Supramolecular systems composed of α-helical peptides

Hydrophobic helical peptides having alternating hydrophobic amino acid and Aib in the sequence were synthesized to construct supramolecular systems. Three types of supramolecular systems were constructed by the peptides and the derivatives in different environments. First, the dispersion of TFA · H-(Ala-Aib)₈-OBzl in water was studied by dynamic light scattering, which suggests the formation of a vesicular structure with an average diameter of 76 nm. We call the peptide assembly in water “peptosome”. Second, Boc-Ser(Ant)-(Ala-Aib)₈-OMe spanned the phospholipid bilayer membrane and formed a helix-bundle structure. The bundle structure was supported by ion-channel formation in the membrane. Third, Boc-(Ala-Aib)₈-OMe and Boc-(Leu-Aib)₈-OBzl formed a two-dimensional crystal at the air-water interface. Boc-(Ala-Aib)₁₂-OBzl also formed a monolayer in a solid state at the air-water interface, but the helix orientation was perpendicular to the interface, which presents a contrast to the parallel orientation of the former hexadecapeptides.     

Molecular dynamics simulations of the interfacial and structural properties of dimethyldodecylamine-N-oxide micelles

A series of large-scale atomistic molecular dynamics simulations were conducted to study the structural and interfacial properties of nonionic dimethyldodecylamine-N-oxide (DDAO) micelles with an aggregation number of 104 in pure water, which was determined using small-angle neutron scattering (SANS). From these simulations, the micelles were found to be generally ellipsoidal in shape with axial ratios of ～1.3-1.4, which agrees well with that found from small-angle neutron scattering measurements. The resulting micelles have an area per DDAO molecule of 94.8 ?(2) and an average number of hydration water molecules per DDAO molecule of ～8. The effect of the encapsulation of ethyl butyrate (CH(3)(CH(2))(2)COOCH(2)CH(3), C(4)) and ethyl caprylate (CH(3)(CH(2))(6)COOCH(2)CH(3), C(8)) on the structural and interfacial properties of the nonionic DDAO aggregates was also examined. In the presence of the C(4) oil molecules, the aggregates were found to be less ellipsoidal and more spherical than the pure DDAO micelles, while the aggregates in the presence of the C(8) oil molecules were almost perfect spheres. In addition, the C(4) oil molecules move into the core of the aggregates, while the C(8) oil molecules stay in the headgroup region of the aggregates. Finally, the structural properties of two micelles formed from different starting states (a "preassembled" sphere and individual DDAO molecules distributing in water) were found to be nearly identical.     

Interweaving 3D network with double helical tubes filled by 1D coordination polymer chains

The hydrothermal reaction of mellitic acid, 4,4'-bipydine, and Cu(CH(3)COO)(2).H(2)O gave rise to a novel 3D supramolecular architecture interpenetrated by three types of coordination polymer motifs. Two independent [[Cu(2)(mellitate)(4,4'-bpy)(H(2)O)(2)](2)(-)] 3D polymers incorporating helical substructures were interwoven into a 3D network with double-stranded helical tubes that host 1D linear polymers [Cu(4,4'-bpy)(H(2)O)(4)](2+)](n).     

A computational study on the structures of methylamine-carbon dioxide-water clusters: evidence for the barrier free formation of the methylcarbamic acid zwitterion (CH3NH2+COO-) in interstellar water ices

We investigated theoretically the interaction between methylamine (CH(3)NH(2)) and carbon dioxide (CO(2)) in the presence of water (H(2)O) molecules thus simulating the geometries of various methylamine-carbon dioxide complexes (CH(3)NH(2)/CO(2)) relevant to the chemical processing of icy grains in the interstellar medium (ISM). Two approaches were followed. In the amorphous water phase approach, structures of methylamine-carbon dioxide-water [CH(3)NH(2)/CO(2)/(H(2)O)(n)] clusters (n = 0-20) were studied using density functional theory (DFT). In the crystalline water approach, we simulated methylamine and carbon dioxide interactions on a fragment of the crystalline water ice surface in the presence of additional water molecules in the CH(3)NH(2)/CO(2) environment using DFT and effective fragment potentials (EFP). Both the geometry optimization and vibrational frequency analysis results obtained from these two approaches suggested that the surrounding water molecules which form hydrogen bonds with the CH(3)NH(2)/CO(2) complex draw the carbon dioxide closer to the methylamine. This enables, when two or more water molecules are present, an electron transfer from methylamine to carbon dioxide to form the methylcarbamic acid zwitterion, CH(3)NH(2)(+)CO(2)(-), in which the carbon dioxide is bent. Our calculations show that the zwitterion is formed without involving any electronic excitation on the ground state surface; this structure is only stable in the presence of water, i.e. in a methyl amine-carbon dioxide-water ice. Notably, in the vibrational frequency calculations on the methylcarbamic acid zwitterion and two water molecules we find the carbon dioxide asymmetric stretch is drastically red shifted by 435 cm(-1) to 1989 cm(-1) and the carbon dioxide symmetric stretch becomes strongly infrared active. We discuss how the methylcarbamic acid zwitterion CH(3)NH(2)(+)CO(2)(-) might be experimentally and astronomically identified by its asymmetric CO(2) stretching mode using infrared spectroscopy.     

