Aggregation behavior of giant amphiphiles prepared by cofactor reconstitution

We report on biohybrid surfactants, termed "giant amphiphiles", in which a protein or an enzyme acts as the polar head group and a synthetic polymer as the apolar tail. It is demonstrated that the modification of horseradish peroxidase (HRP) and myoglobin (Mb) with an apolar polymer chain through the cofactor reconstitution method yields giant amphiphiles that form spherical aggregates (vesicles) in aqueous solution. Both HRP and Mb retain their original functionality when modified with a single polystyrene chain, but reconstitution has an effect on their activities. In the case of HRP the enzymatic activity decreases and for Mb the stability of the dioxygen myoglobin (oxy-Mb) complex is reduced, which is probably the result of a disturbed binding of the heme in the apo-protein or a reduced access of the substrate to the active site of the enzyme or protein.     

环氧酰胺类化合物在OD和AD柱上手性拆分的比较

在ChiralcelOD和ChiralpakAD等二支多糖类手性固定相上,以各种不同配比的正己烷-异丙醇为洗脱剂对十三种带有不同取代基的环氧酰胺类化合物的对映体进行了手性拆分。考察了这些外消旋体在这二支手性柱上的色谱行为。实验表明,环氧酰胺与手性固定相之间的手性作用(例如:偶极-偶极作用、氢键作用、π-π作用)和非手性作用(例如:空间效应)等的综合因素是支配手性拆分过程的主要原因。方法已用于环氧酰胺不对称反应产物的光学纯度鉴定。     

Enantiomeric Discrimination by Surface‐Enhanced Raman Scattering–Chiral Anisotropy of Chiral Nanostructured Gold Films

A surface‐enhanced Raman scattering‐chiral anisotropy (SERS‐ChA) effect is reported that combines chiral discrimination and surface Raman scattering enhancement on chiral nanostructured Au films (CNAFs) equipped in the normal Raman scattering Spectrometer. The CNAFs provided remarkably higher enhancement factors of Raman scattering (EFs) for particular enantiomers, and the SERS intensity was proportional to the enantiomeric excesses (ee) values. Except for molecules with mesomeric species, all of the tested enantiomers exhibited high SERS‐ChA asymmetry factors (g), ranging between 1.34 and 1.99 regardless of polarities, sizes, chromophores, concentrations and ee. The effect might be attributed to selective resonance coupling between the induced electric and magnetic dipoles associated with enantiomers and chiral plasmonic modes of CNAFs.     

Investigation of the synergistic effect with chiral D-penicillamine functionalized gold nanoparticle as an additive for enantiomeric separation in capillary electrophoresis

The authors describe a synergistic system for nanoparticle based chiral separation. It is based on the use of a conventional chiral selector hydroxyproyl-β-cyclodextrin and a kind of gold nanoparticle functionalized with D-penicillamine as an additive. This nanomaterial displays a synergistic effect on the efficiency of the enantioseparation of the chiral drugs amlodipine, tropicamide, and ofloxacin. A comparative study on the enantioseparation capability of three separation systems, viz. (a) single hydroxyproyl-β-cyclodextrin system, (b) achiral citrate capped gold nanoparticle/ hydroxyproyl-β-cyclodextrin system, and (c) chiral D-penicillamine functionalized gold nanoparticle/ hydroxyproyl-β-cyclodextrin system was performed. The results show that the D-penicillamine functionalized gold nanoparticle/hydroxyproyl-β-cyclodextrin synergistic system has remarkable superiority. The effects of concentrations of D-penicillamine functionalized gold nanoparticle and hydroxyproyl-β-cyclodextrin, of buffer pH value and concentration, and of applied voltage on the performance of enantioseparation were investigated.     

The determination of enantiomeric excess of valine by ODESSA solid-state NMR experiment

The enantiomeric excess (ee) can be determined by many methods; one among them is nuclear magnetic resonance in solid-state (SS NMR). In this study we used the SS NMR ODESSA experiment for determination of the ee of valine.     

Design, synthesis and characterisation of guanosine-based amphiphiles

A small library of sugar-modified guanosine derivatives has been prepared, starting from a common intermediate, fully protected on the nucleobase. Insertion of myristoyl chains and of diverse hydrophilic groups, such as an oligoethylene glycol, an amino acid or a disaccharide chain, connected through in vivo reversible ester linkages, or of a charged functional group provided different examples of amphiphilic guanosine analogues, named G1-G7 herein. All of the sugar-modified derivatives were positive in the potassium picrate test, showing an ability to form G-tetrads. CD spectra demonstrated that, as dilute solutions in CHCl(3), distinctive G-quadruplex systems may be formed, with spatial organisations dependent upon the structural modifications. Two compounds, G1 and G2, proved to be good low-molecular-weight organogelators in polar organic solvents, such as methanol, ethanol and acetonitrile. Ion transportation experiments through phospholipid bilayers were carried out to evaluate their ability to mediate H(+) transportation, with G5 showing the highest activity within the investigated series. Moreover, G3 and G5 exhibited a significant cytotoxic profile against human MCF-7 cancer cells in in vitro bioassays.     

