Linker Molecules Research Articles

Synthesis and Exfoliation of a New Layered Mesoporous Zr-MOF Comprising Hexa- and Dodecanuclear Clusters as Well as a Small Organic Linker Molecule.

A new layered mesoporous Zr-MOF of composition [Zr30O20(OH)26(OAc)18L18] was synthesized by employing 5-acetamidoisophthalic acid (H2L) using acetic acid as the solvent. The new MOF, denoted as CAU-45, exhibits a honeycomb structure of stacked layers which comprise both hexa- and dodecanucelar zirconium clusters. Its structure was solved from submicrometer-sized crystals by continuous rotation electron diffraction (cRED). Liquid phase exfoliation and size selection were successfully performed on the material.

Stereoselective Oxidative Bioconjugation of Amino Acids and Oligopeptides to Aldehydes

AbstractThe first stereoselective, near‐equimolar, and metal‐free oxidative bioconjugation of amino acids and oligopeptides to aldehydes is presented. Based on a newly developed organocatalytic oxidative concept, the C‐terminal and side‐chain carboxylic acid functionalities of amino acids and oligopeptides are shown to couple in a stereoselective manner to α‐branched aldehydes catalyzed by a chiral primary amine and a quinone as oxidizing agent. The oxidative coupling generally proceeds in high yield. For aspartic acid, selective coupling of the side‐chain, or the C‐terminal carboxylic acid, is demonstrated depending on the protection strategy. The stereoselective, oxidative bioconjugation concept is extended to a series of oligopeptides where coupling to carboxylic acid functionalities is presented. Bioorthogonal linker molecules for further functionalization are obtained by merging the oxidative coupling strategy with the click concept. It is demonstrated that the configuration of the new stereocenter is determined exclusively by the organocatalyst.

Stereoselective Oxidative Bioconjugation of Amino Acids and Oligopeptides to Aldehydes.

The first stereoselective, near-equimolar, and metal-free oxidative bioconjugation of amino acids and oligopeptides to aldehydes is presented. Based on a newly developed organocatalytic oxidative concept, the C-terminal and side-chain carboxylic acid functionalities of amino acids and oligopeptides are shown to couple in a stereoselective manner to α-branched aldehydes catalyzed by a chiral primary amine and a quinone as oxidizing agent. The oxidative coupling generally proceeds in high yield. For aspartic acid, selective coupling of the side-chain, or the C-terminal carboxylic acid, is demonstrated depending on the protection strategy. The stereoselective, oxidative bioconjugation concept is extended to a series of oligopeptides where coupling to carboxylic acid functionalities is presented. Bioorthogonal linker molecules for further functionalization are obtained by merging the oxidative coupling strategy with the click concept. It is demonstrated that the configuration of the new stereocenter is determined exclusively by the organocatalyst.

Extending the photobleaching lifetime in the presence of an optical tweezers by wavefront engineering

Here we lay the foundations for a novel approach to simultaneously performing optical force spectroscopy and single-molecule fluorescence measurements by adapting techniques from wavefront engineering. Our method relies upon the axial displacement (i.e. along the direction of propagation of the trap laser) of an appropriately constructed Laguerre-Gaussian (LG), or ‘donut’ beam, to generate an optical force on a surface tethered microsphere. With this geometry, one maintains a region of near-infrared (IR) light below the microsphere, where a biomolecule of interest can be placed, that is low enough in intensity to not significantly interfere with fluorescence measurements. We are thus able to separate the fluorescence illumination from the trap light without having to physically separate the two by several micrometers, or employ long DNA linker molecules as handles. As a proof of principal, we show that within the region of low IR intensity, directly below the trap center, the photobleaching lifetime of the organic dye Alexa-647, which is highly sensitive to the intense trap light, is significantly extended.

