Monomeric System Research Articles

Antimicrobial Properties of Monomeric and Dimeric Catanionic Surfactant System.

Cationic gemini surfactants are used due to their broad spectrum of activity, especially surface, anticorrosive and antimicrobial properties. Mixtures of cationic and anionic surfactants are also increasingly described. In order to investigate the effect of anionic additive on antimicrobial activity, experimental studies were carried out to obtain MIC (minimal inhibitory concentration) against E. coli and S. aureus bacteria. Two gemini surfactants (12-6-12 and 12-O-12) and two single quaternary ammonium salts (DTAB and DDAC) were analyzed. The most commonly used commercial compounds of this class, i.e., SDS and SL, were used as anionic additives. In addition, computer quantum mechanical studies were also carried out to confirm the relationship between the structure of the mixture and the activity. The obtained results of microbiological tests and quantum mechanical calculations are in agreement with each other and show the lack of synergism in catanionic mixtures in the case of antibacterial activity.

Gold nanoclusters stabilized with dopa-containing ligands: Catalyst-indicator integrated probe for tumor cell screening

Elevated hydrogen peroxide (H2O2) levels not only inflict cellular damage but also serve as a harbinger for various diseases. Tumor cells, in particular, often exhibit an abundance of H2O2. Hence, the detection of this pivotal molecule assumes paramount importance in monitoring physiological states and expediting cancer diagnosis. To this end, we have ingeniously devised an enzyme-free and monomeric system for intracellular H2O2 detection. Our astute selection of dopa-containing peptidomimetics, replete with ortho-bisphenol and amino acid moieties, has engendered the synthesis of distinctive fluorescent gold nanoclusters (AuNCs). These nanoclusters not only function as a peroxidase-like catalyst, catalyzing the decomposition of H2O2 into hydroxyl radicals (·OH), but also serve as an indicator, with their fluorescence quenched in response to varying H2O2 concentrations. Experimental results evince that our GDpE-AuNCs exhibit remarkable sensitivity, boasting a detection limit of 0.49 μM and a linear range of 5–1000 μM. Moreover, the amalgamation of catalyst and indicator within a single structure, facilitating efficient cellular uptake, engenders intracellular H2O2 detection and discernment of tumor cells. This pioneering approach bequeaths a valuable assay probe for monitoring physiological states and ushering in early disease diagnosis.

Pickering emulsion-guided monomeric delivery of monophosphoryl lipid A for enhanced vaccination

Immunological adjuvants are vaccine components that enhance long-lasting adaptive immune responses to weakly immunogenic antigens. Monophosphoryl lipid A (MPLA) is a potent and safe vaccine adjuvant that initiates an early innate immune response by binding to the Toll-like receptor 4 (TLR4). Importantly, the binding and recognition process is highly dependent on the monomeric state of MPLA. However, current vaccine delivery systems often prioritize improving the loading efficiency of MPLA, while neglecting the need to maintain its monomeric form for optimal immune activation. Here, we introduce a Pickering emulsion-guided MPLA monomeric delivery system (PMMS), which embed MPLA into the oil-water interface to achieve the monomeric loading of MPLA. During interactions with antigen-presenting cells, PMMS functions as a chaperone for MPLA, facilitating efficient recognition by TLR4 regardless of the presence of lipopolysaccharide-binding proteins. At the injection site, PMMS efficiently elicited local immune responses, subsequently promoting the migration of antigen-internalized dendritic cells to the lymph nodes. Within the draining lymph nodes, PMMS enhanced antigen presentation and maturation of dendritic cells. In C57BL/6 mice models, PMMS vaccination provoked potent antigen-specific CD8+ T cell-based immune responses. Additionally, PMMS demonstrated strong anti-tumor effects against E.G7-OVA lymphoma. These data indicate that PMMS provides a straightforward and efficient strategy for delivering monomeric MPLA to achieve robust cellular immune responses and effective cancer immunotherapy.

Dendritic Glycerol-Cholesterol Amphiphiles as Drug Delivery Systems: A Comparison between Monomeric and Polymeric Structures.