Controlled self-assembly of filled micelles on nanotubes

We have used coarse-grained molecular dynamics simulations to show that hydrated lipid micelles of preferred sizes and amounts of filling with hydrophobic molecules can be self-assembled on the surfaces of carbon nanotubes. We simulated micelle formation on a hydrated (40,0) carbon nanotube with an open end that was covered with amphiphilic double-headed CH(3)(CH(2))(14)CH(((CH(2)OCH(2)CH(2))(2)(CH(2)COCH(2)))(2)H)(2) or single-headed CH(3)(CH(2))(14)CH(2)((CH(2)OCH(2)CH(2))(2)(CH(2)COCH(2)))(4)H lipids and filled with hexadecane molecules. Once the hexadecane molecules inside the nanotube were pressurized and the lipids on its surface were dragged by the water flowing around it, kinetically stable micelles filled with hexadecane molecules were sequentially formed at the nanotube tip. We investigated the stability of the thus-formed kinetically stable filled micelles and compared them with thermodynamically stable filled micelles that were self-assembled in the solution.     

Supramolecular structural variations with changes in anion and solvent in silver(I) complexes of a semirigid, bitopic tris(pyrazolyl)methane ligand

The bitopic ligand p-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2) (pz = pyrazolyl ring) that contains two tris(pyrazolyl)methane units connected by a semirigid organic spacer reacts with silver(I) salts to yield [p-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2)(AgX)(2)]( infinity ), where X = CF(3)SO(3)(-) (1), SbF(6)(-) (2), PF(6)(-) (3), BF(4)(-) (4), and NO(3)(-) (5). Crystallization of the first three compounds from acetone yields [p-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2)(AgCF(3)SO(3))(2)]( infinity ) (1a), [p-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2)(AgSbF(6))(2)[(CH(3))(2)CO](2)]( infinity ) (2b), and [p-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2)AgPF(6)]( infinity ) (3a), where the stoichiometry for the latter compound has changed from a metal:ligand ratio of 2:1 to 1:1. The structure of 1a is based on helical argentachains constructed by a kappa(2)-kappa(1) coordination to silver of the tris(pyrazolyl)methane units. These chains are organized into a tubular 3D structure by cylindrical [(CF(3)SO(3))(6)](6)(-) clusters that form weak C-H...O hydrogen bonds with the bitopic ligand. The same kappa(2)-kappa(1) coordination is present in the structure of 2a, but the structure is organized by six different tris(pyrazolyl)methane units from six ligands bonding with six silvers to form a 36-member argentamacrocycle core. The cores are organized in a tubular array by the organic spacers where each pair of macrocycles sandwich six acetone molecules and one SbF(6)(-) counterion. The structure of 3a is based on a kappa(2)-kappa(0) coordination mode of each tris(pyrazolyl)methane unit forming a helical coordination polymer, with two strands organized in a double stranded helical structure by a series of C-H...pi interactions between the central arene rings. Crystallization of 2-4 from acetonitrile yields complexes of the formula [p-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2)[(AgX)(2)(CH(3)CN)(n)]]( infinity ) where n = 2 for X = SbF(6)(-) (2b), X = PF(6)(-) (3b) and n = 1 for X = BF(4)(-) (4b). All three structures contain argentachains formed by a kappa(2)-kappa(1) coordination mode of the tris(pyrazolyl)methane units linked by the organic spacer and arranged in a 2D sheet structure with the anions sandwiched between the sheets. Crystallization of 5 from acetonitrile yields crystals of the formula [p-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2)(AgNO(3))(2)(CH(3)CN)(4)]( infinity ), where the nitrate is bonded to the silver. The argentachains, again formed by kappa(2)-kappa(1) coordination, are arranged in W-shaped sheets that have an overall configuration very different from 2b-4b. Treating [p-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2)(AgSbF(6))(2)]( infinity ) with a saturated aqueous solution of KPF(6) or KO(3)SCF(3) slowly leads to complete exchange of the anion. Crystallization of a sample that contains an approximately equal mixture of SbF(6)(-)/PF(6)(-) from acetonitrile yields [p-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2)[Ag(2)(PF(6))(0.78(1))(SbF(6))(1.22(1))(CH(3)CN)(2)][(CH(3)CN)(0.25) (C(4)H(10)O)(0.25)]]( infinity ), a compound with a sheet structure analogous to 2b-4b. Crystallization of the same mixture from acetone yields [p-C(6)H(4)[CH(2)OCH(2)C(pz)(3)](2)(AgSbF(6))[(CH(3))(2)CO](1.5)]( infinity ), where the metal-to-ligand ratio is 1:1 and the [C(pz)(3)] units are kappa(2)-kappa(0) bonded forming a coordination polymer. The supramolecular structures of all species are organized by a combination of C-H...pi, pi-pi, or weak C-H-F(O) hydrogen bonding interactions.     

