Development and screening of epoxy‐spacer‐phage cryogels for affinity chromatography: Enhancing the binding capacity

Macroporous epoxy cryogels can be used as an alternative for classical matrices in affinity chromatography. Due to the structural properties of cryogels, with pores of up to 100 μm, crude samples can be processed at high speed without previous manipulations such as clarification or centrifugation. Also, we previously used a peptide‐expressing M13 bacteriophage as an affinity ligand. These ligands show high specificity toward the target to be purified. Combination of both, leads to a relative cost‐effective one‐step chromatographic set‐up delivering a high purity sample (>95%), however, so far with limited capacity. To increase the binding capacity of the affinity columns, we now inserted spacers between the chromatographic matrix and the phage ligand. Both linear spacers, di‐amino‐alkanes (C₂–C₁₀), and branched polyethyleneimine spacers with different molecular weights (800 Da–10 kDa) were analyzed. Two types of peptide expressing phage ligands, a linear 15‐mer and a cyclic 6‐mer, were used for screening. Up to a tenfold increase in binding capacity was observed depending on the combination of phage ligand and spacer type.     

Efficient and versatile synthesis of new porphyrins bearing an N3O moiety: ligands for mimicking cytochrome c oxidase

Two new generations of ligands for cytochrome c oxidase mimicking have been designed and synthesized via an efficient, convergent, and versatile synthesis. These porphyrins are functionalized with both an internal nitrogen base on one side and a triaza (N3) or a triaza-phenol (N3O) moiety on the other side, attached to the macrocycle by various spacers. Unlike tailed porphyrins, the triaza motif as well as the nitrogen base are linked by two points.     

Controllable biotinylated poly(ethylene-co-glycidyl methacrylate) (PE-co-GMA) nanofibers to bind streptavidin-horseradish peroxidase (HRP) for potential biosensor applications

Poly(ethylene-co-glycidyl methacrylate) (PE-co-GMA) nanofibers with abundant active epoxy groups on surfaces were fabricated through a novel manufacturing process. The prepared PE-co-GMA nanofibers with different average diameters ranging from 100 to 400 nm were aminated by reacting the epoxy groups with 1,3-diaminopropane. The resulting aminated PE-co-GMA nanofibers were subsequently biotinylated and then successfully applied to immobilize streptavidin-horseradish peroxidase (HRP) conjugate via specific, strong and rapid binding of biotin and streptavidin. The streptavidin-HRP immobilized PE-co-GMA nanofibers showed high activity, efficiency, sensitivity as well as good reusability. The results demonstrated that PE-co-GMA nanofibers prepared could be a promising candidate as solid support materials for potential biosensor applications.     

Density functional theory study of ligand binding on CdSe (0001), (0001), and (1120) single crystal relaxed and reconstructed surfaces: implications for nanocrystalline growth

To gain a better understanding of the influence of ligand-surface interactions on nanocrystalline growth, periodic density functional theory calculations were employed in the study of the binding of organic ligands on the relaxed nonpolar (1120) and polar Se terminated (0001) surfaces and the relaxed and vacancy and adatom reconstructed Cd terminated (0001) surface. We examined chemisorption properties of phosphine, amine, phosphine oxide, carboxylic acid, and phosphinic acid model ligands, including preferred binding sites and geometries, vibrational frequencies, and binding energetics, and compared findings to intrinsic growth via addition of CdSe molecules or Cd and Se atoms. Our results indicate that binding of the ligands is preferred in the electron-poor 1-fold sites on all surfaces, with secondary coordination of the acidic ligands through the hydroxyl hydrogen to the electron-rich surface sites. In general ligand adsorption directly obstructs binding sites for growth species on the (1120) surface and only indirectly on the two polar surfaces. The order of binding affinities on the (1120) and (0001) surfaces is PH(3) < OPH(3) approximately HCOOH < NH(3) < OPH(2)OH and that on the (0001) surface is OPH(3) approximately HCOOH < OPH(2)OH < NH(3) < PH(3). Our findings corroborate the experimental observation that incorporation of the nonbulky phosphinic acid-type ligands with high affinity and high selectivity for both the (1120) and (0001) surfaces strongly enhances unidirectional growth on the (0001) surface, while incorporation of either bulky ligands or ligands with moderate affinity does not. Higher affinity of all traditionally used ligands for the (1120) surface compared to the (0001) surface also suggests that new ligands should be engineered to achieve the synthesis of novel shapes that require preferential growth on the (1120) surface.     

