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Central Ring (central + ring)
Selected AbstractsDifferentiation of isomeric flavone/isoflavone aglycones by MS2 ion trap mass spectrometry and a double neutral loss of CORAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 17 2003Fabian Kuhn The fragmentation behaviour of seven pairs of isomeric flavone/isoflavone aglycones (solely hydroxylated and/or methoxylated) was studied using ion trap mass spectrometry with atmospheric pressure ionisation (API, both electrospray and APCI) in the positive and negative ion modes. A major difference was found in the neutral loss of 56,u, which was a common feature of all isoflavones in API(+). It was identified as a double loss of CO by accurate mass tandem mass spectrometric (MS/MS) measurements using a hybrid quadrupole time-of-flight (Q-TOF) instrument. Fragmentation of daidzein with 13C-isotope labelling of the carbon C2 showed that this double loss occurred from the central ring of the molecule. A mechanism for this selective fragmentation is given. Further isoflavone-specific fragmentations were used to develop a guideline for the identification of isoflavone structures. A software-based neutral loss scan of 56,u in the API(+)-MS2 mode was applied to extracts of leaves of Lupinusalbus and to soy flour. The structure elucidation guideline allowed identification of hydroxy and/or methoxy isoflavones. Structures could be confirmed for those available as reference compounds. Copyright © 2003 John Wiley & Sons, Ltd. [source] Fine structure of Eimer's organ in the coast mole (Scapanus orarius)THE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 5 2007Paul D. Marasco Abstract Eimer's organ is a small, densely innervated sensory structure found on the glabrous rhinarium of most talpid moles. This structure consists of an epidermal papilla containing a central circular column of cells associated with intraepidermal free nerve endings, Merkel cell neurite complexes, and lamellated corpuscles. The free nerve endings within the central cell column form a ring invested in the margins of the column, surrounding 1,2 fibers that pass through the center of the column. A group of small-diameter nociceptive free nerve endings that are immunoreactive for substance P surrounds this central ring of larger-diameter free nerve endings. Transmission electron microscopy revealed a high concentration of tonofibrils in the epidermal cells of the central column, suggesting they are more rigid than the surrounding keratinocytes and may play a mechanical role in transducing stimuli to the different receptor terminals. The intraepidermal free nerve endings within the central column begin to degrade 15 ,m from the base of the stratum corneum and do not appear to be active within the keratinized outer layer. The peripheral free nerve endings are structurally distinct from their counterparts in the central column and immunocytochemical double labeling with myelin basic protein and substance P indicates these afferents are unmyelinated. Merkel cell-neurite complexes and lamellated corpuscles are similar in morphology to those found in a range of other mammalian skin. Anat Rec, 2007. © 2007 Wiley-Liss, Inc. [source] Function of macular area in retinopathy of prematurityACTA OPHTHALMOLOGICA, Issue 2007AM SHAMSHINOVA Purpose: To assess the bioelectric activity of the retina at different stages of the retinopathy of prematurity (RP). Methods: 21 children with RoP (stage 1-4, 6-14 years old, born at 27-32 week of gestation with the birth weight of 730-1800g) were examined. In 4 of children the prophylactic laser coagulation of avascular retina was performed in the active phase. Visual acuity (VA) at the stage 1 of RoP amounted to 0,75; at the stage 2: 0,5; at the stage 3: 0,25 and at the stage 4: 0,02. Macular (MBN Moscow) and mf ERG( Roland Concult Germany) were examined. Results: There was no correlation between VA values and parameters of multifocal (mf) and macular (m) ERG. Patients with RP of stage1 showed a moderate reduction of b-wave magnitude of mERG at its normal latency. This correlated with mfERG data in central hexagons 15 degrees. The magnitude and latency of mERG were changed to a great extent in RP patients of stages 2-3. The waves N1 and P1 of mERG were also heavily decreased at normal latency. The patients with severe retinal