The application of micelles as drug delivery systems has gained a great deal of attention as a means to overcome the current several drawbacks present in conventional cancer treatments. In this work, we highlight the comparison of polymeric and monomeric amphiphilic systems with a similar hydrophilic-lipophilic balance (HLB) in terms of their biocompatibility, aggregation behavior in aqueous solution, and potential in solubilizing hydrophobic compounds. The polymeric system consists of non-ionic polymeric amphiphiles synthesized via sequential RAFT polymerization of polyglycerol first-generation [G1] dendron methacrylate and cholesterol methacrylate to obtain poly(G1-polyglycerol dendron methacrylate)-block-poly(cholesterol methacrylate) (pG1MA-b-pCMA). The monomeric system is a polyglycerol second-generation [G2] dendron end-capped to a cholesterol unit. Both amphiphiles form spherical micellar aggregations in aqueous solution, with differences in size and the morphology in which hydrophobic molecules can be encapsulated. The polymeric and monomeric micelles showed a low critical micelle concentration (CMC) of 0.2 and 17 μg/mL, respectively. The results of our cytotoxicity assays showed that the polymeric system has significantly higher cell viability compared to that of the monomeric amphiphiles. The polymeric micelles were implemented as drug delivery systems by encapsulation of the hydrophobic small molecule doxorubicin, achieving a loading capacity of 4%. In summary, the results of this study reveal that using cholesterol as a building block for polymer synthesis is a promising method of preparation for efficient drug delivery systems while improving the cell viability of monomeric cholesterol.

Adsorption and Removal of Composite Contaminants in Water Using Thermoplastic Polyurethane Nanofiber Membranes with Polydopamine–Polyethyleneimine Coatings

Dye wastewater containing bisphenol A (BPA) and dyes as pollutants has not been adequately studied. Our previous study revealed that thermoplastic polyurethane (TPU) nanofiber membranes (NFMs) modified by the addition of polyethyleneimine (PEI) and polydopamine (PDA) satisfactorily adsorb dyes. Herein, we first optimized the synthesis conditions for such membranes, noting a PEI/PDA monomer ratio of 2:2 and a deposition time of 48 h to be optimal. Experiments using these membranes revealed that binary systems containing BPA and the dyes (Congo red (CR), Eosin yellow (EY), or sunset yellow (SY)) exhibit three adsorption behaviors. CR and BPA compete with each other for adsorption sites, decreasing the maximum adsorption capacity (Qmax) for CR 208.3 mg/g (in a monomeric system) to 182.4 mg/g. The adsorption rates for CR and BPA decreased from 0.002 min−1 and 0.331 min−1 in the monomeric systems to 8.37 × 10−4 min−1 and 0.072 min−1, respectively, in the binary CR–BPA system, exhibiting antagonistic effects. When EY and BPA coexisted, Qmax for EY increased from 60.0 (monomeric) to 71.9 mg/g, whereas that for BPA increased from 35.6 to 43.2 mg/g, showing a synergistic effect due to the possible bridging effect. The adsorption sites for SY and BPA are independent of each other. The novelty of this study is the finding that PDA/PEI-TPU NFMS exhibited high adsorption capacity for dyes and BPA in binary composite systems and PDA/PEI-TPU NFMs showed different adsorption patterns for three dye–BPA binary composite systems. The preparation of PDA/PEI-TPU NFMs and the investigation of the adsorption mechanism for dye–BPA binary composite systems are not only of theoretical importance but also provide experimental and data support for practical applications.

Phase inversion emulsification of paraffin oil/polyethylene wax blend in water: A comparison between mixed monomeric and monomeric/gemini surfactant systems

Despite the environmental attractiveness of phase inversion emulsification, polyethylene wax-based emulsions are prepared by high-energy emulsification methods. In this research, phase inversion emulsification of paraffin oil/high density polyethylene wax (PEW) blend in water was conducted using mixed surfactants systems. Sorbitan monooleate (Span 80) was used as the oil-soluble surfactant, while either polysorbate 80 (Tween 80) or a synthesized sunflower oil-based gemini surfactant (SF6) was utilized as the water-soluble surfactant. In order to conduct phase inversion emulsification, the 85 °C water phase containing 5 wt% Tween 80 or SF6 was added to the melted oil phase containing 30 to 60 wt% PEW in the blend and 5 wt% Span 80 at 120 °C with the addition rate of 5 mL/min. Phase inversion point was detected by monitoring the dissolution of the emulsion in water during emulsification and proved by electrical conductivity measurements. A lower effectiveness was found for the mixed monomeric surfactant system compared to the gemini surfactant-containing system. For each surfactant system, the trend of change in water phase volume fraction at phase inversion point upon increase in the PEW content in the oil phase was in accordance with the trend of change in the interfacial tension between the water phase and the oil phase. Using the mixed monomeric/gemini surfactant system resulted in emulsions with larger values of absolute zeta potential and drop sizes comparable to their monomeric surfactant-containing counterparts. The absolute zeta potential of the emulsions containing 30, 50, and 60 wt% PEW in the blend was about 70, 54, and 13 mV higher in case of using the mixed monomeric/gemini surfactant system. The gemini surfactant-containing emulsions demonstrated less shear-thinning behavior and the general trend of change in their viscosity and storage modulus with formulation was in agreement with that in the enthalpy of melting of the dried emulsions. Usage of the mixed monomeric/gemini surfactant system led to higher long-term stability of the emulsions, revealed by lower rate of water evaporation from the emulsions. The results of the current study can be applied for preparation of non-polar polyethylene wax-based emulsions using phase inversion emulsification technique. This investigation also opens up the opportunity to use efficient gemini surfactants in low-energy phase inversion emulsification.