Abstract 6242: Development of alphalex™-toxin low pH targeting conjugates for the treatment of solid tumors

Abstract Maytansines and their derived maytansinoid DMx compounds are high potency microtubule targeting compounds that have an extremely narrow therapeutic window. Unacceptable dose limiting systemic toxicity has limited the therapeutic potential of these potent anti-oncogenic compounds. Targeting maytansinoids to the tumor is the only feasible method of unlocking the clinical potential of such toxic molecules. To date Trastuzumab-DM1 (Kadcyla®) remains the only approved antibody-maytansinoid conjugate on the market. Most preclinical maytansinoid conjugates to date face the same issues encountered by Kadcyla® - tumor restriction by target antigen and the potential for off target release of payload. alphalexTM is a tumor targeting technology consisting of a unique variant of pH-Low Insertion Peptide (pHLIP®; references 1-3), cleavable small molecule linker and anti-cancer agent warhead. alphalexTM thereby allows for antigen independent targeting of the tumor and enables intracellular delivery of the warhead by leveraging the low pH microenvironment of the tumor, a universal feature common to all tumors due to the Warburg effect. Here we demonstrate the ability to conjugate the maytansinoids DM1 and DM4 to alphalexTM via both direct and linker-mediated conjugation. We have demonstrated the ability of our alphalexTM-DM4 conjugate candidates (CBX-13) to have single digit nanomolar potency in vitro as well as exquisitely potent and long-lasting anti-tumor activity in a HER2-negative xenograft model that is un-targetable by competing therapies. In particular we have demonstrated that CBX-13 safely delivers amounts of maytansinoid in vivo that otherwise result in systemic toxicity and death when dosed as free warhead. Based on the SAR of this first generation of maytansinoid conjugates we are further optimizing our alphalexTM - maytansinoid conjugation strategy with the goal of moving forward with IND-enabling studies in the near future.

Photoresponsive Photoacid-Macroion Nano-Assemblies.

In this study, light-responsive nano-assemblies with light-switchable size based on photoacids are presented. Anionic disulfonated napthol derivates and cationic dendrimer macroions are used as building blocks for electrostatic self-assembly. Nanoparticles are already formed under the exclusion of light as a result of electrostatic interactions. Upon photoexcitation, an excited-state dissociation of the photoacidic hydroxyl group takes place, which leads to a more highly charged linker molecule and, subsequently, to a change in size and structure of the nano-assemblies. The effects of the charge ratio and the concentration on the stability have been examined with absorption spectroscopy and ζ-potential measurements. The influence of the chemical structure of three isomeric photoacids on the size and shape of the nanoscale aggregates has been studied by dynamic light scattering and atomic force microscopy, revealing a direct correlation of the strength of the photoacid with the changes of the assemblies upon irradiation.

Ionic Liquids Grafted Cellulose Nanocrystals for High-Strength and Toughness PVA Nanocomposite.

The surface functionalization of cellulose nanocrystals (CNCs) is of significant importance for promoting its diverse applications. However, the efficient strategy reported so far for cation functionalization of CNCs remains limited owing to the electrostatic attraction between cationic modifiers and electronegative CNCs. Herein, a cationized CNC (CNC-LA-IL) has been successfully prepared in aqueous media by grafting the [VBIm][BF4], a kind of ionic liquid (IL), on the surface of a sulfated CNC using lactic acid (LA) as a linker molecule. This surface functionalization not only converts the negative charge of CNC suspensions to a positive charge (zeta potential reversed from -35 to +40 mV) but also leads to enhanced thermal stability and redispersibility of the dried CNC. To examine the reinforcing effect of IL-modified CNCs, poly(vinyl alcohol) (PVA)/CNC-LA-IL nanocomposite films were further prepared by the solution casting method. To one's surprise, the as-prepared PVA/CNC-LA-IL films exhibit extraordinary improvement in both the tensile strength (92%) and the toughness (166%) with only a 0.3 wt % CNC loading. This study provides a green and facile method to achieve ionic liquids grafted CNCs for high-performance nanocomposites.

Capture and Release of Protein–Nanoparticle Conjugates by Reversible Covalent Molecular Linkers

A hybrid approach to covalently detachable molecules for nanoparticle capture and release from several custom-functionalized surfaces is described. This new surface chemistry capability provides a means for reversible binding of functionalized nanoparticles without relying on costly nucleic acid-based complexation. A new surface linker motif was devised wherein custom molecules were synthesized with components for surface anchoring, cleavage, and target capture through biotin-streptavidin binding. All capture-and-release chemistry is performed using physiological conditions (aqueous, pH 7). Covalent cleavage of linker molecules was achieved through incorporation of a tunable orthogonal reversible covalent (TORC) hydrazone functional group which underwent exchange with a competitive hydrazide aided by an aniline catalyst. The influence of the linker architecture on hydrazone exchange and nanoparticle release was probed by altering the distance between hydrazone and biotin groups using different length PEG spacers. Cleavable linkers were used to functionalize microwells, magnetic separation beads, and gold-coated glass surfaces. Upon functionalization, all surface types bound streptavidin and conjugated nanoparticles regardless of the linker structure. Conversely, the extent of hydrazone exchange as well as release of nanoparticles were influenced both by the hydrazone surface density and the linker molecular structure.

