Interesting chemical and physical features of the products of the reactions between trivalent lanthanoids and a tetradentate Schiff base derived from cyclohexane-1,2-diamine

The initial use of a tetradentate Schiff base (LH₂) derived from the 2 : 1 condensation between 2-hydroxyacetophenone and cyclohexane-1,2-diamine in 4f-metal chemistry is described. The 1 : 2 reaction of Ln(NO₃)₃·xH₂O (Ln = lanthanoid or yttrium) and LH₂ in MeOH/CH₂Cl₂ has provided access to isostructural complexes [Ln(NO₃)₃(L'H₂)(MeOH)] in moderate to good yields. Surprisingly, the products contain the corresponding Schiff base ligand L'H₂ possessing six aliphatic -CH₂- groups instead of the -CH-(CH₂)₄-CH- unit of the cyclohexane ring, i.e. an unusual ring-opening of the latter has occurred. A mechanism for this Ln^III-assisted/promoted LH₂ → L'H₂ transformation has been proposed assuming transient Ln^II species and a second LH₂ molecule as the H₂ source for the reduction of the cyclohexane moiety. DFT calculations provide strong evidence for the great thermodynamic stability of the products in comparison with analogous complexes containing the original intact ligand. The structures of the Pr^III, Sm^III, Gd^III, Tb^III, and Ho^III complexes have been determined by single-crystal X-ray crystallography. The 9-coordinate Ln^III centre in the molecules is bound to six oxygen atoms from the three bidentate chelating nitrato groups, two oxygen atoms that belong to the bidentate chelating organic ligand, and one oxygen atom from the coordinated MeOH group. In the overall neutral bis(zwitterionic) L'H₂ ligand, the acidic H atoms are clearly located on the imino nitrogen atoms and this results in the formation of an unusual 16-membered chelating ring. The coordination polyhedra defined by the nine donor atoms around the 4f-metal-ion centres can be best described as distorted, spherical capped square antiprisms. The Eu^III, Tb^III, and Dy^III complexes exhibit Ln^III-based luminescence in the visible region, with the coordinated L'H₂ molecule acting as the antenna. Ac magnetometry experiments show that the Dy^III member of the family behaves as an SIM at zero field and under external dc fields of 0.1 and 0.2 T without the enhancement of the peaks' maxima, suggesting that QTM is not the relaxation path. The Gd^III complex behaves, rather unexpectedly, as a SIM with two different magnetic relaxation paths occurring at very close temperatures; this behaviour is tentatively attributed to a very small axial zero-field splitting (D ∼ 0.1 cm^-1), which cannot be detected by magnetization or susceptibility experiments. The prospects of the present, first results in the lanthanoid(III)-LH₂ chemistry are discussed.

High nuclearity structurally - related Mn supertetrahedral T4 aggregates

The simultaneous employment of 1,3-propanediol and di-2-pyridyl ketone in Mn carboxylate chemistry has provided access to three new, structurally-related [Mn₂₄] and [Mn₂₃] clusters. They are based on nanosized supertetrahedal T4 Mn/O structural cores and exhibit slow relaxation of magnetization below 3.5 K.

Influence of ligand positional isomerism on the molecular and supramolecular structures of cobalt(II)-phenylimidazole complexes

In a study to evaluate the impact of flexible positional isomeric ligands on the coordination geometry and self-assembly process of 3d metal complexes, the synthesis of eight new cobalt(II) complexes with the 2-phenylimidazole (LH) and 5-phenylimidazole (L'H) ligands has been carried out. A variety of parameters/conditions have been probed using the general Co^II/X^-/LH or L'H (X^- = Cl^-, Br^-, I^-, NO₃^-, NCS^-, ClO₄^-, SO₄^2-) reaction system. Interestingly, X-ray analyses reveal two distinct groups of complexes: reactions with LH only lead to tetrahedral or quasi-tetrahedral complexes {i.e. [CoCl₂(LH)₂] (1), [CoI₂(LH)₂] (2), [Co(NO₃)₂(LH)₂] (3), [Co(NCS)₂(LH)₂] (4)}, whereas L'H favours octahedral coordination {i.e. [Co(L'H)₄(MeCN)(H₂O)]I₂ (5), [Co(L'H)₄(MeCN)(H₂O)](NO₃)₂ (6) and [Co(NCS)₂(L'H)₄)]·2MeOH (7·2MeOH)}. A tetrahedral [Co(NCS)₂(L'H)₂)] (8) complex was also concurrently isolated with complex 7. The effects of the positional isomeric ligands LH and L'H and of the coordinated inorganic anions on the stoichiometry and packing arrangements of the complexes are thoroughly discussed. The supramolecular assembly is firmly directed, in all types of complexes, by robust N-H...X (X = Cl, I, O or S) motifs, leading to varying dimensionalities (1D, 2D or 3D) and packing arrangements. The formation of these motifs has been activated by choosing appropriate anions X, acting as terminal ligands or counterions. At a second level of organization, additional subordinate C-H...X (X = Cl, I, O or S), C-H...π and π...π intermolecular interactions complement the rigidity of the complexes' packing towards compact 3D assemblies. Hirshfeld surface analyses provided insight into the intermolecular interactions, allowed quantification of the individual contact types and comparison between the complexes.

