Hydrophobic species

The adsorption of collectors on sulfide mineral occurs by two separate mechanisms chemical and electrochemical. The former results in the presence of chemisorbed metal xanthate (or other thiol collector ion) onto the mineral surface. The latter yields an oxidation product (dixanthogen if collector added is xanthate) that is the hydrophobic species adsorbed onto the mineral surface. The chemisorption mechanism is reported to occur with galena, chalcocite and sphalerite minerals, whereas electrochemical oxidation is reportedly the primary mechanism for pyrite, arsenopyrite, and pyrrhotite minerals. The mineral, chalcopyrite, is an example where both the mechanisms are known to be operative. Besides these mechanisms, the adsorption of collectors can be explained from the point of interfacial energies involved between air, mineral, and solution. 

To use liposomes as delivery systems, drug is added during the formation process. Flydrophilic compounds usually reside in the aqueous portion of the vesicle, whereas hydrophobic species tend to remain in the lipid proteins. The physical characteristics and stability of lipsomal preparations depend on pH, ionic strength, the presence of divalent cations, and the nature of the phospholipids and additives used [45 47],... 

Modified silica with a C18 reversed-phase sorbent has historically been the most popular packing material, owing to its greater capacity compared to other bonded silicas, such as the C8 or CN types [22]. Applications of C18 sorbents include the isolation of hydrophobic species from aqueous solutions. The mechanism of interaction with such sorbents depends on van der Waals forces, and secondary interactions such as hydrogen bonding and dipole-dipole interactions. Nevertheless, the main drawbacks of such sorbents are their limited breakthrough volumes for polar analytes, and their narrow pH stability range. For these reasons, reversed-phase polymeric sorbents are also used frequently in environmental applications for the trace enrichment of soluble molecules that are not isolated by reversed-phase sorbents such as C18. 

Partitioning of metal complexes into the lipid bilayer of membranes is only significant for hydrophobic species. FA and HA, and their metal complexes, are not expected to enter to a significant extent into the lipid bilayer, due to their large molecular size. Uptake of hydrophobic metal species by diffusion across... 

Residues of incompletely degraded surfactants can also enter the aquatic environment via WWTP effluents, and these can follow various fates. More hydrophobic species with low water solubilities are prone to bind to suspended particles or to sediments (see Chapter 6.2.1) [58-60] and in very rare cases may cross the water-gas phase boundary to enter the atmosphere [61]. 

Although the nature of the hydrophobic entity responsible for the self-induced flotation of sulphide minerals remains somewhat obscure, most reported results clearly show that it is only when the environment becomes slightly oxidizing that flotation is observed. The elemental sulphur and polysulphide-intermediates in the oxidation of sulphide to sulphur have ever been suggested to be of the hydrophobic species. Whatever it is, there is no doubt that sulphur can generate hydrophobicity and floatability. 

Pyrite oxidation reactions include the reactions producing hydrophobic species ... 

Abstract In the beginning, the mixed potential model, which is generally used to explain the adsorption of collectors on the sulphide minerals, is illustrated. And the collector flotation of several kinds of minerals such as copper sulphide minerals, lead sulphide minerals, zinc sulphide minerals and iron sulphide minerals is discussed in the aspect of pulp potential and the nature of hydrophobic entity is concluded from the dependence of flotation on pulp potential. In the following section, the electrochemical phase diagrams for butyl xanthate/water system and chalcocite/oxygen/xanthate system are all demonstrated from which some useful information about the hydrophobic species are obtained. And some instrumental methods including UV analysis, FTIR analysis and XPS analysis can also be used to investigated sulphide mineral-thio-collector sytem. And some examples about that are listed in the last part of this chapter. 

There is lack of consensus in the published electrochemical studies of flotation of galena and the nature of the important hydrophobic species responsible for... 

The UV spectra of the cyclohexane solution extracted from jamesonite acted by DDTC solution, shown in Fig. 4.34, indicates that the adsorption of diethyl dithiocarbamate on the surface of jamesonite is almost the same at pH = 4 and 7, but decreases with the increasing of pH in the base solution. Because the UV spectra in Fig. 4.33 and Fig. 4.34 are similar with peaks at 230 mn and 260 nm, it indicates that the hydrophobic species on jamesonite should be the mixture of diethyl dithiocarbamate and its dimmer. 

After ethyl xanthate interacts with marmatite, the UV spectra of the hydrophobic species on marmatite surface extracted by cyclohexane are shown in Fig. 4.37. There are three UV peaks, lying in 228 nm, 263 nm and 286 nm respectively. It is... 

The FTIR reflection spectra of ethyl xanthate adsorption on jamesonite are shown in Fig. 4.42. It can be seen that the characteristic absorption bands of lead ethyl xanthate at 1020,1112 and 1206 cm" appeared on the surface of jamesonite, indicating the primary hydrophobic species on jamesonite surface to be lead ethyl xanthate. It is possible that antimony ethyl xanthate was formed on jamesonite surface simultaneity like lead ethyl xanthate. 

FTIR reflection spectra of diethyl dithiocarbamate adsorption on pyrrhotite at pulp pH = 7.0 are demonstrated in Fig. 4.46. From Fig. 4.46, it can be seen that the characteristic absorption bands of dimmer of diethyl dithiocarbamate at 1468, 1425,1350,1269,1201,1139,1064,1005 and 968 cm appear on the surface of pyrrhotite, indicating the dominating hydrophobic species on pyrrhotite surface to be disulphide of dithiocarbamate. FiuTher, the effect of pulp potential on the adsorption of dithiocarbamate on pyrrhotite was examined and the results are presented in Fig. 4.47. It follows that at pH = 8.8 the dithiocarbamate adsorption on p)TThotite is mainly of disulphide independent of potential in die range of 297 - 687 mV due to the occurrence of almost the same disulphide characteristic band. However, the intensity of the IR signals changes at various potential values. It demonstrates the intensity of the IR signals of the characteristic peaks of thiouram disulphide and hence its adsorption on pyrrhotite decreases with the increase of the potential from 297 - 687 mV. At pH= 8.8, flotation recovery and... 

