bluuebunny/crossref_metadata_2025 huggingface dataset:
Heterometallic Molecular Squares and Polymers Based On Self‐Assembly Reactions of Multiply Bonded Dirhenium Complexes
Authors: Bera Jitendra K. , Bacsa John , Smucker Bradley W. , Dunbar Kim R.
Published: January 2004

Self‐assembly reactions of the triply‐bonded dirhenium complex cis‐[Re2Cl2(dppm)2(O2CC5H4N‐4)2] with cis‐protected PtII and ZnII precursors have produced heterometallic squares. Analogous reactions with Ag(O3SCF3), cis‐[Re2Cl4(O2CCH3)2(H2O)2] and [Rh2(O2CCH3)4] have yielded mixed‐metal polymeric structures. These results demonstrate that the isonicotinate ligand is useful for accessing heterometallic structures involving metal−metal bonded complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis and X‐ray Crystal Structures of Cobalt and Copper Complexes of 1,3‐Bis(benzotriazolyl)propanes
Authors: Børsting Philip , Steel Peter J.
Published: January 2004

Two propylene‐bridged bis‐benzotriazole ligands,1and2, were used to obtain three novel coordination polymers with cobalt(II), copper(II) and copper(I). The complexes were structurally characterised by X‐ray crystallography. The complex [Co(1)Cl2]n,3, possesses a helical zigzag chain structure in which tetrahedral CoCl2centres are bridged by molecules of1having an extended conformation. The complex [Cu(1)Cl2]n,4, exhibits a more complex supramolecular architecture, which extends in two dimensions, with bridging through Cu2Cl4dimeric units in one direction and through the organic ligand in an orthogonal direction. The complex [Cu(2)Cl]n,6, has a one‐dimensional polymeric structure involving 16‐membered M2L2rings bridged by Cu2Cl2units. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Spectroscopic Characterization of an FeIV Intermediate Generated by Reaction of XO− (X = Cl, Br) with an FeII Complex Bearing a Pentadentate Non‐Porphyrinic Ligand − Hydroxylation and Epoxidation Activity
Authors: Balland Véronique , Charlot Marie‐France , Banse Frédéric , Girerd Jean‐Jacques , Mattioli Tony A. , Bill Eckhard , Bartoli Jean‐François , Battioni Pierrette , Mansuy Daniel
Published: January 2004

Mononuclear FeIV intermediates have been generated in MeOH upon reaction of sodium hypochlorite or hypobromite with a ferrous complex bearing the pentadentate ligands N‐methyl‐N,N′,N′‐tris(2‐pyridylmethyl)ethane‐1,2‐diamine (L52) or N‐methyl‐N,N′,N′‐tris(2‐pyridylmethyl)propane‐1,3‐diamine (L53). These highly unstable green complexes are characterized by an absorption band at ca. 750 nm. Mössbauer data indicate that the iron center is low spin (S = 1) with an axial electronic structure, allowing identification of the mononuclear FeIV complexes as [L5FeIVO]2+ or [L5FeIVOCH3]3+. In acetonitrile/dichloromethane solutions, the L53FeIV system exhibits very selective activities toward hydroxylation of cyclohexane or epoxidation of cyclooctene and cis‐stilbene. Computational studies performed on [L5FeIVO]2+ and on the model compound [(NH3)5FeIVO]2+ reveal that the ground state possesses two unpaired electrons in the two π* orbitals, as known for O2. Electronic spectra computed by time‐dependent DFT exhibit only one band in the visible region that is essentially due to d‐d transitions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Phenylcyanamido Ligand Building Molecular, 1‐D, and 2‐D Systems − Syntheses, Crystal Structures and Magnetic Properties
Authors: Escuer Albert , Sanz Núria , Mautner Franz A. , Vicente Ramon
Published: January 2004

Several MnII compounds have been synthesised with the phenylcyanamido ligand, C6H5−NCN−, and characterised by means of single crystal X‐ray structure determination. The reported compounds show a wide variety of nuclearity: mononuclear, dinuclear, 1‐D, and 2‐D compounds are present in which the phenylcyanamido anion (pcyd−) acts as a bridging ligand. The mononuclear compound [Mn(pcyd)2(phen)2] (1) crystallises in the orthorhombic system, Pbcn space group; dinuclear compound [{Mn(pcyd)(phen)(MeOH)}2(μ1,3‐pcyd)2] (2) crystallises in the monoclinic system, C2/c space group; 1‐D chain [Mn(4‐bzpy)2(μ1,3‐pcyd)2]n·MeOH (3·MeOH) crystallises in the triclinic system, P$\bar 1$
space group; 2‐D network [Mn(μ1,3‐pcyd)2(μ‐4,4′‐bpy)]n·MeOH (4·MeOH) crystallises in the monoclinic system, C2 space group. Susceptibility measurements on compounds 2−4 reveal moderate AF coupling in all cases. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Reduction of 1,2‐Bis[(2,6‐diisopropylphenyl)imino]acenaphthene (dpp‐bian) with Alkali Metals − A Study of the Solution Behaviour of (dpp‐bian)n−[M+]n (M = Li, Na; n = 1−4) with UV/Vis, ESR and 1H NMR Spectroscopy
Authors: Fedushkin Igor L. , Skatova Alexandra A. , Chudakova Valentina A. , Cherkasov Vladimir K. , Fukin Georgy K. , Lopatin Mikhail A.
Published: January 2004

