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The mechanical properties of seven zeolitic imidazolate frameworks (ZIFs) based on five unique network topologies have been systematically characterized by single-crystal nanoindentation studies. We demonstrate that the elastic properties of ZIF crystal structures are strongly correlated to the framework density and the underlying porosity. For the systems considered here, the elastic modulus was found to range from 3 to 10 GPa, whereas the hardness property lies between 300 MPa and 1.1 GPa. Notably, these properties are superior to those of other metal--organic frameworks (MOFs), such as MOF-5. In substituted imidazolate frameworks, our results show that their mechanical properties are mainly governed by the rigidity and bulkiness of the substituted organic linkages. The framework topology and the intricate pore morphology can also influence the degree of mechanical anisotropy. Our findings present the previously undescribed structure-mechanical property relationships pertaining to hybrid open frameworks that are important for the design and application of new MOF materials. elastic properties | metal-organic frameworks | nanohardness | nanoporosity | zeolitic imidazolate frameworks doi/ 10.1073/pnas.1003205107

The biodistribution profiles in mice of two pyrrole-imidazole polyamides were determined by PET. Pyrrole-imidazole polyamides are a class of small molecules that can be programmed to bind a broad repertoire of DNA sequences, disrupt transcription factor-DNA interfaces, and modulate gene expression pathways in cell culture experiments. The [sup.18]F-radiolabeled polyamides were prepared by oxime ligation between 4-[[sup.18]F]-fluorobenzaldehyde and a hydroxylamine moiety at the polyamide C terminus. Small animal PET imaging of radiolabeled polyamides administered to mice revealed distinct differences in the biodistribution of a 5-ring [beta]-linked polyamide versus an 8-ring hairpin, which exhibited better overall bioavailability. In vivo imaging of pyrrole-imidazole polyamides by PET is a minimum first step toward the translation of polyamide-based gene regulation from cell culture to small animal studies. biodistribution | fluorine-18 | oxime | radiosynthesis

The electrochemistry of imidazolium and phosphonium ions and the characterization of a radical derived from the one-electron reduction of 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride are described. The absence of phosphoranes and phosphoryl in the phosphonium ionic liquids (PhosILs) has indicated that they are a suitable choice as solvent for strongly basic, carbon-centered reagents.

The synthetic method to access nitroxides with pH-dependent EPR spectra is described. The method can find application in the nonivasive EPR-based method for pH monitoring in biophysical and biomedical studies.

The characteristics and physical properties of ionic liquids consisting of 1-butyl-3-methylimidazolium cation with various perfluorinated anions and the bis(trifluoromethylsulfonyl)imide anion with various cations are discussed.

Linear and nonlinear Raman spectroscopy is used for examining the local structure formation in alkyl-imidazolium-based ionic liquids. Broad band assignable to collective modes of local structures with different sizes are found in liquid [C.sub.n]mim[p[F.sub.6]] (n = 4, 6,8).

A study to examine the structural properties of liquids and crystals of dialkylimidazolium salts using ab initio calculations and molecular dynamics simulations is conducted. Results suggest the identification of unusual features arising from the competition between electrostatic, dispersion and hydrogen-bonding interactions at the origin of observed structural patterns.

The results of anharmonic frequency calculations on neutral imidazole ([C.sub.3][N.sub.2][H.sub.4], Im), protonated imidazole (Im[H.sup.}), and its complexes with water (Im[H.sup.}) [([H.sub.2]O).sub.n] are described. The frequency of the NH stretch was seen to increase with the removal of a water molecule or replacement of water with [N.sub.2] and the anharmonicity in the NH stretch modes of (Im[H.sup.}) have some contribution from coupling effects.

The facile and mild highly enantioselective alkynylation of aldehydes using the dual acid/base catalysis in which the 1,1'-bi-2-naphthol (BINOL)/Ti[(OiPr).sub.4] complex would activate aldehydes and NMI would promote the deprotonation of terminal alkynes at room temperature is presented.

The study is done to determine the heme coordination states of inducible nitric oxide synthase with a Re (I) sensitizer coupled to nitro-L-arginine by an imidazole-alkyl molecular wire. It is demonstrated that Re (I) when applied can initiate quick photoreduction of the ferriheme in the active site of the enzyme.

An intramolecular general acid catalysis of the hydrolysis of 2-(2'-imidazolium)phenyl hydrogen phosphate (IMPP) is described, demonstrating the bond length-reactivity correlations for the reactions of the phosphate monoester monoanions. The analysis reveals that the reaction should involve a near-planar conformation of the imidazolium and the phenyl groups in the activated complex.

