表面活性剂与环糊精的相互作用及在日化工业中的应用

讨论了与环糊精作用后表面活性剂物理化学性质的变化,并对主客体ｍｏｌ比进行了探讨,对环糊精－表面活性剂体系的理论意义和实际应用进行了细致的总结。     

Selective Separation of Toluene from n‐Heptane via Emulsion Liquid Membranes Containing Substituted Cyclodextrins as Carrier

Abstract

The selective separation of toluene from n‐heptane is investigated using unsubstituted α‐cyclodextrin (αCD), β‐cyclodextrin (βCD) and also with two substituted CDs as a carrier in oil/water/oil‐type emulsion liquid membranes. The separation factor for toluene to n‐heptane is evaluated from the extraction of an equimolar mixture of toluene and n‐heptane. βCD shows the highest selectivity followed by αCD, hydroxypropyl‐αCD and hydroxypropyl‐βCD. The separation performances, represented by the permeation rate and separation factor, are analyzed systematically by varying the operating parameters: contact time, concentration of carriers, volume fraction of the membrane phase, and the relative amount of solvent. In this paper the effects of carriers and interfacial tension on dispersed phase drop size, internal droplets size, and size distribution are also systematically investigated.     

The Third Extracellular Loop of Mammalian Odorant Receptors Is Involved in Ligand Binding

Mammals recognize chemicals in the air via G protein-coupled odorant receptors (ORs). In addition to their orthosteric binding site, other segments of these receptors modulate ligand recognition. Focusing on human hOR1A1, which is considered prototypical of class II ORs, we used a combination of molecular modeling, site-directed mutagenesis, and in vitro functional assays. We showed that the third extracellular loop of ORs (ECL3) contributes to ligand recognition and receptor activation. Indeed, site-directed mutations in ECL3 showed differential effects on the potency and efficacy of both carvones, citronellol, and 2-nonanone.     

Characterizing Binding Interactions That Are Essential for Selective Transport through the Nuclear Pore Complex

Specific macromolecules are rapidly transported across the nuclear envelope via the nuclear pore complex (NPC). The selective transport process is facilitated when nuclear transport receptors (NTRs) weakly and transiently bind to intrinsically disordered constituents of the NPC, FG Nups. These two types of proteins help maintain the selective NPC barrier. To interrogate their binding interactions in vitro, we deployed an NPC barrier mimic. We created the stationary phase by covalently attaching fragments of a yeast FG Nup called Nsp1 to glass coverslips. We used a tunable mobile phase containing NTR, nuclear transport factor 2 (NTF2). In the stationary phase, three main factors affected binding: the number of FG repeats, the charge of fragments, and the fragment density. We also identified three main factors affecting binding in the mobile phase: the avidity of the NTF2 variant for Nsp1, the presence of nonspecific proteins, and the presence of additional NTRs. We used both experimentally determined binding parameters and molecular dynamics simulations of Nsp1FG fragments to create an agent-based model. The results suggest that NTF2 binding is negatively cooperative and dependent on the density of Nsp1FG molecules. Our results demonstrate the strengths of combining experimental and physical modeling approaches to study NPC-mediated transport.     

Mass Spectrometry,Ion Mobility Separation and Molecular Modelling: A Powerful Combination for the Structural Characterisation of Substituted Cyclodextrins Mixtures

When working on the synthesis of substituted cyclodextrins (CDs), the main challenge remains the analysis of the reaction media content. Our objective in this study was to fully characterise a complex isomers mixture of Lipidyl-βCDs (LipβCD) obtained with a degree of substitution 1 (DS = 1) from a one-step synthesis pathway. The benefit of tandem mass spectrometry (MS/MS) and ion mobility separation hyphenated with mass spectrometry (IM-MS) was investigated. The MS/MS fragment ion‘s relative intensities were analysed by principal component analysis (PCA) to discriminate isomers. The arrival time distribution (ATD) of each isomer was recorded using a travelling wave ion mobility (TWIM) cell allowing the determination of their respective experimental collision cross section (CCS_exp). The comparison with the predicted theoretical CCS (CCS_th) obtained from theoretical calculations propose a regioisomer assignment according to the βCD hydroxyl position (2, 3, or 6) involved in the reaction. These results were validated by extensive NMR structural analyses of pure isomers combined with molecular dynamics simulations. This innovative approach seems to be a promising tool to elucidate complex isomer mixtures such as substituted cyclodextrin derivatives.     

