Magnetism in small bimetallic Mn-Co clusters

Effects of alloying on the electronic and magnetic properties of Mn$_{x}$Co$_{y}$ ($x+y$=$n$=2-5; $x$=0-$n$) and Mn$_2$Co$_{11}$ nanoalloy clusters are investigated using the density functional theory (DFT). Unlike the bulk alloy, the Co-rich clusters are found to be ferromagnetic and the magnetic moment increases with Mn-concentration, and is larger than the moment of pure Co$_n$ clusters of same size. For a particular sized cluster the magnetic moment increases by 2 $\mu_B$/Mn-substitution, which is found to be independent of the size and composition. All these results are in good agreement with recent Stern-Gerlach (SG) experiments [Phys. Rev. B {\bf 75}, 014401 (2007) and Phys. Rev. Lett. {\bf 98}, 113401 (2007)]. Likewise in bulk Mn$_x$Co$_{1-x}$ alloy, the local Co-moment decreases with increasing Mn-concentration.Comment: 11 pages, 15 figures. To appear in Physical Review

Graphene supported plasmonic photocatalyst for hydrogen evolution in photocatalytic water splitting

It is well known that the noble metal nanoparticles show active absorption in the visible region because of the existence of the unique feature known as surface plasmon resonance (SPR). Here we report the effect of plasmonic Au nanoparticles on the enhancement of the renewable hydrogen (H2) evolution through photocatalytic water splitting. The plasmonic Au/graphene/TiO2 photocatalyst was synthesized in two steps: first the graphene/TiO2 nanocomposites were developed by the hydrothermal decomposition process; then the Au was loaded by photodeposition. The plasmonic Au and the graphene as co-catalyst effectively prolong the recombination of the photogenerated charges. This plasmonic photocatalyst displayed enhanced photocatalytic H2 evolution for water splitting in the presence of methanol as a sacrificial reagent. The H2 evolution rate from the Au/graphene co-catalyst was about 9 times higher than that of a pure graphene catalyst. The optimal graphene content was found to be 1.0 wt %, giving a H2 evolution of 1.34 mmol (i.e., 26 μmolhˉ¹), which exceeded the value of 0.56 mmol (i.e., 112 μmolhˉ¹) observed in pure TiO2. This high photocatalytic H2 evolution activity results from the deposition of TiO2 on graphene sheets, which act as an electron acceptors to efficiently separate the photogenerated charge carriers. However, the Au loading enhanced the H2 evolution dramatically and achieved a maximum value of 12 mmol (i.e., 2.4 mmolhˉ¹) with optimal loading of 2.0 wt% Au on graphene/TiO2 composites. The enhancement of H2 evolution in the presence of Au results from the SPR effect induced by visible light irradiation, which boosts the energy intensity of the trapped electron as well as active sites for photocatalytic activity

On the hierarchical classification of G Protein-Coupled Receptors

Motivation: G protein-coupled receptors (GPCRs) play an important role in many physiological systems by transducing an extracellular signal into an intracellular response. Over 50% of all marketed drugs are targeted towards a GPCR. There is considerable interest in developing an algorithm that could effectively predict the function of a GPCR from its primary sequence. Such an algorithm is useful not only in identifying novel GPCR sequences but in characterizing the interrelationships between known GPCRs. Results: An alignment-free approach to GPCR classification has been developed using techniques drawn from data mining and proteochemometrics. A dataset of over 8000 sequences was constructed to train the algorithm. This represents one of the largest GPCR datasets currently available. A predictive algorithm was developed based upon the simplest reasonable numerical representation of the protein's physicochemical properties. A selective top-down approach was developed, which used a hierarchical classifier to assign sequences to subdivisions within the GPCR hierarchy. The predictive performance of the algorithm was assessed against several standard data mining classifiers and further validated against Support Vector Machine-based GPCR prediction servers. The selective top-down approach achieves significantly higher accuracy than standard data mining methods in almost all cases

Probing the role of the cation–π interaction in the binding sites of GPCRs using unnatural amino acids

We describe a general application of the nonsense suppression methodology for unnatural amino acid incorporation to probe drug–receptor interactions in functional G protein-coupled receptors (GPCRs), evaluating the binding sites of both the M2 muscarinic acetylcholine receptor and the D2 dopamine receptor. Receptors were expressed in Xenopus oocytes, and activation of a G protein-coupled, inward-rectifying K^+ channel (GIRK) provided, after optimization of conditions, a quantitative readout of receptor function. A number of aromatic amino acids thought to be near the agonist-binding site were evaluated. Incorporation of a series of fluorinated tryptophan derivatives at W6.48 of the D2 receptor establishes a cation–π interaction between the agonist dopamine and W6.48, suggesting a reorientation of W6.48 on agonist binding, consistent with proposed “rotamer switch” models. Interestingly, no comparable cation–π interaction was found at the aligning residue in the M2 receptor

The timing of cranial radiation in elderly patients with newly diagnosed glioblastoma multiforme

