Dual-action acid/base- and base/acid-controllable molecular switch.

[Structure: see text] We report a molecular switch that not only can be switched between its complexed and decomplexed states through the sequential addition of an acid and a base (NH4+ and Proton Sponge, respectively) but also can be operated equally through the sequential addition of basic and acidic reagents (Et2NH and TFA, respectively).

UV-activated multilayer nanomatrix provides one-step tunable carbohydrate structural characterization in MALDI-MS.

The structure-specific fragmentation of gas-phase ions in tandem mass spectrometry among other techniques provides an efficient analytical method for confirming unknown analytes or for elucidating chemical structures. Using concentration-dependent UV-absorbing matrix-functionalized magnetic nanoparticles and matrix-assisted laser desorption-ionization mass spectrometry (MALDI MS), we developed a single-step pseudo-MS/MS approach for tunable ionization and fragmentation to facilitate structure determination. Without chemical derivatization, we have demonstrated that this approach successfully distinguished isomeric sets of di-, tri- and tetrasaccharides. Low concentration of nanomatrix provided an enhanced signal for accurate mass determination of the intact molecular ions of analytes present in the sample. In contrast, high concentration of nanomatrix induced extensive and unique fragmentation, including high-energy facile bond breakage (A- and X-type cross-ring cleavages), which facilitated the linkage and sequence characterization of oligosaccharides without conventional tandem mass spectrometric instrumentation. The practicality of this approach for complex sample analysis was evaluated by an oligosaccharide mixture, wherein molecular ions are unambiguously observed and signature product ions are distinguishable enough for molecular identification and isomer differentiation by this simple tunable approach. By probing the roles of the multilayer nanomatrix components: matrix (energy absorption), silane-coating (energy pooling and dissipation) and core Fe3O4 (fragmentation), a plausible energy transfer mechanism was proposed based on a computational study and photoelectron experiments. The differentiation of tri- and tetra-oligosaccharide shown in this study not only demonstrated the first step toward glycan characterization by nanoparticle-assisted MALDI-MS, but also shed some insight on the nanoparticle-mediated energy transfer dynamics behind our approach.

Synthesis and Properties of Polyether Adducts of Hexafluoropentanedionatosilver(I).

A series of polyether [CH(3)O(CH(2)CH(2)O)(m)()CH(3), with m = 2 (diglyme), 3 (triglyme), 4 (tetraglyme)] mono- or hemiadducts of hexafluoropentanedionatosilver(I) have been synthesized and in selected cases structurally characterized. Decomposition of [Ag(hfa)(diglyme)](2) (hfa = hexafluoropentanedionato) in air affords a mixture of products including crystals of [Ag(2)(hfa)(O(2)CCF(3))(diglyme)(2)]. The structure of [Ag(hfa)(diglyme)](2) consists of two silver cations which are bridged by four oxygens from two hfa ligands; each Ag(I) ion is also coordinated to a chelating diglyme molecule. In comparison, ligation of a longer polyether chain results in a monomeric species [Ag(hfa)(tetraglyme)]. The compounds are soluble in a range of solvents including supercritical carbon dioxide (scCO(2)). Crystal data for [Ag(hfa)(diglyme)](2) (150 K): a = 21.376(3) Å, b = 8.4143(17) Å, c = 21.067(3) Å, beta = 124.05(1) degrees, monoclinic space group C2/c; Z = 8. Crystal data for [Ag(2)(hfa)(O(2)CCF(3))(diglyme)(2)] (150 K): a = 9.0945(12) Å, b = 9.4110(13) Å, c = 17.803(2) Å, alpha = 96.109(14) degrees, beta = 101.649(13) degrees, gamma = 105.06(2) degrees, triclinic space group P&onemacr;; Z = 2. Crystal data for [Ag(hfa)(tetraglyme)] (150 K): a = 14.152(3) Å, b = 16.996(3) Å, c = 8.620(2) Å, beta = 106.99(2) degrees, monoclinic space group P2(1)/c; Z = 4.

Stabilizing Heterobimetallic Complexes Containing Unsupported Ti-M Bonds (M = Fe, Ru, Co): The Nature of Ti-M Donor-Acceptor Bonds.