An excess of lithium or sodium in diethyl ether consistently reduces 1,2‐bis[(2,6‐diisopropylphenyl)imino]acenaphthene (dpp‐bian) to the mono‐, di‐, tri‐ and tetraanion, (dpp‐bian)n−[M+]n (M = Li, Na; n = 1−4). The process of reduction is easily observed by the change in colour of the solution, on going from the neutral ligand (yellow) to the monoanion (red), the dianion (green for Na or Li in Et2O; dark blue, followed by green, for Li in TMEDA), the trianion (brown) and the tetraanion (red‐brown). In each reduction the maximum of the absorption, caused by electron transition from the HOMO of the respective form (dpp‐bian)n− (n = 1−4), is shifted to the long‐wavelength region in comparison to the previously reduced state. The disproportionation reactions (dpp‐bian)1− ⇄ (dpp‐bian)0 + (dpp‐bian)2− and (dpp‐bian)2− ⇄ (dpp‐bian)1− + (dpp‐bian)3− take place in solution along with the reduction process, thus causing the presence of three reduced forms of the ligand at the same time in the first and second stages of the reduction. Paramagnetic (dpp‐bian)1− and (dpp‐bian)3− are characterised by ESR spectroscopy. For the diamagnetic forms (dpp‐bian)2− and (dpp‐bian)4− 1H NMR spectra were recorded. The complex [Li+(dpp‐bian)(TMEDA)] (1), which formed from the initial stage of the reduction of dpp‐bian with lithium metal in TMEDA, was isolated in a crystalline form and its molecular structure was determined by single‐crystal X‐ray diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
A New Alternating Ferro‐Antiferromagnetic One‐Dimensional Azido‐Bridged (Arylazoimidazole)manganese(II), [Mn(TaiEt)(N3)2]n [TaiEt = 1‐Ethyl‐2‐(p‐tolylazo)imidazole], Exhibiting Bulk Weak Ferromagnetic Long‐Range Ordering
Authors: Ray Umasankar , Jasimuddin Sk. , Ghosh Barindra Kumar , Monfort Montserrat , Ribas Joan , Mostafa Golam , Lu Tian ‐Huey , Sinha Chittaranjan
Published: January 2004

1‐Ethyl‐2‐(p‐tolylazo)imidazole [p‐Me−C6H4−N=N−C3H2N2− Et‐1; TaiEt], an unsymmetrical N,N′‐blocker, and azide (N3−), a versatile intermediary, coordinate to manganese(II) forming an alternating chain with the formula [Mn(TaiEt)(N3)2]n (1). The compound crystallizes in the triclinic P$\bar 1$
space group with a = 7.9297(7) Å, b = 9.5883(9) Å, c = 11.8366(11) Å, α = 103.555(2)°, β = 105.811(2)°, γ = 104.280(2)°, and Z = 2. The structure consists of neutral chains in which each manganese(II) center is alternately bridged by two end‐on and two end‐to‐end azide ligands. The unsymmetrical arylazo heterocycle chelator creates a strong distortion around the metal center [N−Mn−N′ bite 67.7°; Mn−N′(azo) distance 2.562 Å]. The magnetic properties of 1 have been investigated over the temperature range 2−300 K. Magnetic data are analyzed on the basis of an alternating ferro‐ and antiferromagnetic Heisenberg chain of the manganese(II) ions, described by the spin Hamiltonian H = −J1ΣS2iS2i+1−J2ΣS2i+1S2i+2. The J exchange parameters are 2.65 ± 0.12 cm−1 and −14.5 ± 0.15 cm−1, respectively. Magnetic studies at low temperatures indicate long‐range ordering (canting) with a remnant magnetism that vanishes above 40 K. The canting phenomenon has been studied by various techniques including an EPR spectroscopic investigation at different temperatures and appears to be due to the local distortion around each metal center and the π‐π stacking in the 3‐D network. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
New Vanadium(V) Complexes with Salicylaldehyde Semicarbazone Derivatives: Synthesis, Characterization, and in vitro Insulin‐Mimetic Activity − Crystal Structure of [VvO2(salicylaldehyde semicarbazone)]
Authors: Noblía Pabla , Baran Enrique J. , Otero Lucía , Draper Patricia , Cerecetto Hugo , González Mercedes , Piro Oscar E. , Castellano Eduardo E. , Inohara Toshifumi , Adachi Yusuke , Sakurai Hiromu , Gambino Dinorah
Published: January 2004

The new dioxo(semicarbazone)vanadium(V) complexes cis‐VO2L, where L = salicylaldehyde semicarbazone (L1), salicylaldehyde 4‐n‐butylsemicarbazone (L2), or salicylaldehyde 4‐(2‐naphthyl)semicarbazone (L3), have been synthesized, characterized by 1H and 13C NMR and FTIR spectroscopy and tested for bioactivity as potential insulin‐mimetic agents. All dioxovanadium(V) complexes exhibited essentially no in vitro insulin‐mimetic activity, but the VO2L2 complex developed activity in the presence of ascorbic acid, similar to that of vanadyl sulfate. The molecular structure of the novel complex VO2L1 has been solved by X‐ray diffraction methods. It crystallizes in the tetragonal space group P42/n with a = 12.7674(7), c = 11.5308(5) Å, and Z = 8. The vanadium atom is in a distorted square‐pyramidal coordination, with L1 acting as a tridentate ligand through its azomethyne nitrogen atom, carbonyl oxygen atom and deprotonated phenol oxygen atom. The coordination sphere is completed by two oxo ligands at cis positions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Syntheses, Structures, and Magnetic Properties of Copper(II) Complexes with 1,3‐[Bis(2‐pyridylmethyl)amino]benzene (1,3‐tpbd) as Ligand
Authors: Foxon Simon P. , Torres Gemma Romualdo , Walter Olaf , Pedersen Jens Zacho , Toftlund Hans , Hüber Martina , Falk Karsten , Haase Wolfgang , Cano Joan , Lloret Francesc , Julve Miguel , Schindler Siegfried
Published: January 2004