Diastereomeric and enantiomeric resolution of methoxytetrahydronaphthalene derivatives, melatonin ligand receptors, by HPLC on amylose chiral stationary phases

Summary Five methoxytetrahydronaphthalene derivatives, new agonist and antagonist ligands for melatonin receptors, were resolved into their diastereomers by analytical HPLC methods using derivatized amylose, chiral stationary phases. Separation was by using normal phase methodology with a mobile phase ofn-hexane-alcohol (ethanol or 2-propanol) and a silica-based amylose tris-(S)-1-phenylethylcarbamate (Chiralpak AS), or tris-3,5-dimethylphenylcarbamate (Chiralpak AD). The effects of structural variation in the solutes were noted. Baseline separation was easily obtained in many cases.     

巴拉苏酰胺对映体的色谱分离研究

利用手性HPLC法对天然产物(+)-巴拉苏酰胺(balasubramide)及其对映体进行分离和光学纯度测定。在手性分离过程中,考察了两种不同的手性固定相和不同比例的流动相(正己烷和异丙醇),以进行手性分离方法的优化。结果表明:正己烷和异丙醇(70/30,V/V)在手性柱Chiralpak AD-H上获得最佳分离。光学活性的巴拉苏酰胺的对映体过量值高于98%,其分离因子(α)和分离度为2.15和21.80。本研究为光学活性的巴拉苏酰胺及其后续衍生物光学纯度控制提供了方法学基础。     

Infrared spectroscopy of racemic and enantiomeric forms of atenolol

The molecular structure of conformational isomorphs given by X-ray diffraction for racemic and enantiomeric atenolol were optimized at the HF/6-31G* level of theory and the infrared spectra of the structure were calculated. These spectra are used to characterize the differences between the various atenolol conformers. The spectra of the (R,S)- and S-atenolol solid forms were recorded and the bands corresponding to the functional groups identified with the aid of the calculated spectra, fitting analysis, temperature effect and H/D isotopic exchange. Particular attention was paid to the stretch vibration modes of the functional groups present in the atenolol.     

Adsorption of linear and star-shaped polyelectrolytes to monolayers of charged amphiphiles

Adsorption of polyelectrolytes has been studied employing monolayers of ionic amphiphiles at the air water interface as model surfaces. The adsorption of polyelectrolytes from a solution brought into contact with the amphiphile monolayer results in changes of the monolayer structure and properties. Monitoring these changes can be done by recording the changes in surface pressure. The kinetics of the adsorption depends strongly on the nature of the polyelectrolyte. Depending on the structure of the polyelectrolyte a purely diffusion controlled adsorption or a sequence of diffusion controlled adsorption and ordering processes have been identified to determine the kinetics. The influence of the molecular architecture on the polyelectrolyte adsorption has been further studied employing linear and star shaped poly(acrylic acid) and poly(N-propyl-4-vinyl pyridinium bromides), respectively. An unexpected behavior with an induction period in the adsorption kinetics of both polymers has been found. Furthermore, the degree of branching has only very minor effects on the adsorption kinetics.     

Generation and reactivity of enantiomeric (BINOLato)Ni+ complexes with chiral secondary alcohols in the gas phase

In the presence of secondary alcohols, electrospray ionization of dilute methanolic solutions of nickel(II) salts and 1,1'-bis-2-naphthol (BINOL) leads to complexes of the formal composition [(BINOLato)Ni(CH3CH(OH)R)]+ (BINOLato refers to a singly deprotonated (R)- or (S)-1,1'-bis-2-naphthol ligand; R=CH3, C2H5, n-C3H7, n-C4H9, n-C5H11, n-C6H13, c-C6H11, and C6H5). Upon collision-induced dissociation, each mass-selected nickel complex either loses the entire secondary alcohol ligand or undergoes bond activation followed by elimination of the corresponding ketone, as revealed by deuterium labeling. When enantiomeric BINOLato ligands (R or S) are combined with chiral secondary alcohols (R or S), differences in the branching ratios between these channels for the two stereoisomers of the secondary alcohols provide insight into the chiral discrimination operative in the C--H- and O--H-bond activation processes. For saturated alkan-2-ols, the chiral discrimination is low, and if any preference is observed at all, ketone elimination from the homochiral complexes (R,R and S,S) is slightly favored. In contrast, the diastereomeric (BINOLato)Ni+ complexes of 1-phenylethanol exhibit preferential ketone losses for the heterochiral systems (S,R and R,S).     

Synthesis of racemic and enantiomeric 3-pyrrolidinyl derivatives of nucleobases

The synthesis of novel 3-pyrrolidinyl derivatives of nucleobases is described. Starting from malic acid, we improved the synthesis of both racemic and optically active N-benzyl-3-hydroxypyrrolidine-2,5-diones, which were transformed in four steps into N-tert-butyloxycarbonyl-3-mesyloxypyrrolidines, the key synthons for the alkylation of purine and pyrimidine nucleobases. Alkylations of cesium salts of purines and sodium salts of pyrimidines with N-tert-butyloxycarbonyl-3-mesyloxypyrrolidines proceeded smoothly, giving high yields of 9-substituted purine derivatives and moderate yields of 1-substituted pyrimidine derivatives. Using (S)-N-tert-butyloxycarbonyl-3-mesyloxypyrrolidine as the same intermediate for the synthesis of both enantiomeric N-Boc-3-pyrrolidinyladenines, and considering the results obtained on chiral HPLC analysis of the products, we proved that nucleophilic displacement of the mesyloxy group proceeded with inversion and not with retention of the configuration. Prepared compounds were tested for cytostatic and antiviral properties, but no significant activity was found.     

