Methane cycling in the carbonate critical zone.

The carbonate critical zone (CZ) is characterized by extensive groundwater-surface water exchange that leads to highly variable redox states of groundwater. Changes in redox condition may cause either production or consumption of methane (CH), thereby providing an atmospheric source or sink of this important greenhouse gas. To assess how groundwater-surface water exchange affects redox state and CH cycling in the carbonate CZ, we measured CH concentrations and C isotopes in water from streams, spring systems, and wells in north-central Florida.

Statistical evidence of recharge and supply controlling nitrate variability at springs discharging from the upper Floridan Aquifer.

Over the last several decades, rising nitrate concentrations in springs discharging from north Florida's karstic Upper Floridan Aquifer have coincided with proliferation of algae in Florida spring runs and subsequent ecosystem degradation. As agriculture and development are primary contributors to groundwater nitrate and are predicted to continue expanding, understanding unique contributions and transmission pathways of nitrate pollution is vital to restoring impaired spring ecosystems. In this study, we use statistics and signal processing to analyze continuous nitrate timeseries data collected over five years at four north Florida springs.

Highly Tactic Cyclic Polynorbornene: Stereoselective Ring Expansion Metathesis Polymerization of Norbornene Catalyzed by a New Tethered Tungsten-Alkylidene Catalyst.

The tungsten alkylidyne [(t)BuOCO]W≡C((t)Bu) (THF)2 (1) reacts with CO2, leading to complete cleavage of one C═O bond, followed by migratory insertion to generate the tungsten-oxo alkylidene 2. Complex 2 is the first catalyst to polymerize norbornene via ring expansion metathesis polymerization to yield highly cis-syndiotactic cyclic polynorbornene.

Multicomponent assembly of 4-aza-podophyllotoxins: A fast entry to highly selective and potent anti-leukemic agents.

The aim of this study was the synthesis and lead structure selection of a best anti-leukemic agent from a library of aza-podophyllotoxin analogues (APTs). To this end, we report a scalable, modified multicomponent reaction using a "sacrificial" aniline partner as a more general route to rapidly construct the pivotal library of 50 APT analogues. Our preliminary structure activity relationship studies for anti-leukemic activity also address the innate toxicity of these compounds against non-malignant cells.