Nature of reactant and influence of water on the supramolecular patterns and luminescent properties of organic salts comprising (1,1′-biphenyl)-4,4′-disulfonate and triphenylmethanaminium

Fourteen supramolecular compounds have been obtained by the reaction of 1,1′-biphenyl-4,4′-disulfonic acid and triphenylmethylamine, which exhibit seven types of packing diagram in view of the nature of reactant and influence of water.

Studies on the electrochemical growth of (Per)2[Au(mnt)2]

The first stages of the electrocrystallization of (Per)(2)[Au(mnt)(2)] salt from dichloromethane on gold, platinum, and highly orientated pyrolytic graphite (HOPG) were investigated by cyclic voltammetry, atomic force microscopy, and X-ray photoelectron spectroscopy in order to understand the determinant factors for nucleation and crystal growth. The crystal growth occurs from adsorbed films of dithiolate on gold or platinum and of perylene on HOPG, after homogeneous nucleation, and it is controlled by the low diffusion of the species toward the growing surface.

Do homochiral aggregates have an entropic advantage?

The present work seeks to illuminate the underlying principles which control the aggregation of chiral building blocks into larger aggregates by examining the role that entropy plays in this process. Entropic effects are first examined within the confines of a simple model system, and the results are then compared to experimental data on clusters of amino acids. The model system predicts that the formation of a specific structure is more likely to occur from an enantiopure solution because forming a particular structure from a racemic solution is hindered by significant entropic barriers. These predictions are in good agreement with the experimental results. In our examination of clusters of all of the amino acids, clusters which are unusually abundant are found only when enantiopure solutions are sampled. Furthermore, the majority of all clusters exhibit no preference for chiral composition, suggesting that entropic effects negate any changes in enthalpy. Although the experimental data are not comprehensive, our results strongly suggest that specificity in homochiral clusters is entropically advantageous compared to specificity in racemic clusters.

Thermal Formation of Homochiral Serine Clusters and Implications for the Origin of Homochirality

Spontaneous assembly of amino acids into vapor-phase clusters occurs on heating the solid compounds in air. In comparison to the other amino acids, serine forms clusters to an unusual extent, showing a magic number octamer on sublimation; this octamer can be ionized and characterized by mass spectrometry. Two isomers of the vapor-phase serine octamer are generated, the minor one at 130 degrees C and the major at 220 degrees C. The higher temperature cluster shows a strong homochiral preference, as confirmed by isotopic labeling experiments. This serine cluster, like that generated earlier from solution in electrospray ionization experiments, undergoes gas-phase enantioselective substitution reactions with other amino acids. These reactions transfer the chirality of serine to the other amino acid through enantioselective incorporation into the octamer. Other serine pyrolysis products include alanine, glycine, ethanolamine, and small dipeptides, and many of these, too, are observed to be incorporated into the thermally formed serine octamers. Chiral chromatographic analysis confirmed that L-serine sublimation produced DL-alanine, glycine, and ethanolamine, while in the presence of hydrogen sulfide, L-serine yielded L-cysteine. The data demonstrate that sublimation of serine under relatively mild conditions yields chirally enriched serine octamers and that the chiral preference of the starting serine can be transferred to other compounds through cluster-forming chemical reactions.

Sulfate anion helices formed by the assistance of a flip-flop water chain

A flip-flop extended water structure assists the formation of sulfate anion helices (both left- and right-handed) in a crystalline hydrate of a simple organic-inorganic compound [C6H10N2]SO4. 1.5H2O (1).

Advanced oxidation of caffeine in water: on-line and real-time monitoring by electrospray ionization mass spectrometry

High performance liquid chromatography (HPLC), ultraviolet spectroscopy (UV), and total organic carbon (TOC) analyses show that caffeine is quickly and completely degraded underthe oxidative conditions of the UV/H2O2,TiO2/ UV, and Fenton systems but that the organic carbon content of the solution decreases much more slowly. Continuous on-line and real-time monitoring by electrospray ionization mass (ESI-MS) and tandem mass spectrometric experiments (ESI-MS/MS) as well as high accuracy MS measurements and gas chromatography-mass spectrometry analysis show that caffeine is first oxidized to N-dimethylparabanic acid likely via initial OH insertion to the C4=C8 caffeine double bond. A second degradation intermediate, di(N-hidroxymethyl)parabanic acid, has been identified by ESI-MS and characterized by ESI-MS/MS and high accuracy mass measurements. This polar and likely relatively unstable compound, which is not detected by off-line GC-MS analysis, is likely formed via further oxidation of N-dimethylparabanic acid at both of its N-methyl groups and constitutes an unprecedented intermediate in the degradation of caffeine.