Intramolecular Triplet-Triplet Annihilation Photon Upconversion in Diffusionally Restricted Anthracene Polymer.

In the strive to develop triplet–triplet annihilation photon upconversion (TTA-UC) to become applicable in a viable technology, there is a need to develop upconversion systems that can function well in solid states. One method to achieve efficient solid-state TTA-UC systems is to replace the intermolecular energy-transfer steps with the corresponding intramolecular transfers, thereby minimizing loss channels involved in chromophore diffusion. Herein, we present a study of photon upconversion by TTA internally within a polymeric annihilator network (iTTA). By the design of the annihilator polymer and the choice of experiment conditions, we isolate upconversion emission governed by iTTA within the annihilator particles and eliminate possible external TTA between separate annihilator particles (xTTA). This approach leads to mechanistic insights into the process of iTTA and makes it possible to explore the upconversion kinetics and performance of a polymeric annihilator. In comparison to a monomeric upconversion system that only functions using xTTA, we show that upconversion in a polymeric annihilator is efficient also at extremely low annihilator concentrations and that the overall kinetics is significantly faster. The presented results show that intramolecular photon upconversion is a versatile concept for the development of highly efficient solid-state photon upconversion materials.

Antibacterial Activity of the Mixed Systems Containing 1,2-Dodecanediol against Staphylococcus aureus and Staphylococcus epidermidis.

1,2-Alkanediols are characteristic cosmetic ingredients because these moisturizers exhibit the antibacterial activity against Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis). However, the antimicrobial behavior in mixed systems containing several active ingredients is unclear because previous reports focus on an antibacterial system containing only 1,2-alkanediol. In this study, the minimal inhibitory concentration (MIC) and the fractional inhibitory concentration (FIC) were evaluated for 1,2-dodecanediol/lactic acid, 1,2-dodecanediol/myristic acid, 1,2-dodecanediol/methylparaben, and 1,2-dodecanediol/isopropyl methylphenol mixed systems to show the effect of the addition of other antimicrobial components to 1,2-dodecanediol. The antibacterial property of 1,2-dodecanediol/lactic acid mixed system was almost similar compared to 1,2-dodecanediol monomeric system. On the other hand, the antimicrobial activity of 1,2-dodecanediol against S. epidermidis was inhibited in the 1,2-dodecanediol/myristic acid mixed system. Because the selective antimicrobial activity of myristic acid against S. aureus was demonstrated in the mixed system. The present findings are useful for designing formulations of cosmetics and body cleansers containing 1,2-dodecanediol.

Synthesis of a metal chelating monomer for radiation polymer dosimetry

To enhance the performance of polymeric dosimeters it is necessary to design novel formulations considering the mechanisms that register the absorbed dose (e.g. induced polymerization) and the readout method. The combination of the advantages of polymeric dosimetry, such as response stability and high sensitivity in a tissue-equivalent material, together with the high optical absorbance commonly found in colored metal-ligand complexes, represents a promissory strategy to achieve new dosimetry systems with enhanced optical properties. Addressing this scope, herein this study reports the synthesis of a vinylic monomer that was polymerized for the first time induced by X-Ray radiation, being also capable of forming highly colored complexes with metal ions. The chelating monomer was obtained from glycidyl methacrylate and iminodiacetic acid, purified and fully characterized. Then, the reactivity of a monomeric system containing the obtained monomer, N-isopropylacrylamide and N,N′-methylenebisacrylamide was evaluated. Two different initiation methods, namely chemically initiated polymerization and X-ray promoted polymerization were compared. Finally, the ability of the obtained polymers to chelate Cu2+ ions and the corresponding changes in their optical properties were studied.

