Rafal Kruszynski

New bond-valence parameters for lanthanides.

The bond-valence method, especially the valence-sum rule, is very useful for checking if the structures formed by trivalent lanthanides are correct. In this work bond-valence parameters (Rij), which connect bond valences and bond lengths, have been computed for a large number of bonds taken from the Cambridge Structural Database, Version 5.24 (2002) [Allen (2002). Acta Cryst. B58, 380-388]. The calculated values of bond-valence parameters for metal-organic compounds decrease with an increase in lanthanide atomic number; the Rij values are also smaller than bond-valence parameters calculated for inorganic compounds. A summary of bond-valence sums calculated for Rij given in this work and reported in the literature, and a functional correlation between lanthanide-oxygen distances and coordination number are presented.

AIDS-related lymphoma screen results and molecular structure determination of a new crown ether bearing aziridinylcyclophosphazene, potentially capable of ion-regulated DNA cleavage action

The tetraaziridinyl PNP-lariat ether has been tested in the in vitro disease-oriented antitumor screen and evaluated further in an investigational AIDS-related lymphoma screen in vitro. This compound shows remarkable cytostatic activity. The crystal and molecular structure has been determined. The PNP-lariat ether has a pseudo-mirror plane perpendicular to the ring plane. The crown ether has an internal pseudo-threefold axis of symmetry. The so-called macrocyclic CC shortening effect is observed in the crown ether. All crown ether oxygen atoms are directed toward the interior of the ring and exist in an almost ideal envelope conformation. The cyclophosphazene ring is distorted from planarity and all PN bond lengths within the ring are equal with the mean value being 1.588(3) A.

Enzymatic degradation studies of endomorphin-2 and its analogs containing N-methylated amino acids

In this paper, we describe the synthesis of novel endomorphin-2 analogs, containing N-methylated amino acids, consecutively in each position. The receptor-binding profile of the new analogs and their stability against enzymatic cleavage by commercially available peptidases, carboxypeptidase Y and aminopeptidase M, and a rat brain homogenate are reported. The best analog of this series, [Sar2]endomorphin-2, was almost equipotent with the parent peptide in the mu-receptor-binding assay and was also highly resistant to enzymatic degradation. This analog may be a suitable candidate for the in vivo antinociceptive studies.

New lanthanide-nitrogen bond-valence parameters.

The bond-valence parameters (R(ij)), which connect bond valences and bond lengths, have been computed for lanthanide-nitrogen bonds. It has been found that values of bond-valence parameters decrease with increasing lanthanide atomic number in coordination compounds, and that they are smaller than the R(ij) parameters of inorganic compounds. As expected, the lanthanide-nitrogen bond-valence parameters are larger than lanthanide-oxygen bond-valence parameters. There are no obvious dependencies between the number of N atoms in the coordination sphere and the bond-valence parameter value.

Bond-valence parameters of lanthanides.

Ln-O and Ln-N bond-valence parameters have been computed in coordination complexes for lanthanides (Ln) at oxidation states other than +3 (Ce(IV), Sm(II), Eu(II) and Yb(II)). Moreover, Ln-Cl, Ln-S and Ln-C(pi-bonded) bond-valence parameters are presented, as calculated for coordination compounds. In general, the bond-valence parameters decrease in the order Ln-O > Ln-C > Ln-N > Ln-Cl > Ln-S. It has been found that the values of bond-valence parameters decrease with increasing lanthanide atomic number for coordination compounds. As expected, the values of lanthanide-oxygen and lanthanide-nitrogen bond-valence parameters diminish with increasing lanthanide oxidation state. Several examples are given where the total valence of the lanthanide ion is apparently incorrectly assigned, as well as cases where bond-valence method calculations confirm the doubtful oxidation state assignment.

Conformationally Restricted Peptides as Tools in Opioid Receptor Studies

The discovery of endogenous opioid peptides with their limited receptor selectivity more than two decades ago implicated their involvement in analgesia and initiated efforts to understand the molecular mechanisms underlying their action. Opioid peptides mediate their physiological and pharmacological effects through three major opioid receptor types (mu, delta, kappa), but the role of each of these receptors is not easy to distinguish. There has therefore, been an increasing need for potent and selective agonists and antagonists in this area. The incorporation of conformational constraints into analogs of biologically active peptides is a well-known approach for enhancing receptor selectivity and modulating efficacy. Conformational restriction has proven a valuable means for assessing disparities between the peptide binding characteristics at each of the opioid receptor types, since peptide analogs designed with appropriate conformational constraints possess the ability to adopt the conformation required for interaction at one receptor type but not another. In efforts to obtain better conformational integrity various conformationally restricted analogs of endogenous opioid peptides have been developed. In this paper we review the development of opioid analogs whose conformation was restricted either globally through different types of cyclization (such as amide bond formation, disulfide and monosulfide bridges, carbonyl and amine bridges) or locally, through incorporation of side-chain conformational constraints at a specific amino acid residue by synthesizing cyclic amino acids or constraining torsion angles by suitable substitutions. These two approaches have led to the development of potent and very selective agonists and antagonists at all three opioid receptor types.

