Metal-penicillamine interactions. Part 1. Preparation and crystal structure of a 1:1 complex of mercuric chloride with d-penicillamine, 2[μ3-Cl){HgSC(CH3)2CH(NH3)COO}3·3(μ2-Cl)· 2(H3O)·(H2O·Cl)3

A 1:1 complex of mercuric chloride with D-peniccillamine has been isolated and characterised as 2[(μ₃-Cl){HgSC(CH₃)₂CH(NH₃)COO}3]·3(μ₂-Cl)·2(H₃O)·(H₂O·Cl)₃. The compound crystallises in cubic space group P4₁32, with a = 18.679(5) Å and Z = 4. The structure, refined to R_F = 0.086 for 443 observed Mo-Kα diffractometer data, features a triply bridging chloride ion linking three equivalent [HgSC(CH₃)₂CH(NH₃)COO]⁺ units [Hg-Cl = 2.37(1) Å, Hg-Cl-Hg′ = 98.5(9)°]. The carboxylate groups of a pair of adjacent penicillamine ligands are strongly linked via a symmetrical O?H?O hydrogen bond of length 2.24(8) Å, and neighboring pyramidal trinuclear [μ₃-Cl){HgSC(CH₃)₂CH(NH₃)-COO}₃]²⁺ moieties are further connected by symmetrical chloride bridges [Hg-Cl = 3.06(2) Å; HgClHg′' = 79.6(7)°] to form a three-dimensional network. The voids in the lattice are filled by hydronium ions and novel planar cyclic hydrogen-bonded (H₂O·Cl^?)₃ rings of edge O-H?Cl = 2.46(4) Å.     

Separation of Tryptophan Enantiomers by Ligand‐Exchange Chromatography With Novel Chiral Ionic Liquids Ligand

Chiral ionic liquids (CILs) with amino acids as cations have been applied as novel chiral ligands coordinated with Cu²⁺ to separate tryptophan enantiomers in ligand exchange chromatography. Four kinds of amino acid ionic liquids, including [L‐Pro][CF₃COO], [L‐Pro][NO₃], [L‐Pro]₂[SO₄], and [L‐Phe][CF₃COO] were successfully synthesized and used for separation of tryptophan enantiomers. To optimize the separation conditions, [L‐Pro][CF₃COO] was selected as the model ligand. Some factors influencing the efficiency of chiral separation, such as copper ion concentration, CILs concentration, methanol ratio (methanol/H₂O, v/v), and pH, were investigated. The obtained optimal separation conditions were as follows: 8.0 mmol/L Cu(OAc)₂, 4.0 mmol/L [L‐Pro][CF₃COO] ,and 20% (v/v) methanol at pH 3.6. Under the optimum conditions, acceptable enantioseparation of tryptophan enantiomers could be observed with a resolution of 1.89. The results demonstrate the good applicability of CILs with amino acids as cations for chiral separation. Furthermore, a comparative study was also conducted for exploring the mechanism of the CILs as new ligands in ligand exchange chromatography. Chirality 26:160–165, 2014. © 2014 Wiley Periodicals, Inc.     

Biodefluorination and biotransformation of fluorotelomer alcohols by two alkane‐degrading Pseudomonas strains