The preparation and the Diels-Alder chemistry of the reactions of various 4-vinylimidazole derivatives, which are normally prepared from the corresponding 4-iodoimidazoles or urocanic acid, are studied. The results show that these substrates participate in the Diels-Alder reactions with monoactivated dienophiles, as many of the substrates are also found to have terminally substituted vinyl moieties.

Various methodologies are employed to study the structure and stereochemistry of the four interconverting diastereomers of N'-carbamoyl-4,5-dihydroxy-2-oxoimidazolidine nucleosides, which are formed on the oxidation of 2'-deoxycytidine. The analysis demonstrates a linear increase in the rate of the isomerization with an increase in the pH.

The time-resolved phosphorescence spectra and anisotropy of quinoxaline are measured in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-HFP), in its supercooled state near the glass-transition temperature, where the solvent response times are between 5 ms and 2 s. A microscopic model can rationalize the decoupling of solvation dynamics from the longitudinal time scales and the limitation of this effect to the viscous regime.

Terahertz time-domain spectroscopy (THz-TDS) is used to measure the THz complex dielectric spectra of imidazolium ionic liquids. The results have shown that the interion vibrations have contributed to the THz dielectric spectra, indicating that even in the liquid phase the ionic liquids have local structures similar to their solid-phase structures.

Extreme ultraviolet (EUV) light is used to probe the molecular beam of [1-ethyl-3--methylimidazolium][bis(trifluoromethylsulfonyl)imide)] ([emim][[Tf.sub.2]N]) and related ionic liquids (IL) vapors by single photon ionization. The experiments have shown that vaporized isolated ion-pairs might undergo a dissociative photoionization to produce the intact cation and neutral fragments of the anion.

The preparation and characterization of new interhalogen ionic liquids and their utility in electrolytes for dye-sensitized solar cells are described. The analysis has shown that the new type of low-viscous interhalogen ionic liquids containing a mixture of redox species has provided promising alternatives to viscous ionic liquids based on alkylimidazolium iodides.

Computational electronic tools are used to study the redox properties, photochemical behavior and electronic features of the imidazoline derivative naphazoline (NP) (2-(1-naphthylmethyl)-2-imidazoline). The difference in photochemical behavior between the protonated and unprotonated species has allowed for an efficient quenching in the basic structure but clear naphthalene to imidazolene charge transfer upon HOMO to LUMO excitation in the protonated form.

A two-dimensional (2D) iron(II) spin crossover (SC) complex, [[Fe.sup.II][(H[L.sup.H,Me]).sub.2][(Cl[O.sub.4]).sub.2].1.5MeCN, where (H[L.sup.H,Me] = imidazol-4-yl-methylidene-8-amino-2-methylquinoline), is synthesized. The effect of the solvent molecule and the coexistence of bifurcated hydrogen bonds and [pi]-[pi] interactions on SC behavior are examined.

Relatively mild and highly efficient Cul-catalyzed N-arylation procedures for imidazoles with aryl and heteroaryl bromides or chlorides which were developed in the presence of (S)-pyrrolidinylmethylimidazole and C[s.sub.2]C[O.sub.3] is reported. The catalyst system is effective for aryl bromides and to a less extent, for aryl chlorides and provides an excellent complement to the Pd- or Cu-catalyzed methods which could find wide application among synthetic and medicinal chemists in industry and academics.

A large number of researches are conducted to analyze and demonstrate the synthesis, characterization and voltammetry of [[bmim].sub.4][[alpha]-[S.sub.2][W.sub.18] and its related salts, the reduction of which leads to precipitation of arrays on the surface. The ability of the cations and the polyoxometalate anions to form ion clusters and to the lower solubilities of the reduced salts are found to highly affect the dissolution of the reduced surface films.

Biimidazole and bis(amide)bipyridine molybdenum carbonyl complexes were prepared and their reactions with anions were studied. The neutral complexes [Mo[(CO).sub.4](N-N)] (1,2) and [MoCl([[eta].sup.3]-methylallyl)[(CO).sub.2](N-N) (3,4) were found to be insoluble due to intermolecular hydrogen bonding and [Mo([[eta].sup.3]-methylallyl)(CNBu)(C[O.sub.2])(N-N)]B[Ar'.sub.4] (5,6) displayed a high solubility in moderately polar organic solvents.

