CH-π Multi-Interaction-Driven Recognition and Isolation of Planar Compounds in a Spheroidal Polyaromatic Cavity

π-π Interactions are established as a powerful supramolecular tool, whereas the usability of CH-π interactions has been rather limited so far. Here we present (i) selective binding of planar polyaromatics and (ii) effective isolation of planar metal complexes by a polyaromatic capsule, utilizing multiple CH-π interactions. In the spheroidal cavity, one molecule of large and medium-sized polyaromatic molecules (i. e., coronene and pyrene) is exclusively bound from mixtures bearing the same number of aromatic CH groups. Theoretical studies reveal that multiple host-guest CH-π interactions (up to 32 interactions) are the predominant driving force for the observed selectivity. In addition, one molecule of planar metal complexes (i. e., porphine and bis(acetylacetonato) Cu(II) complexes) is quantitatively bound by the capsule through aromatic and aliphatic CH-π multi-interactions, respectively. The ESR and theoretical studies demonstrate the isolation capability of the capsular framework and an unusual polar environment in the polyaromatic cavity.     

Recognition of Multiple Methyl Groups on Aromatic Rings by a Polyaromatic Cavity

The methyl group is a small substituent, usually showing relatively weak or no interactions with other functional groups and metal ions. Herein, we present the recognition of the number of methyl groups on synthetic and natural aromatic compounds (i.e., benzene and xanthine derivatives, respectively) by the 1 nm‐sized polyaromatic cavity of a coordination capsule in water. Detailed competitive encapsulation experiments as well as X‐ray crystallographic analysis revealed that multiple guest–host CH₃–polyaromatic interactions in the confined nanospace are key driving forces for the high selectivity.     

Evolving the Promiscuity of Elizabethkingia meningoseptica Oleate Hydratase for the Regio‐ and Stereoselective Hydration of Oleic Acid Derivatives

The addition of water to non‐activated carbon–carbon double bonds catalyzed by fatty acid hydratases (FAHYs) allows for highly regio‐ and stereoselective oxyfunctionalization of renewable oil feedstock. So far, the applicability of FAHYs has been limited to free fatty acids, mainly owing to the requirement of a carboxylate function for substrate recognition and binding. Herein, we describe for the first time the hydration of oleic acid (OA) derivatives lacking this free carboxylate by the oleate hydratase from Elizabethkingia meningoseptica (OhyA). Molecular docking of OA to the OhyA 3D‐structure and a sequence alignment uncovered conserved amino acid residues at the entrance of the substrate channel as target positions for enzyme engineering. Exchange of selected amino acids gave rise to OhyA variants which showed up to an 18‐fold improved conversion of OA derivatives, while retaining the excellent regio‐ and stereoselectivity in the olefin hydration reaction.     

DNA-bound lipids: computer modeling of DNA interaction with stearic acid and unsaturated fatty acids

It was shown for the first time by computer experiments that fatty acids are strongly bound to DNA. This is consistent with the presence of free fatty acids in the specimens of DNA-bound lipids isolated from various cells. Binding of all fatty acids to the DNA minor groove is stronger than to the major groove, which is correlated with the presence of two pools of free fatty acids isolated from DNA specimens by biochemical methods. Since DNA polymerase is also bound to the DNA minor groove, fatty acids can play an important role in the regulation mechanism of DNA replication and signal transmission. The energy of interaction of fatty acids with DNA depends on both the number of double bonds and the geometric configuration of the fatty acid and the nucleotide composition of DNA. Dependence on the bond energy in the DNA—fatty acid complex on the nucleotide composition attests to the possibility of site-specific binding of lipids to DNA. On passing from a saturated fatty acid to unsaturated acids containing one, two, or three double trans-bonds, the bond energy of DNA with the fatty acid gradually decreases. The presence of one or three double cis-bonds results in weakening of the strength of the DNA—fatty acid complexes compared to those with the saturated acid. The strongest binding between DNA and fatty acid was found for the unsaturated acid with two double cis-bonds (linoleic). This can be explained by the fact that the bent (boomerang) shape of the molecule of this acid follows the curve of the DNA helix. The pattern of variation of the energy of DNA complexes with stearic, linoleic, oleic, and linolenic acids correlates with experimental data on the melting points of these complexes: the more stable the DNA—fatty acid complex, the lower the melting point of DNA.     

