Synthesis of 5-substituted pyrrole-2-carboxaldehydes. Part I. Generation of formal 5-lithiopyrrole-2-carboxaldehyde equivalents by bromine–lithium exchange of 2-bromo-6-(diisopropylamino)-1-azafulvene derivatives

1995 ◽  
Vol 73 (5) ◽  
pp. 675-684 ◽  
Author(s):  
Sylvie L. Berthiaume ◽  
Brian L. Bray ◽  
Petr Hess ◽  
Yanzhou Liu ◽  
Michael L. Maddox ◽  
...  
Keyword(s):  
Variable Temperature ◽  
Substantial Contribution ◽  
Ground State Structure ◽  
Conformational Preference ◽  
Dimethylamino Group ◽  
Sterically Demanding ◽  
Subsequent Hydrolysis ◽  
Electrophilic Reagents ◽  
Dominant Process ◽  
Formal Equivalent

The first known lithiated 1-azafulvene derivatives, e.g., 8 and 13a, were generated by a low-temperature bromine–lithium exchange procedure with tert-butyllithium. These lithio species show substantial stability at ≤ −90 °C because, at these temperatures, the sterically demanding 6-diisopropylamino moiety, unlike the dimethylamino group, completely inhibits nucleophilic addition to C-6. At higher temperatures, the addition of tert-butyllithium to C-6 is significant and it can become the dominant process. The lithio species 8 is a useful formal equivalent of 5-lithiopyrrole-2-carboxaldehyde since, on reaction with electrophilic reagents and subsequent hydrolysis, a wide variety of regiochemically pure 5-substituted pyrrole-2-carboxaldehydes is formed. The 6-dialkylamino-1-azafulvenes described herein exist predominantly or exclusively as the syn conformer in solution at room temperature. This conformational preference is confirmed by a significance NOE effect between H-4 and H-6 in the parent diisopropylamino compound 3f. The origin of the syn conformational preference stems from a substantial contribution of the charge-separated form 16 to the ground state structure of these compounds, a phenomenon that is strongly supported by variable temperature NMR measurements on 2-bromo-6-diisopropylamino-1-azafulvene (3c). Keywords: 2-bromo-6-diisopropylamino-1-azafulvenes, stereochemistry, lithiation, pyrrole-2-carboxaldehydes.

scholarly journals Desolvation and aggregation of sterically demanding alkali metal diarylphosphides

2017 ◽  
Vol 46 (40) ◽  
pp. 13824-13834 ◽  
Author(s):  
Keith Izod ◽  
Peter Evans ◽  
Paul G. Waddell
Keyword(s):  
Alkali Metal ◽  
Low Temperatures ◽  
Variable Temperature ◽  
Nmr Studies ◽  
Sterically Demanding

Variable-temperature NMR studies reveal that sterically bulky alkali metal diarylphosphides are subject to a monomer–dimer equilibrium in solution, where the monomer is favoured at low temperatures.

Self-Assembly of Hydrogels From Elastin-Mimetic Block Copolymers

2002 ◽  
Vol 724 ◽  
Author(s):  
Elizabeth R. Wright ◽  
R. Andrew McMillan ◽  
Alan Cooper ◽  
Robert P. Apkarian ◽  
Vincent P. Conticello
Keyword(s):  
Block Copolymers ◽  
Self Assembly ◽  
Triblock Copolymers ◽  
Variable Temperature ◽  
Inverse Temperature ◽  
Temperature Transition ◽  
Scanning Calorimetry ◽  
Design Synthesis ◽  
Inverse Temperature Transition ◽  
Functional Biomaterials

AbstractTriblock copolymers have traditionally been synthesized with conventional organic components. However, triblock copolymers could be synthesized by the incorporation of two incompatible protein-based polymers. The polypeptides would differ in their hydrophobicity and confer unique physiochemical properties to the resultant materials. One protein-based polymer, based on a sequence of native elastin, that has been utilized in the synthesis of biomaterials is poly (Valine-Proline-Glycine-ValineGlycine) or poly(VPGVG) [1]. This polypeptide has been shown to have an inverse temperature transition that can be adjusted by non-conservative amino acid substitutions in the fourth position [2]. By combining polypeptide blocks with different inverse temperature transition values due to hydrophobicity differences, we expect to produce amphiphilic polypeptides capable of self-assembly into hydrogels. Our research examines the design, synthesis and characterization of elastin-mimetic block copolymers as functional biomaterials. The methods that are used for the characterization include variable temperature 1D and 2D High-Resolution-NMR, cryo-High Resolutions Scanning Electron Microscopy and Differential Scanning Calorimetry.