Fluorotelomer alcohols [FTOHs, F(CF₂)_nCH₂CH₂OH, n = 4, 6, and 8] are emerging environmental contaminants. Biotransformation of FTOHs by mixed bacterial cultures has been reported; however, little is known about the microorganisms responsible for the biotransformation. Here we reported biotransformation of FTOHs by two well‐studied Pseudomonas strains: Pseudomonas butanovora (butane oxidizer) and Pseudomonas oleovorans (octane oxidizer). Both strains could defluorinate 4:2, 6:2, and 8:2 FTOHs, with a higher degree of defluorination for 4:2 FTOH. According to the identified metabolites, P. oleovorans transformed FTOHs via two pathways I and II. The pathway I led to the production of x:2 ketone [dominant metabolite, F(CF₂)_xC(O)CH₃; x = n ? 1, n = 6 or 8], x:2 sFTOH [F(CF₂)_xCH(OH)CH₃], and perfluorinated carboxylic acids (PFCAs, perfluorohexanoic, or perfluorooctanoic acid). The pathway II resulted in the formation of x:3 polyfluorinated acid [F(CF₂)_xCH₂CH₂COOH] and relatively minor shorter‐chain PFCAs (perfluorobutyric or perfluorohexanoic acid). Conversely, P. butanovora transformed FTOHs by using the pathway I, leading to the production of x:2 ketone, x:2 sFTOH, and PFCAs. This is the first study to show that individual bacterium can bio‐transform FTOHs via different or preferred transformation pathways to remove multiple ? CF₂? groups from FTOHs to form shorter‐chain PFCAs. Biotechnol. Bioeng. 2012; 109: 3041–3048. © 2012 Wiley Periodicals, Inc.     

Potassium-controlled synthesis of heterotopic macrocycles based on isothiosemicarbazide

The macrocyclisation reaction of 3,3′-(3,6-dioxaoctane-1,8-diyldioxy)-bis(2-hydroxybenzaldehyde) (1) with S-methylisothiosemicarbazide hydroiodide (H₂NNC(SCH₃)NH₂·HI) in the presence of potassium triflate, followed by addition of M(CH₃COO)₂·nH₂O, where M=Ni, Cu, Zn, afforded [NiLKI₃] (2), [NiLK(CF₃SO₃)] (3), [CuLK(CF₃SO₃)(CH₃OH)] (4) and [(ZnILK)₂CH₃OH] (5), respectively. Compounds 2-5 have been characterised by X-ray crystallography. IR, electronic, mass, ¹H, ¹³C{¹H} and ¹⁹F{¹H} NMR spectra are reported. Magnetic susceptibility measurements and ESR spectra of 4 indicate weak intermolecular spin-spin interactions, which are mostly dipolar in origin.     

Synthesis,crystal structure and magnetic behaviour of dimeric and polymeric gadolinium carboxylates with pentafluoropropionic acid

The three novel gadolinium(III) containing compounds (NH₃CH₃)[Gd(CF₃CF₂COO)₄(H₂O)] (1), (NH₃C₂H₅)[Gd(CF₃CF₂COO)₄(H₂O)] (2) and ((CH₃)₄N)[Gd(CF₃CF₂COO)₃(H₂O)₂]CF₃CF₂COO (3) were synthesized and structurally characterized by X-ray crystallography. In the crystal structures of 1 and 2, the gadolinium ions are bridged by carboxylate groups to dimers with a Gd³⁺–Gd³⁺ distance of 451.6(2) (1) and 451.8(3) pm (2), respectively. In the crystal structure of 3 the Gd³⁺ ions are bridged by carboxylate groups to chains with almost the same Gd³⁺–Gd³⁺ distances (494.0(8) and 503.4(7) pm). The magnetic behaviour of 1 and 2 was investigated in the temperature range of 1.76–300 K. The magnetic data indicate weak antiferromagnetic interactions within the dimeric unit.     

Optically active iridium complexes with cyclopentadienyl-phosphine ligands: synthesis and oxidative addition of methyl iodide