Coordination assemblies of CdII with 2,2′:6′,2′′-terpyridine (terpy), 2,3,5,6-tetra-(2-pyridyl)pyrazine (tppz) and pseudohalide ions – structural diversification and luminescence properties

Nine new terpy- or tppz-containing cadmium(II) coordination compounds, [Cd(μ1,5-dca)(NO3)(terpy)]n (1), [Cd(μ1,5-dca)(terpy)(H2O)]n·n(dca) (2), [Cd(μ1,3-N3)(NO3)(terpy)]n (3), [Cd(N3)(NO3)(terpy)(H2O)] (4), [Cd2(μ1,1-N3)2(N3)2(terpy)2] (5), [Cd(μ1,5-dca)(NO3)(tppz)]n (6), [Cd(dca)(NO3)(tppz)(H2O)] (7), [Cd2(μ1,1-N3)2(NO3)2(μ-tppz)]n·2nMeOH (8) and [Cd2(μ1,1-N3)(μ1,3-N3)(m-tppz)]n (9), have been successfully synthesized in the reaction of Cd(NO3)2 with multidentate N-heterocyclic ligands and inorganic ions (N3− and N(NC)2− abbreviated as dca−). The resulting compounds were structurally characterized by single crystal X-ray diffraction analysis and further characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (XRPD), and thermogravimetric analyses (TGA). The X-ray studies demonstrated a cooperative impact of the polypyridyl ligand and the auxiliary inorganic ion on the final molecular architectures of cadmium(II) coordination compounds. Different topologies, ranging from mononuclear molecular to two-dimensional coordination networks, were confirmed for 1–9. The photoluminescence behaviour of 1–9 was also discussed. All of these coordination compounds are luminescent in the solid state, with the emission maxima varying in the visible light region within the range of 460–600 nm. The difference in emission behaviour for 1–9 is attributed to the coordination environments of the metal ions and the rigidity of solid-state crystal packing.

Synthesis, molecular, crystal and electronic structure of [ RuCl 2 ( PPh 3 ) 2 ( C 3 N 2 H 4 ) 2 ]

The reaction of ½RuCl2ðPPh3Þ3� complex with pyrazole has been examined. A new ruthenium complex – ½RuCl2 ðPPh3Þ2ðC3N2H4Þ2� has been obtained and characterised by IR and UV–Vis measurements. Crystal and molecular structure of the complex has been determined. 2003 Elsevier Science B.V. All rights reserved.

Reactivity of [ReOX3(AsPh3)2] (X = Cl, Br) complexes towards gaseous nitric oxide. Crystal, molecular and electronic structure of [ReBr3(NO)(OAsPh3)2], [ReCl3(NO)(AsPh3)2][ReCl4(AsPh3)2], [ReCl4(OASPh3)2] and [ReBr3(NO)(AsPh3)2]

Abstract The reactions of the complexes [ReOX 3 (AsPh 3 ) 2 ] (X=Cl, Br) with gaseous nitric oxide and the reactions of the compounds [NBu 4 ] 2 [ReX 5 (NO)] (X=Cl, Br) with an excess of triphenylarsine have been examined. [ReOBr 3 (AsPh 3 ) 2 ] reacts with nitric oxide to give mer , cis -[ReBr 3 (NO)(OAsPh 3 ) 2 ] ( 1 ), whereas the reaction of the chlorine oxocomplex with NO leads to three products: [ReCl 3 (NO)(OAsPh 3 ) 2 ] ( 2 ), mer , trans -[ReCl 3 (NO)(AsPh 3 ) 2 ][ReCl 4 (AsPh 3 ) 2 ] ( 3 ) and cis -[ReCl 4 (OAsPh 3 ) 2 ] ( 4 ). The compounds [NBu 4 ] 2 [ReX 5 (NO)] (X=Cl, Br) react with an excess of AsPh 3 to give 3 and mer , trans -[ReBr 3 (NO)(AsPh 3 ) 2 ] ( 5 ), respectively. The complexes obtained in these reactions have been characterised by IR, UV–Vis and magnetical measurements. Crystal and molecular structures have been determined for complexes 1 and 3 – 5 . EPR spectra have been recorded for compounds 1 and 5 .

Synthesis, spectroscopic characterization, X-ray structure, and DFT calculations of (Cu(tppz)(SCN) 2 )

This article presents a combined experimental and computational study of [Cu(tppz)(SCN)2], where ttpz stands for 2,3,5,6-tetra-(2-pyridyl)pyrazine. The compound has been studied by IR, UV–Vis spectroscopy, and single crystal X-ray analysis. The geometry around copper atom may be described as a distorted square pyramid. The equatorial plane is defined by three nitrogen atoms of tppz and one nitrogen atom of thiocyanate group. The apical site is occupied by nitrogen atom of the second SCN− ion. The electronic spectrum of [Cu(tppz)(SCN)2] was analyzed, and bands were assigned through the DFT/TDDFT procedures.