Liquid Chromatographic Resolution of Racemic α-Hydroxycarboxylic Acids on Ligand Exchange Chiral Stationary Phases

Two ligand exchange chiral stationary phases (CSPs) based on (S)-leucinol derivative, sodium N-((S)-1-hydroxymethyl-3-methylbutyl)-N-undecylaminoacetate, and (R)-phenylglycinol derivative, sodium N-((R)-2-hydroxy-1-phenylethyl)-N-undecylaminoacetate, covalently bonded to silica gel have been successfully applied in the resolution of nine -hydroxycarboxylic acids. The latter was more effective than the former, the separation factors () being 1.05 to 2.12 while the resolution factors (R_S) varying from 0.18 to 5.29 on the latter. The chromatographic resolution behaviors were dependent on the type and the content of organic modifier and the content of CuSO₄ in aqueous mobile phase and the column temperature. A possible chiral recognition mechanism was also proposed based on the chromatographic resolution behaviors.     

New determination method of the neutron diffraction system resolution at the Algerian Es-Salam research reactor

The aim of this article is to determine the resolution of the neutron diffraction system (NDS) installed around the Algerian Es Salam research reactor. By using a new method based on neutron radiography technique we have measured the beam divergence at the exit of Soller Collimator (α₂) and hence determine effective collimations. The determination of the adequate resolution of our NDS is performed on experimental results obtained from neutron diffraction patterns for different collimation divergences (α₂) and (α₃) values obtained from several apertures sizes (S ₂) and (S ₃).     

Enantioselective Catalysis CXLI [1]. Tridentate Ligands with 1-(Pyridin-2-yl)ethylamine as Chiral Building Block in the Enantioselective Transfer Hydrogenation of Acetophenone

Summary.  A series of novel tridentate ligands with nitrogen and oxygen donor sites was synthesized starting from enantiomerically pure (S)- and (R)-1-(pyridin-2-yl)ethylamine, the preparation and resolution of which was developed. The new optically active ligands were tested as in situ catalysts together with Ru(PPh₃)₃Cl₂ in the enantioselective transfer hydrogenation of acetophenone with isopropanol. The secondary amine ligand (S)-2,4-di-tert-butyl-6-(1-(pyridin-2-yl)ethylamino)methylphenol gave the best results with almost quantitative conversion and 47%ee. Received August 17, 2001. Accepted August 27, 2001     

Angle‐resolved XPS of fluorinated and semi‐fluorinated side‐chain polymers

Angle‐resolved XPS data (elemental quantification and high‐energy‐resolution C 1s) are presented for ten polymers with side‐chains of the form ? OCO(CF₂)_yF, ? COO(CH₂)₂OCO(CF₂)_yF (y = 1, 2, 3) and ? COO(CH₂)_x(CF₂)_yF (x = 1, y = 1, 2, 3; x = 2, y = 8). Particular attention was paid to charge compensation and speed of data acquisition, with co‐addition from multiple fresh samples to give spectra with good energy resolution and good signal‐to‐noise ratio free from the effects of x‐ray‐induced degradation. Water contact angles for the polymers are also reported. The XPS data demonstrate preferential surface segregation of fluorine‐containing groups for all but the shortest side‐chain polymer, where the ? OCOCF₃ side‐chain either does not surface segregate or is too short for surface segregation to be detectable by angle‐resolved XPS. In the other polymers studied the relative positions of functional groups in the side‐chains correlate with the angle‐resolved behaviour of the corresponding C 1s components. This shows that the surface side‐chains are oriented towards the polymer surface. For the ? COO(CH₂)₂OCO(CF₂)_yF (y = 1) side‐chain, the angle‐resolved C 1s data suggest reduced ordering and linearity compared with y = 2 and 3. For any particular series of polymers, e.g. ? COO(CH₂)_x(CF₂)_yF, the water contact angles increase with y, consistent with burying of the hydrophilic ester groups as y increases. For any particular value of y the sequence of water contact angles is ? COO(CH₂)_x(CF₂)_yF > ? OCO(CF₂)_yF ～ ? COO(CH₂)₂OCO(CF₂)_yF, suggesting greater ordering and density of fluorocarbon species at the surface of the ? COO(CH₂)_x(CF₂)_yF side‐chain polymers compared with the other polymers studied. For the ? COO(CH₂)₂(CF₂)₈F polymer a water contact angle of 124° is measured, which is greater than that of poly(tetrafluoroethene). The ? COO(CH₂)₂OCO(CF₂)F polymer is unusual in that it shows a particularly low water contact angle (83° ), suggesting that the probe fluid is able to sense both ester groups, consistent with the reduced ordering of the side‐chain detected by angle‐resolved XPS. Copyright © 2004 John Wiley & Sons, Ltd.     

