Aliphatic Backbone Research Articles

A Highly Active PBP–Iridium Catalyst for the Dehydrogenation of Dimethylamine–Borane: Catalytic Performance and Mechanism

AbstractA long‐tethered boron‐containing (P‐B‐P) pincer ligand with an aliphatic backbone was synthesized. Oxidative addition of the B−H bond in the ligand to [Ir(coe)2Cl]2 (coe=cyclooctene) afforded the (P‐B‐P)Ir(H)Cl complex. A catalyst system comprising the iridium complex and KOtBu showed excellent performance in the dehydrocoupling of N,N‐dimethylamine–borane (DMAB), releasing 1 equivalent of dihydrogen gas from a concentrated solution of DMAB at a low catalyst loading of 0.05 mol % and with an initial turnover frequency of approximately 3400 h−1. The dihydride (P‐B‐P)Ir(H)2 complex also catalyzed the dehydrogenation of DMAB and was postulated as one of the intermediates in the catalytic cycle.

Electrochemically engineered single Li-ion conducting solid polymer electrolyte on titania nanotubes for microbatteries

Abstract Single Li-ion conducting p -sulfonated poly(allyl phenyl ether) (SPAPE) is electrochemically synthesized directly on TiO 2 nanotubes in the range of −1.5 to −1.8 V vs. Ag/AgCl. The electrochemical deposition conditions are studied by cyclic voltammetry and chronoamperometry; the polymer formation can be followed by electrochemical impedance spectroscopy. The polymer structure is analyzed by NMR and FTIR spectroscopies, showing the formation of linear aliphatic chains with methyl-oxy-benzene sulfonate side groups. SEM observations of the polymer morphology show that a thin (∼300 nm) and continuous layer is obtained depending on the electrochemical synthesis conditions. The combination of a mobile aliphatic backbone, ether groups with reduced cation affinity and immobile anions grafted on the side chains allows obtaining a single lithium-ion conducting polymer. Half-cell battery tests against Li metal show an excellent cycling performance with high areal capacity (up to 110 μAh cm −2 ) and very good retention especially at large C-rates, studied up to 12 C.

Versatile Manganese Catalysis for the Synthesis of Poly(silylether)s from Diols and Dicarbonyls with Hydrosilanes.

Poly(silylether)s are interesting materials because of their degradation property under hydrolytic conditions and have been prepared via hydrosilylation polymerization from dicarbonyl and hydrosilanes, and via dehydrogenative cross-coupling of diols and hydrosilanes under catalytic conditions. Here, we present a manganese–salen compound based on an inexpensive and nontoxic metal that could effectively catalyze both polymerization reactions with hydrosilane. A series of poly(silylether)s containing various aliphatic and aromatic backbones have been synthesized from diol and dicarbonyl substrates. Moderate to high yields of polymers with number-average molecular weights up to 15 kg/mol are obtained. Because of the dual activity of the manganese catalyst, unsymmetrical substrates with mixed functional groups, such as p-hydroxybenzaldehyde, p-hydroxy benzylalcohol, and 3-(4-hydroxyphenyl)-1-propanol, have been employed to afford poly(silylether)s with multiple silicon connectivity in the main chain.

New side chain cholesterol-functionalised aliphatic polycarbonate copolymer: synthesis and phase behaviour

ABSTRACTA new side cholesterol-functionalised liquid crystal (LC) copolymer based on aliphatic polycarbonate backbone was synthesised. The chemical structures of the block copolymers obtained in this study were characterised with Fourier Transform Infrared Spectroscopy (FT-IR) and Proton Nuclear Magnetic Resonance (1H NMR) spectra. Their thermal stability and phase behaviours were investigated with thermogravimetric analysis (TGA) measurements, differential scanning calorimetry, and polarising optical microscopy. The molecular organisation in the mesophase was studied by temperature-dependent X-ray diffraction (XRD). As a result, the block copolymer bearing side cholesteryl groups showed a glass transition at 15.8°C and a smectic A (SmA) to isotropic phase transition at 151.3°C on heating cycle. XRD indicated that the block LC copolymer showed an interdigitated molecular arrangement of the mesogenic units within the smectic layers. This partial bilayer structure was similar to the SmA phase formed by polar mesogens.