The dimer [Ir(μ-Cl)(C₈H₁₄)₂]₂ reacts with the ligands (S)-(C₅H₄CH₂CH(Ph)PPh₂)Li and (R)-(C₅H₄CH(Cy)CH₂PPh₂)Li to give (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(C₈H₁₄)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(C₈H₁₄)], which upon treatment with CH₃I at room temperature afford the cationic iridium(III) compounds (S,S_Ir)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(C₈H₁₄)][I] as a single diastereomer, and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(C₈H₁₄)][I] as a 9:1 mixture of two diastereomers. If the oxidative addition reaction is performed at reflux in methylene chloride, the starting complexes convert to the neutral compounds (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(I)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(I)] as 1.6:1 and 3.3:1 mixtures of diastereoisomers, respectively. Carbonyl iridium complexes are synthesized by reacting [IrCl(CO)(PPh₃)₂] with the ligands to afford (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CO)] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CO)]. They give upon treatment with CH₃I the cationic species (S)-[Ir(η⁵-C₅H₄CH₂CH(Ph)PPh₂-κP)(CH₃)(CO)][I] and (R)-[Ir(η⁵-C₅H₄CH(Cy)CH₂PPh₂-κP)(CH₃)(CO)][I] as 1.6:1 and 3:1 mixture of diastereomers, respectively. No migratory-insertion of the methyl group into the carbonyl-metal bond has been observed even after prolonged heating.     

Macromolecular ionophores. 1. Chiral recognition properties of poly[(1→6)-2,5-anhydro-D-glucitol] toward racemic amino acid ester

The chiral recognition property of poly[(1→6)-2,5-anhydro-3,4-di-O-alkyl-D-glucitol] ( 1 ) toward racemic RCH (CO₂CH₃)NH₃⁺ · PF₆^? ( 2 · HPF₆) has been studied using a transport system involving an aqueous source and receiving phases separated by a chloroform phase containing 1 . Transport rates for aromatic guests 2a (R = Ph) and 2b (R = CH₂Ph) were faster than those for aliphatic guests, 2c (R = CH(CH₃)₂) and 2d (R = CH₂CH(CH₃)₂), using the polymer substituted with methyl groups ( 1a ). The enantiomeric excess (e.e.) was 10.9% for 2a as a maximum value and decreased in the order of 2a > 2c > 2b = 2d . When the transport of 2a · HPF₆ was carried out using the polymers with 3,4-di-O-methyl ( 1a ), ethyl ( 1b ), allyl ( 1c ), and pentyl ( 1d ) groups, the e.e. was 22.0% for 1d as a maximum value and increased in the order of 1a < 1b < 1c < 1d . The formation of a complex between 1a and 2a · HPF₆ was confirmed by ¹H and ¹³C NMR spectral measurements. © 1995 Wiley-Liss, Inc.     

Semi-rigid tripeptide agonists of melanocortin receptors

A series of 30 RCO–HfR–NH₂ derivatives show preference for the mouse MC1R vs MC3-5Rs. trans-4-HOC₆H₄CHCHCO–HfR–NH₂ (13) [EC₅₀ (nM): MC1R 83, MC3R 20500, MC4R 18130 and MC5R 935; ratio 1:246:217:11] is 11 times more potent than the lead compound LK-394 Ph(CH₂)₃CO–HfR–NH₂ (2) and only 11 times less potent than the native tridecapeptide α-MSH at mMC1R. Differences in conformations of 2 and 13 are discussed.     

The kinetics of ligand substitution in bis(N-alkylsalicylaldiminato)nickel(II) Complexes: a study on the reactivity of square-planar versus octahedral coordination

The bis(N-alkylsalicylaldiminato)nickel(II) complexes Ni(R-sal)₂ with R = CH(CH₂OH)CH(OH)Ph (I), R = CH(CH₃)CH(OH)Ph (II) and R = CH₂CH₂Ph (III; Ph = phenyl) were prepared and characterized. In the solid state I and II are paramagnetic (μ = 3.2 and 3.3 BM at 20 °C, respectively), whereas III is diamagnetic. It follows from the UV-Vis spectra that in acetone solution I is six-coordinate octahedral and III is four-coordinate planar, the spectrum of II showing characteristics of both modes of coordination. Vis spectrophotometry and stopped-flow spectrophotometry were applied to study the kinetics of ligand substitution in I–III by H₂salen (= N,N′-disalicylidene-ethylenediamine) in the solvent acetone at different temperatures. The kinetics follow a second-order rate law, rate = k[H₂-salen] [complex]. At 20 °C the sequence of rate constants is k(III):k(II):k(I) = 11 850:40.6:1. The activation parameters are ΔH^≠(I) = 112, ΔH^≠(II) = 40.7, ΔH^≠(III) = 35.7 kJ mol⁻¹ and ΔS^≠(I) = 92, ΔS^≠(II) = −103, ΔS^≠(III) = −89 J K⁻¹ mol⁻¹. The enormous difference in rate between complexes I, II and III, which is less pronounced in methanol, is attributed to the existence of a fast equilibrium planar ⇌ octahedral, which is established in the case of I and II by intramolecular octahedral coordination through the hydroxyl groups present in the organic group R. An A-mechanism is suggested to control the substitution in the sense that the entering ligand attacks the four-coordinate planar complex, the octahedral complex being kinetically inert.     

