Ethylene glycol molecule

One of the main advantages of the stochastic dynamics methods is that dramatic tirn savings can he achieved, which enables much longer stimulations to he performed. Fc example, Widmalm and Pastor performed 1 ns molecular dynamics and stochastic dynamic simulations of an ethylene glycol molecule in aqueous solution of the solute and 259 vvatc jnolecules [Widmalm and Pastor 1992]. The molecular dynamics simulation require 300 hours whereas the stochastic dynamics simulation of the solute alone required ju 24 minutes. The dramatic reduction in time for the stochastic dynamics calculation is du not only to the very much smaller number of molecules present hut also to the fact the longer time steps can often he used in stochastic dynamics simulations. 

A new ethylene glycol molecule can condense with the carboxyl group on one end of the product, and another terephthalic acid molecule can condense with the hydroxyl group on the other end. As a result, the polymer grows at both ends and becomes... 

Fee CJ (2007) Size comparison between proteins PEGylated with branched and linear poly (ethylene glycol) molecules. Biotechnol Bioeng 98 725-731... 

Ethylene glycol can be mixed In all proportions with water, so that activity changes in the solution also have to be accounted for. This can be accomplished by using celt EMF measurements. Figure 3.79 shows the result. Only part of Ap.z.c. may now be identified with x- This part is much lower than for the alcohols of table 3.9 in view of the structure of the ethylene glycol molecule, this outcome is expected. 

In this chapter, the molecular weight of PEG will be denoted in Daltons (Da) or kilodaltons (kDa). For example, a PEG with a molecular weight of 20000 daltons will be referred to as PEG 20000 daltons of PEG 20-kDa or just PEG 20000. Each ethylene glycol molecule in PEG has a molecular weight of 44 daltons. This would... 

Compound (69) is monomeric in benzene solution, dimerization being prevented by steric strain.Aluminium ethylene dioxide is prepared by treating aluminium s-butoxide with ethylene glycol, followed by heating to 150 °C. It is tetrameric, with seven ethylene glycol molecules present. Spectroscopic considerations indicate a structure like (70). ... 

Typically, the reaction was carried out in 1,2-dichloromethane solution ([ECHJq = 6mol -T1 [EG]o = 0.6 mol l x) at 20 °C with 0.1 mol l-1 of BF3 - ether complex. At 81 % conversion oligomer having Mn = 820 was isolated. This value is very close to the one calculated on the assumption that each ethylene glycol molecule participates in the formation of one chain. Mn calcd. = 800. 

In order to investigate the conformational stability of ethylene glycol molecule in the sodalite cage, a molecular dynamic simulation is performed on the force field MM+ as well as semi-empirical PM3. As the result, the gauche(+) conformer is confirmed to be more stable than the gauche(-) one in the sodalite cage. 

The more pronounced changes in the ethylene glycol spectrum produced by the presence of calcium, zinc, or strontium ions were interpreted as resulting from bldentate coordination of the metal ions accompanied by conversion of the ethylene glycol molecules from the trans conformation to the gauche conformation in order to form the complex. The validity of this Interpretation was also subjected to further experimental exploration. 

Scheme 6.2 The production of the polyester poly(ethylene terephthalate), PET. The linking of the terephthahc acid and ethylene glycol molecules occurs at 210 C, and polymerisation and regeneration of ethylene glycol at 270 °C...

In modeling the polycondensation kinetics, there is also a question of how we define the reaction rate constants. In the above reaction represented by a functional-group modeling framework, the forward rate constant k is the reaction rate constant for reaction of a methyl ester group with a hydroxyl group, not the reaction rate constant for DMT and ethylene glycol molecules. For example, the above reaction can be represented as follows ... 

Two recent studies indicate the influence of strong specific interactions on the effective intramolecular potential. Depner et al. used both LD and MD to investigate the dynamics of polyethylene oxide (PEO) in water [50]. They found that the equilibrium distribution of torsional angles observed in the MD simulations differed from that predicted by the LD simulations. Widmalm and Pastor performol LD and MD simulations on one ethylene glycol molecule in water [51]. They found that the effective barrier for isomerization observed in the MD simulations was lower than that expected on the t is of intramolecular potentials alone. 

For example, the polyethylene-block-poly(ethylene glycol) molecule shown in Figure 4.5 is a block copolymer, one section of which is the... 

The only detailed information available on the structures of organo-clays is from studies of vermiculite and kaolinite complexes. Unfortunately, smectites do not form three-dimensionally ordered structures. For the organo-smectites, it is possible to roughly determine the orientation of the molecules in the interlayer space based on the dimensions of the molecules, assumptions as to how the molecules are attached to the clay smface and measured increases in the interlayer spacing compared to the untreated clay mineral. In certain c lses it is possible to calculate the X-ray diffraction intensities for model structrues and compare these with measured values. For example, Reynolds (1965) showed that the ethylene glycol molecule is oriented with the symmetry plane of the molecule oriented normal to the clay layer and coordinating the interlayer Ca ions in a structure with only one-dimensional... 

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