PDBe: improved findability of macromolecular structure data in the PDB.

The Protein Data Bank in Europe (PDBe), a founding member of the Worldwide Protein Data Bank (wwPDB), actively participates in the deposition, curation, validation, archiving and dissemination of macromolecular structure data. PDBe supports diverse research communities in their use of macromolecular structures by enriching the PDB data and by providing advanced tools and services for effective data access, visualization and analysis. This paper details the enrichment of data at PDBe, including mapping of RNA structures to Rfam, and identification of molecules that act as cofactors. PDBe has developed an advanced search facility with ∼100 data categories and sequence searches. New features have been included in the LiteMol viewer at PDBe, with updated visualization of carbohydrates and nucleic acids. Small molecules are now mapped more extensively to external databases and their visual representation has been enhanced. These advances help users to more easily find and interpret macromolecular structure data in order to solve scientific problems.

PDBe: towards reusable data delivery infrastructure at protein data bank in Europe.

The Protein Data Bank in Europe (PDBe, pdbe.org) is actively engaged in the deposition, annotation, remediation, enrichment and dissemination of macromolecular structure data. This paper describes new developments and improvements at PDBe addressing three challenging areas: data enrichment, data dissemination and functional reusability. New features of the PDBe Web site are discussed, including a context dependent menu providing links to raw experimental data and improved presentation of structures solved by hybrid methods. The paper also summarizes the features of the LiteMol suite, which is a set of services enabling fast and interactive 3D visualization of structures, with associated experimental maps, annotations and quality assessment information. We introduce a library of Web components which can be easily reused to port data and functionality available at PDBe to other services. We also introduce updates to the SIFTS resource which maps PDB data to other bioinformatics resources, and the PDBe REST API.

Molecular Manipulations of a Utility Nitrogen-Heterocyclic Carbene by Sodium Magnesiate Complexes and Transmetallation Chemistry with Gold Complexes.

Expanding the scope and applications of anionic N-heterocyclic carbenes (NHCs), a novel series of magnesium NHC complexes is reported using a mixed sodium-magnesium approach. Sequential reactivity of classical imidazol- 2-ylidene carbene IPr with NaR and MgR2 (R=CH2 SiMe3 ) affords [(THF)3 Na(µ-IPr- )MgR2 (THF)] (2) [IPr- =:C{[N(2,6-iPr2 C6 H3 )]2 CHC] containing an anionic NHC ligand, whereas surprisingly sodium magnesiate [NaMgR3 ] fails to deprotonate IPr affording instead the redistribution coordination adduct [IPr2 Na2 MgR4 ] (1). Compound 2 undergoes selective C2-methylation when treated with MeOTf furnishing novel abnormal NHC complex [{aIPrMe MgR2 }2 ] (3). Dissolving 3 in THF led to the dissociation of this complex into MgR2 and aIPrMe with the latter isomerizing to the olefinic NHC IPr=CH2 . The ability of 2 and 3 to transfer their anionic and abnormal NHC ligands, respectively to AuI metal fragments has been investigated allowing the isolation and structural characterization of [RAu(µ-IPr- )MgR(THF)2 ] (4) and [aIPrMe AuR] (5) respectively. In both cases transfer of an alkyl R group is observed. However while 3 can also transfer its abnormal NHC ligand to give 5, in 4 the anionic NHC still remains coordinated to Mg via its C4 position, whereas the {AuR} fragment occupies the C2 position previously filled by a donor-solvated {Na(THF)3 }+ cation.

PDBe: improved accessibility of macromolecular structure data from PDB and EMDB.

The Protein Data Bank in Europe (http://pdbe.org) accepts and annotates depositions of macromolecular structure data in the PDB and EMDB archives and enriches, integrates and disseminates structural information in a variety of ways. The PDBe website has been redesigned based on an analysis of user requirements, and now offers intuitive access to improved and value-added macromolecular structure information. Unique value-added information includes lists of reviews and research articles that cite or mention PDB entries as well as access to figures and legends from full-text open-access publications that describe PDB entries. A powerful new query system not only shows all the PDB entries that match a given query, but also shows the 'best structures' for a given macromolecule, ligand complex or sequence family using data-quality information from the wwPDB validation reports. A PDBe RESTful API has been developed to provide unified access to macromolecular structure data available in the PDB and EMDB archives as well as value-added annotations, e.g. regarding structure quality and up-to-date cross-reference information from the SIFTS resource. Taken together, these new developments facilitate unified access to macromolecular structure data in an intuitive way for non-expert users and support expert users in analysing macromolecular structure data.

