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J. Am (j + be)
Selected AbstractsPotential roles for BMP and Pax genes in the development of iris smooth muscleDEVELOPMENTAL DYNAMICS, Issue 2 2005Abbie M. Jensen Abstract The embryonic optic cup generates four types of tissue: neural retina, pigmented epithelium, ciliary epithelium, and iris smooth muscle. Remarkably little attention has focused on the development of the iris smooth muscle since Lewis ([1903] J. Am. Anat. 2:405,416) described its origins from the anterior rim of the optic cup neuroepithelium. As an initial step toward understanding iris smooth muscle development, I first determined the spatial and temporal pattern of the development of the iris smooth muscle in the chick by using the HNK1 antibody, which labels developing iris smooth muscle. HNK1 labeling shows that iris smooth muscle development is correlated in time and space with the development of the ciliary epithelial folds. Second, because neural crest is the only other neural tissue that has been shown to generate smooth muscle (Le Lievre and Le Douarin [1975] J. Embryo. Exp. Morphol. 34:125,154), I sought to determine whether iris smooth muscle development shares similarities with neural crest development. Two members of the BMP superfamily, BMP4 and BMP7, which may regulate neural crest development, are highly expressed by cells at the site of iris smooth muscle generation. Third, because humans and mice that are heterozygous for Pax6 mutations have no irides (Hill et al. [1991] Nature 354:522,525; Hanson et al. [1994] Nat. Genet. 6:168,173), I determined the expression of Pax6. I also examined the expression of Pax3 in the developing anterior optic cup. The developing iris smooth muscle coexpresses Pax6 and Pax3. I suggest that some of the eye defects caused by mutations in Pax6, BMP4, and BMP7 may be due to abnormal iris smooth muscle. Developmental Dynamics 232:385,392, 2005. © 2004 Wiley-Liss, Inc. [source] Reactions of gaseous ions.JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2001Editor's Note: The following paper is the first in a series that describes the gas phase reactions of positive ions derived from compounds such as methane and ethylene with other gas phase molecules to produce secondary ions. These very careful experiments formed the basis of chemical ionization, one of the ionization techniques that revolutionized mass spectrometry at that time and a technique still very much in use today. At elevated pressures in a mass spectrometer ion source reactions occur between certain ions and the neutral species present. We have studied the various secondary ions formed in methane and ethylene at elevated pressures and have determined the reactions by which they are formed and the rates of these reactions. The rates are all extremely fast. The reaction rates have been treated by classical collision theory and it has been shown that to a fair approximation the cross-sections and reaction rate constants can be predicted from a simple balance of rotational and polarization forces. [Reprinted from J. Am. Chem. Soc. 1957; 79: 2419.] Copyright © 1957 by the American Chemical Society and reprinted by permission of the copyright owner. [source] The polarisability potential as a steric index,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2010Cristopher Camacho Abstract The acid-catalysed hydrolysis of carboxylic esters is the reference chemical reaction used for the empirical evaluation of steric effects. In this work, the polarisability potential (Hehre, et al., J. Am. Chem. Soc. 1986, 108, 1711,1712) is identified as quantum-mechanical size of substituent groups. Correlation is found between this quantity and reactivity features of the reference reaction. Copyright © 2010 John Wiley & Sons, Ltd. [source] Deprotonation and radicalization of glycine neutral structuresJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 1 2008Gang Yang Abstract Ab initio calculations at MP2/6-311++G(d,p) theoretical level were performed to study the deprotonation and radicalization processes of 13 glycine neutral structures (A. G. Császár, J. Am. Chem. Soc. 1992; 114: 9568). The deprotonation processes to glycine neutral structures take place at the carboxylic sites instead of , -C or amido sites. Two carboxylic deprotonated structures were obtained with the deprotonation energies calculated within the range of 1413.27,1460.03,kJ,·,mol,1, which are consistent with the experimental results. However, the radicalization processes will take place at the , -C rather than carboxylic O or amido sites, agreeing with the experimental results. Seven , -C radicals were obtained with the radical stabilization energies calculated within the range of 44.87,111.78,kJ,·,mol,1. The population analyses revealed that the main conformations of the neutral or radical state are constituted by several stable structures, that is, the other structures can be excluded from the future considerations and thus save computational resources. Copyright © 2007 John Wiley & Sons, Ltd. [source] Vibrational analysis of Ni(II)- and Cu(II)-octamethylchlorin by polarized resonance Raman and Fourier transform infrared spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 6-7 2001Robert J. Lipski We measured the polarized resonance Raman spectra of Cu(II)-2,2,7,8,12,13,17,18-octamethylchlorin in CS2 at various excitation wavenumbers in a spectral region covering the Qy, Qx and Bx optical absorption bands. Additionally, we measured the FTIR-Raman spectrum of the highly overcrowded spectral region between 1300 and 1450 cm,1. The spectral decomposition was carried out by a self-consistent global fit to all spectra obtained. The thus identified Raman and IR lines were assigned by comparison with the resonance Raman spectra of Cu(II)-octaethylporphyrin, by utilizing their depolarization ratio dispersions and by a normal mode analysis. The latter was based on a modified transferable molecular mechanics force field of Ni(II)-octaethylporphyrin [E. Unger, M. Beck, R.J. Lipski, W. Dreybrodt, C.J. Medforth, K.M. Smith and R. Schweitzer-Stenner, J. Phys. Chem. B103, 10229 (1999)]. A comparison of normal mode patterns obtained for Cu(II)-octamethylchlorin and Cu(II)-octaethylporphyrin revealed that some modes are significantly distorted by the reduction of the pyrrole ring, in accordance with results which Boldt et al. reported earlier for Ni(II)-octaethylchlorin [N.J. Boldt, F.J. Donohoe, R.R. Birge and D.F. Bocian, J. Am. Chem. Soc.109, 2284 (1987)]. In contrast to conclusions drawn from this study, however, the results of our vibrational analysis and several further lines of evidence suggest that the normal modes of corresponding chlorines and porphyrins are still comparable, because they display contributions from the same local coordinates. Thus, the classical normal mode classification developed for metalloporphyrins is also applicable to metallochlorins. Finally, we performed a preliminary analysis of the absorption spectrum and the resonance excitation profiles and depolarization ratio dispersions of some Raman lines. The results show that the electronic properties of Cu(II)-octamethylchlorin can still be described in terms of Gouterman's four orbital model [M. Gouterman, J. Chem. Phys.30, 1139 (1959)]. In regions of the Q bands, Raman scattering of A1 modes is determined by interferences between Franck, Condon coupling and interstate Herzberg, Teller coupling between Qx(Qy) and Bx(By) states. The B2 modes are resonance enhanced by Herzberg, Teller coupling between Qx and Qy and between Qx(Qy) and By(Bx). Franck, Condon coupling of A1 modes with large contributions from C,Cm stretching vibrations is comparatively strong for Qx. This is interpreted as reflecting the expansion of the chlorin macrocycle by an electronic transition into this excited state. Copyright © 2001 John Wiley & Sons, Ltd. [source] Structural analysis of lithium lanthanum titanate with perovskite structurePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2009Koji Ohara Abstract Neutron and high-energy X-ray diffraction analysis of polycrystalline La4/3-xLi3xTi2O6 have been performed to clarify the extent of disorder of the distribution of La and Li ions and to understand the relation of these distributions to ionic conduction. The distributions of the La and Li ions in a 10 × 10 × 20 cubic box (i.e., 10 × 10 × 10 unit cell) super-structure, in which Ti and O atoms are fixed onto their regular sites, were obtained by the reverse Monte Carlo (RMC) structural modelling of both diffraction data sets. When the occupancy of La ions in the planes perpendicular to the c-axis is analysed, one can find a La-rich and La-poor layers alternating, which is consistent with the results of earlier Rietveld analysis (Stramare et al., Chem. Mater. 15, 3974 (2003) [1]). Of particular interest, the Li ions are found mainly on the interstitial sites between the O-3 triangle plane of the TiO6 octahedron and a La ion, which is different from the earlier work (Yashima et al., J. Am. Chem. Soc. 127, 3491 (2005) [2]). (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Segmented post-column analyte addition; a concept for continuous response control of liquid chromatography/mass spectrometry peaks affected by signal suppression/enhancementRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2005Anton Kaufmann A novel technique, "segmented post-column analyte addition", is proposed to visualize and compensate signal suppression/enhancement effects in electrospray ionization tandem mass spectrometry (ESI-MS/MS). Instead of delivering a constant flow of analyte solution between the liquid chromatography (LC) column exit and the ESI interface into the eluent resulting from LC separation of analyte-free matrix in order to determine retention time widows in which suppression/enhancement is unimportant (King et al., J. Am. Soc. Mass Spectrom. 