The diester quats used for fabric softening are hydrophobic species with very limited water solubility. In water they form lamellar phases and liposomes at low concentration. The low water solubility in combination with the hydrolytic instability makes formulation of softener products a demanding task, and a plethora of patents and patent applications related to ester quat formulations have been published during the last decade [21], The diester... 

The formation of a compact structure accompanying the complexation of PMMA with PEO and the lower flexibility of the PMMA chain in the complex than that of the PAA chain have been confirmed by viscometry [ 16], membrane contraction [2], and polarized luminescence techniques [3]. In addition, comparison of the dynamic light-scattering behavior of PMAA/PEO and PMAA/PEO" in solution shows that the pyrene label, which acts as a hydrophobic species, allows the labeled PEO to aggregate intermolecularly much faster than unlabeled PEO does [30]. 

Mechanism of Separation. There are several requirements for chiral recognition. (/) Formation of an inclusion complex between the solute and the cydodextrin cavity is needed (4,10). This has been demonstrated by performing a normal-phase separation, eg, using hexane—isopropanol mobile phase, on a J3-CD column. The enantiomeric solute is then restricted to the outside surface of the cydodextrin cavity because the hydrophobic solvent occupies the interior of the cydodextrin. (2) The inclusion complex formed should provide a rdatively "tight fit" between the hydrophobic species and the cydodextrin cavity. This is evident by the fact that J3-CD exhibits better enantioselectivity for molecules the size of biphenyl or naphthalene than it does for smaller molecules. Smaller compounds are not as rigidly held and appear to be able to move in such a manner that they experience the same average environment. (5) The chiral center, or a substituent attached to the chiral center, must be near to and interact with the mouth of the cydodextrin cavity. When these three requirements are fulfilled the possibility of chiral recognition is favorable. 

In fact, there are other considerations that complicate the compositional issue still further. The ad-variants bear a further optically active center as a result of the chain-branch position, which is likely to be racemic (it is adjacent to a carbonyl moiety). Because it is remote through space from other optical centers in a-acids and other optically active hop-derived components, it is unlikely to have a practical bearing on the properties and therefore the application of these compounds. More relevant though is the observation of minor components of the a-acids that have both shorter and longer side chains than the more abundant co-, n-, and ad-variants. Given that hydrophobicity is related to the potency of the brewing value of the hop-derived components, there is justification for the quantification of particularly the more hydrophobic species, as recently exemplified by Wilson et al. (18). 

Polymeric reversed phase resins are synthesized from divinylbenzene with styrene, methylstyrene or other styrenic monomers. Divinylbenzene is the major component and provides crosslinking. These resins are macroporous, and the surface area is usually in excess of 300 m2 / g. This surface area provides the adsorptive surface for retention of hydrophobic species. These resins can be used for matrix elimination of surfactants, weak carboxylic acids, fats, proteins, etc. 

Hydrophobic species bearing hydrocarbon chains present vitamin B12 or vitamin B6 type activity [5.37]. Such systems lend themselves to inclusion in membrane or micellar media. They thus provide a link with catalysis in more or less organized media such as membranes, vesicles, micelles, polymers [5.39-5.41] (see Section 7.4). Water soluble cyclophanes showing, for example, transaminase [5.42], acetyl transfer [5.43], pyruvate oxidase [5.44] or nucleophilic substitution [5.45] activity have been described. 

The simplest use of micelles is in the solubilization of hydrophobic species and early experiments showed that [ZnTPP] in TritonX-100 micelles could act as a cliromophore in the photochemical reduction of MV2+ by ethanethiol or TEOA. Hydrogen was produced if hydrogenase or colloidal Pt were added.331 Zinc porphyrins in neutral micelles (TritonX-100) produce332 hydrogen on photolysis in the presence of TEOA, bipy and K2[PtCl6J. 

The presence of a hydrophobic-hydrophilic interface can dramatically change the reaction conditions. The hydrophobic core will selectively absorb hydrophobic species from the solution (Fig. 12), and this will result in a redistribution of monomer concentrations between the core and bulk solution. Because the probability of attachment for each comonomer is determined by its concentration in a relatively small reaction volume near an active chain end, the active center inside the hydrophobic core will mainly attach more hydrophobic species on the other hand, when the active center is located on the globule surface, it will mainly attach polar (soluble) monomers. In this way, the two-layer globule will grow, retaining its core-shell structure with a predominantly hydrophobic core and a hydrophilic outer envelope (see Fig. 12). 

Because of the strong attraction of hydrophobic species for insoluble materials such as humic matter, many organic pollutants in the aquatic environment are held by sediments in bodies of water. Bioaccumulation of these materials must, therefore, consider transfer from sediment to water to organism, as illustrated in Figure 5.4. 

Ionic liquids show interesting properties with respect to their miscibility with other liquids. They can be broadly divided into hydrophilic and hydrophobic species, which are either miscible or largely immiscible with water. The aqueous miscibility of ionic liquids can be understood by applying the well-known Hofmeister [63] scale of hydrophobicity to their component ions [64], The aqueous miscibility of ionic liquids also depends strongly on temperature, a fact that has been exploited in novel chemical processes [65]. Mixtures of ILs and organic phases also show interesting properties [66, 67], though we will not discuss them in detail in this chapter. 

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