Understanding the Subtleties of Frustrated Lewis Pair Activation of Carbonyl Compounds by N-Heterocyclic Carbene/Alkyl Gallium Pairings.

This study reports the use of the trisalkylgallium GaR3 (R=CH2 SiMe3 ), containing sterically demanding monosilyl groups, as an effective Lewis-acid component for frustrated Lewis pair activation of carbonyl compounds, when combined with the bulky N-heterocyclic carbene 1,3-bis(tert-butyl)imidazol-2-ylidene (ItBu) or 1,3-bis(tert-butyl)imidazolin-2-ylidene (SItBu). The reduction of aldehydes can be achieved by insertion into the C=O functionality at the C2 (so-called normal) position of the carbene affording zwitterionic products [ItBuCH2 OGaR3 ] (1) or [ItBuCH(p-Br-C6 H4 )OGaR3 ] (2), or alternatively, at its abnormal (C4) site yielding [aItBuCH(p-Br-C6 H4 )OGaR3 ] (3). As evidence of the cooperative behaviour of both components, ItBu and GaR3 , neither of them alone are able to activate any of the carbonyl-containing substrates included in this study NMR spectroscopic studies of the new compounds point to complex equilibria involving the formation of kinetic and thermodynamic species as implicated through DFT calculations. Extension to ketones proved successful for electrophilic α,α,α-trifluoroacetophenone, yielding [aItBuC(Ph)(CF3 )OGaR3 ] (7). However, in the case of ketones and nitriles bearing acidic hydrogen atoms, C-H bond activation takes place preferentially, affording novel imidazolium gallate salts such as [{ItBuH}+ {(p-I-C6 H4 )C(CH2 )OGaR3 }- ] (8) or [{ItBuH}+ {Ph2 C=C=NGaR3 }- ] (12).

Developing lithium chemistry of 1,2-dihydropyridines: from kinetic intermediates to isolable characterized compounds.

Generally considered kinetic intermediates in addition reactions of alkyllithiums to pyridine, 1-lithio-2-alkyl-1,2-dihydropyridines have been rarely isolated or characterized. This study develops their "isolated" chemistry. By a unique stoichiometric (that is, 1:1, alkyllithium/pyridine ratios) synthetic approach using tridentate donors we show it is possible to stabilize and hence crystallize monomeric complexes where alkyl is tert-butyl. Theoretical calculations probing the donor-free parent tert-butyl species reveal 12 energetically similar stereoisomers in two distinct cyclotrimeric (LiN)3 conformations. NMR spectroscopy studies (including DOSY spectra) and thermal volatility analysis compare new sec-butyl and iso-butyl isomers showing the former is a hexane soluble efficient hydrolithiation agent converting benzophenone to lithium diphenylmethoxide. Emphasizing the criticalness of stoichiometry, reaction of nBuLi/Me6 TREN with two equivalents of pyridine results in non-alkylated 1-lithio-1,4-dihydropyridine⋅Me6 TREN and 2-n-butylpyridine, implying mechanistically the kinetic 1,2-n-butyl intermediate hydrolithiates the second pyridine.

S-alkylation of soft scorpionates.

The alkylation reactions of soft scorpionates are reported. The hydrotris(S-alkyl-methimazolyl)borate dications (alkyl = methyl, allyl, benzyl), which were prepared by the reaction of Tm(Me) anion and primary alkyl halides, have been isolated and structurally characterised. The reaction is, however, not universally successful. DFT analysis of these alkylation reactions (C=S versus B-H alkylation) indicates that the observed outcome is driven by kinetic factors. Extending the study to incorporate alternative imine thiones (mercaptobenzothiazole, bz; thiazoline, tz) led to the structural characterisation of di[aquo-µ-aquohydrotris(mercaptobenzothiazolyl)boratosodium], which contains sodium atoms in the κ(3)-S,S,S coordination mode. Alkylation of Na[Tbz] and Na[tzTtz] leads to decomposition resulting in the formation of the simple S-alkylated heterocycles. The analysis of the species involved in these reactions shows an inherent weakness in the B-N bond in soft scorpionates, which has implications for their use in more advanced chemistry.