New amphiphilic polycarbonates with side functionalized cholesteryl groups as biomesogenic units: synthesis, structure and liquid crystal behavior

In this study, a series of new side cholesterol-functionalized amphipathic copolymers based on an aliphatic polycarbonate backbone were synthesized and characterized.

Scaling Properties and Related Issues in the Charge Transport through Molecular Junctions

In this paper, we discuss a law of corresponding states (LCS) deduced theoretically and validated experimentally against a variety of current-voltage I-V data measured in molecular junctions fabricated under different experimental platforms. It holds, e.g.: for benchmark nanojunctions based on molecules with σ-saturated aliphatic backbones and localized electrons, and molecules containing π-conjugated rings and delocalized electrons, wherein conductance varies over five orders of magnitude; for CP-AFM (conducting probe atomic force microscope) and STM (scanning tunneling microscope) break junctions; for molecular junctions having typical metallic (silver, gold, platinum) or graphene electrodes. Unprecedented, this law of corresponding states is able to quantitatively reproduce measurements on real junctions very accurately without need to empirically adjust any parameter to experiment. This is in contrast even with the celebrated van der Waals law of corresponding states, which, without parameter adjustment to experiment, provides a rather poor quantitative description of real (classical) fluids. This LCS emphasizes the special role played by the peak (alias transition) voltage in molecular electronics.

Novel 1,2,3-triazolium-based dicationic amphiphiles synthesized using click-chemistry approach for efficient plasmid delivery.

Herein, we report the synthesis, characterization and evaluation of the transfection efficiencies of a series of dicationic amphiphiles designed to construct quaternary ammonium ion-based cationic lipids varying in chain length of the hydrophobic back bone connected individually through head group to a 1,2,3-triazolium cation consisting of 2-hydroxy ethyl chain as substitution. Accordingly, three dicationic amphiphiles were synthesized by "click chemistry" approach and formulated to bilayered vesicles using DOPE as a co-lipid. The transfection efficacies of these novel lipid formulations were measured and correlated with the results obtained from various physicochemical techniques. Importantly, the observed gradient in the activity profile, where the transfection potential increased with decreasing chain length of the lipid hydrophobic back bone, highlights the synergistic interplay of the lipid alkyl chain length in coordination with charge delocalization in modulating the transfection potency of these 1,2,3-triazolium-based lipids.

Simultaneous Anionic Ring-Opening and Condensation Reactions for the Synthesis of Aliphatic–N-Alkyl Aromatic Copolyamides

The copolymerization of e-caprolactam with ethyl 4-(butylamino)benzoate was shown to occur in the presence of sodium salts and an acyllactam as activator in a one-step bulk reaction. The mechanism is based on the deprotonation of the two monomers yielding activated species able to attack an acyllactam or an ester group at the polymer chain ends. Novel copolyamides with different percentages of aromatic/aliphatic units were synthesized in a one-step bulk copolymerization within a few minutes at 140 °C and characterized by NMR spectroscopy, size exclusion chromatography, and thermal analysis (DSC). This methodology, combining simultaneous anionic ring-opening and condensation reactions, affords a new synthetic pathway to introduce an aromatic unit in an aliphatic polyamide backbone, and more specifically a polyamide 6 containing about 20 mol % of N-alkyl aromatic amides was prepared.

Structural Engineering of Biodegradable PCL Block Copolymer Nanoassemblies for Enzyme-Controlled Drug Delivery in Cancer Cells.

