Molecular Design, Synthetic Strategies, and Applications of Cationic Polythiophenes.

This review delves into the synthesis of cationic-functionalized oligothiophenes and polythiophenes, their properties, and their diverse applications from the year 2002 to 2019. Pristine polythiophene chains are hydrophobic and are not easily converted into a form that is useful for broad applications or for device fabrications. Functional modification of the polymer side chain especially with cationic pendant groups imparts favorable properties to the system, such as solubility in aqueous medium and affinity with anions and negatively charged species, alongside the extensive π conjugation that provides unique optoelectronic characteristics. This review provides a detailed account of the design and the different synthetic strategies to access cationic polythiophenes (CPTs) via chemical oxidation using iron(III) chloride (FeCl3), via metal catalyzed and initiated polymerization, and via postpolymerization functionalization approaches. CPTs have been traditionally used in sensing and as a component in optoelectronic devices; the utility of these systems has been extended to biomedical applications, such as nonviral gene delivery, cell targeting and imaging, anticancer, antifungal, and bactericidal actions, and biofilm formation, and to use as a molecular probe. A summary and outlook are also presented, discussing the remaining challenges and the future direction for this field.

Room temperature synthesis and binding studies of solution-processable histamine-imprinted microspheres.

Accurate quantification of histamine levels in food and in biological samples is important for monitoring the quality of food products and for the detection of pathophysiological conditions. In this study, solution processable histamine-imprinted microspheres were synthesized at 30°C via dilute free radical phototochemical polymerization technique using ethylene glycol dimethacrylate (EGDMA) as the crosslinker and methacrylic acid (MAA) as the monomer. The processability of the resulting polymer is dictated by the monomer feed concentration (eg, 4 wt% 80:20 EGDMA:MAA formulation) and solvent (acetonitrile). Whereas, the particle size is influenced by the monomer feed concentration, the presence of template molecule, and independent of the crosslinker content. Evaluation of the binding performance of the photochemically imprinted polymers (PCP) with different crosslinker content (80 and 90 wt%) indicated that the selective binding capacity was notably higher in PCP-80 (N= 16.0 µmol/g) compared to PCP-90 (N= 10.1 µmol/g) when analyzed via frontal analysis capillary electrophoresis (FACE) using Freundlich isotherm. In addition, PCP-80 microspheres are more selective toward histamine than conventional thermal polymers (CTP-80) prepared at 60°C in the presence of structural analogs such as histidine, imidazole, and tryptamine under cross-rebinding and competitive conditions. These results demonstrated that histamine-selective imprinted polymers can be obtained readily using room temperature photochemical polymerization where these materials can be subsequently used as recognition element for optical-based histamine sensing.

Assessment of the binding performance of histamine-imprinted microspheres by frontal analysis capillary electrophoresis.

Frontal analysis capillary electrophoresis was used to evaluate the binding performance of molecularly imprinted microspheres (MIM) toward its template histamine and analogs at pH 7, and compared to the high performance liquid chromatographic method. In both methods, batch binding was employed and the binding parameters were calculated from the measured concentration of unbound amine analytes and afforded comparable histamine equilibrium dissociation constants (Kd ∼ 0.4 mM). FACE was easily carried out at shorter binding equilibration time (i.e. 30 min) and without the need to separate the microspheres, circumventing laborious and, in the case of the system under study, inefficient sample filtration. It also allowed for competitive binding studies by virtue of its ability to distinctly separate intact microspheres and all tested amines which could not be resolved in HPLC. Kd 's for nonimprinted (control) microspheres (NIM) from FACE and HPLC were also comparable (∼ 0.6 mM) but at higher histamine concentrations, HPLC gave lower histamine binding. This discrepancy was attributed to inefficient filtration of the batch binding samples prior to HPLC analysis resulting in an over-estimation of the concentration of free histamine brought about by the presence of unfiltered histamine-bound microspheres.

Gram-Scale Synthesis and Kinetic Study of Bright Carbon Dots from Citric Acid and Citrus japonica via a Microwave-Assisted Method.

