Home About us Contact
|
Home About us Contact | ||
|
|
||
Hydrophobic Environment (hydrophobic + environment)
Selected AbstractsHydrophobic Chemistry in Aqueous Solution: Stabilization and Stereoselective Encapsulation of Phosphonium Guests in a Supramolecular HostEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2004Julia L. Brumaghim Abstract Encapsulation of guest molecules inside supramolecular host assemblies provides a way to stabilize reactive species in aqueous solution. The stabilization of reactive phosphonium/ketone adducts of the general formula [R1MeC(OH)PR3]+ by encapsulation as guest molecules within a [Ga4L6]12, tetrahedral metal,ligand assembly is reported; although these cations decompose in aqueous solution, encapsulation inside the hydrophobic cavity of the assembly lengthens their lifetimes considerably, in some cases up to weeks. By varying the phosphane (PMe3, PEt3, PPhMe2, and PPh2Me) and ketone (acetone, methyl ethyl ketone, 1,1,1-trifluoroacetone, and fluoroacetone) which form these adducts, as well as the pD of the solutions, it was determined that the pH of the solution as well as the size and shape of the guest cations play an important role in the stability of these host,guest complexes. Encapsulation of chiral guests in the chiral [Ga4L6]12, assembly results in the formation of diastereomers, as characterized by 1H, 19F, and 31P NMR spectroscopy. Although the [Ga4L6]12, assembly is formed from non-chiral ligands, the assembly itself has ,,,, or ,,,, chirality around the metal centers. Due to the chirality of this assembly, diastereomeric selectivity is observed upon initial guest encapsulation (typical diastereomeric excesses are 30,50%). This initial diastereomeric selectivity decreases over time to reach an equilibrium but does not become 1:1, indicating both kinetic and thermodynamic processes promote selective guest encapsulation. These experiments demonstrate further the applications of nanoscale reaction vessels, self-assembled by design from non-chiral ligands, in providing a chiral and hydrophobic environment for guest molecules in aqueous solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Carbohydrate expression and modification during keratinocyte differentiation in normal human and reconstructed epidermisEXPERIMENTAL DERMATOLOGY, Issue 5 2003Bruno Méhul Abstract:, Using fluorescein isothiocyanate (FITC)-labeled lectins we were able to demonstrate the presence of specific carbohydrate moieties in normal human and reconstructed epidermis. Evidence is provided that in both cases the strongly reduced lectin staining at the level of the stratum corneum is the result of a hindered accessibility of the lectins in this lipid-rich hydrophobic environment. Isolated corneocytes and purified cornified envelopes (CEs) exhibited clearly glycosylated structures reacting with distinct lectins. The presence of glycosidase activity, particularly in the upper layers of the epidermis characterized by an acidic environment (pH 5.5), indicates that modifications of the sugar residues might be important in epidermal homeostasis, barrier behavior and desquamation. Absent or strongly reduced glycosidase activity in the stratum corneum of reconstructed epidermis with an impaired pH gradient could be in part responsible for the reduced barrier function and the lack of desquamation in this model. [source] Aspergillus nidulans,-galactosidase of glycoside hydrolase family 36 catalyses the formation of ,-galacto-oligosaccharides by transglycosylationFEBS JOURNAL, Issue 17 2010Hiroyuki Nakai The ,-galactosidase from Aspergillus nidulans (AglC) belongs to a phylogenetic cluster containing eukaryotic ,-galactosidases and ,-galacto-oligosaccharide synthases of glycoside hydrolase family 36 (GH36). The recombinant AglC, produced in high yield (0.65 g·L,1 culture) as His-tag fusion in Escherichia coli, catalysed efficient transglycosylation with ,-(1,6) regioselectivity from 40 mm 4-nitrophenol ,- d -galactopyranoside, melibiose or raffinose, resulting in a 37,74% yield of 4-nitrophenol ,- d -Galp -(1,6)- d -Galp, ,- d -Galp -(1,6)-,- d -Galp -(1,6)- d -Glcp and ,- d -Galp -(1,6)-,- d -Galp -(1,6)- d -Glcp -(,1,,2)- d -Fruf (stachyose), respectively. Furthermore, among 10 monosaccharide acceptor candidates (400 mm) and the donor 4-nitrophenol ,- d -galactopyranoside (40 mm), ,-(1,6) linked galactodisaccharides were also obtained with galactose, glucose and mannose in high yields of 39,58%. AglC did not transglycosylate