Investigations on the behaviour of acidic, basic and neutral compounds in capillary electrochromatography on a mixed-mode stationary phase

This work describes the separation of acidic, basic and neutral organic compounds as well as inorganic anions in a single run by capillary electrochromatography employing a stationary phase which exhibits both strong anion-exchange and reversed-phase chromatographic characteristics. The positive surface charge of this stationary phase provided a substantial anodic electroosmotic flow. The analytes were separated by a mixed-mode mechanism which comprised chromatographic interactions (hydrophobic interactions, ion-exchange) as well as electrophoretic migration. The influence of ion-exchange and hydrophobic interactions on the retention/migration of the analytes could be manipulated by varying the concentration of a competing ion and/or the amount of organic modifier present in the background electrolyte. Additionally the effects of pH changes on both the chromatographic interactions as well as the electrophoretic migration of the analytes were investigated.     

Development of a new reaction system for the synthesis of highly optically active alpha,gamma-substituted gamma-butyrolactones

A highly useful method for the synthesis of optically active alpha,gamma-substituted gamma-butyrolactones has been developed. The SmI(2)-induced reductive coupling of chiral 2-alkyl acrylates derived from isosorbide with ketones in the presence of (1S)-(-)-2,10-camphorsultam as a proton source give the chiral alpha,gamma-substituted gamma-butyrolactones in good yields and high enantiomeric purities (up to >99% ee for trans and 75% ee for cis). The reaction system has been investigated with various ketones, and it is demonstrated that this system is very effective for trans-alpha,gamma-substituted gamma-butyrolactones. Both the chiral auxiliary and the hindered proton source in this system are necessary for the observed excellent ee values of the products. The absolute configuration of the trans products is assigned on the basis of the X-ray crystal structure.     

Mass spectrometry of nitroazoles: 2—the mass spectra of methyl substituted nitroimidazoles

The mass spectra of six isomers of methylnitroimidazoles are reported and discussed. All compounds exhibit strong molecular ions, along with the characteristic fragmentations of aromatic nitro compounds. In some cases ortho effects—losses of OH^., H₂O, CHO^., CH₂O—are observed, due to interactions of adjacent substituents.     

Reduction of 4-arylidene-1,3-(2H,4H)isoquinolinediones

Catalytic hydrogenation of some 4-arylidene-1,3-(2H,4H)isoquinolinediones (1) afforded the corresponding 4-arylmethyl-1,3-(2H,4H)isoquinolinediones (2) , but reduction of 1 by sodium borohydride gave 4-arylmethyl-1(2H)isoquinolones (isocarbostyrils, 3). Compounds of type 1 studied had aryl substituents phenyl, 3,4-dimethoxyphenyl, 3,4-methyleneoxyphenyl and 2-furyl. In one example of sodium borohydride reduction of an N-methylisoquinolinedione derivative (1) the heterocylic ring was opened, and 2-(1-hydroxymethyl-2-phenylethenyl)-N-methylbenzamide (4) was obtained from 4-benzylidene-2-methyl-1,3-(2H,4H)isoquinolinedione.     

Die Hydrohalogenierung von Hexaphenyldigerman und die Schwingungsspektren einiger Ge2(C6H5) n X6−n -Verbindungen

The reactions of Ge₂(C₆H₅)₆ with HCl and HBr lead in nearly quantitative yields to the 1,1,2,2-tetrahalo derivatives Cl₂(C₆H₅)GeGe(C₆H₅)Cl₂ (I) and Br₂(C₆H₅)GeGe(C₆H₅)Br₂ (II), resp. The Si?Ge bond of (C₆H₅)₃SiGe(C₆H₅)₃ is cleaved under the conditions of hydrohalogenation. The vibrational spectra of Ge₂Br₆, Ge₂(C₆H₅)₆, I, and II are reported. The influence of vibrational coupling on ν GeGe in these compounds is discussed in detail, including vibrational calculations.     

Die Fehlordnung des Natriumazides und deren Einfluß auf die thermische Zersetzung, 2. Mitt.: Berechnung der Polarisationsenergie für den Ausbau eines Ionenpaares aus Natriumazid

Zusammenfassung Zur Berechnung der Polarisationsenergie nach dem Konzept eines starren Gitters wird zuerst die Polarisierbarkeit des N₃ ^– in NaN₃ berechnet. Mit den bekannten Daten für die Brechungsindizes in den Hauptachsen kann nach einer Methode vonMott der erforderliche Polarisierbarkeitstensor aufgestellt werden. Um Argumente für die Berechtigung des Verfahrens zu erhalten, wird die Polarisierbarkeit des Chlorions in NaCl analog berechnet. Unter Zugrundelegung der vonPauling gegebenen Strukturdaten des NaN₃ wird dann die Polarisationsenergie mit Hilfe verallgemeinerter Grundlagen für den Ausbau eines Ionenpaares aus NaN₃ und NaCl berechnet, während Dipol—Dipol-Wechselwirkungen abgeschätzt werden. Vernachlässigt man den Beitrag der Verschiebungspolarisation, so erhält man für die gesamte Polarisationsenergie bei NaN₃ 3,4 eV und bei NaCl 4,2 eV, wasSchottky-Fehlordnung vermuten läßt. Der Zusammenhang mit der Fehlerbildungsenergie wird im Anschluß daran diskutiert.