Evaluating cis-2,6-dimethylpiperidide (cis-DMP) as a base component in lithium-mediated zincation chemistry.

Most recent advances in metallation chemistry have centred on the bulky secondary amide 2,2,6,6-tetramethylpiperidide (TMP) within mixed metal, often ate, compositions. However, the precursor amine TMP(H) is rather expensive so a cheaper substitute would be welcome. Thus this study was aimed towards developing cheaper non-TMP based mixed-metal bases and, as cis-2,6-dimethylpiperidide (cis-DMP) was chosen as the alternative amide, developing cis-DMP zincate chemistry which has received meagre attention compared to that of its methyl-rich counterpart TMP. A new lithium diethylzincate, [(TMEDA)LiZn(cis-DMP)Et2] (TMEDA=N,N,N',N'-tetramethylethylenediamine) has been synthesised by co-complexation of Li(cis-DMP), Et2Zn and TMEDA, and characterised by NMR (including DOSY) spectroscopy and X-ray crystallography, which revealed a dinuclear contact ion pair arrangement. By using N,N-diisopropylbenzamide as a test aromatic substrate, the deprotonative reactivity of [(TMEDA)LiZn(cis-DMP)Et2] has been probed and contrasted with that of the known but previously uninvestigated di-tert-butylzincate, [(TMEDA)LiZn(cis-DMP)tBu2]. The former was found to be the superior base (for example, producing the ortho-deuteriated product in respective yields of 78% and 48% following D2O quenching of zincated benzamide intermediates). An 88% yield of 2-iodo-N,N-diisopropylbenzamide was obtained on reaction of two equivalents of the diethylzincate with the benzamide followed by iodination. Comparisons are also drawn using 1,1,1,3,3,3-hexamethyldisilazide (HMDS), diisopropylamide and TMP as the amide component in the lithium amide, Et2Zn and TMEDA system. Under certain conditions, the cis-DMP base system was found to give improved results in comparison to HMDS and diisopropylamide (DA), and comparable results to a TMP system. Two novel complexes isolated from reactions of the di-tert-butylzincate and crystallographically characterised, namely the pre-metallation complex [{(iPr)2N(Ph)C=O}LiZn(cis-DMP)tBu2] and the post-metallation complex [(TMEDA)Li(cis-DMP){2-[1-C(=O)N(iPr)2]C6H4}Zn(tBu)], shed valuable light on the structures and mechanisms involved in these alkali-metal-mediated zincation reactions. Aspects of these reactions are also modelled by DFT calculations.

Soft scorpionate anions as platforms for novel heterocycles.

Soft scorpionates have thus far been seen mainly as a family of ligands. Their chemistry is extended here to the production of novel cationic macrocycles using dihaloalkanes. By replacing the dihaloalkanes with mild oxidising agents (NO(+), I2) we obtain two unique polycyclic heterocycles. The mechanism which leads to the formation of these polycyclic heterocycles is investigated using ab initio DFT calculations.

Monomerizing alkali-metal 3,5-dimethylbenzyl salts with tris(N, N-dimethyl-2-aminoethyl)amine (Me6TREN): structural and bonding implications.

The series of alkali-metal (Li, Na, K) complexes of the substituted benzyl anion 3,5-dimethylbenzyl (Me2C6H3CH2(-)) derived from 1,3,5-trimethylbenzene (mesitylene) have been coerced into monomeric forms by supporting them with the tripodal tetradentate Lewis donor tris(N,N-dimethyl-2-aminoethyl)amine, [N(CH2CH2NMe2)3, Me6TREN]. Molecular structure analysis by X-ray crystallography establishes that the cation-anion interaction varies as a function of the alkali-metal, with the carbanion binding to lithium mainly in a σ fashion, to potassium mainly in a π fashion, with the interaction toward sodium being intermediate between these two extremes. This distinction is due to the heavier alkali-metal forcing and using the delocalization of negative charge into the aromatic ring to gain a higher coordination number in accordance with its size. Me6TREN binds the metal in a η(4) mode at all times. This coordination isomerism is shown by multinuclear NMR spectroscopy to also extend to the structures in solution and is further supported by density functional theory (DFT) calculations on model systems. A Me6TREN stabilized benzyl potassium complex has been used to prepare a mixed-metal ate complex by a cocomplexation reaction with tBu2Zn, with the benzyl ligand acting as an unusual ditopic σ/π bridging ligand between the two metals, and with the small zinc atom relocalizing the negative charge back on to the lateral CH2 arm to give a complex best described as a contacted ion pair potassium zincate.