Quantitative analysis of global 5-methyl- and 5-hydroxymethylcytosine in TET1 expressed HEK293T cells

DNA methylation at the 5-position of cytosine bases (5-methylcytosine, 5mC) in genomic DNA is representative epigenetic modification and is involved in many cellular processes, including gene expression and embryonic development. The hydroxylation of 5mC provide 5-hydroxymethylcytosine (5hmC), the so-called sixth base rediscovered recently in mammalian cells, is also considered to act as an epigenetic regulator. We report herein the immunochemical assessment of 5hmC achieved by an enzyme-linked immunosorbent assay (ELISA) using our linker technology. The keys to this assay are 1) the immobilization of genomic DNA with the bifunctional linker molecule, and 2) quantitative analysis by using guaranteed standard samples containing defined amounts of 5hmC. We succeeded in the sensitive and quantitative detection of 5hmC as well as 5mC in HEK293T cells transfected with TET1, and also monitored the effect of ascorbate on the TET1 catalyzed conversion of 5mC to 5hmC. Our linker technology enables the rapid and stable immobilization of genomic samples and thus contributes to the realization of a reproducible 5hmC evaluation method.

Trastuzumab-deruxtecan: an investigational agent for the treatment of HER2-positive breast cancer

ABSTRACT Introduction The prognosis of patients with HER2-positive breast cancer was dramatically changed by the introduction of targeted therapies. With trastuzumab, pertuzumab, and T-DM1 widely used as (neo)adjuvant therapy today, novel treatment options are required to optimize treatment of HER2-positive metastatic disease. Trastuzumab-deruxtecan is an antibody-drug conjugate (ADC) consisting of a monoclonal humanized immunoglobulin G1 antibody, a linker molecule, and the exatecan derivative DXd. T-DXd has a higher drug to antibody ratio compared with T-DM1; in addition, membrane permeability of DXd is high, resulting in an increased bystander effect. Results from early clinical development suggest a clinically relevant activity of T-DXd in heavily pretreated patients with HER2-positive metastatic breast cancer progressing on T-DM1. Interstitial lung disease was a side-effect requiring special attention and was observed in approximately 13% of patients. Areas covered This article reviews preclinical and clinical data on T-DXd. A systematic literature search was performed to identify relevant publications. The search included original research articles, abstracts from major conferences, and reviews and was limited to English-language publications. Expert opinion T-DXd is an efficacious and tolerable drug and harbors promise as a key addition to the therapeutic field in HER2-positive breast cancer.

New Scandium‐containing Coordination Polymers with Linear Linker Molecules: Crystal Structures and Luminescence Properties

Two new scandium‐containing coordination polymers, with the formulae {(CH3)2NH2}[Sc(BPDC)2] (1) and [Sc(OH) (BPyDC)] (2) were solvothermally synthesized by using the linear linker molecules biphenyl‐4,4'‐dicarboxylic acid (H2BPDC) and 2,2'‐bipyridine‐5,5'‐dicarboxylic acid (H2BPyDC). Crystal structures were determined from single‐crystal and powder X‐ray diffraction data, respectively. The crystal structures of 1 and 2 contain isolated ScO6 or chains of trans corner‐sharing ScO6 octahedra as the inorganic building unit (IBU), which are connected by the linker molecules to a 3D framework or a layered structure, respectively. The compounds were characterized by IR‐spectroscopy, elemental analysis, thermogravimetric analysis and photoluminescence spectroscopy. 1 shows blue emission at 400 nm, while 2 exhibits intense green emission at 550 nm with a high quantum yield (QY) of 69 %.

