More complex, less complicated? Explicit solvation of hydroxyl groups for the analysis of VCD spectra.

Solute-solvent interactions and in particular hydrogen bonding can significantly influence the appearance of vibrational spectra due to band shifts, intensity changes and band broadening. In VCD spectroscopy, solvation may also lead to sign changes and thus an overall drastic change in the spectral pattern. As the VCD spectral analysis relies heavily on the comparison with computed spectra, such solvent effects have to be accounted for in the calculations. For simple model systems with one stereocenter, we have previously shown for carboxylic acids and hydroxyl groups that considering solvation explicitly improves the match substantially. In the present study we evaluate if explicit solvation is always necessary and if larger, more complex molecules featuring several stereocenters show the same susceptibility to H-bonding induced spectral changes as the previously investigated model systems. We analyse the spectra of the diastereomeric pairs menthol/neomenthol and borneol/isoborneol and study both experimentally and computationally the influence of hydrogen bonding to dimethylsulfoxide-d6 (DMSO-d6) and acetonitrile-d3 (ACN-d3) on their VCD spectral signatures. Further chiral alcohols with tertiary hydroxyl group (terpinen-4-ol and cedrol) and more complex structures with multiple stereocenters (cholesterol) are investigated to show that solvent effects on the spectra become less pronounced. We related this to the increasing number of vibrational bands that are insensitive to solvation and thus overlap with actually affected modes. As a consequence, the analysis of the spectra does not require consideration of explicit solvation and in this respect becomes less complicated.

Fatty acid supply with complementary foods and LC-PUFA status in healthy infants: results of a randomised controlled trial.

PURPOSE: Introduction of complementary food usually leads to decreasing intakes of long-chain n-3 polyunsaturated fatty acids (n-3 LC-PUFA), compared to full breastfeeding. In the randomised controlled PINGU intervention trial, we tested the effects of complementary foods with different contents of alpha-linolenic acid (ALA) and docosahexaenoic acid (DHA) on term infant LC-PUFA status. METHODS: Healthy infants born at term were randomised to receive from the introduction of complementary feeding at the age of 4 to 6 months until age of 10 months ready-made complementary meals either with ALA-rich rapeseed oil (intervention group (IG)-R), with salmon twice weekly to provide preformed DHA (IG-F), or with linoleic acid-rich corn oil (control group, CG). Fatty acid composition was assessed in erythrocyte (RBC) and plasma glycerophospholipids. RESULTS: Complete data of fatty acids in RBC (plasma) were available from 158 (155) infants. After intervention, infants assigned to IG-F showed higher RBC and plasma percentages of eicosapentaenoic acid (EPA), DHA, and total n-3 LC-PUFA than CG (each p < 0.001). In IG-R, levels of ALA and the ratio of ALA to LA in plasma and RBC (all p < 0.0001) as well as RBC-EPA (p < 0.0001) were higher than in CG, while DHA levels did not differ between IG-R and CG. CONCLUSIONS: Regular fish consumption during complementary feeding enhances infant EPA and DHA status. The usage of rapeseed oil in small amounts concordant with EU-law for commercial meals enhances endogenic EPA-synthesis, but does not affect DHA status. Provision of oily fish with complementary feeds is advisable to prevent a decline of DHA status. CLINICAL TRIAL REGISTRATION: www.clinicaltrials.gov , identifier: NCT01487889, title: Polyunsaturated fatty acids in child nutrition-a German multimodal optimisation study (PINGU).