Freedom Farmers Redmond, LaDonna; White, Monica M
01/2019
eBook
In May 1967, internationally renowned activist Fannie Lou Hamer purchased forty acres of land in the Mississippi Delta, launching the Freedom Farms Cooperative (FFC). A community-based rural and ...economic development project, FFC would grow to over 600 acres, offering a means for local sharecroppers, tenant farmers, and domestic workers to pursue community wellness, self-reliance, and political resistance. Life on the cooperative farm presented an alternative to the second wave of northern migration by African Americans--an opportunity to stay in the South, live off the land, and create a healthy community based upon building an alternative food system as a cooperative and collective effort.Freedom Farmersexpands the historical narrative of the black freedom struggle to embrace the work, roles, and contributions of southern black farmers and the organizations they formed. Whereas existing scholarship generally views agriculture as a site of oppression and exploitation of black people, this book reveals agriculture as a site of resistance and provides a historical foundation that adds meaning and context to current conversations around the resurgence of food justice/sovereignty movements in urban spaces like Detroit, Chicago, Milwaukee, New York City, and New Orleans.
Oxidations of aliphatic C–H bonds, known since the 1800s, have only recently been considered for use in organic synthesis.
Aliphatic C–H bonds are among the least reactive in organic chemistry, yet ...enzymes have evolved that not only oxidize them, but can discriminate between individual tertiary (3°) and secondary (2°) C–H bonds in complex molecules. Chemists considered reactivity differences between these inert bonds too minor for a small-molecule catalyst to discriminate (
1
); bio-inspired catalysts with intricate binding pockets were thought to be the only viable solution (
2
). This view pervaded because the reported examples of selective aliphatic C–H oxidations halogenations (
3
), alkylations (
4
), aminations (
5
), hydroxylations (
6
), and dehydrogenations (
7
) were not sufficiently high in yield or predictable in site selectivity to be useful in synthesis, except in some special cases such as steroids (see below). In the past several years, however, aliphatic C–H oxidations and simple rules for predicting their selectivities have been emerging prominently in synthetic planning. Powerful small-molecule catalysts have been invented that furnish high enough yields (>50%) to be preparatively useful and can predictably discriminate between aliphatic C–H bonds even within complex molecules that have many possible sites of oxidation.
The atomistic change of C(sp3 )–H to C(sp3 )–O can have a profound impact on the physical and biological properties of small molecules. Traditionally, chemical synthesis has relied on pre-existing ...functionality to install new functionality, and directed approaches to C–H oxidation are an extension of this logic. The impact of developing undirected C–H oxidation reactions with controlled site-selectivity is that scientists gain the ability to diversify complex structures at sites remote from existing functionality, without having to carry out individual de novo syntheses. This Perspective offers a historical view of why, as recently as 2007, it was thought that the differences between aliphatic C–H bonds of the same bond type (for example, 2° aliphatic) were not large enough to distinguish them preparatively with small-molecule catalysis in the absence of directing groups or molecular recognition elements. We give an account of the discovery of Fe(PDP)-catalyzed non-directed aliphatic C–H hydroxylations and how the electronic, steric, and stereoelectronic rules for predicting site-selectivity that emerged have affected a shift in how the chemical community views the reactivity among these bonds. The discovery that site-selectivity could be altered by tuning the catalyst i.e., Fe(CF3-PDP) with no changes to the substrate or reaction now gives scientists the ability to exert control on the site of oxidation on a range of functionally and topologically diverse compounds. Collectively, these findings have made possible the emerging area of late-stage C–H functionalizations for streamlining synthesis and derivatizing complex molecules.
