Theoretical study of two C30H20 isomers with a dodecahedrane cage and two pentaprismane cages sharing two pentagons

Structures, energies, and vibrational frequencies have been calculated for two C₃₀H₂₀ isomers with a dodecahedrane cage and two pentaprismane cages at the B3LYP/6‐31G* level of theory. Thus, two C₃₀H₂₀ isomers have the form of coplanar tri‐cage molecules. The symmetry of one C₃₀H₂₀ isomer is of D_5d and that of another is of C_2V. The heat of formation for two C₃₀H₂₀ isomers have been estimated. Heats of formation of two C₃₀H₂₀ isomers as well as the vibrational analysis indicate that two C₃₀H₂₀ isomers enjoy sufficient stability to allow for its experimental preparation. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

1H NMR study of the conformation and absolute stereochemistry of two spirocyclic NK-1 antagonists

The binding affinities at the human NK-1 receptor of two spirocyclic compounds were found to be similar despite being epimeric at a key stereocentre. This unexpected result prompted a thorough investigation of the solution conformations of the two compounds. This revealed that a conformational switch in the tetrahydrofuran ring enabled the C-3-aryl group to be equatorial in both cases, leading to a similar juxtaposition of the aryl rings.     

Theoretical study of two C50H40 isomers with three dodecahedrane cages sharing two pentagons

Structures, energies, and vibrational frequencies have been calculated for two C₅₀H₄₀ isomers with three dodecahedrane cages sharing two pentagons at the B3LYP/6‐31G* level of theory. Thus, two C₅₀H₄₀ isomers have the form of coplanar tri‐dodecahedrane‐cage molecules. The symmetry of one isomer is D_5d and that of another is C_2V. Heats of formation and vertical ionization energies for two C₅₀H₄₀ isomers have been estimated in this study. Heats of formation as well as vibrational analysis indicate that two C₅₀H₄₀ isomers enjoy sufficient stability to allow for its experimental preparation. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Kallisteine A and B, two new coumarins from the roots of Peucedanum paniculatum L, a species endemic to Corsica

From the dichloromethane extract of the roots of Peucedanum paniculatum L., two new coumarins, a species endemic to Corsica, have been isolated. Their structures were elucidated, on the basis of spectroscopic studies, particularly 1D and 2D NMR spectroscopy, as 6-(7'-beta-cyclolavandulyl)-7-hydroxycoumarin 1 and a spirodihydrofurano-coumarin 2 (Kallisteine A and B).     

Syntheses,Spectroscopic, Structural,Fluorescent and Thermal Properties of Bis(saccharinato)copper(II) Complexes with two Bis(pyridylamine) Ligands

Two new copper(II) complexes of saccharinate (sac) with bis(2‐pyridylmethyl)amine (bpma) and N,N′‐bis[1‐(pyridin‐2‐yl)ethylidene]ethane‐1,2‐diamine (bapen), [Cu(bpma)(sac)₂] · H₂O ( 1 ) and [Cu(bapen)(sac)₂] ( 2 ), were synthesized and characterized by elemental analysis, TG‐DTA, X‐ray diffraction, and UV/Vis and IR spectroscopy, respectively. In 1 , the copper(II) ion is coordinated by two N‐bonded sac ligands, and three nitrogen atoms of bpma, in a distorted square‐pyramidal coordination arrangement, whereas the arrangement around the copper ion in 2 is a distorted octahedron with two N‐coordinated sac ligands and a tetradentate bapen ligand. In addition to hydrogen bonding involving the water molecule in 1 , the mononuclear species of 1 and 2 are further connected by weak intermolecular C–H ··· π and C–H ··· O interactions to form a three‐dimensional network. Both complexes are luminescent at room temperature and their emissions seem to be due to ligand‐based π–π* transitions.     

