Development of group 4 and 5 complexes with N,O chelating supporting ligands as catalysts for the alpha-alkylation of amines

The use of stoichiometric, catalytic and theoretical methods in the development of an early transition metal catalyst for the α-alkylation of amines is described herein. The investigation is primarily focused on a series of mono(amidate) complexes of tantalum with varying steric and electronic properties. The amidate binding mode and catalytic activity of these complexes is significantly influenced by sterics. Corresponding bis(amidate) complexes are less active as catalysts for the α-alkylation of amines but offers a platform to study the hemi-lability of amidate ligands as well as tantalaziridine formation in these systems. A model 5-membered metallacycle is synthesized and characterized. Isotopic labeling studies with the most active mono(amidate) precatalyst reveal off-cycle reactions and suggest that tantalaziridine formation is rapid and reversible. Preliminary kinetic investigations implicate alkene insertion as the turnover limiting step, consistent with stoichiometric investigations. In addition, the use of radical probes in ligand backbones and an alkene substrate contradicts a one electron mechanism. Quantum chemical calculations are used to develop a theoretical model of the proposed catalytic cycle. The hemi-lability of amidate ligands is highlighted with the optimization of both κ¹(O) and κ²(N,O) minima and transition states. Here, protonolysis is calculated to be the turnover limiting step with small changes in geometry having a significant effect on the potential energy surface. The unlikelihood of a radical mechanism is supported by the computations of triplet species. A survey of established steric parameters has been completed for asymmetric amidate ligands to be used as a predictive tool for catalyst design. The calculated values can be related to the catalytic activity of mono(amidate) and axially chiral tantalum precatalysts. Diamide and diurea proligands featuring a neutral chalcogen atom tether are installed on zirconium and tantalum. The zirconium species form well-defined κ⁴(N,N,O,O) complexes with fluxional behaviour observed for the tantalum species in solution. No evidence of bonding is observed between the chalcogen donor and any metal centre. Fundamental differences in the redox potentials for ligands and complexes are investigated using cyclic voltammetry. The tantalum complexes are found to catalyze the α-alkylation of amines with the zirconium species being competent precatalysts for hydroamination.Science, Faculty ofChemistry, Department ofGraduat

Is restrained eating a risk factor for weight gain in a general population?

BACKGROUND: In modern societies characterized by abundant and accessible foods, restrained eating may become an adaptive behavior to limit weight gain. OBJECTIVE: We assessed the relations between eating behavior (EB) and adiposity in a general population over a 2-y period. DESIGN: We recruited 466 adults and 271 adolescents in 1999 on a geographical basis to participate in a longitudinal study. At the initial examination and 2 y later, they answered an EB questionnaire, the Three-Factor Eating Questionnaire-R18, which measured cognitive restraint (CR), uncontrolled eating, and emotional eating. On the same occasions, several measures of adiposity were also obtained: body mass index (BMI; in kg/m2), waist circumference, the sum of 4 skinfold thicknesses, and percentage body fat. Relations between EB and adiposity were tested separately in adults and adolescents by using mixed linear regressions after adjustment for age, sex, and (in adolescents) Tanner pubertal stage. RESULTS: At baseline, CR was positively associated with BMI in normal-weight subjects (mean BMI: 21.4 in the lowest to 23.3 in the highest CR quintile; P < 0.001) but not in overweight adults (P = 0.25). Initial CR did not predict change in adiposity variables (BMI change: P = 0.79 in adults, P = 0.57 in adolescents and young adults). Conversely, a high initial BMI was associated with a larger increase in CR (beta = 20.1, P < 0.0001 in adults; beta = 21.7, P = 0.003 in adolescents and young adults). CONCLUSIONS: Restrained eating is strongly associated with adiposity in normal-weight subjects but not in overweight subjects. However, restrained eating does not promote weight gain

Is restrained eating a risk factor for weight gain in a general population?

BACKGROUND: In modern societies characterized by abundant and accessible foods, restrained eating may become an adaptive behavior to limit weight gain. OBJECTIVE: We assessed the relations between eating behavior (EB) and adiposity in a general population over a 2-y period. DESIGN: We recruited 466 adults and 271 adolescents in 1999 on a geographical basis to participate in a longitudinal study. At the initial examination and 2 y later, they answered an EB questionnaire, the Three-Factor Eating Questionnaire-R18, which measured cognitive restraint (CR), uncontrolled eating, and emotional eating. On the same occasions, several measures of adiposity were also obtained: body mass index (BMI; in kg/m2), waist circumference, the sum of 4 skinfold thicknesses, and percentage body fat. Relations between EB and adiposity were tested separately in adults and adolescents by using mixed linear regressions after adjustment for age, sex, and (in adolescents) Tanner pubertal stage. RESULTS: At baseline, CR was positively associated with BMI in normal-weight subjects (mean BMI: 21.4 in the lowest to 23.3 in the highest CR quintile; P < 0.001) but not in overweight adults (P = 0.25). Initial CR did not predict change in adiposity variables (BMI change: P = 0.79 in adults, P = 0.57 in adolescents and young adults). Conversely, a high initial BMI was associated with a larger increase in CR (beta = 20.1, P < 0.0001 in adults; beta = 21.7, P = 0.003 in adolescents and young adults). CONCLUSIONS: Restrained eating is strongly associated with adiposity in normal-weight subjects but not in overweight subjects. However, restrained eating does not promote weight gain

