Poly{dl-lactide-b-[oligo(ethylene glycol) methyl ether (meth)acrylate)]} block copolymers. Synthesis,characterization, micellization behavior in aqueous solutions and encapsulation of model hydrophobic compounds

A series of well-defined poly{dl -lactide-b-[oligo(ethylene glycol) methyl ether (meth)acrylate)]} (PDLLA-b-POEG[M]A) functional amphiphilic diblock copolymers was synthesized by employing a multistep procedure involving: (a) ring-opening polymerization of dl -lactide using n-decanol and stannous octoate as the initiating system, (b) esterification reaction of the PDLLA hydroxyl end groups with 2-bromoisobutyryl bromide, (c) atom transfer radical polymerization of OEG(M)A with the newly created bromoisobutyryl initiating site, and (d) incorporation of biotin or folic acid at the POEGA chain ends using click chemistry. The products were characterized by NMR spectroscopy and SEC analysis. The aggregation behavior of the synthesized block copolymers was investigated by dynamic light scattering at 25°C in aqueous solutions. The hydrophobic model compounds Nile red and pyrene were efficiently incorporated into the copolymer aggregates in aqueous solutions. High partition coefficient values were determined by fluorescence spectroscopy.     

Diblock copolymers of polystyrene‐b‐poly(1,3‐cyclohexadiene) exhibiting unique three‐phase microdomain morphologies

The synthesis and molecular characterization of a series of conformationally asymmetric polystyrene‐block‐poly(1,3‐cyclohexadiene) (PS‐b‐PCHD) diblock copolymers (PCHD: ～90% 1,4 and ～10% 1,2), by sequential anionic copolymerization high vacuum techniques, is reported. A wide range of volume fractions (0.27 ≤ ?_PS ≤ 0.91) was studied by transmission electron microscopy and small‐angle X‐ray scattering in order to explore in detail the microphase separation behavior of these flexible/semiflexible diblock copolymers. Unusual morphologies, consisting of PCHD core(PCHD‐1,4)–shell(PCHD‐1,2) cylinders in PS matrix and three‐phase (PS, PCHD‐1,4, PCHD‐1,2) four‐layer lamellae, were observed suggesting that the chain stiffness of the PCHD block and the strong dependence of the interaction parameter χ on the PCHD microstructures are important factors for the formation of this unusual microphase separation behavior in PS‐b‐PCHD diblock copolymers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1564–1572     

Lithium-Ion Desolvation Induced by Nitrate Additives Reveals New Insights into High Performance Lithium Batteries

Electrolyte additives have been widely used to address critical issues in current metal (ion) battery technologies. While their functions as solid electrolyte interface forming agents are reasonably well-understood, their interactions in the liquid electrolyte environment remain rather elusive. This lack of knowledge represents a significant bottleneck that hinders the development of improved electrolyte systems. Here, the key role of additives in promoting cation (e.g., Li⁺) desolvation is unraveled. In particular, nitrate anions (NO₃⁻) are found to incorporate into the solvation shells, change the local environment of cations (e.g., Li⁺) as well as their coordination in the electrolytes. The combination of these effects leads to effective Li⁺ desolvation and enhanced battery performance. Remarkably, the inexpensive NaNO₃ can successfully substitute the widely used LiNO₃ offering superior long-term stability of Li⁺ (de-)intercalation at the graphite anode and suppressed polysulfide shuttle effect at the sulfur cathode, while enhancing the performance of lithium–sulfur full batteries (initial capacity of 1153 mAh g⁻¹ at 0.25C) with Coulombic efficiency of ≈100% over 300 cycles. This work provides important new insights into the unexplored effects of additives and paves the way to developing improved electrolytes for electrochemical energy storage applications.     

Porphyrin decorated CdSe quantum dots for direct fluorescent sensing of metal ions

In this study, we report on a novel hybrid structure for the direct sensing of metal ions based on the use of CdSe quantum dots functionalized with tetrapyridyl-substituted porphyrin, a cation-selective carrier. It is shown that the porphyrin ion carrier coordinates to Cd atoms of the CdSe quantum dots through the Lewis basic pyridyl groups. The porphyrin-quantum dot ligation allows for the direct communication between the porphyrin and the underlying CdSe quantum structure. The quantum yield of CdSe is maintained despite the robust capping generated when the unmetallated porphyrins coordinate onto the quantum dots. Upon coordination with zinc ions, this porphyrin capping is shown to strongly contribute to the increase in the fluorescence efficiency of CdSe, via an activating interaction with the quantum dots surface. The results provide the grounds for the development of highly sensitive and selective nano-optode sensing systems.     

