104,570 research outputs found
Employing Arynes in Unique Multicomponent Reactions and a Strain-Release Ene Reaction
No full textArynes are highly reactive electrophilic intermediates, extensively used for synthesizing various benzo-fused heterocycles and 1,2-disubstituted benzenes. Among the numerous reactions of arynes, multicomponent coupling (MCC) has been widely used to synthesize versatile and structurally complex 1,2-disubstituted benzenes. In a conventional aryne MCC, the nucleophile having no acidic hydrogen adds to the highly electrophilic aryne generating the aryl anion intermediate, which is subsequently intercepted by the electrophile to furnish 1,2-disubstituted arenes. In this context, Mr. Subrata Bhattacharjee has demonstrated the synthetic potential of KI as the nucleophilic iodide source in aryne three-component coupling using aldehydes as the third component. This mild and transition-metal-free coupling reaction allowed the straightforward synthesis of 2-iodobenzyl alcohols in moderate to good yields with good functional group compatibility. Mr. Subrata could also use KBr and KCl as the nucleophilic trigger and N-methylisatin and CO2 as the electrophilic third components in this aryne multicomponent coupling (MCC).
In the vast realm of transition-metal-free aryne MCCs, only aprotic nucleophiles are employed as triggers, and the use of protic nucleophiles is not demonstrated. This is because, in many cases, the use of protic nucleophiles leads to the protonation of the generated aryl anion intermediates leading to the arylation. In this line, Mr. Bhattacharjee has employed thiophenols as a protic nucleophilic trigger in the transition-metal-free and Grignard reagent-free three-component coupling involving arynes. Employing aldehydes as the third component, the reaction allowed the mild and broad scope synthesis of 2-arylthio benzyl alcohol derivatives in good yields. Moreover, Mr. Subrata has extended the reaction to selenophenol as the nucleophilic trigger, and activated ketones as the third component.
Mr. Bhattacharjee has also synthesised biologically important S-aryl dithiocarbamates by the aryne three component coupling involving CS2 and aliphatic amines. This transition-metal-free and mild reaction is scalable and operates with good functional group compatibility. Contrary to the known aryne MCCs involving amines and CO2, this reaction proceeds via the initial addition of amines to CS2 followed by the trapping with arynes to furnish the desired products. Mr. Bhattacharjee has presented detailed experiments and DFT studies to get insight into the mode of addition and product formation. Moreover, using 3-triflyloxybenzyne, a four-component coupling with the incorporation of THF was also presented.
The aryne ene reaction, although well-known, has not enjoyed widespread use in synthesis, primarily because of poor selectivity and low yields due to the competing [4+2], [2+2] pathways. However, the emergence of contemporary methods to generate arynes under mild conditions has led to significant advancements in the aryne ene reaction. Over the past two decades, a significant number of efficient and selective processes have been described, employing a wide range of substrates, including alkenes, alkynes, allenes etc. In this context, Mr. Bhattacharjee have demonstrated a unique strain-release ene reaction bicyclo[1.1.0]butanes (BCBs) employing arynes by utilizing the substantial π-character of the strained central C–C bond of the BCBs. The ene reaction proceeds under mild conditions and results in the formation of substituted cyclobutene derivatives in excellent yields
Letter, [Author unclear] to Paulina T. Merritt
No full textHandwritten letter to Paulina Merritt from an unknown author, October 1, 1876.
Control design based on analytical stability criteria for optimized kinesthetic perception in scaled teleoperation
No full textFig. 2 in On the status of some species of Cheirostylis Blume (Orchidaceae) from India
No full textFig. 2. – 'Cheirostylis munnacampensis A. N. Rao'. A. Flower; B. Petal; C. Labellum; D. Column with anther-cap – Cheirostylis yunnanensis Rolfe; E. Flower; F-G. Petal; H. Labellum (partly fragmented); I. Portion of hypochile with appendages (magnified); J. Column. [A-D: after RO, 1988; E-J: T. K. Paul 43698, CAL, dissected from dry and pressed specimen]Published as part of Bhattacharjee, Avishek, 2012, On the status of some species of Cheirostylis Blume (Orchidaceae) from India, pp. 31-35 in Candollea 67 (1) on page 35, DOI: 10.15553/c2012v671a3, http://zenodo.org/record/570865
Psychophysical evaluation of control scheme designed for optimal kinesthetic perception in scaled teleoperation
No full textHandwritten biographical information on Paulina T. McClung Merritt
No full textA handwritten biography of Paulina T. McClung Merritt by an unknown author, 1892.
Heterogeneous and tissue-specific regulation of effector T cell responses by IFN-gamma during Plasmodium berghei ANKA infection.
No full textIFN-γ and T cells are both required for the development of experimental cerebral malaria during Plasmodium berghei ANKA infection. Surprisingly, however, the role of IFN-γ in shaping the effector CD4(+) and CD8(+) T cell response during this infection has not been examined in detail. To address this, we have compared the effector T cell responses in wild-type and IFN-γ(-/-) mice during P. berghei ANKA infection. The expansion of splenic CD4(+) and CD8(+) T cells during P. berghei ANKA infection was unaffected by the absence of IFN-γ, but the contraction phase of the T cell response was significantly attenuated. Splenic T cell activation and effector function were essentially normal in IFN-γ(-/-) mice; however, the migration to, and accumulation of, effector CD4(+) and CD8(+) T cells in the lung, liver, and brain was altered in IFN-γ(-/-) mice. Interestingly, activation and accumulation of T cells in various nonlymphoid organs was differently affected by lack of IFN-γ, suggesting that IFN-γ influences T cell effector function to varying levels in different anatomical locations. Importantly, control of splenic T cell numbers during P. berghei ANKA infection depended on active IFN-γ-dependent environmental signals--leading to T cell apoptosis--rather than upon intrinsic alterations in T cell programming. To our knowledge, this is the first study to fully investigate the role of IFN-γ in modulating T cell function during P. berghei ANKA infection and reveals that IFN-γ is required for efficient contraction of the pool of activated T cells
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Partial Orders with Respect to Continuous Covariates and Tests for the Proportional Hazards Model
No full textSeveral omnibus tests of the proportional hazards assumption have been proposed in the literature. In the two-sample case, tests have also been developed against ordered alternatives like monotone hazard ratio and monotone ratio of cumulative hazards. Here we propose a natural extension of these partial orders to the case of continuous covariates. The work is motivated by applications in biomedicine and economics where covariate e¤ects often decay over lifetime. We develop tests for the proportional hazards assumption against ordered alternatives and propose a graphical method to identify the nature of departures from proportionality. The proposed tests do not make restrictive assumptions on the underlying regression model, and are applicable in the presence of multiple covariates and frailty. Small sample performance and applications to real data highlight the usefulness of the framework and methodology
Pelevin’s Trinity in the novel “t”: author – protagonist – reader
No full textThe article attempts to interpret Pelevin's artistic strategy in the novel "T" by exploring its subject organization and addressing the key problems of the author, the protagonist, and the reader as they are seen by the researcher. The article analyzes the peculiarities of constructing the narrative reality in the novel "T", and goes on to discuss Pelevin's philosophic models of the development of the humankind, and the emergence of his new anthropology
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