Racemic Tartrate/Malate Anions Combine with Racemic Complex Cations to Form Optically Active Ionic Crystals

Spontaneous resolution has attracted continuing attention in various research fields since Pasteur's work on the crystallization behavior of racemic tartrate. Here, a unique example of this phenomenon is reported, involving ionic crystals generated from racemic RR/SS- tartrate or R/S-malate and racemic ΔΔ/ΛΛ-[Ag₃Rh₂(2-aminoethanethiolato)₆]³⁺ (ΔΔ/ΛΛ-[ 1 ]³⁺) in water. RR- and SS-tartrate selectively recognize the ΛΛ and ΔΔ isomers of [ 1 ]³⁺ to produce ionic crystals of (ΛΛ-[ 1 ])₂(RR-tartrate)₃ and (ΔΔ-[ 1 ])₂(SS-tartrate)₃, respectively, which can undergo spontaneous resolution. While spontaneous resolution also occurs when using R/S-malate, R- and S-malate select the opposite isomers of [ 1 ]³⁺ to give ionic crystals of (ΔΔ-[ 1 ])₂(R-malate)₃ and (ΛΛ-[ 1 ])₂(S-malate)₃, respectively. In the presence of S-aspartate, (ΛΛ-[ 1 ])₂(R-tartrate)₃ and (ΔΔ-[ 1 ])₂(S-tartrate)₃ are preferentially crystallized from ΔΔ/ΛΛ-[ 1 ]³⁺ and RR/SS-tartrate at solution pH values of 6 and 10, respectively. This finding provides significant insight into the optical resolution of chemical species by spontaneous resolution and the origin of homochirality in nature.     

Pseudomonas sp. Lipase Immobilized on Magnetic Porous Polymer Microspheres as an Effective and Recyclable Biocatalyst for Resolution of Allylic Alcohols

Magnetic porous polymeric microspheres containing epoxy groups were prepared by suspension polymerization (denoted as magnetic Fe₃O₄@GEM microspheres). Fe₃O₄@GEM with a specific surface area of 30.41 m²/g, average pore diameter of 17.13 nm, and pore volume of 0.13 cm³/g exhibited superparamagnetic behavior with the saturation magnetization of 7.1 emu/g. The content of epoxy groups on Fe₃O₄@GEM was 0.22 mmol/g. Pseudomonas sp. lipase (PSL) was covalently immobilized onto the Fe₃O₄@GEM microspheres through the reaction between the amino groups of the enzyme and the epoxy groups on the microspheres. PSL/Fe₃O₄@GEM exhibited enhanced enantioselectivity for the resolution of allylic alcohol to the corresponding optically active (S)‐allylic alcohol and (R)‐allylic alcohol acetate compared to free PSL. The enantiomeric excess of (S)‐l‐pheny‐2‐propen‐1‐ol for the former (98.1%) was 81.7 times that of the latter (1.2%) when the immobilized PSL was used for transesterification resolution of (R,S)‐l‐pheny‐2‐propen‐1‐ol. Furthermore, the ee_s and ee_p values were still retained at 95.2% and 95.4% after PSL/Fe₃O₄@GEM was recycled 10 times, indicating that PSL/Fe₃O₄@GEM had very good reusability. In addition, the transesterification resolution of (R,S)‐1‐(4‐methylphenyl)‐2‐propen‐1‐ol and (R,S)‐1‐(4‐bromophenyl)‐2‐propen‐1‐ol was catalyzed by PSL/Fe₃O₄@GEM, affording ideal ee_s and ee_p values of 99.3%, 97.4% and 99.6%, 98.2%, respectively. Therefore, PSL/Fe₃O₄@GEM demonstrated its potential as a highly efficient enzymatic reactor and Fe₃O₄@GEM would be very promising carriers for immobilizing enzymes in industrial application.     

