Preparation of methyl (1R,2S,5S)- and (1S,2R,5R)-2-amino-5-tert-butyl-cyclopentane-1-carboxylates by parallel kinetic resolution of methyl (RS)-5-tert-butyl-cyclopentene-1-carboxylate

Comparison of the kinetic and parallel kinetic resolutions of methyl (RS)-5-tert-butyl-cyclopentene-1-carboxylate allows for the efficient synthesis of both (1R,2S,5S)- and (1S,2R,5R)-enantiomers of methyl 2-amino-5-tert-butyl-cyclopentane-1-carboxylate.     

Molecular nitrides containing group 4 and 5 metals: single and double azatitanocubanes

Treatment of [[Ti(eta(5)-C(5)Me(5))(micro-NH)](3)(micro(3)-N)] (1) with the imido complexes [Ti(NAr)Cl(2)(py)(3)] (Ar=2,4,6-C(6)H(2)Me(3)) and [Ti(NtBu)Cl(2)(py)(3)] in toluene affords the single azatitanocubanes [[Cl(2)(ArN)Ti]( micro(3)-NH)(3)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]].(C(7)H(8)) (2.C(7)H(8)) and [[Cl(2)Ti](micro(3)-N)(2)(micro(3)-NH)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]] (3), respectively. Similar reactions of complex 1 with the niobium and tantalum imido derivatives [[M(NtBu)(NHtBu)Cl(2)(NH(2)tBu)](2)] (M=Nb, Ta) in toluene give the single azaheterometallocubanes [[Cl(2)(tBuN)M](micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]] (M=Nb (4), Ta (5)), both complexes react with 2,4,6-trimethylaniline to yield the analogous species [[Cl(2)(ArN)M](micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]].(C(7)H(8)) (Ar=2,4,6-C(6)H(2)Me(3), M=Nb (6.C(7)H(8)), Ta (7.C(7)H(8))). Also the azaheterodicubanes [M[micro(3)-N)(2)(micro(3)-NH)](2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)](2)].2C(7)H(8) [M=Ti (8.2C(7)H(8)), Zr (9.2C(7)H(8))], and [M[(micro(3)-N)(5)(micro(3)-NH)][Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)](2)].2 C(7)H(8) (Nb (10.2C(7)H(8)), Ta (11.2C(7)H(8))) were prepared from 1 and the homoleptic dimethylamido complex [M(NMe(2))(x)] (x=4, M=Ti, Zr; x=5, M=Nb, Ta) in toluene at 150 degrees C. X-ray crystal structure determinations were performed for 6 and 10, which revealed a cube- and double-cube-type core, respectively. For complexes 2 and 4-7 we observed and studied by DNMR a rotation or trigonal-twist of the organometallic ligands [[Ti(eta(5)-C(5)Me(5))(micro-NH)](3)(micro(3)-N)] (1) and [(micro(3)-N)(micro(3)-NH)(2)[Ti(3)(eta(5)-C(5)Me(5))(3)(micro(3)-N)]](1-). Density functional theory calculations were carried out on model complexes of 2, 3, and 8 to establish and understand their structures.     

Measurement of the electron distribution function in flowing afterglow plasma by means of Langmuir probe

Conclusion In the present report an attempt has been made to use the second derivative method for measurements of the electron distribution function in flowing afterglow plasma. It has been shown that using the cross-correlation technique, this method seems to be a useful tool for flowing afterglow plasma investigation.     

Use of non-aqueous capillary electrophoresis for the quality control of commercial saffron samples

A non-aqueous capillary electrophoresis (NACE) method for quantifying the seven crocin metabolites that are the major biologically active ingredients of saffron was developed. Separation is done by using a fused silica capillary filled with a 12.5 mM H3BO3/37.5 mM sodium tetraborate methanolic solution as background electrolyte. The results obtained were compared with the total index "safranal value", widely used as a quality measure of saffron products. The comparison revealed that the proposed NACE method provides useful information not obtained in the safranal value. Infact, samples with a similar safranal value can contain crocin metabolites in different concentrations and relative proportions. This new method is very useful for quality control in commercial saffron samples.     