Car-Parinello molecular dynamics (CPMD) simulations of the liquid imidazolium chloride/Al[Cl.sub.3] by inserting one pair of [[C.sub.2][C.sub.1]im] into liquid Al[Cl.sub.3] forming an acidic mixture is described. Large anions within the equilibrium phase are found for both simulations and these large anion species are formed to account for the lack of electrons present in the acidic melt.

The reaction of N-tosylaziridines with nitriles and carbonyls to produce imidazolines and oxazolidines is studied in the presence of a variety of Lewis acids. The results have shown that the reaction can proceed through either 2-aryl-N-sulfonylaziridines ([S.sub.N]1) or alkyl-N-tosylazidines ([S.sub.N]2) fashion.

A study was conducted to explore the photoisomerization and thermal isomerization behaviors of an extensive series of arylazoimidazoles. The findings suggested that the fast thermal isomerization is influence by the self-catalyzed and protic molecule-assisted tautomerization to a hydrazone form.

A study analyzes the X-ray crystallographic and biochemical characterization of the action of an iimidazole-dioxolane compound on heme oxygenase (HO), which is a potential therapeutic target in cancer. The analysis reveals that the catalytic reactions of the HO complexes stop completely in the presence of the imidazole-dioxolane compound, as verdoheme has lower reactivity with oxygen as compared to the heme.

The high-resolution single-crystal X-ray structure for the coordination of the 1-methylimidazole (Meimid) ligand to U[O.sub.2][Ac.sub.2] (Ac=C[H.sub.3]C[O.sub.2]) is presented. Findings confirm the direct participation of the nitrogen atom of the Meimid ligand in binding to the uranium center.

A computational approach is presented based on quantum-chemical methods to predict reliable [super 1]H and [super 13]C NMR parameters of a series of 1-alkyl-3-methylimidazolium ionic liquids. A computational evidence of the existence of a chemical equilibrium is found between freely separated ions and ion-pair species of ionic liquids in different molecular environments.

A study was conducted to investigate in detail the [super 1]H NMR spectra of the ferriheme center and nearby protein residues in the high- and low-spin forms of the nitrophorins (NPs) from Rhodnius prolixus. The structures of the ferriheme complexes in terms of the orientation of the histidine imidazole ligand orientations depends on the heme cavity shape and could be altered by mutation of amino acids with side chains (phenyl vs tyrosyl) near the potential position where a heme vinyl group would be in one of the isomers.

The deuteron quadrupole coupling constants Cq, asymmetry parameters [eta], and electric field gradient orientation for the imidazolium and primary ammonium groups and for a water of crystallization are determined by a deuterium NMR study at 14 T of a single crystal of L-histidine hydrochloride monohydrate. Density functional cluster calculations give an excellent fit to the imidazolium tensor magnitudes and orientations, when appropriate corrections for vibrational averaging are taken into account.

A facile synthesis of several coordination polymers of W/Cu/S clusters containing inclined (4,4) or parallel (4,4) interpenetrating and noninterpenetrating multidimensional frameworks is demonstrated. The findings suggest that under similar reaction conditions the employment of different solvents or copper sources resulted in different structures for copper thiotungstate cluster building blocks as well as differences in networks' interpenetration modes.

Pulsed field ionization-zero electron kinetic energy (ZEKE) spectroscopy and second-order Moller-Plesset (MP2) theory are used to explore Al- and Cu-imidazole, which are produced in laser-vaporization supersonic molecular beams. The results have shown that Al-imidazole has larger bond dissociation energy than Cu-imidazole and the weaker bonding of the Cu complex is attributed to the antibonding interaction and the electron repulsion between the Cu 4s and N lone-pair electrons.

A study on the responses of the catalytic center to external perturbations is studied and density functional theory calculations on an active-site model of catalase compound I are conducted. Results reveal that oxo-iron heme systems are chameleonic species that are influenced by external perturbations and change their character and catalytic properties depending on the local environment.

The anion of 4-imidazolecarboxylic acid (HL) stabilizes hydroxo complexes of trivalent lanthanides of the type ML[(OH).sup.+] (M= La, Pr) and M2[L.sub.n][(OH).sub.6-n]. Compositions and stability constants of the complexes are determined by potentiometric titrations.

The reaction of copper(I) iodine with 1,3-imidazolidine-2-thione (SC3H6N2) in a 1:2 molar ratio (M/L) has formed unusual one dimensional polymers {Cu6([mu]3-SC3H6N2)4([mu]-SC3H6N2)2([mu]-I)2I4}n and {Cu6(mu3-SC3H6N2)4([mu]-SC3H6N2)4([mu]-I)4I2}n. It is found that in the reactions of copper(I) salts with 1,3-imidazolidine-2-thione, the anions have influenced the bonding properties of the thione ligand.

