Even-electron ions: a systematic study of the neutral species lost in the dissociation of quasi-molecular ions

The collision-induced dissociations of the even-electron [M + H](+) and/or [M - H](-) ions of 121 model compounds (mainly small aromatic compounds with one to three functional groups) ionized by electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) have been studied using an ion trap instrument, and the results are compared with the literature data. While some functional groups (such as COOH, COOCH(3), SO(3)H in the negative ion mode, or NO(2) in both the positive and negative ion modes) generally promote the loss of neutrals that are characteristic as well as specific, other functional groups (such as COOH in the positive ion mode) give rise to the loss of neutrals that are characteristic, but not specific. Finally, functional groups such as OH and NH(2) in aromatic compounds do not lead to the loss of a neutral that reflects the presence of these substituents. In general, the dissociation of [M + H](+) and [M - H](-) ions generated from aliphatic compounds or compounds containing an aliphatic moiety obeys the even-electron rule (loss of a molecule), but deviations from this rule (loss of a radical) are sometimes observed for aromatic compounds, in particular for nitroaromatic compounds. Thermochemical data and ab initio calculations at the CBS-QB3 level of theory provide an explanation for these exceptions. When comparing the dissociation behaviour of the even-electron [M + H](+) and/or [M - H](-) ions (generated by ESI or APCI) with that of the corresponding odd-electron [M](+) ions (generated by electron ionization, EI), three cases may be distinguished: (1) the dissociation of the two ionic species differs completely; (2) the dissociation involves the loss of a common neutral, yielding product ions differing in mass by one Da, or (3) the dissociations lead to a common product ion.     

Bulk melting of ice at the limit of superheating

The ice-water phase transition after an ultrafast temperature jump is studied in HDO:D2O (15 M) ice with use of 2-color IR spectroscopy. The OH-stretching vibration is applied for rapid heating of the sample and for fast and sensitive probing of local temperature and structure. For energy depositions beyond the limit of superheating (330 +/- 10 K) partial melting in two steps is observed and assigned to (i) catastrophic melting within the thermalization time of the excited ice lattice of 5 +/- 2 ps and (ii) secondary melting with a time constant of 33 +/- 5 ps that is assigned to interfacial melting at the generated phase boundaries. The latter process is found to consume energy amounts in agreement with the latent heat of melting and is accompanied by an accelerated temperature and pressure decrease of the residual ice component.     

Synthese und Charakterisierung von Aquapentachloroplatinaten(IV) – Struktur von [K(18-Krone-6)][PtCl5(H2O)]

Synthesis and Characterization of Aquapentachloroplatinates(IV) – Structure of [K(18-crown-6)][PtCl₅(H₂O)] The crown ether complex of the aquapentachloroplatinic acid of the composition [H₁₃O₆][PtCl₅(H₄O₂)] · 2(18-cr-6) ( 2 ) reacts with K₂CO₃ and [NⁿBu₄]OH in aqueous solution to give [K(18-cr-6)][PtCl₅(H₂O)] ( 5 a ) and [NⁿBu₄][PtCl₅(H₂O)] · ¹/₂ (18-cr-6) · H₂O ( 5 b ), respectively. Both compounds were characterized by microanalysis, vibrational (IR, Raman) and NMR (¹H, ¹³C, ¹⁹⁵Pt) spectroscopy. The X-ray structure analysis of 5 a (orthorhombic, pnma; a = 16,550(4), b = 18,044(3), c = 7,415(1) Å; Z = 4; R1 = 0,0183; wR2 = 0,0414) reveals that the crystal is threaded by chains built up of [PtCl₅(H₂O)]^? and [K(18-cr-6)]⁺ units. There are tight K …? Cl contacts (d(K? Cl1)) = 3,0881(9) Å and O_W? H? O_cr hydrogen bridges (d(O1 …? O2) = 2,806(3) Å) between these units. The coordination polyhedron [PtCl₅O] has approximately C_4v symmetry.     

Flavin Adenine Dinucleotide and N5,N10‐Methenyltetrahydrofolate are the in planta Cofactors of Arabidopsis thaliana Cryptochrome 3

Members of the cryptochrome/photolyase family (CPF) of proteins utilize noncovalently bound light‐absorbing cofactors for their biological function. Usually, the identity of these cofactors is determined after expression in heterologous systems leaving the question unanswered whether these cofactors are identical to the indigenous ones. Here, cryptochrome 3 from Arabidopsis thaliana was expressed as a fusion with the green fluorescent protein in Arabidopsis plants. Besides the confirmation of the earlier report of its localization in chloroplasts, our data indicate that fractions of the fusion protein are present in the stroma and associated with thylakoids, respectively. Furthermore, it is shown that the fusion protein expressed in planta contains the same cofactors as the His₆‐tagged protein expressed in Escherichia coli, that is, flavin adenine dinucleotide and N⁵,N¹⁰‐methenyltetrahydrofolate. This demonstrates that the heterologously expressed cryptochrome 3, characterized in a number of previous studies, is a valid surrogate of the corresponding protein expressed in plants. To our knowledge, this is also a first conclusive analysis of cofactors bound to an Arabidopsis protein belonging to the CPF and purified from plant tissue.     

Preparation,purification, and analysis of alkylated cyclodextrins

Methods of alkylation of α-, β- and γ-cyclodextrins have been optimized with regard to the parameters of reaction, degree of alkylation and yields. The analysis of the reaction mixtures and of the isolated single species has been performed by high temperature GC and HPLC. The phase systems of the preferably applied HPLC have been carefully adjusted by variation of both the stationary and mobile phases to the very different hydrophobicities of the various alkylated CD species which have been synthesized. Several partially or fully alkylated CD species were isolated from preparative scale HPLC separations in high purity.     

Antibakterielle wirkstoffe. VIII . Die aminomethinylierung in der reihe der aminothiazole

The three-component reaction comprising the interaction of 2-amino-4-antipyrinyl-5-ethylthiazole (1) with s-triazine (2) and pyrrolidine leads to 4-anitpyrinyl-5-ethyl-2-[(4-pyrrolidinyl)methyleneamino]thiazole (5). Structure 5 is supported by ¹H- and ¹³C-NMR spectroscopy.     

Tumorhemmende wirkstoffe, XIII [1] aromatisch carbocyclisch und heterocyclisch substituierte 2-perfluoralkylpyrimido[1,2-a]benzimidazole

The interaction of 2-aminobenzimidazole with the appropriate β-diketones carrying fluoroalkyl groupings has led to the 2-perfluoroalkylpyrimido[1,2-a]benzimidazoles as follows: 4-phenyl-, 4-(2'-naphthyl)-, 4-(3'-pyridyl)-, 4-(2'-furyl)-, and 4-(2,-thienyl)-2-trifluoromethylpyrimido[1,2-a]benzimidazole, and 4-(2'-thienyl)-2-(heptafluoropropylpyrimido [1,2-a]benzimidazole.