Biodegradable block copolymer chemical structures were engineered as drug nanocarriers to precisely program the enzyme-controlled release of anticancer drugs at intracellular compartments in cancer cells. New classes of amide and ester side chain-substituted caprolactone monomers were designed by multistep organic synthesis and polymerized under ring opening processes to make new classes of substituted polycaprolactone-block-polyethylene glycol copolymers. These block copolymers were self-assembled as stable nanoparticles of <200 nm in water. The polymer nanoparticles were found to be excellent scaffolds for loading a wide range of anticancer drugs and stabilized them at extracellular circulating conditions (37 °C in PBS). At the intracellular level, lysosomal-esterase enzyme biodegraded the aliphatic polyester PCL backbone and facilitated the release of drugs in a steady and controlled manner. In vitro drug release studies confirmed that the amide-PCL block copolymers exhibited controlled drug release compared to that of their non-hydrogen-bonded ester-PCL blocks or unsubstituted PCL blocks. The influence of hydrogen bonding interactions on the drug release profiles of PCL nanoparticles were studied by FT-IR and time-resolved fluorescent decay measurements. Cytotoxicity experiments in cervical cancer (HeLa) and breast cancer (MCF-7) cell lines demonstrated that amide diblock copolymer nanoassemblies show slow and prolonged cell killing. The new block copolymers were capable of loading multiple anticancer drugs like doxorubicin (DOX), curcumin (CUR), camptothecin (CPT), and methotrexate (MTX) that largely differ in pharmacokinetics as well as fluorescent regions for cellular imaging. Interestingly, these different drugs could be delivered to the intracellular compartments of the cancer cells by an identical enzyme-controlled delivery pathway from a single biodegradable block copolymer nanoscaffold. Confocal microscopic images exhibited that the engineered block copolymer nanoparticles were capable of transporting all of these drugs across the cell membrane and accumulating them predominantly in the cytoplasm and peri-nuclear region. The present investigation presents a new opportunity in the structural engineering of biodegradable diblock copolymer nanoassemblies for enzyme-controlled multiple-anticancer-drug administration in cancer therapy.

Molecular Simulations of Hydrogen Bond Cluster Size and Reorientation Dynamics in Liquid and Glassy Azole Systems.

We simulated the dynamics of azole groups (pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, and tetrazole) as neat liquids and tethered via linkers to aliphatic backbones to determine how tethering and varying functional groups affect hydrogen bond networks and reorientation dynamics, both factors which are thought to influence proton conduction. We used the DL_Poly_2 molecular dynamics code with the GAFF force field to simulate tethered systems over the temperature range 200-900 K and the corresponding neat liquids under liquid state temperatures at standard pressure. We computed hydrogen bond cluster sizes; orientational order parameters; orientational correlation functions associated with functional groups, linkers, and backbones; time scales; and activation energies associated with orientational randomization. All tethered systems exhibit a liquid to glassy-solid transition upon cooling from 600 to 500 K, as evidenced by orientational order parameters and correlation functions. Tethering the azoles was generally found to produce hydrogen bond cluster sizes similar to those in untethered liquids and hydrogen bond lifetimes longer than those in liquids. The simulated rates of functional group reorientation decreased dramatically upon tethering. The activation energies associated with orientational randomization agree well with NMR data for tethered imidazole systems at lower temperatures and for tethered 1,2,3-triazole systems at both low- and high-temperature ranges. Overall, our simulations corroborate the notion that tethering functional groups dramatically slows the process of reorientation. We found a linear correlation between gas-phase hydrogen bond energies and tethered functional group reorientation barriers for all azoles except for imidazole, which acts as an outlier because of both atomic charges and molecular structure.

Homo‐ and Heteroleptic Copper(I) Complexes with Diazabutadiene Ligands: Synthesis, Solution‐ and Solid‐State Structural Studies

The preparation of novel copper(I) complexes of diazabutadiene (DAB) ligands with aliphatic backbones is reported. [Cu(DABR)2](BF4), [Cu(DABR)(NCMe)2](BF4) and [CuCl(DABR)] are easily synthesised and air‐stable. These complexes, which remain scarce in the literature, have been fully characterised, and their behaviour both in the solid state as well as in solution has been studied by means of X‐ray crystallography, NMR and UV/Vis spectroscopy.

Enzyme and pH dual responsive l -amino acid based biodegradable polymer nanocarrier for multidrug delivery to cancer cells

We report a new pH and enzyme dual responsive biodegradable polymer nanocarrier to deliver multiple anticancer drugs at the intracellular compartment in cancer cells. Natural l-aspartic acid was converted into multifunctional monomer and polymerized to yield new classes of biodegradable aliphatic polyester in-build with pH responsiveness. The transformation of side chain BOC urethanes into cationic NH3+ in the acidic endosomal environment disassembled the polymers nanoparticles (pH trigger-1). The biodegradation of aliphatic polyester backbone by esterase enzyme ruptured the nanoassemblies and released the drugs in the cytoplasm (trigger-2). The polymer scaffolds were capable of delivering multiple drugs such as doxorubicin, topotecan, and curcumin (CUR). The cytotoxicity of the nascent and drug-loaded nanoparticles were tested in cervical (HeLa) and breast (MCF-7) cancer cell lines. The nascent polymer nanoscaffolds were found to be nontoxic to cells whereas their drug-loaded nanoparticles exhibited excellent killing. Confocal microscopic images revealed that the drug-loaded polymer nanoparticles were taken up by the cells and the dual degradation process delivered the drugs to nucleus and established the proof-of-concept. The present investigation opens up new platform for l-amino acid based polyester scaffolds, for the first time, in the intracellular drug delivery in cancer treatment. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3279–3293

Applications of "Hot" and "Cold" Bis(thiosemicarbazonato) Metal Complexes in Multimodal Imaging.

