Production of streptomycin from chitin using Streptomyces griseus in bioreactors of different configuration

Streptomyces griseus was cultured in three different bioreactors in a medium containing chitin flakes. When a conventional bioreactor stirred by two sets of Rushton impellers and operated at high speed was used, the yield of streptomycin (3.1 mg/l) was the highest observed and occurred at approximately 500 hours. Cultivation of S. griseus in a bioreactor stirred at low speed by a U-shaped paddle resulted in a lower yield of streptomycin (1.8 mg/l) but this was achieved in a shorter period of time (400 hours). Increasing the concentration of chitin from 5 to 10 % w/v had no significant effect on either of these two parameters. The use of a novel vertical basket bioreactor in which the chitin flakes were contained within a wire mesh basket and were gently fluidised by air, enabled comparatively high yields of streptomycin (2.8 mg/l) in the relatively short time of 300 hours

Direct FTIR assay of streptomycin in agar

Streptomycin titres in samples of agar media on which various species of streptomycetes were cultured were obtained by Fourier Transform Infra Red (FTIR) spectroscopy. Titres were directly comparable to those obtained by bioassay based on Bacillus subtilis inhibition. Analysis by this method could be used to facilitate the isolation of high level antibiotic-producing mutants

Chitin in a dual role as substrate for Streptomyces griseus and as adsorbent for streptomycin produced during fermentation

Streptomycin production from chitin by Streptomyces griseus was compared using two different types of bioreactor. The first was equipped with a combined U-shaped paddle and Rushton impeller. Also employed was a bioreactor of novel design in which the chitin was contained in a wire mesh basket that was totally submerged in a liquid salts medium. During operation the chitin was gently fluidised by air admitted into the basket. Fermentation was continued in both bioreactors until maximum antibiotic titres were achieved whereupon operation was interrupted to allow the streptomycin adsorbed to the chitin substrate to be extracted into pH 3.0 buffer before continuing fermentation of the same batch of chitin a second time. At a chitin concentration of 10 % (w/v) the highest streptomycin yields (c. 5.5 mg/L) were obtained using the stirred bioreactor, however growth occurred more rapidly in the vertical basket bioreactor

Ancient engineering : selective ceramic processing in the Middle Balsas Region of Guerrero, Mexico

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (v. 2, p. 343-355).Previous experimental research into ancient pottery production has proven that potters can produce vessels with varying materials properties, such as thermal shock resistance and permeability. These properties are differentially useful for certain tasks, such as cooking or water-cooling. In certain cases, such as the use of shell temper in North America, an improvement in thermal shock resistance seems to provide an explanation for why the new temper was adopted along with the introduction of a new food type -- maize. It remains an unanswered question, however, whether potters in a large variety of situations were choosing to alter their production techniques or materials to produce pots intended for different functions that exhibit different materials properties. I investigated this question by applying techniques and concepts from materials science, anthropology, and archaeology. This combination of materials science and social science was pioneered by Heather Lechtman and Dorothy Hosler, and is called the "materials approach." My research focuses specifically on pottery production in the Middle Balsas Region of Guerrero, Mexico, from approximately 300 BC to AD 1300. I investigated whether potters in the Middle Balsas were using different production techniques or raw materials for vessels that were intended for specific functions. I chose the Middle Balsas Region as the geographical focus for my research because little systematic archaeological investigation has focused on that area, especially in the Late Preclassic and Classic periods (300 BC-AD 900). In order to gather appropriate data, I mapped, surface collected, and excavated at three Middle Balsas sites. I then categorized the pottery and analyzed a selected portion via thin section analysis/petrography.(cont.) The combination of field work and laboratory analyses that I used provided me with data on the production techniques practiced by Middle Balsas potters and allowed me to identify what wares and vessel shapes were characteristic of various time periods. I determined that Middle Balsas potters produced a consistent set of wares and vessel shapes made from a variety of clay sources, and that the clays I identified in their vessels always contained a consistent volume fraction of non-plastic inclusions. The majority of the clays used in these vessels naturally contain the high levels of non-plastic inclusions identified. When the clays did not contain this volume fraction of inclusions, the potters added a sand temper to the clays to reach their "ideal" volume fraction. The consistency that I identified in the production of Middle Balsas pottery lasted over one thousand years, which is unusual in Mesoamerica. I suggest that this production pattern may have occurred because a small number of potters who used a specific, shared technique made the vessels for the entire community.by Jennifer L. Meanwell.Ph.D

