A new photocleavable linker in solid-phase chemistry for ether cleavage

We have designed a new linker (1) for the solid-phase synthesis that cleaves ether bonds photolytically. The linker was prepared in nine steps and anchored to the support via an amide bond. Photocleavage is a two-step process in which the immobilized alcohols are released by photolytic generation of a radical that undergoes a spontaneous beta-bond scission. The pivaloyl linker (1) was found to cleave off alcohols in high yields and purities. Only traces of acid (pH approximately 5.5) are necessary for an efficient cleavage.     

MOF Decomposition and Introduction of Repairable Defects Using a Photodegradable Strut

Photoswitchable components can modulate the properties of metal organic frameworks (MOFs); however, photolabile building blocks remain underexplored. A new strut NPDAC (2-nitro-1,4-phenylenediacetic acid) that undergoes photodecarboxylation has been prepared and incorporated into a MOF, using post-synthetic linker exchange (PSLE) from the structural analogue containing PDAC (p-phenylenediacetic acid). Irradiation of NPDAC-MOF leads to MOF decomposition and concomitant formation of amorphous material. In addition to complete linker exchange, MOFs containing a mixture of PDAC and NPDAC can be obtained through partial linker exchange. In NPDAC30-MOF, which contains approximately 30 % NPDAC, the MOF retains crystallinity after irradiation, but the MOF contains defect sites consistent with loss of decarboxylated NPDAC linkers. The defect sites can be repaired by exposure to additional PDAC or NPDAC linkers at a much faster rate than the initial exchange process. The photoremoval and replacement process may lead to a more general approach to customizable MOF structures.     

Tricarboranyl pentaerythritol-based building block

A new tricarborane building block based on pentaerythritol was prepared for applications in boron neutron capture therapy (BNCT). Its X-ray single-crystal structure revealed a high degree of steric congestion. To enable the attachment of the building block to other moieties, a succinimidyl linker has been introduced at the focal point, and a generation-2 hexacarborane-containing dendron carrying 60 boron atoms has been prepared using a 2,2-bis(hydroxymethyl)propionic acid core.     

Preparation of highly selective stationary phases for high-performance liquid chromatographic separation of enantiomers by direct copolymerization of monomers with single or twin chiral ligands

Uniformly sized macroporous polymer beads, which can be used as chiral stationary phase (CSP), have been prepared by the staged templated suspension polymerization process using chiral monomer as one of the copolymerization components. This approach enables the preparation of CSPs for which properties such as pore size, pore volume, surface area, chemistry, and chiral ligands can be tuned over a broad range. Several types of well-defined chiral monomers were prepared and allowed to assess synergistic effect of multiple selectors attached to a branched linker as well as the effect of the length and chemistry of the linker. Microscale batch screening was used for simple and rapid evaluation of selectivity. The most promising candidate CSPs were prepared on a larger scale and packed into HPLC columns. Their performance was demonstrated on the separation of racemic N-(3,5-dinitrobenzoyl)-alpha-amino acid alkylamides. The highest separation factors alpha of up to 27 were observed for CSPs prepared from monomers containing the branched spacer. These highly selective CSPs also enabled the separation of larger amounts of the target racemates upon column overload conditions.     

Effect of multivalency on the performance of enantioselective separation media for chiral HPLC prepared by linking multiple selectors to a porous polymer support via aliphatic dendrons

Chiral stationary phases (CSPs) containing L-proline indananilide chiral selectors attached through a multivalent dendritic linker to monodisperse macroporous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) beads have been prepared using two different approaches. The convergent method involves the preparation of ligands in solution and their subsequent attachment to the support. The divergent approach is based on the stepwise "on-bead" formation of the linker using methods that are typical of solid-phase synthesis. While the convergent CSPs feature well-defined ligands, their loading is relatively low. In contrast, the divergent technique affords CSPs with higher loading but with more limited control over precise ligand architecture. Excellent enantioselectivities characterized by separation factors of up to 31 were achieved for the separation of racemic N-(3,5-dinitrobenzoyl)-alpha-amino acid alkyl amides with these new CSPs under normal-phase HPLC conditions.     