Comparative thermal analysis study of two biopolymers, starch and cellulose

The degradation of cellulose and starch samples in air and nitrogen has been investigated by thermal analysis techniques. The techniques employed were differential thermal analysis, rising temperature and temperature jump thermogravimetry. Rate data were obtained from these experiments and Arrhenius parameters calculated from these values. This data was used to determine the mechanism by which the cellulose and starch samples degraded. The Arrhenius parameters were also calculated. The behavior of starch and cellulose upon thermal analysis were compared and are reported.E _act for corn starch was found to be 474 kJ mol^–1 and for a cellulose 242 kJ mol^–1.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Mass spectral study of Boc-carbo-beta3-peptides: differentiation of two pairs of positional and diastereomeric isomers

A mass spectral study of a series of new Boc-C-linked carbo-beta(3)-peptides prepared from C-linked carbo-beta(3)-amino acids (Caa) was carried out using liquid secondary ion mass spectrometry (LSIMS), electrospray ionization (ESI) and tandem mass spectrometry. Using the nomenclature of Roepstorff and Fohlman, the positive ion high- and low energy collision-induced dissociation (CID) of [M + H - Boc + H](+) ions of the peptides produce both N- and C-terminus ions, y(n) (+) and b(n) (+) ions, with high abundance and other ions of low abundance. Further, characteristic fragment ions of carbohydrate moiety are observed. In contrast to the CID of protonated peptide acids, the CID of [M - H](-) ions of the beta(3)-peptide acids do not give b(n)(-) ions and show abundant z(n)(-) and c(n) (-) ions which are insignificant in the former. Two pairs of positionally isomeric Boc-carbo-beta(3)-dipeptides were differentiated by the CID of [M + H](+) ions in LSIMS and ESIMS. The fragment ion [M + H - C(CH(3))(3) + H](+) formed from [M + H](+) by the loss of 2-methylprop-2-ene is relatively more abundant in the dipeptide Boc-NH-beta-hGly-Caa(S)-OCH(3) (14) containing the sugar moiety at the C-terminus whereas it is insignificant in Boc-NH-Caa(S)-beta-hGly-OCH(3) (13), which has the sugar moiety at the N-terminus. Similarly, two pairs of diastereomeric dipeptides were distinguished by the high- and low-energy CID of [M + H](+) ions. The loss of 2-methylprop-2-ene is more pronounced for Boc-NH-Caa(R)-beta-hGly-OCH(3) (17) and Boc-NH-Caa(R)-Caa(S)-OCH(3) (18) isomers whereas it is insignificant for Boc-NH-Caa(S)-beta-hGly-OCH(3) (13) and Boc-NH-Caa(S)-Caa(S)-OCH(3) (2) isomers. This was attributed to a favorable configuration of the carbohydrate moiety favoring the 'H' migration involved in the loss of 2-methylprop-2-ene from the [M + H](+) ions of isomers 17 and 18 compared with the unfavorable configuration of the carbohydrate moiety in isomers 13 and 2.     

Enzyme inhibitors as chemical tools to study enzyme catalysis: rational design, synthesis, and applications

Carefully designed molecules that are intimately related to the reaction mechanism of enzymes are often highly selective and potent inhibitors that serve as extremely useful chemical probes for understanding the reaction mechanism and structure of enzymes. This article describes the design, synthesis, and applications of specific inhibitors of two mechanistically distinct groups of enzymes, ATP-dependent amide ligases and Ser- and Thr-hydrolases. Our strategy is based on the premise that stable analogues of the transition state (transition-state analogues) are highly potent inhibitors that serve as good mechanistic probes, and that a key structure of a good inhibitor of one enzyme is also utilized for the inhibitors of other enzymes that share the same chemistry in their catalyzed reactions, irrespective of the degree of structural similarity and evolutionary link between the enzymes. According to these principles, we designed and synthesized a series of phosphinate- and sulfoximine-based transition-state analogue inhibitors of glutathione synthetase, gamma-glutamylcysteine synthetase and asparagine synthetase. For the second group of enzymes, we synthesized a gamma-monofluorophosphono glutamate analogue for mechanism-based affinity labeling of gamma-glutamyltranspeptidase and fluorescent phosphonic acid esters for the active-site titration of lipase. These inhibitors were used successfully as ligands for detailed kinetic analyses, X-ray crystallography, and mass analysis of the enzymes to identify the key amino acid residues responsible for catalysis and substrate recognition in the transition state.     