6-Bromo-1,3-di-2-propynyl-1H-imidazo[4,5-b]pyridin-2(3H)-one

The room-temperature reaction of propargyl bromide and 6-bromo-1,3-dihydro­imidazo[4,5-b]pyridin-2-one in dimethyl­formamide yields the title compound, C12H8BrN3O, which features nitro­gen-bound propynyl substituents. The imidazopyridine fused ring is almost planar (r.m.s. deviation = 0.011 Å); the propynyl chains point in opposite directions relative to the fused ring. One acetyl­enic H atom is hydrogen bonded to the carbonyl O atom of an inversion-related mol­ecule, forming a dimer; adjacent dimers are linked by a second acetyl­ene–pyridine C—H⋯N inter­action, forming a layer motif

By Default: How Mothers in Different-Sex Dual-Earner Couples Account for Inequalities in Pandemic Parenting

Mothers did a disproportionate share of the child care during the COVID-19 pandemic—an arrangement that negatively impacted their careers, relationships, and well-being. How did mothers account for these unequal roles? Through interviews and surveys with 55 mothers (and 14 fathers) in different-sex, prepandemic dual-earner couples, we found that mothers (and fathers) justified unequal parenting arrangements based on gendered structural and cultural conditions that made mothers’ disproportionate labor seem “practical” and “natural.” These justifications allowed couples to rely on mothers by default rather than through active negotiation. As a result, many mothers did not feel entitled to seek support with child care from fathers or nonparental caregivers and experienced guilt if they did so. These findings help explain why many mothers have not reentered the workforce, why fathers’ involvement at home waned as the pandemic progressed, and why the pandemic led to growing preferences for inegalitarian divisions of domestic and paid labor

Post-depositional alteration of calcium carbonate phases in archaeological ceramics: depletion and redistribution effects

The final stage in the life history of prehistoric pottery prior to archaeological recovery is usually the longest, and frequently the most dynamic. The remains of archaeological ceramics spend hundreds to thousands of years deposited within the upper layers of the earth’s crust where they encounter the same diagenetic environmental processes as the surrounding natural materials. Harsh conditions of subterranean environments induce physical stresses and chemical reactions, causing alterations of ceramic structure and composition. This is especially true of carbonate-rich ceramics, as carbonate phases are soluble when deposited within acidic environments. This paper examines common carbonate depletion and accretion effects of post-depositional environments on ancient ceramics from two rather different geological and archaeological contexts: Mesoamerica and the Mediterranean. Potters in both regions produce vessels with carbonate-rich materials—clays, calcite, limestone—that alter due to long exposure to low-pH sediments and continual water table fluctuations. Ceramic petrography is employed to identify traces of carbonate alterations within ceramic microstructure and to characterize fabrics. Elemental compositions of the same sherds are characterized through either scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS), inductively coupled plasma mass spectrometry and optical emission spectrometry (ICP-MS/OES) or neutron activation analysis (NAA). This method enabled comparison of the differing effects of post-depositional alteration of carbonate phases on bulk composition signatures commonly used to determine provenance

Revealing the Mechanism for Covalent Inhibition of Glycoside Hydrolases by Carbasugars at an Atomic Level

Mechanism-based glycoside hydrolase inhibitors are carbohydrate analogs that mimic the natural substrate’s structure. Their covalent bond formation with the glycoside hydrolase makes these compounds excellent tools for chemical biology and potential drug candidates. Here we report the synthesis of cyclohexene-based α-galactopyranoside mimics and the kinetic and structural characterization of their inhibitory activity toward an α-galactosidase from Thermotoga maritima (TmGalA). By solving the structures of several enzyme-bound species during mechanism-based covalent inhibition of TmGalA, we show that the Michaelis complexes for intact inhibitor and product have half-chair (2H3) conformations for the cyclohexene fragment, while the covalently linked intermediate adopts a flattened half-chair (2H3) conformation. Hybrid QM/MM calculations confirm the structural and electronic properties of the enzyme-bound species and provide insight into key interactions in the enzyme-active site. These insights should stimulate the design of mechanism-based glycoside hydrolase inhibitors with tailored chemical properties

Deuterium Exchange between Arenes and Deuterated Solvents in the Absence of a Transition Metal: Synthesis of D-Labeled Fluoroarenes

Producción CientíficaFluoroarenes can be selectively deuterated by H/D exchange with common deuterated solvents in the presence of a catalytic amount of an alkali metal carbonate or, for the less acidic arenes, stoichiometric quantities of potassium phosphate. This is a sustainable method that does not need transition metal catalysis or the multistep synthesis of a main-group orga- nometallics. This exchange needs to be taken into account when using H/D scrambling as a mechanistic probe in reactions involving fluoroarenes.MINECO-SGPI, grant CTQ2016-80913-PJunta de Castilla y León (grant VA062G18