The electrophilic halogenation of arenes is perhaps the simplest method to prepare aryl halides, which are important structural motifs in agrochemicals, materials, and pharmaceuticals. However, the nucleophilicity of arenes is weakened by the electron-withdrawing substituents, whose electrophilic halogenation reactions usually require harsh conditions and lead to limited substrate scopes and applications. Therefore, the halogenation of arenes containing electron-withdrawing groups (EWGs) and complex bioactive compounds under mild conditions has been a long-standing challenge. Herein, we describe Brønsted acid-catalyzed halogenation of arenes with electron-withdrawing substituents under mild conditions, providing an efficient protocol for aryl halides. The hydrogen bonding of Brønsted acid with the protic solvent 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) enables this transformation and thus solves this long-standing problem.
Research on dropping out of school has focused on characteristics of the individual or institution that correlate with the dropout decision. Many of these characteristics are nonmanipulable, and all are measured at one point in time, late in the youngster’s school career. This paper describes two models for understanding dropping out as a developmental process that may begin in the earliest grades. The frustration-self-esteem model has been used for years in the study of juvenile delinquency; it identifies school failure as the starting point in a cycle that may culminate in the student’s rejecting, or being rejected by, the school. The participation-identification model focuses on students’ “involvement in schooling,” with both behavioral and emotional components. According to this formulation, the likelihood that a youngster will successfully complete 12 years of schooling is maximized if he or she maintains multiple, expanding forms of participation in school-relevant activities. The failure of a youngster to participate in school and class activities, or to develop a sense of identification with school, may have significant deleterious consequences. The ability to manipulate modes of participation poses promising avenues for further research as well as for intervention efforts.
The high performance and low cost of dye-sensitized solar cells (DSSCs) have drawn great interest from both academic and industrial circles. The research on exploring novel efficient sensitizers, especially on inexpensive metal-free pure organic dyes, has never been suspended. The donor-π bridge-acceptor (D-π-A) configuration is mainstream in the design of organic sensitizers due to its convenient modulation of the intramolecular charge-transfer nature. Recently, it has been found that incorporation of additional electron-withdrawing units (such as benzothiadiazole, benzotriazole, quinoxaline, phthalimide, diketopyrrolopyrrole, thienopyrazine, thiazole, triazine, cyanovinyl, cyano- and fluoro-substituted phenyl) into the π bridge as internal acceptors, termed the D-A-π-A configuration, displays several advantages such as tuning of the molecular energy levels, red-shift of the charge-transfer absorption band, and distinct improvement of photovoltaic performance and stability. We apply the D-A-π-A concept broadly to the organic sensitizers containing additional electron-withdrawing units between electron donors and acceptors. This review is projected to summarize the category of pure organic sensitizers on the basis of the D-A-π-A feature. By comparing the structure-property relationship of typical photovoltaic D-A-π-A dyes, the important guidelines in the design of such materials are highlighted.
Replacement of Pt-based oxygen reduction reaction (ORR) catalysts with non-precious metal catalysts (NPMCs) such as Fe/N/C is one of the most important issues in the commercialization of proton exchange membrane fuel cells (PEMFCs). Despite numerous studies on Fe/N/C catalysts, a fundamental study on the development of a versatile strategy is still required for tuning the kinetic activity of a single Fe-N 4 site. Herein, we report a new and intuitive design strategy for tuning and enhancing the kinetic activity of a single Fe-N 4 site by controlling electron-withdrawing/donating properties of a carbon plane with the incorporation of sulfur functionalities. The effect of electron-withdrawing/donating functionalities was elucidated by experimentation and theoretical calculations. Finally, the introduction of an oxidized sulfur functionality decreases the d-band center of iron by withdrawing electrons, thereby facilitating ORR at the Fe-N 4 site by lowering the intermediate adsorption energy. Furthermore, this strategy can enhance ORR activity without a decrease in the stability of the catalyst. This simple and straightforward approach can be a cornerstone to develop optimum NPMCs for application in the cathodes of PEMFCs.
