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1.
Remko Achten Arie Koudijs Marcel Giesbers Antonius T. M. Marcelis Corresponding author Ernst J. R. Sudhölter 《Liquid crystals》2013,40(3):277-285
Two series of non‐symmetric banana‐shaped compounds, both with one alkyl and one alkenyl terminal tail, have been synthesized and studied. Both series were compared with the corresponding series with two saturated terminal alkyl tails. All the compounds have a bent central 1,3‐phenylene bis(4‐benzoyloxy)benzoate core; their mesophases were characterized by polarizing optical microscopy, differential scanning calorimetry, X‐ray diffraction and switching current response experiments. In all four series one of the terminal tails is varied from OC8H17 to OC16H33. The other terminal tails are OC11H23, O(CH2)9CH?=?CH2, OC10H21 and O(CH2)8CH?=?CH2. The short‐tailed compounds show monotropic or enantiotropic B1 phases and the long‐tailed compounds the B2 phase. The introduction of one terminal vinyl group slightly lowers the transition temperatures. The introduction of a second terminal vinyl group further suppresses the liquid crystalline properties. All compounds with B2 phases have layer spacings that suggest a tilt of ~45° of the bent molecules in the layers, and their switching behaviour is antiferroelectric. 相似文献
2.
Joanna Bojarska Milan Remko Izabela D. Madura Krzysztof Kaczmarek Janusz Zabrocki Wojciech M. Wolf 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(4):328-345
Recently, fluorenylmethoxycarbonyl (Fmoc) amino acids (e.g. Fmoc–tyrosine or Fmoc–phenylalanine) have attracted growing interest in biomedical research and industry, with special emphasis directed towards the design and development of novel effective hydrogelators, biomaterials or therapeutics. With this in mind, a systematic knowledge of the structural and supramolecular features in recognition of those properties is essential. This work is the first comprehensive summary of noncovalent interactions combined with a library of supramolecular synthon patterns in all crystal structures of amino acids with the Fmoc moiety reported so far. Moreover, a new Fmoc‐protected amino acid, namely, 2‐{[(9H‐fluoren‐9‐ylmethoxy)carbonyl](methyl)amino}‐3‐{4‐[(2‐hydroxypropan‐2‐yl)oxy]phenyl}propanoic acid or N‐fluorenylmethoxycarbonyl‐O‐tert‐butyl‐N‐methyltyrosine, Fmoc‐N‐Me‐Tyr(t‐Bu)‐OH, C29H31NO5, was successfully synthesized and the structure of its unsolvated form was determined by single‐crystal X‐ray diffraction. The structural, conformational and energy landscape was investigated in detail by combined experimental and in silico approaches, and further compared to N‐Fmoc‐phenylalanine [Draper et al. (2015). CrystEngComm, 42 , 8047–8057]. Geometries were optimized by the density functional theory (DFT) method either in vacuo or in solutio. The polarizable conductor calculation model was exploited for the evaluation of the hydration effect. Hirshfeld surface analysis revealed that H…H, C…H/H…C and O…H/H…O interactions constitute the major contributions to the total Hirshfeld surface area in all the investigated systems. The molecular electrostatic potentials mapped over the surfaces identified the electrostatic complementarities in the crystal packing. The prediction of weak hydrogen‐bonded patterns via Full Interaction Maps was computed. Supramolecular motifs formed via C—H…O, C—H…π, (fluorenyl)C—H…Cl(I), C—Br…π(fluorenyl) and C—I…π(fluorenyl) interactions are observed. Basic synthons, in combination with the Long‐Range Synthon Aufbau Modules, further supported by energy‐framework calculations, are discussed. Furthermore, the relevance of Fmoc‐based supramolecular hydrogen‐bonding patterns in biocomplexes are emphasized, for the first time. 相似文献
3.