Giant Heterometallic [Mn36Ni4]0/2- and [Mn32Co8] "Loops-of-Loops-and-Supertetrahedra" Molecular Aggregates

We report the synthesis, crystal structures and magnetic properties of the giant heterometallic [Mn₃₆Ni₄]^2−/0 (compounds 1, 2)/[Mn₃₂Co₈] (compound 3) “loops-of-loops-and-supertetrahedra” molecular aggregates and of a [Mn₂Ni₆]²⁺ compound (cation of 4) that is structurally related with the cation co-crystallizing with the anion of 1. In particular, after the initial preparation and characterization of compound [Mn₂Ni₆(μ₄-O)₂(μ₃-OH)₃(μ₃-Cl)₃(O₂CCH₃)₆(py)₈]²⁺[Mn₃₆Ni₄(μ₄-O)₈(μ₃-O)₄(μ₃-Cl)₈Cl₄(O₂CCH₃)₂₆(pd)₂₄(py)₄]²⁻ (1) we targeted the isolation of (i) both the cationic and the anionic aggregates of 1 in a discrete form and (ii) the Mn/Co analog of [Mn₃₆Ni₄]²⁻ aggregate. Our synthetic efforts toward these directions afforded the discrete [Mn₃₆Ni₄] “loops-of-loops-and-supertetrahedra” aggregate [Mn₃₆Ni₄(μ₄-O)₈(μ₃-O)₄(μ₃-Cl)₈Cl₂(O₂CCH₃)₂₆(pd)₂₄(py)₄(H₂O)₂] (2), the heterometallic Mn/Co analog [Mn₃₂Co₈(μ₄-O)₈(μ₃-O)₄(μ₃-Cl)₈Cl₂(μ₂-OCH₂CH₃)₂(O₂CCH₃)₂₈(pd)₂₂(py)₆] (3) and the discrete [Mn₂Ni₆]²⁺ cation [Mn₂Ni₆(μ₄-O)₂(μ₃-OH)₄(μ₃-Cl)₂(O₂CCH₃)₆(py)₈](ClO₄)(OH) (4). The structure of 1 consists of a mixed valence [Mn28IIIMn8IINi4II]²⁻ molecular aggregate that contains two Mn8IIINi2II loops separated by two Mn6IIIMn4II supertetrahedral units and a [Mn2IIINi6II]²⁺ cation based on two [Mn^IIINi3II(μ₄-O)(μ₃-OH)_1.5(μ₃-Cl)_1.5]⁴⁺ cubane sub-units connected through both mono- and tri-atomic bridges provided by the μ₄-O²⁻ and carboxylate anions. The structures of 2–4 are related to those of the compounds co-crystallized in 1 exhibiting however some differences that shall be discussed in detail in the manuscript. Magnetism studies revealed the presence of dominant ferromagnetic interactions in 1–3 that lead to large ground state spin (S_T) values for the “loops-of-loops-and-supertetrahedra” aggregates and antiferromagnetic exchange interactions in 4 that lead to a low (and possibly zero) S_T value. In particular, dc and ac magnetic susceptibility studies revealed that the discrete [Mn₃₆Ni₄] aggregate exhibits a large S_T value ~ 26 but is not a new SMM. The ac magnetic susceptibility studies of the [Mn₃₂Co₈] analog revealed an extremely weak beginning of an out-of-phase tail indicating the presence of a very small relaxation barrier assignable to the anisotropic Co²⁺ions and a resulting out-of-phase ac signal whose peak is at very low T.

