End Of Side Chain Research Articles

Molecular Dynamics Simulations of Comb-Branched Poly(epoxide ether)-Based Polymer Electrolytes

Molecular dynamics (MD) simulations using many-body polarizable force field were performed on comb-branched poly(epoxide ether) (PEPE) polymer electrolytes doped with lithium bistrifluoromethanesulfonamide (LiTFSI) salt as a function of temperatures from 333 to 423 K at ether oxygen (EO) to lithium ratio of 20. MD simulations predicted electrolyte conductivity in good agreement with experiments. The fraction of solvent-separated ions and lithium cation environment for PEPE/LiTFSI were similar to those found for the linear poly(ethylene oxide) (PEO)/LiTFSI electrolyte. The Li+ cations had the highest probability to be coordinated by EOs near the PEPE polymer backbone and the lowest probability being coordinated by EO's at the end of side chains. Segmental dynamics of the backbone was slower by 2 orders of magnitude compared to the dynamics of side-chain ends. The Li+ self-diffusion coefficient was approximately an order of magnitude lower than the TFSI- anion self-diffusion coefficient. Visualization of the lithium motion revealed that the most mobile Li+ cations moved by hopping from a side chain to another without being complexed by the backbone. The influence of the backbone−Li+ interactions and the backbone stiffness on ion transport was investigated in MD simulations performed on the PEPE/LiTFSI-like electrolytes with the same PEPE architecture but a very stiff backbone that does not complex lithium cations. The ion transport in these model electrolytes was compared to that of the original PEPE/LiTFSI electrolyte.

Influence of the core structure on the development of polar order and superstructural chirality in liquid crystalline phases formed by silylated bent-core molecules: naphthalene derivatives

Bent-core molecules based on a bent 2,7-disubstituted naphthalene unit and heptamethyltrisiloxane units at one or both ends of the aliphatic side chains were synthesized and investigated by polarized light microscopy, differential scanning calorimetry, X-ray scattering and electrooptical investigations. The effect of fluorine substitution at the periphery of the rigid core and of the replacement of ether oxygens by carboxylate groups as linking units between the aromatic core and the flexible terminal chains was also investigated. All compounds form broad regions of liquid crystalline phases. Different types of non-polar and polar, i.e. antiferroelectric and ferroelectric switching smectic phases, and columnar phases were observed, depending on the molecular structure. Most interestingly, a temperature dependent transition from an antiferroelectric switching to a ferroelectric switching oblique columnar phase was observed. All double-silylated compounds show switching by a collective rotation around the molecular long axis, a process which switches the superstructural chirality in these LC systems.

Influence of the core structure on the development of polar order and superstructural chirality in liquid crystalline phases formed by silylated bent-core molecules: lateral substituents

The influence of lateral substituents was studied for a new series of bent-core liquid crystals with heptamethyltrisiloxane units at both ends of the aliphatic side chains. These materials were investigated by polarized light microscopy, differential scanning calorimetry, X-ray scattering and electro-optical methods. An antiferroelectric switching columnar phase was found for the non-substituted compound. Different types of non-switching columnar phases were obtained for molecules having substituents (CH, NO) in the bay position, whereas a temperature-dependent transition from polar to non-polar smectic phases was found for molecules having substituents (Cl, CN) adjacent to one of the ester linking units. For the CN-substituted compound a new phase sequence SmCP-SmC-Cub-Iso was observed. The occurrence of the cubic phase is associated with a steric frustration due to the bulky silyl groups. The special rectangular columnar mesophase of the nitro-substituted compound is discussed with respect to its relation to B7-type mesophases.

Design of β-carboline derivatives as DNA-targeting antitumor agents

This research studied the structure-activity relationship of β-carboline derivatives as antitumor agents, in which 41 synthesized compounds and their cytotoxicity to tumor and normal cell lines were assayed. It was proved that substituent in position-9 of the β-carboline ring could reinforce the DNA intercalating ability and consequently cytotoxicity to tumor cell lines, and the amidation of amino group at the end of the DNA targeting side chain in position-3 could cripple the DNA intercalating activity of these compounds, which resultingly initiated the cytotoxic selectivity to tumor cell lines rather than to normal ones. Furthermore, the S and G2-M arrest induced by these compounds confirmed that they could target DNA and lead to DNA destructions in Hela cells. In short, this study may provide a framework to design a novel antitumor drug that could surpass Adriamycin.

