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Ramos L.,Institute of Organic Chemistry
Journal of Chromatography A | Year: 2012

Sample preparation procedures in use in many application areas are still tedious and manually intensive protocols. These characteristics mean that sample treatment is considered the most time-consuming and error-prone part of the analytical scheme. The increasing demand for faster, more cost-effective and environmental friendly analytical methods is a major incentive to improve these conventional procedures and has spurred research in this field during the last decades. This review provides an overview of the most relevant developments and successful approaches proposed in recent years concerning sample preparation. The current state-of-the-art is discussed on the basis of examples selected from representative application areas and involving conventional instrumental techniques for the final determination of the target compounds. Emphasis will be on those techniques and approaches that have already demonstrated their practicality by the analysis of real-life samples, and in particular on those dealing with the determination of minor organic components. The potential of the latest developments in this field for sample treatment simplification and complete hyphenation and integration of analytical process is discussed and the most pressing remaining limitations evaluated. © 2011 Elsevier B.V. Source


Jazwinski J.,Institute of Organic Chemistry
Nuclear Magnetic Resonance | Year: 2014

The most important papers on the calculations of indirect spin-spin coupling constants and their applications, mainly in organic chemistry, have been reviewed. The monograph includes chapters on the compounds exhibiting rotational or conformational flexibility, through-space couplings, spin-spin couplings via pnicogen bonds and hydrogen bonds, interactions in van der Waals complexes, the calculations including relativistic effects, and finally the section on new methods, benchmark calculations and reviews. Calculation methods, basis sets, software used for the calculations, as well as the index of spin-spin couplings have been included. Altogether 101 works have been cited. The survey covers the period from June 2012 to May 2013. © The Royal Society of Chemistry 2014. Source


News Article
Site: http://www.rdmag.com/rss-feeds/all/rss.xml/all

Use of copper as a fluorescent material allows for the manufacture of inexpensive and environmentally compatible organic light-emitting diodes (OLEDs). Thermally activated delayed fuorescence (TADF) ensures high light yield. Scientists of Karlsruhe Institute of Technology (KIT), CYNORA, and the University of St Andrews have now measured the underlying quantum mechanics phenomenon of intersystem crossing in a copper complex. The results of this fundamental work are reported in the Science Advances journal and contribute to enhancing the energy efficiency of OLEDs. Organic light-emitting diodes are deemed tomorrow's source of light. They homogeneously emit light in all observation directions and produce brilliant colors and high contrasts. As it is also possible to manufacture transparent and flexible OLEDs, new application and design options result, such as flat light sources on window panes or displays that can be rolled up. OLEDs consist of ultra-thin layers of organic materials, which serve as emitter and are located between two electrodes. When voltage is applied, electrons from the cathode and holes (positive charges) from the anode are injected into the emitter, where they form electron-hole pairs. These so-called excitons are quasiparticles in the excited state. When they decay into their initial state again, they release energy. Excitons may assume two different states: Singlet excitons decay immediately and emit light, whereas triplet excitons release their energy in the form of heat. Usually, 25 percent singlets and 75 percent triplets are encountered in OLEDs. To enhance energy efficiency of an OLED, also triplet excitons have to be used to generate light. In conventional light-emitting diodes heavy metals, such as iridium and platinum, are added for this purpose. But these materials are expensive, have a limited availability, and require complex OLED production methods. It is cheaper and environmentally more compatible to use copper complexes as emitter materials. Thermally activated delayed fluorescence (TADF) ensures high light yields and, hence, high efficiency: Triplet excitons are transformed into singlet excitons which then emit photons. TADF is based on the quantum mechanics phenomenon of intersystem crossing (ISC), a transition from one electronic excitation state to another one of changed multiplicity, i.e. from singlet to triplet or vice versa. In organic molecules, this process is determined by spin-orbit coupling. This is the interaction of the orbital angular momentum of an electron in an atom with the spin of the electron. In this way, all excitons, triplets and singlets, can be used for the generation of light. With TADF, copper luminescent material reaches an efficiency of 100 percent. Stefan Bräse and Larissa Bergmann of KIT's Institute of Organic Chemistry (IOC), in cooperation with researchers of the OLED technology company CYNORA and the University of St Andrews, United Kingdom, for the first time measured the speed of intersystem crossing in a highly luminescent, thermally activated delayed fluorescence copper(I) complex in the solid state. The results are reported in the Science Advances journal. The scientists determined a time constant of intersystem crossing from singlet to triplet of 27 picoseconds (27 trillionths of a second). The reverse process - reverse intersystem crossing - from triplet to singlet is slower and leads to a TADF lasting for an average of 11.5 microseconds. These measurements improve the understanding of mechanisms leading to TADF and facilitate the specific development of TADF materials for energy-efficient OLEDs.