The House Fly Attractants in Mushrooms

A house fly attracting substance, referred to as D₃ in the preceeding paper,¹⁾ was identified with 1,3-diolein.

Among the related compounds, 1- and 2-monoolein and α,ω-glycol monooleate with the formula: CH₃(CH₂)₇CH=CH(CH₂)₇COO(CH₂)_nOH (n≦6), were found to have activities ten times that of 1,3-diolein.     

Kinetic and mechanistic studies on the ruthenium induced activation of methylamine to oxidation

When aqueous solutions containing [Ru(NH₂CH₃)₆]²⁺ are exposed to oxygen [Ru(NH₂CH₃)₅(OH]²⁺ is produced as an identifiable intermediate as a result of the slow replacement of co-ordinated methylamine by water, and the subsequent rapid oxidation of this ruthenium(II) aquo complex. The [Ru(NH₂CH₃)₅(OH)]²⁺ ion then undergoes another slow reaction, probably the replacement of another methylamine ligand by water. All subsequent reactions leading to Ru(CN)₃·3H₂O are rapid. Rate data are reported, and a mechanism involving β-elimination from co-ordinated methylamine is postulated.     

Molecular orbital study of complexes of zinc(II) with sulphide, thiomethanolate, thiomethanol, dimethylthioether, thiophenolate, formiate, acetate, carbonate, hydrogen carbonate, iminomethane and imidazole. Relationships with structural and catalytic zinc in some metallo-enzymes.

Geometry optimization and energy calculations have been performed at the density functional B3LYP/LANL2DZ level on hydrogen sulfide (HS-), dihydrogensulfide (H2S), thiomethanolate (CH3S-), thiomethanol (CH3SH), thiophenolate (C6H5S-), methoxyde (CH3O-), methanol (CH3OH), formiate (HCOO-), acetate (CH3COO-), carbonate (CO3(2-)), hydrogen carbonate (HCO3-), iminomethane (NH=CH2), [ZnS], [ZnS2]2-, [Zn(HS)]+, [Zn(H2S)]2+, [Zn(HS)4]2-, [Zn(CH3S)]+, [Zn(CH3S)2], [Zn(CH3S)3]-, [Zn(CH3S)4]2-, [Zn(CH3SH)]2+, [Zn(CH3SCH3)]2+, [Zn(C6H5S)]+, [Zn(C6H5S)2], [Zn(C6H5S)3]-, [Zn(HS)(NH=CH2)2]+, [Zn(HS)2(NH=CH2)2], [Zn(HS)(H2O)]+, [Zn(HS)(HCOO)], [Zn(HS)2(HCOO)]-, [Zn(CH3O)]+, [Zn(CH3O)2], [Zn(CH3O)3]-, [Zn(CH3O)4]2, [Zn(CH3OH)]2+, [Zn(HCOO)]+, [Zn(CH3COO)]+, [Zn(CH3COO)2], [Zn(CH3COO)3]-, [Zn(CO3)], [Zn(HCO3)]+, and [Zn(HCO3)(Imz)]+ (Imz, 1,3-imidazole). The computed Zn-S bond distances are 2.174A for [ZnS], 2.274 for [Zn(HS)]+, 2.283 for [Zn(CH3S)]+, and 2.271 for [Zn(C6H5S)]+, showing that sulfide anion forms stronger bonds than substituted sulfides. The nature of the substituents on sulfur influences only slightly the Zn-S distance. The optimized tetra-coordinate [Zn(HS)2(NH=CH2)2] molecules has computed Zn-S and Zn-N bond distances of 2.392 and 2.154A which compare well with the experimental values at the solid state obtained via X-ray diffraction for a number of complex molecules. The computed Zn-O bond distances for chelating carboxylate derivatives like [Zn(HOCOO)]+ (1.998A), [Zn(HCOO)]+ (2.021), and [Zn(CH3COO)]+ (2.001) shows that the strength of the bond is not much influenced by the substituent on carboxylic carbon atom and that CH3- and HO- groups have very similar effects. The DFT analysis shows also that the carboxylate Ligand has a preference for the bidentate mode instead of the monodentate one, at least when the coordination number is small.     

