Corneal topography measurement by means of radial shearing interference: Part III – measurement errors

This work contains results of computer simulation researches, which define requirements for measurement conditions, which should be fulfilled so that measurement results ensure allowable errors. They define: allowable measurement errors (interferogram's scanning) and conditions, which should fulfill computer programs, so that errors introduced by mathematical operations and computer are the smallest.     

Development of long-lifetime metal-ligand probes for biophysics and cellular imaging

Metal-ligand complexes containing ruthenium, osmium, or rhenium display a high photostability, with polarized emission and decay times from 100 ns to 100 Μs. Such probes have considerable potential in biophysics, clinical chemistry, and fluorescence microscopy. In this review we sumrecent developments from this laboratory on the spectral properties of conjugatable metalligand complexes. We also suggest how improved probes can be developed based on the selection of organic ligands.     

Optimum experimental design for a regression on a hypercube-generalization of Hoel's result

In the note Hoel's result (1965, Ann. Math. Statist., 36, 1097–1106) is generalized to a large family of experimental design optimality criterions. Sufficient conditions for optimality criterion are given, which ensure existence of the optimum experimental design measure which is a product of design measures on lower dimensional domains.     

Synthesis and spectral studies of gold(III) complexes with guanidine derivatives

New trivalent gold (d⁸ electronic configuration) halide complexes with guanidino–pyrimidines have been synthesized and delineated. The complexes have been identified and characterized by elemental analysis, u.v.–vis. electronic absorption spectra, i.r. oscillation spectra and by ¹H-n.m.r. and ¹³C-n.m.r. spectra. All substituted guanidine ligands in these chelates form part of a six-membered pseudo-heterocyclic ring where the nitrogen atoms of the guanidine group and the nitrogen atom of pyrimidine, piperidine or the morpholine heterocyclic ring bond to the metal.     

Effect of metal ionic radius and chelate ring alternation motif on stabilization of trivalent nickel and copper in binuclear complexes with double cis-oximato bridges

Oxime ligands are able to form stable binuclear species with copper(II) ions in aqueous solution. They also have a strong tendency to decrease the Mn+/(n-1)+ redox potentials of the central ions. Ligands possessing the hydroxyimino groups together with other powerful sigma-donor groups can be very efficient chelating agents able to facilitate the stabilisation of high oxidation states of 3d-metals. Here we report the synthesis, structural characterization and redox behaviour of mononuclear and binuclear complexes based on hydroxyiminoamide tetradentate open-chain ligands. In all mononuclear anionic complexes the central atom is situated in a square-planar surrounding of four nitrogen atoms. This pseudo-macrocyclic conformation is due to the presence of short intramolecular hydrogen bonds uniting the cis-oximate oxygen atoms. The square-planar surrounding of the strong sigma-donors facilitates efficient stabilization of the trivalent state of copper and nickel ions. In cyclic voltammetry studies the quasi-reversible processes M2+-->M3+ can be observed. In the binuclear complexes the coordinatively saturated octahedral ion M[prime or minute] is bound to the two oxygen atoms of the bridging oximate groups and the four nitrogen atoms of the tetradentate ligand tren. Two metal ions (M and M') are linked by the double cis-oximate bridge and are incorporated in a six-membered bimetallic chelate ring. Metallamacrocycle formation leads to certain changes in the structural parameters of the binuclear complexes as compared to those observed in the mononuclear species. Also the study of the electrochemical activity of binuclear complexes has shown important differences in their redox behaviour as compared to their mononuclear precursors.     

Crystal structure of 7-cyano-6,7-dimethyl-1-phenyl-1,3,6,7-tetrahydro-2,1-benzoxaphospole 1-oxide

The crystals (C₁₆H₁₈NO₂P,M _r=287.30) are orthorhombic, space group Pbca witha=8.200(2),b=14.857(2), andc=24.396(5)Å,V=2972.1 ų,Z=8,D _x=1.284 mg m^–3,(MoK)=0.71069 Å,=1.90 cm^–1,F(000)=216,T=295K. FinalR=0.044 for 1673 observed reflections collected on a diffractometer. Structure solved by direct methods.Cis-junction and double bond in the six-membered ring cause its almost ideal sofa conformation. The two neighboring methyl groups are cis, and cyano substituent is in an equatorial position. There is a shortintramolecular H(o-phenyl)O(endocyclic) contact of 2.53(3)Å and the phenyl ring is in a less favorable rotational orientation due to molecular packing.     

