Proton endor study of the photoexcited triplet state PT in Rps. sphaeroides R-26 photosynthetic reaction centres

The photoexcited triplet state PT of Rhodopseudomonas sphaeroides R-26 has been investigated by ENDOR measurements performed on frozen photosynthetic reaction centre solutions. For the first time hyperfine data could be obtained for PT. These data indicate a delocalisation of the triplet state over two bacteriochlorophyll a molecules

Stimulation of Adenosine A 3 Receptors in Cerebral Ischemia: Neuronal Death, Recovery, or Both?

The role of the adenosine A 3 receptor continues to baffle, and, despite an increasing number of studies, the currently available data add to, rather than alleviate, the existing confusion. The reported effects of adenosine A 3 receptor stimulation appear to depend on the pattern of drug administration (acute vs. chronic), dose, and type of the target tissue. Thus, while acute exposure to A 3 receptor agonists protects against myocardial ischemia, it is severely damaging when these agents are given shortly prior to cerebral ischemia. Mast cells degranulate when their A 3 receptors are stimulated. Degranulation of neutrophils is, on the other hand, impaired. While reduced production of reactive nitrogen species has been reported following activation of A 3 receptors in collagen-induced arthritis, the process appears to be enhanced in cerebral ischemia. Indeed, immunocytochemical studies indicate that both pre- and postischemic treatment with A 3 receptor antagonist dramatically reduces nitric oxide synthase in the affected hippocampus. Even more surprisingly, low doses of A 3 receptor agonists seem to enhance astrocyte proliferation, while high doses induce their apoptosis. This review concentrates on the studies of cerebral A 3 receptors and, based on the available evidence, discusses the possibility of adenosine A 3 receptor serving as an integral element of the endogenous cerebral neuroprotective complex consisting of adenosine and its receptors.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75391/1/j.1749-6632.1999.tb07984.x.pd

Association of Insurance Expansion With Surgical Management of Thyroid Cancer

Importance: To our knowledge, thyroid cancer incidence is increasing faster than any other cancer type and is currently the fifth most common cancer among women. While this rise is likely multifactorial, there has been scarce consideration of the effect of insurance statuses on the treatment of thyroid cancer. Objective: We evaluate the association of insurance expansion with thyroid cancer treatment using the 2006 Massachusetts health reform, which serves as a unique natural experiment. Design, Setting, and Participants: We used the Agency for Healthcare Research and Quality State Inpatient Databases to identify patients with government-subsidized or self-pay insurance or private insurance who were admitted to a hospital with thyroid cancer and underwent a thyroidectomy between 2001 and 2011 in Massachusetts (n = 8534) and 3 control states (n = 48 047). Difference-in-differences models were used to evaluate an association between the 2006 Massachusetts health care reform and thyroid cancer treatment, and participants were controlled for age, sex, comorbidities, and secular trends. Main Outcomes and Measures: Change in the thyroidectomy rate for thyroid cancer treatment was the primary outcome evaluated. Results: The Massachusetts cohort consisted of 6443 women (75.5%) and 2091 men (24.5%), of whom 6388 (79.6%) were white, 391 (4.9%) were black, 527 (6.6%) were Hispanic, 424 (5.3%) were Asian/Pacific Islander, 63 (0.8%) were Native American, and 228 (2.8%) were other. The participants from control states included 36 818 women (76.6%) and 11 229 men (23.4%), of whom 30 432 (65.5%) were white, 3818 (8.2%) were black, 6462 (13.9%) were Hispanic, 2591 (5.6%) were Asian/Pacific Islander, 211 (0.5%) were Native American, and 2947 (6.3%) were other. Before the 2006 Massachusetts insurance expansion, patients with government-subsidized or self-pay insurance had lower thyroidectomy rates for thyroid cancer in Massachusetts and the control states compared with patients with private insurance. The Massachusetts insurance expansion was associated with a 26% increased rate of undergoing a thyroidectomy (incident rate ratio, 1.26; 95% CI, 1.04-1.52; P = .02) and a 22% increased rate of neck dissection (incident rate ratio, 1.22; 95% CI, 1.07-1.37; P = .002) for treating cancer compared with control states. Conclusions and Relevance: The 2006 Massachusetts health reform, which is a model for the Affordable Care Act, was associated with a 26% increased rate of thyroidectomy for treating thyroid cancer. Our study suggests that insurance expansion may be associated with increased access to the surgical management of thyroid cancer. Further studies need to be conducted to evaluate the effect of healthcare expansion at a national level

Structured near-infrared Magnetic Circular Dichroism spectra of the Mn₄CaO₅ cluster of PSII in T. vulcanus are dominated by Mn(IV) d-d 'spin-flip' transitions