The methods of theoretical chemistry have been used to elucidate molecular properties of selected and novel antiangiogenic
agents (semaxanib, sunitinib, N-methylsunitinib, sorafenib, motesanib, ABT-869, vatalanib, vandetanib, AEE 788, CP-547632, A-1, A-2, A-3, and A-4). The geometries
and energies of these drugs have been computed using HF/6-31G(d), Becke3LYP/6-31G(d) and Becke3LYP/6-31++G(d,p) model chemistries.
Wherever possible the most stable conformations of inhibitors studied are stabilized by means of intramolecular hydrogen bonds.
Water has a remarkable effect on the geometry of the antiangiogenic agents studied. Computed partition coefficients (ALOGPS
method) varied between 2.3 and 5. Compounds studied are described as lipophilic inhibitors. Semaxanib is inhibitor with lowest
lipophilicity. The antiangiogenic agents studied are only slightly soluble in water; their computed solubility (log S) from interval between −3.4 and −5.4 is sufficient for fast absorption. Selection criteria for drug-like properties of VEGFR2
inhibitors investigated were designed. Based on these criteria, three compounds (A-2, A-3, and A-4) were selected for synthesis
and biological testing for antianiogenic activity on VEGFR2 receptor. 相似文献
4.
The IdoA2S structural unit of heparin (subunit G) may oscillate among the three conformations (4C1, 1C4, and 2So). Only the twisted boat conformation allowed the biologically active pentasaccharide unit of heparin (DEFGH) to bind to antithrombin. Our work reports, in detail, the results of systematic large-scale theoretical investigations of the three basic conformations (4C1, 1C4, and 2So) of the IdoA2S structural unit of heparin, its anionic forms, and its sodium salt using the B3LYP/6-311++G(d, p) and B3LYP/6-31+G(d) model chemistries. According to our calculations, the most stable structure of these molecules corresponds to the 2So skew-boat conformation. This form is also the most stable in a water solution. The 2So conformation of neutral molecules is not maintained in the anionic species. With anions, both 1C4 and 4C1 conformations are present. The relative stability of individual species of the substituted iduronic acid affects extra stabilization by means of intramolecular hydrogen bonds. The calculated macroscopic pKa of 1,4-DiOMe IdoA2S are as follows: pKa = 0.25 for the terminal C(2)-OSO3H group, pKa = 3.67 for the terminal C(5)-CO2H group, and pKa = 14.00 for the C(3)-OH hydroxyl group. The computed Gibbs interaction energies, DeltaGdegrees , for the reaction 1,4-DiOMe IdoA2S(2-) + 2Na+ <==> 1,4-DiOMe IdoA2SNa2 (4C1, 1C4, and 2So conformations) are negative and span a rather small energy interval (from -1244 to -1290 kJ mol(-1)). 相似文献
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6.
Boersma YL Pijning T Bosma MS van der Sloot AM Godinho LF Dröge MJ Winter RT van Pouderoyen G Dijkstra BW Quax WJ 《Chemistry & biology》2008,15(8):782-789
Lipases are successfully applied in enantioselective biocatalysis. Most lipases contain a lid domain controlling access to the active site, but Bacillus subtilis Lipase A (LipA) is a notable exception: its active site is solvent exposed. To improve the enantioselectivity of LipA in the kinetic resolution of 1,2-O-isopropylidene-sn-glycerol (IPG) esters, we replaced a loop near the active-site entrance by longer loops originating from Fusarium solani cutinase and Penicillium purpurogenum acetylxylan esterase, thereby aiming to increase the interaction surface for the substrate. The resulting loop hybrids showed enantioselectivities inverted toward the desired enantiomer of IPG. The acetylxylan esterase-derived variant showed an inversion in enantiomeric excess (ee) from -12.9% to +6.0%, whereas the cutinase-derived variant was improved to an ee of +26.5%. The enantioselectivity of the cutinase-derived variant was further improved by directed evolution to an ee of +57.4%. 相似文献
7.
