Stoichiometric Mismatch Research Articles

Preparation of Unsaturated Linear Aliphatic Polyesters Using Condensation Polymerization

A versatile method for preparing linear, unsaturated polyesters through condensation polymerization of trans-β-hydromuconic acid (HMA) with a variety of diols using Sn(Oct)2 and Novozyme-435 as catalysts was explored. Poly(1,8-octanediol hydromuconoate) was the highest molecular weight homopolymer prepared with a 〈Mn〉 of 10.5 × 103 g/mol and polydispersity of 2.0. These materials showed unique melting behavior that was dependent on the number of carbons in the diol. Melting points ranged from 40 to 70 °C. Copolymers where the amount of HMA was diluted by adipic acid were prepared and had a 〈Mn〉 as high as 13.0 × 103 g/mol and polydispersities below 2.0. The double bonds of these materials were chemically modified through epoxidation in yields greater than 93% and with no degradation of the polymer backbone. Materials with hydroxyl end groups were prepared through stoichiometric mismatch. Unsaturated poly(ester ether)s that are amorphous liquids with Tg below −40 °C were prepared using diethylene glycol as...

Stoichiometric mismatch between littoral invertebrates and their periphyton food

Abstract: Ecological stoichiometry is considered a key concept in understanding con-straints in energy transfer at the plant-herbivore interface. However, whether this con-cept is relevant for benthic freshwater ecosystems is not fully known. Therefore, afield survey was conducted in 2003 during the growing season in the littoral zone ofLake Constance, a large pre-alpine lake in central Europe. The aim was to assess tem-poral variation in the elemental stoichiometric composition in both herbivorous macro-invertebrates and their food resource, the periphyton in two different lakes. The peri-phyton showed large temporal and spatial variation in carbon, nitrogen, and phospho-rus content, with particularly high molar C:P ratios of up to 1225:1. Periphyton C:Pand C:N ratios were often high and constantly above the Redfield ratio that is consid-ered optimal for autotrophic growth. In contrast to the pronounced fluctuations in thenutrient ratios of their food resource, the herbivorous macroinvertebrates showed onlyvery little variation in their nutrient ratios, which indicated that they are homeostatic,i.e., physiologically restricted to a comparatively narrow range of C:P and C:N ratios.Distinct species-specific C : P and C : N ratios were found for different taxonomicgroups of macroinvertebrates, which indicated different requirements of optimal die-tary C:P and C:N ratios and which might influence the ability of the taxa to competefor limiting elemental nutrients. Considering the temporally very high C:P and C:Nratios of the periphytic resource and the very low ratios of the consumer body tissue,this stoichiometric mismatch is likely to constrain growth and reproduction of these lit-toral invertebrates. Therefore, the concept of stoichiometric food quality limitationmight also be applicable to the littoral food web in lakes.Key words: benthos, C:N:P ratio, ecological stoichiometry, herbivory, homeostasis,lake littoral, macroinvertebrates, mismatch, nutrient ratios, phosphorus.

Electronic and vibrational spectra of InP quantum dots formed by sequential ion implantation

Sequential ion implantation of indium and phosphorus into silica combined with controlled thermal annealing has proven to be a novel and effective technique to fabricate InP quantum dots in dielectric hosts. This technique has been applied to synthesize other III–V and II–VI quantum dots. Due to the unique bimodal distribution of the indium in a silica host and a stoichiometric mismatch between the indium and phosphorus concentration profiles, it is believed that two different-sized InP quantum dots were fabricated. More importantly, we have shown that the infrared reflectance technique is a very effective method to identify the species in the dielectric host and is also a powerful tool to investigate surface phonon modes.