Effects of monolayer structures on long-range electron transfer in helical peptide monolayer

Self-assembled monolayers of alpha-helical peptides were prepared on gold, and the effects of the monolayer structures (kind of constituent amino acid, molecular orientation, and molecular packing) on long-range electron transfer through the helical peptides were studied. The helical peptides were 16mer peptides having a thiophenyl linker at the N-terminal for immobilization on gold and a redox active ferrocene moiety at the C-terminal as an electron-transfer probe. The peptides were immobilized on gold by a gold-sulfur linkage and the electron transfer from the ferrocene moiety to gold was studied by electrochemical methods. When two types of the peptides, one with the repeating unit of Leu-Aib (Aib represents 2-aminoisobutyric acid) and the other with that of Ala-Aib, were compared, the electron transfer was found one order slower in the Leu-Aib peptide monolayer than that in the Ala-Aib peptide monolayer. The self-assembled monolayers of the Ala-Aib peptide with mixing of three different lengths of the peptides, 8mer, 12mer, and 16mer without a ferrocene moiety, were also prepared. The monolayer regularity in terms of molecular orientation and packing was higher roughly in the order of the monolayers mixed with 16mer > 12mer > no additive > 8mer, but the electron transfer became faster in the opposite order. The logarithms of the standard rate constants showed a nearly linear relationship with the direct distances between the ferrocene moiety and gold (beta = 0.32 A (-1)). Some data deviated from this linear relationship, but the deviations could be explained from the difference in the molecular packing, which was evaluated from the monolayer capacitance. It is thus concluded that an electron is transferred along a few molecules along the surface normal so that the vertical orientation or the increase of the interchain backbone separation slows down the electron transfer. Further, it is demonstrated that a tightly packed monolayer, where vibrational mode is restricted, suppresses the electron transfer. Three models are proposed to account for the observed molecular dynamics effects on the basis of either electron-transfer mechanism of electron tunneling or sequential hopping.     

Phosphino carboxylic acid ester functionalized carbosilane dendrimers: nanoscale ligands for the Pd-catalyzed hydrovinylation reaction in a membrane reactor

Phosphino carboxylic acid ester terminated G(0) compounds Si(CH(2))(3)SiMe(2)(C(6)H(4)CH(2)OC(O)(CH(2))(n)()CH(2)PPh(2)(4) (9a and 9b; n = 1, 2) and the carbosilane dendrimers Si(CH(2))(3)Si((CH(2))(3)SiMe(2)(C(6)H(4)CH(2)OC(O)(CH(2))(n)()CH(2) PPh(2))(3)(4) (10a and 10b; n = 1, 2) have been prepared as hemilabile nanoscale ligands for the palladium-catalyzed codimerization of olefins. The hydrovinylation of styrene was carried out in a continuously operated nanofiltration membrane reactor. Under continuous conditions, the selectivity of the reaction is increased considerably. Monomeric model complexes and the dendritic catalysts were compared for their activity and selectivity in batch reactions. The Pd catalyst complexes were prepared in situ from the dendritic ligands and an (allyl)palladium(II) precursor.     