Study of metal-amino acid [Cr(III)-Trp]2+ complex and ninhydrin reaction: role of gemini micellar solution on rate constant

In this article, the study of metal-amino acid complex and ninhydrin reaction was examined in gemini micellar solution using a UV-visible spectrophotometric measurement. The role of varying amounts of gemini micellar systems on rate constant of the study was investigated. Initially, rate constant (k ψ) enhances, below cmc and levelling-off areas are, then, noticed up to 400 × 10−5 mol dm−3. Later, gemini offers a third region of fast enhancement k ψ above 400 × 10−5 mol dm−3. Gemini surfactant series provided more efficient implications on the study than pure water and their monomeric traditional surfactant system. The values of rate constant, k ψ, were determined under a set of different experimental reaction situations with the help of a computer-based procedure. Such unfamiliar behaviour developed by gemini micellar solutions was treated by pseudo-phase model of micellar activity. An electrical conductometric measurement was employed to measure critical micellar concentration (cmc) of pure gemini micellar solutions and mixed systems. Several activation parameters were also determined by Eyring’s equation and different constants. Data obtained confirmed that lower values of activation enthalpy (ΔH #) with large negative activation entropy (ΔS #) were attained in gemini than aqueous. A plausible reaction mechanism of the study has been discussed and proposed.

Tri-Manganese(III) Salen-Based Cryptands: A Metal Cooperative Antioxidant Strategy that Overcomes Ischemic Stroke Damage In Vivo.

Oxidative stress is one of the hallmarks of ischemic stroke. Catalase-based (CAT) biomimetic complexes are emerging as promising therapeutic candidates that are expected to act as neuroprotectants for ischemic stroke by decreasing the damaging effects from H2O2. Unfortunately, these molecules result in the unwanted production of the harmful hydroxyl radical, HO•. Here, we report a series of salen-based tri-manganese (Mn(III)) metallocryptands (1-3) that function as catalase biomimetics. These cage-like molecules contain a unique "active site" with three Mn centers in close proximity, an arrangement designed to facilitate metal cooperativity for the effective dismutation of H2O2 with minimal HO• production. In fact, significantly greater oxygen production is seen for 1-3 as compared to the monomeric Mn(Salen) complex, 1c. The most promising system, 1, was studied in further detail and found to confer a greater therapeutic benefit both in vitro and in vivo than the monomeric control system, 1c, as evident from inter alia studies involving a rat model of ischemic stroke damage and supporting histological analyses. We thus believe that metallocryptand 1 and its analogues represent a new and seemingly promising strategy for treating oxidative stress related disorders.

Extracellular Electron Transfer Mechanisms in a Moderately Halophilic Bacterium from the Great Salt Lake for High Salinity Heavy Metal Biosensing

High saline contamination events are a growing problem due to the increase in frequency and severity of hurricanes and the accompanying torrential rains.1 Storms affecting coastal areas can flood Superfund sites, which are designated hazardous waste sites managed by the Environmental Protection Agency (EPA), and other dangerous industrial waste sites. These events can result in the release of harmful pollutants into the environment, including heavy metals.2 The dimension of the contaminated area, as well as the cost and labor intensive approaches utilized, make the monitoring through standard laboratory methods complicated.3 Accordingly, a comprehensive screening of a community after a contamination event is not feasible. In this contest, biosensors offer a cost-effective alternative. Microbial biosensors are of particular interest for environmental monitoring due to their stability, wide range of analytes, and the ability to report on physiological toxicity.4 However, high salinities pose stress on the cellular membrane of bacteria cells, and few microbes can survive in salinities higher than the ocean (~3.5% NaCl). Such salinities can frequently occur after a natural disaster, due to stagnant water and subsequent evaporative water loss, demonstrating a need for a halophilic microorganism that can report on toxic contaminants. A bacterium that has these characteristics was previously isolated for electroactivity and further evaluated for use in the microbial analysis of toxic pollutants applicable for a widescale screening process in high saline contamination events.5 The bacterium, Salinivibrio EAGSL, was found to tolerate from 0.1 M to 3 M NaCl and showed anode-respiring capability. The bacterium was isolated as a new strain based on 16s rRNA gene sequencing.6 Therefore bioinformatics was employed for sequencing and assembling the genome to discover traits for NaCl, heavy metal, and general environmental stress factors. Interestingly, bioinformatics analysis contributed to unveiling the mechanism of extracellular electron transfer in this bacterium. The strategies for arsenic analysis included a high throughput 96-well plate cytotoxicity assay and an electrochemical assay for steps towards an online hazardous contaminant detection system. The 96-well plate assay provided a screening method for ~50 samples at once, taking around 6 hours to detect concentrations of 75 μM arsenic. To overcome the need for sampling and analysis, an electrochemical method was also developed for continuous monitoring of toxic contaminants in high saline. The net result is a microbial cytotoxicity assay to evaluate the toxicity of contaminants in a high saline environment. Additionally, this study elucidated the endogenous electron mediation mechanism in this bacterium through bioinformatics and electrochemical characterization, in addition to performance with an exogenous monomeric mediation system for increased current output.