Atmospheric Pressure Gas-Phase H/D Exchange of Serine Octamers

The recently discovered homochiral serine octamer has been a focus of interest because of its possible implications for the origin of homochirality in living systems. Electrospray ionization (ESI) and sonic spray ionization (SSI) tandem mass spectrometry have been used to generate this unusually stable magic number cluster. Several structures have been suggested for the serine octamer, based on tandem mass spectrometry, ion mobility measurements, and quantum mechanical calculations. We now report experimental hydrogen/deuterium (H/D) exchange data, which demonstrate the existence of two different structures for the serine octamer. These forms undergo exchange at significantly different rates. One form may correspond to solution-phase assembled clusters and the other to octamers formed during the ionization process. Experiments done at higher resolution confirm that the experimental observations made here apply to the serine octamer without interference from metaclusters, namely, higher order clusters (Ser(16) + 2H)(+2), etc., the (12)C isotopes of which have mass-to-charge ratios identical to the protonated octamers. H/D exchange of racemic serine shows predominantly the extensively exchanged ion population, as well as providing evidence that racemic serine generates abundant metaclusters. The evidence presented here shows that one type of serine octamer is responsible for the strong chiral effects associated with the formation of these magic number clusters. These slowly exchanging more fragile clusters are the octamers that might have played a role in homochirogenesis.

Multidimensional frameworks assembled from silver(I) coordination polymers containing flexible bis(thioquinolyl) ligands: role of the intra- and intermolecular aromatic stacking interactions

The two flexible multidentate ligands 1,3-bis(8-thioquinolyl)propane (C3TQ) and 1,4-bis(8-thioquinolyl)butane (C4TQ) were reacted with AgX (X = CF(3)SO(3)(-) or ClO(4)(-)) to give four new complexes: ([Ag(C3TQ)](ClO(4)))(n)() 1, ([Ag(C3TQ)](CF(3)SO(3)))(n)() 2, ([Ag(2)(C4TQ)(CF(3)SO(3))(CH(3)CN)](CF(3)SO(3)))(n)() 3, and ([Ag(C4TQ)](ClO(4)))(n)() 4. All complexes have been characterized by elemental analysis, IR, and (1)H NMR spectroscopy. Single-crystal X-ray analysis showed that chain structures form for all complexes in which the quinoline rings interact via various intra- (1) or intermolecular (2, 3, and 4) pi-pi aromatic stacking interactions, which in the latter cases results in multidimensional structures. Additional weak interactions, such as Ag.O and Ag.S contacts and C-H.O hydrogen bonding, are also present and help form stable, crystalline materials. It was found that the (CH(2))(n) spacers (n = 3 or 4) affect the orientation of the two terminal quinolyl rings, thereby significantly influencing the specific framework structure that forms. If the same ligand is used, on the other hand, then the different counteranions have the greatest effect on the final structure.

Amino acid clusters formed by sonic spray ionization

A novel ion source based on the principle of sonic spray ionization has been built and used to optimize mass spectrometric conditions for generating amino acid clusters. The ion source employs a simple pneumatic spray operated at extremely high nebulizing gas flow rates. Several factors that affect the performance of the cluster source are identified, and information from these observations provides insights into the mechanisms of gas phase ion formation. Serine is used as a model system in optimizing instrumental and sample parameters to maximize cluster ion formation. The sonic spray results for this oligomer compare favorably with electrospray data, showing an order of magnitude better signal intensity and excellent signal-to-noise ratios. The performance of the system for the protonated serine octamer includes a limit of detection of 10 nM and a linear dynamic range of 4 orders of magnitude. Ion formation was observed to go into saturation above 1 mM. This result and data on pH, electrolyte concentration, and solvent composition are interpreted as supporting a charge residue model of sonic spray ionization. Other amino acids can be substituted for serine in the octamer, with a strong chiral preference in favor of homochiral cluster formation in the cases of threonine and cysteine. These amino acids show a preference for substitution of more than two serine molecules. Phenylalanine, asparagine, tryptophan, and tyrosine also substitute into the serine octamer; however, the process yields only two incorporations and only small chiral effects.

Hierarchical assembly of homochiral porous solids using coordination and hydrogen bonds

A family of homochiral metal carboxylate coordination polymers have been synthesized by treating 2,2'-dihydroxy-1,1'-binaphthalene-6,6'-dicarboxylic acid (H(2)BDA) with metal salts at elevated temperatures. BDA ligands link adjacent metal centers to form 1D coordination polymeric chains using the carboxylate functionality, while the hydroxyl groups of BDA ligands form H-bonds with carboxylate oxygen atoms to link 1D coordination polymeric chains into open frameworks of higher dimensionality. We also present evidence for the important role played by H-bonds in the stabilization of open framework structures which allows for the hierarchical assembly of chiral porous solids.