A novel alpha-helix-liked metallohelicate series and their structural adjustments for the isomorphous substitution

A novel metallohelical motif is well designed and synthesized by mimicking the alpha-helical fold structure of protein. The 1D helical structures of [Cd(CH2(COO)2)(SC(NH2)2)2]n (I) and [Zn(CH2(COO)2) (SC(NH2)2)2]n (II) are primarily induced and stabilized by the multiple long-range intrahelix hydrogen bonds. Malonate dianion acts as a bidentate ligand coordinated with metal ions to form the backbone of the helix, and thiourea molecules that bend into the helical turn are involved in the intrahelix hydrogen-bond system. The metal ion occupations in the helix of I and II can be freely substituted by simply controlling the initial ratio of those two metal ions. Single crystals of three mixed metal ion complexes of [Cd0.77Zn0.23(CH2(COO)2)(SC(NH2)2)2]n (III), [Cd0.50Zn0.50(CH2(COO)2)(SC(NH2)2)2]n (IV), and [Cd0.21Zn0.79(CH2(COO)2)(SC(NH2)2)2]n (V) were synthesized from systems with an initial Cd/Zn mole ratio of 1:1 for III, 1:2 for IV, and 1:8 for V. They are isomorphous as confirmed by X-ray characterization. When the metal ion is substituted, the multiple intrahelix hydrogen interaction motifs of the coordination polymer structure are self-adjusted to sustain their 1D helical motifs.     

Helical water chain mediated proton conductivity in homochiral metal-organic frameworks with unprecedented zeolitic unh-topology

Four new homochiral metal-organic framework (MOF) isomers, [Zn(l-L(Cl))(Cl)](H(2)O)(2) (1), [Zn(l-L(Br))(Br)](H(2)O)(2) (2), [Zn(d-L(Cl))(Cl)](H(2)O)(2) (3), and [Zn(d-L(Br))(Br)](H(2)O)(2) (4) [L = 3-methyl-2-(pyridin-4-ylmethylamino)butanoic acid], have been synthesized by using a derivative of L-/D-valine and Zn(CH(3)COO)(2)·2H(2)O. A three-periodic lattice with a parallel 1D helical channel was formed along the crystallographic c-axis. Molecular rearrangement results in an unprecedented zeolitic unh-topology in 1-4. In each case, two lattice water molecules (one H-bonded to halogen atoms) form a secondary helical continuous water chain inside the molecular helix. MOFs 1 and 2 shows different water adsorption properties and hence different water affinity. The arrangement of water molecules inside the channel was monitored by variable-temperature single-crystal X-ray diffraction, which indicated that MOF 1 has a higher water holding capacity than MOF 2. In MOF 1, water escapes at 80 °C, while in 2 the same happens at a much lower temperature (～40 °C). All the MOFs reported here shows reversible crystallization by readily reabsorbing moisture. In MOFs 1 and 2, the frameworks are stable after solvent removal, which is confirmed by a single-crystal to single-crystal transformation. MOFs 1 and 3 show high proton conductivity of 4.45 × 10(-5) and 4.42 × 10(-5) S cm(-1), respectively, while 2 and 4 shows zero proton conductivity. The above result is attributed to the fact that MOF 1 has a higher water holding capacity than MOF 2.     

The "missing link": the gas-phase generation of platinum-methylidyne clusters Pt(n)CH+ (n=1, 2) and their reactions with hydrocarbons and ammonia

Electrospray ionization (ESI) of tetrameric platinum(II) acetate, [Pt(4)(CH(3)COO)(8)], in methanol generates the formal platinum(III) dimeric cation [Pt(2)(CH(3)COO)(3)(CH(2)COO)(MeOH)(2)](+), which, upon harsher ionization conditions, sequentially loses the two methanol ligands, CO(2), and CH(2)COO to form the platinum(II) dimer [Pt(2)(CH(3)COO)(2)(CH(3))](+). Next, intramolecular sequential double hydrogen-atom transfer from the methyl group concomitant with the elimination of two acetic acid molecules produces Pt(2)CH(+) from which, upon even harsher conditions, PtCH(+) is eventually generated. This degradation sequence is supported by collision-induced dissociation (CID) experiments, extensive isotope-labeling studies, and DFT calculations. Both PtCH(+) and Pt(2)CH(+) react under thermal conditions with the hydrocarbons C(2)H(n) (n=2, 4, 6) and C(3)H(n) (n=6, 8). While, in ion-molecule reactions of PtCH(+) with C(2) hydrocarbons, the relative rates decrease with increasing n, the opposite trend holds true for Pt(2)CH(+). The Pt(2)CH(+) cluster only sluggishly reacts with C(2)H(2), but with C(2)H(4) and C(2)H(6) dihydrogen loss dominates. The reactions with the latter two substrates were preceded by a complete exchange of all of the hydrogen atoms present in the adduct complex. The PtCH(+) ion is much less selective. In the reactions with C(2)H(2) and C(2)H(4), elimination of H(2) occurs; however, CH(4) formation prevails in the decomposition of the adduct complex that is formed with C(2)H(6). In the reaction with C(2)H(2), in addition to H(2) loss, C(3)H(3)(+) is produced, and this process formally corresponds to the transfer of the cationic methylidyne unit CH(+) to C(2)H(2), accompanied by the release of neutral Pt. In the ion-molecule reactions with the C(3) hydrocarbons C(3)H(6) and C(3)H(8), dihydrogen loss occurs with high selectivity for Pt(2)CH(+), but in the reactions of these substrates with PtCH(+) several reaction routes compete. Finally, in the ion-molecule reactions with ammonia, both platinum complexes give rise to proton transfer to produce NH(4)(+); however, only the encounter complex generated with PtCH(+) undergoes efficient dehydrogenation of the substrate, and the rather minor formation of CNH(4)(+) indicates that C-N bond coupling is inefficient.     