Binding of ligands containing carbonyl and phenol groups to iron(iii): new Fe6, Fe10 and Fe12 coordination clusters

The initial use of ligands 2'-hydroxyacetophenone (HL¹), 2-hydroxybenzophenone (HL²) and 2,2'-dihydroxybenzophenone (H₂L³) in iron(iii) chemistry is described. The syntheses and crystal structures are reported for five iron(iii) clusters: [Fe₁₀O₄(OMe)₁₄(L¹)₆(MeOH)₂](NO₃)₂·3MeOH (1·3MeOH), [Fe₁₂O₄(OH)(OMe)₁₇(L¹)₈](ClO₄)₂·2H₂O (2·2H₂O), [Fe₁₀O₄(OMe)₁₄Cl₄(L²)₄(MeOH)₂] (3), [Fe₁₀O₄(OMe)₁₄(L²)₆(py)₂](ClO₄)₂·MeOH (4·MeOH), where py = pyridine, and [Fe₆O₂(OEt)₆(O₂CMe)₂(L³)₂(HL³)₂] (5). The molecular structures of the decanuclear clusters 1, 3 and 4 are organized around a {Fe₁₀(μ₄-O)₄(μ₃-OMe)₂(μ-OMe)₁₂}⁸⁺ core consisting of ten {Fe₃O₄} face-sharing defective cubane units. The core of 2 consists of a {Fe₁₂(μ₄-O)₄(μ₃-OMe)₄(μ-OH)(μ-OMe)₁₃}¹⁰⁺ unit composed of twelve {Fe₃O₄} face-sharing defective cubanes. The ligands (L¹)^- and (L²)^- in 1-4 adopt the O,O'-bidentate chelating coordination mode and their roles are to terminate the further aggregation of the Fe^III/O^2-/RO^- cores. Complex 5 contains the {Fe₆(μ₄-O)₂(μ-OEt)₆(μ-O_carbonyl)₂}⁴⁺ core, where the μ-O_carbonyl atoms are the bridging carbonyl oxygens of the two η¹:η²:η¹:μ (L³)^2- ligands; the (HL³)^- groups behave as O_phenolate, O_carbonyl-bidentate chelating ligands with the neutral hydroxyl group being unbound to the Fe^III atoms. The core is composed of four {Fe₃O₄} face-sharing defective cubanes. The Fe^III atoms in 1-5 are all six-coordinate with distorted octahedral geometries. The IR spectra of the complexes are discussed in terms of the known coordination modes of the ligands and the ionic character of nitrates and perchlorates. Variable-temperature magnetic susceptibility and variable-field magnetization measurements establish that 2, 3 and 5 have S = 3, 0 and 5 ground states, respectively. The susceptibility data for 5 were fitted using a 3-J model indicating the simultaneous presence of both antiferromagnetic and ferromagnetic Fe^IIIFe^III exchange interactions. Known magnetostructural correlations in oxido-bridged iron(iii) systems have been applied to rationalise the magnetic behaviour of the three clusters. The results of the present study demonstrate the utility of HL¹, HL² and H₂L³ in the stabilisation of robust iron(iii)/oxido/alkoxido clusters.

Interesting copper(ii)-assisted transformations of 2-acetylpyridine and 2-benzoylpyridine

Novel Cu^II-assisted transformations have been observed in the reactions of copper(ii) sources and 2-pyridyl ketones.

Supramolecular features in the engineering of 3d metal complexes with phenyl-substituted imidazoles as ligands: the case of copper(ii)

Interesting packing features are present in eleven Cu(ii) complexes with phenyl-substituted imidazoles.

Discrete and encapsulated molecular grids: homometallic Mn15 and heterometallic Mn24Ni2 aggregates

Two molecular grid-like clusters are reported, one is a discrete [3 × 5] grid and the other a [3 × 4] grid within a Mn12Ni2 loop. Both Mn24Ni2 and Mn15 aggregates display novel and aesthetically pleasing structures with the former one being among the highest nuclearity heterometallic MnxMy clusters (M = any transition metal ion).