Versatile solid-phase synthesis of secondary amines from alcohols. Development of an N-Boc-(o-nitrobenzene)sulfonamide linker

The development of a versatile amine releasing linker based on the modified o-nitrobenzene sulfonamide protective group is described. This new N-Boc-o-nitrobenzenesulfonamide (Boc-ONBS) linker enables the elaboration on resin of primary and secondary amines by sequential substitution of the sulfonamide moiety using the Mitsunobu reaction. A 16-member array of secondary and Boc protected primary amines was then prepared using this linker.     

Preparation of molecularly imprinted polymeric fibers using a single bifunctional monomer for the solid‐phase microextraction of parabens from environmental solid samples

In this study, molecularly imprinted polymer fibers for solid‐phase microextraction have been prepared with a single bifunctional monomer, N,O‐bismethacryloyl ethanolamine using the so‐called “one monomer molecularly imprinted polymers” method, replacing the conventional combination of functional monomer and cross‐linker to form high fidelity binding sites. For comparison, imprinted fibers were prepared following the conventional approach based on ethylene glycol dimethacrylate as cross‐linker and methacrylic acid as monomer. The recognition performance of the new fibers was evaluated in the solid‐phase microextraction of parabens, and from this study it was concluded that they provided superior performance over conventionally formulated fibers. Ultimately, real‐world environmental testing on spiked solid samples was successful by the molecularly imprinted solid‐phase microextraction of samples, and the relative recoveries obtained at enrichment levels of 10 ng/g of parabens were within 78–109% for soil and 83–109% for sediments with a relative standard deviation <15% (n = 3).     

Rapid preparation of multifunctional surfaces for orthogonal ligation by microcontact chemistry

Microcontact chemistry has been applied to patterned glass and silicon substrates by successive reaction of unprotected and monoprotected heterobifunctional linkers with alkene-terminated self-assembled monolayers (SAMs) to produce bi-, tri-, and tetrafunctional surfaces. Photochemical microcontact printing of an azide thiol linker followed by immobilization of an acid thiol linker on an undecenyl-terminated SAM results in a well-defined, micropatterned surface with terminal azide, acid, and alkene groups. Biologically relevant molecules (biotin, carbohydrates) have been selectively attached to the surface by means of orthogonal ligation chemistry, and the resulting microarrays display selective binding to fluorescently labeled proteins. An orthogonally addressable, tetrafunctional surface (azide, acid, alkene, and amine) can be prepared by an additional printing step of a tert-butyloxycarbonyl (Boc)-protected alkyne amine linker on the azide structures by using the copper(I)-catalyzed azide-alkyne Huisgen cycloaddition and subsequent removal of the protective group.     

A Novel Hydrazine Linker Resin and Its Application for the Solid-Phase Synthesis of alpha-Branched Primary Amines

A novel hydrazine linker resin for solid-phase organic synthesis has been developed. Starting from Merrifield resin, the new N-butyl-N-methylpolystyrene-hydrazine linker is prepared in three steps. Polymer-supported hydrazones, readily prepared from aldehydes and the hydrazine resin, react with alkyl- and arylorganolithium reagents under 1,2-addition to the C-N double bond to afford the corresponding hydrazines. Release from solid support was achieved by reductive N-N bond cleavage using the borane-tetrahydrofuran complex. The resulting alpha-branched primary amines were protected as their amides or carbamates, respectively, and, after purification, were obtained in good overall yields and in high purity (12 examples).     

Synthesis of new peptidic glycoclusters derived from beta-alanine. Part 2: optionally modulated distance between side-chain branched points

The synthesis of an asymmetric glycocluster 1 has been achieved using two glycocluster units 12 and 13, prepared by coupling the cluster chain unit 4 with each omega-amino acid (beta-alanine and 6-aminocapronic acid) trichloroethyl ester, and peptidic C-terminal block glycocluster 16, prepared by coupling the bifunctional linker 14 with sugar unit 9. This method facilitated the synthesis of the cluster optionally modulated the distance between the side-chain branched points by using various omega-amino acids. We also synthesized glycodendron 2 using the same intermediate.     

