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Antimalarial peroxides  [PDF]
DEJAN M. OPSENICA,BOGDAN A. ?OLAJA
Journal of the Serbian Chemical Society , 2009,
Abstract: The problem of endemic malaria continues unabated globally. Malaria affects 40 % of the global population, causing an estimated annual mortality of 1.5–2.7 million people. The World Health Organization (WHO) estimates that 90 % of these deaths occur in sub-Saharan Africa among infants under the age of five. While a vaccine against malaria continues to be elusive, chemotherapy remains the most viable alternative towards treatment of the disease. During last years, the situation has become urgent in many ways, but mainly because of the development of chloroquine-resistant (CQR) strains of Plasmodium falciparum (Pf). The discovery that artemisinin (ART, 1), an active principle of Artemisia annua L., expresses a significant antimalarial activity, especially against CQR strains, opened new approaches for combating malaria. Since the early 1980s, hundreds of semisynthetic and synthetic peroxides have been developed and tested for their antimalarial activity, the results of which were extensively reviewed. In addition, in therapeutic practice, there is no reported case of drug resistance to these antimalarial peroxides. This review summarizes recent achievements in the area of peroxide drug development for malaria chemotherapy.
Bond rupture mechanism enables to explain in block asymmetry of elaxation, force-velocity curve and the path of energy dissipation in muscle  [PDF]
Eugene V. Rosenfeld
Quantitative Biology , 2015,
Abstract: Bond rupture mechanism enables to explain in block asymmetry of elaxation, force-velocity curve and the path of energy dissipation in muscle
Electro-Magnetic Earthquake Bursts and Critical Rupture of Peroxy Bond Networks in Rocks  [PDF]
F. Freund,D. Sornette
Physics , 2006, DOI: 10.1016/j.tecto.2006.05.032
Abstract: We propose a mechanism for the low frequency electromagnetic emissions and other electromagnetic phenomena which have been associated with earthquakes. The mechanism combines the critical earthquake concept and the concept of crust acting as a charging electric battery under increasing stress. The electric charges are released by activation of dormant charge carriers in the oxygen anion sublattice, called peroxy bonds or positive hole pairs (PHP), where a PHP represents an $O_3X/^{OO}\backslash YO_3$ with $X,Y = Si^{4+}, Al^{3+}...$, i.e. an $O^-$ in a matrix of $O^{2-}$ of silicates. We propose that PHP are activated by plastic deformations during the slow cooperative build-up of stress and the increasingly correlated damage culminating in a large ``critical'' earthquake. Recent laboratory experiments indeed show that stressed rocks form electric batteries which can release their charge when a conducting path closes the equivalent electric circuit. We conjecture that the intermittent and erratic occurrences of EM signals are a consequence of the progressive build-up of the battery charges in the Earth crust and their erratic release when crack networks are percolating throughout the stressed rock volumes, providing a conductive pathway for the battery currents to discharge. EM signals are thus expected close to the rupture, either slightly before or after, that is, when percolation is most favored.
Study on pivot-point vibration of molecular bond-rupture events by quartz crystal microbalance for biomedical diagnostics
Yuan YJ, Jia R
International Journal of Nanomedicine , 2012, DOI: http://dx.doi.org/10.2147/IJN.S26808
Abstract: udy on pivot-point vibration of molecular bond-rupture events by quartz crystal microbalance for biomedical diagnostics Original Research (2201) Total Article Views Authors: Yuan YJ, Jia R Published Date January 2012 Volume 2012:7 Pages 381 - 391 DOI: http://dx.doi.org/10.2147/IJN.S26808 Received: 04 October 2011 Accepted: 08 November 2011 Published: 24 January 2012 Yong J Yuan, Renjie Jia Laboratory of Biosensing and MicroMechatronics, School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu, Sichuan, People's Republic of China Abstract: Bond-rupture scanning for biomedical diagnostics is examined using quartz crystal microbalance (QCM) experiments and microparticle mechanics modeling calculations. Specific and nonspecific interactions between a microparticle and its binding QCM surface can be distinguished by gradually increasing the amplitude of driving voltage applied to QCM and monitoring its frequency changes. This research proposes a mechanical model of interactions between biological molecules and a QCM substrate surface. The mechanical force required to break a biotin–streptavidin bond was calculated through a one-pivot-point bottom-up vibration model. The bond-rupture force increases with an increase of the microparticle radius, the QCM resonant frequency, and the amplitude of driving voltage applied to the QCM. The significance of the research on biological molecular bond rupture is extremely important in characterizing microbial (such as cells and virus) specificity, due to the force magnitude needed to break bonds using a transducer.