The dinuclear copper(II) complexes {[Cu2(1,3‐tpbd)(H2O)(OAc)2](ClO4)2}0.23{[Cu2(1,3‐tpbd)(H2O)2(OAc)](ClO4)3}0.77·0.77H2O (1), [Cu2(1,3‐tpbd)(H2O)2(OAc)2](ClO4)2·2H2O (2), and the tetranuclear copper(II) complex [Cu4(1,3‐tpbd)2(H2O)2(SO4)4]·8H2O (3) {1,3‐tpbd = 1,3‐bis[bis(2‐pyridylmethyl)amino]benzene} were synthesised and structurally characterised by X‐ray diffraction. Variable‐temperature (2.0−290 K) magnetic susceptibility measurements on these complexes as well as on the dinuclear copper(II) complex [Cu2(1,3‐tpbd)(H2O)2(ClO4)3]ClO4 (4) (whose structure was published earlier) were performed. In contrast to 2 and 3, significant ferromagnetic coupling with J = +9.3 cm−1 was observed for 4 (the Hamiltonian being defined as Hˆ = −J Sˆ1·Sˆ2). Density functional theory (DFT) calculations were used successfully for the interpretation of the ferromagnetic coupling observed in 4. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis, Crystal Structures, and Magnetic Properties of a Mono‐ and a Dinuclear Copper(II) Complex of the 2,4,6‐Tris(2‐pyridyl)‐1,3,5‐triazine Ligand
Authors: Glaser Thorsten , Lügger Thomas , Fröhlich Roland
Published: January 2004

The reaction of 2,4,6‐tris(2‐pyridyl)‐1,3,5‐triazine (tptz) with Cu(BF4)2·3H2O and N,N‐bis(3‐aminopropyl)methylamine (Medpt) yielded the monomeric complex [(tptz)CuII(Medpt)](BF4)2·2MeOH (1) whereas reaction of tptz with CuCl2·2H2O yielded the dinuclear complex [{CuIICl2}(tptz){CuIICl2(MeOH)}] (2). The molecular structures of 1 and 2 were established by single‐crystal X‐ray diffraction studies. The copper ion in complex 1 is elongated octahedral with the nitrogen atoms of Medpt and the triazine nitrogen atom of tptz in the equatorial positions, and the two pyridyl nitrogen atoms of tptz in axial positions. The two CuII ions in complex 2 are bridged by tptz, coordinating to Cu1 in a terpyridine‐like fashion and to Cu2 in a bipyridine‐like coordination mode. The triazine nitrogen atom bound to Cu1 is coordinated in an equatorial position whereas the triazine nitrogen atom bound to Cu2 is situated in the apical position. The equatorial plane of Cu1 is coplanar with the 1,3,5‐triazine plane whereas the equatorial plane of Cu2 is perpendicular to the 1,3,5‐triazine plane. Intermolecular interactions in the solid state result in both compounds in “dimeric units” due to hydrogen bonding. Both complexes were investigated by variable‐temperature magnetic susceptibility measurements. Through‐space dipolar couplings and/or weak through‐bond interactions in complex 1 result in a small intermolecular antiferromagnetic interaction (J = −0.09 cm−1). The intramolecular exchange coupling in the dinuclear complex 2 is antiferromagnetic (J = −2.5 cm−1). This antiferromagnetic interaction was analyzed in view of the molecular structure considering spin‐polarization, superexchange and orbital‐orthogonality. A spin‐polarization pathway seems to be the leading contribution which does not involve the 1,3 bridging pathway. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
The “Rebound Controversy”: An Overview and Theoretical Modeling of the Rebound Step in C−H Hydroxylation by Cytochrome P450
Authors: Shaik Sason , Cohen Shimrit , de Visser Samuël P. , Sharma Pankaz K. , Kumar Devesh , Kozuch Sebastian , Ogliaro François , Danovich David
Published: January 2004

C−H hydroxylation by the enzyme cytochrome P450 is one of Nature’s important and most ubiquitous processes. There is strong evidence that the mechanism proceeds by initial hydrogen abstraction, from the alkane, by the high‐valent iron−oxo species of the enzyme, followed by a rebound of the alkyl radical to form the ferric−alcohol product complex (the Groves “rebound” mechanism). Nevertheless, the “rebound” mechanism is still controversial due to the ultrashort radical lifetimes deduced from radical‐clock experiments. This review describes the main elements of the controversy and its updated resolution by theory, with an emphasis on the controversial rebound step. The theoretically derived model for alkane hydroxylation is found to involve two‐state reactivity (TSR). In TSR, radicals are produced on two different spin‐state surfaces, and thereafter they react differently; on the low‐spin surface, the rebound proceeds with no product rearrangement and the lifetime of the radicals is ultrashort (or zero), while on the high‐spin surface the barrier for rebound is substantial and the lifetime of the radical is sufficiently long that rearrangement may compete with product formation by rebound. A new valence‐bond model is developed to model the rebound barrier on the high‐spin surface and conceptualize its dependence on the nature of the alkyl radical. The possible intermediacy of carbocationic intermediates alongside radicals is discussed. It is shown that the TSR scenario provides a satisfactory rationale for the controversial findings in the field, and makes verifiable predictions. One of the predictions of TSR is that the ratio of unrearranged to rearranged products, [U/R], will be subject to an intrinsic isotope effect that is substrate‐dependent. This prediction and its possible verification by experiment are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
New Complexes of Niobium(V) and Tantalum(V) with Monoanionic NNO Heteroscorpionate Ligands
Authors: Otero Antonio , Fernández‐Baeza Juan , Antiñolo Antonio , Tejeda Juan , Lara‐Sánchez Agustín , Sánchez‐Barba Luis , Rodríguez Ana M.
Published: January 2004

A new synthetic route based on bis(3,5‐dimethylpyrazol‐1‐yl)acetic acid (Hbdmpza) (1) has afforded the alcohol 2,2‐bis(3,5‐dimethylpyrazol‐1‐yl)ethanol (Hbdmpze) in good yield. This alcohol and the related lithium compound [{Li(bdmpza)(H2O)}4] are excellent precursors for introducing these scorpionate ligands into transition metal complexes. For example, the lithium compound and Hbdmpze (the latter after prior addition of nBuLi) react with a solution of MCl5 (M = Nb, Ta) in THF to give, after stirring for 12 h at −70 °C, a solution from which the complexes [MCl4(κ3‐bdmpzx)] (x = a, M = Nb 2, Ta 3; x = e, M = Nb 4, Ta 5) have been isolated. When solutions of 2−5 in THF were stirred at ca. 20 °C for 48 h, the oxo complexes [MCl2(O)(κ3‐bdmpzx)] (x = a, M = Nb 6, Ta 7; x = e, M = Nb 8, Ta 9) were isolated. The structures of these complexes have been determined by spectroscopic methods and the X‐ray crystal structure of 8 has been established. Finally, a new class of heteroscorpionate‐metal complexes containing an alkoxide ligand has been prepared. Direct reaction of the complexes [MCl4(κ3‐bdmpza)] (M = Nb 2, Ta 3) with several alcohols gave the complexes [MCl3(κ3‐bdmpza)(OR)] (M = Nb, R = Me 10, Et 11, iPr 12, tBu 13; M = Ta, R = Me 14, Et 15, iPr 16, tBu 17) after the appropriate workup. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis, Characterization and Electrochemistry of the Novel Dawson‐Type Tungstophosphate [H4PW18O62]7− and First Transition Metal Ions Derivatives
Authors: Mbomekalle Israel‐Martyr , Keita Bineta , Lu Yu Wei , Nadjo Louis , Contant Roland , Belai Nebebech , Pope Michael T.
Published: January 2004