Reaction between Yttrium Nitrate and 2,2':6',2"-Terpyridine (terpy) in MeCN: Preparation, Crystal Structures and Spectroscopic Characterization of [Y (NO3)3(terpy)(H2O )] and [Y(NO3)3(terpy)(H2O )] · terpy · 3 MeCN

The reaction of Y(NO3)3 · 5H2O and 2,2':6',2"-terpyridine (terpy) in MeCN leads to [Y(N03 )3(terpy)(H2O )] (1) and [Y(N03 )3(terpy)(H2O )] terpy-3MeCN (2) in good yields depending on the isolation conditions. The structures of both complexes were determined by single-crystal X-ray crystallography. The YIII atom in 1 is 9-coordinate and ligation is provided by one terdentate terpy molecule, two chelating nitrates, one monodentate nitrate and one terminal H2O molecule; the coordination polyhedron about the metal may be viewed as a tricapped trigonal prism. The YIII atom in 2 is 10-coordinate and its coordination sphere consists of three nitrogen atoms from the terdentate terpy, six oxygen atoms from the three chelating nitrates (one of them being “anisobidentate”) and one oxygen atom from a terminal H2O molecule; the polyhedron about the metal may be viewed as a distorted sphenocorona. The interstitial terpy is strongly hydrogen-bonded to the O atom of the coordinated H2O molecule to form [Y(NO3 )3(terpy)(H20)] ··· terpy pairs. The new complexes were characterized by IR and 1H NMR spectroscopies. The YIII/NO3 -/terpy chemistry is compared to the already well-developed LnIII/NO3 -/terpy chemistry (Ln = lanthanide).

(2E,4E,6E)-3-Methyl-7-(pyren-1-yl)octa-2,4,6-trienoic acid

The title compound, C(25)H(20)O(2), was synthesized by a Wittig reaction between triphen-yl[1-(pyren-1-yl)eth-yl]phospho-nium bromide and ethyl (2E,4E)-3-methyl-6-oxohexa-2,4-dienoate, in the presence of n-butyl lithium, followed by saponification. It was obtained pure in the all-trans configuration following crystallization from ethyl acetate. The asymmetric unit contains two independent mol-ecules (A and B), which are arranged almost parallel to each other within the crystal structure. The triene chain is not coplanar with the pyrene ring system, forming dihedral angles of 52.8 (1) and 42.2 (1)° for mol-ecules A and B, respectively. Inter-molecular hydrogen bonds between the carboxyl groups of the mol-ecules link them into centrosymmetric pairs, AA and BB, each with the R(2) (2)(8) graph-set motif.

High nuclearity single-molecule magnets: a mixed-valence Mn26 cluster containing the di-2-pyridylketone diolate dianion

The employment of the dianion (dpkd(2-)) of the gem-diol form of di-2-pyridylketone (dpk) as a tetradentate chelate in manganese chemistry is reported, and the synthesis, crystal structure, and magnetochemical characterization of [Mn26O16(OMe)12(dpkd)12(MeOH)6](OH)6 x solv (3 x solv) are described. The reaction of Mn(ClO4)2 x 6 H2O, dpk, NaOMe, and NEt3 (2:1:4:2) in MeCN/MeOH affords complex 3, which possesses a rare metal topology and is mixed-valence (4 Mn(II), 22 Mn(III)). The complicated [Mn26(mu4-O)10(mu3-O)6(mu3-OMe)12(mu-OR)12](18+) core of 3 consists of an internal Mn(III)16 cage of adjacent Mn4 tetrahedra surrounded by an external Mn(II)4Mn(III)6 shell. The latter is held together by the alkoxide arms of twelve eta(1):eta(2):eta(1):eta(1):mu3 dpkd(2-) groups. Variable-temperature, solid-state direct current (dc), and alternating current (ac) magnetization studies were carried out on 3 in the 1.8-300 K range. Complex 3 is predominantly antiferromagnetically coupled with a resulting S = 6 ground state, a conclusion confirmed by the in-phase (chi'(M)) ac susceptibility data. The observation of out-of-phase (chi''(M)) ac susceptibility signals suggested that 3 might be a single-molecule magnet, and this was confirmed by single-crystal magnetization vs dc field sweeps that exhibited hysteresis, the diagnostic property of a magnet. Combined ac chi''(M) and magnetization decay vs time data collected below 1.1 K were used to construct an Arrhenius plot; the fit of the thermally activated region above approximately 0.1 K gave U(eff) = 30 K, where U(eff) is the effective relaxation barrier. At lower temperatures, the complex exhibits temperature-independent relaxation, characteristic of ground-state quantum tunneling of magnetization between the lowest-lying M(s) = +/-6 levels. The combined work demonstrates the ligating flexibility of dipyridyl-diolate chelates and their usefulness in the synthesis of polynuclear Mn(x) clusters with interesting magnetic properties, without requiring the co-presence of carboxylate ligands.