粉煤灰基氧氟沙星分子印迹聚合物的制备及其应用

以工业废料粉煤灰微球为基质,氧氟沙星 (OFL) 为模板分子,采用表面印迹法制备印迹材料MIP。通过紫外光谱法结合理论分析选择实验条件,并对该印迹材料结构、吸附行为进行研究。结果表明,该印迹材料对氧氟沙星具有良好的特异识别性和优良的亲和性。与以硅胶为载体制备的印迹聚合物相比,该材料吸附容量更高和印迹效果更好。将其作为固相萃取填料对鸡产品进行分离富集,与C18柱相比,分离富集效果更好。结合UPLC,对实际样品中氧氟沙星进行分析,回收率为82.0%-96.7%,相对标准偏差低于5.5%,可用于鸡产品中氧氟沙星分离分析。     

Complexation of the triphosphate anion: tuning the structure of cyclen based macrotricycles with 1,3-dimethylbenzene and 2,6-dimethylpyridine linkers. A potentiometric and NMR study

The host-guest interaction between orthophosphate, pyrophosphate and triphosphate anions and three cyclen-based macrotricyclic ligands was investigated by potentiometric measurements and NMR spectroscopy. The ligands differ from one another by the nature of their spacers, which are 1,3-dimethylbenzene (TMC), 2,6-dimethylpyridine (TPyC) or a combination of the two (TMPyC). In aqueous solution, each ligand gave protonated species that further formed ternary complexes after binding with anions; these complexes were analyzed as a result of hydrogen bond formation and coulombic attraction between the organic host and the inorganic guest. The equilibrium constants found for all the detected species are reported and the selectivity, illustrated with species distribution diagrams, is discussed. The results unambiguously showed that the ligand possessing a single supplementary anchoring site (the pyridinyl spacer) exhibited the greatest affinity for the phosphate species in a large p[H] range.     

Bis(1,3-dithiole-2-chalcogenones) and tetrathiafulvalenes in the synthesis of bridged tetrathiafulvalene-containing structures

Bis(1,3-dithiole-2-chalcogenones) in which the 1,3-dithiole fragments are linked through various bridging groups were synthesized by different methods. Some of these compounds were converted into substituted tetrathiafulvalenes with bridged 1,3-dithiole rings. The same structures were synthesized from preliminarily prepared symmetric tetrathiafulvalenes containing 2-cyanoethylsulfanyl groups in both 1,3-dithiole rings. Similar spacers were used to bridge two tetrathiafulvalene fragments. Syntheses of the involved initial compounds were described.     

Ligand-receptor interactions in tethered polymer layers

The binding of small proteins to ligands that are attached to the free ends of polymers tethered to a planar surface is studied using a molecular theory. The effects of changing the intrinsic binding equilibrium constant of the ligand-receptor pair, the polymer surface coverage, the polymer molecular weight, and the protein size are studied. The results are also compared with the case where ligands are directly attached to the surface without a polymer acting as a spacer. We found that within the biological range of binding constants the protein adsorption is enhanced by the presence of the polymer spacers. There is always an optimal surface coverage for which ligand-receptor binding is a maximum. This maximum increases as the binding energy and/or the polymer molecular weight increase. The presence of the maximum is due to the ability of the polymer-bound proteins to form a thick layer by dispersing the ligands in space to optimize binding and minimize lateral repulsions. The fraction of bound receptors is unity for a very small surface coverage of ligands. The very sharp decrease in the fraction of bound ligand-receptor pairs with surface coverage depends on the polymer spacer chain length. We found that the binding of proteins is reduced as the size of the protein increases. The orientation of the bound proteins can be manipulated by proper choice of the grafted layer conditions. At high polymer surface coverage the bound proteins are predominantly perpendicular to the surface, while at low surface coverage there is a more random distribution of orientations. To avoid nonspecific adsorption on the surface, we studied the case where the surface is covered by a mixture of a relatively high molecular weight polymer with a ligand attached to its free end and a low molecular weight polymer without ligand. These systems present a maximum in the binding of proteins, which is of the same magnitude as when only the long polymer-ligand is present. Moreover, when the total surface coverage in the mixed layers of polymers is high enough, nonspecific adsorption of the proteins on the surface is suppressed. The use of the presented theoretical results for the design of surface modifiers with tailored abilities for specific binding of proteins and optimal nonfouling capabilities is discussed.     