Following the synthesis of pure [H4PW18O62]7− (PW18), its derivatives monosubstituted with M (M = MoVI, VIV, VV, MnII, FeIII, CoII, NiII CuII and ZnII) were obtained. All compounds were characterized by elemental analysis, IR, UV/visible and 31P NMR spectroscopy. Their cyclic voltammetry properties were studied as a function of pH and systematically compared with those of their analogs derived from the symmetrical species, [P2W18O62]6−(P2W18). Comparison of the two unsubstituted precursors revealed that the merging of the first two waves of the monophosphate occurred in a less acidic medium than for the diphosphate. The observations point to the higher basicity of the reduced forms of PW18 compared with those of P2W18. The fingerprint pattern observed for α2‐P2W17M derivatives in media of pH = 3 consisted of the splitting of the third W redox system into two one‐electron closely spaced waves which is in contrast to the same system in α1‐P2W17M. This peculiarity was also obtained for several of the present α2‐PW17M systems in media of pH = 3 and confirmed that α2‐substituted derivatives were indeed formed. The absence of this peculiar behavior in some other derivatives is consistent with smooth variations of acid‐base properties from one derivative to the next. The electrocatalytic properties of all the compounds are illustrated by the reduction of nitrite by reduced PW18 and of nitrate by reduced α2‐PW17Cu. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Tuning the Magnetic Properties of a Dinuclear Copper Complex: From Ferromagnetic to Antiferromagnetic Coupling
Authors: Foxon Simon P. , Walter Olaf , Koch Robert , Rupp Holger , Müller Paul , Schindler Siegfried
Published: January 2004

A novel structural motif in oxalate bridged copper(II) complexes has been prepared namely a metallamacrocyclic compound of the dinucleating ligand 1,3‐bis[bis(2‐pyridylmethyl)amino]benzene (= 1,3‐tpbd). It could be demonstrated that the magnetic properties of copper(II) complexes of the 1,3‐tpbd ligand can be adjusted from weakly ferromagnetic (J = +9.3 cm−1) to strongly antiferromagnetic [J = −366(9) cm−1] by variation of the additional ligands (e.g. perchlorate, azide, oxalate etc.). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis, Spectroscopic Properties, and Structure of [Tetrakis(2,4‐dimethyl‐3‐pentyloxy)phthalocyaninato]metal Complexes
Authors: Liu Wei , Lee Chi‐Hang , Chan Hoi‐Shan , Mak Thomas C. W. , Ng Dennis K. P.
Published: January 2004

A series of highly soluble [tetrakis(2,4‐dimethyl‐3‐pentyloxy)phthalocyaninato]metal complexes [MPc(OC7H15)4] (M = Zn, Pd, Co) were prepared by cyclic tetramerization of 3‐(2,4‐dimethyl‐3‐pentyloxy)phthalonitrile (2) in the presence of the corresponding metal salts and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) in n‐pentanol. For M = Zn and Pd, two major isomers with a C4h and C2v symmetry were isolated by column chromatography and characterized with various spectroscopic methods, while the cobalt analogue showed only the C4h isomer. The (phthalocyaninato)manganese complex [MnClPc(OC7H15)4] was also synthesized by metallation of the metal‐free phthalocyanine H2Pc(OC7H15)4 formed by treating 2 with CeCl3 and DBU in n‐pentanol. The structures of the C4h isomers of the (phthalocyaninato)zinc and ‐cobalt complexes and the C4 isomer of the manganese analogue were also established by X‐ray diffraction analyses. The palladium counterpart formed a novel 1:1 inclusion complex with oxalic acid, the crystal structure of which was also determined. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis and Structural Studies of Rhenium(V) Complexes Stabilized by a Monoanionic Cyclen Ligand
Authors: Xavier Catarina , Paulo António , Domingos Angela , Santos Isabel
Published: January 2004

The novel cationic (oxo)ReV complexes [ReO(cyclen‐H)Cl]X [X = Cl (3a), BPh4 (3b)] and [ReO(cyclen‐H)I]I (4) have been prepared by treating cyclen (1,4,7,10‐tetrazacyclododecane) with (Bu4N)[ReOCl4] (1) and cis‐[ReO2I(PPh3)2] (2), respectively. The X‐ray structural analyses of 3a and 4, as well as 1H NMR spectroscopy, showed that the macrocyclic ligand is coordinated in the unprecedented monoanionic form. 1H and 13C NMR spectroscopy also demonstrated that 3a,b and 4 exist in solution as single isomers. To the best of our knowledge, 3a and 4 are the first examples of structurally characterized oxo complexes of d transition elements with cyclen bound to the metal atom through one amido and three amine groups. In both complexes, the geometry around the ReV center is best described as distorted octahedral. The terminal oxo and halo ligands are coordinated in relative cis positions, and the amido and three amino nitrogen atoms from cyclen occupy the four remaining coordination positions. The Re−N(amido) bonds [1.894(9) Å in 3a and 1.888(12) Å in 4] are trans to the halo ligands and, as expected, are considerably shorter than the Re−N(amine) bonds, which span from 2.110(6) to 2.246(8) Å and from 2.124(8) to 2.268(10) Å for cations the cations of 3a and 4, respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
(Neocuproin)zinc Thiolates: Attempts at Modeling Cobalamin‐Independent Methionine Synthase
Authors: Seebacher Jan , Ji Mian , Vahrenkamp Heinrich
Published: January 2004