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For the determination of the polarization energy based upon the model of a rigid lattice, the polarizability of the azide ion in sodium azide is calculated. WithMott's method and the known data for the refractive indices along the main directions the polarizability tensor can be constructed. An analogous calculation is performed for the polarizability of the chlorine ion in NaCl in order to test arguments of our method. WithPauling's data of the NaN₃ structure, the polarization energy for the removal of an ion pair from both NaN₃ and NaCl is calculated by means of a generalized basis estimating dipole—dipole interactions. Neglecting the displacement polarization, one obtains for the total polarization energy a value of 3,4 eV for NaN₃, and 4,2 eV for NaCl, resp., pointing atSchottky-disorder. The connection with the energy of defect formation is discussed hereupon.

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Mit 6 Abbildungen     

Non-aqueous capillary electrophoretic enantioseparation of N-derivatized amino acids using cinchona alkaloids and derivatives as chiral counter-ions

A non-aqueous capillary electrophoretic method developed with quinine and tert.-butyl carbamoylated quinine as chiral selectors for the enantioseparation of N-protected amino acids was applied to the investigation of other quinine derivatives as chiral additives. The optimum composition of the background electrolyte was found to be 12.5 mM ammonia, 100 mM octanoic acid and 10 mM chiral selector in an ethanol-methanol (60:40, v/v) mixture. Under these conditions, a series of chiral acids, as various benzoyl, 3,5-dinitrobenzoyl and 3,5-dinitrobenzyloxycarbonyl amino acid derivatives were investigated with regards to selectand-selector relationships and enantioselectivity employing quinine, quinidine, cinchonine, cinchonidine, tert.-butyl carbamoylated quinine, tert.-butyl carbamoylated quinidine, dinitrophenyl carbamoylated quinine and cyclohexyl carbamoylated quinine as chiral selector.     

Selective metal cation activation of a DNA alkylating agent: synthesis and evaluation of methyl 1,2,9, 9a-Tetrahydrocyclopropa[c]pyrido[3,2-e]indol-4-one-7-carboxylate (CPyI)

The synthesis of methyl 1,2,9,9a-tetrahydrocyclopropa[c]pyrido[3, 2-e]indol-4-one-7-carboxylate (CPyI) containing a one carbon expansion of the C ring pyrrole found in the duocarmycin SA alkylation subunit and its incorporation into analogues of the natural product are detailed. The unique 8-ketoquinoline structure of CPyI was expected to provide a tunable means to effect activation via selective metal cation complexation. The synthesis of CPyI was based on a modified Skraup quinoline synthesis followed by a 5-exo-trig aryl radical cyclization onto an unactivated alkene with subsequent TEMPO trap or 5-exo-trig aryl radical cyclization onto a vinyl chloride for synthesis of the immediate precursor. Closure of the activated cyclopropane, accomplished by an Ar-3' spirocyclization, provided the CPyI nucleus in 10 steps and excellent overall conversion (29%). The evaluation of the CPyI-based agents revealed an intrinsic stability comparable to that of CC-1065 and duocarmycin A but that it is more reactive than duocarmycin SA and the CBI-based agents (3-4x). A pH-rate profile of the addition of nucleophiles to CPyI demonstrated that an acid-catalyzed reaction is observed below pH 4 and that an uncatalyzed reaction predominates above pH 4. The expected predictable activation of CPyI by metal cations toward nucleophilic addition was found to directly correspond to established stabilities of the metal complexes with the addition product (Cu(2+) > Ni(2+) > Zn(2+) > Mn(2+) > Mg(2+)) and provides the opportunity to selectively activate the agents upon addition of the appropriate Lewis acid. This tunable metal cation activation of CPyI constitutes the first example of a new approach to in situ activation of a DNA binding agent complementary to the well-recognized methods of reductive, oxidative, or photochemical activation. Resolution and synthesis of a full set of natural product analogues and subsequent evaluation of their DNA alkylation properties revealed that the CPyI analogues retain identical DNA alkylation sequence selectivity and near-identical DNA alkylation efficiencies compared to the natural products. Consistent with past studies and even with the deep-seated structural change in the alkylation subunit, the agents were found to exhibit potent cytotoxic activity that directly correlates with their inherent reactivity.     

Overtone spectroscopy of H2O clusters in the V(OH) = 2 manifold: infrared-ultraviolet vibrationally mediated dissociation studies

Spectroscopy and predissociation dynamics of (H2O)2 and Ar-H2O are investigated with vibrationally mediated dissociation (VMD) techniques, wherein upsilon(OH) = 2 overtones of the complexes are selectively prepared with direct infrared pumping, followed by 193 nm photolysis of the excited H2O molecules. As a function of relative laser timing, the photolysis breaks H2O into OH and H fragments either (i) directly inside the complex or (ii) after the complex undergoes vibrational predissociation, with the nascent quantum state distribution of the OH photofragment probed via laser-induced fluorescence. This capability provides the first rotationally resolved spectroscopic analysis of (H2O)2 in the first overtone region and vibrational predissociation dynamics of water dimer and Ar-water clusters. The sensitivity of the VMD approach permits several upsilon(OH) = 2 overtone bands to be observed, the spectroscopic assignment of which is discussed in the context of recent anharmonic theoretical calculations.     

Dissociation patterns in N2O following electron impact

A number of dissociation channels in N₂0 have been observed by time-of-flight spectroscopy following electron impact excitation. The metastable atoms and molecules produced were directly detected. Excited N₂ molecules were produced in the A³Σ_u⁺, B³Π_g and B′³Σ_u^? states in conjunction with ground state oxygen atoms. A number of additional dissociation channels were monitored by observing the production of oxygen and nitrogen atoms in Rydberg states. The results indicate the existence of potential minima in some of the repulsive surfaces involved.