Synthesis of Structurally Varied 1,3‐Disiloxanediols and Their Activity as Anion‐Binding Catalysts

A series of new 1,3‐disiloxanediols has been synthesized, including naphthyl‐substituted and unsymmetrical siloxanes, and demonstrated as a new class of anion‐binding catalysts. In the absence of anions, diffusion‐ordered spectroscopy (DOSY) displays self‐association of 1,3‐disiloxanediols through hydrogen‐bonding interactions. Binding constants determined for 1,3‐disiloxanediol catalysts indicate strong hydrogen‐bonding and anion‐binding abilities with unsymmetrical siloxanes displaying different hydrogen‐bonding abilities for each silanol group.     

A comparison study between polymeric ligand and monomeric ligand for oligopeptide adsorption

This work aimed to compare two types of affinity ligands, i.e. polymeric and monomeric ligands, by investigating their adsorption affinity, capacity and selectivity to oligopeptide. The peptide NH(2)-VVRGCTWW-COOH (VW-8) was chosen as the target adsorbate, while histidine (His), aspartic acid (Asp), and leucine (Leu) were selected as the ligands, respectively. For each kind of ligand, both monomeric (M) and polymeric (P) forms were introduced onto the Sepharose matrix respectively to obtain the corresponding adsorbents. Both affinity tests using isothermal titration calorimetry (ITC) and adsorption capacities using static adsorption experiments indicated that the adsorbents with polymeric ligands (MX-P) exhibited better adsorption ability for VW-8 than the adsorbents with monomeric ligands (MX-M). In particular, the MX-PHis exhibited its affinity constant of 2.39 × 10(6) M(-1) and its adsorption capacity of 77.4 mg/g for VW-8, which was approximately 8-10 times higher than that of MX-MHis. Such distinct adsorption abilities between polymeric and monomeric ligands were interpreted based on nuclear magnetic resonance (NMR) and ITC data, and the results indicated that such better characters of polymeric ligands were ascribed to their good flexibility which facilitated the cooperative effects as well as the accessibility of ligands to the peptide. Additionally, the selective adsorption experiments indicated that all the adsorbents with polymeric ligands exhibited good selectivity to the peptide VW-8.     

Synergetic recognition and separation of kelthane and pyridaben base on magnetic molecularly imprinted polymer nanospheres

We present novel magnetic composite nanospheres for the preparation of a nanoiron oxide/carbon dots/β‐cyclodextrin/molecularly imprinted polymer for the selective solid‐phase extraction kelthane and pyridaben from vegetables. The molecularly imprinted polymer was synthesized on the surface of nano‐iron oxide/carbon dots via a chemical polymerization procedure, where kelthane‐β‐cyclodextrin and pyridaben‐β‐cyclodextrin inclusion complexes were used as template molecules, and their adsorption behavior was investigated in detail. Characterization analysis and binding experiments revealed that magnetic composite nanospheres had outstanding magnetic properties, a large adsorption capacity, and high competitive selectivity for kelthane and pyridaben. The magnetic composite nanospheres were employed as an adsorbent in solid‐phase extraction for the determination of kelthane and pyridaben in vegetable samples. The recoveries of kelthane and pyridaben were 92.8–105.2 and 94.4–104.6%, respectively.     

Enantioselective allylic alkylation using polymer-supported palladium catalysts

Chiral 2′-(4″,5″-dihydro-2″-oxazolyl)-6′-(1-hydroxyalkyl)pyridines were grafted via ester-linkages directly to cross-linked polystyrene and to polyethyleneglycol-containing resins TentaGel and ArgoGel functionalized with carboxylic acid groups or via spacers containing a carboxylic acid group. The polymeric ligands were used in the palladium-catalyzed substitution of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate. The enantioselectivities (up to 80% ee) were similar to those observed employing an analogous monomeric catalyst.     

