diatomics-in-molecules Dotaz Zobrazit nápovědu
Density functional theory (DFT) studies on adsorption of several gaseous homo- and hetero-diatomic molecules (AB) including H2, O2, N2, NO and CO on external surface of H-capped pristine armchair (5, 5) single-walled carbon nanotube (SWCNT) were conducted. Structures of C70H10 and the corresponding C70H10-AB adducts were fully optimized at the B3LYP/6-311G* level of theory. Calculated HOMO/LUMO energy gaps (Eg), (13)C NMR chemical shifts and IR/Raman parameters were analyzed and critically compared with available experimental data. Significant changes of carbon NMR atom chemical shifts (up to -100 ppm) and shielding anisotropies (up to -180 ppm) at sites of addition were observed. Functionalized SWCNTs produced IR and Raman spectra different from the pristine nanotube model. The selective changes in vibrational spectra will help in assigning the topology of functionalization at the nanotube wall.
- MeSH
- elektrony MeSH
- kvantová teorie * MeSH
- magnetická rezonanční spektroskopie MeSH
- molekulární konformace MeSH
- molekulární modely * MeSH
- nanotrubičky uhlíkové chemie MeSH
- Ramanova spektroskopie * MeSH
- spektroskopie infračervená s Fourierovou transformací MeSH
- termodynamika MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Phthalocyanines (Pcs) are promising photosensitizers for use in various branches of science and industry. In the presence of visible light and diatomic oxygen, phthalocyanines can react to produce singlet oxygen, a member of reactive oxygen species able to damage different molecules and tissues. The aim of this study was to investigate the ability of phthalocyanines to degrade natural toxins in the presence of visible light. As the representative of hardly degradable toxins, a group of cyanobacterial peptide toxins--microcystin-LR--was chosen for this study. According to our results, phthalocyanines are able to degrade 61.5% of microcystins within a 48-hour incubation (38% of microcystins was degraded after 24 h and 24% after 12 h of incubation). Although other oxidants like hydrogen peroxide or ozone are able to degrade microcystins within several hours, we assume that by optimizing the spectrum emitted by light source and by changing the absorption characteristics of Pcs, microcystins degradation by phthalocyanines could be more effective in the near future.
Oxid dusnatý je dvouatomová, plynná molekula s jedním nepárovým valenčním elektronem. Fyzikální vlastnosti, jako je rozpustnost, difuzibilita a biologický poločas, spolurozhodují o chemické reaktivitě oxidu dusnatého. Oxid dusnatý je nestabilní volný radikál, signální molekula v cévách, imunitním systému i v centrální nervové soustavě. Reaktivita oxidu dusnatého za fyziologických a patologických podmínek je závislá na jeho koncentraci a na místě vzniku. Oxid dusnatý hraje důležitou roli u různých patologických stavů, jako je septický šok, kardiovaskulární onemocnění, artritida, diabetes mellitus, roztroušená skleróza, astma a hypertenze. Syntázy oxidu dusnatého jsou hemoflavoproteiny odpovědné za syntézu oxidu dusnatého z L-argininu prostřednictvím dvou následných monooxygenázových reakcí. N-terminálová, hemova doména syntáz oxidu dusnatého je funkčně podobná cytochromu P450, ale nebyla potvrzena strukturální shoda mezi cytochromem P450 a N-terminálovými doménami syntáz oxidu dusnatého. Prostetické skupiny flavinadenindinukleotid a flavinmononukleotid C-terminálové, reduktázové domény syntáz oxidu dusnatého vykazují velkou podobnost sekvencí aminokyselin s NADPH cytochrom P450 reduktázou. Prostřednictvím reduktázové domény probíhá přenos elektronů z NADPH pro katalytické reakce syntázy oxidu dusnatého. Přítomnost kalmodulinové vazebné domény, která spojuje hemovou a reduktázovou doménu, je závazná pro tvorbu oxidu dusnatého u všech izoforem syntáz oxidu dusnatého. Syntázy oxidu dusnatého jsou také nepřímo regulovány různými signálními dráhami, které jsou zprostředkovány kinázami v důsledku přítomnosti fosforylačních míst v reduktázové doméně. Studium mechanizmů působení syntáz oxidu dusnatého se stalo jedním z nejsledovanějších z hlediska základních biochemických mechanizmů, fyziologických procesů a aplikací v medicíně, na mnoho otázek však zatím neznáme odpověď.
Nitric oxide is a diatomic gaseous molecule with unpaired electron in the molecule. Physical properties such as solubility, diffusibility and half-life decide the chemical reactivity of nitric oxide. Nitric oxide is the unstable free radical in vessels, immune system and central nervous system. The reactivity of nitric oxide under physiological and pathological conditions depends upon its concentration and site of production. Nitric oxide is thought to play a role in many pathological situations: septic shock, cardiovascular diseases, arthritis, diabetes, multiple sclerosis, asthma, and hypertension. Nitric oxide synthase is a self-sufficient flavohemoprotein capable of producing nitric oxide from L-arginine by two successive monooxygenation steps. Although the N-terminal heme domain functionally resembles cytochromes P450, no structural similarities exist between cytochrome P450 and nitric oxide synthases heme domains. The C-terminal domain of nitric oxide synthases containing flavin adenine dinucleotide and flavin mononucleotide as cofactors exhibits a high degree of sequence similarity with NADPH-cytocrome P450 reductase. The reductase domains serve as an intermediary for the transfer of electrons from NADPH for the catalytic reaction. The connecting domain between the oxygenase and the reductase domains of nitric oxide synthase isoforms binds calmodulin in the presence of calcium. The binding of calmodulin to all nitric oxide synthase isoforms is obligatory for the production of nitric oxide. At the same time, the presence of one or more phosphorylation sites in nitric oxide synthase puts them among the kinase-mediated signaling pathways. This also means that nitric oxide synthases are regulated indirectly by the events that regulate kinases. This field of research of nitric oxide synthase regulation has become one of the most actively pursued and much has been learned from basic biochemical mechanisms to physiological processes and to medical applications, but many more questions still remain to be answered.
Strong excitonic interactions are a key design strategy in photosynthetic light harvesting, expanding the spectral cross-section for light absorption and creating considerably faster and more robust excitation energy transfer. These molecular excitons are a direct result of exceptionally densely packed pigments in photosynthetic proteins. The main light-harvesting complexes of diatoms, known as fucoxanthin-chlorophyll proteins (FCPs), are an exception, displaying surprisingly weak excitonic coupling between their chlorophyll (Chl) a's, despite a high pigment density. Here, we show, using single-molecule spectroscopy, that the FCP complexes of Cyclotella meneghiniana switch frequently into stable, strongly emissive states shifted 4-10 nm toward the red. A few percent of isolated FCPa complexes and ∼20% of isolated FCPb complexes, on average, were observed to populate these previously unobserved states, percentages that agree with the steady-state fluorescence spectra of FCP ensembles. Thus, the complexes use their enhanced sensitivity to static disorder to increase their light-harvesting capability in a number of ways. A disordered exciton model based on the structure of the main plant light-harvesting complex explains the red-shifted emission by strong localization of the excitation energy on a single Chl a pigment in the terminal emitter domain due to very specific pigment orientations. We suggest that the specific construction of FCP gives the complex a unique strategy to ensure that its light-harvesting function remains robust in the fluctuating protein environment despite limited excitonic interactions.