Photosystem II passes through four metastable S-states in catalysing light-driven water oxidation. Variable temperature variable field (VTVH) Magnetic Circular Dichroism (MCD) spectra in PSII of Thermosynochococcus (T.) vulcanus for each S-state are reported. These spectra, along with assignments, provide a new window into the electronic and magnetic structure of Mn₄CaO₅. VTVH MCD spectra taken in the S₂state provide a clear g=2, S=1/2 paramagnetic characteristic, which is entirely consistent with that known by EPR. The three features, seen as positive (+) at 749nm, negative (-) at 773nm and (+) at 808nm are assigned as ⁴A→²E spin-flips within the d³ configuration of the Mn(IV) centres present. This assignment is supported by comparison(s) to spin-flips seen in a range of Mn(IV) materials. S₃ exhibits a more intense (-) MCD peak at 764nm and has a stronger MCD saturation characteristic. This S₃ MCD saturation behaviour can be accurately modelled using parameters taken directly from analyses of EPR spectra. We see no evidence for Mn(III) d-d absorption in the near-IR of any S-state. We suggest that Mn(IV)-based absorption may be responsible for the well-known near-IR induced changes induced in S₂ EPR spectra of T. vulcanus and not Mn(III)-based, as has been commonly assumed. Through an analysis of the nephelauxetic effect, the excitation energy of S-state dependent spin-flips seen may help identify coordination characteristics and changes at each Mn(IV). A prospectus as to what more detailed S-state dependent MCD studies promise to achieve is outlined.We recognise the support of the Australian Research Council through grants DP110104565 and DP150103137 (E.K.), FT140100834 (N.C) and MEXT/JSPS of Japan through a Grant-in-Aid for Specially Promoted Research No. 24000018 (J.R.S.)

Coal fly ash: Linking immersion freezing behavior and physicochemical particle properties

To date, only a few studies have investigated the potential of coal fly ash particles to trigger heterogeneous ice nucleation in cloud droplets. The presented measurements aim at expanding the sparse dataset and improving process understanding of how physicochemical particle properties can influence the freezing behavior of coal fly ash particles immersed in water. Firstly, immersion freezing measurements were performed with two single particle techniques, i.e., the Leipzig Aerosol Cloud Interaction Simulator (LACIS) and the SPectrometer for Ice Nuclei (SPIN). The effect of suspension time on the efficiency of the coal fly ash particles when immersed in a cloud droplet is analyzed based on the different residence times of the two instruments and employing both dry and wet particle generation. Secondly, two cold-stage setups, one using microliter sized droplets (Leipzig Ice Nucleation Array) and one using nanoliter sized droplets (WeIzmann Supercooled Droplets Observation on Microarray setup) were applied. We found that coal fly ash particles are comparable to mineral dust in their immersion freezing behavior when being dry generated. However, a significant decrease in immersion freezing efficiency was observed during experiments with wet-generated particles in LACIS and SPIN. The efficiency of wet-generated particles is in agreement with the cold-stage measurements. In order to understand the reason behind the deactivation, a series of chemical composition, morphology, and crystallography analyses (single particle mass spectrometry, scanning electron microscopy coupled with energy dispersive X-ray microanalysis, X-ray diffraction analysis) were performed with dry- and wet-generated particles. From these investigations, we conclude that anhydrous CaSO4 and CaO - which, if investigated in pure form, show the same qualitative immersion freezing behavior as observed for dry-generated coal fly ash particles - contribute to triggering heterogeneous ice nucleation at the particle-water interface. The observed deactivation in contact with water is related to changes in the particle surface properties which are potentially caused by hydration of CaSO4 and CaO. The contribution of coal fly ash to the ambient population of ice-nucleating particles therefore depends on whether and for how long particles are immersed in cloud droplets

Thermally Activated Delayed Fluorescence in a Y3N@C80 Endohedral Fullerene: Time-Resolved Luminescence and EPR Studies

The endohedral fullerene Y3N@C80 exhibits luminescence with reasonable quantum yield and extraordinary long lifetime. By variable-temperature steady-state and time-resolved luminescence spectroscopy, it is demonstrated that above 60 K the Y3N@C80 exhibits thermally activated delayed fluorescence with maximum emission at 120 K and a negligible prompt fluorescence. Below 60 K, a phosphorescence with a lifetime of 192±1 ms is observed. Spin distribution and dynamics in the triplet excited state is investigated with X- and W-band EPR and ENDOR spectroscopies and DFT computations. Finally, electroluminescence of the Y3N@C80/PFO film is demonstrated opening the possibility for red-emitting fullerene-based organic light-emitting diodes (OLEDs)

Direct observation of structurally encoded metal discrimination and ether bond formation in a heterodinuclear metalloprotein

Although metallocofactors are ubiquitous in enzyme catalysis, how metal binding specificity arises remains poorly understood, especially in the case of metals with similar primary ligand preferences such as manganese and iron. The biochemical selection of manganese over iron presents a particularly intricate problem because manganese is generally present in cells at a lower concentration than iron, while also having a lower predicted complex stability according to the Irving–Williams series (MnII ZnII). Here we show that a heterodinuclear Mn/Fe cofactor with the same primary protein ligands in both metal sites self-assembles from MnII and FeII in vitro, thus diverging from the Irving–Williams series without requiring auxiliary factors such as metallochaperones. Crystallographic, spectroscopic, and computational data demonstrate that one of the two metal sites preferentially binds FeII over MnII as expected, whereas the other site is nonspecific, binding equal amounts of both metals in the absence of oxygen. Oxygen exposure results in further accumulation of the Mn/Fe cofactor, indicating that cofactor assembly is at least a two-step process governed by both the intrinsic metal specificity of the protein scaffold and additional effects exerted during oxygen binding or activation. We further show that the mixed-metal cofactor catalyzes a two-electron oxidation of the protein scaffold, yielding a tyrosine–valine ether cross-link. Theoretical modeling of the reaction by density functional theory suggests a multistep mechanism including a valyl radical intermediate