Novel multifunctional polymeric materials with predominant cis microstructures derived from α‐norbornenyl macromonomer and stable macroinitiator via ring‐opening metathesis polymerization and atom transfer radical polymerization

AbstractNovel star‐like polymeric materials with high cis content could be obtained by using α‐norbornenyl macromonomers and highly stable macroinitiators derived from an active norbornene derivative [5‐(2‐bromo‐2‐methylpropionylaminomethyl)bicyclo[2.2.1]hept‐2‐ene (NBBrMPAM)], which was synthesized by the reaction of norbornene methylene amine and 2‐bromo‐2‐methylpropionyl bromide. The α‐norbornenyl macromonomer (NBPMMA), which is polymethyl methacrylate containing norbornenyl end group, was prepared by atom transfer radical polymerization (ATRP) using NBBrMPAM as an initiator. Star‐like polynorbornene with high cis microstructure (cis/trans = 72/28) was obtained directly by ring‐opening metathesis polymerization of NBPMMA macromonomer having number molecular weight (Mn) as low as 6.39 × 103. Random ring‐opening metathesis copolymerization of NBPMMA and norbornene derivative containing carbazole group (NBCbz) was carried out at 25 °C by using Ru catalyst [(Cy3P)2Cl2Ru = CHPh, Cy = cyclohexyl, Ph = phenyl]. High cis (cis/trans = 63/37) organo‐soluble star‐like random poly(NBPMMA‐co‐NBCbz) was successfully obtained with high number‐average molecular weight (Mn) of 4.76 × 104 and molecular weight distribution polydispersity index of 1.78. Organo‐soluble comb‐shaped copolymers with MMA could be successfully obtained using ATRP macroinitiator [poly(HNBBrMPAM)] in diluted macroinitiator solution with a concentration less than 3.64 × 10−2 mol.L−1. This is the first ever attempt to prepare novel star‐like organo‐soluble polymeric materials with high cis microstructure via the combination of ring‐opening metathesis polymerization and ATRP. Multimodification could be considered to be carried out by using the functional bromo group at the end of side chains. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3382–3392, 2006

Study of EVOH based single ion polymer electrolyte: Composition and microstructure effects on the proton conductivity

A comb-like EVOH based single ion polymer electrolyte (EVOH- g-SPEG) was synthesized by sulfonification of EVOH grafts 2-(2-chloroethoxy) ethanol (C 4H 9O 2Cl)/2-[2-(2-chloroethxy) ethoxy] ethanol (C 6H 13O 3Cl) with 1, 3-propane sultone. The main chain of the comb-like polymer is hydrophobic polyethylene segments; the side chain is hydrophilic poly (ethylene glycol) (PEG) segment, which can solubilize large amounts of inorganic salts. The sulfonic acid group was introduced onto the end of the PEG side chain. The acid form of SPE was successfully obtained by being dialyzed from the products with acid solution. The saturation water sorption of EVOH- g-SPEG membrane increased with the side chain length and the immersion time. The XRD results indicate that the water in SPE membrane region can destroy the membrane crystalline structure and the water absorption membranes are nearly amorphous. AFM phase images of the hydration membranes clearly show the hydrophilic domains, with sizes increasing from 10 to 35 nm as a function of the side chain length. A phase inversion could be observed when n ≥ 5, which was consistent with a rapid increase in water absorption. And the ion conductivity is also measured by AC impedance. The conductivity is greatly influenced by ion exchange capacity and water sorption. The comb-like EVOH- g-SPEG polymer electrolyte grafts with 2 PEG side chain provides the highest ionic conductivity (1.65 × 10 − 3 S cm − 1 ). The comb-like polymer could be a candidate as new polymeric electrolyte material for fuel cells and other electrochemical devices.