Developing a hetero-alkali-metal chemistry of 2,2,6,6-tetramethylpiperidide (TMP): stoichiometric and structural diversity within a series of lithium/sodium, lithium/potassium and sodium/potassium TMP compounds.

Studied extensively in solution and in the solid state, Li(TMP) (TMP=2,2,6,6-tetramethylpiperidide) is an important utility reagent popular as a strongly basic, weakly nucleophilic tool for C-H metallation. Recently, there has been a surge in interest in mixed metal derivatives containing the bulky TMP anion. Herein, we start to develop hetero (alkali metal) TMP chemistry by reporting the N,N,N',N'-tetramethylethylenediamine (TMEDA)-hemisolvated sodium-lithium cycloheterodimer [(tmeda)Na(µ-tmp)(2) Li], and its TMEDA-free variant [{Na(µ-tmp)Li(µ-tmp)}(∞)], which provides a rare example of a crystallographically authenticated polymeric alkali metal amide. Experimental observations suggest that the former is a kinetic intermediate en route to the latter thermodynamic product. Furthermore, a third modification, the mixed potassium-lithium-rich cycloheterotrimer [(tmeda)K(µ-tmp)Li(µ-tmp)Li(µ-tmp)], has also been synthesised and crystallographically characterised. On moving to the bulkier tridentate donor N,N,N',N'',N''-pentamethyldiethylenediamine (PMDETA), the additional ligation forces the sodium-lithium and potassium-dilithium ring species to open giving the acyclic arc-shaped complexes [(pmdeta)Na(µ-tmp)Li(tmp)] and [(pmdeta)K(µ-tmp)Li(µ-tmp)Li(tmp)], respectively. Completing the series, the potassium-lithium and potassium-sodium derivatives [(pmdeta)K(µ-tmp)(2) M] (M=Li, Na) have also been isolated as closed structures with a distinctly asymmetric central MN(2) K ring. Collectively, these seven new bimetallic compounds display five distinct structural motifs, four of which have never hitherto been witnessed in TMP chemistry and three of which are unprecedented in the vast structural library of alkali metal amide chemistry.

Molecular structures of THF-solvated alkali-metal 2,2,6,6-tetramethylpiperidides finally revealed: X-ray crystallographic, DFT, and NMR (including DOSY) spectroscopic studies.

The often studied THF solvates of the utility alkali-metal amides lithium and sodium 2,2,6,6-tetramethylpiperidide are shown to exist in the solid state as asymmetric cyclic dimers containing a central M(2)N(2) ring and one molecule of donor per metal to give a distorted trigonal planar metal coordination. DFT studies support these structures and confirm the asymmetry in the ring. In C(6)D(12) solution, the lithium amide displays a concentration-dependent equilibrium between a solvated and unsolvated species which have been shown by diffusion-ordered NMR spectroscopy (DOSY) to be a dimer and larger oligomer, respectively. A third species, a solvated monomer, is also present in very low concentration, as proven by spiking the NMR sample with THF. In contrast, the sodium amide displays a far simpler C(6)D(12) solution chemistry, consistent with the solid-state dimeric arrangement but with labile THF ligands.

Expanding Mg-Zn hybrid chemistry: inorganic salt effects in addition reactions of organozinc reagents to trifluoroacetophenone and the implications for a synergistic lithium-magnesium-zinc activation.