多胺配体及其配合物的合成与热力学性质研究

合成并表征了5个多胺配体N，N′-二(1，10-菲罗啉-2-亚甲基)-1，2-乙二胺(L1)，1，7-二(1，10-菲罗啉-2-亚甲基)-1，4，7-三氮杂庚烷(L2)，1，10-二(1，10-菲罗啉-2-亚甲基)-1，4，7，10-四氮杂癸烷(L3)，1，13-二(1，10-菲罗啉-2-亚甲基)-1，4，7，10，13-五氮杂十三烷(L4)，N，N′-二(1,10-菲罗啉-2-亚甲基)-1，3-丙二胺(L5)。利用pH电位滴定法在25.0 ± 0.1 ℃时测定了这5个配体的质子化常数及其与Co(Ⅱ)，Ni(Ⅱ)，Cu(Ⅱ)和Zn(Ⅱ)形成配合物的稳定常数，并且试图解释了这5个系列配合物的差异。     

Towards a rational spacer design for bivalent inhibition of estrogen receptor

Estrogen receptors are known drug targets that have been linked to several kinds of cancer. The structure of the estrogen receptor ligand binding domain is available and reveals a homodimeric layout. In order to improve the binding affinity of known estrogen receptor inhibitors, bivalent compounds have been developed that consist of two individual ligands linked by flexible tethers serving as spacers. So far, binding affinities of the bivalent compounds do not surpass their monovalent counterparts. In this article, we focus our attention on the molecular spacers that are used to connect the individual ligands to form bivalent compounds, and describe their thermodynamic contribution during the ligand binding process. We use computational methods to predict structural and entropic parameters of different spacer structures. We find that flexible spacers introduce a number of effects that may interfere with ligand binding and possibly can be connected to the low binding affinities that have been reported in binding assays. Based on these findings, we try to provide guidelines for the design of novel molecular spacers.     

Syntheses and structural characterization of dinuclear and tetranuclear iron(III) complexes with dinucleating ligands and their reactions with hydrogen peroxide

The iron(III) complexes [Fe(2)(HPTB)(mu-OH)(NO(3))(2)](NO(3))(2).CH(3)OH.2H(2)O (1), [Fe(2)(HPTB)(mu-OCH(3))(NO(3))(2)](NO(3))(2).4.5CH(3)OH (2), [Fe(2)(HPTB)(mu-OH)(OBz)(2)](ClO(4))(2).4.5H(2)O (3), [Fe(2)(N-EtOH-HPTB)(mu-OH)(NO(3))(2)](ClO(4))(NO(3)).3CH(3)OH.1.5H(2)O (4), [Fe(2)(5,6-Me(2)-HPTB)(mu-OH)(NO(3))(2)](ClO(4))(NO(3)).3.5CH(3)OH.C(2)H(5)OC(2)H(5).0.5H(2)O (5), and [Fe(4)(HPTB)(2)(mu-F)(2)(OH)(4)](ClO(4))(4).CH(3)CN.C(2)H(5)OC(2)H(5).H(2)O (6) were synthesized (HPTB = N,N,N',N'-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, N-EtOH-HPTB = N,N,N',N'-tetrakis(N' '-(2-hydroxoethyl)-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, 5,6-Me(2)-HPTB = N,N,N',N'-tetrakis(5,6-dimethyl-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane). The molecular structures of 2-6 were established by single-crystal X-ray crystallography. Iron(II) complexes with ligands similar to the dinucleating ligands described herein have been used previously as model compounds for the dioxygen uptake at the active sites of non-heme iron enzymes. The same metastable (mu-peroxo)diiron(III) adducts were observed during these studies. They can be prepared by adding hydrogen peroxide to the iron(III) compounds 1-6. Using stopped-flow techniques these reactions were kinetically investigated in different solvents and a mechanism was postulated.     

Preparation of a boronate-functionalized affinity hybrid monolith for specific capture of glycoproteins

A novel strategy for preparation of a boronate affinity hybrid monolith was developed using a Cu(I)-catalyzed 1,3-dipolar azide–alkyne cycloaddition (CuAAC) reaction of an alkyne–boronate ligand with an azide-functionalized monolithic intermediate. An azide-functionalized hybrid monolith was first synthesized via a single-step procedure to provide reactive sites for click chemistry; then the alkyne–boronate ligands were covalently immobilized on the azide-functionalized hybrid monolith via an in-column CuAAC reaction to form a boronate affinity hybrid monolith under mild conditions. The boronate affinity monolith was characterized and evaluated by means of elemental analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. The boronate affinity hybrid monolith exhibited excellent specificity toward nucleosides and glycoproteins, which were chosen as test cis-diol-containing compounds under neutral conditions. The binding capacity of the monolith for the glycoprotein ovalbumin was 2.36 mg?·?g^-1 at pH 7.0. The practicability of the boronate affinity hybrid monolithic material was demonstrated by specific capture of the glycoproteins ovalbumin and ovotransferrin from an egg sample.

