Electrostatic attraction between molecule

Many biological processes involve an associa tion between two species in a step prior to some subsequent transformation This asso ciation can take many forms It can be a weak associ ation of the attractive van der Waals type or a stronger interaction such as a hydrogen bond It can be an electrostatic attraction between a positively charged atom of one molecule and a negatively charged atom of another Covalent bond formation between two species of complementary chemical re activity represents an extreme kind of association It often occurs in biological processes in which aide hydes or ketones react with amines via imine inter mediates... 

Two types of chemical bonds, ionic and covalent, are found in chemical compounds. An ionic bond results from the transfer of valence electrons from the atom of an electropositive element (M) to the atom(s) of an electronegative element (X). It is due to coulombic (electrostatic) attraction between the oppositely charged ions, M (cation) and X (anion). Such ionic bonds are typical of the stable salts formed by combination of the metallic elements (Na, K, Li, Mg, etc.) with the nonmetallic elements (F, Cl, Br, etc.). As an example, the formation of the magnesium chloride molecule from its elemental atoms is shown by the following sequence ... 

When sodium reacts with chlorine to form NaCl, an electron moves from a sodium atom to a chlorine atom. The result is a compound composed of sodium ions and chloride ions, Na Ch, held together by an ionic bond. Ionic bonds do not hold molecules together by sharing electrons they hold them together because of the electrostatic attraction between the two oppositely charged ions. 

Table I. This is probably due to electrostatic attraction between polymer and particle and to the porous and flexible nature of the polymer molecule.

Phosphate is charged (2—) so when it is incorporated into an enzyme, alterations in the electrostatic attractions between parts of the enzyme molecule will occur causing a change in the three-dimensional conformation of the protein. The effect may be to expose the active site to allow substrate binding (if phosphorylation activates the enzyme) or may hide the active site, so switching off the enzyme. 

The anion dissociates, and the coordinatively unsaturated metal center then picks up a monomer molecule for subsequent enchainment. This dissociative model has been favored in the past [16, 21-23, 27-28] since it allows a convenient explanation of the observed polymer stereochemistry by considering only the roles of the ligand and the alkyl chain in the cationic metallocene complex. However, anion dissociation opposes the electrostatic attraction between cation and anion and is therefore energetically expensive. So does it operate at all ... 

The attractive forces that can hold molecules together include van der Waals interaction, electrostatic attraction (when molecules are charged or polar), and hydrogen bonding. Since there is no clear border between a very weak hydrogen bond and van der Waals interaction, the latter requires some explanation. 

A crystal can be dissociated into molecules by means other than evaporation it can be crushed or split, and the work required to overcome the electrostatic attraction between the ions is reflected in the hardness of the crystal. For crystals of similar structure, the harder ones will contain ions with higher charges, so that MgO is harder than NaF. Crystals of the XY2 type can be built up from molecules in an analogous manner, and their properties will, in the main, be similar to those of compounds of the type XY. 

---