The applications of coordination chemistry to molecular imaging has become a matter of intense research over the past 10 years. In particular, the applications of bis(thiosemicarbazonato) metal complexes in molecular imaging have mainly been focused on compounds with aliphatic backbones due to the in vivo imaging success of hypoxic tumors with PET (positron emission tomography) using (64) CuATSM [copper (diacetyl-bis(N4-methylthiosemicarbazone))]. This compound entered clinical trials in the US and the UK during the first decade of the 21(st) century for imaging hypoxia in head and neck tumors. The replacement of the ligand backbone to aromatic groups, coupled with the exocyclic N's functionalization during the synthesis of bis(thiosemicarbazones) opens the possibility to use the corresponding metal complexes as multimodal imaging agents of use, both in vitro for optical detection, and in vivo when radiolabeled with several different metallic species. The greater kinetic stability of acenaphthenequinone bis(thiosemicarbazonato) metal complexes, with respect to that of the corresponding aliphatic ATSM complexes, allows the stabilization of a number of imaging probes, with special interest in "cold" and "hot" Cu(II) and Ga(III) derivatives for PET applications and (111) In(III) derivatives for SPECT (single-photon emission computed tomography) applications, whilst Zn(II) derivatives display optical imaging properties in cells, with enhanced fluorescence emission and lifetime with respect to the free ligands. Preliminary studies have shown that gallium-based acenaphthenequinone bis(thiosemicarbazonato) complexes are also hypoxia selective in vitro, thus increasing the interest in them as new generation imaging agents for in vitro and in vivo applications.

Aerobic biodegradation of toluene-2,4-di(8:2 fluorotelomer urethane) and hexamethylene-1,6-di(8:2 fluorotelomer urethane) monomers in soils.

Aerobic soil biodegradation of toluene-2,4-di(8:2 fluorotelomer urethane) (FTU) and hexamethylene-1,6-di(8:2 fluorotelomer urethane) (HMU) in a forest soil and FTU in an agricultural silty clay loam soil was monitored for up to 6 months. Fluorotelomer alcohols were measured in headspace and parent monomers and all metabolites in soil extracts. Negligible degradation of FTU biodegradation occurred in the agricultural soil with 94 ± 15% recovered at day 180. However, in the forest soil, both FTU and HMU degradation was evident with significant losses of 24% (117 d) and 27% (180 day), respectively, and concomitant increases in the terminal metabolite, perfluorooctanoic acid (PFOA) concentrations were well above what could result from residual 8:2 FTOH. Kinetic modeling estimated half-lives for FTU (aromatic backbone) and HMU (aliphatic backbone) in the forest soil to be 3-5 months and 15.9-22.2 months, respectively. The addition of a structurally similar non-fluorinated FTU analog, toluene-2,4-dicarbamic acid diethyl ester (TDAEE) enhanced production of terminal end products from 8:2 FTOH degradation. However, there was no clear evidence that TDAEE enhanced cleavage of the urethane bond, thus TDAEE appeared to just serve as an additional carbon source. TDAEE's half-life was ∼ one week. A second addition of TDAEE appeared to retard subsequent degradation of FTU exemplifying the microbial dynamics and diversity impacting degradation of polyfluoroalkyl substances. Enhanced degradation of HMU was observed upon re-aeration indicating oxygen may have been limiting during some periods although degradation of intermediate metabolites to terminal metabolites was still occurring, albeit at slower rates.

Transition metal complexes of polyhydroxamic acid grafted on chitosan

Graft copolymerisation of acrylamide onto chitosan using ammonium ceric nitrate as an initiator was studied. Then –CONH2 functional groups converted to the –CONHOH moieties by addition of NH2OH·HCl solution for 36 h in base media. Evidence for graft-copolymerisation was obtained by infrared spectroscopy, 1H and 13C-NMR data. Polyhydroxamic acid grafted on chitosan (Chit-g-PHA) was prepared and studied as specific binders for the transition M2+ and M3+ ions. Their architecture is based on aliphatic backbones, as many functional groups in hydroxamate chelating units. One of the most usages of Chit-g-PHA is transition metal complexes. Polyhydroxamic acid grafted on chitosan in pH = 5 coordinated to Cu2+ and Fe3+, in pH = 6, 8 coordinated to Cr2+ and Ni2+ respectively.