Temperature dependence of second critical micelle concentration of dodecyldimethylbenzylammonium bromide in aqueous solution

The specific conductivity of dodecyldimethylbenzylammonium bromide (C12BBr) in aqueous solutions, in the temperature range of 15 to 40 °C, has been measured as a function of molality. The two breaks which were found on the conductivity against molality plots were attributed to the critical micelle concentration, cmc, and second critical micelle concentration, 2^nd cmc, respectively. The ratio of the slopes, S, of the three linear fragments on the plots, S2/S1 and S3/S1, was attributed to the degree of ionization of the micelles at cmc and 2^nd cmc respectively. It was shown that the values of the 2^nd cmc estimated above 27 °C are only apparent due to thermal disintegration of the micelles. In the temperature range of 15 to 27 °C, the values of the 2^nd cmc increase gradually and the plot of the 2^nd cmc against temperature is concave. The ratio of 2^nd cmc/cmc for C12BBr at 25 °C amounts to 15 and appears to be high compared to the literature values for other surfactants. For comparative purposes the cmc and 2^nd cmc values were also estimated conductometrically for decyldimethylbenzylammonium bromide (C10BBr) at 25 °C. The 2^nd cmc value for this surfactant is higher compared to the value for the C12 homologue by a factor of 2.6.The standard Gibbs free energies of micellization at cmc and at the 2^nd cmc were estimated from the experimental data for both surfactants at 25 °C.     

Comparative receptor mapping of serotoninergic 5-HT3 and 5-HT4 binding sites*

The clinical use of currently available drugs acting at the5-HT₄ receptor has been hampered by their lack of selectivityover 5-HT₃ binding sites. For this reason, there is considerableinterest in the medicinal chemistry of these serotonin receptor subtypes, andsignificant effort has been made towards the discovery of potent and selectiveligands. Computer-aided conformational analysis was used to characterizeserotoninergic 5-HT₃ and 5-HT₄ receptorrecognition. On the basis of the generally accepted model of the5-HT₃ antagonist pharmacophore, we have performed a receptormapping of this receptor binding site, following the active analog approach(AAA) defined by Marshall. The receptor excluded volume was calculated as theunion of the van der Waals density maps of nine active ligands(pK_i 8.9), superimposed in pharmacophoric conformations.Six inactive analogs (pK_i < 7.0) were subsequently used todefine the essential volume, which in its turn can be used to define theregions of steric intolerance of the 5-HT₃ receptor. Five activeligands (pK_i 9.3) at 5-HT₄ receptors wereused to construct an antagonist pharmacophore for this receptor, and todetermine its excluded volume by superimposition of pharmacophoricconformations. The volume defined by the superimposition of five inactive5-HT₄ receptor analogs that possess the pharmacophoric elements(pK_i 6.6) did not exceed the excluded volume calculated forthis receptor. In this case, the inactivity may be due to the lack of positiveinteraction of the amino moiety with a hypothetical hydrophobic pocket, whichwould interact with the voluminous substituents of the basic nitrogen ofactive ligands. The difference between the excluded volumes of both receptorshas confirmed that the main difference is indeed in the basic moiety. Thus,the 5-HT₃ receptor can only accommodate small substituents inthe position of the nitrogen atom, whereas the 5-HT₄ receptorrequires more voluminous groups. Also, the basic nitrogen is located at ca.8.0 Å from the aromatic moiety in the 5-HT₄ antagonistpharmacophore, whereas this distance is ca. 7.5 Å in the5-HT₃ antagonist model. The comparative mapping of bothserotoninergic receptors has allowed us to confirm the three-componentpharmacophore accepted for the 5-HT₃ receptor, as well as topropose a steric model for the 5-HT₄ receptor binding site. Thisstudy offers structural insights to aid the design of new selective ligands,and the resulting models have received some support from the synthesis of twonew active and selective ligands: 24 (K_i(5-HT₃)= 3.7 nM; K_i(5-HT₄) > 1000 nM) and 25(K_i(5-HT₄) = 13.7 nM;K_i(5-HT₃) > 10 000 nM).     