Structure,properties, and nature of the BrF‐HX complexes: An Ab initio study

Structure and properties of complexes (energies and charge transfer) of complexes BrF‐HX (X = F, Cl, Br, I) have been investigated at the MP2/aug‐cc‐pVDZ (aug‐cc‐pVDZ‐pp basis sets for I) level. Two types of geometries (hydrogen‐bonded and halogen‐bonded) are observed. The calculated interaction energies show that the halogen bonded structures are more stable than the corresponding hydrogen‐bonded structures. To study the nature of the intermolecular interactions, symmetry‐adapted perturbation theory (SAPT) energy decomposition analysis reveals that the BrF‐HX complexes are dominantly electrostatic in nature. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Latrunculins: NMR study,two new toxins and a synthetic approach

A complete ¹H and ¹³C NMR assignment of one of the latrunculins (B) was accomplished with the aid of 2D NMR COSY and CH shift-correlation experiments. The various H-H Coupling constants have been datermined and a conformation of the macrolide and the tetrahydropyran (THP) ring suggested on basis of the J-values and measured NOE's. The absolute configuration of latrunculin-A($\text{1}$) was determined on the grounds of its earlier X-Ray analysis, and a chemical degradation to a known compound. Two novel latrunculins, -C($\text{3}$) and -D($\text{4}$), were isolated from the Red Sea sponge $\text{L. magnifica}$ and their structures elucidated. Starting with L-cysteine a synthon for the latrunculins has been synthesized.     

Hydrothermal synthesis,crystal structure and photoluminescence of two homochiral zinc(II) coordination polymers

Metal–organic frameworks (MOFs) have potentially useful applications and an intriguing variety of architectures and topologies. Two homochiral coordination polymers have been synthesized by the hydrothermal method, namely poly[(μ‐N‐benzyl‐L‐phenylalaninato‐κ⁴O,O′:O,N)(μ‐formato‐κ²O:O′)zinc(II)], [Zn(C₁₆H₁₆NO₂)(HCOO)]_n, (1), and poly[(μ‐N‐benzyl‐L‐leucinato‐κ⁴O,O′:O,N)(μ‐formato‐κ²O:O′)zinc(II)], [Zn(C₁₃H₁₈NO₂)(HCOO)]_n, (2), and studied by single‐crystal X‐ray diffraction, elemental analyses, IR spectroscopy and fluorescence spectroscopy. Compounds (1) and (2) each have a two‐dimensional layer structure, with the benzyl or isobutyl groups of the ligands directed towards the interlayer interface. Photoluminescence investigations show that both (1) and (2) display a strong emission in the blue region.     

Simulated annealing study of diblock copolymer thin films confined between two homogeneous surfaces.

Thin films of symmetric diblock copolymers confined between two parallel surfaces have been systematically investigated by means of simulated annealing on a simple cubic lattice. The study was carried out for systems with different film thicknesses and surface-polymer interactions. Very regular equilibrium morphologies of lamella are formed in almost all cases. The dependence of lamellar orientations, total energy, chain-conformation entropy, and free energy of the confined films on the film thickness and the strength of surface-polymer interactions has been studied systematically. The influence of packing frustration on morphology is observed and the mechanisms of lamellar orientations are investigated.     

A classical dataset from Williams,and its role in the study of supersaturated designs

A Plackett‐Burman type dataset from a paper by Williams [1], with 28 observations and 24 two‐level factors, has become a standard dataset for illustrating construction (by halving) of supersaturated designs (SSDs) and for a corresponding data analysis. The aim here is to point out that for several reasons this is an unfortunate situation. The original paper by Williams contains several errors and misprints. Some are in the design matrix, which will here be reconstructed, but worse is an outlier in the response values, which can be observed when data are plotted against the dominating factor. In addition, the data should better be analysed on log‐scale than on original scale. The implications of the outlier for SSD analysis are drastic, and it will be concluded that the data should be used for this purpose only if the outlier is properly treated (omitted or modified). Copyright © 2008 John Wiley & Sons, Ltd.     