Aryl‐Phosphonate Lanthanide Complexes and Their Fluorinated Derivatives: Investigation of Their Unusual Relaxometric Behavior and Potential Application as Dual Frequency 1H/19F MRI Probes

A series of low molecular weight lanthanide complexes were developed that have high ¹H longitudinal relaxivities (r₁) and the potential to be used as dual frequency ¹H and ¹⁹F MR probes. Their behavior was investigated in more detail through relaxometry, pH‐potentiometry, luminescence, and multinuclear NMR spectroscopy. Fitting of the ¹H NMRD and ¹⁷O NMR profiles demonstrated a very short water residence lifetime (<10 ns) and an appreciable second sphere effect. At lower field strengths (20 MHz), two of the complexes displayed a peak in r₁ (21.7 and 16.3 mM ^?1 s^?1) caused by an agglomeration, that can be disrupted through the addition of phosphate anions. NMR spectroscopy revealed that at least two species are present in solution interconverting through an intramolecular binding process. Two complexes provided a suitable signal in ¹⁹F NMR spectroscopy and through the selection of optimized imaging parameters, phantom images were obtained in a MRI scanner at concentrations as low as 1 mM . The developed probes could be visualized through both ¹H and ¹⁹F MRI, showing their capability to function as dual frequency MRI contrast agents.     

Effect of processing temperature on growing bamboo-like carbon nanotubes by chemical vapor deposition

The present article demonstrates a simple, eco-friendly route for the fabrication of carbon nanotubes (CNTs) with different morphologies, including the fascinating bamboo-like structures without complex catalyst/support preparation procedures. A thermal chemical vapor deposition (CVD) technique that utilized natural pozzolan supports and a solid carbon source, that is, a mixture of camphor and ferrocene in a weight ratio of 20:1, was carried out at different temperatures where the ferrocene played also the role of catalyst. The pozzolan chemical composition and mineral identification were determined by energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. The morphology of the fabricated CNTs was studied via scanning and transmission electron microscopies (SEM and TEM). It was revealed that both conventional tubular and bamboo-like nanotubes grow at 750 °C while the bamboo-like morphology prevails at 850 °C. The better nanostructure uniformity at higher deposition temperature was accompanied by an improved nanotube graphitization degree that was verified by Raman spectroscopy. Yet, the reduction of the CNTs production yield was recorded by thermogravimetric analysis (TGA). The experimental data are interpreted and discussed as an interplay between the CNTs processing temperature, morphology and growth mechanism. Thus, the growth of either tubular or bamboo-like nanostructures is suggested to be ruled by the competitive surface and bulk diffusions of carbon onto and into the catalyst surface. The growth depends on the size of catalyst nanoparticles sintered at different temperatures. The favorable role of the pozzolan supporting materials in the formation of bamboo-like tubes is emphasized.     

Diels–Alder Polymer Networks with Temperature‐Reversible Cross‐Linking‐Induced Emission

A novel synthetic strategy gives reversible cross‐linked polymeric materials with tunable fluorescence properties. Dimaleimide‐substituted tetraphenylethene (TPE‐2MI), which is non‐emissive owing to the photo‐induced electron transfer (PET) between maleimide (MI) and tetraphenylethene (TPE) groups, was used to cross‐link random copolymers of methyl (MM), decyl (DM) or lauryl (LM) methacrylate with furfuryl methacrylate (FM). The mixture of copolymer and TPE‐2MI in DMF showed reversible fluorescence with “on/off” behavior depending on the Diels–Alder (DA)/retro‐DA process, which is easily adjusted by temperature. At high temperatures, the retro‐DA reaction is dominant, and the fluorescence is quenched by the photo‐induced electron transfer (PET) mechanism. In contrast, at low temperatures, the emission recovers as the DA reaction takes over. A transparent PMFM/TPE‐2MI polymer film was prepared which shows an accurate response to the external temperature and exhibited tunable fluorescent “turn on/off” behavior. These results suggest the possible application in areas including information security and transmission. An example of invisible/visible writing is given.     

