4-Aminobicyclo[2.2.2]octanone Derivatives with Antiplasmodial and Antitrypanosomal Activities

4-Aminobicyclo[2.2.2]octanones were converted to their N-oxides and to 4-aminobicyclo[2.2.2]octanes. Furthermore, the 6,7-bis-(4-methoxyphenyl) analogues were synthesized. All products were screened for their activities against Trypanosoma b. rhodesiense and Plasmodium falciparum. The pharmacological results were compared with those of formerly tested bicyclo[2.2.2]octanones and bicyclo[2.2.2]octanols. Structure-activity relationships are discussed.     

A fluorescence-based method for direct measurement of submicrosecond intramolecular contact formation in biopolymers: an exploratory study with polypeptides.

A fluorescent amino acid derivative (Fmoc-DBO) has been synthesized, which contains 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) as a small, hydrophilic fluorophore with an extremely long fluorescence lifetime (325 ns in H2O and 505 ns in D2O under air). Polypeptides containing both the DBO residue and an efficient fluorescence quencher allow the measurement of rate constants for intramolecular end-to-end contact formation. Bimolecular quenching experiments indicated that Trp, Cys, Met, and Tyr are efficient quenchers of DBO (k(q) = 20, 5.1, 4.5, and 3.6 x 10(8) M(-1) x s(-1) in D2O), while the other amino acids are inefficient. The quenching by Trp, which was selected as an intrinsic quencher, is presumed to involve exciplex-induced deactivation. Flexible, structureless polypeptides, Trp-(Gly-Ser)n-DBO-NH2, were prepared by standard solid-phase synthesis, and the rates of contact formation were measured through the intramolecular fluorescence quenching of DBO by Trp with time-correlated single-photon counting, laser flash photolysis, and steady-state fluorometry. Rate constants of 4.1, 6.8, 4.9, 3.1, 2.0, and 1.1 x 10(7) s(-1) for n = 0, 1, 2, 4, 6, and 10 were obtained. Noteworthy was the relatively slow quenching for the shortest peptide (n = 0). The kinetic data are in agreement with recent transient absorption studies of triplet probes for related peptides, but the rate constants are significantly larger. In contrast to the flexible structureless Gly-Ser polypeptides, the polyproline Trp-Pro4-DBO-NH2 showed insignificant fluorescence quenching, suggesting that a high polypeptide flexibility and the possibility of probe-quencher contact is essential to induce quenching. Advantages of the new fluorescence-based method for measuring contact formation rates in biopolymers include high accuracy, fast time range (100 ps-1 micros), and the possibility to perform measurements in water under air.     

Reaktion des hydridodicobalt-kations [(C5H5Co)2(μ-PMe2)2(μ-H)]+ mit C2(CO2Me)2: Bildung und kristallstruktur eines zweikernkomplexes mit O=C(OMe)CH=C(CO2Me)PMe2 als 6-elektronen-donorligand

[(C₅H₅Co)₂(μ-PMe₂)₂(μ-H)]BF₄ ([II]BF₄) reacts with C₂(CO₂Me)₂ to give the products III and IV. The ionic compound III which formally is a $\text{1}\text{1}$ adduct of [II]BF₄ and C₂(CO₂Me)₂ has been characterized by X-ray structure analysis. III contains the group O=C(OMe)CH=C(CO₂Me)PMe₂ as a 6-electron donor ligand chelated to a cobalt atom and π-bonded to the other cobalt atom. Complex IV is a neutral compound which also can be obtained from [C₅H₅Co(μ-PMe₂)]₂ (I) and C₂(CO₂Me)₂.     

On the matrix monotonicity of generalized inversion

Let A, B be two matrices of the same order. We write A>B(A>?B) iff A? B is a positive (semi-) definite hermitian matrix. In this paper the well-known result if

$\text{A>B>θ, then B}{}^{\mathrm{?1}}\text{>A}{}^{\mathrm{?1}}\text{> θ}$

(cf. Bellman [1, p.59]) is extended to the generalized inverses of certain types of pairs of singular matrices A,B?θ, where θ denotes the zero matrix of appropriate order.     

Messung der Polarisation von Neutronen der9Be(α,n)12C-Reaktion

The angular distribution of the polarization of neutrons from the⁹Be(,n)¹²C reaction leading to the ground state in¹²C has been investigated at -energies of 2.40 and 2.80 MeV. The polarization has been determined by left-right asymmetry measurements of the intensities of neutrons elastically scattered on⁴He nuclei. Values of the analysing power of⁴He have been calculated using the phase shift data of Stammbach and Walter [1]. The degree of polarization observed varies between + 55% and —44%. All results obtained in this experiment are in good agreement with the results of polarization measurements of other authors except the results of Lietz et al. [2].     

Zur Defokussierungsabhängigkeit der elektronenmikroskopischen Netzebenenabbildung

The defocusing dependence of the lattice plane image contrast in the region of interplanar spacings between 8 Å and 1.4 Å is investigated experimentally and interpreted theoretically using calculated phase contrast transfer characteristics. On the one hand, it is well-known that in the case of coaxial illumination optimum image contrast is obtained if using suitable underfocus, on the other hand, contradictory statements exist for the conditions of contrast formation if using tilted illumination. In the present paper it is shown that in this case optimum contrast is attained with an appropriate overfocus. A possible explanation is given which takes into account the influence of the deviation from the exact symmetrically tilted illumination.     

Near-IR photoluminescence from Si/Ge nanowire-grown silicon wafers: effect of HF treatment

We present the room-temperature near-infrared (NIR) photoluminescence (PL) properties of Si/Ge nanowire (NW)-grown silicon wafers which were treated by vapor of HF:HNO₃ chemical mixture. This treatment activates or enhances the PL intensity in the NIR region ranging from 1000 nm to 1800 nm. The PL consists of a silicon band-edge emission and a broad composite band which is centered at around 1400–1600 nm. The treatment modifies the wafer surface particularly at defect sites especially pits around NWs and NW surfaces by etching and oxidation of Si and Ge. This process can induce spatial confinement of carriers where band-to-band (BB) emission is the dominant property in Si-capped strained Si/Ge NW-grown wafers. Strong signals were observed at sub-band-gap energies in Ge-capped Si/Ge NW-grown wafers. It was found that NIR PL is a competitive property between the Si BB transition and deep-level emission, which is mainly attributable to Si-related defects, Ge dots and strained Ge layers. The enhancement in BB and deep-level PL is discussed in terms of strain, oxygen-related defects, dot formation and carrier-confinement effects. The results demonstrate the effectiveness of this method in enhancing and tuning NIR PL properties for possible applications.