Evaluation of a new linker system cleaved using samarium(II) iodide. Application in the solid phase synthesis of carbonyl compounds

A new linker design for solid phase synthesis has been developed that is cleaved under mild, neutral conditions using samarium(II) iodide. The feasibility of the linker approach has been illustrated in the solid phase synthesis of ketones and amides using an oxygen linker. Insights into the mechanism of the samarium(II) iodide cleavage reaction are described and the potential of a sequential cleavage carbon-carbon bond forming process is assessed.     

利用水相合成的CdTe纳米晶构建超晶格结构研究--纳米晶聚集体的调控

用巯基丙酸作稳定剂,在水溶液中制备了CdTe纳米晶.通过加入Cd2+、聚丙烯酸(PAA)以及长期放置分别得到了CdTe纳米晶的聚集体,改变Cd2+浓度或PAA加入量可以调控聚集体的尺寸.过量的Cd2+加速了聚集体的形成,通过与纳米晶表面羧酸根的静电相互作用,Cd2+成为连接不同CdTe纳米晶的“桥梁”.PAA链上大量的羧基与CdTe纳米晶有较强的配位相互作用,可以诱导纳米晶聚集.新制CdTe纳米晶在长期放置时,表面的羧基与Cd2+的相互作用导致纳米晶逐渐聚集.在聚集过程中纳米晶表面结构得到改善,并引起荧光增强.这些结果表明通过控制各种聚集条件,可以得到不同尺寸的聚集体.     

Preparation and characterization of a novel molecularly imprinted polymer for the separation of glycyrrhizic acid

Molecularly imprinted polymers of glycyrrhizic acid were prepared by solution polymerization using glycyrrhizic acid as the template molecule, N‐vinypyrrolidone as functional monomer, N ,N‐methylene bisacrylamide as cross‐linker and ascorbic acid and hydrogen peroxide as initiators. Focused on the adsorption capacity and separation degree of the polymer to glycyrrhizic acid, the effects of the monomers, crosslinker and initiators were investigated and optimized. Finally, the structure of the polymer was characterized by using Fourier transform infrared spectroscopy and scanning electron microscopy. To obtain objective results, non‐imprinted molecular polymers prepared under the same conditions were also characterized. The adsorption quantity of the polymer was measured by high‐performance liquid chromatography. Under the optimum conditions, the maximum adsorption capacity of glycyrrhizic acid approached 15 mg/g, and the separation degree was as high as 2.5. The adsorption kinetics could be well described by a pseudo‐first‐order model, while the thermodynamics of the adsorption process could be described by the Langmuir model.     

Preparative manipulation of gold nanoparticles by reversible binding to a polymeric solid support

A preparative scheme is presented for controlled modification of gold nanoparticles (NPs) by using reversible binding to a polymeric solid support through boronic acid chemistry. Octanethiol-capped Au NPs were bound to a boronic acid functionalized resin by custom-synthesized bifunctional linker molecules. The NPs were chemically released from the resin to the solution, with one (or a few) linker molecules embedded in their capping layer. This was confirmed by rebinding the linker-derivatized NPs to a boronic resin, exploiting the reversibility of the boronic acid/diol chemistry. The same scheme was employed to demonstrate a new method for affinity separation of NPs by means of a solid-phase reaction. The use of boronic acid provides versatility and chemical reversibility, while the polymeric solid support affords the separation and preparative aspects. The method presented here may be useful in various facets of NP handling, manipulation, and separation.     

A new water soluble 3,6,9-trioxaundecanedioic acid-based linker and biotinylating reagent

Biotinylated peptides often have low solubility in water. In this Letter, we describe a new method to synthesize a biotinylating reagent for water-solubilizing hydrophobic peptides. The biotinyl-6-aminohexanoic derivatives prepared contain a hydrophilic 3,6,9-trioxaundecanedioic acid linker moiety between the biotin and the peptide to improve the water solubility, and also to function as a spacer. The monoesterified derivative of 3,6,9-trioxaundecanedioic acid was synthesized, and the Fmoc-protected ethylenediamine was used to link to the carboxylic group of biotin. The hydrophilic nature of this new biotin-peptide conjugate was also demonstrated in a comparative analysis of compounds containing a biotinyl-6-aminohexanoic acid or 3,6,9-trioxaundecanedioic acid derivative.     