Internal magnetic driven self-assembly of gold-nickel nanowires as SERS substrate for thiram fungicide detection using handheld Raman spectrometer

Designing three-dimensional (3D) arrays of metal nanomaterials without linker molecules is challenging for the fabrication of high-performance surface-enhanced Raman scattering (SERS) substrates. In this study, self-assembly of bi-segmented gold-nickel nanowires (Au-Ni NWs) solely driven by internal magnetic coupling of Ni tips was developed for fabrication of SERS substrates. Au-Ni NWs were fabricated using template-based electrodeposition technique. The variation of Au-Ni NWs arrangement was strongly influenced by aspect ratios of Ni segment. SERS intensity and Raman mapping measurements of 4-mercaptobenzoic acid (4-MBA) coated Au-Ni NWs were performed to evaluate analytical enhancement factor (EF) and hotspot location. The tip-to-tip Au-Ni NWs orientation so-called hybrid structure between firecracker and star arrangements gave the strongest EF about 106 and the largest SERS hotspot regions. These developed Au-Ni NWs arrayed on silicon wafers were used as SERS substrates for a demonstration of thiram detection. The linear response was in the range of 100 to 800 ppb with about 29.7 ppb limit of detection. As a proof of concept, a study for feasibility test of thiram contaminated watermelon seed detection was evaluated using handheld Raman spectrometer. This sensing platform could be used for on-site rapid detection of fungicide residual in biological samples.

Polymorphous Indium Metal-Organic Frameworks Based on a Ferrocene Linker: Redox Activity, Porosity, and Structural Diversity.

The metallocene-based linker molecule 1,1'-ferrocenedicarboxylic acid (H2FcDC) was used to synthesize four different polymorphs of composition [In(OH)(FeC12H8O4)]. Using conventional solvent-based synthesis methods and varying the synthetic parameters such as metal source, reaction temperature, and solvent, two different MOFs and one 1D-coordination polymer denoted as CAU-43 (1), In-MIL-53-FcDC_a (2), and In-FcDC (3) were obtained. Furthermore, thermal treatment of CAU-43 (1) at 190 °C under vacuum yielded a new polymorph of 2, In-MIL-53-FcDC_b (4). Both MOFs 2 and 4 crystallize in a MIL-53 type structure, but in different space groups C2/m for 2 and P1̅ for 4. The structures of the four title compounds were determined by single-crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD), or a combination of three-dimensional electron diffraction measurements (3D ED) and PXRD. N2 sorption experiments of 1, 2, and 4 showed specific surface areas of 355 m2 g-1, 110 m2 g-1, and 140 m2 g-1, respectively. Furthermore, the electronic properties of the title compounds were characterized via Mössbauer and EPR spectroscopy. All Mössbauer spectra showed the characteristic doublet, proving the persistence of the ferrocene moiety. In the cases of 1, 3, and 4, appreciable impurities of ferrocenium ions could be detected by electron paramagnetic resonance spectroscopy. Cyclovoltammetric experiments were performed to demonstrate the accessible redox activity of the linker molecule of the title compounds. A redox process of FcDC2- with oxidation (between 0.86 and 0.97 V) and reduction wave (between 0.69 and 0.80 V) was observed.

Graphene-Based Biosensor for Early Detection of Iron Deficiency.

Iron deficiency (ID) is the most prevalent and severe nutritional disorder globally and is the leading cause of iron deficiency anemia (IDA). IDA often progresses subtly symptomatic in children, whereas prolonged deficiency may permanently impair development. Early detection and frequent screening are, therefore, essential to avoid the consequences of IDA. In order to reduce the production cost and complexities involved in building advanced ID sensors, the devices were fabricated using a home-built patterning procedure that was developed and used for this work instead of lithography, which allows for fast prototyping of dimensions. In this article, we report the development of graphene-based field-effect transistors (GFETs) functionalized with anti-ferritin antibodies through a linker molecule (1-pyrenebutanoic acid, succinimidyl ester), to facilitate specific conjugation with ferritin antigen. The resulting biosensors feature an unprecedented ferritin detection limit of 10 fM, indicating a tremendous potential for non-invasive (e.g., saliva) ferritin detection.

