Synthesis,characterization and biological activity of bis(3‐Aryl‐1‐hexahydropyrimidinyl)methanes. Novel heterocyclic polyamine derivatives

A method is described for the synthesis of bis(3‐aryl‐1‐hexahydropyrimidinyl)methanes 1, by condensation of N‐aryl‐1,3‐propanediarnines 2 with formaldehyde. The reaction mechanism involves N‐arylhexahydropyrimidines 3 as intermediates. Such compounds can also be prepared efficiently by a methylene exchange reaction between bis‐hexahydropyrimidines 1 and the corresponding diamines 2. The antimicrobial activity of compounds 1 was evaluated by the disk diffusion method and some of them showed moderate to good growth inhibition activity.     

Copper and Silver Atoms in the β-Cage of a Zeolite: Model Calculations

The electronic structures of the 4-4 SBU, the β-cage, and the β-cage with two 4-4 SBU's attached to it have been studied by means of EH-MO calculations. No indication of the formation of a band structure has been found. The HOMO region consists of many closely spaced, localized states, 98.6% of them concentrated on the O-atoms. Reversible color changes of Cu⁺¹ and Ag⁺¹ zeolites observed upon hydration-dehydration experiments can be understood as charge-transfer transitions from the HOMO concentrated on the zeolite O-atoms to the metal cations. As soon as the Cu⁺¹ or Ag⁺¹ are partially hydrated, the ns* and np* states are shifted to higher energies. The luminescence observed with dehydrated Cu⁺¹-zeolites X is caused by a 4p*←HOMO absorption, followed by spontaneous 4s*←4p* emission. After a detailed study of a Cu⁺¹ in the 6-6 SBU, we discuss the electronic structure of a β-cage filled with 1,2,4,8, and 9 Cu⁺¹. In each case, the β-cage is found to be too small to allow the formation of a band structure. The levels caused by the added copper are distinctly quantized. Calculations on [Ag₃(H₂O)₃]³⁺ in a β-cage are reported. The direct interaction between the Ag-atoms is significant. As a consequence, the states formed by Ag 5s and 5p atomic orbitals are delocalized over the three Ag-centers. In both the Cu⁺¹ and the Ag⁺¹ zeolites, the ligand-field picture is found to be insufficient to explain the electronic structure, when the metal is coordinated to the zeolite oxygen framework.     

Deviation from Ohm's law in electric field assisted capillary liquid chromatography

Earlier studies of electric field assisted LC (EF-LC) have shown that the effect on charged analytes of the application of an electric field over a capillary LC column is relatively small. Charged analytes can only be affected by the electric field while present in the mobile phase, which makes the effective time for influence of the electric field t(0) independent of retention time. Because the charged analytes only can be affected for a short time the electric field strength ought to be high in order to increase the impact of the electric field on the separation. We have, however, found that only a relatively low electric field strength can be used in EF-LC when pressure is used as main driving force. The useful field strength was limited by a dramatic increase in the current. This increase in current was found to origin from an increased concentration of buffer ions that have an electrophoretic mobility towards the pumped flow.     

Comparison of low-order multireference many-body perturbation theories

Tests have been made to benchmark and assess the relative accuracies of low-order multireference perturbation theories as compared to coupled cluster (CC) and full configuration interaction (FCI) methods. Test calculations include the ground and some excited states of the Be, H(2), BeH(2), CH(2), and SiH(2) systems. Comparisons with FCI and CC calculations show that in most cases the effective valence shell Hamiltonian (H(v)) method is more accurate than other low-order multireference perturbation theories, although none of the perturbative methods is as accurate as the CC approximations. We also briefly discuss some of the basic differences among the multireference perturbation theories considered in this work.     