(Z)-tert-Butyl 2-(4-amino-9H-fluoren-9-yl-idene)acetate

The title compound, C₁₉H₁₉NO₂, obtained as an almost equimolar mixture (as shown by ¹H NMR) with the E isomer through a Wittig reaction between 4-amino-9H-fluoren-9-one and the stabilized ylide Ph₃P=CHCO₂C(CH₃)₃, was obtained pure in the Z configuration following crystallization from toluene. The mol­ecule shows a planar arrangement of the ring system and the new double bond, whereas the carbonyl O atom forms a 45.1 (3)° dihedral angle with it. The mol­ecules are linked by N—H⋯O hydrogen bonds, forming cyclic structures with R₄⁴(24) graph-set motifs. These motifs are connected to each other, giving rise to a sheet structure parallel to the ab plane. The linkage within the sheets is further enhanced by π–π stacking inter­actions between the fluorene units [centroid–centroid distance = 3.583 (2) Å].

A toxin-like gene in rainbow trout: Cloning, expression, and gene organization

The 'three-finger' protein family consists of structurally related proteins which display a variety of biological functions. Snake venom alpha-neurotoxins, Ly-6 alloantigens, urokinase-type plasminogen activator receptor (uPAR) and the complement regulatory protein CD59 are members of this protein family. Their characteristic feature is the disposition of four disulfide bridges forming a hydrophobic core. Here it is reported the cloning and characterization of a toxin-like gene (toxin-1) in the rainbow trout (Oncorhynchus mykiss). Phylogenetic analysis showed that trout toxin-1 classified into the short-chain neurotoxins (60-65 residues), confining to a distinct group. Trout toxin-1 gene contains three exons interrupted by two introns, in line with the other toxin members of the 'three-finger' family. Trout liver, brain, and spleen express the toxin-1 gene and its encoded protein is identified in trout plasma. This is the first report of a toxin-like gene which has been described so far in teleost.

A Large [Mn10Na]4 Loop of Four Linked Mn10 Loops

A large [Mn10Na]4 loop-of-loops aggregate was prepared from the use of 1,3-propanediol (pdH2) in manganese carboxylate chemistry. It is constructed from four [Mn10(mu3-O)2(O2CMe)13(pd)6(py)2]- loops linked through Na+ ions and exhibits a saddlelike topology. Magnetic characterization showed that the Mn10 loop has an S approximately 4 ground-state spin and displays frequency-dependent in-phase and out-of-phase alternating current signals and also hysteresis loops that, however, are not typical of single-molecule magnets because of the existence of intermolecular interactions between the Mn10 units.

Insights into DNA replication: the crystal structure of DNA polymerase B1 from the archaeon Sulfolobus solfataricus

To minimize the large number of mispairs during genome duplication owing to the large amount of DNA to be synthesized, many replicative polymerases have accessory domains with complementary functions. We describe the crystal structure of replicative DNA polymerase B1 from the archaeon Sulfolobus solfataricus. Comparison between other known structures indicates that although the protein is folded into the typical N-terminal, editing 3'-5'exonuclease, and C-terminal right-handed polymerase domains, it is characterized by the unusual presence of two extra alpha helices in the N-terminal domain interacting with the fingers helices to form an extended fingers subdomain, a structural feature that can account for some functional features of the protein. We explore the structural basis of specific lesion recognition, the initial step in DNA repair, describing how the N-terminal subdomain pocket of archaeal DNA polymerases could allow specific recognition of deaminated bases such as uracil and hypoxanthine in addition to the typical DNA bases.