Newly observed peroxides and the water effect on the formation and removal of hydroxyalkyl hydroperoxides in the ozonolysis of isoprene
D. Huang,Z. M. Chen,Y. Zhao,H. Liang
Atmospheric Chemistry and Physics Discussions , 2013, DOI: 10.5194/acpd-13-5279-2013
Abstract: The ozonolysis of alkenes is considered to be an important source of atmospheric peroxides, which serve as oxidants, reservoirs of HOx radicals, and components of secondary organic aerosols (SOAs). Recent laboratory investigations of this reaction identified hydrogen peroxide (H2O2) and hydroxymethyl hydroperoxide (HMHP). Although larger hydroxyalkyl hydroperoxides (HAHPs) were also expected, their presence is not currently supported by experimental evidence. In the present study, we investigated the formation of peroxides in the gas phase ozonolysis of isoprene at various relative humidities on a time scale of tens of seconds, using a quartz flow tube reactor coupled with the online detection of peroxides. We detected a variety of conventional peroxides, including H2O2, HMHP, methyl hydroperoxide, bis-hydroxymethyl hydroperoxide, and ethyl hydroperoxide, and interestingly found three unknown peroxides. The molar yields of the conventional peroxides fell within the range of values provided in the literature. The three unknown peroxides had a combined molar yield of ~30% at 5% relative humidity (RH), which was comparable with that of the conventional peroxides. Unlike H2O2 and HMHP, the molar yields of these three unknown peroxides were inversely related to the RH. On the basis of experimental kinetic and box model analysis, we tentatively assigned these unknown peroxides to C2–C4 HAHPs, which are produced by the reactions of different Criegee intermediates with water. Our study provides experimental evidence for the formation of large HAHPs in the ozonolysis of isoprene (one of the alkenes). These large HAHPs have a sufficiently long lifetime, estimated as tens of minutes, which allows them to become involved in atmospheric chemical processes, e.g. SOA formation and radical recycling. These standards are needed to accurately specify HAHPs, although their synthesis is a challenge.
Screening of brazilian plants for the presence of peroxides
Schenkel, Eloir Pedro;Rücker, Gerhard;Manns, Detlef;Falkenberg, Miriam B.;Matzenbacher, Nelson I.;Sobral, Marcos;Mentz, Lilian A.;Bordignon, Sérgio A.L.;Heinzmann, Berta M.;
Revista Brasileira de Ciências Farmacêuticas , 2002, DOI: 10.1590/S1516-93322002000200008
Abstract: chloroform or dichloromethane extracts of 357 southern brazilian plant species were tested for the presence of peroxides by thinlayer chromatography, using the spray reagent from huber & fr?hlke. from the species tested, 71 (20%) showed positive results and most of them (56%) are asteraceae species. the species tested were mainly from asteraceae, but 55 more families were screened, in a total of 77 genera surveyed.
UV Spectral Properties of Benzophenone. Influence of Solvents and Substituents  [PDF]
G. T. Castro,S. E. Blanco,O. S. Giordano
Molecules , 2000, DOI: 10.3390/50300424
Abstract: The effect of the solvent and the substituents on the UV spectroscopic properties of substituted benzophenones was studied.
The Effects of Substituents and Solvents on the Conformation of Benzophenones  [cached]
Athena Mantas,Sonia E. Blanco,Ferdinando H. Ferretti
Internet Electronic Journal of Molecular Design , 2004,
Abstract: Natural and synthetic benzophenones are compounds of great scientific and applied interest due to the varied biological and physicochemical properties that they posses. As part of a program aimed at investigating new physicochemical properties of substituted benzophenones, we carry out a study on the influence of the substituents and solvents upon the molecular conformations of these compounds. In the future, we expect to propose relationships between the molecular structural parameters with diverse experimental properties of the compounds that are currently being determined in our laboratory. The HF/6-31G(d) and B3LYP/6-31G(d) methods were used for calculations. Onsager's and Tomasi's models were used to analyze the solvent effects on the nine benzophenones studied. A conformational equilibrium was proposed between the two conformers of benzophenones with the greatest thermodynamic stability. The total energies, torsional angles, dipole moments, structural and reactivity molecular parameters, and conformational equilibrium constants were calculated in vacuum, ethanol, methanol and water. The calculated magnitudes were correlated with Hammett's substituent constants and parameters of solvating solvents. The benzophenones investigated have non-planar structures. Very good linear relationships between the molecular dihedral angles and Hammett's p-substituent constants were obtained. Electron-donating substituents increase the planarity of the substituted benzoyl group that involves phenyl ring A of the molecules, as well as the folding of phenyl ring B. The conformational equilibrium constants of o-hydroxy-benzophenones ranged approximately between 10-7-10-6. On the other hand, it was concluded that greater hydrogen-bond donor capability of a solvent increases the polarization of the compounds and consequently, increases their dipole moments. It was further concluded that the electron-donating groups increase the strength of the intramolecular hydrogen bond and that in the solvents used the o-hydroxy-benzophenones possess an important intramolecular hydrogen bond of the moderate class.