The stabilization of unsupported Ti-M (M = Fe, Ru, Co) heterodinuclear complexes has been achieved by use of amidotitanium building blocks containing tripodal amido ligands. Salt metathesis of H(3)CC(CH(2)NSiMe(3))(3)TiX (1) and C(6)H(5)C(CH(2)NSiMe(3))(3)TiX (2) as well as HC{SiMe(2)N(4-CH(3)C(6)H(4))}(3)TiX (3) (X = Cl, a; Br, b) with K[M(CO)(2)Cp] (M = Fe, Ru) and Na[Co(CO)(3)(PR(3))] (R = Ph, Tol) gave the corresponding stable heterobimetallic complexes of which H(3)CC(CH(2)NSiMe(3))(3)Ti-M(CO)(2)Cp (M = Fe, 6; Ru, 7) and HC{SiMe(2)N(4-CH(3)C(6)H(4))}(3)Ti-M(CO)(2)Cp (M = Fe, 12; Ru, 13) have been characterized by X-ray crystallography. 6: monoclinic, P2(1)/n, a = 15.496(3) Å, b = 12.983(3) Å, c = 29.219(3) Å, beta = 104.52(2) degrees, Z = 8, V = 5690.71 Å(3), R = 0.070. 7: monoclinic, P2(1)/c, a = 12.977(3) Å, b = 12.084(3) Å, c = 18.217(3) Å, beta = 91.33(2) degrees, Z = 4, V = 2855.91 Å(3), R = 0.048. 12: monoclinic, I2/c, a = 24.660(4) Å, b = 15.452(3) Å, c = 20.631(4) Å, beta = 103.64(3) degrees, Z = 8, V = 7639.65 Å(3), R = 0.079. 13: monoclinic, I2/c, a = 24.473(3) Å, b = 15.417(3) Å, c = 20.783(4) Å, beta = 104.20(2) degrees, Z = 8, V = 7601.84 Å(3), R = 0.066. (1)H- and (13)C-NMR studies in solution indicate free internal rotation of the molecular fragments around the Ti-M bonds. Fenske-Hall calculations performed on the idealized system HC(CH(2)NH)(3)Ti-Fe(CO)(2)Cp (6x) have revealed a significant degree of pi-donor-acceptor interaction between the two metal fragments reinforcing the Ti-Fe sigma-bond. Due to the availability of energetically low-lying pi-acceptor orbitals at the Ti center this partial multiple bonding is more pronounced that in the tin analogue HC(CH(2)NH)(3)Sn-Fe(CO)(2)Cp (15x) in which an N-Sn sigma-orbital may act as pi-acceptor orbital.

Template Assembly of Polyiodide Networks at Complexed Metal Cations: Synthesis and Structures of [Pd2 Cl2 ([18]aneN2 S4 )]1.5 I5 (I3 )2 and [K([15]aneO5 )2 ]I9.

The cations [Pd2 Cl2 L]2+ and [KL2'+ (L = [18]aneN2 S4 , L' =[15]aneO5 ) have been used as templates for the synthesis of unique three-dimensional polyiodide networks. The metal cations in [Pd2 Cl2 L]1.5 I5 (I3 )2 are linked into infinite chains by pairwise hydrogen bonding; the resulting cationic polymers run through channels formed by the extended polyiodide network. [KL2' ]I9 shows a three-dimensional network of puckered cubic cages of I9- ions whose cavities are occupied by the metal cations (section from the structure shown on the right).

Template Assembly of Metal Aggregates by Imino-Carboxylate Ligands.

Lanthanide, main group, and transition metal ion templates provide different polynuclear cages from [M(L)] (M=Ni, Mn; (L)2-=CH2[CH2N=C(CH3)COO-]2). Templating with lanthanum results in a 12-coordinate LaIII ion encapsulated by six [Ni(L)] units, whereas with sodium four Na+ ions are trapped inside a tricapped trigonal prismatic [{Ni(L)}9] cage. With manganese, an octahedrally coordinated MnII ion is surrounded by six [Mn(L)] fragments in a twisted trigonal-prismatic configuration (see picture).

Substituent effect on the structural behavior of modified cyclodextrin: a molecular dynamics study on methylated ß-CDs.

A series of methylated and non-methylated ß-cyclodextrin (ß-CD) structures in three macrocyclic configurations (a-c) were studied with molecular dynamics (MD) simulations to elucidate the dynamic behavior of the different CD structures using a continuum water model with the AMBER* force field. A set of parameters were defined to describe the geometric dimensions of the CD, such as its cavity shape, the upper and lower rim sizes, and the tilting of each of the glucose rings. Correlation analyses between the different parameters were carried out, and they have provided insights into the different dynamic behaviors for the different CD structures. Detailed analyses on the crystal structures of the different methylated and non-methylated ß-CD complexes were also carried out using the defined parameters. Correlation of parameters from crystal structures and MD simulations has allowed us to identify the effect that crystal packing/guest inclusion has on the CD geometries. The overall analysis approach can be a useful tool for other related macrocyclic structures, such as modified α-, ß-CDs or even calixarenes.

Configuration effects of H-bonded sites and rigid core lengths on h-bonded banana-shaped liquid crystalline supramolecules consisting of symmetric trimers and asymmetric heterodimers.