Several new complexes [(neo)Zn(SR)2] [neo = neocuproin (2,9‐dimethylphenanthroline)] have been synthesized and structurally characterised. They react in a stepwise fashion with the alkylating agents CH3I and (CH3)2SO4 to afford the thioethers CH3SR and first the mixed complexes [(neo)Zn(SR)X] (X = I, CH3SO4) and then [(neo)ZnX2]. Similar alkylations occur with benzyl iodide, but not with trimethyl phosphate in nonpolar media. Under these conditions, thiolate exchange with [PPN]SR does not occur which indicates that the alkylations take place at the zinc‐bound thiolates. In polar solvents (methanol, DMSO), thiolate exchange occurs readily, and at higher temperatures (CH3)3PO4 also acts as an alkylating agent which indicates that under these conditions free thiolate is available in solution. Qualitative kinetic data support the associative alkylation mechanism in nonpolar media and the change of mechanism in polar media. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Novel Room Temperature Inorganic Ionic Liquids
Authors: Dai Liyi , Yu Shuyuan , Shan Yongkui , He Mingyuan
Published: January 2004

New inorganic ionic liquids (IIL) consisting of an inorganic polyoxometalate anion with the Keggin structure and a sodium cation, that is Na13[Ln(TiW11O39)2]·xH2O [where Ln = lanthanide (type 1)], Na5[MTiW11O39]·xH2O and Na6[MTiW11O39]·xH2O [where M = transition metal (type 2)], were prepared and their physicochemical properties were investigated. These ionic liquids were characterized by NMR and IR spectroscopy and by elemental analysis. Their melting point, viscosity, conductivity, thermal stability, and miscibility with water and organic solvents were determined. When the temperature is below ambient temperature (about 298 K) these ionic liquids are almost immiscible with water. When the temperature is raised, the solubility of the new ionic liquids increases sharply. The influence of the size and of the charge density of both the cations and anions on these properties was examined. The most remarkable feature of IILs is that water is their indispensable component. The role of the water molecule in ionic liquids is similar to that of crystalline water in hydrated compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Solid‐State Models of Ion Solvation: Crystal Structures of Dimethyl Sulfoxide Solvates of Alkaline Earth Cations
Authors: Harrowfield Jack M. , Richmond William R. , Skelton Brian W. , White Allan H.
Published: January 2004

Structural studies of the dimethyl sulfoxide solvates of the perchlorates of Mg, Sr and Ba show the presence of a variety of complex ion species indicative of the forms possible in solution. While Mg(ClO4)2·6dmso contains the expected [Mg(dmso)6]2+ cation, the crystallised strontium species contains a mononuclear [Sr(dmso)6]2+ cation and two dinuclear species, the complex [(dmso‐O)5Sr(μ‐dmso‐O)3Sr(OH2)(dmso‐O)3]4+ containing both seven‐ and eight‐coordinate Sr metal centres, and [{(dmso‐O)5Sr(μ‐dmso‐O)}2]4+ containing seven‐coordinate Sr metal centres. The barium complex, of empirical formula Ba(ClO4)2·5dmso, contains a centrosymmetric dimer, [Ba2(dmso‐O)6(μ‐dmso‐O)4(O2ClO2)2]2+, involving an unsymmetrically chelating perchlorate and a nine‐coordinate Ba metal centre. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Palladium‐Catalyzed Regioselective Cyclotrimerization of Acetylenes in Supercritical Carbon Dioxide
Authors: Cheng Jin‐Sheng , Jiang Huan‐Feng
Published: January 2004

The cyclotrimerization process of different substituted alkynes occurred smoothly in supercritical carbon dioxide for the first time. The reactions are catalyzed by palladium chloride. High yields and regioselectivities were observed when 2 equiv. of CuCl2 and 5 mL of MeOH were added. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Cavitands at Work: From Molecular Recognition to Supramolecular Sensors
Authors: Pinalli Roberta , Suman Michele , Dalcanale Enrico
Published: January 2004

Exploitation of the molecular recognition properties of a given receptor in analytical applications requires mastering of specific host‐guest interactions at interfaces. This review outlines the issues involved in turning PV‐bridged cavitands into selective layers for mass sensors, as a case study for gas‐solid interfaces. The specific interactions operating at each phase level can be ferreted out by use of MS and crystallographic analyses, respectively. Their influence on sensor selectivity can be enhanced by exposure of the guest (analyte) to a network of cooperative interactions encoded in a single cavitand receptor. On the other hand, high layer permeability − necessary to achieve fast and reversible sensor responses − increases non‐specific dispersion interactions. Shifting of the balance towards selectivity without loss of reversibility represents the major challenge facing those wishing to venture into the field of supramolecular sensors. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Mechanism of Photoinduced Reactions between 1‐Acetylisatin and Aldehydes
Authors: Zhang Yan , Wang Lei , Zhu Ye , Xu Jian‐Hua
Published: January 2004

