Anion-it interactions

Anion-it interaction is also recognized in halide associates with aromatic rings when the latter represents a part of the (positively charged) metal-ion complex and/or when it-bonding is supported by hydrogen bonding. 

Figure 3.9 Molecular structures of compounds 107 (a) and 108 (b), showing the anion-it interactions. The it — Jt stacking (the centroids are indicated) between the organic components is reflected. Distances are in A.

Br", 30 M for Cl" and 34 for I". On the other hand, the association constant for receptor A lacking the electron-deficient aromatic ring required for the anion-JT interaction, were too small to be determined using the same titration methodology. The enhanced affinity exhibited by receptor B over receptor A with the array of halides is attributed to the existence of anion- it interaction in the anion complex. 

Perraud O, Robert V, Gomitzka H, Martinez A, Dutasta J-P (2012) Combined cation—it and anion—it interactions for zwitterion recognition. Angew Chem Int Ed 51 504-508... 

In presence of polyamines the maximum of light absorption of indicated triphenylmethane dyes displaces on 10-30 nm, for azo dyes the shift of the band reaches 50-80 nm. The greatest difference of light absorption of associates and reagents is watched for BKM at pH 5,05, for BPR at pH 4,20, for CPR in an interval pH 5,05-5,45. At these pH dyes are anions, it promotes interaction with a cationic surface-active substance. The ratios between polymer and BKM, BPR, CPR are established by spectroscopy method, its equal 1 20, 1 20 and 1 30 accordingly. 

Water is a polar molecule and as a result will orient itself differently around cations and anions. It will align its dipole to present the most favorable interaction possible hydrogen atoms will be closer to an anion whereas oxygen atoms will be closer to a cation. 

Dihydro-l,3-diborolenes are accessible as pentaorgano derivatives " and serve as ideal precursors of the diborolyl radieal. The formation of the radical and its interaction with a metal center is formally described as a metal oxidation. The resulting 2,3-dihydro-1,3-diborolyI ligand is either a three-electron donor or an anionic four-electron donor. l,3,4,5-Tetraethyl-2-methyl-2,3-dihydro-l,3-diborole reacts with [T -CpNi(CO)2] or (T7 -Cp>2Ni in hot mesitylene to yield a sandwich complex and a triple-decked complex ... 

In addition to four atoms in a row, a four-atom deiocaiized framework can have a centrai atom surrounded by three other atoms with which it interacts. An exampie is the carbonate anion, whose Lewis structure dispiays resonance ... 

As with the previous element, the dangerous reactions of antimony derivatives are linked to the behaviour of the anion. The element is reducing and apart from its interaction with two metals it gives rise to dangerous reactions with strong oxidants. 

It seems possible that a very hydrophilic anion such as OH- might not in fact penetrate the micellar surface (Scheme 1) so that its interaction with a cationic micelle would be non-specific, and it would exist in the diffuse, Gouy-Chapman layer adjacent to the micelle. In other words, OH" would not be bound in the Stem layer, although other less hydrophilic anions such as Br, CN or N 3 probably would bind specifically in this layer. In fact the distinction between micellar and aqueous pseudophases is partially lost for reactions of very hydrophilic anions. The distinction is, however, appropriate for micellar reactions of less hydrophilic ions. 

The surface charge of a fibre has an important influence on its interaction with chemicals (both particulate and soluble) which are added to the aqueous fibre suspension. Their anionicity gives them a high affinity towards cationic additives, and many additives are produced in a cationic form in order to maximise their retention. The pH of the aqueous paper-making system is also important in these interactions. The surface charge of cellulose, because it arises from the dissociation of acidic groups, is dependent upon pH (see... 

Anions and uncharged analytes tend to spend more time in the buffered solution and as a result their movement relates to this. While these are useful generalizations, various factors contribute to the migration order of the analytes. These include the anionic or cationic nature of the surfactant, the influence of electroendosmosis, the properties of the buffer, the contributions of electrostatic versus hydrophobic interactions and the electrophoretic mobility of the native analyte. In addition, organic modifiers, e.g. methanol, acetonitrile and tetrahydrofuran are used to enhance separations and these increase the affinity of the more hydrophobic analytes for the liquid rather than the micellar phase. The effect of chirality of the analyte on its interaction with the micelles is utilized to separate enantiomers that either are already present in a sample or have been chemically produced. Such pre-capillary derivatization has been used to produce chiral amino acids for capillary electrophoresis. An alternative approach to chiral separations is the incorporation of additives such as cyclodextrins in the buffer solution. 

In flotation, when sphalerite is activated by Cu or Fe the ZnS surface will exhibit good reactivity to organic collector. Our calculation shows that when the surface is doped by transition metal ions, the surface ions will be rendered more ionic property, which benefits the interaction between the mineral surface and the collector anions. It gives more profoimd explanation for Cu activated behavior to ZnS. 

This greater interaction of the betaine with anions than with cations is seen also in its interaction with other surfactants (17)... 

A similar example of curing inhibition In an acidic medium has been observed when moderate amounts of salicylic acid were added to epoxy-amine matrix systems. (26) Such behavior may beresponsible for the poor bond strengths observed with the NTMP-containing oxide-primer specimens. In environments containing an aggressive species (e.g.. Cl ), the anion may interact with and become incorporated into the NTMP-oxide matrix, whereby it can attack the metal surface. 

The electrostatic cation-anion interactions will depend on the properties of the anion its charge, its size, its shape, its polarizability. Large anions lead to weaker interactions because of larger cation-anion distances ion-paired complexes of divalent AEC s will be much more destabilized by an increase in anionic size than AC complexes ... 

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