To verify whether the maximum or the minimum Fukui function site is better for protonation reactions or an altogether different local reactivity descriptor, viz., the charge is necessary, we calculate the Fukui functions (using a finite-difference approximation as well as a frozen-core approximation) and charges (Mulliken, Hirshfeld, and natural population analysis schemes) of several hydroxylamine derivatives, their sulfur-containing variants, and amino acids using B3LYP/6-311G(d,p) technique. While the Fukui functions provide the wrong selectivity criterion for hard−hard interactions, the charges are found to be more reliable, vindicating Klopman's idea. It is transparent from the present results that the hard−hard interactions are better explained in terms of charges, whereas the Fukui functions can properly account for soft−soft interactions known to be frontier-controlled.

Spin-polarized density functional theory is used to analyze chemical reactivity from a more general point of view, which distinguishes between the changes produced by charge transfer between the interacting species (changes in the total number of electrons, N = + TVj where f refers to spin-up or a and , to spin-down or ß) and the changes produced by the redistribution of the electronic density of each of the interacting species (changes in the spin number, Ns = Af -7V|). It is found that the response of the system to changes in N and the external potential is given in terms of the chemical potential, the hardness, the electronic density, and the Fukui function, while the response of the system to changes in 7VS and an external magnetic field is given in terms of a new set of parameters which we have named the spin potential, the spin hardness, the spin density, and the spin Fukui function. Making use of the Kohn-Sham approach to density functional theory, it is shown that the generalized Fukui functions can be reduced to a set of spin-polarized classical frontier orbitals by imposing frozen core approximations.

We studied the energetics of finite and infinite polyalanine chains in the α-helical and extended structure by employing density-functional theory. On the basis of these results we extracted the energy of hydrogen bonds (hb's) and their interactions by taking the full peptide−peptide connectivity (backbone) of proteins into account. We focus on two limiting cases:  an isolated hb and one within an infinite α-helical chain. In the infinite chain the cooperativity within an infinite network of hb's strengthens each individual bond by more than a factor of 2. This effect has important consequences for the stability of α-helices.

No abstract

In Chile, childhood obesity rates are high. The purpose of this article is to compare BMI growth characteristics of normal (N), overweight (OW), and obese (OB) 5‐year olds from 0 to 5 years and explore the influence of some prenatal factors on these patterns of growth. The study was done on a retrospective cohort of 1,089 5‐year olds with birth weight >2,500 g. Weight and height were obtained from records at nine occasions (0–36 months); at 52 and 60 months, we measured them. At 60 months, children were classified as N, OW, and OB. At each age, BMI and z‐score of BMI (BMI Z) differences were compared among groups. The influence of birth weight, pre‐pregnancy BMI, and prenatal variables (weight gain, smoking, and presence of diabetes and preeclampsia) on BMI Z differences between N and OB was also explored. Adiposity rebound (AR) was not observed for the N, although for the OW, it occurred ∼52 months and for the OB at ∼24 months. BMI Z differences between N and OB were significant from birth, but were greatest between 6–12 and 36–52 months. Additional adjustment by birth weight, pre‐pregnancy BMI, and prenatal variables decreased the BMI Z differences for the first 24 months with virtually no effect after this age. Accelerated growth in OB children from post‐transition countries occurs immediately after birth, much earlier than the AR. The influence of prenatal factors on adiposity acquisition may extend at most until 2 years of life, although BMI gains thereafter are more related to postnatal variables.

No abstract

We analyzed the response to strain of an infinite polyalanine chain in the alpha-helical conformation using density functional theory. Under compressive strain the alpha-helix is found to undergo structural transitions to a pi-helix when the length of the helix is reduced by more than 10%. Under tensile strain the structure changes into a 3(10)-helix when the length is stretched by more than 10%. Our analysis of these transitions shows that they proceed essentially in two steps: At first there is mainly a length change, and only with some delay the helix twist adjusts.

We introduce and test a nucleophilicity index as a new descriptor of chemical reactivity. The index is derived from a perturbation model for the interaction between the nucleophile and a positive test charge. The computational implementation of the model uses an isoelectronic process involving the minimum values of the electronic part of the perturbed molecular electrostatic potential. The working expression defining the nucleophilicity index encompasses both the electrostatic contributions and the second-order polarization effects in a form which is consistent with the empirical scales previously proposed. The index is validated for a series of neutral nucleophiles in the gas phase for which the nucleophilicity pattern has been experimentally established within a spectroscopic scale.