Solubility requirements

For samples that meet the solubility requirements of the SEC approach, analyses were also reported for additives in polymers such as PVC and PS [28,29]. Direct SEC analysis of PVC additives such as plasticisers and thermal stabilisers in dissolution mode has been described [28,30,31 ]. In the analysis of a dissolved PS sample using a SEC column of narrow pore size, the group of additives was separated on a normal-phase column after elution of the polymer peak [21]. Column-loading capacity of HPSEC for the analysis of additives, their degradation products and any other low-MW compounds present in plastics has been evaluated for PS/HMBT, PVC/TNPP and PVC/TETO (glyceryl tri[l-14C] epoxyoleate) [31]. It was shown that HPSEC can be used to separate low-MW compounds from relatively large amounts of polymers without serious loss of resolution of the additives the technique has also been used for the group analysis of chlorohydrin transformation products of the TETO model compound [32]. 

Steric Stabilization. Steric stabilization was a term first introduced by Heller to explain how adsorbed polyethylene oxide polymers increased the salt concentration required for flocculation of negatively charged aqueous suspensions.(6) Heller s systems were stabilized by both mechanisms, as are most commercial dispersions today, aqueous and non-aqueous. Much of the more recent literature on steric stabilizers has been preoccupied with solubility requirements, for the solubility of polymers is a delicate matter and very sensitive to temperature and solvent... 

In principle, Gibbs free energies of transfer for trihalides can be obtained from solubilities in water and in nonaqueous or mixed aqueous solutions. However, there are two major obstacles here. The first is the prevalence of hydrates and solvates. This may complicate the calculation of AGtr(LnX3) values, for application of the standard formula connecting AGt, with solubilities requires that the composition of the solid phase be the same in equilibrium with the two solvent media in question. The other major hurdle is that solubilities of the trichlorides, tribromides, and triiodides in water are so high that knowledge of activity coefficients, which indeed are known to be far from unity 4b), is essential (201). These can, indeed, be measured, but such measurements require much time, care, and patience. 

Powder light and small packaging lenient solubility requirement for ingredients no cleaning action without dissolution caking problem during storage... 

Depending on the drug substance properties and the medical indication, the appropriate formulation is chosen. Drug substances which have a good solubility may be formulated in a simple tablet formulation, while drug substance candidates with low solubilities require special delivery systems like microemulsion formulations. 

Water solubility is determined by polymer structure (linear, branched, etc.), concentration and placement of charged species [ionomeric (cationic or anionic) or amphoteric (cationic and anioiuc)], hydrophihc/hydrophobic substituents, and hydrogen bonding, to name the more commonly encountered factors. In general, polymer water solubility requires polar functional... 

Because of the small ionic radius of lithium ion, most simple salts of lithium fail to meet the minimum solubility requirement in low dielectric media. Examples are halides, LiX (where X = Cl and F), or the oxides Li20. Although solubility in nonaqueous solvents would increase if the anion is replaced by a so-called soft Lewis base such as Br , I , S , or carboxylates (R—C02 ), the improvement is usually realized at the expense of the anodic stability of the salt because these anions are readily oxidized on the charged surfaces of cathode materials at <4.0 V vs Li. 

Limitations Unsuitable for final cleavage step Problematic in multistep syntheses Different solubilities required... 

Classical MALDI-MS requires that the material should be soluble in a suitable solvent. A suitable solvent means a solvent that is sufficiently volatile to allow it to be evaporated prior to the procedure. Further, such a solvent should dissolve both the polymer and the matrix material. Finally, an ideal solvent will allow a decent level of polymer solubility, preferably a solubility of several percentage and greater. For most synthetic polymers, these qualifications are only approximately attained. Thus, traditional MALDI-MS has not achieved its possible position as a general use modern characterization tool for synthetic polymers. By comparison, MALDI-MS is extremely useful for many biopolymers where the polymers are soluble in water. It is also useful in the identification of synthetic polymers, such as PEO where the solubility requirements are fulfilled. Thus, for PEO we have determined the molecular weight distribution of a series of compounds with the separations in ion fragment mass 44 Da corresponding to CH2-CH2 units. 

At the beginning of the project, it is often difficult to have a precise idea of the projected therapeutic dose. Projects usually start with an estimated average potency of 1 mg/kg, once daily dose as an optimal approach. When initial pharmacokinetic/ pharmacodynamic (PK/PD) data becomes available one can better refine the TCP. Table 3.1 gives some guidelines on how to adjust the solubility requirement depending on the therapeutic dose and compound permeability. 