2000; 11: 942), segmented packets of analyte-containing solvent and analyte-free solvent were infused into an LC eluent resulting from separation of an analyte-containing sample. The obtained, superimposed, periodic spikes are much narrower than the analyte peak eluting from the column. The height of the spikes is affected by signal suppression phenomena to the same extent as the analyte signal, and hence variations of the spike height can be used to correct the peak area of analyte peaks affected by signal suppression/enhancement. Copyright © 2005 John Wiley & Sons, Ltd. [source] Probing the ,-Helical Structural Stability of Stapled p53 Peptides: Molecular Dynamics Simulations and AnalysisCHEMICAL BIOLOGY & DRUG DESIGN, Issue 4 2010Zuojun Guo Reactivation of the p53 cell apoptosis pathway through inhibition of the p53-hDM2 interaction is a viable approach to suppress tumor growth in many human cancers and stabilization of the helical structure of synthetic p53 analogs via a hydrocarbon cross-link (staple) has been found to lead to increased potency and inhibition of protein,protein binding (J. Am. Chem. Soc. 129: 5298). However, details of the structure and dynamic stability of the stapled peptides are not well understood. Here, we use extensive all-atom molecular dynamics simulations to study a series of stapled ,-helical peptides over a range of temperatures in solution. The peptides are found to exhibit substantial variations in predicted ,-helical propensities that are in good agreement with the experimental observations. In addition, we find significant variation in local structural flexibility of the peptides with the position of the linker, which appears to be more closely related to the observed differences in activity than the absolute ,-helical stability. These simulations provide new insights into the design of ,-helical stapled peptides and the development of potent inhibitors of ,-helical protein,protein interfaces. [source] On the Analyses of Mixture Vapor Pressure Data: The Hydrogen Peroxide/Water System and Its Excess Thermodynamic FunctionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2004Stanley L. Manatt Dr. Abstract Reported here are some aspects of the analysis of mixture vapor pressure data using the model-free Redlich,Kister approach that have heretofore not been recognized. These are that the pure vapor pressure of one or more components and the average temperature of the complex apparatuses used in such studies can be obtained from the mixture vapor pressures. The findings reported here raise questions regarding current and past approaches for analyses of mixture vapor pressure data. As a test case for this analysis approach the H2O2,H2O mixture vapor pressure measurements reported by Scatchard, Kavanagh, and Tickner (G. Scatchard, G. M. Kavanagh, L. B. Ticknor, J. Am. Chem. Soc.1952, 74, 3715,3720; G. M. Kavanagh, PhD. Thesis, Massachusetts Institute of Technology (USA), 1949) have been used; there is significant recent interest in this system. It was found that the original data is fit far better with a four-parameter Redlich,Kister excess energy expansion with inclusion of the pure hydrogen peroxide vapor pressure and the temperature as parameters. Comparisons of the present results with the previous analyses of this suite of data exhibit significant deviations. A precedent for consideration of iteration of temperature exists from the little-known work of Uchida, Ogawa, and Yamaguchi (S. Uchida, S. Ogawa, M. Yamaguchi, Japan Sci. Eng. Sci.1950, 1, 41,49) who observed significant variations of temperature from place to place within a carefully insulated apparatus of the type traditionally used in mixture vapor pressure measurements. For hydrogen peroxide, new critical constants and vapor pressure,temperature equations needed in the analysis approach described above have been derived. Also temperature functions for the four Redlich,Kister parameters were derived, that allowed calculations of the excess Gibbs energy, excess entropy, and excess enthalpy whose values at various temperatures indicate the complexity of H2O2,H2O mixtures not evident in the original analyses of this suite of experimental results. [source] Homogeneous [RuIII(Me3tacn)Cl3]-Catalyzed Alkene cis -Dihydroxylation with Aqueous Hydrogen PeroxideCHEMISTRY - AN ASIAN JOURNAL, Issue 1 2008Wing-Ping Yip Dr. Abstract A simple and green method that uses [Ru(Me3tacn)Cl3] (1; Me3tacn=N,N,,N,,-trimethyl-1,4,7-triazacyclononane) as catalyst, aqueous H2O2 as the terminal oxidant, and Al2O3 and NaCl as additives is effective in the cis -dihydroxylation of alkenes in aqueous tert -butanol. Unfunctionalized alkenes, including cycloalkenes, aliphatic alkenes, and styrenes (14 examples) were selectively oxidized to their corresponding cis -diols in good to excellent yield (70,96,%) based on substrate conversions of up to 100,%. The preparation of cis -1,2-cycloheptanediol (119,g, 91,% yield) and cis -1,2-cyclooctanediol (128,g, 92,% yield) from cycloheptene and cyclooctene, respectively, on the 1-mol scale can be achieved by scaling up the reaction without modification. Results from Hammett correlation studies on the competitive oxidation of para -substituted styrenes (,=,0.97, R=0.988) and the detection of the cycloadduct [(Me3tacn)ClRuHO2(C8H14)]+ by ESI-MS for the 1 -catalyzed oxidation of cyclooctene to cis -1,2-cyclooctanediol are similar to those of the stoichiometric oxidation of alkenes by cis -[(Me3tacn)(CF3CO2)RuVIO2]+ through [3+2] cycloaddition (W.-P. Yip, W.-Y. Yu, N. Zhu, C.-M. Che, J. Am. Chem. Soc.2005, 127, 14239). [source] | ||||||||||||||||||||||