Clustering in complex ionic liquids in two dimensions

Two-dimensional ionic liquids with single site anion and cation-neutral dimer are studied by computer simulations and integral equation techniques, with the aim of characterizing differences with single site anion-cation mixtures, and also with three-dimensional equivalents of both models, in order to see the competition between the Coulomb interactions and the clustering restrictions due to reduced dimension. We find that the addition of the neutral site to the cation suppresses the liquid-gas transition which occurs in the case of the monomeric Coulomb system. Instead, bilayer membrane type ordering is found at low temperatures. The agreement between the energies and the structural correlations predicted by theory and the simulation is excellent until very close to the no-solution region predicted by the theory. These findings suggest various relations between the nature of the clustering at low temperatures, and the inability of the theory to enter this region.

Inclusion of aggregation effect to evaluate the performance of organic dyes in dye-sensitized solar cells

Two new indoline-based D-A-π-A dyes, D3F and D3F2 (see Scheme 1), are developed on the basis of the reported D3 by insertion of one or two F atoms on benzothiadiazole group. Our central aim is to explore high-efficiency organic dyes applied in dye-sensitized solar cells by inclusion of a simple group rather than by employment of new complicated groups. The performance of two new designed organic dyes, D3F and D3F2, is compared with that of D3 from various aspects including absorption spectrum, light harvesting efficiency, driving force, and open-circuit voltage. Besides the isolated dye, the interfacial property between dye and TiO2 surface is studied. D3F and D3F2 do not show absolute superiority than D3 not only for the isolated dyes but also for the monomeric adsorption system. However, D3F and D3F2 would effectively reduce the influence of aggregation resulting in the much smaller intermolecular electronic coupling. Although the aggregation has attracted much attention recently, it is studied alone in most of studies. To comprehensively evaluate the performance of dye-sensitized solar cells, it is necessary to consider aggregation along with electron injection time from dye into TiO2 rather than only static items, such as, band gap and absorption region.

Interfacial polymerization: A facile technique for developing solvent resistant nanofiltration (SRNF) membrane

Interfacial polymerization (IP) is recently evolved method to fabricate solvent resistant nanofiltration (SRNF) membrane. Herein the preparation of SRNF is presented which involves the polymerization of piperazine (PIP) and trimesoyl chloride (TMC) on the surface of inert support i.e. Celgard 2400. The extent of interfacial polymerization (IP) on Celgard 2400 membrane was examined afterwards by different analytical techniques including atomic force microscopy (AFM), scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR). Their outcome revealed obvious surface modification of Celgard 2400 with thin and homogenous polyamide layer. Furthermore, the sugar (dextrose, sucrose and raffinose) solutions were passed from SRNF membranes to calculate the molecular weight cutoff (MWCO). Based on sugar rejection, the value of MWCO of SRNF membranes come in the range of nanofiltration (> 300 Da). An economical, chemical resistant, homemade NF Cell was fabricated to conduct permeation study through these membranes. Effect of various reaction conditions i.e. monomer concentrations, curing temperature and reaction time on the synthesis of SRNF membranes was optimized. Bromothymol blue (BTB) was selected dye in ethanol to permeate across SRNF membranes. The rise in monomer concentrations augments the rejection of BTB thereby declining ethanol flux, owing to more even surface coverage of Celgard 2400 membrane. Moreover, the reaction time and curing temperature affect the BTB rejection and ethanol flux in the same way. The pore size in SRNF membranes was estimated theoretically by Hagen-Poiseuille as ~0.59 nm. In conclusion, PIP-TMC monomeric system synthesized stable, homogenous and effective SRNF membranes with distinct rejection and flux values.