The molecular structure of trimeric units (D-E-F and F-G-H) and the pentamer D-E-F-G-H of heparin (sodium salts and their anionic forms) was studied using the B3LYP/6-31G(d) method. The equilibrium structure of the sodium salts of the trimers and pentamer investigated in the isolated state was determined by multidentate coordination of the sodium cations with oxygen atoms of the sulfate, carboxyl, and hydroxyl (hydroxymethyl) groups, respectively. The displacement of Na+ ions from the binding sites in the sodium salt of oligosaccharides studied resulted in the appreciable change of the overall conformation of the corresponding anion. Upon dissociation, a large change in both the position of the sulfate groups and the conformation across the glycosidic bonds was observed. The stable energy conformations around the glysosidic bonds found for the pentamer investigated are compared and discussed with the available experimental X-ray structural data for the structurally related heparin-derived pentasaccharides in cocrystals with proteins. 相似文献
8.
Július ille Martin ramko Vladimír Garaj Milan Remko 《Journal of Molecular Structure》2009,911(1-3):137-143
The structure and gas-phase metal affinities (M = Cu2+, Ni2+, and Zn2+) of formohydroxamic acid derivatives R–C(O)NHOH (R = H, NH2, CH3, CF3 and Phenyl) were studied using the B3LYP/6-311+G(d,p) method of DFT theory. In order to evaluate the conformational behavior of these systems in water, we carried out CPCM-SCRF optimization calculations at the B3LYP/6-311+G(d,p) levels of theory. The obtained optimized geometries and interaction affinities of the gas and solution phase were compared. The following order of stability was found for ionic complexes of the transition metals: Cu2+ > Ni(t)2+ > Zn2+. The same stability order would be expected according to the Irving–Williams order of stability constants. The high-spin complexes of the Ni2+ were more stable than the low-spin complexes. The solvent effect reduced the observed relative stability of individual metallic complexes of substituted hydroxamic acids. 相似文献
9.
Nady N Schroën K Franssen MC Fokkink R Mohy Eldin MS Zuilhof H Boom RM 《Journal of colloid and interface science》2012,388(1):191-200
The effect of pH on the build-up of polyelectrolyte multilayers, PEMs, composed by poly-L-lysine and heparin onto two different substrates, silica and gold, has been studied by means of ellipsometry and quartz crystal microbalance with dissipation, QCM-D. Ellipsometry results indicate that the dry mass grows exponentially with the number of layers, and that this amount is larger as the pH values are raised. From QCM-D data the viscoelastic properties of the multilayered structure have been obtained. These data reflect that PEMs become more viscoelastic as the pH values are increased for silica substrates, while for gold the highest viscoelastic behavior is obtained at neutral pH and the elastic behavior becomes dominant as the pH is further increased or decreased. By combining these two surface techniques it has been also possible to determine the solvent content in the multilayers and reach a deeper understanding of the internal structure. 相似文献
10.
Remko Achten Evelien A. W. Smits R. Amaranatha Reddy Marcel Giesbers Antonius T. M. Marcelis Ernst J. R. Sudh lter 《Liquid crystals》2006,33(1):57-65
The synthesis and mesomorphic properties of 30 bent-core compounds with a fluorine substituent in one of the outer rings are reported. The banana-shaped compounds are all derived from resorcinol and contain esters as linking groups between the five aromatic rings. The different mesophases have been characterized by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction studies and electro-optical investigations. The compounds with the longer terminal chains exhibit an antiferroelectric SmCP phase. Upon introduction of a fluorine substituent the layer spacing increases, as compared with the corresponding unsubstituted compound. The introduction of one terminal vinyl group in the mono-substituted bent-core mesogens has no significant influence on the liquid crystalline properties and the switching remains antiferroelectric. Due to the introduction of the terminal double bond, these banana-shaped compounds are suitable for the preparation of siloxane polymers or attachment to a hydrogen-terminated silicon surface. 相似文献