Reversible polymers formed from self-complementary monomers using quadruple hydrogen bonding.

Units of 2-ureido-4-pyrimidone that dimerize strongly in a self-complementary array of four cooperative hydrogen bonds were used as the associating end group in reversible self-assembling polymer systems. The unidirectional design of the binding sites prevents uncontrolled multidirectional association or gelation. Linear polymers and reversible networks were formed from monomers with two and three binding sites, respectively. The thermal and environmental control over lifetime and bond strength makes many properties, such as viscosity, chain length, and composition, tunable in a way not accessible to traditional polymers. Hence, polymer networks with thermodynamically controlled architectures can be formed, for use in, for example, coatings and hot melts, where a reversible, strongly temperature-dependent rheology is highly advantageous.

Fluorene benzothiadiazole co-oligomer based aqueous self-assembled nanoparticles.

Self-assembled π-conjugated nanoparticles with tunable optical characteristics are appealing for sensing and imaging applications due to their intrinsic fluorescence, supramolecular organization and dynamics. Here we report on the facile synthesis of fluorene benzothiadiazole co-oligomers in which structural backbone alterations induce bathochromically shifted optical characteristics. Moreover, the nature of the oligomer side-chains revealed the role of bulkiness and polarity on the optical and self-assembly behavior. Co-assemblies were prepared that showed energy transfer between the different oligomers which allows for tuning of the emission color. These compounds thus extend the π-conjugated-oligomer toolbox from which nanoparticles can be prepared with tailored physicochemical properties that may result in supramolecular materials for biosensing.

Switching from infliximab innovator to biosimilar in patients with inflammatory bowel disease: a 12-month multicentre observational prospective cohort study.

BACKGROUND: Infliximab biosimilars have become available for treatment of inflammatory bowel disease (IBD). However, data showing long-term safety and effectiveness of biosimilars in IBD patients are limited. AIM: To study prospectively the switch from infliximab innovator to biosimilar in an IBD cohort with 12 months follow-up to evaluate safety and effectiveness. METHODS: Adult IBD patients from two hospitals treated with infliximab innovator (Remicade; Janssen Biotech,  Horsham ,  Pennsylvania, USA) were switched to infliximab biosimilar (Inflectra; Hospira, Lake Forest, Illinois, USA) as part of routine care, but in a controlled setting. Blood samples were taken just before the first, second, fourth and seventh infusion of biosimilar. Infliximab trough levels, antibodies-to-infliximab (ATI), CRP and ESR were measured and disease activity scores were calculated. RESULTS: Our cohort consisted of 133 IBD patients (64% CD, 36% UC). Before switching we found widely varying infliximab levels (median 3.5 µg/mL). ATI were detected in eight patients (6%). Most patients were in remission or had mild disease (CD: 82% UC: 90%). After switching to biosimilar, 35 patients (26%) discontinued therapy within 12 months, mostly due to subjective higher disease activity (9%) and adverse events (AE, 9.8%). AE included general malaise/fatigue (n = 7), arthralgia (n = 2), skin problems (n = 2) and infusion reactions (n = 2). No differences in IFX levels, CRP, and disease activity scores were found between the four time points (P ≥ .0917). CONCLUSIONS: We found no differences in drug levels and disease activity between infliximab innovator and biosimilar in our IBD cohort, indicating that biosimilars are safe and effective. The high proportions of discontinuers were mostly due to elective withdrawal or subjective disease worsening.

Carborane-ß-cyclodextrin complexes as a supramolecular connector for bioactive surfaces.

Supramolecular chemistry provides an attractive entry to generate dynamic and well-controlled bioactive surfaces. Novel host-guest systems are urgently needed to provide a broader affinity and applicability portfolio. A synthetic strategy to carborane-peptide bioconjugates was therefore developed to provide an entry to monovalent supramolecular functionalization of ß-cyclodextrin coated surfaces. The ß-cyclodextrin·carborane-cRGD surfaces are formed efficiently and with high affinity as demonstrated by IR-RAS, WCA, and QCM-D, compare favourable to existing bio-active host-guest surface assemblies, and display an efficient bioactivity, as illustrated by a strong functional effect of the supramolecular system on the cell adhesion and spreading properties. Cells seeded on the supramolecular surface displaying bioactive peptide epitopes exhibited a more elongated morphology, focal adhesions, and stronger cell adhesion compared to control surfaces. This highlights the macroscopic functionality of the novel supramolecular immobilization strategy.

Molecular interference in antibody-antigen interaction studied with magnetic force immunoassay.