Dicarboxylate-bridged (Mo2)n (n = 2, 3, 4) paddle-wheel complexes: potential intermediate building blocks for metal-organic frameworks

The treatment of the dimeric paddle-wheel (PW) compound [Mo(2)(NCCH(3))(10)][BF(4)](4)1 with oxalic acid (0.5 equiv.), 1,1-cyclobutanedicarboxylic acid (1 equiv.), 5-hydroxyisophthalic acid (1 equiv.) (m-bdc-OH) or 2,3,5,6-tetrafluoroterephthalic acid (0.5 or 1 equiv.) leads to the formation of macromolecular dicarboxylate-linked (Mo(2))(n) entities (n = 2, 3, 4). The structure of the compounds depends on the length and geometry of the organic linkers. In the case of oxalic acid, the dimeric compound [(CH(3)CN)(8)Mo(2)(OOC-COO)Mo(2)(NCCH(3))(8)][BF(4)](6)2 is formed selectively, whereas the use of 2,3,5,6-tetrafluoroterephthalic acid affords the square-shaped complex [(CH(3)CN)(6)Mo(2)(OOC-C(6)F(4)-COO)](4)[BF(4)](8)3. Bent linkers with a bridging angle of 109° and 120°, respectively, lead to the formation of the molecular loop [(CH(3)CN)(6)Mo(2)(OOC-C(4)H(6)-COO)](2)[BF(4)](4)4 and the bowl-shaped molecular triangle [(CH(3)CN)(6)Mo(2)(m-bdc-OH)](3)[BF(4)](6)5. All complexes are characterised by X-ray single crystal diffraction, NMR ((1)H, (11)B, (13)C and (19)F) and UV-Vis spectroscopy.     

Tubular microstructures made from nonchiral single-chain fluorinated amphiphiles: impact of the structure of the hydrophobic chain on the rolling-up of bilayer membrane

The nonchiral, single-chain fluorinated amphiphiles derived from dimorpholinophosphate, C(n)F(2n+1)(CH(2))(m)OP(O)[N(CH(2)CH(2))(2)O](2) (FnCmDMPs), form hollow tubular bilayer-based self-assemblies when dispersed in water, ethanol/water mixtures, and dimethylformamide. The fluorinated tubules are highly stable and sturdy. Upon heating, they transform reversibly into giant multilamellar vesicles. Uncommon U-shaped and V-shaped coiled membranes were obtained from mixtures of FnCmDMPs. Depending on conditions, fluorinated tubules can evolve with time into collapsed flattened crystallized needles. The successive steps involved in the formation and evolution of these tubules were identified, and the specific features of fluorinated chains that are relevant to membrane coiling and tubule formation are discussed.     

Zeolite ionic crystals assembled through direct incorporation of polyoxometalate clusters within 3D metal-organic frameworks

Polyoxometalate-based metal-organic frameworks {[Gd(dpdo)(4)(H(2)O)(3)](PMo(12)O(40))(H(2)O)(2)CH(3)CN}(n) (2), {[Dy(dpdo)(4)(H(2)O)(3)](PMo(12)O(40))(H(2)O)(20CH(3)CN}(n) (3), {[Gd(dpdo)(4)(H(2)O)(3)](H(3)O)(SiMo(12)O(40))(dpdo)(0.5)(CH(3)CN)(0.5) (H(2)O)(3)}(n) (4), {[Ho(dpdo)(4)(H(2)O)(3)](H(3)O)(SiMo(12)O(40))(dpdo)(0.5)(CH(3)CN)(0.5)(H(2)O)(3)}(n) (5), {[Ni(dpdo)(2)(CH(3)CN) (H(2)O)(2)](2)(SiMo(12)O(40))(H(2)O)(2)}(n) (6), and {[Ni(dpdo)(3)](4)(PW(12)O(40))(3)[H(H(2)O)(27)(CH(3)CN)(12)]}(n) (7) (where dpdo is 4,4'-bipyridine-N,N'-dioxide) were constructed via self-assembly by embedding Keggin-type polyanions within the intercrystalline voids as guests or pillars. Compounds 2 and 3 are isomorphic and exhibit three-dimensional (3D) noninterwoven 64 frameworks with distorted-honeycomb cavities occupied by the polyanions. Compounds 4 and 5 are comprised of 3D noninterwoven frameworks formed by linking the adjacent folded sheets through hydrogen bonds and pi-pi stacking interactions relative to the free isolated dpdo ligand. Compound 6 is a pillar-layered framework with the [SiMo(12)O(40)](4-) anions located on the square voids of the two-dimensional bilayer sheets formed by the dpdo ligands and nickel(II) ions. Compound 7 is a 3D metal-organic framework formed by nickel(II) and 4,4'-bipyridine-N,N'-dioxide with the globular Keggin-structure [PW(12)O(4)](3-) anion as the template. A large protonated water cluster H(+)(H(2)O)(27) is trapped and stabilized within the well-modulated cavity.     