Several series of novel banana-shaped H-bonded symmetric trimers (with two H-bonds) and asymmetric heterodimers (with one H-bond) were self-assembled by appropriate molar ratios of proton donors (H-donors) and acceptors (H-acceptors). The influences of H-bonded linking positions and aromatic ring numbers (4-8 aromatic rings in the rigid cores) as well as the chain lengths (n, m = 12 or 16, respectively, in the flexible parts) on the mesomorphism and the switching behavior of the bent-core supramolecules were evaluated and theoretically analyzed. Except for the supramolecular structures with longer rigid cores or shorter flexible chains possessing the rectangular columnar (Col(r) or B1) phase, the SmC(A)P(A) phase was revealed in most supramolecular asymmetric heterodimers and switched to the SmC(S)P(F) phase by applying electric fields. The polar smectic C phase was dominated for those with H-bonded sites apart from the core center. Interestingly, the SmA and nematic phases were observed in H-bonded asymmetric dimers with H-bonded sites close to the core center, which theoretically proved that the polar smectic C phase was disfavored due to an unfavorable bend angle (smaller than the lower limit of 110 degrees ) in the lowest-energy H-bonded conformer. Compared with the fully covalently bonded analogue, lower transition temperatures and lower threshold voltages were developed in the H-bonded asymmetric dimers with the polar smectic C phase. On the basis of the theoretical calculations of molecular modeling, the existence of polar switching behavior in the polar smectic C phase of asymmetric heterodimers was proven to be associated with their configurations with higher dipole moments and suitable bend angles. Furthermore, the lack of polar switching behavior in supramolecular symmetric trimers, which exhibited the regular SmC phase with weak electrical stabilities, was related to their configurations with smaller dipole moments and confirmed by theoretical calculations.

A molecular cage-based [2]rotaxane that behaves as a molecular muscle.

We report a molecular cage-based [2]rotaxane that functions as an artificial molecular muscle through the control of the addition and removal of fluoride anions. The percentage change in molecular length of the [2]rotaxane is about 36% between the stretched and contracted states, which is larger than the percentage change (approximately 27%) in human muscle.

Extended structures of polyiodide salts of transition metal macrocyclic complexes.

The structures of five polyiodide salts, [Co([9]aneS3)2]I11 (1), [Ni([9]aneS3)2]I6 (2), [Ni([9]aneS3)2]I10 (3), [Pd([12]aneS4)]I6 (4) and [Pd([14]aneS4)]I10.MeCN (5), containing the template cations [Co([9]aneS3)2]3+, [Ni([9]aneS3)2]2+, [Pd([12]aneS4)]2+ and [Pd([14]aneS4)]2+ ([9]aneS3=1,4,7-trithiacyclononane, [12]aneS4=1,4,7,10-tetrathiacyclododecane, [14]aneS4=1,4,8,11-tetrathiacyclotetradecane) exhibit a range of polyiodide and polyanionic framework structures. In (1) the charge on the CoIII cation is balanced by three I3- anions, which along with a neutral di-iodine molecule form I(11)3- rings in an extended structure comprising undulating chains of alternating I11(3-) rings and complex cations. In (2) the complex cation is linked to two tri-iodide anions by S...I interactions into well separated sheets of cations and anions, while in (3), I5- anions are linked by I...I interactions into helices which are cross-linked by S...I contacts to form sheets. Rather longer I...I contacts in (4) assemble I3- ions into 2x2 rods, which are linked into a three-dimensional network by S...I contacts. In (5) the N atom of the acetonitrile solvent molecule forms an array of four weak C-H...N hydrogen bonds to the macrocycle. The extended structure comprises corrugated zigzag chains of polyiodide rings formed by linked I_5;- units; the complex cations are attached to the polyiodide network by S...I contacts, which link the chains to form layers.

Is [N+-H...O] hydrogen bonding the most important noncovalent interaction in macrocycle-dibenzylammonium ion complexes?

We report a new host molecule in which one diethylene glycol chain (i.e., a loop possessing only three oxygen atoms) incorporated along with two phenolic aromatic rings is linked by a xylene spacer into a macroring. The design of the molecular structure of this macrocycle "amplifies" any potential [cation...pi], [N+-H...pi], and [N+C-H...pi] interactions between the dibenzylammonium (DBA+) ion and the phenolic rings of the macrocycle; as such, these species display a very strong binding affinity in CD3NO2 (Ka = 15,000 M(-1)). The macroring also coordinates to bipyridinium ions in a [2]pseudorotaxane fashion, which makes it the smallest macrocycle (i.e., a 25-membered ring) known to complex both DBA+ and bipyridinium ions in solution. To confirm unambiguously that these pseudorotaxanes exist in solution, we synthesized their corresponding interlocked molecules, namely rotaxanes and catenanes.