There are few and conflicting studies on the optimal timing of initial cranial radiation in the treatment of glioblastoma multiforme (GBM) but none of them have addressed this issue in the elderly population. We used the linked Surveillance, Epidemiology, and End Results (SEER) Medicare database to investigate whether the time interval from surgery to initiation of radiation is a significant prognostic factor for survival in subjects aged ≥65 years with newly diagnosed GBM. Cox modeling was used to assess the effect of waiting time on overall survival. We identified a total of 1,375 patients, 296 with biopsies and 1,079 with resections. The median time to the initiation of radiotherapy was 15 days post operation (interquartile range 12–21). In the univariate Cox analysis of those who had debulking surgeries, a waiting time of >22 days showed a significant inverse relationship with survival (hazard ratio [HR] = 0.82, 95% CI 0.70–0.97, p = 0.02), but after adjustment for confounders, it was not a statistically significant factor in the final Cox model (HR = 0.99, 95% CI 0.97–1.01, p = 0.14). Therefore, waiting time was not a significant prognostic factor for subjects with biopsies in both the univariate and multivariate analyses. Although effort should be made to initiate radiotherapy as soon as possible after surgical resection/biopsy, a brief delay similar to that experienced by our cohort does not have a significant impact on survival

Association of Regional Variation in Primary Care Physicians’ Colorectal Cancer Screening Recommendations with Individual Use of Colorectal Cancer Screening

Introduction: Studies show that the recommendations of a primary care physician for colorectal cancer screening may be one important influence on an individual's use of screening. However, another possible influence, the effect of regional differences in physicians' beliefs and recommendations on screening use, has not been assessed. Methods: We linked data from the National Health Interview Survey on the use of colorectal cancer screening by respondents aged 50 years or older, by hospital-referral region, with data from the Survey of Colorectal Cancer Screening Practices on the colorectal cancer screening recommendations of primary care physicians, by region. Our principal independent variables were the proportion of physicians in a region who recommended screening at age 50 and continuing screening at the recommended frequency. Results: On average, 53.3% of physicians in a region correctly recommended initiating colorectal cancer screening, and 64.8% advised screening at the recommended frequency. Of adults who lived in regions where less than 30% of physicians correctly recommended initiating screening, 47.3% had been screened, in contrast to 54.8% in areas where 70% or more of physicians made correct recommendations. Seventy-one percent of respondents living in regions where less than 30% of physicians advised screening at the recommended frequency were current on screening, in contrast to 79.9% of respondents living in regions where 70% or more of physicians made this recommendation. These differences were statistically significant after adjustment for individual characteristics. Conclusion: Strategies to improve colorectal cancer screening recommendations of primary care physicians may improve the use of screening for millions of Americans

Inhibiting transthyretin conformational changes that lead to amyloid fibril formation

Insoluble protein fibrils resulting from the self-assembly of a conformational intermediate are implicated as the causative agent in several severe human amyloid diseases, including Alzheimer's disease, familial amyloid polyneuropathy, and senile systemic amyloidosis. The latter two diseases are associated with transthyretin (TTR) amyloid fibrils, which appear to form in the acidic partial denaturing environment of the lysosome. Here we demonstrate that flufenamic acid (Flu) inhibits the conformational changes of TTR associated with amyloid fibril formation. The crystal structure of TTR complexed with Flu demonstrates that Flu mediates intersubunit hydrophobic interactions and intersubunit hydrogen bonds that stabilize the normal tetrameric fold of TTR. A small-molecule inhibitor that stabilizes the normal conformation of a protein is desirable as a possible approach to treat amyloid diseases. Molecules such as Flu also provide the means to rigorously test the amyloid hypothesis, i.e., the apparent causative role of amyloid fibrils in amyloid disease

Experimental and theoretical investigation of ligand effects on the synthesis of ZnO nanoparticles

ZnO nanoparticles with highly controllable particle sizes(less than 10 nm) were synthesized using organic capping ligands in Zn(Ac)2 ethanolic solution. The molecular structure of the ligands was found to have significant influence on the particle size. The multi-functional molecule tris(hydroxymethyl)-aminomethane (THMA) favoured smaller particle distributions compared with ligands possessing long hydrocarbon chains that are more frequently employed. The adsorption of capping ligands on ZnnOn crystal nuclei (where n = 4 or 18 molecular clusters of(0001) ZnO surfaces) was modelled by ab initio methods at the density functional theory (DFT) level. For the molecules examined, chemisorption proceeded via the formation of Zn...O, Zn...N, or Zn...S chemical bonds between the ligands and active Zn2+ sites on ZnO surfaces. The DFT results indicated that THMA binds more strongly to the ZnO surface than other ligands, suggesting that this molecule is very effective at stabilizing ZnO nanoparticle surfaces. This study, therefore, provides new insight into the correlation between the molecular structure of capping ligands and the morphology of metal oxide nanostructures formed in their presence