Local Hydration Environments of Amino Acids and Dipeptides Studied by X-ray Spectroscopy of Liquid Microjets

The nitrogen K-edge spectra of aqueous proline and diglycine solutions have been measured by total electron yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at neutral and high pH. All observed spectral features have been assigned by comparison to the recently reported spectrum of aqueous glycine and calculated spectra of isolated amino acids and hydrated amino acid clusters. The sharp preedge resonances at 401.3 and 402.6 eV observed in the spectrum of anionic glycine indicate that the nitrogen terminus is in an "acceptor-only" configuration, wherein neither amine proton is involved in hydrogen bonding to the solvent, at high pH. The analogous 1s --> sigma(NH) preedge transitions are absent in the NEXAFS spectrum of anionic proline, implying that the acceptor-only conformation observed in anionic glycine arises from steric shielding induced by free rotation of the amine terminus about the glycine CN bond. Anionic diglycine solutions exhibit a broadened 1s --> pi(CN) resonance at 401.2 eV and a broad shoulder resonance at 403 eV, also suggesting the presence of an acceptor-only species. Although this assignment is not as unambiguous as for glycine, it implies that the nitrogen terminus of most proteins is capable of existing in an acceptor-only conformation at high pH. The NEXAFS spectrum of zwitterionic lysine solution was also measured, exhibiting features similar to those of both anionic and zwitterionic glycine, and leading us to conclude that the alpha amine group is present in an acceptor-only configuration, while the end of the butylammonium side chain is fully solvated.

Versatility of the dipolar filter selection: From 1H nuclear spin diffusion experiment to the measurement of nuclear Overhauser effect in homopolymer melts

Dipolar filters select 1H magnetization according to local dipolar dephasing, which corresponds to site mobility in systems with heterogeneous molecular mobility. Combined with a conventional exchange experiment, it is usually applied to polymeric samples exhibiting structures on the nanometer length scale associated with a strong dynamic contrast. There, the resulting 1H nuclear spin diffusion experiment yields the size of the structure. When the same experiment is applied to homopolymer melts exhibiting a weak dynamic contrast and dynamic heterogeneities on significant shorter length scales, the recorded magnetization decay is in agreement with decays expected from a heterogeneous nanostructure. However, dipolar filters actually can also select mobile parts of the repeat unit, e.g. the end of the alkyl side chains and the subsequent magnetization transfer then can occur via cross relaxation due to non coherent zero-quantum transitions (nuclear Overhauser effect, NOE). The difficulties of distinguishing these two cases are examined and it is demonstrated that NOE experiments exploiting magnetization selection via the dipolar filter allow quantifying the local dynamics of the side chains. This opens new possibilities for measurements of local dynamics in non isotopically labeled homopolymer melts.

Redetermination of 14-deoxyandrographolide

The title compound [systematic name: ent-3β-hydr­oxy-8(17),13(14)-labdadiene-16,15-olide], C20H30O4, contains two trans fused six-membered rings, with a lactone ring at the end of an equatorial side chain. The six-membered rings are in chair conformations and the lactone ring is planar. There is an infinite chain of both inter- and intra­molecular O—H⋯O hydrogen bonds along the b axis. The present study is a confirmation of the results of previous structure determinations of 14-deoxyandrographolide by Medforth, Chang, Chen, Olmstead & Smith [J. Chem. Soc. Perkin Trans. 2 (1990), pp. 1011--1016] and Rajnikant, Gupta, Singh, Lal, Gupta & Varghese [Mol. Cryst. Liq. Cryst. Sect. C (1996), 6, 227–233].

Sialyl Lewis x analogs based on a quinic acid scaffold as the fucose mimic

(−)-Quinic acid was used as a starting material for the preparation of sialyl Lewis x mimetics in order to target E-selectin. Spatial orientation of the hydroxyl groups of quinic acid could mimic the l-fucose ones. Introduction of a side chain ending with a carboxylic acid was effected to replace the sialic acid interaction at the carbohydrate recognition domain. A first series of derivatives, incorporating amino acids linked to quinic acid, were tested for their affinity and found to interact with E-selectin with IC 50 within the millimolar range.