Mechanistic Insight into Nanomolar Binding of Multivalent Neoglycopeptides to Wheat Germ Agglutinin

Multivalent carbohydrate–protein interactions are frequently involved in essential biological recognition processes. Accordingly, multivalency is often also exploited for the design of high‐affinity lectin ligands aimed at the inhibition of such processes. In a previous study (D. Schwefel et al., J. Am. Chem. Soc. 2010 , 132, 8704–8719) we identified a tetravalent cyclopeptide‐based ligand with nanomolar affinity to the model lectin wheat germ agglutinin (WGA). To unravel the structural features of this ligand required for high‐affinity binding to WGA, we synthesized a series of cyclic and linear neoglycopeptides that differ in their conformational freedom as well as the number of GlcNAc residues. Combined evidence from isothermal titration calorimetry (ITC), enzyme‐linked lectin assays (ELLA), and dynamic light scattering (DLS) revealed different binding modes of tetra‐ and divalent ligands and that conformational preorganization of the ligands by cyclization is not a prerequisite for achieving high binding affinities. The high affinities of the tetravalent ligands rather stem from their ability to form crosslinks between several WGA molecules. The results illustrate that binding affinities and mechanisms are strongly dependent on the used multivalent system which offers opportunities to tune and control binding processes.     

Design, optimization and evaluation of specific affinity adsorbent for oligopeptides

A major challenge in the development of affinity adsorbents is the design of specific adsorbents for target molecules. In this paper, a two-step strategy was used to design a specific adsorbent for oligopeptides. Based on the structural characteristics of target peptide DFLAE (DE5), the affinity ligand CDenHis bearing hydrophobic inclusion and electrostatic interaction sites was prepared by grafting histidine onto β-cyclodextrin (CD) using ethylenediamine; ligands with single hydrophobic inclusion or electrostatic interaction sites (CDen and HisOMe) were used as reference ligands. Results indicated that the binding affinity (K(a)) of CDenHis with DE5 was 6.23×10(4)M(-1), 23- and 61-fold higher than that of CDen and HisOMe, respectively. Computer simulations were used to further optimize the steric configuration of CDenHis. It was found that the optimized ligand CDdnHis exhibited a much improved binding affinity for DE5 (K(a)=1.02×10(5)M(-1)). Moreover, the corresponding adsorbent A-CDdnHis not only showed much better adsorption ability compared with A-CDenHis, but also excellent adsorption specificity for DE5-containing peptides. Kinetic analysis and adsorption mechanism studies suggested that the configuration matching of CDdnHis with DE5 and the cooperation of multiple interactions led to the fast and selective adsorption of DE5-containing peptides to A-CDdnHis.     

3-醛基-2-羟基-5-甲基苯甲酸二胺类Schiff碱配体的合成

合成了3-醛基-2-羟基-5-甲基苯甲酸,将其与乙二胺,1,2-丙二胺,1,3-丙二胺反应合成了3种Sch iff碱配体.用元素分析,IR,MS,1H NMR和13C NMR对它们进行了结构表征.     

Enhanced guest affinity and enantioselectivity through variation of the Gd3+ [15-metallacrown-5] side chain

Supramolecular hosts that bind guests reversibly are investigated for potential catalysis and separations applications. Chiral Ln(3+)[15-Metallacrown-5] metallocavitands bind carboxylate guests in hydrophobic cavities generated by their ligand side chains. A thermodynamic study on Gd(3+)[15-metallacrown-5] hosts with ligands bearing phenyl side chains containing 0, 1, and 2 methylene spacers (1-pgHA, 1-pheHA, 1-hpheHA, respectively) is presented to quantitatively assess how guest affinity and chiral selectivity can be enhanced through changes to the ligand side chain. Guest binding affinity was measured with cyclic voltammetry using ferrocene carboxylate as a redox probe. K(a) values between ferrocene carboxylate and 1-pgHA and 1-pheHA were 4800 ± 400 M(-1) and 4400 ± 700 M(-1), respectively. Significantly stronger binding affinity of 12,100 ± 700 M(-1) was measured with 1-hpheHA, a result of the longer side-chains more completely encapsulating the guest. A similar trend was observed with benzoate. The side chain also influenced enantioselectivity, as K(S)/K(R) values of up to 2.2 ± 0.6 were measured. The side chain dependent guest binding supports the development of highly selective Ln(3+)[15-Metallacrown-5] hosts for use in catalysis and separations through careful ligand design.