Regioselective Gas-Phase n-Butane Transfer Dehydrogenation via Silica-Supported Pincer-Iridium Complexes

2020 ◽  
Author(s):  
Boris Sheludko ◽  
Cristina Castro ◽  
Chaitanya Khalap ◽  
Thomas Emge ◽  
Alan Goldman ◽  
...  
Keyword(s):  
Gas Phase ◽  
Active Site ◽  
Lower Cost ◽  
Open Systems ◽  
Iridium Complexes ◽  
Terminal Olefin ◽  
Molecular Precursors ◽  
Sterically Demanding ◽  
Olefin Production ◽  
Steam Cracking

<b>Abstract:</b> The production of olefins via on-purpose dehydrogenation of alkanes allows for a more efficient, selective and lower cost alternative to processes such as steam cracking. Silica-supported pincer-iridium complexes of the form [(≡SiO-<sup>R4</sup>POCOP)Ir(CO)] (<sup>R4</sup>POCOP = κ<sup>3</sup>-C<sub>6</sub>H<sub>3</sub>-2,6-(OPR<sub>2</sub>)<sub>2</sub>) are effective for acceptorless alkane dehydrogenation, and have been shown stable up to 300 °C. However, while solution-phase analogues of such species have demonstrated high regioselectivity for terminal olefin production under transfer dehydrogenation conditions at or below 240 °C, in open systems at 300 °C, regioselectivity under acceptorless dehydrogenation conditions is consistently low. In this work, complexes <a>[(≡SiO-<i><sup>t</sup></i><sup>Bu4</sup>POCOP)Ir(CO)] </a>(<b>1</b>) and [(≡SiO-<i><sup>i</sup></i><sup>Pr4</sup>PCP)Ir(CO)] (<b>2</b>) were synthesized via immobilization of molecular precursors. These complexes were used for gas-phase butane transfer dehydrogenation using increasingly sterically demanding olefins, resulting in observed selectivities of up to 77%. The results indicate that the active site is conserved upon immobilization.

Stochastic Computing via In Operando Modulation of Rectification in Molecular Tunneling Junctions

2020 ◽  
Author(s):  
Xinkai Qiu ◽  
Sylvia Rousseva ◽  
Gang Ye ◽  
Jan C. Hummelen ◽  
Ryan Chiechi
Keyword(s):  
Self Assembly ◽  
Variable Temperature ◽  
Self Assembled Monolayers ◽  
Microfluidic Channels ◽  
Proof Of Concept ◽  
Glycol Ethers ◽  
Stochastic Computing ◽  
Assembled Monolayers ◽  
In Operando ◽  
Tunneling Junctions

This paper describes the reconfiguration of molecular tunneling junctions during operation via the self-assembly of bilayers of glycol ethers. We use well-established functional groups to modulate the magnitude and direction of rectification in assembled tunneling junctions by exposing them to solutions containing different glycol ethers. Variable-temperature measurements establish that rectification occurs by a bias-dependent tunneling-hopping mechanism and that glycol ethers, beside being an unusually efficient tunneling medium, behave identically to alkanes. We fabricated memory bits from crossbar junctions prepared by injecting eutectic Ga-In into microfluidic channels. Two 8-bit registers were able to perform logical AND operations on bit strings encoded into chemical packets as microfluidic droplets that alter the composition of the crossbar junctions through self-assembly to effect memristor-like properties. This proof of concept work demonstrates the potential for fieldable molecular-electronic devices based on tunneling junctions of self-assembled monolayers and bilayers.

EMPOWERING WOMEN THROUGH ENTREPRENEURSHIP: ASPECTS AND APPROACHES

2014 ◽  
Vol 6 (01) ◽  
Author(s):  
JAVED ALAM SHEIKH
Keyword(s):  
Economic Development ◽  
Developed Countries ◽  
Substantial Contribution ◽  
Economic Empowerment ◽  
World Population ◽  
Least Developed Countries ◽  
The Road ◽  
Road Map ◽  
The World ◽  
The Status

Almost 50 per cent of the world population is constituted by the women and they have been making substantial contribution to socio-economic development. But, unfortunately their tremendous contribution remains unrecognized and unnoticed in most of the developing and least developed countries causing the problem of poverty among them. Empowering women has become the key element in the development of an economy. With women moving forward, the family moves, the village moves and the nation moves. Hence, improving the status of women by way of their economic empowerment is highly called for. Entrepreneurship is a key tool for the economic empowerment of women around the world for alleviating poverty. Entrepreneurship is now widely recognized as a tool of economic development in India also. In this paper I have tried to discuss the reasons and role of Women Entrepreneurship with the help of Push and Pull factors. In the last I have also discussed the problems and the road map of Women Entrepreneurs development in India.

The Case for Muslim Constitutional Interpretive Activity

1990 ◽  
Vol 7 (1) ◽  
pp. 69-75
Author(s):  
Kathleen Moore
Keyword(s):  
African American ◽  
Substantial Contribution ◽  
Constitutional Rights ◽  
Religious Groups ◽  
Racial Hatred ◽  
Special Diet ◽  
Court Record ◽  
Religious Associations ◽  
Islamic Faith ◽  
The Right