Reactions of a platinum(III) dimeric complex with alkynes in water: novel approach to alpha-aminoketone, alpha-iminoketone, and alpha,beta-diimine via ketonyl-Pt(III) dinuclear complexes

Reaction of the platinum(III) dimeric complex [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(NO(3))(2)](NO(3))(2) (1), prepared in situ by the oxidation of the platinum blue complex [Pt(4)(NH(3))(8)((CH(3))(3)CCONH)(4)](NO(3))(5) (2) with Na(2)S(2)O(8), with terminal alkynes CH[triple bond]CR (R = (CH(2))(n)CH(3) (n = 2-5), (CH(2))(n)CH(2)OH (n = 0-2), CH(2)OCH(3), and Ph), in water gave a series of ketonyl-Pt(III) dinuclear complexes [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(2)COR)](NO(3))(3) (3, R = (CH(2))(2)CH(3); 4, R = (CH(2))(3)CH(3); 5, R = (CH(2))(4)CH(3); 6, R = (CH(2))(5)CH(3); 7, R = CH(2)OH; 8, R = CH(2)CH(2)OH; 9, R = (CH(2))(2)CH(2)OH; 10, R = CH(2)OCH(3); 11, R = Ph). Internal alkyne 2-butyne reacted with 1 to form the complex [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(CH(3))COCH(3))](NO(3))(3) (12). These reactions show that Pt(III) reacts with alkynes to give various ketonyl complexes. Coordination of the triple bond to the Pt(III) atom at the axial position, followed by nucleophilic attack of water and hydrogen shift from the enol to keto form, would be the mechanism. The structures of complexes 3.H(2)O, 7.0.5C(3)H(4)O, 9, 10, and 12 have been confirmed by X-ray diffraction analysis. A competitive reaction between equimolar 1-pentyne and 1-pentene toward 1 produced complex 3 and [Pt(2)(NH(3))(4)((CH(3))(3)CCONH)(2)(CH(2)CH(OH)CH(2)CH(2)CH(3))](NO(3))(3) (14) at a molar ratio of 9:1, suggesting that alkyne is more reactive than alkene. The ketonyl-Pt(III) dinuclear complexes are susceptible to nucleophiles, such as amines, and the reactions with secondary and tertiary amines give the corresponding alpha-amino-substituted ketones and the reduced Pt(II) complex quantitatively. In the reactions with primary amines, the once formed alpha-amino-substituted ketones were further converted to the iminoketones and diimines. The nucleophilic attack at the ketonyl group of the Pt(III) complexes provides a convenient means for the preparation of alpha-aminoketones, alpha-iminoketones, and diimines from the corresponding alkynes and amines.     

Zinc diphosphonates templated by organic amines: syntheses and characterizations of [NH3(CH2)2NH3]Zn(hedpH2)2*2H2O and [NH3(CH2)nNH3(CH2)nNH3]Zn2(hedpH)2*2H2O (n=4,5,6) (hedp=1-hydroxyethylidenediphophonate)