Exploring the Molecular Basis for Selective Binding of Homoserine Dehydrogenase from Mycobacterium leprae TN toward Inhibitors: A Virtual Screening Study

Homoserine dehydrogenase (HSD) from Mycobacterium leprae TN is an antifungal target for antifungal properties including efficacy against the human pathogen. The 3D structure of HSD has been firmly established by homology modeling methods. Using the template, homoserine dehydrogenase from Thiobacillus denitrificans (PDB Id 3MTJ), a sequence identity of 40% was found and molecular dynamics simulation was used to optimize a reliable structure. The substrate and co-factor-binding regions in HSD were identified. In order to determine the important residues of the substrate (l-aspartate semialdehyde (l-ASA)) binding, the ASA was docked to the protein; Thr163, Asp198, and Glu192 may be important because they form a hydrogen bond with HSD through AutoDock 4.2 software. After use of a virtual screening technique of HSD, the four top-scoring docking hits all seemed to cation–π ion pair with the key recognition residue Lys107, and Lys207. These ligands therefore seemed to be new chemotypes for HSD. Our results may be helpful for further experimental investigations.     

The Mechanism of Selective Recognition of Lipid Substrate by hDHHC20 Enzyme

S-acylation is a post-translational linkage of long chain fatty acids to cysteines, playing a key role in normal physiology and disease. In human cells, the reaction is catalyzed by a family of 23 membrane DHHC-acyltransferases (carrying an Asp-His-His-Cys catalytic motif) in two stages: (1) acyl-CoA-mediated autoacylation of the enzyme; and (2) further transfer of the acyl chain to a protein substrate. Despite the availability of a 3D-structure of human acyltransferase (hDHHC20), the molecular aspects of lipid selectivity of DHHC-acyltransferases remain unclear. In this paper, using molecular dynamics (MD) simulations, we studied membrane-bound hDHHC20 right before the acylation by C12-, C14-, C16-, C18-, and C20-CoA substrates. We found that: (1) regardless of the chain length, its terminal methyl group always reaches the “ceiling” of the enzyme’s cavity; (2) only for C16, an optimal “reactivity” (assessed by a simple geometric criterion) permits the autoacylation; (3) in MD, some key interactions between an acyl-CoA and a protein differ from those in the reference crystal structure of the C16-CoA-hDHHS20 mutant complex (probably, because this structure corresponds to a non-native dimer). These features of specific recognition of full-size acyl-CoA substrates support our previous hypothesis of “geometric and physicochemical selectivity” derived for simplified acyl-CoA analogues.     

AgNO3/MCM-41/NiFe2 O4的制备及吸附烯烃行为研究

基于长链烯烃/烷烃络合分离的目标,设计构造了AgNO3/MCM-41/NiFe2 O4磁性吸附剂。样品采用X射线衍射( XRD),N2吸附-脱附,红外线光谱分析( FTIR)和振动样品磁强计( VSM)等手段进行表征,结果表明磁性吸附剂中NiFe2 O4呈尖晶石结构,AgNO3最佳负载量为0.2 g/g AgNO3,且单层分散于MCM-41六方孔道内,其比表面积为717.89 m2/g,孔径为2.94 nm。利用磁性吸附剂对C11烯烃/C11烷烃混合物进行液相络合吸附分离研究,实验表明AgNO3/MCM-41/NiFe2 O4对长链烯烃分子具有选择性吸附功能,在100 min内达到吸附平衡,单级平衡吸附量为2.14 g/g。考察了吸附剂重复使用对吸附选择性和磁回收率的影响,使用10次后,吸附剂可保持较高的回收率(98.9%),烯烃吸附选择性略有降低,但仍能实现对烯烃的选择性吸附。     

MT1‐Selective Melatonin Receptor Ligands: Synthesis,Pharmacological Evaluation,and Molecular Dynamics Investigation of N‐{[(3‐O‐Substituted)anilino]alkyl}amides

