Unprecedented Structural Features Research Articles

Combined Experimental and Theoretical Investigation of Ligand and Anion Controlled Complex Formation with Unprecedented Structural Features and Photoluminescence Properties of Zinc(II) Complexes

By using two potential tridentate ligands, HL1 [4-chloro-2-[(2-morpholin-4-yl-ethylimino)-methyl]-phenol] and HL2 [4-chloro-2-[(3-morpholin-4-yl-propylimino)-methyl]-phenol], which differ by one methylene group in the alkyl chain, four new ZnII complexes, namely, [Zn(L2H)2](ClO4)2 (1), [Zn(L1)(H2O)2][Zn(L1)(SCN)2] (2), [Zn(L1)(dca)]n (3), and [Zn2(L1)2(N3)2(H2O)2] (4) [where dca = dicyanamide anion] were synthesized and structurally characterized. The results indicate that the slight structural difference between the ligands, HL1 and HL2, because of the one methylene group connecting the nitrogen atoms provokes a chemical behavior completely different from what was expected. Any attempt to isolate the Zn(L2) complexes with thiocyanato, dicyanamido, and azide was unsuccessful, and perchlorate complex 1 was always obtained. In contrast, with HL1 we obtained structural diversity on varying the anions, but we failed to isolate the analogous perchlorate complex of HL1. Single-crystal X-ray analyses revealed th...

ChemInform Abstract: Porous Materials in Catalysis: Challenges for Mesoporous Materials

AbstractReview: 134 refs.

Porous materials in catalysis: challenges for mesoporous materials

The discovery of ordered mesoporous materials has opened great opportunities for new applications in heterogeneous catalysis, thanks to their hitherto unprecedented intrinsic structural features. Evidence shows that, however, these materials have not met the researchers' expectations mainly because of the severe limitations related to the strength of acid sites and to the thermal/hydrothermal stability, significantly lower than those of zeolites and due to the amorphous nature of the mesostructured materials. These features are highlighted in the first part of this review, where the peculiarities of mesostructured materials are compared with those of zeolite catalysts in some reactions of industrial interest. New synthesis strategies, especially designed for preparing materials with improved physico-chemical and textural properties, together with the catalytic features of the resulting materials, are described and discussed in the second part of the review.

Structural Modulation and Phase Transitions in La2CoO4.14 Investigated by Synchrotron X-ray and Neutron Single-Crystal Diffraction

We report a combined synchrotron X-ray and neutron diffraction study on as-grown La(2)CoO(4.14) single-crystal from 10 to 470 K. Unprecedented structural features in terms of a (3 + 2)D incommensurate modulation have been detected and characterized in the Low Temperature Orthorhombic (LTO) phase already at room temperature despite the complex twinning that was unravelled. A new intermediate phase between the LTO and High Temperature Tetragonal (HTT) phases has been observed for the first time (in the range of 413-433 K). The transformation from LTO to this so-called HTLO (High Temperature Less Orthorhombic) phase is associated to a lowering of orthorhombicity and a loss of one modulation vector, yielding a (3 + 1)D incommensurate modulation. Conversely, above 433 K the HTT phase appears as nonmodulated but exhibits a strong dynamic disorder of CoO(6) octahedra, which has been characterized in detail by reconstruction of nuclear densities via the Maximum Entropy Method (MEM).

Facile, Solution-Based Synthesis of Soft, Nanoscale Janus Particles with Tunable Janus Balance

We present a novel, versatile, and simple solution-based routine to produce soft, nanosized Janus particles with tunable structural and physical properties at high volume yield. This process is based on the cross-linking of compartments within precisely defined multicompartment micelles (MCMs), which are themselves formed by the self-assembly of ABC triblock terpolymers. Therein, the C blocks form the stabilizing corona emanating from B compartments, which in turn reside on an A core. Cross-linking of the B compartments allows to permanently fixate the phase-separated state and dissolution in a good solvent for all blocks breaks up the MCMs into single Janus particles. They now consist of a core of cross-linked B blocks and two phase-separated hemispheres of A and C. The process gives access to unprecedented structural features such as tunable core diameter and control over the Janus balance ranging from dominant A side to equal hemispheres to dominant C side. We demonstrate that this simple one-pot approach can be extended to a range of triblock terpolymers with different block lengths and block chemistries to furnish a library of tailor-made Janus particles with widely tunable physical properties. Such a diversity and simplicity has remained unreachable with our previously developed approach using the controlled cross-linking of bulk morphologies. We show that this new synthetic route can be upscaled to a high volume yield of 10 wt %, thereby enabling large-scale applications. We further demonstrate the effect of the Janus balance on colloidal self-assembly. Janus particles with a dominant hydrophobic and a small hydrophilic patch aggregate into large clusters in water, but merely di- or trimerize in chloroform.