Hydrogen atom abstraction from aliphatic (2a, 2b) and aromatic (2c, 2d, 2e) aldehydes by the triplet nπ* state of 1‐acetylisatin (1) yielded triplet (isatin ketyl‐aldehyde acyl) radical pairs, which follow an out‐of‐cage pathway in subsequent reactions to give a series of radical coupling products 4−7. This out‐of‐cage mechanism is supported by examination of the primary products at various degrees of conversions during the course of the reaction, by the results of addition reactions of thermally generated isatin acyl radical with neutral 1, and by calculation of the charge density distribution in the acyl radicals and in ground state 1. Therefore, the oxygen‐philic attack of the acyl radical, which had escaped out of cage from the triplet radical pair, at the C(3) carbonyl oxygen atom of a ground state 1 selectively afforded the thermodynamically more stable addition radical B. The recombination of two radicals B gave the 3‐indolinone dimers 4 and 5 as diastereomers, while coupling of B with the isatin ketyl furnished the dihydroisoindigo derivative 6. Isatide 7 was also formed by ketyl radical recombination. The product ratio is dependent on the structure of the aldehyde. For 2d and 2e, each with an electron‐donating substituent in the benzene ring, the corresponding acyl radicals are less electrophilic because of a diminished positive charge density at the carbonyl carbon atom, and the formation of the addition radical B is a slow process relative to the encounter and recombination of the isatin ketyl radicals. As a result, products 6d and 6e from cross‐coupling of the isatin ketyl and radical B are formed in much lower yields than 6a, 6b, and 6c. The 3‐acetyloxy‐2‐indolinone 3 turned out to be a secondary product derived from the decomposition of 6 during the workup procedures. Since all the primary products are formed by out‐of‐cage radical pair combination processes, no chain mechanism is involved. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Diastereo‐ and Enantioselective Synthesis of Novel β‐Lactam‐Containing 1,4‐Benzodiazepines through a Ketene−Imine Cycloaddition Reaction
Authors: del Pozo Carlos , Macías Alberto , López‐Ortiz Fernando , Ángel Maestro Miguel , Alonso Eduardo , González Javier
Published: January 2004

Novel tricyclic scaffolds that incorporate a β‐lactam ring fused to the d bond of a 1,4‐benzodiazepine seven‐membered ring have been synthesized in a process that constitutes one of the few examples of Staudinger‐type reactions involving ketimines described so far. In addition the creation of an asymmetric quaternary center has been achieved. The combination of these two “privileged structures” in a single compound is bound to confer interesting biological properties upon them. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Convenient Route to 2‐(Trialkylstannyl)cyclopropylamines and Their Application in Palladium‐Catalyzed Cross‐Coupling Reactions
Authors: Wiedemann Stefan , Rauch Karsten , Savchenko Andrei , Marek Ilan , de Meijere Armin
Published: January 2004

The 2‐(trialkylstannyl)‐N,N‐dialkylcyclopropylamines 3 were obtained by titanium‐mediated aminocyclopropanation of tributylvinylstannane with N,N‐dialkylformamides in yields of 80−84% and with excellent diastereoselectivities (trans/cis > 45:1). The resulting stannanes could advantageously be applied in Stille cross‐coupling reactions with aryl iodides, providing the pure trans‐2‐aryl‐(N,N‐dialkylamino)cyclopropanes 8 in yields ranging from 45 to 67% (six examples). The coupling of ethyl (E)‐3‐iodoacrylate (9) gave ethyl cis‐5‐(dibenzylamino)cyclopent‐2‐enecarboxylate (10) as a single diastereomer in 54% yield. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Coupling Reactions of 1,4‐Dicuprio‐1,3‐dienes: Formation of Carbocycles
Authors: Chen Chao , Xi Chanjuan , Lai Chunbo , Wang Ruji , Hong Xiaoyin
Published: January 2004

The coupling reaction of 1,4‐dicuprio‐1,3‐dienes in the presence of benzoquinone forms cyclobutadienes, which are easily transformed into cyclooctatetraene derivatives. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis and Some Properties of Aryl‐ and Aryloxy‐Substituted Phthalocyanines and Their Metal Complexes: A Comparison with Porphyrazine and Naphthalocyanine Analogues
Authors: Vagin Sergej , Hanack Michael
Published: January 2004

The preparation of new octakis[m‐(trifluoromethyl)phenyl]‐ and octakis[m‐(trifluoromethyl)phenoxy]phthalocyanines (6a and 6b) and their complexes with magnesium (5a, 5b) and indium (7a, 7b) is described. Their spectroscopic properties and solubilities are discussed in relation to those of metal‐free and metallated octakis[m‐(trifluoromethyl)phenyl]porphyrazine, as well as those of metal m‐(trifluoromethyl)phenyl‐ and m‐(trifluoromethyl)phenoxy‐substituted 2,3‐naphthalocyanines. A drastic decrease in the solubilities of the metal‐free phthalocyanines in CH2Cl2 was observed on comparing them with m‐CF3‐phenyl‐substituted porphyrazine. However, their solubilities in THF were high enough for NMR spectra to be recorded. Insertion of (chloro)indium into the cavities of these phthalocyanines noticeably enhances the solubilization of the macrocycles, including in CH2Cl2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Immunomodulatory α‐Galactoglycosphingolipids: Synthesis of a 2′‐O‐Methyl‐α‐Gal‐GSL and Evaluation of Its Immunostimulating Capacity
Authors: Barbieri Lucia , Costantino Valeria , Fattorusso Ernesto , Mangoni Alfonso , Aru Elisabetta , Parapini Silvia , Taramelli Donatella
Published: January 2004

The total synthesis of 1‐2‐docosanoylamino‐O‐(2‐O‐methyl‐α‐D‐galactopyranosyl)‐1,3,4‐octadecanetriol (2), a 2′‐methoxy analog of the immunostimulating α‐galactoglycosphingolipid 1, is reported. Stereoselective α‐glycosylation of the azido precursor of sphingosine was successfully performed for the first time using an improved Mukaiyama reaction. When assayed in a 72 h splenocyte proliferation test, compound 2 was significantly less stimulatory than the non‐methylated compound 1, suggesting that the galactose 2‐OH group is essential for the immunostimulatory activity of α‐Gal‐GSLs. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Phosphane‐Catalyzed Knoevenagel Condensation: A Facile Synthesis of α‐Cyanoacrylates and α‐Cyanoacrylonitriles
Authors: Yadav Jhillu S. , Reddy Basi V. Subba , Basak Ashok K. , Visali Boddapati , Narsaiah Akkirala Venkat , Nagaiah Kommu
Published: January 2004