Syntheses,supramolecular networks and Hirshfeld surface and thermal analyses of two new cadmium chloride coordination polymers with an N,O‐chelating ligand

Two new coordination polymers, namely poly[[(3‐aminopyrazin‐4‐ium‐2‐carboxylate‐κ²N¹,O)di‐μ‐chlorido‐cadmium(II)] monohydrate], {[CdCl₂(C₅H₅N₃O₂)]·H₂O}_n, (1), and poly[2‐amino‐3‐carboxypyrazin‐1‐ium [(3‐aminopyrazine‐2‐carboxylato‐κ²N¹,O)di‐μ‐chlorido‐cadmium(II)] monohydrate], {(C₅H₆N₃O₂)[Cd(C₅H₄N₃O₂)Cl₂]·H₂O}_n, (2), have been synthesized from the reaction of cadmium(II) chloride and 3‐aminopyrazine‐2‐carboxylic acid (Hapca) under mild conditions in acidic media. The two coordination polymers have been characterized by single‐crystal X‐ray diffraction and show chloride‐bridged zigzag chains with octahedrally coordinated metal ions, where Hapca acts as a bidentate ligand via the π‐conjugated N atom and a carboxylate O atom. The chains are further interconnected via noncovalent interactions into three‐dimensional supramolecular networks. The dominant H…O and H…Cl interactions for both compounds were quantified using Hirshfeld surface analysis. The thermal stability and topological analysis of the two‐dimensional networks of (1) and (2) are also discussed.     

Synthesis, Structure and Photoluminescence of Two Zinc Carboxyl－ate Polymers with Different Coordination Architectures

The hydrothermal reaction of ZnO with benzene‐1,4‐dicarboxylic add gave Zn·BDC·2H₂O (1) and Zn‐BDC·H₂O (2) (BDC = benzene‐1, 4‐dicarboxylate), respectively. Polymer 1 (C₄H₄O₃ZH_0.5) shows a one‐dimensional zigzag chain structure built up from the alternate connection of tetrahedral ZnO₄ and BDC units. Polymer 2 (C₄H₃O_2.5Zn_0.5) possesses a three‐dimensional framework containing infinite zigzag Zn·Zn·Zn pseudochains generated by five‐coordinate zinc centers and a rectangular channel system including three groups of different straight channels along the [001], [010] and [60–1] directions. The two metal‐organic polymeric compounds exhibit strong photoluminescent emission bands at 402 nm (λ_ex = 260 nm) (for 1) and at 344 nm and 385 nm (λ_ex = 279 nm) (for 2) in the solid state at room temperature.     

Development and validation of two methods based on high-performance liquid chromatography-tandem mass spectrometry for determining 1,2-benzopyrone, dihydrocoumarin, o-coumaric acid, syringaldehyde and kaurenoic acid in guaco extracts and pharmaceutical preparations

In this study, two HPLC-ESI-MS/MS methods were developed and validated for the determination of 1,2-benzopyrone (COU), o-coumaric acid (OCA), kaurenoic acid (KAU), syringaldehyde (SYR), and dihydrocoumarin (DIH) in guaco extracts and pharmaceutical preparations (syrup and oral solution). The chromatographic separation was achieved using a C18 XBridge 150×2.1-mm (5-μm particle size) column maintained at 25°C. The mobile phases consisted of a gradient of water and acetonitrile containing 0.05% formic acid or 5 mM ammonium formate for the positive and negative ion modes, respectively. All of the calibration curves showed excellent coefficients of correlation (r≥0.9970) over the ranges of 1.25-400 ng/mL for coumarin, 10-600 ng/mL for dihydrocoumarin, 5-250 ng/mL for KAU, and 25-500 ng/mL for o-coumaric acid and syringaldehyde. The range of recovery was 96.3-103% with an RSD% of <4.85% for intraday and interday precision. The results indicate that the developed methods are fast, efficient, and sensitive for the quantification of the guaco metabolites in extracts and pharmaceutical forms while avoiding purification and derivatization steps.     