Sum frequency generation spectroscopy is used to study the influence of water on the surface of the water-miscible ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4]. The results suggest that water has no drastic effect on the surface orientation of [BMIM][BF4] cation for concentrations from 0.0002[X.sub.IL] to 1[X.sub.IL].

Two complexes of octaehtyloxophlorin, (Py)2Fe(OEPO), (Im)2[Fe.sup.III](OEPO).2THF, and (Im)2[Fe.sup.III](OEPO).1.6CHCl2, were examined by single-crystal diffraction and EPR and NMR studies. The results how that both complexes exist in the Fe(III)/oxophlorin trianion form rather than the Fe(II)/oxophlorin radical.

Pyrrole-imidazole (Py-Im) polyamides containing stereospecifically [alpha]-amino- or [alpha]-hydroxyl-substituted [gamma]-aminobutyric acid as a 5-TG-3 recognition element are synthesized by machine-assisted Fmoc solid-phase synthesis. Surface plasmon resonance (SPR) assays and molecular modeling studies collectively suggest that the (S)-[alpha]-hydroxyl-[gamma]-aminobutyric acid [gammaSO] may act as a 5-TG-3 recognition unit.

A study presents a biochemical and structural analysis of [N.sup.5]-carboxyaminoimidazole ribonucleotide ([N.sup.5]-CAIR) mutase (PurE), obtained from the acidophilic bacterium Acetobacter aceti. The results show that PurE facilitates protonation of CAIR C4 in the reverse, nonbiosynthetic direction, as the resulting CAIR is strongly stabilized by the interactions with the enzyme and the water molecule.

The molecular dynamics (MD) simulations of the aqueous interface of the hydrophobic [BMI][[Tf.sub.2]N] ionic liquid (IL), composed of 1-butyl-3-methylimidazolium cations ([BMI.sup.+]) and bis(trifluoromethylsulfonyl)-imide anions ([Tf.sub.2][N.sup.-]), is reported. The results have helped in understanding the analogies and differences of aqueous interfaces with hydrophobic ILs, compared to classical organic liquids.

The controlled decomposition of [Pt.sub.2][(dba).sub.3] (dba = dibenzylideneacetone) dispersed in 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI.B[F.sub.4]) and hexafluorophosphate (BMI.P[F.sub.6]) ionic liquids in the presence of cyclohexene by molecular hydrogen have produced Pt(0) nanoparticles. The SAXS analysis has shown the formation of a semi-organized ionic liquid layer surrounding the metal particles with an extended molecular length of around 2.8 nm in BMI.B[F.sub.4] and 3.3 nm in BMI.P[F.sub.6].

Zinc N-confused porphyrin (ZnNCP), a structural isomer of zinc tetraphenylporphyrin, were used to construct donor-acceptor dyads, as a donor and fullerene as an electron acceptor, with imidazole-appended fulleropyrrolidine and are characterized by optical absorption and emission, ESI-mass, NMR and electrochemical methods. Evidence of photoinduced charge separation from the singlet excited ZnNCP to the appended fullerene is established from time-resolved emission and nanosecond transient absorption studies.

The mechanism of chlorination of the 2,2,5,5-tetramehylimidazolidin-4-one (TMIO) with hypochlorous acid and N-chlorosuccinimide (NCS) is investigated both in the gas and solution phases. The hypochlorous acid as a chlorinating agent has showed that solvation plays an important role in the reaction energetics and the solvation has altered the kinetic and thermodynamic preferences of the reaction outcome.

Neutron diffraction was used to determine the liquid structure of 1,3-dimethylimidazolium bis{(trifluoromethyl)sulfonyl}amide {[dmim](NT[f.sub.2])}. The liquid structure of 1,3-dimethylimidazolium bis{(trifluoromethyl)sulfonyl}amide shows a decreasing affinity for hydrogen bonding with the cation as a function of both charge density and anion size.

A theoretical mechanistic study of the formation of imidazo[1,2-a]pyrazine-3,6-diones derived from alpha-amino acids using pyrolysis and silica-catalyzed process is presented. The cyclocondensation of N-acylated diketopiperazincs into bicyclic amidines is endothermic for Gly and exothermic for [alpha]-aminoisobutic acid.

A new, base-stable, imidazolium room-temperature ionic liquid (RTIL) is prepared and applied to the addition of Grignard reagents to carbonyl compounds. These reactions occur readily at ambient temperature to afford the alcohol products in good to excellent yield.