monosaccharides without the 6-hydroxymethyl group, i.e. xylose, l -arabinose, l -fucose and l -rhamnose, or with axial 3-OH, i.e. gulose, allose, altrose and l -rhamnose. Structural modelling using Thermotoga maritima GH36 ,-galactosidase as the template and superimposition of melibiose from the complex with human GH27 ,-galactosidase supported that recognition at subsite +1 in AglC presumably requires a hydrogen bond between 3-OH and Trp358 and a hydrophobic environment around the C-6 hydroxymethyl group. In addition, successful transglycosylation of eight of 10 disaccharides (400 mm), except xylobiose and arabinobiose, indicated broad specificity for interaction with the +2 subsite. AglC thus transferred ,-galactosyl to 6-OH of the terminal residue in the ,-linked melibiose, maltose, trehalose, sucrose and turanose in 6,46% yield and the ,-linked lactose, lactulose and cellobiose in 28,38% yield. The product structures were identified using NMR and ESI-MS and five of the 13 identified products were novel, i.e. ,- d -Galp -(1,6)- d -Manp; ,- d -Galp -(1,6)-,- d -Glcp -(1,4)- d -Glcp; ,- d -Galp -(1,6)-,- d -Galp -(1,4)- d -Fruf; ,- d -Galp -(1,6)- d -Glcp -(,1,,1)- d -Glcp; and ,- d -Galp -(1,6)-,- d -Glcp -(1,3)- d -Fruf. [source] Structure of a new `aspzincin' metalloendopeptidase from Grifola frondosa: implications for the catalytic mechanism and substrate specificity based on several different crystal formsACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2001Tetsuya Hori Crystal structures of a peptidyl-Lys metalloendopeptidase (MEP) from the edible mushroom Grifola frondosa (GfMEP) were solved in four crystal forms. This represents the first structure of the new family `aspzincins' with a novel active-site architecture. The active site is composed of two helices and a loop region and includes the HExxH and GTxDxxYG motifs conserved among aspzincins. His117, His121 and Asp130 coordinate to the catalytic zinc ligands. An electrostatically negative region composed of Asp154 and Glu157 attracts a positively charged Lys side chain of a substrate in a specific manner. A Tyr133 side chain located on the S1, pocket had different configurations in two crystal forms and was not observed in the other crystal forms. The flexible Tyr133 plays two roles in the enzymatic function of GfMEP. The first is to provide a hydrophobic environment with Phe83 in order to accommodate the alkyl part of the Lys side chain of a substrate and the second is as a `proton donor' to the oxyanion of the tetrahedral transition state to stabilize the reaction transition state. [source] Structure of a d -tagatose 3-epimerase-related protein from the hyperthermophilic bacterium Thermotoga maritimaACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2009Haruhiko Sakuraba The crystal structure of a d -tagatose 3-epimerase-related protein (TM0416p) encoded by the hypothetical open reading frame TM0416 in the genome of the hyperthermophilic bacterium Thermotoga maritima was determined at a resolution of 2.2,Å. The asymmetric unit contained two homologous subunits and a dimer was generated by twofold symmetry. The main-chain coordinates of the enzyme monomer proved to be similar to those of d -tagatose 3-epimerase from Pseudomonas cichorii and d -psicose 3-epimerase from Agrobacterium tumefaciens; however, TM0416p exhibited a unique solvent-accessible substrate-binding pocket that reflected the absence of an ,-helix that covers the active-site cleft in the two aforementioned ketohexose 3-epimerases. In addition, the residues responsible for creating a hydrophobic environment around the substrate in TM0416p differ entirely from those in the other two enzymes. Collectively, these findings suggest that the substrate specificity of TM0416p is likely to differ substantially from those of other d -tagatose 3-epimerase family enzymes. [source] UV resonance Raman study of streptavidin binding of biotin and 2-iminobiotin: Comparison with avidinBIOPOLYMERS, Issue 6 2001John Clarkson Abstract UV resonance Raman (UVRR) spectroscopy is used to study the binding of biotin and 2-iminobiotin by streptavidin, and the results are compared to those previously obtained from the avidin,biotin complex and new data from the avidin,2-iminobiotin complex. UVRR difference spectroscopy using 244-nm excitation reveals changes to the tyrosine (Tyr) and tryptophan (Trp) residues of both proteins upon complex formation. Avidin has four Trp and only one Tyr residue, while streptavidin has eight Trp and