Resin-bound triaryl bismuthanes and bismuth diacetates: novel multidirectional linkers and novel resin-bound arylation reagents

A general synthesis of resin-bound triaryl bismuthanes and resin-bound triaryl bismuth diacetates starting from commercially available chloromethyl polystyrene is reported. For the first time resin-bound bismuth has been utilized as part of a multidirectional linker system for solid-phase organic synthesis and as a resin-bound arylation reagent.     

Solar ultraviolet-B radiation increases phenolic content and ferric reducing antioxidant power in Avena sativa

We examined the influence of solar ultraviolet-B radiation (UV-B; 280-320 nm) on the maximum photochemical efficiency of photosystem II (F(v)/F(m)), bulk-soluble phenolic concentrations, ferric-reducing antioxidant power (FRAP) and growth of Avena sativa. Treatments involved placing filters on frames over potted plants that reduced levels of biologically effective UV-B by either 71% (reduced UV-B) or by 19% (near-ambient UV-B) over the 52 day experiment (04 July-25 August 2002). Plants growing under near-ambient UV-B had 38% less total biomass than those under reduced UV-B. The reduction in biomass was mainly the result of a 24% lower leaf elongation rate, resulting in shorter leaves and less total leaf area than plants under reduced UV-B. In addition, plants growing under near-ambient UV-B had up to 17% lower F(v)/F(m) values early in the experiment, and this effect declined with plant age. Concentrations of bulk-soluble phenolics and FRAP values were 17 and 24% higher under near-ambient UV-B than under reduced UV-B, respectively. There was a positive relationship between bulk-soluble phenolic concentrations and FRAP values. There were no UV-B effects on concentrations of carotenoids (carotenes + xanthophylls).     

Influence of solar ultraviolet-B radiation on Antarctic terrestrial plants: results from a 4-year field study.

We examined the influence of solar ultraviolet-B radiation (UV-B; 280-315 nm) on the performance of Antarctic vascular plants (Colobanthus quitensis and Deschampsia antarctica) by placing filters that either absorbed or transmitted most solar UV-B over tundra along the Antarctic Peninsula for four consecutive growing seasons. The difference in biologically effective UV-B levels between our treatments was 65%, which was similar to the enhancement in ambient UV-B levels that appeared attributable to ozone depletion during the first 2 months of the growing season (November and December) at our site (62%). In both species, exposure to UV-B reduced vegetative growth, primarily through slower leaf elongation rates that led to shorter fully expanded leaves. In C. quitensis, exposure to UV-B also led to reductions in leaf longevity, branch production, cushion diameter growth, aboveground biomass, and thickness of the non-green cushion base and litter layer. Exposure to UV-B accelerated the development of reproductive structures and increased the number of panicles (D. antarctica) and capsules (C. quitensis) that reached maturity per unit of ground surface area covered by mother plants. However, this effect was offset by a tendency for these panicles and capsules to produce fewer spikelets and seeds. Ultimately, UV-B exposure did not effect the numbers of spikelets or seeds produced per unit of ground surface area. While seeds from plants exposed to UV-B tended to be lighter, germination rates were similar between UV-B treatments. The relative reductions in leaf elongation rates in D. antarctica attributable to UV-B exposure increased from the first (23%) through the fourth (43%) growing season, and relative reductions in leaf longevity in C. quitensis tended to increase from the first (9%) through the fourth (19%) growing season, suggesting that UV-B growth responses tended to be cumulative over successive years.     

The influence of ultraviolet-B radiation on growth, hydroxycinnamic acids and flavonoids of Deschampsia antarctica during Springtime ozone depletion in Antarctica

We examined the influence of solar ultraviolet-B radiation (UV-B; 280-320 nm) on the growth, biomass production and phenylpropanoid concentrations of Deschampsia antarctica during the springtime ozone depletion season at Palmer Station, along the Antarctic Peninsula. Treatments involved placing filters on frames over potted plants that reduced levels of biologically effective UV-B either by 83% (reduced UV-B) or by 12% (near-ambient UV-B) over the 63 day experiment (7 November 1998-8 January 1999) when ozone depletion averaged 17%. Plants growing under near-ambient UV-B had 41% and 40% lower relative growth rates and net assimilation rates, respectively, than those under reduced UV-B. The former plants produced 50% less total biomass as a result of having 47% less aboveground biomass. The reduction in aboveground biomass was a result of a 29% lower leaf elongation rate resulting in shorter leaves and 59% less total leaf area in plants grown under reduced UV-B. p-Coumaric, caffeic and ferulic acids were the major hydroxycinnamic acids, and luteolin derivatives were the major flavonoids in both insoluble and soluble leaf extracts. Concentrations of insoluble p-coumaric and caffeic acid and soluble ferulic acids were 38%, 48% and 60% higher, respectively, under near-ambient UV-B than under reduced UV-B. There were no UV-B effects on concentrations of insoluble or soluble flavonoids.     

Iron-assisted nucleophilic aromatic substitution on solid phase

Iron-assisted S(N)Ar reactions were performed for the first time on solid phase, and a library of 36 unsymmetrically substituted phenylpiperazines and phenyl-1,4-diazepanes was synthesized with this novel strategy. The scope of iron-assisted S(N)Ar reactions on solid phase was investigated, and reactions of representative nucleophiles from groups VI (O, S, and Se) and V (N and P) of the periodic table were examined. Decomplexation of resin-bound iron complexes was achieved with 1,10-phenanthroline under irradiation, thereby overcoming the notorious disadvantages of decomplexation observed in solution-phase chemistry.