ChemInform Abstract: From Sepiamelanin to Chemical Ecology of Opisthobranchs and Diatoms: An Exciting 40 Years Game in the Field of Marine Natural Products

AbstractReview: 49 refs.

Peculiar structural findings in coordination chemistry of malonamide–N,N′-diacetic acid

Unprecedented structural features are found in the coordination chemistry of malonamide–N,N′-diacetic acid. A type of supramolecular interaction involving non-aromatic rings—metallorings—designated as Metal Organic Ring interaction (MORi) is crystallographically well established.

From sepiamelanin to chemical ecology of opisthobranchs and diatoms: an exciting 40 years game in the field of marine natural products

This paper reports the lecture delivered on the occasion of the “Ceremony of Professional Recognition” to the author at the 6th European Conference on Marine Natural Products (Porto, Portugal, 19–23 July 2009). The most recent results obtained studying opisthobranchs and diatoms at ICB are presented after a synthetic overview of the most significant moves played during this exciting 40 years game in the field of Marine Natural Products. In a symbolic manner this career is compared to a chess game. After the “romantic” opening dedicated to the study of natural black (melanin) and red-brown (phaeomelanins) pigments in the prestigious group of Rodolfo A. Nicolaus, the research on marine organisms started in 1969 and rapidly led to the characterization of an impressive number of new compounds exhibiting very unusual structures. Substantially, the “structure hunt” ended with the publication of a series of alkaloids with absolutely unprecedented structural features: the saraines. Slowly, the scientific interest shifted “from structure to function”. Opisthobranchs were selected as models to investigate. The majority of the protective allomones possessed by opisthobranch molluscs are sequestered through the food chain from algae and invertebrates. However, opisthobranchs were also able to biosynthesize many compounds structurally related to typical molecules possessed by their prey. These aspects “from function to ecology, to biosynthesis, to evolution” are discussed in detail.

Assembly of titanium embedded polyoxometalates with unprecedented structural features

Two titanium embedded polyoxometalates with unprecedented structural features are presented: a monotitanium containing tungstoantimonate Na(13)H(3)[TiO(SbW(9)O(33))(2)]·33 H(2)O featuring a {Ti=O}(2+) moiety (1) and a hexatitanium containing tungstoarsenate K(6)[Ti(4)(H(2)O)(10)(AsTiW(8)O(33))(2)]·30 H(2)O containing a {Ti(4)(H(2)O)(10)}(16+) moiety (2). Both compounds have been fully characterised by single crystal X-ray diffraction, elemental analysis, IR and TGA. 1 is constructed from two α-B-{Sb(III)W(9)O(33)} fragments linked by five sodium cations and an unprecedented square pyramidal Ti(O)O(4) group with a terminal Ti=O bond, and 2 exhibits a Krebs-type structure composed of two {AsTiW(8)O(33)} fragments, where one W(VI) centre has been substituted for a Ti(IV) centre in each, fused together via a belt of four additional Ti(IV) centres. This system represents the tungsten Ti-incorporated polyoxoanion with one of the highest Ti:W ratios so far reported. Additionally, 2 could also be isolated as an n-tetrabutylammonium salt and has been further characterised by electrochemistry and electrospray ionisation (ESI) MS studies. Due to the unique nature of these systems, both have been fully investigated using DFT calculations yielding highly interesting results. Structure 1 has been optimised with five sodium atoms in the belt position, which in addition to reducing the high charge of the cluster influence a stabilisation of the antimony lone pairs. Electrostatic potential calculations highlight the high electronegativity of the terminal oxygen on the titanium centre, enhancing real potentiality as a reactive site for catalysis.