six Tyr residues. The spectral changes observed in streptavidin upon the addition of biotin are similar to those observed for avidin. However, the intensity enhancements observed for the streptavidin Trp Raman bands are less than those observed with avidin. The changes observed in the streptavidin Tyr bands are similar to those observed for avidin and are assigned exclusively to the binding site Tyr 43 residue. The Trp and Tyr band changes are due to the exclusion of water and addition of biotin, resulting in a more hydrophobic environment for the binding site residues. The addition of 2-iminobiotin results in spectral changes to both the streptavidin and avidin Trp bands that are very similar to those observed upon the addition of biotin in each protein. The changes to the Tyr bands are very different than those observed with the addition of biotin, and similar spectral changes are observed in both streptavidin and avidin. This is attributable to hydrogen bond changes to the binding site Tyr residue in each protein, and the similar Tyr difference features in both proteins supports the exclusive assignment of the streptavidin Tyr difference features to the binding site Tyr 43. © 2001 John Wiley & Sons, Inc. Biopolymers (Biospectroscopy) 62: 307,314, 2001 [source] Studies on the conformational properties of CP-1042,55, the hinge region of CP-10, using circular dichroism and RP-HPLCCHEMICAL BIOLOGY & DRUG DESIGN, Issue 6 2000E. Lazoura Abstract: The conformational properties of CP-1042,55, a peptide corresponding to the hinge region of CP-10, were investigated using circular dichroism spectroscopy and reverse-phase high-performance liquid chromatography (RP-HPLC). The circular dichroism studies indicated that CP-1042,55 formed considerable secondary structure in the presence of hydrophobic solution environments including 50% acetonitrile, 50% trifluoroethanol and 200 mm sodium dodecyl sulfate, which comprised a mixture of ,-helix and ,-sheet. The effect of temperature on the conformation of CP-1042,55 was investigated between 5 and 40°C, with very small changes in the spectra being observed.RP-HPLC was then used to investigate the effect of temperature on the conformation of CP-1042,55 in the presence of a hydrophobic surface. Using a C18 -adsorbent, CP-1042,55 exhibited a conformational transition at 25°C, which was associated with an increase in the chromatographic contact area and the binding affinity of the peptide for the stationary phase. In addition, near-planar bandbroadening behaviour indicated that conformational species interconverted with rapid rate constants compared with the chromatographic time scale. These results indicated that the conformational change at 25°C in theRP-HPLC system most likely corresponds to the unfolding of an ,-helical and/or ,-sheet structure to an extended coil structure. Therefore, the strong chemotactic properties of this peptide may be attributed to its ability to form considerable secondary structure in the presence of a hydrophobic environment. [source] An Efficient Hybrid, Nanostructured, Epoxidation Catalyst: Titanium Silsesquioxane,Polystyrene Copolymer Supported on SBA-15CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2007Lei Zhang Abstract A novel interfacial hybrid epoxidation catalyst was designed with a new immobilization method for homogeneous catalysts by coating an inorganic support with an organic polymer film containing active sites. The titanium silsesquioxane (TiPOSS) complex, which contains a single-site titanium active center, was immobilized successfully by in-situ copolymerization on a mesoporous SBA-15-supported polystyrene polymer. The resulting hybrid materials exhibit attractive textural properties (highly ordered mesostructure, large specific surface area (>380,m2,g,1) and pore volume (,0.46,cm3,g,1)), and high activity in the epoxidation of alkenes. In the epoxidation of cyclooctene with tert -butyl hydrogen peroxide (TBHP), the hybrid catalysts have rate constants comparable with that of their homogeneous counterpart, and can be recycled at least seven times. They can also catalyze the epoxidation of cyclooctene with aqueous H2O2 as the oxidant. In two-phase reaction media, the catalysts show much higher activity than their homogeneous counterpart due to the hydrophobic environment around the active centers. They behave as interfacial catalysts due to their multifunctionality, that is, the hydrophobicity of polystyrene and the polyhedral oligomeric silsesquioxanes (POSS), and the hydrophilicity of the silica and the mesoporous structure. Combination of the immobilization of homogeneous catalysts on two conventional supports, inorganic solid and organic polymer, is demonstrated to achieve novel heterogeneous catalytic ensembles with the merits of attractive textural properties, tunable surface properties, and optimized environments around the active sites. [source] Cover Picture: (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2008Catal. The cover picture, provided by Sh,, Kobayashi, shows an example of chiral Lewis acid catalysis based on Lewis acid,surfactant combined catalysts (LASCs). Chiral hydrophobic environments made up of scandium(III) dodecylsulfate and a chiral bipyridine ligand catalyze the asymmetric aldol-type reactions of silyl enol ethers in water as the sole solvent. [source] Effects of detergents on the secondary structures of prion protein peptides as studied by CD spectroscopyJOURNAL OF PEPTIDE SCIENCE, Issue 4 2003Dr Yoshihiro Kuroda Abstract Pathogenic prion proteins (PrPSc) are thought to be produced by ,-helical to ,-sheet conformational changes in the normal cellular prion proteins (PrPC) located solely in the caveolar compartments. In order to inquire into the possible conformational changes due to the influences of hydrophobic environments within caveolae, the secondary structures of prion protein peptides were studied in various kinds of detergents by CD spectra. The peptides studied were PrP(129,154) and PrP(192,213); the former is supposed to assume ,-sheets and the latter ,-helices, in PrPSc. The secondary structure analyses for the CD spectra revealed that in buffer solutions, both PrP(129,154) and PrP(192,213) mainly adopted random-coils (,60%), followed by ,-sheets (30%,40%). PrP(129,154) showed no changes in the secondary structures even in various kinds of detergents such as octyl-,- D -glucopyranoside (OG), octy-,- D -maltopyranoside (OM), sodium dodecyl sulfate (SDS), Zwittergent 3,14 (ZW) and dodecylphosphocholine (DPC). In contrast, PrP(192,213) changed its secondary structure depending on the concentration of the detergents. SDS, ZW, OG and OM increased the ,-helical content, and decreased the ,-sheet and random-coil contents. DPC also increased the ,-helical content, but to a lesser extent than did SDS, ZW, OG or OM. These results indicate that PrP(129,154) has a propensity to adopt predominantly ,-sheets. On the other hand, PrP(192,213) has a rather fickle propensity and varies its secondary structure depending on the environmental conditions. It is considered that the hydrophobic environments provided by these detergents may mimic those provided by gangliosides in caveolae, the head groups of which consist of oligosaccharide chains containing sialic acids. It is concluded that PrPC could be converted into a nascent PrPSc having a transient PrPSc like structure under the hydrophobic environments produced by gangliosides. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd. [source] Noncovalent dimerization of paclitaxel in solution: Evidence from electrospray ionization mass spectrometryJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2002Sarah A. Lorenz Abstract Paclitaxel, a unique antimitotic chemotherapy agent that inhibits cell division by binding to microtubules and prevents them from "depolymerizing," has received widespread interest because of its efficacy in fighting certain types of cancer, including breast and ovarian cancer. Paclitaxel undergoes aggregation at millimolar concentrations in both aqueous media and solvents of low polarity (mimicking hydrophobic environments). Its aggregation may have impact on its aqueous stability and its ability to stabilize microtubules. Here, we investigated the dimerization phenomenon of paclitaxel by electrospray ionization mass spectrometry (ESI-MS). Paclitaxel dimers were stable in solutions of acetonitrile/aqueous ammonium acetate (80/20) and aqueous sodium acetate/acetonitrile (92/8 or 95/5) at various pH values. Additional experiments using solution-phase hydrogen/deuterium exchange were employed to ascertain whether or not the observed dimers were formed in solution or as an artifact of the ESI process by ion,molecule reaction. The evidence supports formation of the dimer in solution, and the approach used can be extended to investigation of other types of drug,drug interactions. © 2002 Wiley-Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:2057,2066, 2002 [source] | |||||||||||||||||||