C-H bond oxidation reactions underscore the existing paradigm wherein high reactivity and high selectivity are inversely correlated. The development of catalysts capable of oxidizing strong aliphatic ...C(sp(3))-H bonds while displaying chemoselectivity (that is, tolerance of more oxidizable functionality) remains an unsolved problem. Here, we describe a catalyst, manganese tert-butylphthalocyanine Mn((t)BuPc), that is an outlier to the reactivity-selectivity paradigm. It is unique in its capacity to functionalize all types of C(sp(3))-H bond intramolecularly, while displaying excellent chemoselectivity in the presence of π functionality. Mechanistic studies indicate that Mn((t)BuPc) transfers bound nitrenes to C(sp(3))-H bonds via a pathway that lies between concerted C-H insertion, observed with reactive noble metals such as rhodium, and stepwise radical C-H abstraction/rebound, as observed with chemoselective base metals such as iron. Rather than achieving a blending of effects, Mn((t)BuPc) aminates even 1° aliphatic and propargylic C-H bonds, demonstrating reactivity and selectivity unusual for previously known catalysts.
The insulin receptor substrate proteins IRS1 and IRS2 are key targets of the insulin receptor tyrosine kinase and are required for hormonal control of metabolism. Tissues from insulin-resistant and ...diabetic humans exhibit defects in IRS-dependent signalling, implicating their dysregulation in the initiation and progression of metabolic disease. However, IRS1 and IRS2 are regulated through a complex mechanism involving phosphorylation of >50 serine/threonine residues (S/T) within their long, unstructured tail regions. In cultured cells, insulin-stimulated kinases (including atypical PKC, AKT, SIK2, mTOR, S6K1, ERK1/2 and ROCK1) mediate feedback (autologous) S/T phosphorylation of IRS, with both positive and negative effects on insulin sensitivity. Additionally, insulin-independent (heterologous) kinases can phosphorylate IRS1/2 under basal conditions (AMPK, GSK3) or in response to sympathetic activation and lipid/inflammatory mediators, which are present at elevated levels in metabolic disease (GRK2, novel and conventional PKCs, JNK, IKKβ, mPLK). An emerging view is that the positive/negative regulation of IRS by autologous pathways is subverted/co-opted in disease by increased basal and other temporally inappropriate S/T phosphorylation. Compensatory hyperinsulinaemia may contribute strongly to this dysregulation. Here, we examine the links between altered patterns of IRS S/T phosphorylation and the emergence of insulin resistance and diabetes.
For decades surface enhanced Raman spectroscopy (SERS) has been intensely investigated as a possible solution for performing analytical chemistry at the point of sample origin. Unfortunately, due to ...cost and usability constraints, conventional rigid SERS sensors and microfluidic SERS sensors have yet to make a significant impact outside of the realm of academics. However, the recently introduced flexible and porous paper-based SERS sensors are proving to be widely adaptable to realistic usage cases in the field. In contrast to rigid and microfluidic SERS sensors, paper SERS sensors feature (i) the potential for roll-to-roll manufacturing methods that enable low sensor cost, (ii) simple sample collection directly onto the sensor via swabbing or dipping, and (iii) equipment-free separations for sample cleanup. In this review we argue that movement to paper-based SERS sensors will finally enable point-of-sample analytical chemistry applications. In addition, we present and compare the numerous fabrication techniques for paper SERS sensors and we describe various sample collection and sample clean-up capabilities of paper SERS sensors, with a focus on how these features enable practical applications in the field. Finally, we present our expectations for the future, including emerging ideas inspired by paper SERS.
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•SERS sensors on paper offer one of the best opportunities for analytical chemistry in the field.•Paper SERS sensors have a lower production cost than conventional and microfluidic SERS sensors.•Paper SERS sensors innately offer simple sample collection and sample processing capabilities.•Emerging methods inspired by paper SERS sensors may offer unprecedented ease of use.
Optofluidics - the synergistic integration of photonics and microfluidics - has recently emerged as a new analytical field that provides a number of unique characteristics for enhanced sensing ...performance and simplification of microsystems. In this review, we describe various optofluidic architectures developed in the past five years, emphasize the mechanisms by which optofluidics enhances bio/chemical analysis capabilities, including sensing and the precise control of biological micro/nanoparticles, and envision new research directions to which optofluidics leads.
