The solution structures of ion pairs formed by quarternary ammonium ions derived from quinine alkaloid with small hard anions (BH(4)(-) or Cl(-)) in CDCl(3) have been characterized by nuclear magnetic resonance methods. Structural observations have been correlated with the sense of asymmetric induction observed in the phase-transfer reduction of 9-anthryl trifluoromethyl ketone by borohydride (BH(4)(-)) when catalyzed by the quaternary N-benzylquinine ammonium ion. From interionic nuclear Overhauser effects (NOEs), it appears that the BH(4)(-) ion occupies two of the four trigonal pyramidal sites formed by substituents of the quarternary nitrogen of the catalyst cation. One of these sites is in close proximity to the cation's hydroxyl group that is strictly required for asymmetric induction in the model reaction, while the other site is near the vinyl group on the cation. The vinyl group does not appear to be important for determining the sense or extent of asymmetric induction. Using energy-minimized structures derived from NMR data, it was predicted that the N-(9-methyleneanthryl)quinine-quarternary ammonium catalyst would give improved asymmetric induction in the model reaction due to a preferred anion occupancy at the site near the hydroxyl group. An improvement in enantiomeric excess (ee) is observed using the anthryl-modified catalyst, and NMR studies on the modified catalyst confirm the predicted change in anion binding site occupancies. The changes in site occupancies determined by NMR can be fitted to a simple kinetic model that correctly predicts the extent of change in ee.

No abstract

Tetrabutylammonium ion (1) forms tight ion pairs with small anions (Cl-, BH4 -) in CDCl3 solution. These ion pairs aggregate as a response to increasing solution concentration with little temperature dependence. Maximum aggregate size is approximately four ion pairs, as measured by comparing self-diffusion coefficients of the aggregates with that of an internal nonaggregating standard of the same shape and nominal size, tetrabutylsilane (2). The magnitudes of steady state interionic 1H{1H} NOEs observed between 1 and the BH4 - anion in CDCl3 as a function of temperature in solutions of fixed concentration are well fit to the standard theoretical expression by assuming a single aggregate size that is independent of temperature. A simplified model-free analysis was applied to steady state 15N{1H} NOE and 15N T 1 measured at several magnetic field strengths, using 15N-labeled 1 to obtain estimates for reorientational correlation times for the ion aggregates. A similar analysis of 13C{1H} NOE and 13C T 1 gives local effective correlation times for C−H bond vectors of the 1-CH2 carbon of 1 and order parameters relating the local motion to overall cation motion. Comparison of these correlation times with those obtained from analysis of 29Si{1H} NOE, 13C{1H} NOE, and 13C T 1 for silane 2 provides an estimate of aggregate size which is independent of that obtained by diffusion, with good agreement between the different approaches.

Deuterium oxide (DO) dilution methods have been used to assess body composition in live animals. Estimated body water content can be used to predict body fat and protein, and thus, the amount of energy reserves. It is an alternative method to direct chemical analysis and considered a noninvasive technique that is economical and repeatable. Deuterium oxide use is considered easy, safe, and accurate; however, the traditional methods of analyzing DO are expensive, tedious, and time consuming. The objective of this study was to evaluate the potential for using nuclear magnetic resonance spectroscopy (NMR) to determine body composition in Holstein dairy heifers. Nuclear magnetic resonance is less expensive and requires minutes to calculate the percentage of DO in the blood. This study used 24 newborn dairy heifer calves blocked by birth and randomly assigned to 1 of 3 treatments: (1) 446 g dry matter (DM) of a conventional milk replacer (MR) [CON; 20% crude protein (CP), 20% fat], (2) 669 g DM of a moderately high protein MR (MOD; 26% CP, 18% fat), or (3) 892 g DM of a moderately high protein MR (aggressive, AGG; 26% CP, 18% fat). All calves had free-choice access to starter and water. Both MR and starter were medicated with decoquinate. During weaning (d 43 to 49), the morning MR feeding ceased. On d 50, all MR feedings ended but starter and water intakes were continuously recorded until d 56. When calves were 50 d of age, a baseline blood sample was taken followed by injection of 300 mg of DO/kg of body weight in sterile physiological saline (0.9%). The syringes containing the DO in physiological saline were weighed before and after administration to record the actual dose of DO injected gravimetrically. After injection, the DO was allowed to equilibrate with body water for 1 h. Six blood samples were taken over 6 d (1/d) at 1630 h to estimate the dilution of the tracer. The plasma was aspirated and stored at -20°C until further DO analysis. This new method was validated using 4 calf plasma samples that were sent to an outside laboratory for measurement using an independent validation method. We detected no differences in total body water, protein, fat, or mineral content in calves fed CON, MOD, or AGG; however, results demonstrated that the DO dilution technique and analysis by NMR is an appropriate and easy method to estimate water, protein, ash, and fat in young heifers.

No abstract