Synthesis and DNA binding properties of iminodiacetic acid-linked polyamides: characterization of cooperative extended 2:1 side-by-side parallel binding

A series of iminodiacetic acid (IDA)-linked polyamides (DpPyPyPy-IDA-PyPyPyDp) were prepared and constitute polyamides joined head-to-head by a functionalizable five-atom linker. It was found that the IDA linker exerts a unique influence over the DNA binding conformation differing from both the beta-alanine (extended) or gamma-aminobutyric acid (hairpin) linkers, resulting in cooperative parallel side-by-side 2:1 binding in an extended conformation most likely with a staggered versus stacked alignment. A generalized variant of a fluorescent intercalator displacement (FID) assay conducted on a series of hairpin deoxyoligonucleotides containing a systematically varied A/T-rich binding-site size was used to distinguish between the binding modes of the IDA-linked polyamides.     

Electrochemical Sensor for Oxidation of NO Based on Au-Pt Nanoparticles Self-assembly Film

Au-Pt bimetallic nanoparticles film used as an efficient electrochemical sensor was prepared by self-assembled Au-Pt bimetallic nanoparticles on a glassy carbon (GC) substrate using thioglycolic acid as a linker. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) showed that the Au-Pt nanoparticles self-assembly film was dense and uniform. Electrochemical experiments revealed that Au-Pt bimetallic nanoparticles film/GC electrode showed high electrocatalytic activity to the oxidation of nitric oxide.     

A new glycosylation method. Part 2: Study of carbohydrate elongation onto the gold nanoparticles in a colloidal phase

A new reaction for carbohydrate elongation for synthesis of oligosaccharide using gold colloidal nanoparticles (GCNPs) has been developed. The gold core in this colloidal phase synthesis was prepared by a reduction of tetrachloroauric acid with 30,31-dithia-3,6,9,12,15,18,43,46,49,52,55,58-dodecaoxa-1,60-hexacontanediol. The presented alkanethionyl oligomeric ethylene glycol worked as a stabilizer of GCNPs and as a linker in chemical elongations of carbohydrates. This colloidal phase synthesis has several advantages such as (1) remnants of reagents and glycosyl donors in each reaction could be easily removed by ultrafiltration or gel filtration column chromatography, (2) further purifications are not required, and (3) the reactions can be monitored by MALDI-TOF MS directly without any pretreatment. In fact, we have successfully synthesized lactose derivative on GCNPs and will report these results in this paper.     

Preparation and application of nanocatalysts via surface functionalization of mesoporous materials

Surface immobilization of active species onto mesoporous materials is gaining importance, especially in the design of functionalized mesoporous materials as a nanocatalyst through heterogenization of homogeneous catalytic systems. This article summarizes recent work on the synthesis, characterization and catalytic performance of the functionalized mesoporous catalysts performed by the present authors. A cationic rhenium(I) complex was encapsulated into mesoporous Al-MCM-41 molecular sieve using a ion-exchange method, yielding a new photocatalyst to be active for photocatalytic reduction of CO₂. Surface functionalization of mesoporous silica SBA-15 with sulfonic acid groups was investigated to give a solid acid catalyst. The chemically modified Fe-containing mesoporous materials, which are active for hydroxylation of phenol, were prepared by a surface-grafting method that iron salts are immobilized onto mesoporous Si-MCM-41 with the help of 3-aminopropyltrimethoxysilane as a linker. A cobalt(III) complex was heterogenized onto mesoporous silica SBA-15 containing carboxylic groups in order to utilize as a solid catalyst for the liquid-phase oxidation of aromatic hydrocarbons.     

Sequentially photocleavable protecting groups in solid-phase synthesis

[reaction: see text] A sequential solid-phase peptide synthesis was developed using both photolabile linker and protecting groups. The chromatic sequential lability between a tert-butyl ketone-derived linker (sensitive to irradiation at 305 nm) and a nitroveratryloxycarbonyl (NVOC) group (sensitive at 360 nm) was exploited to prepare Leu-Enkephalin in a 55% overall yield. This new strategy allows the preparation of peptides in essentially neutral medium, by avoiding the use of common deprotection reagents such as trifluoroacetic acid or piperidine.