Distal Substrate Interactions Enhance Plasmepsin Activity

Plasmepsin II (PM II) is an aspartic protease active in hemoglobin (Hb) degradation in the protozoan parasite Plasmodium falciparum. A fluorescence-quenched octapeptide substrate based on the initial hemoglobin cleavage site is recognized well by PM II. C-terminal extension of this peptide has little effect, but N-terminal extension results in higher maximal velocity and dramatic concentration-dependent substrate inhibition. This inhibition, but not the rate stimulation, depends on the presence of a DABCYL group on the peptide N terminus. Using site-directed mutagenesis, we have identified PM II residues that interact with N-terminal amino acids of peptide substrates. The same residues influence degradation of Hb by PM II. Cathepsin E (CatE), a related mammalian aspartic protease, is also stimulated by N-terminally extended substrates. This suggests that distal substrate interactions as far out as P6 may be a general property of aspartic proteases and may be important in substrate and inhibitor recognition. Although PM II and CatE are similar in their ability to cleave Hb-based peptides and Hb alpha-chains, CatE is not able to degrade native Hb, which is a substrate for PM II. Based on these results, we propose that PM II may have the special feature of being a Hb denaturase.

Characteristics of monolayer behavior and multilayer film structures of comb polymers having different kinds of fluorocarbon side-chains.

With comb polymers with different kinds of fluorocarbon side-chains, significant effects of spreading solvents on the monolayers at the air/water interface and the molecular arrangement in the deposited films could be found by the use of trifluoroacetic acid and its mixed solvents with n-hexane, depending on the atoms, fluorine or hydrogen, substituted at the end of the fluorocarbon side-chains. These facts are probably due to intralayer hydrogen bonding cooperating with the carbonyl groups of the long-chain esters. The deposited films of solid substrates were characterized by polarized near-edge X-ray absorption fine structure (NEXAFS) spectroscopy as well as in-plane X-ray diffraction and scanning electron and atomic force microscopy.

Dynamic Formation of Graft Polymers via Radical Crossover Reaction of Alkoxyamines

A novel dynamic polymer reaction system using radical exchange of alkoxyamine units has been demonstrated. Poly(methacrylic ester) having 2,2,6,6-tetramethylpiperidine-1-oxy (TEMPO)-based alkoxyamine units in the side chain and TEMPO-based alkoxyamine-terminated polystyrene were prepared by atom transfer radical polymerization (ATRP) and nitroxide-mediated free radical polymerization (NMP), respectively. By the use of living radical polymerization techniques, the molecular weights of each polymer were accurately controlled. Radical crossover reaction of alkoxyamine units between the side chain and chain end of each polymer afforded the graft polymer which polystyrene chains are connected to the poly(methacrylic ester) backbone. Equilibrium Mn apparently depends on the feed ratio of polymers. The structure of the graft polymers is supported by size exclusion chromatography (SEC) and spectral data. The obtained graft polymer could be transformed reversibly to the starting materials by heating with excess am...

Preparation and evaluation of novel ferroelectric liquid crystalline cyclic siloxane tetramers

Two series of liquid crystalline cyclic siloxane tetramers, one containing the 2-methylbutyl chiral group and the other the 1-methylheptyl chiral group, were prepared to investigate, in a systematic manner, the role of molecular structure of (a) the spacer group, (b) the mesogenic side chain and (c) the chiral end group, on the liquid crystalline behaviour of these novel tetramers. The results from this systematic structure/property correlation study clearly showed the effect of the structure of both the chiral end group and the mesogenic side chain core on the thermal properties and temperature ranges of the SmC* phase (ferroelectric) exhibited by these novel materials. By the appropriate choice of spacer group, mesogenic side chain and chiral end group, a number of cyclic siloxane tetramers exhibiting wide SmC* ranges (ferroelectricity) around room temperature were synthesized.

Geometry of interaction of the histidine ring with other planar and basic residues.