Numerous organic transformations rely on organozinc compounds made through salt-metathesis (exchange) reactions from organolithium or Grignard reagents with a suitable zinc precursor. By combining X-ray crystallography, NMR spectroscopy and DFT calculations, this study sheds new light on the constitution of the organometallic species involved in this important synthetic tool. Investigations into the metathesis reactions of equimolar amounts of Grignard reagents (RMgX) and ZnCl(2) in THF led to the isolation of novel magnesium-zinc hybrids, [{(thf)(2)Mg(µ-Cl)(3)ZnR}(2)] (R=Et, tBu, nBu or o-OMe-C(6)H(4)), which exhibit an unprecedented structural motif in mixed magnesium-zinc chemistry. Furthermore, theoretical modelling of the reaction of EtMgCl with ZnCl(2) reveals that formation of the mixed-metal compound is thermodynamically preferred to that of the expected homometallic products, RZnCl and MgCl(2). This study also assesses the alkylating ability of hybrid 3 towards the sensitive ketone trifluoroacetophenone, revealing a dramatic increase in the chemoselectivity of the reaction when LiCl is introduced as an additive. This observation, combined with recent related breakthroughs in synthesis, points towards the existence of a trilateral Li/Mg/Zn synergistic effect.

Shedding new light on ZnCl2-mediated addition reactions of Grignard reagents to ketones: structural authentication of key intermediates and diffusion-ordered NMR studies.

Building on recent advances in synthesis showing that the addition of inorganic salts to Grignard reagents can greatly enhance their performance in alkylation reactions to ketones, this study explores the reactions of EtMgCl with benzophenone in the presence of stoichiometric or catalytic amounts of ZnCl(2) with the aim of furthering the understanding of the role and constitution of the organometallic species involved in these transformations. Investigations into the metathesis reactions of three molar equivalents of EtMgCl with ZnCl(2) led to the isolation and characterisation (X-ray crystallography and (1)H and (13)C NMR spectroscopy) of novel magnesium "zinc-rich" zincate [{(THF)(6)Mg(2)Cl(3)}(+){Zn(2)Et(5)}(-)] (1), whose complicated constitution in THF solutions was assessed by variable-temperature (1)H DOSY NMR studies. Compound 1 reacted with one equivalent of benzophenone to yield magnesium magnesiate [{(THF)(6)Mg(2)Cl(3)}(+){Mg(2)(OC(Et)Ph(2))(2)Cl(3)(THF)}(-)] (3), whose structure was determined by X-ray crystallography. (1)H NMR monitoring of this reaction showed two equivalents of ZnEt(2) formed as a co-product, which together with the "magnesium only constitution" of 3 provides experimental insights into how zinc can be efficiently recycled in these reactions, and therefore used catalytically. The chemoselectivity of this reaction can be rationalised in terms of the synergic effect of magnesium and zinc and contrasts with the results obtained when benzophenone was allowed to react with EtMgCl in the absence of ZnCl(2), where the reduction of the ketone takes place preferentially. The reduction product [{(THF)(5)Mg(3)Cl(4){OC(H)Ph(CF(3))}(2)] (4) obtained from the reaction of EtMgCl with 2,2,2-trifluoroacetophenone was established by X-ray crystallography and multinuclear ((1)H, (13)C and (19)F) NMR spectroscopy. Compounds 3 and 4 exhibit new structural motifs in magnesium chemistry having MgCl(2) integrated within their constitution, which highlights the new role of this inorganic salt in providing structural support for the newly generated alkoxide ligand.

Structurally powered synergic 2,2,6,6-tetramethylpiperidine bimetallics: new reflections through lithium-mediated ortho aluminations.

Recent times have witnessed many notable advances in metalation chemistry with halide salt supported strategies and alkali-metal mediated metalation being particularly prominent. This article begins with a brief account of both of these avant garde metalation methods focusing on selected recent examples not covered previously in a review. New results in the area of Alkali-Metal Mediated Alumination (AMMAl) are also presented. Thus, the putative lithium aluminate base THF·Li(µ-TMP)(2)Al((i)Bu)(2) (4) is shown to act via TMP basicity to efficiently ortho deprotonate a variety of functionalized aromatic molecules at room temperature, tolerating carboxamide and halide functionalities. These metalated species are electrophilically quenched with elemental iodine. Crystal structure determinations of the metalated intermediates confirm unequivocally that direct alumination of the substrates has occurred. Since the homometallic lithium or aluminum reagents are unable to effect such deprotonations these reactions are synergic in nature and can be considered examples of AMMAl. Drawing together previously published work in the field of AMMAl, together with other pertinent experimental observations and new density functional theory (DFT) computational studies, we propose a potential rationale for the "unusual" reactivity patterns witnessed in this branch of heterometallic synthetic chemistry with respect to other Alkali Metal Mediated Metalations which appear to behave in a more conventional manner.