Tris(triazolyl)borate ligands of intermediate steric bulk for the synthesis of biomimetic structures with hydrogen bonding and solubility in hydrophilic solvents

Tris(triazolyl)borate ligands (Ttz) of intermediate steric bulk were synthesized to investigate their potential for hydrogen bonding and improved solubility in hydrophilic solvents as applied to biomimetic chemistry. The crystal structure of 3-phenyl-5-methyl-1,2,4-triazole (Htz^Ph,Me) revealed hydrogen bonding and π stacking interactions. The new ligand salt, potassium tris(3-phenyl-5-methyl-1,2,4-triazolyl)borate (KTtz^Ph,Me) was synthesized as the first example of a Ttz ligand of intermediate steric bulk. Metathesis between KTtz^Ph,Me and NaCl followed by recrystallization produced [NaTtz^Ph,Me] · 6CH₃OH in which the geometry around the sodium is octahedral with an unusual N₃O₃ donor set; this structure also shows that a hydrogen bonding network is formed by methanol molecules and triazole nitrogens. (Ttz^Ph,Me)ZnCl was synthesized and characterized crystallographically as [(Ttz^Ph,Me)ZnCl] · 0.5CH₃OH in which the zinc is tetrahedral and the triazole rings are within hydrogen bonding distance of CH₃OH. All of these new compounds are methanol soluble to varying degrees and Htz^Ph,Me and KTtz^Ph,Me are soluble in methanol/water mixtures.     

Silver(I) complexes of dibenzo-18-crown-6-ether having cation-π and π-π interactions

Three silver(I) complexes of dibenzo-18-crown-6-ether (DB[18]C6), [Ag(DB[18]C6)(ClO₄)](THF) (1), [Ag(DB[18]6)(CF₃SO₃)]₂(acetone)₂ (2) and [Ag(DB[18]C6)(CF₃COO)]₂(AgCF₃COO)₂ (3) have been synthesized in different solvents and characterized structurally. In each complex, silver ions prefer an octahedral coordination geometry and form close dinuclear complex with DB[18]C6 based on cation-π interaction in η²-fashion. In particular, the coordination unit involving σ bonding at an oxygen group and π-π bonding between two benzene rings is quite unique.     