Among the aromatic residues in protein structures, histidine (His) is unique, as it can exist in the neutral or positively charged form at the physiological pH. As such, it can interact with other aromatic residues as well as form hydrogen bonds with polar and charged (both negative and positive) residues. We have analyzed the geometry of interaction of His residues with nine other planar side chains containing aromatic (residues Phe, Tyr, Trp, and His), carboxylate (Asp and Glu), carboxamide (Asn and Gln) and guanidinium (Arg) groups in 432 polypeptide chains. With the exception of the aspartic (Asp) and glutamic (Glu) acid side-chains, all other residues prefer to interact in a face-to-face or offset-face-stacked orientation with the His ring. Such a geometry is different from the edge-to-face relative orientation normally associated with the aromatic-aromatic interaction. His-His pair prefers to interact in a face-to-face orientation; however, when both the residues bind the same metal ion, the interplanar angle is close to 90 degrees. The occurrence of different interactions (including the nonconventional N-H...pi and C-H...pi hydrogen bonds) have been correlated with the relative orientations between the interacting residues. Several structural motifs, mostly involved in binding metal ions, have been identified by considering the cases where His residues are in contact with four other planar moieties. About 10% of His residues used here are also found in sequence patterns in PROSITE database. There are examples of the amino end of the Lys side chain interacting with His residues in such a way that it is located on an arc around a ring nitrogen atom.

Molecular Dynamics Study of Transport Phenomena in Perfluorosulfonate Ionomer Membranes for Polymer Electrolyte Fuel Cells

A molecular dynamics simulation model has been developed and used to investigate the microscopic transport mechanism and various physical properties in an electrolyte for polymer electrolyte fuel cells. It has successfully reproduced experimental results of diffusion coefficients of positive ions and water molecules in the polymer electrolyte, which are one order of magnitude smaller than those in aqueous solutions, and of O-H vibration spectra having higher frequencies than in liquid water. The low diffusivity in the polymer electrolyte is due to polar particles forming a disordered heterogeneous structure of the hydrophilic region, which constitutes the transport paths for ions and water molecules. About 25% of the positive ions are dissociated from sulfonate anions at the ends of side chains in the hydrated electrolyte and move sequentially from one sulfonate anion to the other in the vicinity of 0.5 nm about two or three times per nanosecond. This transport mechanism of ions means that the main constraining factors for ion transport in the polymer electrolyte are coulombic interactions from the sulfonate anions and tortuosity of the hydrophilic region. Based on the results, guiding principles to enhance ion diffusivity in the polymer electrolyte are proposed. © 2002 The Electrochemical Society. All rights reserved.

Stabilization of hydrophobic domains in hydrogel by intermolecular hydrogen bonds between carboxylic groups at the distal end of alkyl side-chain

The role of intermolecular hydrogen bond on the stability of hydrophobically associated domains of hydrogel, consisting of 12-acryloyloxydodecanoic acid (ADA; hydrophobic) or 6-acryloyloxyhexanoic acid (AHA; hydrophobic) and acrylic acid (AA; hydrophilic), carrying an alkyl side group terminated by carboxylic acid, was studied by swelling behavior in an organic solvent/water mixture. We chose propionic acid (PAc) and 1-propanol (PrOH) as organic solvents whose solubility parameter, log P, logarithmic partition equilibrium coefficient for octanol/water, is similar. The equilibrated swelling ratio of poly(ADA- co-AA) and poly(AHA- co-AA) gels by PAc was higher than by PrOH at a lower composition (ca. 5–15 mol%) and that of homo-polymer poly(AHA) gel by PAc was higher even at a high composition (up to ca. 70 mol%). The variation in swelling with solvent/water composition indicated a cross-over between the two solvent systems and this phenomenon did not depend on the alkyl side-chain length. Using Fourier transfer infrared spectroscopy, we observed the remarkable shift of the wavelength corresponding to the hydrogen bond in PAc aqueous solutions. Non-dissociated short alkanoic acid, which can penetrate hydrophobic domains and form hydrogen bonds with non-dissociated carboxylic groups of the polymer gel, favors the disruption of hydrophobic domains, causing swelling. Intermolecular hydrogen bonds between carboxylic groups of the alkyl side-chain are thus closely involved in the stability of hydrophobic domains in copolymer gel.