A coarse-grained model based on core-oftened potentials for anomalous polymers

Starting from an anomalous monomeric system, where particles interact via a two-scale core-softened potential, we investigate how the system properties evolve inasmuch as particles are put together to form polymers whose chain size varies from 4 up to 32 monomers. We observed that the density and diffusion anomaly regions in the pressure versus temperature phase diagram of the monomeric system is smaller in the monomeric system when compared with the polymers. We also found that the polymers do not fold into themselves to form solid spheres instead they tend to maximize the chain-fluid contact. Also, Rouse and Reptation models can be employed to describe the polymers diffusive behaviour. But, in contrast to results of simulations where mere interacts via Lennard-Jones potentials, our results shown a much shorter entanglement length of at most 8 monomers. Density and diffusion anomalies are present in the core-softened polymeric systems. The mobility of the macromolecules is Rouse-like for the small polymers and Entangle-like for the large polymers.

Can the Hexagonal Ice-like Model Render the Spectroscopic Fingerprints of Structured Water? Feedback from Quantum-Chemical Computations

The spectroscopic features of the multilayer honeycomb model of structured water are analyzed on theoretical grounds, by using high-level ab initio quantum-chemical methodologies, through model systems built by two fused hexagons of water molecules: the monomeric system [H19O10], in different oxidation states (anionic and neutral species). The findings do not support anionic species as the origin of the spectroscopic fingerprints observed experimentally for structured water. In this context, hexameric anions can just be seen as a source of hydrated hydroxyl anions and cationic species. The results for the neutral dimer are, however, fully consistent with the experimental evidence related to both, absorption and fluorescence spectra. The neutral π-stacked dimer [H38O20] can be assigned as the main responsible for the recorded absorption and fluorescence spectra with computed band maxima at 271 nm (4.58 eV) and 441 nm (2.81 eV), respectively. The important role of triplet excited states is finally discussed. The most intense vertical triplet⇨ triplet transition is predicted to be at 318 nm (3.90 eV).

On the interplay between chirality and exciton coupling: a DFT calculation of the circular dichroism in π-stacked ethylene.

The chirality of stacked weakly interacting π-systems was interpreted in terms of Frenkel exciton states and the formation of excitonic circular dichroism (CD) bands was monitored for ethylene stacks of varying sizes. Convergence of CD bands with respect to the system size was observed for stacks involving around 10 molecules. By means of rotation around the C-C double bond in ethylene, chirality was induced in the monomeric system and which was shown to dominate the spectral responses, even for polymer aggregates. In helical assemblies of chiral entities, there will always be a mix of excitonic and monomeric contributions to the CD signal and it is demonstrated that the complex polarization propagator approach in combination with Density Functional Theory is a suitable method to address this situation.

Theoretical investigation of the coupling between hydrogen atoms transfer and stacking interaction in guanine–cytosine dimers

The effect of the stacking interaction on some properties of the guanine-cytosine (G-C) base pair has been studied. In particular, the strength of the hydrogen bonds, the mechanism of hydrogen transfer and the charge redistribution intra- and inter-base pair have been analyzed in the three canonical dimers. The inclusion of both the stacking interaction and of the hydrogen bond interaction between the bases allows us to study both the local and the long-range phenomena of DNA. The comparison of these results with those of the G-C monomeric system supports the idea that the variations of these properties depend from the exact dimer considered and are different for one or another hydrogen bond. Also the different mechanisms of two hydrogen transfer (step to step and concerted) can be modified by the stacking interaction between the base pairs. The comparison with previous data shows that some generalizations found in literature must be analyzed in detail.

Synthesis and characterization of hyperbranched polyurethanes via monomeric A2plus monomeric B3approach

The monomeric A2 plus monomeric B3 approach was employed to prepare hyperbranched polyurethanes (HBPUs) based on 4,4′-methylenediphenyl diisocyanate and trimethylolpropane with the molecular weights ranging from 20,000 to 59,800 g mol−1. Through controlling the concentration and stoichiometric ratio of monomers, gel was successfully prevented in the monomeric A2 plus monomeric B3 system. The structures of HBPUs were characterized by 13C NMR. Molecular weights of HBPUs were characterized by gel permeation chromatography. A gradual increase in HBPU molecular weight as well as degree of branching was observed when the stoichiometric ratio of A2 to B3 increased. It was exhibited that the solution concentration of the reaction had great effect on the gel point and cyclization of the monomeric A2 plus monomeric B3 system. This novel isocyanate terminated HBPUs are expected to be capable of modifying the curing performance of benzoxazine resin. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013