Preparation of planar chiral ferrocenes containing a fluorous alcohol function

Ferrocene reacts with hexafluoroacetone trihydrate in refluxing octane to afford >80% yields of [CpFe(η⁵-C₅H₄C(CF₃)₂OH)] (X-ray), carrying out the reactions at 180 °C gives an additional 5% yield of [Fe(η⁵-C₅H₄C(CF₃)₂OH)₂] (X-ray).The mono alcohol is lithiated with Bu^tOK/BuⁿLi/TMEDA affording partial conversion to mixtures of [CpFe(1,2-η⁵-C₅H₃C(CF₃)₂OH)(X)] and [Fe(η⁵-C₅H₄X)(1,2-η⁵-C₅H₃C(CF₃)₂OH)(X)] (X = SMe, CPh₂OH) upon reaction with Me₂S₂ or OCPh₂.For X = CPh₂OH both structures are crystallographically characterised.Enantiopure [CpFe(1,2-η⁵-C₅H₃C(CF₃)₂OH)(SMe)] can be prepared from (R)-[CpFe(η⁵-C₅H₄S(O)C₆H₄Me)] via [CpFe(1,2-η⁵-C₅H₃S(O)C₆H₄Me)(C(CF₃)₂OH)] (X-ray) or [CpFe(1,2-η⁵-C₅H₃S(O)C₆H₄Me)(SMe)].Related procedures allow the preparation of [CpFe(1,2-η⁵-C₅H₃CPh₂OH)(Y)] (Y = SMe, CHO (X-ray), C(CF₃)₂OH) and[CpFe(1,2-η⁵-C₅H₃C(CF₃)₂OH)(CHO)].     

Chiroptical properties of diastereomeric five-coordinate Pt(II)–olefin complexes. Molecular structure of [PtCl2{(S,S)-(E)-CNCHCHCN}(R,R)-{C6H5CH(CH3)N(CH3)CH2}2]·C6H6

The chiroptical properties of five-coordinate diastereomeric complexes of general formula [PtCl₂(R,R)-{C₆H₅CH(CH₃)N(CH₃)CH₂}₂{olefin}], with olefin ligands having electron-withdrawing substituents, have been investigated. The sign of CD bands in the 28 000–30 000 cm⁻¹ region appears to be correlated to the absolute configuration of the prochiral coordinated alkene. Single-crystal X-ray diffraction structure determination has been performed on the single diastereomer [PtCl₂(E-but-2-enedinitrile)(R,R)-{C₆H₅CH(CH₃)N(CH₃)CH₂}₂]· C₆H₆. The compound crystallizes in the monoclinic space group C2 with a = 17.842(2), b = 8.466(1), c = 10.464(1) Å, β = 109.34(1)°, Z = 2. The number of observed reflections was 1943 and the final R and R_w values were 0.020 and 0.028 respectively. Trigonal-bipyramidal geometry is observed around the Pt atom, with the two Cl atoms in axial positions. The unsaturated ligand lies in the equatorial plane disclosing S,S absolute configuration.     

Preference for bridging versus terminal ligands in magnesium dimers

Magnesium dimers play important roles in inorganic and organometallic chemistry. This study evaluates the inherent bridging ability of a range of different ligands in magnesium dimers. In the first part, the Cambridge Structural Database is interrogated to establish the frequency of different types of ligands found in bridging versus terminal positions in two key structural motifs: one in which there are two bridging ligands (the D _2h “Mg₂(μ-X₂)” structure); the other in which there are three bridging ligands (the C _3v “Mg₂(μ-X₃)” structure). The most striking finding from the database search is the overwhelming preference for magnesium dimers possessing two bridging ligands. The most common bridging ligands are C-, N-, and O-based. In the second part, DFT calculations (at the B3LYP/6-311+G(d) level of theory) are carried out to examine a wider range of structural types for dimers consisting of the stoichiometries Mg₂Cl₃R and Mg₂Cl₂R₂, where R = CH₃, SiH₃, NH₂, PH₂, OH, SH, CH₂CH₃, CH=CH₂, C≡CH, Ph, OAc, F and Br. Consistent with the database search, the most stable magnesium dimers are those that contain two bridging ligands. Furthermore, it was demonstrated that the electronic effect of the bridging ligands is important in influencing the stability of the magnesium dimers. The preference for a bridging ligand, which reflects its ability to stabilize a magnesium dimer, follows the order: OH > NH₂ > C≡CH > SH > Ph > Br > PH₂ = CH=CH₂ > CH₂CH₃ > CH₃ > SiH₃. Finally, the role that the ether solvent Me₂O has on the stability of isomeric Mg₂Cl₂Me₂ dimers was studied. It was found that the first solvent molecule stabilizes the dimers, while the second solvent molecule can either have a stabilizing or destabilizing effect, depending on the isomer structure.     