Molecular interferences are an important challenge in biotechnologies based on antibody-antigen interactions, such as sandwich immunoassays. We report how a sandwich immunoassay with magnetic particles as label can be used to probe interference by surfactants. Surfactants are often used to improve the performance of immunoassays, however the surfactants can affect the involved proteins and the mechanism of action of surfactant molecules on the antibody-antigen system is mostly unknown. As an example, we investigated molecular interference by a nonionic surfactant (Pluronic F-127) in a cardiac troponin (cTn) sandwich immunoassay with two monoclonal antibodies. The influence of the surfactant below the critical micelle concentration (0.00-0.04%) on dissociation properties was quantified in a magnetic tweezers setup, where a force is applied to the molecules via magnetic particle labels. The force-dependent dissociation curves revealed the existence of two distinct cTn-dependent bond types, namely a weak bond attributable to non-specific binding of cTn, and a strong bond attributable to the specific binding of cTn. The dissociation rate constant of the strong bonds increased with the surfactant concentration by about a factor of two. Circular dichroism spectroscopy data showed that the nonionic surfactant influences the conformation of cTn while not noticeably affecting the two monoclonal antibodies. This suggests that the surfactant-induced increase of the dissociation rate of the specific sandwich-type cTn binding may be related to a conformational change of the antigen molecule. The described methodology is an effective tool to study the influence of surfactants and other interferences on assays based on protein interactions.

Twist Sense Bias Induced by Chiral Side Chains in Helically Folded Oligomers.

Cooperative interactions among the side chains of the helically folded phenylene-ethynylene oligomer shown (n=2, 4, 6, 8, 10, 12, 14, 16, 18) can induce a twist sense bias. Therefore, the side chains can play more than just an ancillary role in these conformationally ordered oligomers. The onset of the twist sense bias lags significantly behind the appearance of helical conformations, possibly because a large ensemble of "collapsed" conformations is initially formed.

Determination of dabigatran, rivaroxaban and apixaban by ultra-performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS) and coagulation assays for therapy monitoring of novel direct oral anticoagulants.

BACKGROUND: Three novel direct oral anticoagulants (DOACs) have recently been registered by the Food and Drug Administration and European Medicines Agency Commission: dabigatran, rivaroxaban, and apixaban. To quantify DOACs in plasma, various dedicated coagulation assays have been developed. OBJECTIVE: To develop and validate a reference ultra-performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS) method and to evaluate the analytical performance of several coagulation assays for quantification of dabigatran, rivaroxaban, and apixaban. METHODS: The developed UPLC-MS/MS method was validated by determination of precision, accuracy, specificity, matrix effects, lower limits of detection, carry-over, recovery, stability, and robustness. The following coagulation assays were evaluated for accuracy and precision: laboratory-developed (LD) diluted thrombin time (dTT), Hemoclot dTT, Pefakit PiCT, ECA, Liquid anti-Xa, Biophen Heparin (LRT), and Biophen DiXal anti-Xa. Agreement between the various coagulation assays and UPLC-MS/MS was determined with random samples from patients using dabigatran or rivaroxaban. RESULTS: The UPLC-MS/MS method was shown to be accurate, precise, sensitive, stable, and robust. The dabigatran coagulation assay showing the best precision, accuracy and agreement with the UPLC-MS/MS method was the LD dTT test. For rivaroxaban, the anti-factor Xa assays were superior to the PiCT-Xa assay with regard to precision, accuracy, and agreement with the reference method. For apixaban, the Liquid anti-Xa assay was superior to the PiCT-Xa assay. CONCLUSIONS: Statistically significant differences were observed between the various coagulation assays as compared with the UPLC-MS/MS reference method. It is currently unknown whether these differences are clinically relevant. When DOACs are quantified with coagulation assays, comparison with a reference method as part of proficiency testing is therefore pivotal.

Investigational study of tamoxifen phase I metabolites using chromatographic and spectroscopic analytical techniques.

A comprehensive overview is presented of currently known phase I metabolites of tamoxifen consisting of their systematic name and molecular structure. Reference standards are utilized to elucidate the MS(n) fragmentation patterns of these metabolites using a linear ion trap mass spectrometer. UV-absorption spectra are recorded and absorption maxima are defined. Serum extracts from ten breast cancer patients receiving 40mg tamoxifen once daily were qualitatively analyzed for tamoxifen phase I metabolites using a liquid chromatography-tandem mass spectrometry set-up. In total, 19 metabolites have been identified in these serum samples. Additionally a synthetic method for the preparation of the putative metabolite 3',4'-dihydroxytamoxifen is described.

Synthesis of palmitoylated Ras-peptides and -proteins.