School census autumn 2017 : 16 to 19 reports : user guide

The synthesis of a series of cobalt NHC complexes of the types [Co­(NHC)₂(CO)­(NO)] (NHC = <i>i</i>Pr₂Im (<b>2</b>), <i>n</i>Pr₂Im (<b>3</b>), Cy₂Im (<b>4</b>), Me₂Im (<b>5</b>), <i>i</i>Pr₂ImMe (<b>6</b>), Me₂ImMe (<b>7</b>), Me<i>i</i>PrIm (<b>8</b>), Me<i>t</i>BuIm (<b>9</b>); R₂Im = 1,3-dialkylimidazolin-2-ylidene) and [Co­(NHC)­(CO)₂(NO)] (NHC = <i>i</i>Pr₂Im (<b>13</b>), <i>n</i>Pr₂Im (<b>14</b>), Me₂Im (<b>15</b>), <i>i</i>Pr₂ImMe (<b>16</b>), Me₂ImMe (<b>17</b>), Me<i>i</i>PrIm (<b>18</b>), Me<i>t</i>BuIm (<b>19</b>)) from the reaction of the NHC with [Co­(CO)₃(NO)] (<b>1</b>) is reported. These complexes have been characterized using elemental analysis, IR spectroscopy, multinuclear NMR spectroscopy, and in many cases by X-ray crystallography. Bulky NHCs tend to form the mono-NHC-substituted complexes [Co­(NHC)­(CO)₂(NO)], even from the reaction with an stoichiometric excess of the NHC, as demonstrated by the synthesis of [Co­(Dipp₂Im)­(CO)₂(NO)] (<b>11</b>), [Co­(Mes₂Im)­(CO)₂(NO)] (<b>12</b>), and [Co­(^MecAAC)­(CO)₂(NO)] (<b>20</b>). For <i>t</i>Bu₂Im a preferred coordination via the NHC backbone (“abnormal” coordination at the 4-position) was observed and the complex [Co­(<i>t</i>Bu₂^aIm)­(CO)₂(NO)] (<b>10</b>) was isolated. All of these complexes are volatile, are stable upon sublimation and prolonged storage in the gas phase, and readily decompose at higher temperatures. Furthermore, DTA/TG analyses revealed that the complexes [Co­(NHC)₂(CO)­(NO)] are seemingly more stable toward thermal decomposition in comparison to the complexes [Co­(NHC)­(CO)₂(NO)]. We thus conclude that the cobalt complexes of the type [Co­(NHC)­(CO)₂(NO)] and [Co­(NHC)₂(CO)­(NO)] have potential for application as precursors in the vapor deposition of thin cobalt films

Synthesis and properties of conjugates between silver nanoparticles and DNA-PNA hybrids

We describe the preparation and properties of a stable conjugate between two 15 nm silver nanoparticles (AgNPs) and a DNA-PNA hybrid composed of 10 guanine-cytosine base pairs. We show that the conjugate is spontaneously formed during incubation of a DNA-PNA hybrid, containing phosphorothioate residues at both ends of the DNA strand with AgNPs. The conjugate molecules were separated from individual AgNPs and multiparticle structures by gel electrophoresis. We demonstrate that the absorption spectrum of the conjugate is broader than that of AgNPs, due to the interparticle plasmon coupling

Paramagnetic Molecular Grippers: The Elements of Six-State Redox Switches

The development of semiquinone-based resorcin[4]arene cavitands expands the toolbox of switchable molecular grippers by introducing the first paramagnetic representatives. The semiquinone (SQ) states were generated electrochemically, chemically, and photochemically. We analyzed their electronic, conformational, and binding properties by cyclic voltammetry, ultraviolet/visible (UV/vis) spectroelectrochemistry, electron paramagnetic resonance (EPR) and transient absorption spectroscopy, in conjunction with density functional theory (DFT) calculations. The utility of UV/vis spectroelectrochemistry and EPR spectroscopy in evaluating the conformational features of resorcin[4]arene cavitands is demonstrated. Guest binding properties were found to be enhanced in the SQ state as compared to the quinone (Q) or the hydroquinone (HQ) states of the cavitands. Thus, these paramagnetic SQ intermediates open the way to six-state redox switches provided by two conformations (open and closed) in three redox states (Q, SQ, and HQ) possessing distinct binding ability. The switchable magnetic properties of these molecular grippers and their responsiveness to electrical stimuli has the potential for development of efficient molecular devices