A Mixed-Valent Pentanuclear CuII4CuI Compound Containing a Radical-Anion Ligand

Reaction of 2,4-(2,2'-dipyridylamino)-6-(2-pyridylhydrazino)-1,3,5-triazine, abbreviated dppht (5), with copper(II) chloride in methanol yields a mixed-valent Cu(II)(4)Cu(I) compound (6), also involving the presence of a radical anion. The single-crystal structure determination for [Cu(5)(5(M))(5(MR))Cl(8)] (6) reveals that the original dppht ligand (5) has been monochlorinated at one of its pyridine rings and oxidized at its hydrazyl moiety, generating the ligand 2,4-(2,2'-dipyridylamino)-6-(2-(5-chloropyridyl)azo)-1,3,5-triazine (5(M)). Moreover, the molecular structure of 6 indicates that one of the two coordinated ligands 5(M) is in a radical-anion state, symbolized as 5(MR), characterized by a typical N-N bond length of about 1.33 A for a one-electron reduced azo group. The nature of this unique [Cu(II)(4)Cu(I)(radical)] assembly is corroborated by X-ray absorption spectroscopy, electron paramagnetic resonance, and magnetic susceptibility measurements. Density-functional theory calculations are consistent with the unprecedented structural features and support the spectroscopic data.

A functional hybrid polyoxometalate framework based on a ‘trilacunary’ heteropolyanion [(P4W6O34)2Co2Na2(H2O)2]18−

Using multifunctional organocations a novel heteropolyanion, [(P4W6O34)2Co2Na2(H2O)2]18-, with unprecedented structural features, has been observed, and extension of these clusters from molecules into 1D chains occurs through a dimeric cobalt species, with this material exhibiting reversible colour/magnetic susceptibility changes upon dehydration.

Organotitanoxanes with Unique Structure among Transition-Element Organometallic Oxide Derivatives

The synthesis of novel titanoxane compounds, [{(TiCl)(Ti)[mu-(eta(5)-C5Me4SiMe2O-kappaO)]2(mu-O)}2(mu-O)] (4) and [{Ti[mu-(eta(5)-C5Me4SiMe2O-kappaO)](mu-O)}6] (5), by controlled hydrolysis of a dinuclear titanium/oxo complex is described. Complexes 4 and 5 show unprecedented structural features for organometallic oxide derivatives of transition elements and represent unique fully characterized examples of tetra- and hexanuclear organo-transition-metal oxide compounds with an open-chain and a monocyclic structure, respectively.

Plasmodium cysteine repeat modular proteins 1?4: complex proteins with roles throughout the malaria parasite life cycle

The Cysteine Repeat Modular Proteins (PCRMP1-4) of Plasmodium, are encoded by a small gene family that is conserved in malaria and other Apicomplexan parasites. They are very large, predicted surface proteins with multipass transmembrane domains containing motifs that are conserved within families of cysteine-rich, predicted surface proteins in a range of unicellular eukaryotes, and a unique combination of protein-binding motifs, including a >100 kDa cysteine-rich modular region, an epidermal growth factor-like domain and a Kringle domain. PCRMP1 and 2 are expressed in life cycle stages in both the mosquito and vertebrate. They colocalize with PfEMP1 (P. falciparum Erythrocyte Membrane Antigen-1) during its export from P. falciparum blood-stage parasites and are exposed on the surface of haemolymph- and salivary gland-sporozoites in the mosquito, consistent with a role in host tissue targeting and invasion. Gene disruption of pcrmp1 and 2 in the rodent malaria model, P. berghei, demonstrated that both are essential for transmission of the parasite from the mosquito to the mouse and has established their discrete and important roles in sporozoite targeting to the mosquito salivary gland. The unprecedented expression pattern and structural features of the PCRMPs thus suggest a variety of roles mediating host-parasite interactions throughout the parasite life cycle.