BOLD sensitivity to cortical activation induced by microstimulation: comparison to visual stimulation

Electrical microstimulation via intracortical electrodes is a widely used method for deducing functions of the brain. In this study, we compared the spatial extent and amplitude of BOLD responses evoked by intracortical electrical stimulation in primary visual cortex with BOLD activations evoked by visual stimulation. The experiments were performed in anesthetized rhesus monkeys. Visual stimulation yielded activities larger than predicted from the well-established visual magnification factor. However, electrical microstimulation yielded an even greater spread of the BOLD response. Our results confirm that the effects of electrical microstimulation extend beyond the brain region expected to be excited by direct current spread.     

A New Approach for the Photosynthetic Antenna–Reaction Center Complex with a Model Organized Around an s‐Triazine Linker

Two new artificial mimics of the photosynthetic antenna‐reaction center complex have been designed and synthesized (BDP‐H₂P‐C₆₀ and BDP‐ZnP‐C₆₀). The resulting electron‐donor/acceptor conjugates contain a porphyrin (either in its free‐base form (H₂P) or as Zn‐metalated complex (ZnP)), a boron dipyrrin (BDP), and a fulleropyrrolidine possessing, as substituent of the pyrrolidine nitrogen, an ethylene glycol chain terminating in an amino group C₆₀‐X‐NH₂ (X=spacer). In both cases, the three different components were connected by s‐triazine through stepwise substitution reactions of cyanuric chloride. In addition to the facile synthesis, the star‐type arrangement of the three photo‐ and redox‐active components around the central s‐triazine unit permits direct interaction between one another, in contrast to reported examples in which the three components are arranged in a linear fashion. The energy‐ and electron‐transfer properties of the resulting electron‐donor/acceptor conjugates were investigated by using UV/Vis absorption and emission spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy. Comparison of the absorption spectra and cyclic voltammograms of BDP‐H₂P‐C₆₀ and BDP‐ZnP‐C₆₀ with those of BDP‐H₂P, BDP‐ZnP and BDP‐C₆₀, which were used as references, showed that the spectroscopic and electrochemical properties of the individual constituents are basically retained, although some appreciable shifts in terms of absorption indicate some interactions in the ground state. Fluorescence lifetime measurements and transient absorption experiments helped to elucidate the antenna function of BDP, which upon selective excitation undergoes a rapid and efficient energy transfer from BDP to H₂P or ZnP. This is then followed by an electron transfer to C₆₀, yielding the formation of the singlet charge‐separated states, namely BDP‐H₂P ^.+‐ C₆₀ ^.? and BDP‐ZnP ^.+‐ C₆₀ ^{. ?}. As such, the sequence of energy transfer and electron transfer in the present models mimics the events of natural photosynthesis.     

Kinetic Modeling of α‐Hydrogen Abstractions from Unsaturated and Saturated Oxygenate Compounds by Carbon‐Centered Radicals

Hydrogen abstractions are important elementary reactions in a variety of reacting media at high temperatures in which oxygenates and hydrocarbon radicals are present. Accurate kinetic data are obtained from CBS‐QB3 ab initio (AI) calculations by using conventional transition‐state theory within the high‐pressure limit, including corrections for hindered rotation and tunneling. From the obtained results, a group‐additive (GA) model is developed that allows the Arrhenius parameters and rate coefficients for abstraction of the α‐hydrogen from a wide range of oxygenate compounds to be predicted at temperatures ranging from 300 to 1500 K. From a training set of 60 hydrogen abstractions from oxygenates by carbon‐centered radicals, 15 GA values (ΔGAV^os) are obtained for both the forward and reverse reactions. Among them, four ΔGAV^os refer to primary contributions, and the remaining 11 ΔGAV^os refer to secondary ones. The accuracy of the model is further improved by introducing seven corrections for cross‐resonance stabilization of the transition state from an additional set of 43 reactions. The determined ΔGAV^os are validated upon a test set of AI data for 17 reactions. The mean absolute deviation of the pre‐exponential factors (log A) and activation energies (E_a) for the forward reaction at 300 K are 0.238 log(m³ mol^?1 s^?1) and 1.5 kJ mol^?1, respectively, whereas the mean factor of deviation <ρ> between the GA‐predicted and the AI‐calculated rate coefficients is 1.6. In comparison with a compilation of 33 experimental rate coefficients, the <ρ> between the GA‐predicted values and these experimental values is only 2.2. Hence, the constructed GA model can be reliably used in the prediction of the kinetics of α‐hydrogen‐abstraction reactions between a broad range of oxygenates and oxygenate radicals.