Synthesis, Characterization and Biological Evaluation of 7α-Perfluoroalkylestradiol Derivatives

Linkage of a long CH 2 side chain (‘spacer’) onto C-7α of estradio1-17β (E 2) does not abrogate the binding affinity of this hormone for its receptor. Our purpose was to assess whether the linkage of a CF 2 side chain, which is more bulky and rigid, could also be accommodated by the estrogen receptor (ER). We describe here the synthesis of 7α-perfluorohexylestradiol 7 by perfluoroalkylation of a key silylenolether 2 with FITS-6 (perfluorohexyl-phenyliodoniurn trifluoromethanesulfonate). 7α-Trifluoromethylestradiol 10a was prepared as a fluorinated control compound by UV-light induced trifluoromethylation of 2 with Umemoto reagent ( S-trifluoromethyldibenzo[ b, d]thiophenium trifluoromethanesulfonate). Endocrine properties of these two E 2 derivatives were tested on the MCF-7 breast cancer cell line. Our data reveal that rigidity of the side chain of 7 affected the association of its hormone moiety with the ER to the same extent as a long alkyl side chain. Rigidity also failed to abrogate estrogenicity, as demonstrated by the ability of 7 to enhance ERE-dependent transcription and cell growth. Compound 7 retained the capacity of inducing down regulation of the receptor. Interestingly, no evidence of antiestrogenicity was recorded since this compound behaved like a weak estrogen, exerting a mitogenic effect at high concentration. Of note, control 10a displayed a higher binding affinity than 7 for ER and consequently acted like the latter, albeit with a higher efficiency. Selection of appropriate residues to be linked at the end of a long 7α alkyl side chain is known to be essential for generating strong antiestrogenicity. One may hope that such a property may also hold for perfluorinated chains to produce antiestrogens with strong metabolic stability.

Conformation, structure and molecular solvation: a spectroscopic and computational study of 2-phenoxy ethanol and its singly and multiply hydrated clusters

The conformational landscapes of 2-phenoxy ethanol (POX) and its hydrated clusters have been studied in the gas-phase, providing a model for pharmaceutical β-blockers. A combination of experimental techniques, including resonant two-photon ionisation (R2PI), laser-induced-fluorescence (LIF) and resonant ion-dip infra-red spectroscopy (RIDIRS), coupled with high-level ab initio calculations has allowed the assignment of the individually resolved spectral features to discrete conformational and supra-molecular structures. Assignments were made by comparison of experimental vibrational spectra and partially resolved ultra-violet rotational band contours with those predicted from quantum chemical calculations. The isolated molecule displays a solitary structure with an extended geometry of the side-chain which is stabilised by an intramolecular hydrogen-bond between the alcohol (proton donor) and the ether (proton acceptor) groups of the side-chain. In singly hydrated clusters the water molecule is accommodated by insertion into the intramolecular hydrogen-bond. In the doubly hydrated and higher clusters cyclic structures are generated which incorporate both the water molecules and the terminal OH group of the side-chain; additional (weak) hydrogen bonded interactions with the phenoxy group provide a degree of selectivity but essentially, the water ‘droplet’ forms on the end of the alcohol side-chain.

Ionic poly(p‐phenylene terephthalamide)s: Solubility and thermal stability

AbstractIonic sulfonate groups were incorporated onto molecules of the rigid‐rod polymer poly(p‐phenylene terephthalamide) (PPTA) in two different positions. In one type, S‐PPTA, ionic sulfonate groups were attached to the phenylene ring of the backbone chain. S‐PPTA solubility was achieved in dimethylsulfoxide (DMSO) when 50% of the repeat units contained an ionic group. In the second type, PPTA‐PS, where ionic propanesulfonate groups served as side chains, solubility was achieved in DMSO when 30% of the repeat units contained the ionic group. For both of the partially sulfonated ionic polymers, the thermal stability was enhanced in comparison with the stability of the acid‐form polymers, but it was less than that of PPTA. The effect was more dramatic when the ionic groups were located at the end of side chains. The nature of the counterion also played a role, with doubly ionized calcium giving the best results. Polarized light micrographs of the ionic PPTA polymers displaced birefringent patterns and indicated that greater rigidity was present when the ionic groups were directly attached to the backbone, rather than at the end of a short side chain. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2888–2897, 2001