Evaluation of Metabolite Profiles of Ginseng Berry Pomace Obtained after Different Pressure Treatments and Their Correlation with the Antioxidant Activity

Ginseng berry pomace (GBP) is a byproduct of ginseng berry processing and is rich in numerous bioactive components, including ginsenosides and their derivatives. The application of GBP as a beneficial biomaterial is currently limited. In this study, we aimed to evaluate their potential as a promising source of bioactive compounds using metabolite profiling. The GBP obtained after different ultra-high-pressure (UHP) treatments was analyzed by GC-TOF-MS and UHPLC-LTQ-Orbitrap-MS/MS. In multivariate analyses, we observed a clear demarcation between the control and UHP-treated groups. The results demonstrated that the relative abundance of primary metabolites and a few ginsenosides was higher in the control, whereas UHP treatment contained higher levels of fatty acids and sugars. Furthermore, GBPs were fractionated using different solvents, followed by UHPLC-LTQ-Orbitrap-MS/MS analyses. The heatmap revealed that phenolics (e.g., quercetin, kaempferol) and fewer polar ginsenosides (e.g., F4, Rh2) were abundant in the ethyl acetate fraction, whereas the levels of lignans (e.g., 7-hydroxysecoisolariciresinol, syringaresinol) and fatty acids (e.g., trihydroxy-octadecenoic acid, oxo-dihydroxy-octadecenoic acid) were high in chloroform. Correlation analysis showed that phenolics, less polar ginsenosides, and fatty acids were positively correlated with the antioxidant activity of GBP. Our study highlights GBP as a functional ingredient for the development of high-quality ginseng berry products.     

Electrospray mass spectrometry for the direct accurate mass measurement of ligands in complex with the retinoid X receptor α ligand binding domain

Accurate mass measurements are often used in the structural determination of unknown compounds of low molecular mass (i.e., below approximately 500 Da). Recently, it has been shown that accurate mass measurements also can be made on small denatured proteins (i.e., M(r), approximately 17,000) to confirm their amino acid composition and identify the presence of isoforms. In the current report, we present nondenaturing electrospray (ES) mass spectrometry data on the direct accurate mass measurement of ligands in complex with the retinoid X receptor ligand binding domain (RXR LBD; M(r) 31,370.92). Average mass errors were below 0.198 Da, 6.3 ppm (standard deviation [SD], 0.146; n = 10) for low-affinity fatty acid agonists analyzed in complex with the RXR LBD. Protein consumption was less than 15 pmol, with fatty acid ligands present at concentrations corresponding to their median effective concentration value (low micromolar, determined in transfection assays). Although determination of fatty acid mass was only sufficiently accurate to give nominal mass values, measurements were of sufficient accuracy to assign fatty acid chain length, degree of unsaturation, or cyclization. Using 17beta-estradiol as a control, the ability to observe specific ligand binding is shown for both high- and low-affinity RXRalpha agonists. In addition, binding of a novel synthetic receptor agonist XCT0315908 to the RXRalpha LBD is reported. This compound showed a high degree of complex formation, and the receptor-ligand complex could be mass measured with an average mass error of -0.024 Da, 0.8 ppm (SD, 0.092; n = 9). Thus, specific binding of both nanomolar and micromolar affinity ligands to a nuclear receptor LBD can be directly observed using nondenaturing ES mass spectrometry and accurate mass measurements additionally can be made on intact complexes in the same experiment. This methodology also is applicable when ligands are present as components of mixtures.     

