Synthesis of Telechelic Polyisoprene via Ring-Opening Metathesis Polymerization in the Presence of Chain Transfer Agent

Telechelic polyisoprene was synthesized via the ring-opening metathesis polymerization (ROMP) of 1,5-dimethyl-1,5-cyclooctadiene (DMCOD) in the presence of cis-1,4-diacetoxy-2-butene as a chain transfer agent (CTA). This method afforded telechelic polymer in excellent yield, and the acetoxy groups were successfully removed to yield α,ω-hydroxy end-functionalized polyisoprene with potential for subsequent reactions. Efficient, quantitative incorporation of CTA was achieved, and NMR spectroscopy was utilized to confirm the chemical identity of the polymer end groups. Polymerization of discrete DMCOD monomer generated polyisoprene with excellent regioregularity in the polymer backbone. Successful ROMP of sterically challenging DMCOD in the presence of a CTA for chain end-functionalization was borne out through screening of a variety of Ru-based olefin metathesis catalysts

The condensin complex is required for proper spindle assembly and chromosome segregation in Xenopus egg extracts.

Chromosome condensation is required for the physical resolution and segregation of sister chromatids during cell division, but the precise role of higher order chromatin structure in mitotic chromosome functions is unclear. Here, we address the role of the major condensation machinery, the condensin complex, in spindle assembly and function in Xenopus laevis egg extracts. Immunodepletion of condensin inhibited microtubule growth and organization around chromosomes, reducing the percentage of sperm nuclei capable of forming spindles, and causing dramatic defects in anaphase chromosome segregation. Although the motor CENP-E was recruited to kinetochores pulled poleward during anaphase, the disorganized chromosome mass was not resolved. Inhibition of condensin function during anaphase also inhibited chromosome segregation, indicating its continuous requirement. Spindle assembly around DNA-coated beads in the absence of kinetochores was also impaired upon condensin inhibition. These results support an important role for condensin in establishing chromosomal architecture necessary for proper spindle assembly and chromosome segregation

Trends in the not-from-concentrate orange-juice segment

Agribusiness,

Thermally Stable, Latent Olefin Metathesis Catalysts

Highly thermally stable N-aryl, N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second-generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 h. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C and exhibited a long catalyst lifetime in solution at elevated temperatures

Nonproductive Events in Ring-Closing Metathesis Using Ruthenium Catalysts

The relative TONs of productive and nonproductive metathesis reactions of diethyl diallylmalonate are compared for eight different ruthenium-based catalysts. Nonproductive cross metathesis is proposed to involve a chain-carrying ruthenium methylidene. A second more-challenging substrate (dimethyl allylmethylallylmalonate) that forms a trisubstituted olefin product is used to further delineate the effect of catalyst structure on the relative efficiencies of these processes. A steric model is proposed to explain the observed trends

Brief of Scholars of the History and Original Meaning of the Fourth Amendment as Amici Curiae in Support of Petitioner, Carpenter v. United States, No. 16-402 (U.S. Aug. 14, 2017)

Obtaining and examining cell site location records to find a person is a “search” in any normal sense of the word — a search of documents and a search for a person and her personal effects. It is therefore a “search” within the meaning of the Fourth Amendment in that it constitutes “examining,” “exploring,” “looking through,” “inquiring,” “seeking,” or “trying to find.” Nothing about the text of the Fourth Amendment, or the historical backdrop against which it was adopted, suggests that “search” should be construed more narrowly as, for example, intrusions upon subjectively manifested expectations of privacy that society is prepared to recognize as reasonable.Entrusting government agents with unfettered discretion to conduct searches using cell site location information undermines Fourth Amendment rights. The Amendment guarantees “[t]he right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches.” The Framers chose that language deliberately. It reflected the insecurity they suffered at the hands of “writs of assistance,” a form of general warrant that granted state agents broad discretion to search wherever they pleased. Such arbitrary power was “unreasonable” to the Framers, being “against the reason of the common law,” and it was intolerable because of its oppressive impact on “the people” as a whole. As emphasized in one of the seminal English cases that inspired the Amendment, this kind of general power to search was “totally subversive of the liberty of the subject.” James Otis’s famous speech denouncing a colonial writ of assistance similarly condemned those writs as “the worst instrument of arbitrary power,” placing “the liberty of every man in the hands of every petty officer.” Thus, although those who drafted and ratified the Fourth Amendment could not have anticipated cellphone technology, they would have recognized the dangers inherent in any state claim of unlimited authority to conduct searches for evidence of criminal activity. Cell site location information provides insight into where we go and what we do. Because this information is constantly generated and can be retrieved by the government long after the activities it memorializes have taken place, unfettered government access to cell site location information raises the specter of general searches and undermines the security of “the people.

Increasing Diversity in the City Schools: Unexplored Paths of Opportunity

In its school rezoning and closure process from May 6 - June 3, 2013, the Richmond School Board voted to close 3 schools and change 14 elementary school zones despite opposition that overwhelmingly outweighed support at both public hearings. Though there were a wide range of concerns cited, including the rushed timeline, lack of transparency and absence of clear criteria for closing and rezoning these schools, many stakeholders expressed particular disapproval related to the potential increase in racial isolation that would result from the plan, formally known as Option C. While regional efforts to promote school diversity—a central theme of the Looking Back, Moving Forward conference—remain critical, the school board actions present a specific challenge which could be addressed within a single school system through innovative policies with a record of success in other locales. To that end, this memo has three broad purposes. We identify key demographic changes that present opportunities and challenges for promoting school diversity in Richmond Public Schools (RPS). We also provide a synthesis of more than six decades of social science research showing that integration is still a deeply worthy policy goal. We outline the racial impact of current student assignment policies, in addition to the projected impact of the June 2013 rezoning. And perhaps most importantly, we close with a vision for moving forward in a way that more comprehensively fosters the many benefits of school diversity in Richmond City

Can size distributions of European lake fish communities be predicted by trophic positions of their fish species?

An organism's body size plays an important role in ecological interactions such as predator-prey relationships. As predators are typically larger than their prey, this often leads to a strong positive relationship between body size and trophic position in aquatic ecosystems. The distribution of body sizes in a community can thus be an indicator of the strengths of predator-prey interactions. The aim of this study was to gain more insight into the relationship between fish body size distribution and trophic position in a wide range of European lakes. We used quantile regression to examine the relationship between fish species' trophic position and their log-transformed maximum body mass for 48 fish species found in 235 European lakes. Subsequently, we examined whether the slopes of the continuous community size distributions, estimated by maximum likelihood, were predicted by trophic position, predator-prey mass ratio (PPMR), or abundance (number per unit effort) of fish communities in these lakes. We found a positive linear relationship between species' maximum body mass and average trophic position in fishes only for the 75% quantile, contrasting our expectation that species' trophic position systematically increases with maximum body mass for fish species in European lakes. Consequently, the size spectrum slope was not related to the average community trophic position, but there were negative effects of community PPMR and total fish abundance on the size spectrum slope. We conclude that predator-prey interactions likely do not contribute strongly to shaping community size distributions in these lakes