This method is based on the activation of one cysteine peptide as a sulfenohydrazide derivative by the reaction of the free thiol group of the cysteine peptide with azodicarboxylic acid as a dialkyl ester or dimorpholide depending on the solubility requirements.156 Following the isolation and characterization of the S-activated intermediate, reaction with a second free thiol cysteine component via thiolysis leads to the desired intermolecular disulfide bond, as shown in Scheme 4. 

An additional factor was found to influence the rate of reaction in the experiments involving tetrakis ( -mercaptoethylamine) trinickel (II) ion. The addition of nickel chloride retarded the process. Methanol was used as the solvent to demonstrate that the dependence was actually due to the presence of nickel ion and not an ionic strength effect. Magnesium chloride accelerates the rate slightly, while nickel ion greatly retards the rate of reaction. This effect was studied in greater detail, but solubility requirements necessitated the use of a water-methanol mixed solvent. A solution of 5.5M water in methanol was found to be satisfactory to obtain the necessary solubilities of complex and nickel chloride. 

Proline dissolves readily in dimethyl sulfoxide. Some other amino acids which are less-soluble require longer reaction times and, in some instances, other solvents.11 These details and the scope of the reaction are illustrated in Table I. 

If the moving phase is a liquid, then the technique is called liquid chromatography (LC). In liquid chromatography the sample is first dissolved in the moving phase and injected at ambient temperature. Thus there is no volatility requirement for samples. However, the sample must dissolve in the moving phase. Note that LC has an important advantage over GC The solubility requirement can usually be met by... 

Since most other modeling techniques for polymers are extremely demanding, the limited capabilities of COSMO-RS for efficient prediction of solubilities in polymers can be of great help in practical applications when suitable polymers with certain solubility requirements are desired. One application may be the selection of appropriate membrane polymers for certain separation processes. Predictions of drug solubility in polymers are sometimes of interest for pharmaceutical applications. Furthermore, it is most likely that COSMO-RS can also be used to investigate the mutual compatibility of polymers for blends. This aspect, and many other aspects of the potential of COSMO-RS for polymer modeling, still awaits systematic investigation. 

Nevertheless, since almost all drug compounds are solid at ambient temperature, the calculation of aqueous drug solubility requires knowledge of the chemical potential, Acrystalline state. However, at present, there is no computational method available to reliably predict this chemical potential. Such prediction would involve knowledge about the crystal structure of the compound, which must... 

The choice of the solvent as the reaction medium depends on its ability to allow sufficient concentrations of the reactants to be achieved (solubility requirements) solvating them to an extent commensurate with the desired reactivity of the reactants. At the same time it also depends on the solvent being inert with respect to them and the reaction products, so that it is not itself attacked. Further considerations are the ease with which the products are liberated from excess reactants, if present, and from the solvent itself, possible effects on the relative yields of desired products and undesired by-products, and effects on the rates at which the reactions proceed, see Chapter 2. 

Complete solid solubility requires that components have the same crystal structure, similar atomic size, electronegativity and valency. If any of these conditions are not met, a miscibility gap will occur in the solid state. 

Although ethanol is the usual reaction solvent, lower ketones such as 2-butanone are also useful solvents if an intermediate contains a group reactive to alcohols, e.g., l-(2-carboxyethyl)Fischer s Base hydroiodide.70 In aromatic solvents such as toluene, the condensation proceeds well and the water formed may be removed by azeatroping, but the product generally is easily soluble, requiring concentration of the reaction mixture. Separation of pure spiropyran from colored impurities of similar solubility may then be tedious. 

UCON is a random copolymer of ethylene oxide (EO) and propylene oxide (PO) and can be considered as a synthetic oil. POE is poly(oxyethylene), which is a homopolymer of EO. Random EO-PO copolymers are typical of synthetic oils used as lubricants in textile processing (53, 54). PLURONICS (BASE) are block copolymers of EO and PO. Both of these copolymers can be produced with viscosities ranging from that of a thin oil to that of a thick paste. Oils of appropriate viscosity give hydrodynamic lubrication in the high-speed spinning of synthetic fibers. The hydrophile-lipophile balance (HLB) in these polymers can be varied, by changing the EO-PO composition, to suit the aqueous solubility requirements. 

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