The design of compounds selective for the MT₁ melatonin receptor is still a challenging task owing to the limited knowledge of the structural features conferring selectivity for the MT₁ subtype, and only few selective compounds have been reported so far. N‐(Anilinoalkyl)amides are a versatile class of melatonin receptor ligands that include nonselective MT₁/MT₂ agonists and MT₂‐selective antagonists. We synthesized a new series of N‐(anilinoalkyl)amides bearing 3‐arylalkyloxy or 3‐alkyloxy substituents at the aniline ring, looking for new potent and MT₁‐selective ligands. To evaluate the effect of substituent size and shape on binding affinity and intrinsic activity, both flexible and conformationally constrained derivatives were prepared. The phenylbutyloxy substituent gave the best result, providing the partial agonist 4 a , which was endowed with high MT₁ binding affinity (pK_i=8.93) and 78‐fold selectivity for the MT₁ receptor. To investigate the molecular basis for agonist recognition, and to explain the role of the 3‐arylalkyloxy substituent, we built a homology model of the MT₁ receptor based on the β₂ adrenergic receptor crystal structure in its activated state. A binding mode for MT₁ agonists is proposed, as well as a hypothesis regarding the receptor structural features responsible for MT₁ selectivity of compounds with lipophilic arylalkyloxy substituents.     

氧化氯化法提高甲苯氯化的对位选择性

我们以氧化氯化的间接方法对甲苯进行氯化,发现这种体系较传统的直接氯化法有更好的对位选择性。通过筛选不同的金属氯化物、氧化剂,及各种溶剂、反应温度和反应时间,发现氯化锂/过硫酸氢钾体系在10℃反应12 h,可以得到100%的甲苯转化率和75%的对氯甲苯,反应条件温和简单。     

Analysis of the Enhanced Stability of R(+)-Alpha Lipoic Acid by the Complex Formation with Cyclodextrins

R(+)-alpha lipoic acid (RALA) is one of the cofactors for mitochondrial enzymes and, therefore, plays a central role in energy metabolism. RALA is unstable when exposed to low pH or heat, and therefore, it is difficult to use enantiopure RALA as a pharma- and nutra-ceutical. In this study, we have aimed to stabilize RALA through complex formation with cyclodextrins (CDs). α-CD, β-CD and γ-CD were used for the formation of these RALA-CD complexes. We confirmed the complex formation using differential scanning calorimetry and showed by using HPLC analysis that complexed RALA is more stable than free RALA when subjected to humidity and high temperature or acidic pH conditions. Scanning electron microscopy studies showed that the particle size and shape differed depending on the cyclodextrin used for complexation. Further, the complexes of CD and RALA showed a different particle size distribution pattern compared with that of CD itself or that of the physical mixture of RALA and CD.     

利福平分子印迹聚合物的制备及其吸附行为

以利福平为模板分子、甲基丙烯酸为功能单体、乙二醇二甲基丙烯酸酯为交联剂,制备了利福平分子印迹聚合物. 采用平衡结合方法和Scatchard模型评价了该聚合物的结合特性,考察了其吸附行为. 结果表明,利福平分子印迹聚合物中形成了两类不同的结合位点,得到高亲和力结合位点的离解常数和最大表观结合量分别为31.5 mg/mL和23.34 mg/g,低亲和力结合位点的离解常数和最大表观结合量分别为9.22 mg/mL和12.86 mg/g. 实验结果显示,利福平分子印迹聚合物对利福平呈现出了高的选择吸附特性.     

Selective crystallization of CoAPO-34 and VAPO-5 molecular sieves under microwave irradiation in an alkaline or neutral condition

Syntheses of cobalt- and vanadium-incorporated aluminophosphate molecular sieves (CoAPO and VAPO) with AFI and CHA structures have been studied using an alkaline or neutral gel under microwave irradiation and conventional hydrothermal heating. Microwave synthesis gives rise to the selective crystallization of CoAPO-34 with a CHA structure and VAPO-5 with an AFI structure, while the conventional hydrothermal crystallization brings CoAPO-5 and VAPO-34 through the gradual transformation of CoAPO-34 and VAPO-5, respectively, as the crystallization time increases. These results reveal that the relative stabilities of metal-incorporated aluminophosphate (MeAPO) molecular sieves between AFI and CHA structures depend on the type of incorporated metal ions. This work also suggests that microwave syntheses of MeAPO molecular sieves preferentially induce a kinetically favorable MeAPO phase in a short period of crystallization time. The synthesis of VAPO-5 in an alkaline condition is for the first time reported in this work.     