A Finite Element Method for a Fourth Order Surface Equation With Application to the Onset of Cell Blebbing

A variational problem for a fourth order parabolic surface partial differential equation is discussed. It contains nonlinear lower order terms, on which we only make abstract assumptions, and which need to be defined for specified problems. We derive a semi-discrete scheme based on the surface finite element method, show a-priori error estimates, and use the analytical results to prove well-posedness. Furthermore, we present a computational framework where specific problems can be conveniently implemented and, later on, altered with relative ease. It uses a domain specific language implemented in Python. The high level program control can also be done within the Python scripting environment. The computationally expensive step of evolving the solution over time is carried out by binding to an efficient C++ software back-end. The study is motivated by cell blebbing, which can be instrumental for cell migration. Starting with a force balance for the cell membrane, we derive a continuum model for some mechanical and geometrical aspects of the onset of blebbing in a form that fits into the abstract framework. It is flexible in that it allows for amending force contributions related to membrane tension or the presence of linker molecules between membrane and cell cortex. Cell membrane geometries given in terms of a parametrisation or obtained from image data can be accounted for by the software. The use of a domain specific language to describe the model makes is straightforward to add additional effects such as reaction-diffusion equations modelling some biochemistry on the cell membrane. Some numerical simulations illustrate the approach.

Silver Double Nanorings with Circular Hot Zone.

Silver double nanorings with circular intra-nanogaps between two nanorings of different diameters were synthesized without a linker molecule to confine an incident electromagnetic field in a single entity. We used on-demand, rational, and systematic multi-stepwise reactions consisting of (1) selective etching of gold, (2) rim-on deposition of platinum, (3) eccentric growth of gold, and (4) concentric growth of silver. The resulting silver double nanorings exhibited a high degree of homogeneity in both shape and size, with strongly coupled circular hot zones (or "hot halos", referring to the circular intra-nanogaps capable of focusing the near electromagnetic field) resulting from strong surface plasmon coupling between the inner and outer nanorings. Remarkably, these silver double nanorings exhibited strong, stable, and reproducible single-particle surface-enhanced Raman scattering signals without blinking. The signals appeared independently of polarization directions, which is a unique feature of a circular hot halo. The estimated enhancement factor was between 2 × 108 and 7 × 108. The measured limit of detection was 10-7 M in bulk concentration, and the signal appeared 570 s after sample exposure.

Scandium Metal–Organic Frameworks Containing Tetracarboxylate Linker Molecules: Synthesis, Structural Relationships, and Properties

Three structurally related metal–organic frameworks (MOFs) of composition [Sc2(OH)2(L)] denoted Sc-CAU-9-PTCDA, Sc-CAU-9-TCPB, and Sc-CAU-9-H2TCPP containing the tetratopic linker molecules L14– = PTCDA4– (perylene-3,4,9,10-tetracarboxylate), L24– = TCPB4– (1,2,4,5-tetrakis(4-carboxylatophenyl)-benzene), or L34– = H2TCPP4– (meso-tetra(4-carboxylatophenyl)-porphyrin), have been obtained from solvothermal syntheses. The crystal structures were determined from powder X-ray diffraction data. The title compounds contain chains of trans corner-sharing [ScO6] octahedra, connected by the linker molecules to form three-dimensional networks. Depending on the shape of the respective linker the compounds crystallize in a frz or fry topology and with increasing size of the linker, an expansion of the framework and the formation of accessible channels are observed. The compounds were thoroughly characterized and exhibit high thermal stabilities up to 500 °C. Sc-CAU-9-TCPB and Sc-CAU-9-H2TCPP possess permanent porosity toward nitrogen with specific surface areas of asBET = 1350 m2/g and 650 m2/g, respectively. Luminescence measurements revealed a ligand-based emission in the blue spectral region for Sc-CAU-9-TCPB.

Electrochemical Reduction-Assisted In Situ Fabrication of a Graphene/Au Nanoparticles@polyoxometalate Nanohybrid Film: High-Performance Electrochemical Detection for Uric Acid.