Derivatives and reactions of glutaconaldehyde—XIII: Regiospecific ring opening of 3-substituted pyridines

A number of nucleophilic ring openings of 3-substituted pyridinium salts have been reinvestigated and summarized. The structure of the resulting stable glutaconaldehyde derivatives was investigated in detail by ¹H NMR. It has been concluded that in general nucleophilic pyridinium ring openings are highly regiospecific. In each case investigated to date a single product was isolated, as a result of attack by the nucleophile at only one of the pyridine α-positions. With the OH ion as the only nucleophile, attack occurs at the pyridine C-2, while larger nucleophiles such as amines and carbanions attack at the pyridine C-6. This was found to be the case for a variety of 3-substituted pyridines such as 3-methyl, 3-methoxy-, 3-cyano-, 3 chloro-pyridine.     

FLUORESCENCE PROPERTIES OF PORPHYRIN-GLOBIN FROM HUMAN HEMOGLOBIN

Fluorescence excitation and emission spectra, decays, and quantum yields are reported for the porphyrin-globin of hemoglobin (Hb^desFe) in aqueous solution of pH 8, at 4°C. A very weak fluorescence was observed in the UV (maximum at 334 nm), due to tryptophan and tyrosine residues, in addition to the strong porphyrin emission in the visible (maxima at 624 and 692 nm) reported previously. The absorption and fluorescence properties of the porphyrins of Hb^desFe were compared to those for free porphyrin in organic solvents and in aqueous solution. The close similarity of the fluorescence decays and quantum yields in Hb^desFe and in solution indicate the absence of stronger, specific porphyrin-protein interactions; however, slight spectral shifts point to the existence of water molecules in the Hb^desFe porphyrin environment. The fluorescence study also demonstrates the existence of efficient Trp-porphyrin energy transfer of Förster type. The extent of transfer is in satisfactory agreement with the value expected from crystallographic data for hemoglobin. The results are discussed and compared to previous fluorescence studies of hemoglobin and apohemoglobin. An improved method for the preparation of Hb^desFe is reported.     

Über Münzmetall‐Quecksilber‐Chalkogenidhalogenide. IV1) Hydrothermalsynthese und Kristallstruktur von CuHgSI und CuHg2S2I

On Coinage Metal Mercury Chalcogenide Halides. IV Hydrothermal Synthesis and Crystal Structure of CuHgSI and CuHg₂S₂I The hydrothermal reaction of CuI with α‐HgS in diluted aqueous HI‐solution as solvent at 180 °C yields dark red crystals of CuHgSI. The compound crystallizes orthorhombic in the space group Pna2₁ with a = 718.3(1) pm, b = 834.3(2) pm and c = 698.9(1) pm and Z = 4. CuHg₂S₂I was obtained by the hydrothermal reaction of CuI with α‐HgS in diluted HI‐solution at 300 °C as black crystals. The compound crystallizes orthorhombic in the space group Cmc2₁ with a = 1261.8(3) pm, b = 722.4(1) pm and c = 693.7(1) pm and Z = 4. Both crystal structures could be explained as distorted version of the Wurtzite structure type in which two different types of anion‐lattices are built up.     

α‐Tris(2,4‐pentanedionato‐κ2O,O′)cobalt(III) at 240, 210, 180, 150 and 110 K

The crystal structure of the title compound, [Co(C₅H₇O₂)₃], has been investigated by a multi‐temperature measurement. In contrast to the isomorphous Al compound, the title compound exists in the studied temperature range as its monoclinic α polymorph (space group P2₁/c) and does not undergo a phase transition. Rigid‐body TLS analyses have been performed and the anisotropic thermal expansion tensor α_ij has been determined. The cell axes show a linear expansion behavior with respect to the temperature, but the slope is significantly different. A possible explanation are the different strengths of different intermolecular C—H...O contacts, which run in different crystallographic directions.     

Traceability and its role in interlaboratory comparisons (proficiency testing programmes), modeled on trace element determination in biological materials

 Traceability is not always evident in proficiency testing programs, although this is a requirement in ISO/IEC Guide 43-1. The assigned, or "true", value in most programs is not traceable to an independent entity. The test materials should generally be similar in nature to those routinely tested by participating laboratories. This is far from always the case and it is important to realize that if the difference is large, there may be no traceability to the testing program. It is also important that results from participation in proficiency tests are cited when papers are published, in order to enhance reliability/credibility of the published data.