二茂铁甲酸分子印迹聚合物的制备和识别机理、结合特性

以二茂铁甲酸（FCA）为模板,选用不同的功能单体制备了一系列分子印迹聚合物,用平衡结合实验考察了它们对模板分子的结合性能。 结果表明,以甲基丙烯酸为功能单体制得的印迹聚合物P1对模板分子有很好的选择性,特异性吸附量ΔCP为23.18 μmol/g,印迹因子IF为2.33,竞争性结合实验结果表明,P1可以将模板分子从结构类似物中分离出来。 Scatchard方程研究表明,在研究的浓度范围内聚合物中形成了一类等价的结合位点,其对模板分子的平衡离解常数K=1.94 mmol/L,最大表观结合量Cpmax=92.33 μmol/g。 研究还表明,FCA的羧基是在聚合物的孔穴中产生识别位点的功能基,模板分子上的羧基与MAA的羧基形成双重氢键作用是分子识别的主要作用力。     

Thermospray-mass spectrometric analysis of underivatized monohydroxy fatty acids: application to stimulated platelets

Monohydroxylated fatty acids prepared from polyunsaturated fatty acids of nutritional value were analysed by thermospray-mass spectrometry without prior chemical derivatization. Positive and negative ionization modes were compared. The highest sensitivity was observed with the negative ionization mode with detection limits of 10 pmol based on the 12-hydroxy derivative of eicosatrienoic acid (12-OH-8,10,14-20:3). This is comparable to that obtained by high-performance liquid chromatography with UV detection at 234 nm. Selected ion monitoring based on the fragment [M-H]- allowed a variety of standard monohydroxy fatty acids to be detected. This approach makes possible the analysis of various derivatives generated by thrombin-stimulated platelets (10(9) cells) pre-enriched with minor polyunsaturated fatty acids, even when these derivatives co-elute from the column (e.g., 12-HETE and 14-OH-22:6).     

Docosahexaenoic acid and eicosapentaenoic acid induce changes in the physical properties of a lipid bilayer model membrane

We investigated the effect of fatty acids such as stearic acid (SA, 18:0), oleic acid (OA, 18:1), eicosapentaenoic acid (EPA, 20:5), and docosahexaenoic acid (DHA, 22:6) on a dipalmitoylphosphatidylcholine (DPPC) bilayer by determining the phase transition temperature, fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), and detergent insolubility. Treatment with unsaturated fatty acid broadened and shifted the phase transitions of the DPPC bilayer to a lower temperature. The phase transition temperature and the value of fluorescence anisotropy of DPH at 37 degrees C decreased progressively with increasing treatment amounts of unsaturated fatty acid. A large amount of the DPPC bilayer treated with unsaturated fatty acid was dissolved in Triton X-100, obtaining a low level of detergent insolubility. These modifications of the bilayer physical properties were most pronounced with DHA and EPA treatment. These data show that unsaturated fatty acids, particularly DHA and EPA, induce a marked change in the lipid bilayer structure. The composition of fatty acids in the DPPC bilayer was similar after treatment with various unsaturated fatty acids, suggesting that the different actions of unsaturated fatty acids are attributed to change in the molecular structure (e.g., kinked conformation by double bonds). We further explored the change in physical properties induced by fatty acids dispersed in a water-in-oil-in-water multiple emulsion and found that unsaturated fatty acids acted efficiently on the DPPC bilayer, even when incorporated in emulsion form.     

Hydrophilic Oligo(lactic acid)s Captured by a Hydrophobic Polyaromatic Cavity in Water

Biologically relevant hydrophilic molecules rarely interact with hydrophobic compounds and surfaces in water owing to effective hydration. Nevertheless, herein we report that the hydrophobic cavity of a polyaromatic capsule, formed through coordination‐driven self‐assembly, can encapsulate hydrophilic oligo(lactic acid)s in water with relatively high binding constants (up to K_a=3×10⁵ m ⁻¹). X‐ray crystallographic and ITC analyses revealed that the unusual host–guest behavior is caused by enthalpic stabilization through multiple CH–π and hydrogen‐bonding interactions. The polyaromatic cavity stabilizes hydrolyzable cyclic di(lactic acid) and captures tetra(lactic acid) preferentially from a mixture of oligo(lactic acid)s even in water.     