Cucurbitane Triterpenes from the Fruiting Bodies and Cultivated Mycelia of Leucopaxillus gentianeus

A reinvestigation of the fruiting bodies of the mushroom Leucopaxillus gentianeus, allowed the isolation of two minor cucurbitane triterpenes, namely, cucurbitacin D (5) and the new metabolite 16-deoxycucurbitacin B (6). The latter compound lacks an oxygenated substituent at C-16, an unprecedented structural feature among congeners of cucurbitacin B. The cucurbitanes present in the fruiting bodies were compared with those extracted from mycelia grown on the modified Melin-Norkans (MMN) culture medium. Cucurbitacins B (1) and D (5), as well as leucopaxillones A (3) and B (4), were isolated from both sources; in contrast, 16-deoxycucurbitacin B (6) and a mixture of fatty acid esters of cucurbitacin B (2) were absent in the mycelia. A new triterpene, 18-deoxyleucopaxillone A (7), was isolated from the mycelia, but was not detected in the fruiting bodies. The antiproliferative activity of the isolated triterpenes was determined against the NCI-H460 human tumor cell line, in comparison with the antitumor compound topotecan, a well-known topoisomerase I inhibitor.

Azaspiracid poisoning, the food-borne illness associated with shellfish consumption

Azaspiracid poisoning (AZP) is a recently discovered toxic syndrome that was identified following severe gastrointestinal illness from the consumption of contaminated mussels (Mytilus edulis). The implicated toxins, azaspiracids, are polyethers with unprecedented structural features. Studies toward total toxin synthesis revealed that the initial published structures were incorrect and they have now been revised. These toxins accumulate in bivalve molluscs that feed on toxic microalgae of the genus Protoperidinium, previously considered to be toxicologically benign. Although first identified in shellfish from Ireland, azaspiracid contamination of several types of bivalve shellfish species has now been confirmed throughout the western coastline of Europe. Toxicological studies have indicated that azaspiracids can induce widespread organ damage in mice and that they are probably more dangerous than previously known classes of shellfish toxins. The exclusive reliance on live animal bioassays to monitor azaspiracids in shellfish failed to prevent human intoxications. This was a consequence of poor sensitivity of the assay and the fact that azaspiracids are not exclusively found in the shellfish digestive glands used for toxin testing. The strict regulatory control of azaspiracids in shellfish now requires frequent testing of shellfish using highly specific and sensitive methods involving liquid chromatography-mass spectrometry.

Neoorthosiphonone A: A Nitric Oxide (NO) Inhibitory Diterpene with New Carbon Skeleton from Orthosiphon stamineus.

Abstract From the aerial part of Orthosiphon stamineus from Hainan island of China, a diterpene named neoorthosiphonone A ( 1 ), having a novel carbon framework, has been isolated. Neoorthosiphonone A ( 1 ) possessed a unique unprecedented structural feature of eight-membered ring C in its structure, which may be biogenetically derived from its isopimarane precursor, orthosiphonone A, through the insertion of vinyl group into the C 13 –C 14 bond. Neoorthosiphonone A ( 1 ) displayed potent inhibitory activity on the nitric oxide production in LPS-activated macrophage-like J774.1 cells with an IC 50 value of 7.08 μM, more potent than the positive control l -NMMA.

Neoorthosiphonone A; a nitric oxide (NO) inhibitory diterpene with new carbon skeleton from Orthosiphon stamineus

From the aerial part of Orthosiphon stamineus from Hainan island of China, a diterpene named neoorthosiphonone A (1), having a novel carbon framework, has been isolated. Neoorthosiphonone A (1) possessed a unique unprecedented structural feature of eight-membered ring C in its structure, which may be biogenetically derived from its isopimarane precursor, orthosiphonone A, through the insertion of vinyl group into the C13–C14 bond. Neoorthosiphonone A (1) displayed potent inhibitory activity on the nitric oxide production in LPS-activated macrophage-like J774.1 cells with an IC50 value of 7.08μM, more potent than the positive control l-NMMA.

Is Ag(I) an adequate probe for Cu(I) in structural copper-metallothionein studies? The binding features of Ag(I) to mammalian metallothionein 1.