Meta-metallation of N,N-dimethylaniline: Contrasting direct sodium-mediated zincation with indirect sodiation-dialkylzinc co-complexation.

Previously we reported that direct zincation of N,N-dimethylaniline by the mixed-metal zincate reagent 1 ((TMEDA)Na(TMP)(t-Bu)Zn(t-Bu)) surprisingly led to meta-metallation (zincation) of the aniline, as manifested in the crystalline complex 2 ((TMEDA)Na(TMP)(m-C(6)H(4)-NMe(2))Zn(t-Bu)), and that iodination of these isolated crystals produced the meta-isomer N,N-dimethyl-3-iodoaniline quantitatively. Completing the study here we find that treating the reaction solution with iodine produces a 72% conversion and results in a mixture of regioisomers of N,N-dimethyliodoaniline, with the meta-isomer still the major product (ortho:meta:para ratio, 6:73:21), as determined by NMR. In contrast to this bimetallic method, sodiation of N,N-dimethylaniline with n-BuNa produced the dimeric, ortho-sodiated complex 3 (((TMEDA)Na(o-C(6)H(4)-NMe(2)))(2)), as characterised by X-ray crystallography and NMR. No regioisomers were observed in the reaction solution. Introducing t-Bu(2)Zn to this reaction solution afforded a cocrystalline product in the solid-state, composed of the bis-anilide 4 ((TMEDA)Na(o-C(6)H(4)-NMe(2))(2)Zn(t-Bu)) and the Me(2)N-C cleavage product 5 ({(TMEDA)(2)Na}(+){(t-Bu(2)Zn)(2)(µ-NMe(2))}(-)), which was characterised by X-ray crystallography. NMR studies of the reaction mixture that produces 4 and 5 revealed one additional species, but the mixture as a whole contained only ortho-species and a trace amount of para-species as established by iodine quenching. In an indirect variation of the bimetallic reaction, TMP(H) was added at room temperature to the reaction mixture that afforded 4 and 5. This gave the crystalline product 6 ((TMEDA)Na(TMP)(o-C(6)H(4)-NMe(2))Zn(t-Bu)), the ortho-isomer of the meta-complex 2, as determined from X-ray crystallographic and NMR data. Monitoring the regioselectivity of the reaction by iodination revealed a 16.6:1.6:1.0 ortho:meta:para ratio. Interestingly, when the TMP(H) containing solution was heated under reflux for 18 hours more meta-isomer was produced (corresponding ratio 3.7:4.2:1.0). It is likely that this change has its origin in a retro reaction that produces the original base 1 as an intermediate. Theoretical calculations at the DFT level using the B3LYP method and the 6-311G** basis set were used to probe the energetics of both monometallic and bimetallic systems. In accord with the experimental results, it was found that ortho-metallation was favoured by sodiation; whereas meta- (closely followed by para-) metallation was favoured by direct sodium-mediated zincation.

Structural basis for regioisomerization in the alkali-metal-mediated zincation (AMMZn) of trifluoromethyl benzene by isolation of kinetic and thermodynamic intermediates.