Reproducibility and relative validity of a food-frequency questionnaire among French adults and adolescents.

International audienceOBJECTIVE: Our aim was to evaluate the reproducibility of a food-frequency questionnaire (FFQ) developed in a French population, and its validity against four 24-h dietary recalls (24-HRs). METHODS: A total of 57 adults (aged 18-63), 17 adolescents (aged 14-18) and 20 children (aged 10-14) completed four 24-HRs (one per season) and two FFQs over a 1-year interval. Reproducibility of the FFQ was estimated by intraclass correlation coefficients (ICCs). The validity of FFQ was assessed by comparison with the four 24-HRs. RESULTS: For most nutrients, the first FFQ measurements gave higher mean values than the second FFQ. The ICCs for nutrients ranged from 0.39 for total protein to 0.83 for alcohol. The ICCs were higher for food items consumed daily such as milk (0.80) or sugars and confectionery (0.65), and lower for rarely eaten food such as inner organs (0.11). Nutrient intakes as assessed by FFQs were higher than those from the 24-HRs, except for alcohol. The de-attenuated Pearson's correlation coefficient for nutrients varied from 0.25 (dietary fiber) to 0.90 (alcohol), but the adjustment for energy did not improve these coefficients. When nutrient intakes were categorized into quintiles, FFQ and 24-HRs produced agreement rates (same or adjacent quintile) between 55% (for PUFA) and 95% (for alcohol), while misclassification to an extreme quintile was rare (<5%). CONCLUSION: The FFQ developed for the FLVS II Study can be used to classify adults or adolescents according to their nutrients and food intakes over a 1-year period

Amidate Complexes of Tantalum and Niobium for the Hydroaminoalkylation of Unactivated Alkenes

A series of mono­(amidate) Ta and Nb complexes with varying steric and electronic properties were synthesized. These complexes were screened as precatalysts for the hydroaminoalkylation of alkenes with secondary amines. Sterically demanding mono­(amidate) Ta complexes were determined to be the most effective precatalysts. Isotopic labeling and kinetic studies were undertaken in an effort to elucidate the mechanism. The reaction was shown to be dependent upon catalyst and alkene concentration while being zero order in amine concentration. Mechanistic probes for radical species support a two-electron mechanism. Bis­(amidate) species of Ta and Nb were also synthesized, with metallaaziridine formation observed for both metals. Insertion of acetonitrile into the reactive M–C bond yielded a representative five-membered metallacycle. Off-cycle equilibria and catalyst dormant states have been identified as areas for future catalyst development efforts

Growth curves of anthropometric indices in a general population of French children and comparison with reference data.

Background:The description of growth patterns of the different anthropometric measurements mainly used in epidemiological studies is useful to better understand the development of obesity in children and its consequences.Objective:Our aim was to establish growth curves of anthropometric indices in a general population of French children born during the 1980s and to compare them with the French reference curves based on children born in the 1950s.Design:As part of the Fleurbaix Laventie Ville Sant?tudies I and II (FLVS), 441 girls and 467 boys were examined at least twice between 1993 and 2001. Height, weight and four skinfold thicknesses were measured. Body mass index (BMI), sum of peripheral and truncal skinfolds and truncal-to-peripheral ratio were calculated. Mean growth curves from ages 5 to 17 years were assessed for these indices, calculating means and 95% confidence interval per 1 year age group and by gender.Results:Trajectories with age differed importantly according to the index considered; BMI was the one with the smallest difference between genders and the most linear shape with age. From the age of 5 years and after, the FLVS children were on average taller and had a higher subcutaneous adiposity than children born 30 years earlier. Truncal-to-peripheral ratio was higher in our population; this difference became more marked with puberty in girls.Discussion:This study suggests the existence of a secular trend towards a precocious accelerated growth, and a more truncal adiposity distribution, especially in girls. It is a disquieting trend considering its expected consequences on adult health.European Journal of Clinical Nutrition advance online publication, 5 July 2006; doi:10.1038/sj.ejcn.1602474