Triphenylphosphane (TPP) has been utilized as a novel and efficient catalyst for the Knoevenagel condensation of aldehydes with acidic methylene compounds such as ethyl cyanoacetate and malononitrile to afford substituted olefins. The reaction proceeds smoothly under mild and solvent‐free conditions and the products are obtained in excellent yields with an E‐geometry. This method is applicable for a wide range of aldehydes including aromatic, aliphatic and heterocyclic substrates. Microwave irradiation has been used to achieve enhanced reaction rates and improved yields. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Chemical Resolution of 1,2‐O‐Cyclohexylidene‐3,4‐O‐(tetraisopropyldisiloxane‐1,3‐diyl)‐myo‐inositol and Synthesis of Phosphatidyl‐D‐myo‐inositol 3,5‐Bisphosphate from Both L‐ and D‐Enantiomers
Authors: Han Fushe , Hayashi Minoru , Watanabe Yutaka
Published: January 2004

Chemical resolution of a versatile starting material, 1,2‐Ocyclohexylidene‐3,4‐O‐(tetraisopropyldisiloxane‐1,3‐diyl)myo‐inositol, which is used to access naturally occurring inositol phosphates and phosphatidylinositol phosphates, is described. Starting from both D‐ and L‐enantiomers of the material, the synthesis of phosphatidyl‐D‐myo‐inositol 3,5‐bisphosphate [PtdIns(3,5)P2] has been conveniently accomplished via convergent routes. One of the key reactions in the synthetic procedure was the regioselective phosphorylation of suitably protected 1,2,4‐triol derivatives of inositol. Phosphorylation of the triol attempted in a 1:12 (v/v) pyridine/CH2Cl2 mixture did not proceed at all, whereas in an optimized solvent system, pyridine/CH2Cl2 (1.1:1, v/v), the reaction afforded 68% of the desired 1‐O‐phosphate as a single product. Further investigation by 1H NMR spectroscopy indicated that the reactivity of the three OHs on 1,2,4‐triol derivatives is governed by intermolecular hydrogen bonding, which may be disrupted by an increase in the proportion of pyridine in the reaction solvent. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis Routes Towards the Farnesyl Protein Transferase Inhibitor ZARNESTRATM
Authors: Angibaud Patrick R. , Venet Marc G. , Filliers Walter , Broeckx Rudy , Ligny Yannick A. , Muller Philippe , Poncelet Virginie S. , End Dave W.
Published: January 2004

The discovery that post‐translational farnesylation of Ras oncoprotein was an essential step in exercising its biological effect led to the design of farnesyl protein transferase inhibitors (FTIs) in order to control growth of tumors bearing Ras mutations. Pre‐clinical studies on murine models have confirmed their inhibitory effect on tumor growth and enabled clinical development. R115777 (ZARNESTRATM) is currently undergoing clinical evaluation and recent studies have confirmed its antitumor potential and low toxicity. We wish to describe here the chemical synthesis routes that our group have developed to access ZARNESTRATM. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Calix[4]arene‐Supported N‐Heterocyclic Carbene Ligands as Catalysts for Suzuki Cross‐Coupling Reactions of Chlorotoluene
Authors: Frank Markus , Maas Gerhard , Schatz Jürgen
Published: January 2004

Stable N‐heterocyclic carbenes are generated starting from 5,17‐(bis‐imidazolium)‐substituted calix[4]arenes. Addition of Pd(OAc)2 to these carbenes leads to macrocyclic cis‐palladium chelate complexes in which the distal bridging of the upper rim leads to a strong distortion of the calix[4]arene skeleton which was proven by X‐ray crystal structure determination. Using an in‐situ catalytic system consisting of a calixarene‐imidazolium salt, Cs2CO3 as a base and a source of palladium, a species is formed which can be used to catalyse the Suzuki cross‐coupling of 4‐chloro toluene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Highly Stereoselective Conversion of Aryl Peptidyl Ketones into the Corresponding Peptide Alcohols
Authors: Di Gioia Maria Luisa , Leggio Antonella , Le Pera Adolfo , Liguori Angelo , Siciliano Carlo
Published: January 2004

In this paper we describe the conversion of aryl peptidyl ketones, by a hydride reduction, into the corresponding peptide alcohols. The developed methodology is highly stereoselective and represents a very important application in peptide chemistry for obtaining peptide alcohols. It provides peptide alcohols with definite stereochemistry and in moderate, but satisfactory, yields. The reducing procedure, performed with NaBH3CN and TiCl4, probably proceeds via two diastereomeric cyclic intermediates that show different reactivity. The stereochemistry of the resulting alcohols was established after obtaining them by an alternative synthetic procedure. Furthermore, the methodology adopted keeps the urethane protecting group on the amino function of the N‐terminal amino acid residue. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of 1‐(Alkoxycarbonyl)methylene‐1,3‐dihydroisobenzofurans and 4‐(Alkoxycarbonyl)benzo[c]pyrans by Palladium‐Catalysed Oxidative Carbonylation of 2‐Alkynylbenzyl Alcohols, 2‐Alkynylbenzaldehydes and 2‐Alkynylphenyl Ketones
Authors: Bacchi Alessia , Costa Mirco , Della Cà Nicola , Fabbricatore Marcella , Fazio Alessia , Gabriele Bartolo , Nasi Cristina , Salerno Giuseppe
Published: January 2004

A direct synthesis of 1‐(alkoxycarbonyl)methylene‐1,3‐dihydroisobenzofurans 2 and 5 and 4‐(alkoxycarbonyl)benzo[c]pyrans 3 and 6 by oxidative Pd‐catalysed cyclization/alkoxycarbonylation of 2‐alkynylbenzyl alcohols 1, and of 2‐alkynylbenzaldehydes or 2‐alkynylphenyl ketones 4 is reported. Reactions were carried out in ROH or CH3CN/ROH (R = Me, iPr) as the solvent at 70−105 °C in the presence of catalytic amounts of PdI2 in conjunction with KI under a 4:1 or 3:1 CO/air mixture (2.0 or 3.2 MPa total pressure at 25 °C). The reaction occurs through intramolecular attack by the nucleophilic oxygen atom (either already present in the starting material, as in 1, or generated in situ by ROH attack on carbonyl group, as in 4) on the triple bond coordinated to PdII, followed by alkoxycarbonylation. The presence of substituents at the alkyne terminal position and at the carbon atom α to the hydroxy group play a key role in the selectivity of the process towards the formation of a five‐ or six‐membered ring. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
The Regiochemistry of the Addition of PhSeCl to Arylferrocenylethynes: A Cooperative Effect?
Authors: Brunetti Tiziana , Diddoro Massimo , Di Vona Maria Luisa , Floris Barbara , Galloni Pierluca , Licoccia Silvia
Published: January 2004