Synthesis, structure and optic properties of 2-methylimidazolium and 2-phenylimidazolium uranyl acetates

Two new salts based on heterocyclic organic cations and uranyl triacetate anion were obtained via reaction of zinc uranyl acetate with 2-substituted imidazoles in presence of an excess of acetic acid. Uranyl triacetate anion in [2-MeImH]⁺ [UO₂(CH₃COO)₃]⁻ and [2-PhImH]⁺ [UO₂(CH₃COO)₃]⁻ H₂O has an expected bipyramidal structure with linear uranyl group and three acetate groups laying in equatorial plane. [2-MeImH]⁺ [UO₂(CH₃COO)₃]⁻ structure analysis reveals H-bonded 1D chains connected through N-H···O hydrogen bonds. 2-phenylimidazolium in [2-PhImH]⁺ [UO₂(CH₃COO)₃]⁻ H₂O demonstrate planar geometry without any rotation of its rings, which was not registered before. H-bonds and π-π interactions of phenyl groups in this system lead to complicate 2D “sandwich” layer formation. The main features of IR- and luminescence spectrum of both compounds are also discussed.     

Structural comparison of octahedral MoO22+ complexes of bidentate and linear tetradentate N,S-donor ligands

The structures of MoO₂[NH₂C(CH₃)₂CH₂S]₂ and MoO₂[SC(CH₃)₂CH₂NHCH₂CH₂NHCH₂C(CH₃)₂S] have been determined using X-ray diffraction intensity data collected by counter techniques. MoO₂[NH₂C(CH₃)₂CH₂S]₂ crystallizes in space group Pbca with a = 11.234(3), b = 11.822(3) and c = 20.179(5) Å, V = 2680(2) ų and Z = 8. Its structure is derived from octahedral coordination with cis oxo groups [MoO = 1.705(3) and 1.705(3)], trans thiolate donors cis to the oxo groups [MoS = 2.416(1) and 2.402(1) and N donors trans to oxo [MoN = 2.325(3) and 2.385(4) Å]. MoO₂[SC(CH₃)₂CH₂NHCH₂CH₂NHCH₂C(CH₃)₂S] crystallizes in the space group P2₁/c with a = 10.798(5), b = 6.911(2), c = 20.333(9) Å, β = 95.20°, V = 1511(2) Å₃ and Z = 4. Its structure is very similar to that of MoO₂[NH₂C(CH₃)₂CH₂S]₂ with MoO = 1.714(2) and 1.710(2), MoS = 2.415(1) and 2.404(1) and MoN = 2.316(3) and 2.362(3). The small differences in the geometries of the two compounds are attributed to the constraints of the extra chelate ring in the complex with the tetradentate ligand. The structures in this paper stand in contrast to those reported for complexes of similar ligands wherein steric hindrance produces complexes with a skew trapezoidal bipyramidal structure.     

The reactivity of affinity labels: A kinetic study of the reaction of alkyl halides with thiolate anions—a model reaction for protein alkylation

Factors have been investigated which govern the electrophilic reactivity of alkyl halides with thiolate anions in aqueous solution. In the series of alkyl halides studied, some are potential metal-directed affinity labels, while others are frequently used in protein modification. Previous data on the kinetics of this type of alkylation are compared with the present results. The influence of electronic, polar, and steric factors on alkyl halide reactivity is seen. The following order of reactivity for alkyl halides bearing different α substituents was observed: RCH₂CH(X)COOCH₃ > RCH₂CH(X)CONH₂ > RCH₂CH(X)COOH > RCH₂CH₂X > RCH₂CH(X)CH₂OH. The metal-directed affinity labels are imidazole derivatives, some of which have substituents in their imidazole ring. The effect of the imidazole ring and of ring substitution on reactivity is seen. The nucleophilic reactivity of thiols is highly pH dependent since the thiolate anion (RS^?) is the reactive species, but only minor differences emerged between different free thiolates.