A novel jaspine B-ceramide hybrid modulates sphingolipid metabolism.

A new sphingolipid hybrid molecule was designed to assemble, within a tail-to-tail double-chain structure, the ceramide hydrophilic moiety and the tetrahydrofuran pharmacophore of jaspine B, a natural product known to interfere with sphingolipid metabolism. This compound was prepared through acylation of sphingosine with a jaspine B derivative bearing a COOH group in the terminal position of the aliphatic backbone. This new hybrid molecule was evaluated for its capacities to affect melanoma cell viability and sphingolipid metabolism. While retaining the cytotoxicity of ceramide itself, this compound was shown to lower the sphingomyelin cellular levels and significantly enhance the production of sphingosine-1-phosphate, thus representing a novel sphingolipid metabolism modulator.

ChemInform Abstract: Transition Metals for the Synthesis of Glycopolymers and Glycopolypeptides

AbstractReview: 72 refs.

Proton-conductive inorganic–organic hybrid membranes synthesized from a trimethoxysilylmethylstyrene–fluorophenylvinyl acid copolymer

Inorganic–organic hybrid membranes composed of Si–O networks and an aliphatic main-chain polymer backbone were synthesized from an alkoxysilane derivative and an F-substituted phenylvinylphosphonic acid via copolymerization and sol–gel reaction. Thus, (trimethoxysilylmethyl)styrene (TMSMS) was copolymerized with 3-fluorophenyl- vinylphosphonic acid (FC6H4VPA), and the product was hydrolyzed to afford an inorganic–organic hybrid composite. Spectroscopic analysis revealed that the inorganic–organic hybrid structure was constructed via the polymerization of TMSMS and FC6H4VPA and the condensation of methoxy-Si bonds. The membranes showed good thermal stability up to 180°C, and it was found that the aliphatic chains bound to the F-substituted aromatic rings and the Si–O linkages in the hybrid membranes improved their mechanical properties. In addition, the proton conductivity of the membranes depended on the P/Si ratio of the product and increased as the P content increased. Notably, the conductivity at 130°C for the hybrid membrane synthesized with a TMSMS/FC6H4VPA ratio of 1/6 was 1.6×10−3Scm−1 and 6.4×10−2Scm−1 at low and 100% relative humidity (RH), respectively, while its power density at 140°C and 30% RH was 3.0mW/cm2.

Transition Metals for the Synthesis of Glycopolymers and Glycopolypeptides

AbstractGlycopolymers and glycopolypeptides are an important class of molecules, which can self‐assemble to various interesting biohybrid materials. It is envisaged that the glycans impart good immunological response, and the aliphatic or polypeptide backbone can give tertiary structure for the resulting glycopolymers. The major bottleneck in the synthesis of glycopolymers or glycopolypeptides is the access to suitable building blocks and polymerization methods. This review describes methods that have recently been explored for the successful synthesis of many useful glycomonomers that could be polymerized to afford glycopolymers and/or glycopolypeptides.

A panel of peralkylated sulfur–guanidine type bases: Novel pro-ligands for use in biomimetic coordination chemistry

A series of novel hybrid molecules containing sulfur and nitrogen donor functions simultaneously has been synthesized and characterized. Designed for use in biomimetic coordination chemistry, these molecules are expected to act directly or in specific precursor roles as polyfunctional Lewis bases towards metal-based Lewis acids to form complexes with biological relevance. Their principal architecture is based on aliphatic or aromatic backbones connecting guanidine moieties with sulfur-containing thioether or disulfide portions. Based on acyclic tetramethylguanidino units and their cyclic dimethylethyl-substituted counterparts, a panel of forty-six members of this class of compounds are presented here. The associated denticity extends from bidentate (N/S donor sets) and tridentate (N/N/S donor sets) via tetradentate (N/N/S/S donor sets) to pentadentate (N/N/N/S/S donor sets). Five of these novel systems were structurally characterized and subjected to geometry optimizations using density-functional theory (DFT).