STEREOCHEMISTRY OF SIX-COORDINATE OCTAHEDRAL SILICON(IV) COMPLEXES CONTAINING 2,2-BIPYRIDINE

Abstract

[Si(bpy)₃]⁴⁺ (bpy = 2,2′-bipyridine), synthesized from Sil₄ and 2′.-bipyndine. was optically resolved by a chromatographic method using an SP-Sephadex C-25 column as an adsorbent and a 0.16M aqueous solution of sodium (2R,3R)-(-)-O,O′-dibenzoyltartrate as an eluent. The optical isomers were characterized by measurement of their electronic absorption, circular dichroism, and ¹H NMR spectra. The chromatographic resolution of [SKbpyb]⁴⁺ was also attempted with an aqueous solution of potassium [(2R,3R)-(+)-tartrato]antimonate(III). sodium (2R,3R)-(+)-hydrogentartrate, and sodium (2R,3R)-(+)-tartrate as eluents. Force-field calculations were used to elucidate the chromatographic elution mechanism. [Si(OH)₂(bpy)₂]I₂was also synthesized from Sil₄ and 2′,-bipyridine. The optical resolution of this complex was achieved with sodium [(2R,3R)-(+)-tartrato]antimonate(III).     

Development of new isothiocyanate-based chiral derivatizing agent for amino acids

Summary (1S,2S)-1,3-Diacetoxy-1-(4-nitrophenyl)-2-propylisothiocyanate [(S,S)-DANI] has been developed as a new chiral derivatizing agent for resolution of compounds containing an amino group. The reagent is readily available in both enantiomeric forms. Its applicability was demonstrated by the resolution of representative α-amino acids. The diastereomeric thiourea derivatives produced were separated by reversed-phase (C₁₈) high-performance liquid chromatography, with mixtures of 0.1% aqueous trifluoroacetic acid (pH∼2) and methanol as eluents.     

The effect of analyte lipophilicity on the resolution of α-amino acids on a HPLC chiral stationary phase based on crown ether

The effect of analyte lipophilicity on the resolution of α-amino acids on a chiral stationary phase based on chiral crown ether has been examined by the chromatographic resolution trends for the resolution of a homologous series of five α-amino acids with an alkyl group of different length at the chiral center. The retention factors (k₁ and k₂) for the two enantiomers and the separation factors (α) were found to depend on the lipophilicity of the α-amino acid. In general, the retention factors increased as the organic modifier content in the mobile phase increased, the degree of the enhancement of retention factors being dependent on the analyte lipophilicity. The separation factors also increased as the analyte lipophilicity and the organic modifier content in the mobile phase increased. Possible rationales for these behaviors have been proposed.     

Effect of alkali metals and metal-ammonia complexes on electroosmosis,effective field strength,and resolution in the separation of diuretics by CZE

The counter ion in CZE separation systems affects resolution, effective field strength and electroosmosis. Alkali metals (lithium, sodium, potassium, and cesium), the ammonium ion, and several complexes of metals with ammonia ([Ag(NH₃)₂]⁺, [Cu(NH₃)₄]²⁺, [Zn(NH₃)₄]²⁺, [Cd(NH₃)₄]²⁺, [Ni(NH₃)₆]²⁺, and [Co(NH₃)₆]²⁺) have been studied for their effect on the separation of diuretics. With the alkali metals the electroosmotic flow velocity decreased and the effective field strength and resolution increased as the hydrated radius of the alkali metal decreased. All the metal-ammonia complexes except that with silver greatly reduced the electroosmotic flow velocity (V_eo) and had only a slight effect on the effective field strength (E_eff). Because these complexes had a negligible effect on the ionic strength of the buffer, they enabled high separating power to be maintained during the separation, and hence the use of more energy in the separation system. This yielded better resolution of the compounds, but the analysis time was then compromised. A simultaneous reduction in capillary length and V_eo while maintaining the high voltage enabled increased resolution without an increase in analysis time. The ability to control V_eo by adding small concentrations (< 100 μM ) of metal complexes to the buffer solution makes it possible to adjust the analysis time and capillary length independently while employing high separation power.     