Structural Investigation and Molecular Modeling Studies of Strobilurin-Based Fungicides Active against the Rice Blast Pathogen Pyricularia oryzae

The increasing emergence of fungicide-resistant pathogens requires urgent solutions for crop disease management. Here, we describe a structural investigation of new fungicides obtained by combining strobilurin and succinate dehydrogenase inhibitor pharmacophores. We identified compounds endowed with very good activity against wild-type Pyricularia oryzae, combined in some cases with promising activity against strobilurin-resistant strains. The first three-dimensional model of P. oryzae cytochrome bc1 complex containing azoxystrobin as a ligand was developed. The model was validated with a set of commercially available strobilurins, and it well explains both the resistance mechanism to strobilurins mediated by the mutation G143A and the activity of metyltetraprole against strobilurin-resistant strains. The obtained results shed light on the key recognition determinants of strobilurin-like derivatives in the cytochrome bc1 active site and will guide the further rational design of new fungicides able to overcome resistance caused by G143A mutation in the rice blast pathogen.     

Total Synthesis of (−)‐Doliculide,Structure–Activity Relationship Studies and Its Binding to F‐Actin

Actin, an abundant protein in most eukaryotic cells, is one of the targets in cancer research. Recently, a great deal of attention has been paid to the synthesis and function of actin‐targeting compounds and their use as effective molecular probes in chemical biology. In this study, we have developed an efficient synthesis of (?)‐doliculide, a very potent actin binder with a higher cell‐membrane permeability than phalloidin. Actin polymerization assays with (?)‐doliculide and two analogues on HeLa and BSC‐1 cells, together with a prediction of their binding mode to F‐actin by unbiased computational docking, show that doliculide stabilizes F‐actin in a similar way to jasplakinolide and chondramide C.     

Selective Pharmacophore Models of Dopamine D1 and D2 Full Agonists Based on Extended Pharmacophore Features

This study is focused on the identification of structural features that determine the selectivity of dopamine receptor agonists toward D₁ and D₂ receptors. Selective pharmacophore models were developed for both receptors. The models were built by using projected pharmacophoric features that represent the main agonist interaction sites in the receptor (the Ser residues in TM5 and the Asp in TM3), a directional aromatic feature in the ligand, a feature with large positional tolerance representing the positively charged nitrogen in the ligand, and sets of excluded volumes reflecting the shapes of the receptors. The sets of D₁ and D₂ ligands used for modeling were carefully selected from published sources and consist of structurally diverse, conformationally rigid full agonists as active ligands together with structurally related inactives. The robustness of the models in discriminating actives from inactives was tested against four ensembles of conformations generated by using different established methods and different force fields. The reasons for the selectivity can be attributed to both geometrical differences in the arrangement of the features, e.g., different tilt angels of the π system, as well as shape differences covered by the different sets of excluded volumes. This work provides useful information for the design of new D₁ and D₂ agonists and also for comparative homology modeling of D₁ and D₂ receptors. The approach is general and could therefore be applied to other ligand–protein interactions for which no experimental protein structure is available.     

