130,652 research outputs found
Synthetic phosphorus-substituted analcime, with ordered aluminum and silicon/phosphorus
No full textOrdering of Al and Si on :tetra:M!ttal
ùodes' .of framework struetures h:as' been studied
extensively, particulàrly in feldspars {Smith, 1974) and
zeolite molecular sieves (Breck, 1974; Rabo, 197.6;
rnany recent papets), Alternation of Al ::tl}d ~over
tètrabedral nedes was found. for the nfth.member of' ~
Ìl~W s,er'ie$qf AIPO~ molecular. sieves fSennett, Coheof
Flanigen, Pluth & ;8tì).jth, 1983). Wf; now return te the
problem of ordering of Al, p and Si in the
aluminosilicophosphate zeolites synthssized by
Flanigen & GTQS,e.(197.1). Xsray datawerecollestedin
19~5 oy r..», 8~r1e~ç. R. KIiQ;wLes1 t V" Smirh and L..
G. Dowell for an ,80 '!J.Il1 cube qfzeolit,eP-C depicted in
plate 1 ai Flanìgen & Grose (ì971) andsatisfaétory
refìnement was obtained for an average structnrè. of
analcime tYJl~ with spa,ce group fa'3d, Alrernation of (7P + 118i) and (23M + ~Si) over the tetrahedral sites
was considered, but the Xvray data were inadequate for
il, valid, test, We J;lOw, report .a structural refìnement ,ofa
trapezohedron of'zeoìité P-C (Flanigen &.. Grose, 1911)
in space group [413'2 whieh allows ordering between
(Si,P)and Al over adjacent tetrahedralnodes.
Refìnements of the erystal structnre of analcime
minerals were made: by Cilled & Ferraris. (1964)/
Rtiowles,RiQal,di &. Sm1th (19~5) and Perraris, Jones
& Yerkess (1972} Optical ànd X-rllY anornalies were
reported by Coornbs (i955), and Mazzi &. Galli (1-978),
showed that tetragonal and orthorhombic. varieties
resùlted from pàrtial Sì,AI order over. the tetrahedral
sites. Th~ idea], tòpologica] sYl1lmetry of. analcime is
nubic (la,3d), and a revìew of J(:hOwn phasés related. fa
analcime or leucite is given by Galli, Gottardi &:. Mazz]
(1978)
Biochemistry of mobile zinc and nitric oxide revealed by fluorescent sensors
No full textBiological mobile zinc and nitric oxide (NO) are two prominent examples of inorganic compounds involved in numerous signaling pathways in living systems. In the past decade, a synergy of regulation, signaling, and translocation of these two species has emerged in several areas of human physiology, providing additional incentive for developing adequate detection systems for Zn(II) ions and NO in biological specimens. Fluorescent probes for both of these bioinorganic analytes provide excellent tools for their detection, with high spatial and temporal resolution. We review the most widely used fluorescent sensors for biological zinc and nitric oxide, together with promising new developments and unmet needs of contemporary Zn(II) and NO biological imaging. The interplay between zinc and nitric oxide in the nervous, cardiovascular, and immune systems is highlighted to illustrate the contributions of selective fluorescent probes to the study of these two important bioinorganic analytes.National Science Foundation (Grant Number CHE-0907905)National Institutes of Health (U.S.) (Grant Number GM065519)National Institutes of Health (U.S.) (Grant Number K99GM092970
Reversible binding of nitric oxide to an Fe(iii) complex of a tetra-amido macrocycle
No full textNitric oxide binds reversibly to the Fe(III) complex of a well-developed tetra-amido macrocyclic ligand. Reaction with NO results in formation of a species consistent with an S = 1 {Fe–NO}[superscript 6] ground state as characterized by UV-vis, IR, EPR, and Mössbauer spectroscopy. The resultant nitrosyl is labile and dissociates readily upon purging with N[subscript 2], thus providing a rare example of reversible NO binding to non-heme iron.National Science Foundation (U.S.) (CHE-061194)National Institutes of Health (U.S.) (K99GM092970
Mechanism of Nitric Oxide Reactivity and Fluorescence Enhancement of the NO-Specific Probe CuFL1
No full textThe mechanism of the reaction of CuFL1 (FL1 = 2-{2-chloro-6-hydroxy-5-[(2-methylquinolin-8-ylamino)methyl]-3-oxo-3H-xanthen-9-yl}benzoic acid) with nitric oxide (NO) to form the N-nitrosated product FL1-NO in buffered aqueous solutions was investigated. The reaction is first-order in [CuFL1], [NO], and [OH−]. The observed rate saturation at high base concentrations is consistent with a mechanism in which the protonation state of the secondary amine of the ligand is important for reactivity. This information provides a rationale for designing faster-reacting probes by lowering the pKa of the secondary amine. Activation parameters for the reaction of CuFL1 with NO indicate an associative mechanism (ΔS‡ = −120 ± 10 J/mol·K) with a modest thermal barrier (ΔH = 41 ± 2 kJ/mol; Ea = 43 ± 2 kJ/mol). Variable-pH electron paramagnetic resonance experiments reveal that, as the secondary amine of CuFL1 is deprotonated, electron density shifts to yield a new spin-active species having electron density localized on the deprotonated amine nitrogen atom. This result suggests that FL1-NO formation occurs when NO attacks the deprotonated secondary amine of the coordinated ligand, followed by inner-sphere electron transfer to Cu(II) to form Cu(I) and release of FL1-NO from the metal.National Science Foundation (U.S.) (grant CHE-0907905)National Institutes of Health (U.S.) (Postdoctoral Fellowship (5 F32 GM085930))National Institutes of Health (U.S.) (Postdoctoral Fellowship (1 K99 GM092970
Cell-Trappable Fluorescent Probes for Nitric Oxide Visualization in Living Cells
No full textTwo new cell-trappable fluorescent probes for nitric oxide (NO) are reported based on either incorporation of hydrolyzable esters or conjugation to aminodextran polymers. Both probes are highly selective for NO over other reactive oxygen and nitrogen species (RONS). The efficacy of these probes for the fluorescence imaging of nitric oxide produced endogenously in Raw 264.7 cells is demonstrated.National Science Foundation (U.S.) (grant CHE-0907905)National Institutes of Health (U.S.) (Postdoctoral Fellowship (5 F32 GM085930)
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Hydrogen peroxide differentially modulates cardiac myocyte nitric oxide synthesis
No full textNitric oxide (NO) and hydrogen peroxide (H(subscript 2)O(subscript 2)) are synthesized within cardiac myocytes and play key roles in modulating cardiovascular signaling. Cardiac myocytes contain both the endothelial (eNOS) and neuronal (nNOS) NO synthases, but the differential roles of these NOS isoforms and the interplay of reactive oxygen species and reactive nitrogen species in cardiac signaling pathways are poorly understood. Using a recently developed NO chemical sensor [Cu(subscript 2)(FL2E)] to study adult cardiac myocytes from wild-type, eNOSnull, and nNOSnull mice, we discovered that physiological concentrations of H(subscript 2)O(subscript 2) activate eNOS but not nNOS. H(subscript 2)O(subscript 2)-stimulated eNOS activation depends on phosphorylation of both the AMP-activated protein kinase and kinase Akt, and leads to the robust phosphorylation of eNOS. Cardiac myocytes isolated from mice infected with lentivirus expressing the recently developed H(subscript 2)O(subscript 2) biosensor HyPer2 show marked H2O2 synthesis when stimulated by angiotensin II, but not following β-adrenergic receptor activation. We discovered that the angiotensin-II-promoted increase in cardiac myocyte contractility is dependent on H2O2, whereas β-adrenergic contractile responses occur independently of H(subscript 2)O(subscript 2) signaling. These studies establish differential roles for H(subscript 2)O(subscript 2) in control of cardiac contractility and receptor-dependent NOS activation in the heart, and they identify new points for modulation of NO signaling responses by oxidant stress.National Institutes of Health (U.S.) (grant GM36259)National Institutes of Health (U.S.) (grant HL46457)National Institutes of Health (U.S.) (grant HL48743)National Institutes of Health (U.S.) (grant K99GM092970)National Science Foundation (U.S.) (grant CHE-0907905
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
X-ray structure refinement of mesolite, Na2Ca2Al6Si9O80×8H2O
No full textNa2Ca~AI6Si90Jo.8Hp. M; = 1164•9, orthorhombic.
Fdd2, Cl =. 18•4049 (8), b = 56•655 (6), c
r-; 6•5443 (4)A, V=6823•94A3, Z=8, D.=
2•27 g cm-l, .{(Mo Ku) = O• 7093 A, f-l = 9•4 cm-I,
spherical cr yst al, T = 294 K. F(OOO) = 4688, R (P)
= 0•032, 5267 reflcctions, The mesolite structure has
complete Si/AI ordcr alle! the same frarnework topology
as natrolite and scolccite. The Na atom coordinatcs
four O atoms and two water O atoms in a distorted
trigonal prisrn (Na-O 2.40-2•74, Na-OW 2•34A)
and the Ca atorn coordinatcs Iour frarnework O atoms
and thrce water O atoms in a distorted pentagonal
bipyrarnid (Ca-O 2•S(}-2•54, Ca-OW 2•31-2-36 A).
H atorns werc located for each of the four independent
warcr rnolccules. Thc hydrogen-bonding systcm is
gener ally similar to the arrangernents found in natrolite
and scolcciie. Thc local gcornetry of the water
molcculcs adapis to thc frarncwork distortions
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
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