Identification of a novel high affinity copper binding site in the APP(145-155) fragment of amyloid precursor protein

The copper(II) binding features of the APP(145-155) and APP(145-157) fragments of the amyloid precursor protein, Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-NH2 and Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-Glu-Thr-NH2 were studied by NMR spectroscopy and NMR findings were supported by UV-vis, CD and EPR spectra. Potentiometric measurements were performed only for the more soluble Ac-Glu-Thr-His-Leu-His-Trp-His-Thr-Val-Ala-Lys-Glu-Thr-NH2 peptide fragment. The following was shown: (i) the imidazole rings of all the three His residues are involved in metal coordination; (ii) metal binding induces ionisation of Leu-148 and His-149 amide nitrogens that complete the donor set to copper(II) in the species dominant at neutral pH; (iii) the unusual coordination scheme of the His-Xxx-His-Xxx-His consensus sequence justifies the high specificity for Cu(II) when compared to SOD-like or albumin-like peptides or even in amyloid Abeta fragments. The present findings may represent the key for interpreting the observed requirement of His residues conservation for the redox cycling between Cu(II) and Cu(I) by soluble APP.     

Ultraviolet absorption spectra of pyridinium N-oxide perchlorates in acetonitrile

The UV Spectra of pyridinium N-oxide perchlorates were determined in acetonitrile and compared with the spectrum of pyridine N-oxide. The spectrum of pyridine N-oxide perchlorate is entirely different from the spectra of hydride-bis-pyridine N-oxide perchlorate and pyridine N-oxide. The spectrum of hydride-bis-pyridine N-oxide perchlorate/basic salt/ is similar to that of the conjugate base, but it is not a linear combination of the spectra of the protonated and the unprotanated base species.     

Influence of protonation on the geometry of 2-{[(2,6-dimethylphenoxy)ethyl]amino}-1-phenylethan-1-ol: crystal structures of the free base and of its chloride and 3-hydroxybenzoate salt forms

The aroxyalkylaminoalcohol derivatives are a group of compounds known for their pharmacological action. The crystal structures of four new xylenoxyaminoalcohol derivatives having anticonvulsant activity are reported, namely, 2-{[2-(2,6-dimethylphenoxy)ethyl]amino}-1-phenylethan-1-ol, C₁₈H₂₃NO₂, 1 , the salt N-[2-(2,6-dimethylphenoxy)ethyl]-1-hydroxy-1-phenylethan-2-aminium 3-hydroxybenzoate, C₁₈H₂₄NO₂⁺·C₇H₅O₃^?, 2 , and two polymorphs of the salt (R)-N-[2-(2,6-dimethylphenoxy)ethyl]-1-hydroxy-1-phenylethan-2-aminium chloride, C₁₈H₂₄NO₂⁺·Cl^?, 3 and 3p . Both polymorphs crystallize in the space group P2₁2₁2 and each has two cations and two anions in the asymmetric unit (Z′ = 2). The molecules in the polymorphs show differences in their molecular conformations and intermolecular interactions. The crystal packing of neutral 1 is dominated by intermolecular O—H…N hydrogen bonds, resulting in the formation of one-dimensional chains. In the crystal structures of the salt forms ( 2 , 3 and 3p ), each protonated N atom is engaged in a charge-assisted hydrogen bond with the corresponding anion. The protonation of the N atom also influences the conformation of the molecular linker between the two aromatic rings and changes the orientation of the rings. The crystal packing of the salt forms is dominated by intermolecular O—H…O hydrogen bonds, resulting in the creation of chains and rings. Structural studies have been enriched by the calculation of Hirshfeld surfaces and the corresponding fingerprint plots.