Muslim Involvement: The Court Record 1.Prisoners' RightsCan we rely upon the courts to protect Islam and Muslims from discriminatory treatment? Have the courts considered Islam to be a 'religion' worthy of constitutional protection? The issue of First Amendment protection of Muslim beliefs and practices has arisen most often in cases brought by African-American Muslims who are incarcerated. In fact, the area of law to which Muslims have made their most substantial contribution to date is the area of prisoners' rights litigation. African-American Muslim inmates have been responsible for establishing prisoners' constitutional rights to worship. Cases brought by Muslims have established that prisoners have the right to assemble for religious services; to consult a cleric of their faith; to possess religious publications and to subscribe to religious literature; to wear unobstrusive religious symbols such as medallions; to have prepared a special diet required by their religion; and to correspond with their spiritual leaders. The court record demonstrates that Muslim inmates' religious liberty claims, challenging prison regulations that impinge on the free exercise of the Islamic faith, have been accepted only under certain circumstances. In brief, the responsiveness of the courts to Muslim inmates' claims has turned on a number of factors including: (1) the issue of equality of treatment of all religious groups in prison; (2) the courts' reticence to reverse the decisions of prison officials; (3) the degree to which the inmates' challenges would undermine the fundamental interests of the state (e.g. in prison security and administrative efficiency); and (4) the showing that Islam is parallel in significant ways to the conventional Protestant, Catholic, and Jewish faiths.Constitutional protection of Islamic practices in prison and elsewhere, however, has not been automatic. Many Muslim organizations, the Nation of Islam in particular, have been treated as cults, or suspect and dangerous groups, due in part to the perception that Muslims teach racial hatred, and have not been regarded in the same respect as 'mainline' religious groups. It has been argued before the courts that Muslim doctrine contains political aspirations and economic goals as well as racial prejudice and should be suppressed in the interest of society. The gist of this argument is that certain Muslim groups are primarily political and not religious associations and thus ...

Commodity Heating Medium and Mexican Fruit Fly Mortality

HortScience ◽  
1998 ◽  
Vol 33 (3) ◽  
pp. 533e-533
Author(s):  
Krista C. Shellie
Keyword(s):  
Carbon Dioxide ◽  
Variable Temperature ◽  
Larval Mortality ◽  
Fruit Fly ◽  
Hot Water ◽  
Water Bath ◽  
Controlled Atmosphere ◽  
Mexican Fruit Fly ◽  
Temperature Water ◽  
Heating Medium

The objective of this research was to investigate whether the medium used to transfer heat to a commodity influenced the mortality of Mexican fruit fly larvae. A similar 2-h heat dose was delivered to grapefruit via immersion in a variable temperature water bath or via exposure to a rapidly circulating gas. The concentration of oxygen and carbon dioxide inside the grapefruit was analyzed at 30-min intervals and grapefruit center temperatures recorded every 60 s during heating. The mortality of larvae located inside grapefruit during heating in a controlled atmosphere or in hot water was significantly higher than that of larvae located inside grapefruit heated in air. The internal atmosphere of grapefruit heated in a controlled atmosphere or in hot water contained significantly higher levels of carbon dioxide and lower levels of oxygen than grapefruit heated in air. Larval mortality was compared after larvae were heated in media by rapidly circulating air or by an atmosphere containing 4 kPa of oxygen and 18 kPa of carbon dioxide to evaluate whether the altered atmosphere or a heat-induced fruit metabolite was responsible for enhanced mortality. The significantly higher mortality of larvae heated in media in the presence of an altered atmosphere suggested that the altered atmosphere enhanced larval mortality. Results from this research suggest that reducing oxygen and or increasing the level of carbon dioxide during heating can enhance mortality of the Mexican fruit fly and potentially reduce the heat dose required for quarantine security.

Impact of climate and bulking materials on characteristics of compost from ecological toilets

2012 ◽  
Vol 2 (2) ◽  
pp. 79-86 ◽  
Author(s):  
James W. McKinley ◽  
Rebecca E. Parzen ◽  
Álvaro Mercado Guzmán
Keyword(s):  
Low Carbon ◽  
Pathogen Inactivation ◽  
High Ph ◽  
Moisture Contents ◽  
Urine Diversion ◽  
Ph Values ◽  
Dominant Process ◽  
Nitrogen Ratio ◽  
Storage Times ◽  
Carbon Concentrations

Urine-diversion dehydration toilets (UDDT) are common throughout the developing world, and the toilet product is widely used as compost. There is no comprehensive research to date that characterizes the compost to determine its quality, extent of pathogen inactivation, and the effects of climate and bulking materials on the compost. Compost was collected from 45 UDDT in Bolivia and analyzed for physical, chemical, and biological parameters. Eighty percent and 56% of samples did not meet acceptable compost guidelines for moisture content and pH, respectively, indicating desiccation was the dominant process in UDDT. Bulking materials significantly impacted compost characteristics in terms of pH, carbon, carbon-to-nitrogen ratio, and carbon stability (P &lt; 0.05). Composts with ash exhibited, on average, low carbon concentrations (4.9%) and high pH values (9.7), which can be harmful to plants and composting microorganisms. Composts with sawdust exhibited, on average, high carbon concentrations (40.0%) and carbon-to-nitrogen ratios (31.0). Climate had no significant impact on chemical characteristics, however composts from humid regions had significantly higher moisture contents (34.4%) than those from arid climates (24.8%) (P &lt; 0.05). Viable Ascaris lumbricoides ova were identified in 31% of samples, including samples with high pH, low moisture contents, and long storage times.

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