Uranium carbide dissolution in nitric acid: speciation of organic compounds

The direct dissolution of UC, a potential fuel for generation-IV nuclear reactors, in nitric acid can produce organic complexants that may interfere with the consumed fuel reprocessing based on liquid–liquid extraction. This study shows the presence of 17 % of carboxylic and polycarboxylic acids (e.g. benzenepentacarboxylic acid). 25 % of the carbon mass balance seemed to correspond to unfunctionalized polyaromatic compounds with more than 3–4 aromatic rings. Under an active oxidation process, these compounds become smaller and very functionalized polyaromatic compounds. Structures have been proposed for 8 % of the carbon mass balance.     

Thermodynamic analysis of receptors based on guanidinium/boronic acid groups for the complexation of carboxylates, alpha-hydroxycarboxylates, and diols: driving force for binding and cooperativity

The thermodynamics of guanidinium and boronic acid interactions with carboxylates, alpha-hydroxycarboxylates, and diols were studied by determination of the binding constants of a variety of different guests to four different hosts (7-10). Each host contains a different combination of guanidinium groups and boronic acids. The guests included molecules with carboxylate and/or diol moieties, such as citrate, tartrate, and fructose, among others. The Gibbs free energies of binding were determined by UV/Vis absorption spectroscopy, by use of indicator displacement assays. The receptor based on three guanidinium groups (7) was selective for the tricarboxylate guest. The receptors that incorporated boronic acids (8-10) had higher affinities for guests that included alpha-hydroxycarboxylate and catechol moieties over guests containing only carboxylates or alkanediols. Isothermal titration calorimetry revealed the enthalpic and entropic contributions to the Gibbs free energies of binding. The binding of citrate and tartrate was investigated with hosts 7-10, for which all the binding events were exothermic, with positive entropy. Because of the selectivity of hosts 8-10, a simple boronic acid (14) was also investigated and determined to be selective for alpha-hydroxycarboxylates and catechols over amino acids and alkanediols. Further, the cooperativity of 8 and 9 in binding tartrate was also investigated, revealing little or no cooperativity with 8, but negative cooperativity with 9. A linear entropy/enthalpy compensation relationship for all the hosts 7-10, 14, and the carboxylate-/diol-containing guests was also obtained. This relationship indicates that increasing enthalpy of binding is offset by similar losses in entropy for molecular recognition involving guanidinium and boronic acid groups.     

Charge-remote fragmentation of lithiated fatty acids on a TOF-TOF instrument using matrix-ionization

In numerous studies charge remote fragmentation (CRF) has been shown to be a powerful technique for determination of primary structure by allowing location of double bonds, various functional groups, and branching in a variety of compound types directly by mass spectrometry. Instrumentation and ionization methods traditionally used for CRF, however, are becoming rare, in large part because ESI and MALDI have to a significant extent replaced them. Here we demonstrate that by selecting a matrix that promotes rather than suppresses ionization of fatty acids (FA) by lithium ion adduction, and using a TOF-TOF mass spectrometer for high-energy collisional activation, CRF ions are produced that allow location of double-bond and branching positions. Further, we show that by using solvent-free MALDI sample preparation methods, thus eliminating the inherent segregation of the hydrophobic fatty acid from the hydrophilic LiCl that can occur during the evaporation of solvent, the desired [FA-H+2Li](+) ions are greatly enhanced. Because FAs can be vaporized using laser desorption, matrix assistance in desorption of the fatty acid may occur, but is not necessary. However, the matrix plays a crucial role in enhancing or suppressing ionization. For example, matrix materials with acid (e.g., 2,5-dihydroxybenzoic acid) or hydroxy groups (e.g., dithranol) compete with the FA for Li(+) and because of the high ratio of matrix to analyte, FA lithium adduction is minimized. However, highly electron-deficient matrix materials (e.g., TCNQ) readily donate Li(+) to FAs because of the instability associated with being positively charged.     