PhSeCl adds to arylferrocenylethynes giving two regioisomers, ArC(Cl)=C(SePh)Fc and ArC(SePh)=C(Cl)Fc in different amounts, due to a favourable Se−Fe interaction.77Se NMR spectroscopy was useful for identifying the addition products.Kinetic experiments were also performed and a correlation was found using Hammett σ values. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Cover Picture: Cavitands at Work: From Molecular Recognition to Supramolecular Sensors (Eur. J. Org. Chem. 3/2004)
Authors: Pinalli Roberta , Suman Michele , Dalcanale Enrico
Published: January 2004

The cover picture shows the operating principle of a supramolecular mass sensor. The cavitand receptor is coated on the surface of a quartz crystal microbalance (QCM) and exposed to a flux of the analyte (methanol) in the gas phase (center). All complexation events occurring at the gas/solid interface are collectively recorded by the transducer as a frequency drop (bottom). The molecular interactions responsible for the selective alcohol detection are evidenced in the crystal structure of the complex (top). The Microreview by R. Pinalli, M. Suman and E. Dalcanale covers the issues involved in turning a synthetic receptor into an effective supramolecular gas sensor, namely design and preparation of the receptor as function of the analytes to be detected, evaluation of the complexation properties of the receptor in the solid state and in the gas phase, sensor reversibility and selectivity as function of layer permeability, on p. 451 ff.
Editorial: Electrophoresis 2/2003
Authors: Gaš Bohuslav , Boček Petr
Published: January 2004

No abstracts.
Calibrationless quantitative analysis by indirect UV absorbance detection in capillary zone electrophoresis: The concept of the conversion factor
Authors: Beckers Jozef L. , Boček Petr
Published: January 2004

A new, fast and efficient procedure is described for the simultaneous quantitative analysis of various non‐UV absorbing species in a sample, by capillary zone electrophoresis with indirect UV absorbance detection. The procedure is based on the concept of the conversion factor (CF). The CF of an analyte is defined as the ratio of the measured temporal peak area and the product of its migration time and transfer ratio (TR). Thus defined, the CF is of general validity for all analytes separated and detected in a given background electrolyte (BGE), since it has the same value for the same amounts of various analytes. If a sample is enriched with a known concentration of a standard component and analyzed by CZE, the CF of this standard component can be calculated and then the concentrations of all other analytes can be determined, without the use of any calibration graph. The individual TRs can be determined a priori from tabulated ionic mobilities and pK values of the analytes and of the constituents of the BGE or, for strong analytes, by using experimental data from the electropherogram of the analysis itself. The practical procedure of the analysis includes enrichment of the sample with a known quantity of a suitable standard and a single CZE run of the resulting mixture. The injected volume does not need to be known and thus the procedure also eliminates the injection error. The proposed procedure has been verified experimentally and reproducible and accurate values were obtained by using four different CZE apparatus for the analyses of standard mixtures of cations in three different BGEs.
Study of enzymatic reaction by electrophoretically mediated microanalysis in a partially filled capillary with indirect or direct detection
Authors: Telnarová Magdaléna , Vytisková Soňa , Chaloupková Radka , Glatz Zdeněk
Published: January 2004

Electrophoretically mediated microanalysis (EMMA), in combination with a partial filling technique and indirect or direct detection, is described for the study of enzymes reacting with the high mobiliby inorganic or organic anions as substrates or products. Part of the capillary is filled with a buffer optimized for the enzymatic reaction, the rest of the capillary with the background electrolyte being optimal for the separation of substrates and products. With haloalkane dehalogenase, chosen as a model enzyme, the enzymatic reaction was performed in a 20 mM glycine buffer (pH 8.6). Because of the wide substrate specifity of this enzyme, utilizing chlorinated as well as brominated substrates and producing either nonabsorbing chloride or absorbing bromide ions, two different background electrolytes and detection approaches were adopted. A 10 mM chromate‐0.1 mM cetyltrimethylammonium bromide background electrolyte (pH 9.2) was used in combination with indirect detection and 20 mM β‐alanine‐hydrochloric acid (pH 3.5) in combination with direct detection. The Michaelis constant (Km) of haloalkane dehalogenase for 1‐bromobutane was determined. The Km values 0.59 mM estimated by means of indirect detection method and 0.17 mM by means of direct detection method were comparable with the value 0.13 mM estimated previously by gas chromatography.
Optimisation of selectivity in the separation of aromatic amino acid enantiomers using sulfated ß‐cyclodextrin and dextran sulfate as pseudostationary phases
Authors: Zakaria Philip , Macka Miroslav , Haddad Paul R.
Published: January 2004

Control of selectivity in the enantiomeric separation of three aromatic amino acids (phenylalanine, tyrosine and tryptophan) was demonstrated utilising two separate electrolyte additives. Sulfated‐β‐cyclodextrin (s‐β‐CD) was chosen as the chiral selector while the addition of dextran sulfate provided a means with which to predictably fine‐tune separation selectivity. The two additives were found to interact independently with the amino acids, with the s‐CD providing chiral interactions while the dextran sulfate provided ion‐exchange (IE) interactions. The system was also very robust with reproducibility of migration times being < 2.0% RSD between runs and < 2.6% on using a new capillary. A physical model derived from first principles was also successfully used to describe the two additive system. The model accurately described the observed separations over the range of 0–20 mM s‐β‐CD and 0–1% dextran sulfate with a correlation coefficient of 0.998 between predicted and observed mobilities. The physical model also provided useful information about the system including association constants between the analytes and the pseudostationary phases, together with the mobilities of the associated complexes (analyte‐cyclodextrin and analyte‐dextran sulfate). Selectivity optimisation was achieved using the normalised resolution product and minimum resolution criteria. The physical model also allowed a desired separation selectivity to be obtained, such that experimental conditions could be predicted to lead to a particular migration order.