Die Bestimmung der Ameisens?ure allein oder in Gemischen mit ihren Homologen mittels Kaliumpermanganats in alkalischer L?sung

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Graphical Representations of Speed: Obstacles Preservice K‐8 Teachers Experience

This study examines the difficulties college students experience when creating and interpreting graphs in which speed is one of the variables. Nineteen students, all preservice elementary or middle school teachers, completed an upper‐level course exploring algebraic concepts. Although all of these preservice teachers had previously completed several mathematics courses, including calculus, they demonstrated widespread misconceptions about the variable speed. This study identifies four cognitive obstacles held by the students, provides excerpts of their graphical constructions and verbal interpretations, and discusses potential causes for the confusion. In particular, misconceptions arose when students interpreted the behavior and nature of speed within a graphical context, as well as in situations where they were required to construct a graph involving speed as a variable. The study concludes by offering implications for the teaching and learning of speed and its interpretation within a graphical setting.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Model of the Second Most Abundant Cisplatin-DNA Cross-Link: X-ray Crystal Structure and Conformational Analysis of cis-[(NH(3))(2)Pt(9-MeA-N7)(9-EtGH-N7)](NO(3)).2H(2)O (9-MeA = 9-Methyladenine; 9-EtGH = 9-Ethylguanine)

A model compound of the second most abundant DNA adduct of the antitumor agent cisplatin has been synthesized and structurally and spectroscopically characterized and its conformational behavior examined: cis-[(NH(3))(2)Pt(9-MeA-N7)(9-EtGH-N7)](NO(3))(2).2H(2)O (9-MeA = 9-methyladenine; 9-EtGH = 9-ethylguanine) crystallizes in the monoclinic system, space group P2(1)/n (No. 14) with a = 7.931(2), b = 11.035(3), c = 26.757(6) ?, beta = 94.94(2) degrees, and Z = 4. The two purine bases adopt a head-to-head orientation, with NH(2) of 9-MeA and CO of 9-EtGH being at the same side of the Pt coordination plane. A theoretical conformational analysis of the complex cis-[(NH(3))(2)Pt(Ade)(Gua)](2+) (Ade = adenine; Gua = guanine) based on molecular mechanics calculations of the nonbonded energy has revealed four minimum-energy zones similar to those derived previously for cis-[(NH(3))(2)Pt(Gua)(2)](2+) (Kozelka; et al. Eur. J. Biochem. 1992, 205, 895). This conformational analysis has allowed, together with the calculation of chemical shifts due to ring effects, the attribution of the two conformers observed for cis-[(NH(3))(2)Pt{d(ApG)}](+) by Dijt et al. (Eur. J. Biochem. 1989, 179, 344) to the two head-to-head conformational zones. The orientation of the two nucleobases in the crystal structure of cis-[(NH(3))(2)Pt(9-MeA)(9-EtGH)](2+) corresponds, according to our analysis, roughly to that preferentially assumed by the minor rotamer of cis-[(NH(3))(2)Pt{d(ApG)}](+).     

A rapid technique to determine the internal area function of finite-length ducts using maximum length sequence analysis

This paper describes a rapid technique for reconstruction of the internal area function of a duct using blockage-induced eigenvalue shifts determined from eigenfrequencies measured under two sets of duct termination boundary conditions. A single broad band maximum length sequence (MLS) measurement of short duration is utilized to obtain the transfer function of the duct, which in turn can be utilized to determine its eigenvalue shifts and subsequently its internal area function using an inverse perturbation technique. The reconstruction results display the same order of accuracy as those obtained previously using swept sine measurements of extended duration. An expression for the determination of the area function is presented utilizing resonant frequency information alone, thus rendering duct length determination unnecessary. A computational routine further simplifies the process such that the accuracy of the technique could be ascertained for a range of configurations including longer ducts and ducts that initially have nonuniform internal cross section over their length. Development of a relationship between obstacle length and wavelength of the lowest eigenfrequency required for successful reconstruction is also described. This is an important result for longer ducts where measurement of lower eigenfrequencies may present problems using standard measurement equipment.     

Line Positions and Intensities in the 2nu(2)/nu(4) Vibrational System of (14)NH(3) near 5-7 µm

Line positions and intensities belonging to the vibrational system 2nu(2)/nu(4) of ammonia (14)NH(3) are measured and analyzed between 1200 and 2200 cm(-1) in order to improve the molecular database. For this, laboratory spectra are obtained at 0.006 and 0.011 cm(-1) unapodized resolution and with 4% precisions for the intensities using Fourier transform spectrometers located at the Kitt Peak National Observatory and the Jet Propulsion Laboratory. The observed data contain transitions of the nu(4) fundamental band near 1626.276(1) and 1627.375(2) cm(-1) (for s and a inversion upper states, respectively) and the 2nu(2) overtone band near 1597.470(3) and 1882.179(5) cm(-1) (for s and a inversion states, respectively). A total of 2345 lines with J' 相似文献   

Liquid–liquid extraction of neodymium (III) and europium (III) using synergic mixture of furosemide and tribenzylamine in benzyl alcohol

The extraction behavior of Nd(III) and Eu(III) with 0.05 mol dm⁻³ furosemide in benzyl alcohol as single acidic extractant and then with equimolar (0.05 mol dm⁻³) synergic mixture of furosemide as acidic extractant and tribenzylamine as neutral donor in benzyl alcohol has been studied from aqueous solutions of pH 1 to 6. The effect of various parameters and of various cations and anions on the extraction of these metal ions was investigated. The composition of the extracted adducts was determined by slope analysis method that came out to be [(M(FS)₂)⁺ (CH₃COO)⁻] and [M(FS)₃·3TBA] where M = Nd(III) and Eu(III).

     

Locked pi-expanded chlorins in two steps from simple tetraarylporphyrins

[reaction: see text] Upon tandem Reformatsky reaction, easily accessible porphyrinic ketones give "locked" chlorinic diester. Both ketones and diesters, as bases or palladium complexes, efficiently generate singlet dioxygen, as demonstrated by trapping with cholesterol.