Tracking dynamic cellular processes necessitates fluorescent materials that are photostable, biocompatible, water-soluble, nanosized, and nontoxic. In this study, highly fluorescent carbon dots (CDs) were produced from cheap and readily available sources, citric acid (CA) and Philippine citrus (Citrus japonica Thunb.) or calamansi juice (CJ) via a microwave-assisted method. A number of synthetic conditions were investigated systematically to optimize the preparation of CDs from CA and CJ. The formation mechanism, surface chemistry, and photoluminescence of CA-based CDs (CA-CDs) and CJ-based CDs (CJ-CDs) were evaluated after each stage of pyrolysis in detail using different characterization techniques, such as dynamic light scattering, diffusion-ordered spectroscopy, atomic force microscopy, ζ potential, X-ray diffraction, Fourier transform infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, and absorption/emission spectroscopy. Gram-scale pyrolysis of CA with ethylenediamine (EDA) and CJ with EDA were carried out to provide CA-CDs (CA-18) within 18 min total pyrolysis time at 97% yield and CJ-CDs (CJ-14) within 14 min total pyrolysis time at 7% yield. Aqueous suspensions of CA-18 and CJ-14 CDs gave comparable bright blue luminescence at 462 nm. CA-CDs were shown to be nontoxic for mung beans up to 2 mg/mL, whereas CJ-CDs with higher surface negative charges inhibited growth above 0.5 mg/mL. This study demonstrates that bright CA- and CJ-CDs can be produced in gram-scale quantities using inexpensive methods. The size, amount, and extent of EDA incorporation are important in contributing to the formation of highly emissive particles.

Preparation and Binding Evaluation of Histamine-Imprinted Microspheres via Conventional Thermal and RAFT-Mediated Free-Radical Polymerization.

Elevated histamine (HTM) levels are closely linked to food poisoning as well as to pathophysiological allergic diseases. In this study, HTM-imprinted, solution-processable microspheres were prepared via high-dilution conventional thermal polymerization (CTP) and controlled radical polymerization (CRP) using ethylene glycol dimethacrylate (80 or 90 wt %) and methacrylic acid at 60 °C in acetonitrile and evaluated as recognition materials for sensing applications. The polymers were selective to HTM in binding studies, cross-rebinding, and competitive binding assays against the HTM analogues histidine, imidazole, and tryptamine. The selective binding capacity was significantly higher with CTP-80 (on the basis of mass: 21.0 µmol/g and surface area: 8.08 × 10-2 µmol/m2) than that with both CTP-90 (8.47 µmol/g, 4.49 × 10-2 µmol/m2) and CRP-80 (9.00 µmol/g, 1.19 × 10-2 µmol/m2).

Electronic control of chiral quaternary center creation in the intramolecular asymmetric heck reaction.

The Boehringer-Ingelheim phosphinoimidazoline (BIPI) ligands were applied to the formation of chiral quaternary centers in the asymmetric Heck reaction. Several different substrates were examined in detail, using more than 70 members of this new ligand class. Hammett relationships were determined through systematic variation of the ligand electronics. All substrates showed essentially the same Hammett behavior, where enantioselectivity increased as the ligands were made more electron-deficient. Ligand optimization has led to catalysts which give the highest enantioselectivities reported to date for these difficult systems.

Straightforward synthesis of sphinganines via a serine-derived Weinreb amide.

Sphinganines can be synthesized in just three steps from easily prepared serine-derived Weinreb amide 4. Pre-deprotonation of the acidic (N-H and O-H) protons of 4 allows for its efficient conversion to amino ketones 5. Such ketones can be selectively reduced to either erythro- or threo-sphinganines. Partially protected sphinganines 11 are also readily accessible in five steps from 4. Thus, Weinreb amide 4 represents one of the most versatile templates described to date for sphinganine synthesis.

Probing electronic effects in the asymmetric Heck reaction with the BIPI ligands.

[structure: see text] The new BIPI ligands are phosphinoimidazolines that can be electronically tuned in three different ligand regions to explore electronic effects in asymmetric catalysis. Their application to the asymmetric Heck reaction (AHR) in the creation of a chiral quaternary center is described. Enantioselectivity is shown for the first time to depend linearly on phosphine electron density. Changing the ligand basicity by variation of the R(2) or R(3) substituents reverses facial selectivity.

Synthesis of D-erythro-dihydrosphingosine and D-xylo-phytosphingosine from a serine-derived 1,5-dioxaspiro[3.2]hexane template.

[reaction: see text] A serine-derived 1,5-dioxaspiro[3.2]hexane template is shown to be a useful precursor for both aminodiol and aminotriol sphingoid bases by its conversion to D-erythro-dihydrosphingosine and D-xylo-phytoshingosine.