Enantioselective Fluorogenic Assay of Acetate Hydrolysis for Detecting Lipase Catalytic Antibodies

An enantioselective fluorogenic assay for the kinetic resolution of chiral alkyl acetates is demonstrated with 7-(3-acetoxybutoxy)-2H-1-benzopyran-2-ones (R)- and (S)- 4 or 7-(3-acetoxy-2-methylpropoxy)-2H-1-benzopyran-2-ones (R)- 4 and (S)- 6 . The alcohols released by hydrolysis of these acetates are oxidized by horse-liver alcohol dehydrogenase to unstable β-(aryloxy)carbonyl compounds, which undergo β-elimination of the strongly fluorescent product umbelliferone (=7-hydroxy-2H-1-benzopyran-2-one; 3 ) (λ_em=460±20 nm, λ_ex=360±20 nm). Enantioselectivities are calculated from the reaction rates for each enantiomeric acetate. For a series of representative lipases, the reactivities and enantioselectivities under preparative conditions are predicted accurately. This highly sensitive enantioselective assay detects as little as 10 μg/ml of hydrolytic enzyme, can be carried out in 96-well microtiter plates, and is compatible with cell-culture media. It is, therefore, suited for screening libraries of antibodies for enantioselective lipase catalytic antibodies.     

Synthesis and Characterization of Intramolecularly Stabilized Chiral Dimethylindium Alkoxides and their Use as Cross Coupling Reagents

The enantiomerically pure dimeric N, O‐5‐chelates [Me₂In(μ‐OCH₂CH(R)NMe₂)]₂ {R = Me (S) ( 2 ); R = ⁱPr (S) ( 3 ); R = ⁱBu (S) ( 4 ); R = Bz (S) ( 5 )}, and [Me₂In‐{μ‐(1R, 2S)‐OCH(Ph)CH(Me)NMe₂}]₂ ( 6 ), as well as the achiral dimeric N, O‐6‐chelate [Me₂In(μ‐O(CH₂)₃NMe₂)]₂ ( 7 ) have been synthesized from trimethylindium and equimolar amounts of the corresponding enantiomerically pure dimethylamino alcohols or of the achiral dimethylaminopropanol by elimination of methane. Their ¹H NMR, ¹³C NMR, and mass spectra as well as the X‐ray single crystal structure analyses of [Me₂In{μ‐O(CH₂)₂NMe₂}]₂ ( 1 ), 3, 5, 6 and 7 are described and discussed. The coordinative N→In bonds of the five‐coordinate indium complexes show dynamic dissociation/association processes. 1—6 were found to be useful reagents for the partial kinetic resolution of 2‐carbomethoxy‐1, 1′‐binaphthyl triflate.     

Ezetimibe anhydrate,determined from laboratory powder diffraction data

Ezetimibe {systematic name: (3R,4S)‐1‐(4‐fluorophenyl)‐3‐[(3S)‐3‐(4‐fluorophenyl)‐3‐hydroxypropyl]‐4‐(4‐hydroxyphenyl)azetidin‐2‐one}, C₂₄H₂₁F₂NO₃, is used to lower cholesterol levels by inhibiting cholesterol resorption in the human intestine. The crystal structure of ezetimibe anhydrate was solved from laboratory powder diffraction data by means of real‐space methods using the program DASH [David et al. (2006). J. Appl. Cryst. 39 , 910–915]. Subsequent Rietveld refinement with TOPAS Academic [Coelho (2007). TOPAS Academic User Manual. Version 4.1. Coelho Software, Brisbane, Australia] led to a final R_wp value of 8.19% at 1.75 Å resolution. The compound crystallizes in the space group P2₁2₁2₁ with one molecule in the asymmetric unit. The molecules are closely packed and two intermolecular hydrogen bonds form an extended hydrogen‐bond architecture.     