Home > Press > How copper makes organic light-emitting diodes more efficient: KIT researchers measure intersystem crossing directly in a thermally activated delayed fluorescence copper complex -- publication in Science Advances Abstract: Use of copper as a fluorescent material allows for the manufacture of inexpensive and environmentally compatible organic light-emitting diodes (OLEDs). Thermally activated delayed fuorescence (TADF) ensures high light yield. Scientists of Karlsruhe Institute of Technology (KIT), CYNORA, and the University of St Andrews have now measured the underlying quantum mechanics phenomenon of intersystem crossing in a copper complex. The results of this fundamental work are reported in the Science Advances journal and contribute to enhancing the energy efficiency of OLEDs. Organic light-emitting diodes are deemed tomorrow's source of light. They homogeneously emit light in all observation directions and produce brilliant colors and high contrasts. As it is also possible to manufacture transparent and flexible OLEDs, new application and design options result, such as flat light sources on window panes or displays that can be rolled up. OLEDs consist of ultra-thin layers of organic materials, which serve as emitter and are located between two electrodes. When voltage is applied, electrons from the cathode and holes (positive charges) from the anode are injected into the emitter, where they form electron-hole pairs. These so-called excitons are quasiparticles in the excited state. When they decay into their initial state again, they release energy. Excitons may assume two different states: Singlet excitons decay immediately and emit light, whereas triplet excitons release their energy in the form of heat. Usually, 25 percent singlets and 75 percent triplets are encountered in OLEDs. To enhance energy efficiency of an OLED, also triplet excitons have to be used to generate light. In conventional light-emitting diodes heavy metals, such as iridium and platinum, are added for this purpose. But these materials are expensive, have a limited availability, and require complex OLED production methods. It is cheaper and environmentally more compatible to use copper complexes as emitter materials. Thermally activated delayed fluorescence (TADF) ensures high light yields and, hence, high efficiency: Triplet excitons are transformed into singlet excitons which then emit photons. TADF is based on the quantum mechanics phenomenon of intersystem crossing (ISC), a transition from one electronic excitation state to another one of changed multiplicity, i.e. from singlet to triplet or vice versa. In organic molecules, this process is determined by spin-orbit coupling. This is the interaction of the orbital angular momentum of an electron in an atom with the spin of the electron. In this way, all excitons, triplets and singlets, can be used for the generation of light. With TADF, copper luminescent material reaches an efficiency of 100 percent. Stefan Bräse and Larissa Bergmann of KIT's Institute of Organic Chemistry (IOC), in cooperation with researchers of the OLED technology company CYNORA and the University of St Andrews, United Kingdom, for the first time measured the speed of intersystem crossing in a highly luminescent, thermally activated delayed fluorescence copper(I) complex in the solid state. The results are reported in the Science Advances journal. The scientists determined a time constant of intersystem crossing from singlet to triplet of 27 picoseconds (27 trillionths of a second). The reverse process - reverse intersystem crossing - from triplet to singlet is slower and leads to a TADF lasting for an average of 11.5 microseconds. These measurements improve the understanding of mechanisms leading to TADF and facilitate the specific development of TADF materials for energy-efficient OLEDs. About Karlsruhe Institute of Technology (KIT) Karlsruhe Institute of Technology (KIT) pools its three core tasks of research, higher education, and innovation in a mission. With about 9,400 employees and 24,500 students, KIT is one of the big institutions of research and higher education in natural sciences and engineering in Europe. KIT - The Research University in the Helmholtz Association Since 2010, the KIT has been certified as a family-friendly university. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