Duplexiphane: a polyaromatic receptor containing two adjoined Delta-shaped cavities for an efficient hopping of a single silver cation

A simple synthesis of a polyaromatic receptor (i.e., duplexiphane) containing two adjoined Delta-shaped cavities is accomplished via an intramolecular (double) McMurry coupling, and its structure is established by X-ray crystallography. The binding of silver cation to duplexiphane showed that it binds only a single silver cation with significantly higher efficiency (>100 times) than a model compound containing only one pi-prismand-like cavity, and the single silver cation hops intramolecularly between the two adjoined cavities in duplexiphane.     

Aryl Crown Ethers Based on d-Glucose Scaffold – Highly Selective Receptors of Amino Acid Ester Hydrochlorides

Amino acids are important biomolecules with a broad scope of applications in chemical and biological sciences. Their functions and properties depend on their absolute configuration. Therefore, methods for chiral recognition and separation of amino acids are highly sought after. For the purposes of diagnostic and medicinal applications chiral recognition of amino acids in water is particularly relevant. However synthetic receptors for enantioselective binding of amino acids in aqueous media are rare. Recently we reported a d -glucose-based crown ether for chiral recognition of amino acid esters in water. We achieved enantioselectivities towards amino acids with hydrophobic sidechains which were among the highest ever reported for a small molecule receptor. The binding affinities were however moderate. Herein we disclose analogs of that receptor, containing aryl functionalities in the crown ether fragment. The new receptors show considerably improved binding affinities for amino acid ester hydrochlorides in water, while retaining high enantio- or chemoselectivities.     

Stereoselective and Chiroselective Surface Plasmon Resonance (SPR) Analysis of Amino Acids by Molecularly Imprinted Au‐Nanoparticle Composites

Au nanoparticles (NPs) functionalized with thioaniline and cysteine are used to assemble bis‐aniline‐bridged Au‐NP composites on Au surfaces using an electropolymerization process. During the polymerization of the functionalized Au NPs in the presence of different amino acids, for example, L ‐glutamic acid, L ‐aspartic acid, L ‐histidine, and L ‐phenylalanine, zwitterionic interactions between the amino acids and the cysteine units linked to the particles lead to the formation of molecularly imprinted sites in the electropolymerized Au‐NP composites. Following the elimination of the template amino acid molecules, the electropolymerized matrices reveal selective recognition and binding capabilities toward the imprinted amino acid. Furthermore, by imprinting of L ‐glutamic or D ‐glutamic acids, chiroselective imprinted sites are generated in the Au‐NP composites. The binding of amino acids to the imprinted recognition sites was followed by surface plasmon resonance spectroscopy. The refractive index changes occurring upon the binding of the amino acids to the imprinted sites are amplified by the coupling between the localized plasmon associated with the Au NPs and the surface plasmon wave.     

Controlling multivalent interactions in triply-threaded two-component superbundles

