Decrease In Effective Charge Research Articles

Effective Charge Determination of Dendrigraft Poly-l-lysine by Capillary Isotachophoresis

In this work, capillary isotachophoresis (ITP) was used to determine the effective charge of the first five generations of dendrigraft poly-l-lysines. This approach, which is based on the linear dependence of ITP zone length of the solute on its concentration and effective charge, offers a simple and straightforward method for effective charge determination. The cationic ITP system employed in this work yields good linearity, repeatability and sharp zones. The value of effective charge number per one lysine residue obtained for long linear poly-l-lysine is in a good agreement with the Manning theoretical value (0.5). Results obtained for dendrigraft poly-l-lysines show a dramatic decrease in the effective charge number per lysine residue with increasing generation number, from 0.84 for short oligolysines (generation 1) down to 0.08 for the fifth generation. This decrease in effective charge is due to the proximity of charged groups in the dendrigraft structure of higher generation number.

Lattice dynamics, phase transitions and hydrogen effective charges of betaine phosphite: a comparison with betaine phosphate and their deuterated analogues

The temperature dependence of complete infrared reflection spectra of a betaine phosphite single crystal is reported for the polarizations parallel to a and b axes in the wavenumber range from 10 to . They are compared with previous data that were limited to the range . They are also compared with reflectivity spectra of betaine phosphate, betaine arsenate, deuterated betaine phosphite single crystals and betaine compressed powder. These comparisons allow a mode assignment. Spectra were fitted with the factorized form of the dielectric function. The role of phonons in the behaviour of the dielectric constant in the vicinity of the ferroelectric (FE)-paraelectric (PE) phase transition is discussed. The decrease of effective charges along the FE axis below the FE-PE phase transition is assigned to an increase of oxygen-hydrogen electronic orbital hybridization related to the change of average bond-length.

How delocalised are resonance-stabilised 1-[4-(N-methyl-N-alkylamino)phenyl]-2,2,2-trifluoroethyl carbocations?

An N-trifluoroethyl for N-methyl substitution causes a ≥ 104.1-fold increase in the equilibrium constant for the reaction of 4-Me2NArCH(CF3)+ with 4-nitrobenzoate anion in 20% acetonitrile in water. The N-trifluoroethyl for N-methyl substitution causes a 105.0-fold increase in the dissociation constant for loss of a proton from nitrogen at 4-Me2NH+ArCH(CF3)OH, a reaction in which there is a full unit decrease in charge at nitrogen. These data show that the reaction of 4-Me2NArCH(CF3)+ with 4-nitrobenzoate anion behaves as if there were a decrease in effective charge at nitrogen of ≥ 0.80 units on moving from the carbocation to the neutral nucleophile adduct 4-Me(R)NArCH(CF3)(4-nitrobenzoate). The results suggest that the positive charge at these carbocations is largely localised at nitrogen, so that they more closely resemble iminium ions than benzyl carbocations.