scholarly journals Photochemistry and Spectroscopy of Singlet Oxygen in Solvents. Recent Advances which Support the Old Theory

2016 ◽  
Vol 10 (4s) ◽  
pp. 519-530 ◽  
Author(s):  
Boris Minaev ◽  

Molecular oxygen is a paramagnetic gas with the triplet O2( ) ground state which exhibits just sluggish chemical reactivity in the absence of radical sources. In contrast, the excited metastable singlet oxygen O2( ) is highly reactive; it can oxygenate organic molecules in a wide range of specific reactions which differ from those of the usual triplet oxygen of the air. This makes the singlet oxygen an attractive reagent for new synthesis and even for medical treatments in photodynamic therapy. As an important intermediate O2( ) has attracted great attention of chemists during half-century studies of its reactivity and spectroscopy, but unusual properties of singlet oxygen makes it difficult to unravel all mysterious features. The semiempirical theory of spin-orbit coupling in dioxygen and in collision complexes of O2 with diamagnetic molecules proposed in 1982 year has explained and predicted many photochemical and spectral properties of dioxygen produced by the dye sensitization in solvents. Recent experiments with direct laser excitation of O2 in solvents provide a complete support of the old theory. The present review scrutinizes the whole story of development and experimental verification of this theory.

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Karolina Kula ◽  
Agnieszka Kącka-Zych ◽  
Agnieszka Łapczuk-Krygier ◽  
Radomir Jasiński

Abstract The large and significant increase in carbon dioxide concentration in the Earth’s atmosphere is a serious problem for humanity. The amount of CO2 is increasing steadily which causes a harmful greenhouse effect that damages the Earth’s climate. Therefore, one of the current trends in modern chemistry and chemical technology are issues related to its utilization. This work includes the analysis of the possibility of chemical consumption of CO2 in Diels-Alder processes under non-catalytic and catalytic conditions after prior activation of the C=O bond. In addition to the obvious benefits associated with CO2 utilization, such processes open up the possibility of universal synthesis of a wide range of internal carboxylates. These studies have been performed in the framework of Molecular Electron Density Theory as a modern view of the chemical reactivity. It has been found, that explored DA reactions catalyzed by Lewis acids with the boron core, proceeds via unique stepwise mechanism with the zwitterionic intermediate. Bonding Evolution Theory (BET) analysis of the molecular mechanism associated with the DA reaction between cyclopentadiene and carbon dioxide indicates that it takes place thorough a two-stage one-step mechanism, which is initialized by formation of C–C single bond. In turn, the DA reaction between cyclopentadiene and carbon dioxide catalysed by BH3 extends in the environment of DCM, indicates that it takes place through a two-step mechanism. First path of catalysed DA reaction is characterized by 10 different phases, while the second by eight topologically different phases.


2009 ◽  
Vol 15 (S3) ◽  
pp. 53-54
Author(s):  
Aiying Wu ◽  
P. M. Vilarinho

AbstractLead zirconate - lead titanate (PZT) materials are commercially important piezoelectric and ferroelectrics in a wide range of applications, such as data storage (dynamic access and ferroelectric random access memories) and sensing and actuating devices. PZT with the morphotropic phase boundary composition offers the highest piezoelectric response and at the present there are no fullydeveloped alternative materials to PZT. The importance of PZT associated with the continuous requirements of device miniaturization, imposes the development of high quality PZT thin films with optimized properties. Concomitantly due to the dependence of the final properties of thin films on the details of the microstructure a thoroughly analysis at the local scale of their microstructure is necessary. Sol-gel method, is one of the Chemical Solution Deposition techniques used to prepare oxide thin films, such as PZT. Starting from a solution, a solid network is progressively formed via inorganic polymerisation reactions. Most metal alkoxides used for sol-gel synthesis are highly reactive towards hydrolysis and condensation. Therefore their chemical reactivity has to be tailored via the chemical modification (or complexation) of metal alkoxides to avoid uncontrolled reactions and precipitation. For PZT sol gel thin film preparation, two chemical routes are frequently used depending on the nature of the molecular precursor, namely methotoxyethanol (MOE) route and diol-route.