We have investigated the (1)H NMR spectra, the absorption spectra, the fluorescence spectra and decays, and the electrochemical properties of i). a tritopic receptor in which three benzo[24]crown-8 macrorings are fused onto a triphenylene core, ii). a trifurcated trication wherein three dibenzylammonium ions are linked 1,3,5 to a central benzenoid core, and iii). their 1:1 adduct which constitutes a triply-threaded, two-component supramolecular bundle. X-Ray crystallography has established the precise geometry of this paucivalent recognition motif in the solid state. In addition to [N(+)-H...O] hydrogen bonding and [C-H...O] interactions between the NH(2) (+) centers on the three dibenzylammonium ion containing arms of the trication and the three crown ether rings in the tritopic receptor, there is a stabilizing [pi...pi] stacking interaction between the two aromatic cores. Mass spectrometry and (1)H NMR spectroscopy have confirmed the integrity of the 1:1 adduct beyond the solid state, provided the solvents are relatively apolar (e.g., chloroform and acetonitrile). The intense fluorescence emissions of the two recognition components are quenched upon association with the concomitant appearance of a lower energy, broad fluorescence band originating from the pi-pi stacking in the 1:1 adduct of the aromatic cores in the two matching components. Titration experiments, including Job plots, establish the 1:1 stoichiometry of the adduct, an observation which is also confirmed by electrochemical experiments. The electrochemical results show that, both in the tritopic receptor and in the superbundle itself, the first oxidation process is associated with the hexaalkoxytriphenylene core. The successive oxidation processes of the peripheral dioxybenzene units are affected by charge-transfer interactions in the tritopic receptor, whereas, in the superbundle, such units are not interacting. In acetonitrile solution, dethreading/rethreading of the 1:1 adduct can be controlled quantitatively by addition of base and acid. Dethreading and rethreading is also observed by (1)H NMR spectroscopy when dimethylsulfoxide is added to a solution of the 1:1 adduct in equal volumes of acetonitrile and chloroform. A trifurcated trication where methyl groups are located on the para positions of the three dibenzylammonium ions, which are linked 1,3,5 to the neutral benzenoid core, has been employed to demonstrate that dethreading of the 1:1 adduct involves doubly-threaded and singly-threaded species, that is, the paucivalent site is dismembered in a sequence of logical steps involving stable intermediates. This molecular recognition system is a rare example of a supramolecular entity based on a cooperative binding motif that can be switched on and off by chemical means.     

Chemical profile and biological potential of non-polar fractions from Centroceras clavulatum (C. Agardh) Montagne (Ceramiales, Rhodophyta)

The present study reports the Gas Chromatography-Mass Spectrometry (GC-MS) evaluation of the hexanes and dichloromethane fractions from extracts of the red alga Centroceras clavulatum (C. Agardh) Montagne. Twenty three compounds were identified, totaling ca. 42% of both fractions (0.18 g mass extract). The main constituents of the fractions were hexadecanoic acid (17.6%) and pentadecanoic acid (15.9%). Several secondary metabolites with interesting biological activity, such as (-)-loliolide, neophytadiene, phytol were identified. In addition, several classes of secondary metabolites, including phenolic compounds (e.g., phenylacetic acid), terpene derivatives, fatty acids, halogenated compound (e.g., 2-chlorocyclohexenol), lignoids, steroids, esters, amides (e.g., hexadecanamide), ketones, carboxylic acids, aldehydes and alcohols were observed. The occurrence of several of these structural classes is described for the first time in this species. The same fractions analyzed by GC-MS, and a separate set of polar fractions, were evaluated against two life cycle stages (epimastigote and trypomastigote forms) of the protozoan Trypanosoma cruzi and against phytopatogenic fungi Cladosporium cladosporiodes and C. sphaerospermum. The dichloromethane fraction was active against both T. cruzi forms (epimastigote IC(50) = 19.1 μg.mL-1 and trypomastigote IC(50) = 76.2 μg.mL-1). The hexanes and ethyl acetate fractions also displayed activity against both fungi species (200 μg) by TLC-bioautography.     

Essential oil composition of Prasium majus from Croatia

The essential oils from the aerial parts of Prasium majus L., collected during two years in Croatia, were analysed by GC and GC/MS. Fifty-two compounds were identified, representing 90.3-91.8% of the total oils. The major constituents in both samples were fatty acids (particularly hexadecanoic acid and (Z)-octadec-9-enoic acid), lower aliphatic alcohols, aldehydes and acids (major ones oct-1-en-3-ol and (E,E)-hepta-2,4-dienal) and phenylpropane derivatives (e.g. eugenol). Beta-Caryophyllene was the most abundant terpene and (E)-beta-ionone was the major norisoprenoid.