Four new zinc diphosphonate compounds with formulas [NH(3)(CH(2))(2)NH(3)]Zn(hedpH(2))(2).2H(2)O, 1, [NH(3)(CH(2))(n)()NH(3)]Zn(2)(hedpH)(2).2H(2)O, (n = 4, 2; n = 5, 3; n = 6, 4) (hedp = 1-hydroxyethylidenediphosphonate) have been synthesized under hydrothermal conditions at 110 degrees C and in the presence of alkylenediamines NH(2)(CH(2))(n)()NH(2) (n = 2, 4, 5, 6). Crystallographic data for 1: monoclinic, space group C2/c, a = 24.7422(15), b = 5.2889(2), c = 16.0338(2) A, beta = 117.903(1) degrees, V = 1856.17(18) A(3), Z = 4; 2: monoclinic, space group P2(1)/n, a = 5.4970(3), b = 12.1041(6), c = 16.2814(12) A, beta = 98.619(5) degrees, V = 1071.07(11) A(3), Z = 2; 3: monoclinic, space group P2(1)/n, a = 5.5251(2), b = 12.5968(3), c = 16.1705(5) A, beta = 99.182(1) degrees, V = 1111.02(6) A(3), Z = 2; 4: triclinic, space group P-1, a = 5.4785(2), b = 14.1940(5), c = 16.0682(6) A, alpha = 81.982(2) degrees, beta = 89.435(2) degrees, gamma = 79.679(2) degrees, V = 1217.11(8) A(3), Z = 2. In compound 1, two of the phosphonate oxygens are protonated. The metal ions are bridged by the hedpH(2)(2-) groups through three of the remaining four phosphonate oxygens, forming a one-dimensional infinite chain. The protonated ethylenediamines locate between the chains in the lattice. In compounds 2-4, only one phosphonate oxygen is protonated. Compounds 2 and 3 have a similar three-dimensional open-network structure composed of [Zn(2)(hedpH)(2)](n) double chains with strong hydrogen bonding interactions between them, thus generating channels along the [100] direction. The protonated diamines and water molecules reside in the channels. Compound 4 contains two types of [Zn(2)(hedpH)(2)](n) double chains which are held together by strong hydrogen bonds, forming a two-dimensional network. The interlayer spaces are occupied by the [NH(3)(CH(2))(6)NH(3)](2+) cations and water molecules. The significant difference between structures 2-4 is also featured by the coordination geometries of the zinc atoms. The geometries of those in 2 can be described as distorted octahedral, and those in 3 as distorted square pyramidal. In 4, two independent zinc atoms are found, each with a distorted octahedral and a tetrahedral geometry, respectively.     

Conformational studies of a bombolitin III-derived peptide mimicking the four-helix bundle structural motif of proteins

Bombolitins are five structurally related heptadecapeptides originally isolated from the venom of a bumblebee. In aqueous solution, bombolitins at sufficiently high concentration form oligomeric aggregates with consequent conformational transition from a random coil to the alpha-helical structure. Previous studies suggested that oligomeric aggregates could mimic the four-helix bundle structural motif of proteins. In the present work, we synthesized the following peptide sequence formed by two bombolitin III sequences linked head-to-tail by the tetrapeptide bridge -Gly-Pro-Val-Asp-: I(1)-K(2)-I(3)-M(4)-D(5)-I(6)-L(7)-A(8)-K(9)-L(10)-G(11)-K(12)-V(13)-L(14)-A(15)-H(16)-V(17)-G(18)-P(19)-V(20)-D(21)-I(22)-K(23)-I(24)-M(25)-D(26)-I(27)-L(28)-A(29)-K(30)-L(31)-G(32)-K(33)-V(3)(4)-L(35)-A(36)-H(37)-V(38)-NH(2). The tetrapeptide GPVD connecting the two helical peptide sequences was chosen to facilitate the formation of the helix-loop-helix structural motif. The conformational properties of the peptide were studied by CD, NMR, and molecular dynamics calculations. The results indicate the presence of a helix-loop-helix conformation at 10(-)(5) M concentration. At higher concentrations, NOESY connectivities were detected which are compatible with the presence of dimers or higher aggregates of peptide molecules in the helix-loop-helix structure packed in an antiparallel fashion. Molecular dynamics simulation were run either with NOE distance restraints or without restraints in explicit solvent for extended time. The results of these simulations support the dimerization of the molecules in the helix-loop-helix structure with formation of the four-helix bundle motif.     

Spontaneous resolution of a racemic nickel(II) complex and helicity induction via hydrogen bonding: the effect of chiral building blocks on the helicity of one-dimensional chains