Performed with a desire to advance knowledge of the structures and mechanisms governing alkali-metal-mediated zincation, this study monitors the reaction between the TMP-dialkylzincate reagent [(TMEDA)Na(TMP)((t)Bu)Zn((t)Bu)] 1 and trifluoromethyl benzene C(6)H(5)CF(3) 2. A complicated mixture of products is observed at room temperature. X-ray crystallography has identified two of these products as ortho- and meta-regioisomers of heterotrianionic [(TMEDA)Na(TMP)(C(6)H(4)-CF(3))Zn((t)Bu)], 3-ortho and 3-meta, respectively. Multinuclear NMR data of the bulk crystalline product confirm the presence of these two regioisomers as well as a third isomer, 3-para, in a respective ratio of 20:11:1, and an additional product 4, which also exhibits ortho-zincation of the aryl substrate. Repeating the reaction at 0 degrees C gave exclusively 4, which was crystallographically characterized as [{(TMEDA)(2)Na}(+){Zn(C(6)H(4)-CF(3))((t)Bu)(2)}(-)]. Mimicking the original room-temperature reaction, this kinetic product was subsequently reacted with TMP(H) to afford a complicated mixture of products, including significantly the three regioisomers of 3. Surprisingly, 4 adopts a solvent-separated ion pair arrangement in contrast to the contacted ion variants of 3-ortho and 3-meta. Aided by DFT calculations on model systems, discussion focuses on the different basicities, amido or alkyl, and steps, exhibited in these reactions, and how the structures and bonding within these isolated key metallic intermediates (prior to any electrophilic interception step), specifically the interactions involving the alkali metal, influence the regioselectivity of the Zn-H exchange process.

Multidentate ligands for the synthesis of multimetallic complexes. 2. Formation of a planar Cu4OH motif.

The reaction of the multidentate Schiff base species TrenSal, TrenBrSal, and TEtSal with copper acetate is reported. The heptadentate ligands generate a tetrametallic L(2)Cu(4)OH motif that contains an internalized hydroxide anion. In contrast, the hexadentate TEtSal ligand is found to form an open trimetallic motif. The importance of L(2)Cu(4)OH to the family of copper complexes with an endohedral hydroxide anion is discussed. [(TrenBrSal)(2)Cu(4)OH][OAc] is analyzed by temperature-dependent magnetic measurements.

Surface science of soft scorpionates.

The chemisorption of the soft scorpionate Li[PhTm(Me)] onto silver and gold surfaces is reported. Surface enhanced Raman spectroscopy in combination with the Raman analysis of suitable structural models, namely, [Cu(kappa(3)-S,S,S-PhTm(Me))(PCy(3))], [Ag(kappa(3)-S,S,S-PhTm(Me))(PCy(3))], [Ag(kappa(2)-S,S-PhTm(Me))(PEt(3))], and [Au(kappa(1)-S-PhTm(Me))(PCy(3))], are employed to identify the manner in which this potentially tridentate ligand binds to these surfaces. On colloidal silver surface-enhanced Raman spectroscopy (SERS) spectra are consistent with PhTm(Me) binding in a didentate fashion to the surface, holding the aryl group in close proximity to the surface. In contrast, on gold colloid, we observe that the species prefers a monodentate coordination in which the aryl group is not in close proximity to the surface.

Short communication: A practical farm-based trial to compare ewe nematode control strategies in peri-parturient ewes.

The focus of gastro-intestinal parasite control in the sheep industry is increasingly on finding a balance between maintaining productivity of the flock whilst minimising selection for anthelmintic resistance to preserve anthelmintic efficacy for the future. Periparturient ewes represent the major source of gastro-intestinal parasites for growing lambs and are therefore a priority for parasite control. This study examines the impact on ewe faecal egg counts (FECs), lamb FECs, lamb daily live weight gains (DLWGs) and pasture larval counts of treating groups of ewes two weeks prior to lambing with either, a long-acting moxidectin treatment, short-acting doramectin or control. Six groups of twenty ewes were allocated to individual paddocks, two groups allocated to each treatment, and weekly faecal sampling was performed throughout from the ewes and from six weeks after the start of lambing in the lambs. Treatment group was found to have a significant effect on both ewe FEC (p<0.001) and lamb FEC (p = 0.001) with the group receiving the long-acting anthelmintic having the lowest ewe and lamb FECs. There was no significant effect on the DLWGs of the lambs. Pasture larval counts at the end of the study period were lowest in the long-acting wormer treatment group. The use of long-acting moxidectin may be helpful as part of a parasite control programme by reducing the worm burdens of ewes and their lambs, decreasing the number of anthelmintic treatments required in that year and by reducing pasture contamination for those sheep which will graze the pasture in the next year. However, like all anthelmintics, its use should be judicious to avoid selection for resistance.