2021 ◽  
Author(s):  
Moataz Dowaidar

A feasible alternative to state-of-the-art enzymatic nucleases was created by regulating the cleavage activity of metal complexes using (covalent or non-covalent) homing agents. Targeted AMNs, unlike enzymatic nucleases, break DNA by an oxidative mechanism and can therefore permanently knock off genes. Compared to larger enzymatic nucleases, the modest size of the metal complex may aid cellular transfection. Furthermore, the painstaking construction of the sequence-specific probe permits a metal complex to be directed to dsDNA's minor or major groove. To direct the chemical reactivity of several small-molecule compounds to dsDNA's minor groove, covalently bonded polyamide samples were used. PNA and DNA were also used to construct antisense and antigen hybrids, with Watson–Crick or Hoogsteen base pairing with major groove nucleobases giving sequence recognition. Click chemistry created chimeric AMN-TFOs with desirable focused effects and negligible off-target cleavage. Clip-Phen-modified TFOs, 230 polypyridyl-modified TFOs, 232 and intercalating phenanthrene-modified TFOs are three contemporary instances of copper AMN–TFOs. All three systems have distinct advantages in maintaining the desired 2:1 phenthroline/copper ratio for DNA cleavage (clip-Phen TFOs), caging the copper center and facilitating efficient ROS-mediated strand scission (polypyridyl-modified TFO) and improving triplex stability (polypyridyl-modified TFO) (phenanthrene-TFOs). Cerium (IV)/EDTA complexes, recently shown to bind and hydrolytically cleave ssDNA/dsDNA junctions and used in conjunction with PNA to successfully introduce genome changes in vitro and in vivo, are another important class of targeted chemical nucleases. The chemical reactivity and wide flexibility of metal complex design, combined with their coupling to sequence specific samples for directed applications, show that these compounds have a wide range of untapped applications in biological fields such as chemotherapy, protein engineering, DNA footprinting, and gene editing. Parallel advancements in cell and tissue targeting will be essential to maximise their therapeutic potential, either by using specific ligands or creating new targeting modalities.


1981 ◽  
Vol 36 (12) ◽  
pp. 1628-1631 ◽  
Author(s):  
Grażyna Wenska ◽  
Stefan Paszyc

Abstract Irradiation (λ > 290 nm) of 6-thiopurine and some 9-substituted 6-thiopurines in oxygen saturated tert-butanol leads to hypoxanthine, purine and purine-6-sulfonic acid or their substituted derivatives. Purine and hypoxanthine formation can be sensitized with dyes. The reaction of 6-thiopurine with singlet oxygen has also been performed with purine and hypoxanthine among other products. It seems however that 1O2 is not an important intermediate in the photooxygenation. The photoreaction may have some synthetic value. Hypoxanthines (~50%) or purines (35-45%) were obtained depending on the solvent used.


2019 ◽  
Author(s):  
Victor Suarez-Lledo ◽  
Javier Alvarez-Galvez

BACKGROUND The propagation of health misinformation through social media has become a major public health concern over the last two decades. Although today there is broad agreement among researchers, health professionals, and policy makers on the need to control and combat health misinformation, the magnitude of this problem is still unknown. Consequently, before adopting the necessary measures for the adequate control of health misinformation in social media, it is fundamental to discover both the most prevalent health topics and the social media platforms from which these topics are initially framed and subsequently disseminated. OBJECTIVE This systematic review aims to identify the main health misinformation topics and their prevalence on different social media platforms, focusing on methodological quality and the diverse solutions that are being implemented to address this public health concern. METHODS This systematic review was conducted according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines (PRISMA). We searched PubMed, MEDLINE, Scopus and the Web of Science for articles published in English before March 2019 with a particular focus on studying health misinformation in social media. We defined health misinformation as a health-related claim based on anecdotal evidence, false, or misleading due to the lack of existing scientific knowledge. The criteria for inclusion were: 1) articles that focused on health misinformation in social media, including those in which the authors discussed the consequences or purposes of health misinformation; and 2) studies that described empirical findings regarding the measurement of health misinformation in these platforms. RESULTS A total of 69 studies were identified as eligible, covering a wide range of health topics and social media platforms. The topics were articulated around six principal categories: vaccines (32%), drugs or smoking (22%), non-communicable disease (19%), pandemics (10%), eating disorders (9%), and medical treatments (7%). Studies were mainly based on five methodological approaches: Social Network Analysis (28%), Evaluating Content (26%), Evaluating Quality (24%), Content/Text analysis (16%) and Sentiment Analysis (6%). Health misinformation proved to be the most more prevalent in studies related to smoking products and drugs such as opioids or marijuana. Posts with misinformation reached 87% in some studies focused in smoking products. Health misinformation about vaccines was also very common (43%), but studies reported different levels of misinformation depending on the different vaccines, with the Human Papilloma Virus (HPV) vaccine being the most affected. Secondly, health misinformation related to diets or pro eating disorders (pro-ED) arguments were moderate in comparison to the aforementioned topics (36%). Studies focused on diseases (i.e. non-communicable diseases and pandemics) also reported moderate misinformation rates (40%), especially in the case of cancer. Finally, the lowest levels of health misinformation were related to medical treatments (30%). CONCLUSIONS Prevalence of health misinformation was most common on Twitter and on issues related to smoking products and drugs. However, misinformation is also high on major public health issues such as vaccines and diseases. Our study offers a comprehensive characterization of the dominant health misinformation topics and a comprehensive description of their prevalence in different social media platforms, which can guide future studies and help in the development of evidence-based digital policy actions plans. CLINICALTRIAL


