent the dehydration process to some extent during the subsequent drying step at 393 K. In situ QEXAFS and ex situ EXAFS results also indicated that small oxide clusters were formed in the TEG‐modified catalyst calcined at ～400–470 K which interacted with polymer species derived from TEG. Since the Fischer–Tropsch synthesis activity of the TEG‐modified catalyst increased with an increase in the calcination temperature in a similar temperature range [Koizumi et al. (2011), Appl. Catal. A, 395 , 138–145], it was suggested that such an interaction enables the clusters to be distributed over the support surface uniformly, resulting in enhancing their dispersion. After combustion of polymer species, Co₃O₄‐like species were formed, and agglomeration of the Co₃O₄‐like species at high calcination temperatures was suppressed by the addition of TEG to the impregnating solution. It was speculated that the addition of TEG induced the formation of some surface silicate which worked as an anchoring site for Co₃O₄ and Co⁰ nanoparticles during calcination and H₂ reduction, respectively.     

Soy Oil Microemulsions Made of Anionic Surfactant,Oleic Acid,Diethyleneglycol Ethyl Ether,and Water: Optimized Systems

Soy oil microemulsions has been optimized for systems made of phosphated oleyl ether 3EO as surfactant, oleic acid, diethyleneglycol monoethyl ether, and water. The soy oil solubilization has been estimated as a function of different ratios between surfactant/oleic acid (5/95, 10/90, 15/85, and 20/80) and water/glycol (4/1, 2/1, 1/1, 1/2, and 1/4). The maximum simultaneous solubilization of soy oil and hydrophilic phase (water plus glycol) in ratios 3/1, 1/1, and 1/3 (besides the 1/0 and 0/1) was considered. In order to display the widest microemulsion area, the better ratios surfactant/oleic acid were 10/90, 15/85, and 20/80 when water and glycol ratios were 1/2 and 1/4. For these systems, the transition between W/O, bicontinuous and O/W microemulsions were followed through electrical conductivity changes.     

Synthesis of α,ω‐Bis(oxazolidinone)polyoxyethylene via a Lithium Bromide–Catalyzed Reaction of Oligoethylene Glycol Diglycidyl Ethers with Isocyanates

The synthesis of bis(oxazolidinone)polyoxyethylene derivatives 2a–h from oligoethylene glycols diglycidyl ethers 1a–e and isocyanates is reported. The reaction was achieved by lithium bromide and tributylphosphine oxide. These bis‐oxazolidinones may have important antibacterial activity.