Carbon Monoxide Promotes Respiratory Hemoproteins Iron Reduction Using Peroxides as Electron Donors  [PDF]
Elena A. Sher, Mati Shaklai, Nurith Shaklai
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0033039
Abstract: The physiological role of the respiratory hemoproteins (RH), hemoglobin and myoglobin, is to deliver O2 via its binding to their ferrous (FeII) heme-iron. Under variety of pathological conditions RH proteins leak to blood plasma and oxidized to ferric (FeIII, met) forms becoming the source of oxidative vascular damage. However, recent studies have indicated that both metRH and peroxides induce Heme Oxygenase (HO) enzyme producing carbon monoxide (CO). The gas has an extremely high affinity for the ferrous heme-iron and is known to reduce ferric hemoproteins in the presence of suitable electron donors. We hypothesized that under in vivo plasma conditions, peroxides at low concentration can assist the reduction of metRH in presence of CO. The effect of CO on interaction of metRH with hydrophilic or hydrophobic peroxides was analyzed by following Soret and visible light absorption changes in reaction mixtures. It was found that under anaerobic conditions and low concentrations of RH and peroxides mimicking plasma conditions, peroxides served as electron donors and RH were reduced to their ferrous carboxy forms. The reaction rates were dependent on CO as well as peroxide concentrations. These results demonstrate that oxidative activity of acellular ferric RH and peroxides may be amended by CO turning on the reducing potential of peroxides and facilitating the formation of redox-inactive carboxyRH. Our data suggest the possible role of HO/CO in protection of vascular system from oxidative damage.
Development of a sensitive long path absorption photometer to quantify peroxides in aerosol particles (Peroxide-LOPAP)
P. Mertes, L. Pfaffenberger, J. Dommen, M. Kalberer,U. Baltensperger
Atmospheric Measurement Techniques (AMT) & Discussions (AMTD) , 2012,
Abstract: A new off-line instrument to quantify peroxides in aerosol particles using iodometry in long path absorption spectroscopy has been developed and is called peroxide long path absorption photometer (Peroxide-LOPAP). The new analytical setup features important technical innovations compared to hitherto published iodometric peroxide measurements. Firstly, the extraction, chemical conversion and measurement of the aerosol samples are performed in a closed oxygen-free (~ 1 ppb) environment. Secondly, a 50-cm optical detection cell is used for an increased photometric sensitivity. The limit of detection was 0.1 μM peroxide in solution or 0.25 nmol m 3 with respect to an aerosol sample volume of 1 m3. The test reaction was done at a constant elevated temperature of 40 °C and the reaction time was 60 min. Calibration experiments showed that the test reaction with all reactive peroxides, i.e. hydrogen peroxide (H2O2), peracids and peroxides with vicinal carbonyl groups (e.g. lauroyl peroxide) goes to completion and their sensitivity (slope of calibration curve) varies by only ±5%. However, very inert peroxides have a lower sensitivity. For example, tert-butyl hydroperoxide shows only 37% sensitivity compared to H2O2 after 1 h. A kinetic study revealed that even after 5 h only 85% of this inert compound had reacted. The time trends of the peroxide content in secondary organic aerosol (SOA) from the ozonolysis and photo-oxidation of α-pinene in smog chamber experiments were measured. The highest mass fraction of peroxides with 34% (assuming a molecular weight of 300 g mol 1) was found in freshly generated SOA from α-pinene ozonolysis. Mass fractions decreased with increasing NO levels in the photo-oxidation experiments. A decrease of the peroxide content was also observed with aging of the aerosol, indicating a decomposition of peroxides in the particles.
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