Hydrogen-Bonded Networks Featuring Yttrium(III) Complexes of N,N’-Dimethylurea (DMU): Preparation and Characterization of [Y(DMU)6][YCl6] and [Y(NO3)3(DMU)3]

In order to examine the possibility of using yttrium(III) in the crystal engineering of hydrogenbonded coordination complexes and to compare the molecular and supramolecular YIII/Cl3 or NO3-/DMU chemistry with the already well-developed LnIII/Cl− or NO3−/DMU chemistry (LnIII = lanthanide, DMU = N,N’-dimethylurea), compounds [Y(DMU)6][YCl6] (1) and [Y(NO3)3(DMU)3] (2) have been prepared. The structures of both compounds have been determined by single-crystal Xray diffraction. The structure of 1 consists of octahedral [Y(DMU)6]3+ and [YCl6]3− ions. The YIII ion in 2 is nine-coordinate and ligation is provided by three O-bonded DMU ligands and three bidentate chelating nitrato groups; the coordination polyhedron about the metal can be viewed as a distorted, monocapped square antiprism. The [Y(DMU)6]3+ cations and [YCl6]3− anions self-assemble to form a hydrogen-bonded 3D architecture in 1. Most of the hydrogen-bonding functionalities on the components of 2 create also a 3D network. Two motifs of interionic/intramolecular hydrogen-bonds have been observed: N-H···Cl in 1 and N-H···O(NO3−) in 2. The IR data are discussed in terms of the nature of bonding and the structures of the two complexes

Cadmium Carboxylate Chemistry: Preparation, Crystal Structure, and Thermal and Spectroscopic Characterization of the One-dimensional Polymer [Cd(O2CMe)(O2CPh)(H2O)2]n

Compound [Cd(O2CMe)(O2CPh)(H2O)2]n (1) was initially obtained in a serendipitous way during efforts to prepare a CdII /PhCO2 −/bepy complex (bepy = 2-benzoylpyridine). With the identity of 1 established by single-crystal X-ray crystallography, a rational preparative route to this complex was designed and carried out by reacting Cd(O2CMe)2·2H2O with a slight excess of PhCOOH in MeCN under reflux. The crystal structure of 1 consists of isolated zig-zag chains. The CdII atom is coordinated to five carboxylate and two aqua oxygen atoms creating a distorted, capped trigonal prismatic coordination polyhedron. The acetate group exhibits the η1:η2:μ2 coordination mode, while the benzoate ligand is chelating. There is an extensive hydrogen-bonding network which reinforces the chains and also links them generating sheets. The new complex was characterized by IR, far-IR, Raman, CP MAS and solution 113Cd NMR spectroscopy. The spectroscopic data are discussed in terms of the nature of bonding and the known structure. An anhydrous compound with the empirical formula Cd(O2CMe)(O2CPh) was isolated during the thermal decomposition of 1; the vibrational study of this thermally stable intermediate supports an 1D polymeric structure with 6-coordinate CdII ions.

Dipeptides containing the alpha-aminoisobutyric residue (Aib) as ligands: preparation, spectroscopic studies and crystal structures of copper(II) complexes with H-Aib-X-OH (X=Gly, L-Leu, L-Phe)

Synthetic procedures are described that allow access to new copper(II) complexes with dipeptides containing the alpha-aminoisobutyric residue (Aib) as ligands. The solid complexes [Cu(H(-1)L(A))](n).nH(2)O (1) (L(A)H=H-Aib-Gly-OH), [Cu(H(-1)L(B))(MeOH)](n).nMeOH (2) (L(B)H=H-Aib-L-Leu-OH) and [Cu(H(-1)L(C))](n) (3) (L(C)H=H-Aib-L-Phe-OH) have been isolated and characterized by single-crystal X-ray crystallography, solid-state IR spectra and UV-Vis spectroscopy in solution (H(-1)L(2-) is the dianionic form of the corresponding dipeptide). Complexes 1 and 3 are three-dimensional coordination polymers with similar structures. The doubly deprotonated dipeptide behaves as a N(amino), N(peptide), O(carboxylate), O'(carboxylate), O(peptide) mu(3) ligand and binds to one Cu(II) atom at its amino and peptide nitrogens and at one carboxylate oxygen, to a second metal at the other carboxylate oxygen, while a third Cu(II) atom is attached to the peptide oxygen. The geometry around copper(II) is distorted square pyramidal with the peptide oxygen at the apex of the pyramid. The structure of 2 consists of zigzag polymeric chains, where the doubly deprotonated dipeptide behaves as a N(amino), N(peptide), O(carboxylate), O'(carboxylate) mu(2) ligand. The geometry at copper(II) is square pyramidal with the methanol oxygen at the apex. The IR data are discussed in terms of the nature of bonding and known structures. The UV-Vis spectra show that the solid-state structures of 1, 2 and 3 do not persist in H(2)O.