Phase behavior of amphiphiles at liquid crystals/water interface: A coarse-grained molecular dynamics study

We present a coarse-grained molecular dynamics simulation study of phase behavior of amphiphilic monolayers at the liquid crystal （LC）/water interface. The results revealed that LCs at interface can influence the lateral ordering of amphiphiles. Particularly, the amphiphile tails along with perpendicularly penetrated LCs between tails undergo a two-dimension phase transition from liquid-expanded into a liquid-condensed phase as their area density at interface reaches 0.93. While, the liquid-condensed phase of the monolayer never appears at oil/water interface with isotropic shape oil particles. These findings reveal the penetration of anisotropic LC can promote ordered lateral organization of amphiphiles. Moreover, we find the phase transition point is shifted to lower surface coverage of amphiphiles when the LCs have larger affinity to the amphiphile tails.     

新型环糊精衍生物单6-O-苯基胺甲酰基-β-环糊精的合成及其在手性药物毛细管区带电泳拆分中的应用

合成了新型的环糊精衍生物单6-O-苯基胺甲酰基—β-环糊精，并对合成产物进行了表征。以新型环糊精衍生物为手性选择剂，考察了手性选择剂浓度、缓冲液PH值和浓度及有机溶质对8种手性药物对映体的毛细管电泳分离的影响。结果表明：手性选择剂浓度和缓冲液PH值是影响药物对映体分离的重要因素，有机溶质亦对分离有很大影响。单6-O-苯基胺甲酰基—β-环糊精能使所研究的8种手性药物中的5种达基线分离，3种达部分分离。而在同样条件下．β-环糊精仅能使上述药物中的菜心安达部分分离(及。＝0．67)，这说明我们合成的环糊精衍生物手性拆分能力要强于天然环糊精。我们还就单6-O-苯基胺甲酰基-β-环糊精对手性药物可能的拆分机理进行了探讨。     

Formation and characterization of simple and mixed vesicles based on monomeric and oligomeric phosphate bipolar amphiphiles

Certain phosphate bipolar amphiphiles, both monomeric ( I and II ) and polymeric or rather oligomeric (poly- I and poly- II ), were used as basic materials for the preparation of simple and mixed vesicles. Specifically, it was found that oligomeric phosphate bipolar amphiphiles form stable vesicles in aqueous media. The same oligomeric bolaamphiphiles in mixture with their monomeric counterparts also form stable mixed vesicles with sonication; they are relatively less stable with the “thin film method.” Furthermore, it was shown that the method of spanning the membrane of didodecylphosphate vesicels with the dipolar amphiphile II is not effective for enhancing stability. © 1995 John Wiley & Sons, Inc.     

Recent advances in assemblies of cyclodextrins and amphiphiles: construction and regulation

Cyclodextrins (CDs) had been regarded as destructors in molecular assembly systems for a long time until CD/surfactants were found to assemble into high order structure driven by hydrogen bonding between CDs. Thereafter, intensive researches have been conducted on construction and regulation of CD–amphiphile systems. Here, we summarized the recent progress on construction and regulation of CDs and amphiphiles assembly. The scope of amphiphiles have been extended from surfactants (ionic surfactants, zwitterion surfactants, nonionic surfactants, gemini surfactant, and so on), to nontypical amphiphiles (amines, aromatic molecules, alkanes, and so on). Owing to the abundant choices of guest amphiphiles and dynamic nature of host–guest inclusive interaction, numerous regulation methods (such as enzyme, light, pH, concentration, temperature, and so on) have been used in CD–amphiphile systems. Moreover, remarks and future perspectives are also discussed at the end of this review, which is expected to stimulate progress on both mechanism and application level.     

Chiral Monolithic Silica-Based HPLC Columns for Enantiomeric Separation and Determination: Functionalization of Chiral Selector and Recognition of Selector-Selectand Interaction

This review draws attention to the use of chiral monolithic silica HPLC columns for the enantiomeric separation and determination of chiral compounds. Properties and advantages of monolithic silica HPLC columns are also highlighted in comparison to conventional particle-packed, fused-core, and sub-2-µm HPLC columns. Nano-LC capillary monolithic silica columns as well as polymeric-based and hybrid-based monolithic columns are also demonstrated to show good enantioresolution abilities. Methods for introducing the chiral selector into the monolithic silica column in the form of mobile phase additive, by encapsulation and surface coating, or by covalent functionalization are described. The application of molecular modeling methods to elucidate the selector–selectand interaction is discussed. An application for enantiomeric impurity determination is also considered.