BACKGROUND: The antimalarial drug hydroxychloroquine is thought to be effective in controlling some of the manifestations of systemic lupus erythematosus, but its effectiveness has not been demonstrated conclusively. METHODS: We conducted a six-month, randomized, double-blind, placebo-controlled study of the effect of discontinuing hydroxychloroquine sulfate treatment in 47 patients with clinically stable systemic lupus erythematosus. The patients were randomly assigned to continue their same dose of hydroxychloroquine (n = 25) or to receive placebo (n = 22) for 24 weeks. Ten patients in each group were also taking prednisone. RESULTS: The relative risk of a clinical flare-up, defined as the development of specific clinical manifestations of systemic lupus erythematosus or an increase in their severity, was 2.5 times higher (95 percent confidence interval, 1.08 to 5.58) in the patients taking placebo than in those continuing to take hydroxychloroquine (16 of 22 patients vs. 9 of 25 had flare-ups), and the time to a flare-up was shorter (P = 0.02). The relative risk of a severe exacerbation of disease that required withdrawal from the study was 6.1 times higher (95 percent confidence interval, 0.72 to 52.44) for the patients taking placebo (5 of 22 patients vs. 1 of 25 had severe exacerbations of disease). Changes in the dose of prednisone were not different in the two groups. CONCLUSIONS: Patients with quiescent systemic lupus erythematosus who are taking hydroxychloroquine are less likely to have a clinical flare-up if they are maintained on the drug.
This study examined the effects of gender and social structure on the demand/withdraw pattern of marital conflict. In this pattern, the demander, usually the woman, pressures the other through emotional requests, criticism, and complaints, and the withdrawer, usually the man, retreats through defensiveness and passive inaction. In this study, 31 couples were assessed in 2 conflict situations: 1 in which husband wanted a change in wife and 1 in which wife wanted a change in husband. Data from husbands, wives, and observers consistently revealed a significant main effect of gender (wife-demand/husband-withdraw interaction was more likely than husband-demand/wife-withdraw interaction) and a significant interaction of gender and conflict structure (wife-demand/husband-withdraw interaction was more likely than the reverse only when discussing a change the wife wanted). Separate analyses of demand and withdraw behaviors indicated that both husband and wife were more likely to be demanding when discussing a change they wanted and more likely to be withdrawing when discussing a change their partner wanted. However, men were overall more withdrawn than women, but women were not overall more demanding than men.
Abstract A new and synthetically versatile strategy has been developed for the phosphorescence color tuning of cyclometalated iridium phosphors by simple tailoring of the phenyl ring of ppy (Hppy = 2‐phenylpyridine) with various main‐group moieties in [Ir(ppy‐X) 2 (acac)] (X = B(Mes) 2 , SiPh 3 , GePh 3 , NPh 2 , POPh 2 , OPh, SPh, SO 2 Ph). This can be achieved by shifting the charge‐transfer character from the pyridyl groups in some traditional iridium ppy‐type complexes to the electron‐withdrawing main‐group moieties and these assignments were supported by theoretical calculations. This new color tuning strategy in Ir III ‐based triplet emitters using electron‐withdrawing main‐group moieties provides access to Ir III phosphors with improved electron injection/electron transporting features essential for highly efficient, color‐switchable organic light‐emitting diodes (OLEDs). The present work furnished OLED colors spanning from bluish‐green to red (505–609 nm) with high electroluminescence efficiencies which have great potential for application in multicolor displays. The maximum external quantum efficiency of 9.4%, luminance efficiency of 10.3 cd A −1 and power efficiency of 5.0 lm W −1 for the red OLED (X = B(Mes) 2 ), 11.1%, 35.0 cd A −1 , and 26.8 lm W −1 for the bluish‐green device (X = OPh), 10.3%, 36.9 cd A −1 , and 28.6 lm W −1 for the bright green device (X = NPh 2 ) as well as 10.7%, 35.1 cd A −1 , and 23.1 lm W −1 for the yellow‐emitting device (X = SO 2 Ph) can be obtained.