The crystal structure of the sorcin calcium binding domain provides a model of Ca2+-dependent processes in the full-length protein

Sorcin is a 21.6 kDa calcium binding protein, expressed in a number of mammalian tissues that belongs to the small, recently identified penta-EF-hand (PEF) family. Like all members of this family, sorcin undergoes a Ca2+-dependent translocation from cytosol to membranes where it binds to target proteins. For sorcin, the targets differ in different tissues, indicating that it takes part in a number of Ca2+-regulated processes. The sorcin monomer is organized in two domains like in all PEF proteins: a flexible, hydrophobic, glycine-rich N-terminal region and a calcium binding C-terminal domain. In vitro, the PEF proteins are dimeric in their Ca2+-free form, but have a marked tendency to precipitate when bound to calcium. Stabilization of the dimeric structure is achieved by pairing of the uneven EF-hand, EF5. Sorcin can also form tetramers at acid pH. The sorcin calcium binding domain (SCBD, residues 33-198) expressed in Escherichia coli was crystallized in the Ca2+-free form. The structure was solved by molecular replacement and was refined to 2.2 A with a crystallographic R-factor of 22.4 %. Interestingly, the asymmetric unit contains two dimers. The structure of the SCBD leads to a model that explains the solution properties and describes the Ca2+-induced conformational changes. Phosphorylation studies show that the N-terminal domain hinders phosphorylation of SCBD, i.e. the rate of phosphorylation increased twofold in the absence of the N-terminal region. In addition, previous fluorescence studies indicated that hydrophobic residues are exposed to solvent upon Ca2+ binding to full-length sorcin. The model accounts for these data by proposing that Ca2+ binding weakens the interactions between the two domains and leads to their reorientation, which exposes hydrophobic regions facilitating the Ca2+-dependent binding to target proteins at or near membranes.

Crystallization and X-ray diffraction measurements of a thermophilic archaeal recombinant amidase from Sulfolobus solfataricus MT4

Recombinant amidase is a 55.8 kDa enzyme from the thermophilic archaeon Sulfolobus solfataricus MT4 that catalyses the hydrolysis of aliphatic amides of 2-6 C atoms as well as many aromatic amides. Single crystals of purified amidase were obtained by the hanging-drop method at 294 K. Diffraction data for the native protein (2.55 A resolution) and a putative derivative (2.20 A) have been collected at low temperature using synchrotron radiation. The crystals belong to the rhombohedral space group R3. Structure determination by multiple isomorphous replacement is in progress. It is expected that structural information from this signatured thermostable amidase will increase our knowledge of the molecular mechanisms employed to maintain high-temperature stability in thermophilic proteins.

Two different crystal forms of sorcin, a penta-EF-hand Ca2+-binding protein

Sorcin is a 198 amino-acid Ca(2+)-binding protein that belongs to the penta-EF-hand family. Its Ca(2+)-binding domain (residues 33-198) has been crystallized in the absence of Ca(2+) in two different crystal forms. Two complete data sets have been collected on a synchrotron source under cryocooling conditions from crystals grown using ammonium sulfate as precipitant: monoclinic crystals in space group C2, with unit-cell parameters a = 130.93, b = 103.85, c = 78.55 A, beta = 118.0 degrees, diffracting to 2.1 A, and tetragonal crystals in space group P42(1)2, with unit-cell parameters a = b = 103.33, c = 79.15, diffracting to 2.7 A. Crystals were also grown using PEG 6000 as precipitating agent. They also belong to space group C2, diffract to 2.8 A and their unit-cell parameters are very similar to the first form. Structure determination by molecular replacement has been initiated. Structural information should be useful for elucidating the interaction of sorcin with membrane targets.