abnormalities, like retinal detachment, have subnormal mERG-values with prolonged latency, and moderate decrease of retinal density in the central ring and considerable changes with eccentricity in mfERG. Conclusions: RP patients 1-4 stages showed considerable impairment of macular function independent of the ophthalmoscopic changes. Even occult or weak-manifested of the diseases in the macula might be accompanied with the moderate decrease of macular bioelectric activity, including the abrupt abnormalities of the electrogenesis and neuronal interactions in the macular area. Decline VA d'not always had relation with RP. The pathophysiologic rationale of the latter needs to be elucidated in the future studies. [source] Formation of Trichlorinated Dibenzo- p -dioxins from 2,4-Dichlorophenol and 2,4,5-Trichlorophenolate: A Theoretical StudyCHEMPHYSCHEM, Issue 11 2006Ernesto Suárez Abstract The reaction of the 2,4,5-trichlorophenolate anion with 2,4-dichlorophenol to afford trichlorinated dibenzo- p -dioxins (T3CDDs) is investigated at the B3LYP/6-31+G(d) and B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d)+ZPVE(B3LYP/6-31+G(d)) levels of theory. The first stage of the process corresponds to the formation of a predioxin, which can evolve through four different routes. Two of them lead directly to the products 2,3,7-T3CDD and 1,3,8-T3CDD, and the other two afford different predioxin-type intermediates, which in turn can evolve through all or some of the four routes to give new predioxins or T3CDD. Consequently, the theoretical results obtained show plainly the complex chemistry implied in the formation of dioxins from chlorophenols via anionic mechanisms by disclosing all the critical structures through which the system evolves, thus allowing assessment of the viability of the different mechanistic routes and the accessible products. The statistical thermodynamics treatment at 1 atm and 298.15, 600, 900, and 1200 K indicates that at higher temperatures, the Gibbs energy barrier for the formation of the initial predioxin is clearly the rate-determining step for the whole process, but at lower temperatures the Gibbs energy barrier for this step is similar to those for its evolution into 2,3,7-T3CDD. This result is in contrast with previous proposals that the closure of the central ring is the rate-limiting step. Finally, according to our results the rate constant for the formation of polychlorinated dibenzo- p -dioxins increases with the temperature, in agreement with the experimental observation that the conversion of trichlorophenols increases when going from 600 to 900 K in the gas phase in the absence of catalysts, and with DFT molecular dynamics results. [source] (1,3-Dimethylimidazolidine-2-selone-,Se)bis(1,10-phenanthroline-,2N,N,)copper(II) bis(perchlorate) and bis(2,2,-bipyridyl-,2N,N,)(imidazolidine-2-thione-,S)copper(II) bis(perchlorate)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2007Alexander J. Blake In the first title salt, [Cu(C12H8N2)2(C5H10N2Se)](ClO4)2, the CuII centre occupies a distorted trigonal,bipyramidal environment defined by four N donors from two 1,10-phenanthroline (phen) ligands and by the Se donor of a 1,3-dimethylimidazolidine-2-selone ligand, with the equatorial plane defined by the Se and by two N donors from different phen ligands and the axial sites occupied by the two remaining N donors, one from each phen ligand. The Cu,N distances span the range 1.980,(10),2.114,(11),Ĺ and the Cu,Se distance is 2.491,(3),Ĺ. Intermolecular ,,, contacts between imidazolidine rings and the central rings of phen ligands generate chains of cations. In the second salt, [Cu(C10H8N2)2(C3H6N2S)](ClO4)2, the CuII centre occupies a similar distorted trigonal,bipyramidal environment comprising four N donors from two 2,2,-bipyridyl (bipy) ligands and an S donor from an imidazolidine-2-thione ligand. The equatorial plane is defined by the S donor and two N donors from different bipy ligands. The Cu,N distances span the range 1.984,(6),2.069,(7),Ĺ and the Cu,S distance is 2.366,(3),Ĺ. Intermolecular ,,, contacts between imidazolidine and pyridyl rings form chains of cations. A major difference between the two structures is due to the presence in the second complex of two N,H...O hydrogen bonds linking the imidazolidine N,H hydrogen-bond donors to perchlorate O-atom acceptors. [source] | ||||||||||