Ab-initio calculation of resonance states of H2O

In a dissociation attachment experiment of water, three peaks were observed at 7,9, and 12 eV. The origin of the third peak has been believed to be ²B². However, the calculated energy of this state is 0.6 eV higher than the experimental value. This discrepancy is quite large compared with the case of the lower two peaks. In this study we propose new candidates for resonant states responsible for the third peak. The configurations considered are (3a₁)^?1(3pa₁)², (3a₁)^?1(3pb₁)², (3a₁)^?1(3pb₂)², (3a₁)^?1(3pa₁)¹(3pb₁)¹, (3a₁)^?1(3pb₂)¹(3pa₁)¹, and (3a₁)^?1(3pb₂)¹(3pb₁)¹ which have the parent state (3a₁)^?1(3pa₁)¹, (3a₁)^?1(3pb₁)¹, or (3a₁)^?1(3pb₂)¹. The energy levels arising from these configurations are calculated by a method of configuration interaction. A Few resonance states, which could be responsible for the third peak, are found. New decay process of these states are proposed.     

Bestimmung des Chiralitätssinns der enantiomeren 2,6-Adamantandiole

Determination of the Chirality Sense of the Enantiomeric 2,6-Adamantanediols The enantiomers of 2,6-adamantanediol ( 1 ) are resolved via the diastereoisomeric camphanoates. The (2R,6R)-chirality sense for (?)- 1 and (2S,6S) for (+)- 1 was determined by chemical correlation with (?)-(1R,5R)-bicyclo[3.3.1]nonan-2,6-dion ((1R,5R)- 3 ) of known absolute configuration in the following way: alkylation of the bis(pyrrolidine enamine) of (?)-(1R,5R)- 3 with CD₂I₂ and hydrolysis of the product gives the enantiomer 4 of (4,4-D₂)-2,6-adamantanedione. Reduction of 4 with LiAlH₄ leads to one enantiomer (Scheme 2) of each of the three diols 5 – 7 of known absolute configuration. The three diols are themselves configurational isomers due to the presence of the CD₂ group, but correspond otherwise entirely to the enantiomeric diols 1 . Accordingly, they can also be separated by means of their diastereoisomeric camphanoates to give the diols 5 / 6 and 7 . These samples are easily distinguished and identified by their characteristic ¹H-NMR spectra (cf. Fig. 2). This allows to identify the (2R,6R)- and (2S,6S)-enantiomer of 1 on the basis of their behavior in the resolution experiment analogous to that of the diols 5 / 6 and 7 , respectively. The diol (?)- 1 must have the (2R,6R)-configuration because it forms, like the diols 5 / 6 , with (?)-camphanic acid the diastereoisomeric ester less soluble in benzene. The diol (+)- 1 has (2S,6S)-configuration, because it forms, like 7 , with (+)-camphanic acid the diastereoisomeric ester less soluble in benzene. The bis(4-methoxybenzoate) of (?)-(2R,6R)- 1 shows chiroptical properties which are in accordance with Nakanishi's rule for two chromophores having coupled electric dipol transition moments arranged with a left-handed torsion angle.     

Syntheses and pharmacological characterization of achiral and chiral enantiopure C/Si/Ge-analogous derivatives of the muscarinic antagonist cycrimine: a study on C/Si/Ge bioisosterism