Among the frontier challenges in chemistry in the twenty-first century are the interconnected goals of increasing synthetic efficiency and diversity in the construction of complex molecules. ...Oxidation reactions of C-H bonds, particularly when applied at late stages of complex molecule syntheses, hold special promise for achieving both these goals. Here we report a late-stage C-H oxidation strategy in the total synthesis of 6-deoxyerythronolide B (6-dEB), the aglycone precursor to the erythromycin antibiotics. An advanced intermediate is cyclized to give the 14-membered macrocyclic core of 6-dEB using a late-stage (step 19 of 22) C-H oxidative macrolactonization reaction that proceeds with high regio-, chemo- and diastereoselectivity (>40:1). A chelate-controlled model for macrolactonization predicted the stereochemical outcome of C-O bond formation and guided the discovery of conditions for synthesizing the first diastereomeric 13-epi-6-dEB precursor. Overall, this C-H oxidation strategy affords a highly efficient and stereochemically versatile synthesis of the erythromycin core.
We present a new statistical method to determine the relationship between the stellar masses of galaxies and the masses of their host dark matter haloes over the entire cosmic history from z ∼ 4 to ...the present. This multi-epoch abundance matching (MEAM) model self-consistently takes into account that satellite galaxies first become satellites at times earlier than they are observed. We employ a redshift-dependent parametrization of the stellar-to-halo-mass relation to populate haloes and subhaloes in the Millennium simulations with galaxies, requiring that the observed stellar mass functions at several redshifts are reproduced simultaneously. We show that physically meaningful growth of massive galaxies is consistent with these data only if observational mass errors are taken into account. Using merger trees extracted from the dark matter simulations in combination with MEAM, we predict the average assembly histories of galaxies, separating into star formation within the galaxies (in situ) and accretion of stars (ex situ). Our main results are the peak star formation efficiency decreases with redshift from 23 per cent at z = 0 to 9 per cent at z =4 while the corresponding halo mass increases from 1011.8 to 1012.5 M. The star formation rate of central galaxies peaks at a redshift which depends on halo mass; for massive haloes this peak is at early cosmic times while for low-mass galaxies the peak has not been reached yet. In haloes similar to that of the Milky Way about half of the central stellar mass is assembled after z = 0.7. In low-mass haloes, the accretion of satellites contributes little to the assembly of their central galaxies, while in massive haloes more than half of the central stellar mass is formed ex situ with significant accretion of satellites at z < 2. We find that our method implies a cosmic star formation history and an evolution of specific star formation rates which are consistent with those inferred directly. We present convenient fitting functions for stellar masses, star formation rates and accretion rates as functions of halo mass and redshift.
We examine a sample of ∼250 000 ‘locally brightest galaxies’ selected from the Sloan Digital Sky Survey to be central galaxies within their dark matter haloes. We stack the X-ray emission from these ...haloes, as a function of the stellar mass of the central galaxy, using data from the ROSAT All-Sky Survey. We detect emission across almost our entire sample, including emission which we attribute to hot gas around galaxies spanning a range of 1.2 dex in stellar mass (corresponding to nearly two orders of magnitude in halo mass) down to M
* = 1010.8 M⊙ (M
500 ≈ 1012.6 M⊙). Over this range, the X-ray luminosity can be fit by a power law, either of stellar mass or of halo mass. From this, we infer a single unified scaling relation between mass and L
X which applies for galaxies, groups, and clusters. This relation has a slope steeper than expected for self-similarity, showing the importance of non-gravitational heating. Assuming this non-gravitational heating is predominately due to AGN feedback, the lack of a break in the relation shows that AGN feedback is tightly self-regulated and fairly gentle, in agreement with the predictions of recent high-resolution simulations. Our relation is consistent with established measurements of the L
X–L
K
relation for elliptical galaxies as well as the L
X–M
500 relation for optically selected galaxy clusters. However, our L
X–M
500 relation has a normalization more than a factor of 2 below most previous relations based on X-ray-selected cluster samples. We argue that optical selection offers a less biased view of the L
X–M
500 relation for mass-selected clusters.
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