Homology Modelling of the GABA Transporter and Analysis of Tiagabine Binding

A homology model of the human GABA transporter (GAT‐1) based on the recently reported crystal structures of the bacterial leucine transporter from Aquifex aeolicus (LeuT) was developed. The stability of the resulting model embedded in a membrane environment was analyzed by extensive molecular dynamics (MD) simulations. Based on docking studies and subsequent MD simulations of three compounds, the endogenous ligand GABA and two potent inhibitors, (R)‐nipecotic acid and the anti‐epilepsy drug tiagabine, various binding modes were identified and are discussed. Whereas GABA and (R)‐nipecotic acid, which are both substrates, are stabilised with residues located deep inside the occluded state binding pocket (including residues Tyr 60 and Ser 396), tiagabine, which contains a large aliphatic side chain, is stabilised in a binding mode that extends from the substrate binding pocket (i.e., stabilised by Phe 294) to the extracellular vestibule, where the side chain is stabilised by aliphatic residues. The tiagabine binding mode, reaching from the substrate binding site to the extracellular vestibule, forces the side chain of Phe 294 to adopt a distinct conformation from that found in the occluded conformation of the transporter. Hence, in presence of tiagabine, GAT‐1 is constrained in an open‐to‐out conformation. Our results may be of particular interest for the design of new GAT‐1 inhibitors.     

Rational Design,Synthesis, and DNA Binding Properties of Novel Sequence‐Selective Peptidyl Congeners of Ametantrone

Natural and synthetic compounds characterized by an anthraquinone nucleus represent an important class of anti‐neoplastic agents, the mechanism of action of which is related to intercalation into DNA. Ametantrone (AM) is a synthetic 9,10‐anthracenedione bearing two (hydroxyethylamino)ethylamino residues at positions 1 and 4; along with other anthraquinones and anthracyclines, it shares a polycyclic intercalating moiety and charged side chains that stabilize DNA binding. All these drugs elicit adverse side effects, which represent a challenge for antitumor chemotherapy. In the present work the structure of AM was augmented with appropriate groups that target well‐defined base pairs in the major groove. These should endow AM with DNA sequence selectivity. We describe the rationale for the synthesis and the evaluation of activity of a new series of compounds in which the planar anthraquinone is conjugated at positions 1 and 4 through the side chains of AM or other bioisosteric linkers to appropriate dipeptides. The designed novel AM derivatives were shown to selectively stabilize two oligonucleotide duplexes that both have a palindromic GC‐rich hexanucleotide core, but their stabilizing effects on a random DNA sequence was negligible. In the case of the most effective compound, the 1,4‐bis‐[Gly‐(L ‐Lys)] derivative of AM, the experimental results confirm the predictions of earlier theoretical computations. In contrast, AM had equal stabilizing effects on all three sequences and showed no preferential binding. This novel peptide derivative can be classified as a strong binder regarding the sequences that it selectively targets, possibly opening the exploitation of less cytotoxic conjugates of AM to the targeted treatment of oncological and viral diseases.     

Tyrp1 Mutant Variants Associated with OCA3: Computational Characterization of Protein Stability and Ligand Binding

Oculocutaneous albinism type 3 (OCA3) is an autosomal recessive disorder caused by mutations in the TYRP1 gene. Tyrosinase-related protein 1 (Tyrp1) is involved in eumelanin synthesis, catalyzing the oxidation of 5,6-dihydroxyindole-2-carboxylic acid oxidase (DHICA) to 5,6-indolequinone-2-carboxylic acid (IQCA). Here, for the first time, four OCA3-causing mutations of Tyrp1, C30R, H215Y, D308N, and R326H, were investigated computationally to understand Tyrp1 protein stability and catalytic activity. Using the Tyrp1 crystal structure (PDB:5M8L), global mutagenesis was conducted to evaluate mutant protein stability. Consistent with the foldability parameter, C30R and H215Y should exhibit greater instability, and two other mutants, D308N and R326H, are expected to keep a native conformation. SDS-PAGE and Western blot analysis of the purified recombinant proteins confirmed that the foldability parameter correctly predicted the effect of mutations critical for protein stability. Further, the mutant variant structures were built and simulated for 100 ns to generate free energy landscapes and perform docking experiments. Free energy landscapes formed by Y362, N378, and T391 indicate that the binding clefts of C30R and H215Y mutants are larger than the wild-type Tyrp1. In docking simulations, the hydrogen bond and salt bridge interactions that stabilize DHICA in the active site remain similar among Tyrp1, D308N, and R326H. However, the strengths of these interactions and stability of the docked ligand may decrease proportionally to mutation severity due to the larger and less well-defined natures of the binding clefts in mutants. Mutational perturbations in mutants that are not unfolded may result in allosteric alterations to the active site, reducing the stability of protein-ligand interactions.