The C/Si/Ge-analogous compounds rac-Ph(c-C₅H₉)El(CH₂OH)CH₂CH₂NR₂ (NR₂=piperidino; El=C, rac-3a; El=Si, rac-3b; El=Ge, rac-3c) and (c-C₅H₉)₂El(CH₂OH)CH₂CH₂NR₂ (NR₂=piperidino; El=C, 5a; El=Si, 5b; El=Ge, 5c) were prepared in multi-step syntheses. The (R)- and (S)-enantiomers of 3a–c were obtained by resolution of the respective racemates using the antipodes of O,O′-dibenzoyltartaric acid (resolution of rac-3a), O,O′-di-p-toluoyltartaric acid (resolution of rac-3b), or 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate (resolution of rac-3c). The enantiomeric purities of (R)-3a–c and (S)-3a–c were ≥98% ee (determined by ¹H-NMR spectroscopy using a chiral solvating agent). Reaction of rac-3a–c, (R)-3a–c, (S)-3a–c, and 5a–c with methyl iodide gave the corresponding methylammonium iodides rac-4a–c, (R)-4a–c, (S)-4a–c, and 6a–c (3a–c→4a–c; 5a–c→6a–c). The absolute configuration of (S)-3a was determined by a single-crystal X-ray diffraction analysis of its (R,R)-O,O′-dibenzoyltartrate. The absolute configurations of the silicon analog (R)-4b and germanium analog (R)-4c were also determined by single-crystal X-ray diffraction. The chiroptical properties of the (R)- and (S)-enantiomers of 3a–c, 3a–c·HCl, and 4a–c were studied by ORD measurements. In addition, the C/Si/Ge analogs (R)-3a–c, (S)-3a–c, (R)-4a–c, (S)-4a–c, 5a–c, and 6a–c were studied for their affinities at recombinant human muscarinic M₁, M₂, M₃, M₄, and M₅ receptors stably expressed in CHO-K1 cells (radioligand binding experiments with [³H]N-methylscopolamine as the radioligand). For reasons of comparison, the known C/Si/Ge analogs Ph₂El(CH₂OH)CH₂CH₂NR₂ (NR₂=piperidino; El=C, 7a; El=Si, 7b; El=Ge, 7c) and the corresponding methylammonium iodides 8a–c were included in these studies. According to these experiments, all the C/Si/Ge analogs behaved as simple competitive antagonists at M₁–M₅ receptors. The receptor subtype affinities of the individual carbon, silicon, and germanium analogs 3a–8a, 3b–8b, and 3c–8c were similar, indicating a strongly pronounced C/Si/Ge bioisosterism. The (R)-enantiomers (eutomers) of 3a–c and 4a–c exhibited higher affinities (up to 22.4 fold) for M₁–M₅ receptors than their corresponding (S)-antipodes (distomers), the stereoselectivity ratios being higher at M₁, M₃, M₄, and M₅ than at M₂ receptors, and higher for the methylammonium compounds (4a–c) than for the amines (3a–c). With a few exceptions, compounds 5a–c, 6a–c, 7a–c, and 8a–c displayed lower affinities for M₁–M₅ receptors than the related (R)-enantiomers of 3a–c and 4a–c. The stereoselective interaction of the enantiomers of 3a–c and 4a–c with M₁–M₅ receptors is best explained in terms of opposite binding of the phenyl and cyclopentyl ring of the (R)- and (S)-enantiomers. The highest receptor subtype selectivity was observed for the germanium compound (R)-4c at M₁/M₂ receptors (12.9-fold).     

Crystal Structure of the [(C5H4BMe2)2Fe]‐4,4′‐bipyridine Polymer from High Resolution X‐Ray Powder Diffraction

The crystal structure of [(C₅H₄BMe₂)₂Fe]‐4,4′‐bipyridine [ 2 · bipy]_n has been determined by the method of simulated annealing from high resolution X‐ray powder diffraction at room temperature. The compound is of interest, because it proves that highly ordered organometallic macromolecules can be formed in the solid state via the self‐assembly of N–B‐donor‐acceptor bonds. [ 2 · bipy]_n crystallizes in the triclinic space group, P 1, Z = 2, with unit cell parameters of a = 8.3366(2) Å, b = 11.4378(3) Å, c = 12.6740(5) Å, α = 112.065(2)°, β = 108.979(1)°, γ = 90.551(2)°, and V = 1047.06(6) ų. For the structure solution of [ 2 · bipy]_n 11 degrees of freedom (3 translational, 3 orientational, 5 torsion angles) were determined within several hours, demonstrating that the crystal packing and the molecular conformation of medium sized (< 50 non‐hydrogen atoms) coordination compounds can nowadays be solved routinely from high resolution powder diffraction data.     