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Macrocyclic dicopper(II) complexes derived from 2,6-di(R)formylphenols and various linking diamines are surveyed and their magnetic and structural properties assessed. For those systems with "flat" dinuclear centers and no electronic perturbations associated with electron-withdrawing ligands or ligand groups, the complexes exhibit a "straight-line" relationship between exchange integral and phenoxide bridge angle. Within the angle range 98.8-104.7 degrees, 11 complexes are included with -2J in the range 689-902 cm(-)(1). When electron-withdrawing species are present, either as ligands or as groups bound to the macrocycle itself, considerable suppression of the antiferromagnetic exchange component is observed. Single-crystal X-ray diffraction studies are reported for three complexes. [Cu(2)(L1)(H(2)O)(2)]F(2)(CH(3)OH)(2) (1) crystallized in the triclinic system, space group P&onemacr;, with a = 8.1878(5) Å, b = 9.0346(7) Å, c = 10.4048(7) Å, alpha = 103.672(6) degrees, beta = 101.163(5) degrees, gamma = 104.017(5) degrees, and Z = 1. [Cu(2)(L2)Cl(2)] [Cu(2)(L2) (H(2)O)(2)]Cl(ClO(4)).5.5H(2)O (2) crystallized in the monoclinic system, space group P2(1)/n, with a = 14.4305(5) Å, b = 24.3149(8) Å, c = 18.6584(8) Å, beta = 111.282(3) degrees, and Z = 4. [Cu(2)(L3)(H(2)O)(2)](BF(4))(2) (3) crystallized in the triclinic system, space group P&onemacr;, with a = 8.6127(4) Å, b = 8.6321(7) Å, c = 10.8430(10) Å, a = 74.390(10) degrees, beta = 86.050(10) degrees, gamma = 76.350(10) degrees, and Z = 2. Square pyramidal copper ion stereochemistries are observed in all cases, with axially coordinated halogens or water molecules. Strong antiferromagnetic exchange is observed for all complexes (-2J = 784(8) cm(-)(1), Cu-O-Cu 103.65(10) degrees (1); -2J = 801(11) cm(-)(1), Cu-O-Cu 102.4(3), 107.5(3), 102.9(3), 106.1(3) degrees (2); -2J = 689(3) cm(-)(1), Cu-O-Cu 98.8(4) degrees (3)). The presence of electron-withdrawing CN groups on the periphery of the macrocyclic ligand leads to substantially reduced antiferromagnetic exchange.
Objective. —To examine the attitudes of health care workers regarding the withdrawal of life support. Design. —Cross-sectional survey. Participants. —Attending staff, house staff, and intensive care unit (ICU) nurses in 37 Canadian university-affiliated hospitals. Main Outcome Measures. —Health care workers' ratings of the importance of 17 factors considered in the decision to withdraw life support, and their ratings of five levels of care ranging from comfort measures to intensive care in two of 12 different clinical scenarios. Results. —We surveyed 1361 respondents (149 of 167 potentially eligible ICU attending staff, 142 of 173 ICU house staff, and 1070 of 1455 ICU nurses, with response rates of 89%, 82% and 74%, respectively). The most important factors were likelihood of surviving the current episode, likelihood of long-term survival, premorbid cognitive function, and age of the patient. In choosing the level of care for the patient scenarios, the same option was chosen by more than 50% of respondents in only one of 12 scenarios; opposite extremes of care were chosen by more than 10% of the respondents in eight of 12 scenarios. Respondent characteristics affecting choices included the number of years since graduation, the city and province in which they worked, the number of beds in their ICU, and their assessment of the likelihood that they would withdraw life support in comparison with their colleagues (P Conclusions. —While ICU health care workers consistently identify a number of patient factors as important in decisions to withdraw care, there is extreme variability, which may be explained in part by the values of individual health care providers. (JAMA. 1995;273:703-708)
Wang Xiaolin, Camilla Baasch Andersen; The Chinese Declaration as to Form of Contracts under CISG - Time to Withdraw ?, Uniform Law Review, Volume 8, Issue
BACKGROUND: Mechanical ventilation after bone marrow transplantation is associated with a high mortality rate. The available literature provides conflicting predictors of outcome in relatively small study groups. OBJECTIVE: To identify predictors of death and mortality trends in mechanically ventilated transplant recipients. DESIGN: Nested case-control study. SETTING: The Fred Hutchinson Cancer Research Center in Seattle, Washington, which specializes in bone marrow transplantation. PATIENTS: All survivors (cases, n = 53) and a group of patients matched for year of transplantation who did not survive (controls, n = 106) were selected from all mechanically ventilated patients (n = 865) who received a bone marrow transplant between January 1980 and July 1992. Patients who received mechanical ventilation for less than 24 hours after a procedure or who received mechanical ventilation after a second bone marrow transplantation were excluded. MEASUREMENTS: Surviving patients were defined as those who were alive 30 days after extubation and who were discharged from the hospital. Daily laboratory, physiologic, and treatment variables were collected. RESULTS: Survival was statistically associated with younger age, lower score on the Acute Physiology and Chronic Health Evaluation III, and a shorter time from transplantation to intubation. There were no survivors among an estimated 398 patients who had lung injury and either required more than 4 hours of vasopressor support or had sustained hepatic and renal failure. Through the use of these factors, an accurate prediction of death could have been made in the first 4 days of mechanical ventilation for more than half of the patients who did not survive. During the past 5 years, survival rate has changed from 5% to 16% (P = 0.008), an increase that was not explained by changes in the age of the patients, the rate or timing of intubation, or the percentage of allogeneic transplants that were not HLA-identical. CONCLUSION: Of the patients who required mechanical ventilation after bone marrow transplantation, no one survived with lung injury combined with either hemodynamic instability or hepatic and renal failure. However, survival after mechanical ventilation seems to be improving.