Synthesis,crystal structures and characterizations of two homochiral coordination polymers based on a chiral reduced Schiff base ligand

Two homochiral coordination polymers based on a chiral reduced Schiff base ligand, namely poly[(μ₅‐4‐{[(NR,1S)‐(1‐carboxylato‐2‐phenylethyl)amino]methyl}benzoato)zinc(II)], [Zn(C₁₇H₁₅NO₄)]_n, (1), and poly[(μ₅‐4‐{[(NR,1S)‐(1‐carboxylato‐2‐phenylethyl)amino]methyl}benzoato)cobalt(II)], [Co(C₁₇H₁₅NO₄)]_n, (2), have been obtained by hydrothermal methods and studied by single‐crystal X‐ray diffraction, elemental analyses, powder X‐ray diffraction, thermogravimetric analysis, IR spectroscopy and fluorescence spectroscopy. Compounds (1) and (2) are isostructural and crystallize in the P2₁2₁2₁ space group. Both display a three‐dimensional network structure with a one‐dimensional channel, with the benzyl group of the ligand directed towards the channel. An investigation of photoluminescence properties shows that compound (1) displays a strong emission in the purple region.     

ToF‐SIMS study of 1‐dodecanethiol adsorption on Au,Ag, Cu and Pt surfaces

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has been used to perform a chemical analysis of long‐chain thiol (CH₃(CH₂)₁₁SH)‐treated gold, silver, copper and platinum surfaces. All the mass peaks from positive and negative ion spectra within the range m/z = 0–2000 u are studied. ToF‐SIMS data revealed that on gold, silver and copper substrates 1‐dodecanethiol form dense standing‐up phases, but on platinum being a catalytically active substrate, we were able to identify also surface‐aligned parallel lying molecules in addition to a standing thiolate layer. Our study shows that when ToF‐SIMS spectra are analyzed, not only the existence of oligomers but also metal + hydrocarbon fragments give information about the order of SAM. Copyright © 2008 John Wiley & Sons, Ltd.     

DFT study and Monte Carlo simulation on proton transfers of 2-amino-2-oxazoline, 2-amino-2-thiazoline, and 2-amino-2-imidazoline in the gas phase and in water

Density functional theory (DFT) and Monte Carlo (MC) simulation with free energy perturbation (FEP) techniques have been used to study the tautomeric proton transfer reaction of 2-amino-2-oxazoline, 2-amino-2-thiazoline, and 2-amino-2-imidazoline in the gas phase and in water. Two reaction pathways were considered: the direct and water-assisted transfers. The optimized structures and thermodynamic properties of stationary points for the title reaction system in the gas phase were calculated at the B3LYP/6-311+G(d, p) level of theory. The potential energy profiles along the minimum energy path in the gas phase and in water were obtained. The study of the solvent effect of water on the proton transfer of 2-amino-2-oxozoline, 2-amino-2-thiazoline, and 2-amino-2-imidazoline indicates that water as a solvent is favorable for the water-assisted process and slows down the rate of the direct transfer pathway.     

Feasibility of two multidimensional techniques, heart-cut MDGC and GCxGC, for the separation of PCBs and PBDEs

The feasibility of heart-cut MDGC-ECD and GCxGC-muECD for the separation of polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) has been evaluated. Among the different column combinations tested, the best results were obtained when using either a DB-5 type or an HT-8 column as the first dimension combined with a mid-polar stationary phase (50% phenyl) as the second dimension. The co-elutions between the target PCBs and PBDEs in the first dimension were satisfactorily resolved once transferred to the second column. Repeatability and intermediate precision were satisfactory in both systems, considering retention times in both dimensions. Nevertheless, peak area/volume precision was better for heart-cut MDGC since software for the data analysis in the case of GCxGC was still under development. The need for multiple injections of the same extract on the heart-cut MDGC system was the main drawback since the analysis time it increased. GCxGC becomes then a valuable alternative able to achieve the same performance in one injection. However, the GCxGC data analysis is still very time-consuming and needs further development. The applicability of both separation techniques was shown using a human breast milk sample with low concentrations of PCBs (0.2-227 pg/g fresh weight) and PBDEs (1.2-41 pg/g fresh weight).