Synthesis and structure of the calixarene-like phosph(III)azane macrocycle [{P(mu-N(t)Bu)}2{1,5-(NH)2C10H6}]3

The reaction of [ClP(mu-NtBu)]2 with 1,5-diamino-naphthalene [1,5-(NH2)2C10H6] in Et3N-thf gives the trimeric macrocycle [{P(mu-NtBu)}2{1,5-(NH)2C10H6}]3(1); the X-ray structure of the toluene solvate 1.3toluene reveals a cone-shaped (calixarene-like) arrangement in which toluene guest molecules are trapped within the cavity.     

111In(111Cd) quadrupole interaction in the chalcogenide spinel CdCr2Se4

The¹¹¹Cd quadrupole coupling in the spinel CdCr₂Se₄ is investigated by TDPAC after different sample treatments. The experiments are consistent with Se vacancies causing the non-cubic probe environments and with the assumption that the majority of the¹¹¹In atoms are positioned at A-sites.     

Effect of grinding on thermal reactivity of ceramic clay minerals

The effect of grinding on thermal behavior of pyrophyllite and talc as commonly used ceramic clay minerals was investigated by DTA, TG, emanation thermal analysis (ETA), B.E.T. surface area (s.a.) measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). A vibratory mill was used in this study, grinding time was 5 min. It was found that the grinding caused an increase in surface area and a grain size reduction of the samples. From TG and DTA results it followed that grinding caused a decrease of the temperature at which the structure bound OH groups released. The formation of high temperature phases was enhanced with the ground samples. For the ground talc sample the crystallization of non-crystalline phase into orthorhombic enstatite was observed in the range of 800°C. For ground pyrophyllite a certain agglomeration of grains was observed in the range above 950°C. Moreover, for both clays the ETA characterized a closing up of subsurface irregularities caused by grinding as a decrease of the emanation rate in the range 250–400°C. The comparison of thermal analysis results with the results of other methods made it possible to better understand the effect of grinding on the ceramic clays.     

Organophosphines in PtP2Si2 derivatives – structural aspects

Abstract

In this review, the structural data of monomeric platinum(II) complexes with inner coordination spheres of Pt(η²-P₂L)(SiL)₂, Pt(η²-P₂L)(η²-Si₂L) and Pt(η²-P,SiL)₂ are classified and analyzed. These complexes crystallize in three crystal systems: monoclinic (8 examples), triclinic (4 examples) and orthorhombic (4 examples). Distorted square-planar environments about the Pt(II) atoms are built up by combination of homobi-P,P with two monodentate Si donor ligands; homobi-PP with homo-Si,Si donor ligands, or heterobi-P,Si donor ligands. The chelating ligands create metallacycles with the following angles: 65.0° (SiOSi) < 83.1° (SiC₂Si) < 85.2° (PC₂P) < 88.8° (SiSi₂Si)). The mean Pt-P and Pt-Si bond distances in Pt(η²-P₂L)·(SiL)₂ complexes are 2.319 and 2.365?Å; in Pt(η²-P₂L)(η²-Si₂L) the values are 2.316 and 2.360?Å. The complex [Pt{η²-Me₂P(C₂B₁₀H₁₀)SiMe₂}₂] exists in two isomeric forms, a monoclinic cis- and a triclinic trans-isomer. The structural data are compared and discussed with the complexes of inner coordination spheres: Pt(η²-P₂L)(XL)₂ (X?=?O, N, CN, BL, Cl, SL, SeL, Br, or I) and Pt(η²-P₂L)(η²-X₂L) (X?=?OL, NL, SL or SeL).