Soft ionization definition

The term "molecular ion" by definition refers to a radical cation or anion of an intact molecule. Molecular ions are odd-electron ions, which may thus be generated by El. Unfortimately, the term molecular ion is also frequently used to indicate the even-electron ionic species produced by electrospray and APCl. This obviously is not correct. In the soft ionization techniques, predominantly even-electron protonated molecules are generated in positive-ion mode, and deprotonated molecules in negative ions. In addition, various adduct ions may be generated (Table 2.2). These all are even-electron ions, and should therefore not be referred to as molecular ions. Alternatively, the term protonated molecular ions is used, which again is incorrect one cannot protonate a radical cation ... 

Although the local softness includes, by definition, both the differences of frontier orbitals of the neutral substrate and the differential electron densities between the neutral and ionized states, as expressed in the global softness and Fukui functions, the actual computations of these quantities suffer from some severe practical limitations . 

Introduction of ionization of protein molecules by soft laser desorption, which is basic theory for MALDI-TOF MS and SELDI-TOF MS 1995 Definition of proteomics was first coined... 

Conventionally, the hardness is obtained from the values of the ionization potential (I) and the electron affinity (A), T]=(I-A)/2, through the finite difference method. While the chemical potential is constant everywhere within the molecule, the hardness, and then the softness, is a function of the position. Thus, in addition to the global definition of T] and S, the local hardness [43] and local softness [44] have been introduced. 

The purpose of this work is to start from the basic equations of density functional theory to describe the changes in the energy associated with the transition from one ground-state to another, in terms of different sets of variables. In this process one will find the natural definitions of the hardness and softness kernels, the local hardness, the local softness, the global hardness and the global softness [23]. Then, we will proceed to establish their relation with ionization potentials and electron affinities, in order to confirm their behavior as a measure of chemical hardness or softness [14, 24]. Finally, this theoretical framework will be used to analyze the maximum hardness and the HSAB principles. 

The finite-difference (FD) definition based on vertical ionization energy (IP) and electron affinity (EA) scales was added for experimental assessment (Lackner Zweig, 1983). For comparison, the softness based chemical hardness values based on sphere-charged model of Pearson was also employed (Pearson, 1997). In all cases the atomic values were computed upon hydrogen calibration to its experimental 6.45 eV value. All values are in electron-volts (Putz, 2008c). 

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