Author(s):  
N. Kozhuhova ◽  
V. Strokova ◽  
R. Chizhov ◽  
M. Kozhuhova

Nowadays, the production of high-performance composites is a relevant objective in construction industry. Normally, geological and/or technological conditions of phase formation are responsible for chemical and structural characteristics of raw materials. In this regard, the use of a certain material dictates terms to optimizing production process, efficient use and, therefore, requires to develop a method for quality evaluation of raw materials. This approach allows a considerable time saving and raw materials sources, while the evaluation of final performance characteristics of designed materials is being done. The biggest interest in this area is focused on new types of developed and poorly-studied composite systems which results in a lack of capacity to design materials with known performance and, therefore, constrains the areas of application of construction composites Among such composite systems there are zero cement alkali-aluminosilicate systems or geopolymers. For geopolymers production a wide range of different aluminosilicates with varied characteristics potentially can be used. And also, in each certain case, the quality evaluation methods for aluminosilicates should be different. This study is focused on chemical reactivity assessment method of crystalline (mainly, nanocrystalline) low calcium aluminosilicates exposed to high-alkali media. The solubility degree in high-alkali media and compressive strength performance were evaluated in this study in order to define chemical reactivity of low calcium aluminosilicates. The compressive strength data demonstrated a positive correlation with the crystallinity degree of aluminosilicates.


2012 ◽  
Vol 55 (2) ◽  
pp. 375-397 ◽  
Author(s):  
KOJI YAMAMOTO

ABSTRACTCase-studies of the circle of Samuel Hartlib, one of the most prolific groups of reformers in post-Reformation Europe, are flourishing. The uncovering of rich details has, however, made it difficult to draw a meaningful generalization about the circle's bewilderingly wide range of activities. Focusing on the circle's promotion of ‘useful knowledge’, this article offers an analytical framework for building a new synthesis. The eclectic and seemingly chaotic pursuit of useful knowledge emerged, it will be shown, as differing responses to, and interpretations of, pervasive distrust and the pursuit of reformation. The article thus explores how loosely-shared experience shaped the circle's ambivalent practices of collaboration and exclusion. The study thereby contributes not only to studies of the Hartlib circle, but also to the historiography of post-Reformation culture and burgeoning studies of trust and credibility in the history of science and technology.


Synlett ◽  
2018 ◽  
Vol 29 (20) ◽  
pp. 2608-2622 ◽  
Author(s):  
Wenwei Lin ◽  
Praneeth Karanam ◽  
Ganapuram Reddy

In this account, our group’s efforts towards exploring new substrates as precursors for the Wittig reaction have been discussed. Several new strategies developed by our group for the generation of requisite ylides for the Wittig reaction are highlighted. The idea behind the development of some chemoselective and diversity-oriented strategies are discussed in detail in a progressive manner. These strategies encompass a wide range of substrates that are employed for the synthesis of an array of heterocycles and multifunctional olefins and present a huge scope for their application on an industrial level.1 Introduction2 Development of New Methods to Effect Intramolecular Wittig Reaction3 Development of a Catalytic Wittig Reaction4 New Synthesis of Bis-Heteroarenes5 Direct β-Acylation of 2-Arylidene-1,3-indandiones6 Doubly Chemoselective Protocol for the Diversity-Oriented Synthesis of Coumarin Derivatives7 Conclusion


Minerals ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 2 ◽  
Author(s):  
Qian Peng ◽  
Xuekun Tang ◽  
Kun Liu ◽  
Xianping Luo ◽  
Dongsheng He ◽  
...  

In the study, magnesium oxide (MgO) was used to catalyze peroxymonosulfate (PMS) for the degradation of organic pollutants for the first time. According to the single-factor experiment results, it was determined that MgO could efficiently catalyze PMS to degrade organic matters in a wide range of pH values. Based on radical quenching experiments and electron spinning resonance spectra, singlet oxygen was identified to be the crucial reactive species. Importantly, the oxygen vacancy on the surface of MgO was determined as the key active site, which accelerated the decomposition of PMS to produce singlet oxygen. This study provides an interesting insight into the novel and ignored catalyst of MgO for the highly efficient activation of PMS, which will greatly benefit the Fenton-like catalytic degradation of organic wastewater.


2020 ◽  
Vol 12 (10) ◽  
pp. 949-959
Author(s):  
Ranju Bansal ◽  
Ranjit Singh

Steroidal pyrazolines constitute an interesting and promising scaffold for drug discovery as they display diverse chemical reactivity and a wide range of biological activities. Literature reports indicate potent anticancer potential of steroidal pyrazolines along with broad-spectrum antimicrobial activities. Strong neuroprotective effects with steroids possessing pyrazoline moiety have also been observed. Among all the therapeutically active steroidal pyrazolines, D-ring-substituted derivatives are highly potent and the least toxic. The current and futuristic research approaches in this area are focused towards the exploration of this promising scaffold to develop molecules with widespread pharmacological activities. This review article mainly covers the synthetic and pharmacological aspects of steroidal pyrazolines, which will assist the medicinal chemists working in this area in their scientific endeavors.


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