Magnetic Relaxation Studies on Trigonal Bipyramidal Cobalt(II) Complexes

We report the preparation and the full characterization of a novel mononuclear trigonal bipyramidal Co^II complex [Co(NS₃^iPr)Br](BPh₄) ( 1 ) with the tetradentate sulfur‐containing ligand NS₃^iPr (N(CH₂CH₂SCH(CH₃)₂)₃). The comparison of its magnetic behaviour with those of two previously reported compounds [Co(NS₃^iPr)Cl](BPh₄) ( 2 ) and [Co(NS₃^tBu)Br](ClO₄) ( 3 ) (NS₃^tBu=N(CH₂CH₂SC(CH₃)₃)₃) with similar structures shows that 1 displays a single‐molecule magnet behaviour with the longest magnetic relaxation time (0.051 s) at T=1.8 K, which is almost thirty times larger than that of 3 (0.0019 s) and more than three times larger than that of 2 (0.015 s), though its effective energy barrier (26 cm^?1) is smaller. Compound 1 , which contains two crystallographically independent molecules, presents smaller rhombic parameters (E=1.45 and 0.59 cm^?1) than 2 (E=2.05 and 1.02 cm^?1) and 3 (E=2.00 and 0.80 cm^?1) obtained from theoretical calculations. Compounds 2 and 3 have almost the same axial (D) and rhombic (E) parameter values, but present a large difference of their effective energy barrier and magnetic relaxation which may be attributed to the larger volume of BPh₄^? than ClO₄^? leading to larger diamagnetic dilution (weaker magnetic dipolar interaction) for 2 than for 3 . The combination of these factors leads to a much slower magnetic relaxation for 1 than for the two other compounds.     

Luminescent dual sensor for time-resolved imaging of pCO2 and pO2 in aquatic systems

An optical dual sensor for the two-dimensional detection of pCO₂ and pO₂ is described. Tris(tetraoctylammonium)-8-hydroxypyrene-1,3,6-trisulfonate ((TOA)₃HPTS) acting together with the lipophilic buffer tetraoctylammonium hydrogen carbonate ((TOA)HCO₃) as pCO₂-sensing system along with the oxygen indicator tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) bis(3-(trimethylsilyl)-1-propanesulfonate) (Ru(dpp)₃TMS₂) are incorporated into a single layer ethyl cellulose matrix. A second layer of black silicone rubber served as an optical isolation. The two indicators were simultaneously excited with a 460-nm LED, and a fast-gateable CCD camera was used as the detector. The time-gated imaging scheme enables the mapping of pCO₂ and pO₂ within one measurement, where images in three different time windows during and after a series of square-shaped excitation pulses are recorded. A numerical evaluation method for the resolution of the single parameter maps from these three overall images is described. The response of the sensor has been optimized for use in aquatic systems.     

Preparation and in vitro investigations of triphenyl[ω‐(tetrahydro‐2H‐pyran‐2‐yloxy)alkyl]tin(IV) compounds

The reaction of SnPh₃Li with X(CH₂)_n O–THP (THP = tetrahydro‐2H ‐pyran‐2‐yl; n  = 3, 4, 6, 8, 11; X = Cl, Br) afforded organotin(IV) compounds with the general formula Ph₃Sn(CH₂)_n O–THP ( 1 – 5 ). The tetraorganotin(IV) compounds were characterized using multinuclear NMR and infrared spectroscopies and high‐resolution mass spectrometry. Anticancer activity of the synthesized compounds was tested in vitro against the A2780 (ovarian), A549 (lung), HeLa (adenocarcinoma) and SW480 (colon) tumour cell lines with SRB assay. The in vitro investigations revealed that when a shorter chain was present a higher activity was achieved; however compounds 1 – 5 were found to be less active than cisplatin. In addition, the most active compound, 1 , enters A2780 cells and causes apoptosis by triggering both intrinsic and extrinsic caspase pathways.