In this review, an overview is given and details are provided for the synthesis of lipidated Ras (rat-adeno-sarcoma)-peptides and -proteins. The progress made in the synthesis of the lipidated peptides from the Ras superfamily is discussed with special emphasis on the recently developed solid-phase synthesis methods, since these methods have turned out to be the preferred synthesis method for the majority of the required peptides. Solid-phase lipopeptide synthesis has given access to native and modified peptides on a scale that allows peptide-consuming studies like for ligation to proteins and concomitant X-ray crystal structure determination. The access to these peptides has also enabled biological questions concerning these peptides and proteins to be resolved. The review describes different solid-phase methods, which are individually suited for different types of lipopeptides, differing for example in lipidation pattern or amino acid side-chain functionality, and their ligation to proteins. Finally, an example is provided how these peptides can serve to resolve biological aspects of the Ras family GTPases.

Cooperativity in the folding of helical m-phenylene ethynylene oligomers based upon the 'sergeants-and-soldiers' principle.

The 'Sergeants-and-Soldiers' principle has been examined in a series of m-phenylene ethynylene oligomers containing both chiral and achiral side chains. Circular dichroism (CD) spectroscopy was used to examine the twist sense bias of the helical conformation in the polar solvent acetonitrile. A non-linear dependence of the CD signal on the amount of chiral side chains was observed revealing cooperative interactions among the side chains through the backbone. On the other hand, the experiments indicate that in acetonitrile a full bias of the helicity cannot be accomplished by chiral side chains alone. Nevertheless, the folded oligomers are highly ordered since the placement of a single chiral side chain at the beginning of an oligomer results in the induction of a strong twist sense bias into the ordered helical conformation.

Self-assembly of folded m-phenylene ethynylene oligomers into helical columns.

Circular dichroism spectroscopy has been used to study the self-assembly of two series of m-phenylene ethynylene oligomers in highly polar solvents. The helical conformation of shorter oligomer lengths was found to be stabilized in aqueous acetonitrile solutions, while longer oligomers began to interact intermolecularly. The intermolecular aggregation of the oligomers in aqueous solutions revealed a chain length dependent association that required the presence of a stable helical conformation. Evidence for intermolecular interactions is provided by Sergeants and Soldiers experiments in which the twist sense bias of a chiral oligomer is transferred to an achiral oligomer.

Conformational ordering of apolar, chiral m-phenylene ethynylene oligomers

A series of m-phenylene ethynylene oligomers containing nonpolar, (S)-3,7-dimethyl-1-octanoxy side chains have been synthesized and studied. In apolar alkane solvents, oligomers of sufficient length (n > 10) were found to adopt a helical conformation with a large twist sense bias. In contrast, in chloroform the oligomers adopt a random coil conformation. Surprisingly, the strong twist sense bias was determined to be highly time dependent and is partially attributed to intermolecular aggregation.

Hierarchical formation of helical supramolecular polymers via stacking of hydrogen-bonded pairs in water.

Bifunctional ureido-s-triazines provided with penta(ethylene oxide) side chains are able to self assemble in water, leading to helical columns via cooperative stacking of the hydrogen-bonded pairs (DADA array). Monofunctional ureido-s-triazines do not form such helical architectures. The presence of a linker, covalently connecting the two ureido-s-triazine units, is essential as it generates a high local concentration of aromatic units, favorable for stacking interactions. This hydrophobic stacking of the aromatic units occurs at concentrations as low as 5 x 10(-6) M and can be visualized by using fluorescence spectroscopy. The stacking generates a hydrophobic microenvironment that allows intermolecular hydrogen bonding to occur at higher concentrations because the hydrogen bonds are shielded from competitive hydrogen bonding with water. This hierarchical process results in the formation of a helical self-assembled polymer in water at concentrations above 10(-4) M. Chiral side chains attached to the ureido-s-triazine units bias the helicity of these columns as concluded from CD spectroscopy and "Sergeants and Soldiers" experiments.

Helical self-assembled polymers from cooperative stacking of hydrogen-bonded pairs.

The double helix of DNA epitomizes this molecule's ability to self-assemble in aqueous solutions into a complex chiral structure using hydrogen bonding and hydrophobic interactions. Non-covalently interacting molecules in organic solvents are used to design systems that similarly form controlled architectures. Peripheral chiral centres in assemblies and chiral side chains attached to a polymer backbone, have been shown to induce chirality at the supramolecular level, and highly ordered structures stable in water are also known. However, it remains difficult to rationally exploit non-covalent interactions for the formation of chiral assemblies that are stable in water, where solvent molecules can compete effectively for hydrogen bonds. Here we describe a general strategy for the design of functionalized monomer units and their association in either water or alkanes into non-covalently linked polymeric structures with controlled helicity and chain length. The monomers consist of bifunctionalized ureidotriazine units connected by a spacer and carrying solubilizing chains at the periphery. This design allows for dimerization through self-complementary quadruple hydrogen bonding between the units and solvophobically induced stacking of the dimers into columnar polymeric architectures, whose structure and helicity can be adjusted by tuning the nature of the solubilizing side chains.