The binding abilities of silver(I) to mammalian MT 1 have been studied and compared with those of copper(I), recently reported [Bofill et al. (2001) J Biol Inorg Chem 6:408-417], with the aim of analyzing the suitability of Ag(I) as a Cu(I) probe in Cu-MT studies. The Zn/Ag replacement in recombinant mouse Zn(7)-MT 1 and corresponding Zn(4)-alphaMT 1 and Zn(3)-betaMT 1 fragments, as well as the stepwise incorporation of Ag(I) to the corresponding apo-MTs, have been followed in parallel by various spectroscopic techniques including electronic absorption (UV-vis), circular dichroism (CD) and electrospray mass spectrometry coupled to capillary zone electrophoresis (CZE-ESI-MS). A comparative analysis of the sets of data obtained in the titration of Zn(7)-MT 1, Zn(4)-alphaMT 1 and Zn(3)-betaMT 1 with AgClO(4) at pH 7.5 and 2.5 has led to the reaction pathways followed during the incorporation of silver to these proteins under these specific conditions, disclosing unprecedented stoichiometries and structural features for the species formed. Thus, the Zn/Ag replacement in Zn(7)-MT 1 at pH 7.5 has revealed the subsequent formation of Ag(4)Zn(5)-MT, Ag(7)Zn(3)-MT, Ag(8)Zn(3)-MT, Ag(10)Zn(2)-MT, Ag(12)Zn(1)-MT, Ag(x)-MT, x=14-19, whose structure consists of two additive domains only if Zn(II) remains coordinated to the protein. A second structural role for Zn(II) has been deduced from the different folding found for the Ag(x)-MT species of the same stoichiometry formed at pH 7.5 or 2.5. Comparison of the binding features of Cu(I) and Ag(I) to the entire MT at pH 7.5 shows that, among all the micro(x)Zn(y)-MT (0<or= y<7) species found, only M(I)(4)Zn(5)-MT [(Zn(4))(alpha)(micro(4)Zn(1))(beta)] and M(I)(7)Zn(3)-MT [(micro(3)Zn(2))(alpha)(micro(4)Zn(1))(beta)], which form during the first stages of the Zn(II)/M(I) metal replacement, show comparable 3D structures; thus, they are the only species where Ag(I) ions can be predicted to be an adequate probe for Cu(I).

Polyoxometal cations within polyoxometalate anions. Seven-coordinate uranium and zirconium heteroatom groups in [(UO2)12(μ3-O)4(μ2-H2O)12(P2W15O56)4]32− and [Zr4(μ3-O)2(μ2-OH)2(H2O)4 (P2W16O59)2]14−

Two new composite polyoxotungstate anions with unprecedented structural features, [(UO2)12(μ3-O)4(μ2-H2O)12(P2W15O56)4]32− (1) and [Zr4(μ3-O)2(μ2-OH)2(H2O)4 (P2W16O59)2]14− (2) contain polyoxo-uranium and -zirconium clusters as bridging units. The anions are synthesized by reaction of Na12[P2W15O56] with solutions of UO2(NO3)2 and ZrCl4. The structure of 1 in the sodium salt contains four [P2W15O56]12− anions assembled into an overall tetrahedral cluster by means of trigonal bridging groups formed by three equatorial-edge-shared UO7 pentagonal bipyramids. The structure of anion 2 consists of a centrosymmetric assembly of two [P2W16O59]12− anions linked by a {Zr4O2(OH)2(H2O)4}10+ cluster. Both complexes in solution yield the expected two-line 31P-NMR spectra with chemical shifts of −2.95, −13.58 and −6.45, −13.69 ppm, respectively.

Antimicrobial peptides from amphibian skin: an expanding scenario: Commentary

Many organisms employ antimicrobial peptides to fend off microbial pathogens. Amphibian skin is one of the most generous sources of these peptides. In the past couple of years, intriguing additional insights on various aspects of frog skin peptides have been reported. Several novel molecules, often with unprecedented structural features, have been discovered. Studies focusing on the factors that regulate the in vivo synthesis of skin peptides in response to infection have gained in prominence. Moreover, recent results indicate new possibilities for the development of effective human therapeutics based on antimicrobial peptides and partially disclosed the biotechnological potential of these molecules.