Nanohybrid films had attracted much attention owning to the enhancement of catalytic activity. However, the fabrication time took hours to days, no matter if it was the preparation of nanohybrids or the assembly process. Furthermore, the catalytic efficiency of the nanohybrid film still remained to improve. In this paper, a reduced graphene oxide (rGO)/gold nanoparticles (Au NPs)@polyoxometalate (POM) nanohybrid film was successfully fabricated by combining electrodeposition and electrochemical reduction in situ processes. The assembly process involving no organic or polymer linker molecules [except for a precursor poly(ethylenimine) (PEI) coating for indium tin oxide (ITO)] can be completed within 1 h. The reduced POM K6[P2W18O62]·19H2O (P2W18) was employed as reducing agents and bridging molecules for rGO and Au nanoparticles and the encapsulating molecules for the Au nanoparticles. The most interesting one is the {rGO/Au@P2W18} modified electrode loading only the monolayer catalyst of Au@P2W18 and exhibiting comparable, even better electrochemical detection performance toward uric acid than other sensors with three to eight layers of the catalyst. The amperometric detection displayed a great sensitivity, lower detection limit, wide linear range, good long-time stability, superior selectivity, and reproducibility. The enhanced catalytic property may attribute to the improved conductivity of the film without organic or polymer linker molecules (except for a precursor PEI coating) and the electron transfer in the process of film fabrication.

Polyfluorinated hydroxy and carboxy benzenes as a new type of H-donors for self-assembly with 18-crown-6 ether: Synthesis, supramolecular structure and stability of co-crystals

Potential of polyfluoroaromatic compounds containing OH, COOH, and mixed H-donor functions as co-formers in co-crystallization with 18-crown-6 ether was explored. Pentafluorophenol, 1,3- and 1,4-dihydroxytetrafluorobenzenes and pentafluorobenzoic acid form with 18-crown-6 hydrated co-crystals containing one water molecule per H-donor group upon contact of the solutions with atmospheric moisture; pentafluorophenol gives a co-crystal with double the amount of water in aqueous EtOH. Aminotetrafluorobenzyl alcohol and aminotetrafluorobenzoic acid are capable of forming anhydrous 1:1 and 2:1 co-crystals with 18-crown-6. In the crystalline hydrates, co-formers molecules are connected via water-mediated synthon [C(O)]OH⋯O(H)H⋯Ocr. According to quantum chemical calculations, the participation of each water linker molecule in H-bonding increases the stability of the supramolecular structure by about 100 kJ mol−1. Associates of bifunctional arenes exhibit H-bonded 1D assembly as an only structure-determining motif; molecules of monofunctional arenes in the co-crystals are bound via πF⋯πF stacking to give the H-bonded/π-stacked 1D assembly. The calculated π-stacking energy depends on the nature of the H-donor function (NH2, OH, COOH), decreasing with a decrease in the molecule dipole moment.

Application of corn zein as an anchoring molecule in a carbon nanotube enhanced electrochemical sensor for the detection of gliadin

This research focused on the fabrication of an electrochemical sensor capable of detecting the protein ‘gliadin’, which is responsible for serious autoimmune disorder causing chronic diarrhea, fatigue, weight loss and anemia in people having celiac disease. The fabrication process involves the replacement of toxic synthetic chemicals that are used for anchoring of the capture antibody in the working electrode, by the natural polymer zein coupled with several nanoparticles including, carbon nanotubes, graphene oxide and Laponite®. Novel biodegradable coatings made from zein nanocomposites: zein-graphene oxide (Z-GO), zein-Laponite® (Z-LAP) and zein-multiwalled carbon nanotubes (Z-CNT) using drop casting nanocomposite technique were tested for fabricating the electrochemical sensors using cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS). Pristine zein coated electrode did not generate any oxidation/reduction peaks in the cyclic voltammograms and showed high degree of impedance in the EIS curves. While addition of the three nanoparticles (CNT, LAP, GO) considerably improved the electrical signal, Z-CNT gave the highest and strongest signals compared to other nanomaterials. The active tip of the electrochemical sensor was functionalized through a sequence of layer by layer deposition of Z-CNT nanocomposite, and other linker molecules, where Z-CNT acts as a natural linker molecule with large number of functional groups that offers immobilization of capture antibody and target and ensures high performance. Both CV curves and SWV curves indicated successful sequential immobilization of gliadin antibody onto the Z-CNT coated electrode. The Z-CNT biosensor was successfully able to give CV signals for gliadin allergens for as low as 0.5 ppm, and was highly selective for gliadin, when tested against other food toxins like acrylamide and formamide, and the Z-CNT nanocomposite remained stable over a 30-day period.