Theoretical study of the remote control of hydrogen bond strengths in donor-bridge-acceptor systems: principles for designing effective bridges with substituent tuning.

Remote control of hydrogen bond strengths has been studied based on conjugated donor-bridge-acceptor (pyrrole-bridge-imine) systems. The neutral and protonated states of the imine can change the hydrogen bonding ability of the pyrrole because, in the protonated state, significant partial intramolecular charge transfer (ICT) is induced that causes partial delocalization of the positive charge onto the pyrrole moiety. An efficient bridge, regardless of its length, should help electrons to flow out of pyrrole. A previously developed design strategy for the bridge (low bridge HOMO/LUMO) leads to the study of cyano- and fluoro-substituted conjugated systems. Substitution positions are found to be of key importance for maximizing the protonation-induced response from the donor-bridge-acceptor systems. Our results not only help to identify useful bridge substitution patterns, but also highlight interesting issues regarding the bridge conformation and the fluorine lone-pair effect.

A computational study of regioselectivity in a cyclodextrin-mediated Diels-Alder reaction: revelation of site selectivity and the importance of shallow binding and multiple binding modes.

The use of a cyclodextrin.Diels-Alder transition structure complex (CD.TS) as a model in molecular dynamics simulations has enabled us to gain insight into the controlling factors in the cyclodextrin-mediated Diels-Alder reaction of methyl-p-benzoquinone with isoprene. MD simulations were carried out with multiple binding configurations of the CD.TS (TS=meta-TS, para-TS) complexes at the top and bottom rims of beta-CD. We discovered that i) only shallow binding with the CD is necessary for the regioselectivity, and multiple binding geometries are possible; ii) the narrow bottom rim, with the primary hydroxyl groups, of the CD binds both regio-TSs better than at the wider top rim (secondary hydroxyl groups), which was unexpected from the perspective of shape complementarity that governs the stability of most CD.guest complexes. Overall, the bottom rim of the CD exhibits higher regioisomer discrimination for the meta-TS; iii) structural clustering analyses of the CD.TS configurations (sampled during MD simulations) have enabled us to evaluate the binding energies of the different binding configurations. The result indicates that there is a direct correlation between meta-product selectivity and a higher number of binding configurations favoring the formation of the CD.meta-TS complex. The main forces of stabilization in the CD.TS complexes are the van der Waals interactions when the TS is bound at the top rim. At the bottom rim, closer contacts between polar functional groups of the TS and CD have increased the importance of electrostatic interactions. We found that van der Waals, solvation, and torsional forces are less favorable for complexation at the bottom rim; however, this is compensated by large favorable electrostatic interactions. With insights obtained from the study of CD.TS complexes and MD simulations of the modified heptakis-[6-O-(2-hydroxy)propyl]-beta-CD, we were able to explain why a low selectivity was observed when the Diels-Alder reaction was carried out in this modified CD. Two types of search method [Monte Carlo and multiple minimum (MCMM) and molecular dynamics (MD)] to explore and evaluate the different possible binding geometries of the TS within beta-CD, were discussed.

Retroracemization using new forms of Belokon's original ligand: intermediate NiII complexes of N-((2-[N-(S)-alkylprolylamino]phenyl)phenylmethylene)-(S)-phenylalanine (alkyl is 2-picolyl, 3-picolyl or ethyl).

In the title compounds, [N-(phenyl(2-[N-(S)-(2-picolyl)prolylamino]phenyl)methylene)-(S)-phenylalaninato]nickel(II), [Ni(C(33)H(30)N(4)O(3))], (I), [N-(phenyl(2-[N-(S)-(3-picolyl)prolylamino]phenyl)methylene)-(S)-phenylalaninato]nickel(II) hemihydrate, [Ni(C(33)H(30)N(4)O(3))].0.5H(2)O, (II), and [N-((2-[N-(S)-ethylprolylamino]phenyl)phenylmethylene)-(S)-phenylalaninato]nickel(II), [Ni(C(29)H(29)N(3)O(3))], (III), the Ni(II) centres have approximate square-planar coordination geometries from N(3)O donor sets. The picolyl N atoms in (I) and (II) are too remote from the metal centres to interact significantly, but the metal coordination geometries experience tetrahedral distortion and/or displacement of the metal centre from the N(3)O plane. These are linked to conformational differences between the ligands of the symmetry-independent complexes (Z' = 2), which in turn are related to molecular packing. In (III), where a less sterically demanding ethyl group replaces the picolyl substituents, there are none of the distortions or displacements seen in (I) and (II).