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Williams, Eric S.; Konrad, Thomas R.; Scheckler, William E.; Pathman, Donald E.; Linzer, Mark; McMurray, Julia E.; Gerrity, Martha; Schwartz, Mark Author Information
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOlefin synthesis. Rate enhancement of the elimination of alkyl aryl selenoxides by electron-withdrawing substituentsK. Barry Sharpless and Michael W. YoungCite this: J. Org. Chem. 1975, 40, 7, 947–949Publication Date (Print):April 1, 1975Publication History Published online1 May 2002Published inissue 1 April 1975https://pubs.acs.org/doi/10.1021/jo00895a030https://doi.org/10.1021/jo00895a030research-articleACS PublicationsRequest reuse permissionsArticle Views3961Altmetric-Citations262LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
The effect of electron-withdrawing ligands on the energy barriers of Single-Molecule Magnets (SMMs) is investigated. By introducing highly electron-withdrawing atoms on targeted ligands, the energy barrier was significantly enhanced. The structural and magnetic properties of five novel SMMs based on a dinuclear {Dy2} phenoxo-bridged motif are explored and compared with a previously studied {Dy2} SMM (1). All complexes share the formula [Dy2(valdien)2(L)2]·solvent, where H2valdien = N1,N3-bis(3-methoxysalicylidene) diethylenetriamine, the terminal ligand L = NO3(-) (1), CH3COO(-) (2), ClCH2COO(-) (3), Cl2CHCOO(-) (4), CH3COCHCOCH3(-) (5), CF3COCHCOCF3(-) (6), and solvent = 0.5 MeOH (4), 2 CH2Cl2 (5). Systematic increase of the barrier was observed for all complexes with the most drastic increase seen in 6 when the acac ligand of 5 was fluorinated resulting in a 7-fold enhancement of the anisotropic barrier. Ab initio calculations reveal more axial g tensors as well as higher energy first excited Kramers doublets in 4 and 6 leading to higher energy barriers for those complexes.
DURING the past century, dramatic changes have occurred in physicians' ability to prolong life. A hundred years ago, little more than rudimentary supportive care could be offered to most critically ill patients. Doctors now choose from a vast array of interventions that, when combined with effective therapies for underlying conditions, often greatly prolong survival. Unfortunately, the quality of the additional life so skillfully sought can range from marginally tolerable to positively miserable.These considerations underscore the importance of a clear ethical framework for making decisions about the initiation and withdrawal of all medical treatments. This paper considers basic and advanced . . .
Firmly attached: The short-circuit photocurrent density and conversion yields of solar cells based on pyridine-containing donor–acceptor π-conjugated (D-π-A) dyes (see scheme) are greater than those for conventional D-π-A dye sensitizers that bear a carboxy group as the electron-withdrawing anchoring group. The dyes are attached to the surface by coordinate bonding with the Lewis acid sites of TiO2.
Despite an ethical and legal consensus regarding the right of patients or their surrogates to refuse life-prolonging therapy, surveys show that dying patients in hospitals in the United States frequently receive unwanted interventions.1,2 One reason for this may be a lack of training among physicians and nurses in the clinical aspects of withdrawing intensive life support. Staff members are highly skilled in aggressive life-extending treatment, and some hospitals now have services specializing in palliative care for patients forgoing life-extending treatment. But there may be no one specifically trained in managing the transition from one style of care to the . . .
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