News Article
Site: http://phys.org/chemistry-news/

Now, that chemical biologist and his colleagues at the Johns Hopkins University School of Medicine report that tests of triptolide in human cells and mice are vastly improved by the chemical attachment of glucose to the triptolide molecule. The chemical add-on makes the molecule more soluble and essentially turns it into a "cruise missile" that preferentially seeks out cancer cells, the research says. The change might also decrease side effects in patients and make the drug easier to administer. A summary of the research is published in the journal Angewandte Chemie and was published online on Aug. 30. "We have a long way to go before we can test this derivative of triptolide in humans, and we think that additional adjustments could improve it even more," says Jun O. Liu, Ph.D., professor of pharmacology and molecular sciences at the Johns Hopkins University School of Medicine and a member of the Johns Hopkins Kimmel Cancer Center, "but it already has the key characteristics we've been looking for: It is quite water soluble, and it prefers cancer cells over healthy cells." Liu, a native of a small town north of Shanghai in China, explains that the thunder god vine has been used in traditional Chinese medicine for more than 400 years, mostly to calm an overactive immune system, which can cause diseases like rheumatoid arthritis and multiple sclerosis. His laboratory specializes in figuring out how natural compounds with known healing properties exert their effects on human cells. Five years ago, he and his colleagues discovered that triptolide halts cell growth by interfering with the protein XPB, part of the large protein machine transcription factor IIH, which, in turn, is needed by enzyme complex RNA polymerase II to make mRNA. Because triptolide halts cell growth, it works well to fight the multiplication of cancer cells, Liu says, both in lab-grown cells and in laboratory animals with cancer. Unfortunately, it—and many of its derivatives—has failed to work well in patients because it doesn't dissolve well in water or blood, and has too many side effects due to its indiscriminate killing of healthy cells as well as tumor cells. Liu's latest research sought to "train" triptolide to target cancer cells by exploiting the knowledge that most cancer cells make extra copies of proteins, called glucose transporters. Those transporters form tunnels through a cell's membrane to import enough glucose to fuel rapid growth. By attaching glucose to triptolide, the researchers hoped to trick the cancer cells into importing the cell-killing poison, as had been done successfully with other anticancer drugs. "We were looking for something that could be administered intravenously, remain stable in the blood and then become active as soon as it was imported into cancer cells," says Liu. To begin, the chemists designed and synthesized five derivatives of triptolide, dubbed glutriptolides. Each derivative had glucose attached to the same spot on the triptolide molecule but had different "linkers" connecting them. An initial experiment showed that none of the glutriptolides were good at blocking the activity of purified transcription factor IIH. Liu explains that what might seem like bad news was actually a positive result, since it suggested that the drugs would only be active once they entered cells and had their glucose attachments removed. When the five glutriptolides were tested on human embryonic kidney cells, glutriptolide 2 slowed down cell growth better than the rest and is the only derivative they continued to study. In later test tube and cell experiments, the researchers confirmed that glutriptolide 2 works just like triptolide—by interfering with XPB—though it does so only in higher concentrations. They also showed that a cancer cell line (DLD1-Mut) known to produce lots of glucose transporter 1 was more sensitive to glutriptolide 2's effects than a similar cell line (DLD1-WT) without extra copies of the transporter. When the researchers assessed triptolide's effects on a variety of healthy cells and cancer cells in parallel with glutriptolide 2, they found that triptolide tended to equally slow the growth of healthy cells and cancer cells, while glutriptolide 2 was eight times more effective against cancer cells, on average. Liu says this result suggests that the new compound—if tested in humans—may be more selective against cancer cells and could therefore have fewer side effects. Finally, due to the differences in the compounds' general toxicity, tests showed that mice could tolerate a dose of 0.2 milligram/kilogram of triptolide and 1 milligram/kilogram of glutriptolide 2. At those doses, glutriptolide 2 eradicated tumors more quickly in mice with prostate cancer and prevented tumor cells from reappearing for a full three weeks after treatment had stopped. "We were totally surprised to see that sustained antitumor activity," says Liu. "It's something we want to study further." The group plans to test additional modifications to the biochemical links that connect glucose to triptolide to see if it can further decrease the compound's toxicity to healthy cells and increase its effectiveness against cancerous ones. The work was accomplished through a close international collaboration among three research groups led by Liu, Martin Pomper of the Johns Hopkins University School of Medicine and Biao Yu of the Chinese Academy of Sciences. Other authors of the report include Qing-Li He, Il Minn, Sarah Head and Emmanuel Datan of the Johns Hopkins University School of Medicine, and Qiaoling Wang and Peng Xu of the Shanghai Institute of Organic Chemistry at the Chinese Academy of Sciences. This work was supported by a Synergy Award from the Johns Hopkins University School of Medicine and the Johns Hopkins Institute for Clinical and Translational Research, which is funded in part by the National Center for Advancing Translational Sciences (UL1 TR 001079). A nondisclosure agreement for the invention/technology described in this publication has been executed between The Johns Hopkins University and Rapafusyn Pharmaceuticals Inc. Dr. Liu is a co-founder of and a Scientific Advisory Board Member for Rapafusyn Pharmaceuticals Inc. This arrangement has been reviewed and approved by The Johns Hopkins University in accordance with its conflict of interest policies. More information: Qing-Li He et al, Targeted Delivery and Sustained Antitumor Activity of Triptolide through Glucose Conjugation, Angewandte Chemie International Edition (2016). DOI: 10.1002/anie.201606121

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