The reactions of a racemic four-coordinated nickel(II) complex [Ni(alpha-rac-L)](ClO4)2 (containing equal amount of SS and RR enantiomers) with l- and d-phenylalanine in acetonitrile/water gave two less-soluble six-coordinated enantiomers of {[Ni( f-SS-L)(l-Phe)](ClO4)}n (Delta-1) and {[Ni(f- RR-L)(d-Phe)](ClO4)}n (Lambda-1), respectively. Evaporation the remaining solutions gave two six-coordinated diastereomers of {[Ni 3(f- RR-L)3(l-Phe)2(H 2O)](ClO4)4}n (a-2) and {[Ni3(f- SS-L)3(d-Phe)2(H2O)](ClO4)4}n (b-2), respectively (L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, Phe(-) = phenylalanine anion). The reaction of [Ni(alpha-rac-L)](ClO4)2 with dl-Phe(-) gave a conglomerate of c-1; in which, the SS and RR enantiomers preferentially coordinate to l- and d-Phe(-) respectively to give a racemic mixture of Delta-1 and Lambda-1, and the spontaneous resolution occurs during the reaction, in which each crystal crystallizes to become enantiopure. Removing Phe(-) from Delta-1 and Lambda-1 using perchloric acid gave two enantiomers of [Ni(alpha-SS-L)](ClO4)2 (S-3) and [Ni(alpha-RR-L)](ClO4)2 (R-3). Dissolving S-3 and R-3 in acetonitrile gave two six-coordinated enantiomers of [Ni( f-SS-L)(CH3CN)2](ClO4)2 (S-4) and [Ni( f- RR-L)(CH3CN)2](ClO4)2 (R-4), while dissolving [Ni(alpha-rac-L)](ClO4)2 in acetonitrile gave a racemic twining complex [Ni(f-rac-L)(CH3CN)2](ClO4)2 (rac-4). Delta-1 and Lambda-1 belong to supramolecular stereoisomers, which are constructed via hydrogen bond linking of [Ni( f-SS-L)(l-Phe)](+) and [Ni(f-RR-L)(d-Phe)](+) monomers to form 1D homochiral right-handed and left-handed helical chains, respectively. The reaction of S-3 with d-Phe(-) gave {[Ni(f-SS-L)(d-Phe)](ClO4)}n (5), which shows a motif of a 1D hydrogen bonded zigzag chain instead of a 1D helical chain. Compound a-2/ b-2 contains dimers of [{Ni(f-RR-L)}2(l-Phe)(H2O)](3+)/[{Ni( f- SS-L)}2(d-Phe)(H2O)](3+) and 1D zigzag chains of {[Ni(f-RR-L)(l-Phe)](+)}n /{[Ni(f-SS-L)(d-Phe)](+) n . The homochiral nature of Delta-1/Lambda-1, a-2/b-2, S-3/R-3, and S-4/R-4 are confirmed by the results of circular dichroism (CD) spectra measurements.     

PbnI4n+2(2n+2)- ribbons (n = 3, 5) as dimensional reductions of 2D perovskite layers in cystamine cation based hybrids, also incorporating iodine molecules or reversible guest water molecules

Pb(n)I(4n+2)((2n+2)-) (n = 3, 5) ribbons, which can be regarded as dimensional reductions of 2D perovskite layers, are stabilized by diprotonated cystamine cations in (NH(3)(CH(2))(2)SS(CH(2))(2)NH(3))(4)Pb(3)I(14),I(2) (1) and (NH(3)(CH(2))(2)SS(CH(2))(2)NH(3))(6)Pb(5)I(22).4H(2)O (2). Both 1 and 2 have interesting structural characteristics; it is unprecedented that the ribbons are linked via I(2) molecules incorporated in the lattice of 1, while tetrameric water clusters are trapped in the structure of 2. 2 undergoes a (reversible) water desorption process at 310 K leading to (NH(3)(CH(2))(2)SS(CH(2))(2)NH(3))(6)Pb(5)I(22).2H(2)O (3). The electrical behavior of 2 and 3 has been investigated in the ranges 293-310 K and 310-358 K respectively. Above 310 K, the electronic contribution remains constant while the ionic transference number tends towards unity showing almost pure ionic transport at 360 K (6 x 10(-7) S cm(-1) at 330 K) originating probably from the migration of protons through the hydrogen bonds connecting the water molecules to the cystamine counter cations.     

Microhydration of the magnesium(II) acetate cation in the gas phase

Electrospray ionization of aqueous solutions of magnesium(II) acetate leads to microhydrated magnesium acetate cations of the type [(CH(3)COO)(2m-1)Mg(m)(H(2)O)(n)](+) with m = 1-4 and n = 0-4, which are characterized by mass spectrometry and, for the cluster with three water molecules, also by infrared multiphoton dissociation spectroscopy. Density functional theory is used to determine the energies of microhydration for the mononuclear species [(CH(3)COO)Mg(H(2)O)(n)](+) with n = 0-6 and the associated changes in molecular structure. While bidentate coordination of the acetato ligand is generally preferred, at higher values of n, a switch to a monodentate coordination becomes energetically competitive.