Side-chain Ester Groups Research Articles

Polyethylenes with Combined In-Chain and Side-Chain Functional Groups from Catalytic Terpolymerization of Carbon Monoxide and Acrylate.

Linear polyethylenes with a combination of incorporated in-chain keto as well as side-chain ester groups are formed by Ni(II)-catalyzed terpolymerization of ethylene, carbon monoxide, and methyl acrylate. These possess a random structure, with largely isolated nonalternating in-chain keto groups as well as ester-substituted units adjacent to the polyethylene chain, whereas the solid-state structure of polyethylene is retained. Molecular weights of the terpolymers (Mn ∼ 20.000 g mol-1) are predominantly determined by chain transfer after acrylate incorporation.

Accelerated Post-Polymerization Amidation of Polymers with Side-Chain Ester Groups by Intramolecular Activation.

The catalytic conversion of esters to amides represents new opportunities in the synthetic diversification and upcycling of polymers, as esters are commonly featured in various polymer structures. Yet, direct amidation is typically hampered by poor reaction kinetics and the effects of polymer structure on the reactivity remain poorly understood. We report the accelerated amidation for amines with additional hydrogen bond donating or accepting groups. These amines facilitate the expeditious (co)amidation of polymers with pendant ester groups, displaying at least a 400-fold higher reactivity relative to polyesters with esters in the main chain. Furthermore, a positive correlation between the reactivity and degree of polymerization for poly(methyl acrylate) suggests a hydrogen-bond mediated intramolecular activation of the esters, which was confirmed by FT-IR spectroscopy and basic molecular mechanics modeling. The reported method paves the way to synthesize diverse (co)polymers with amide side chains from readily available polymeric precursors.

Ultra-sensitive detection of Cr2O72− in farmland achieved by an electrosynthesized fluorescent poly(Fmoc-succinimide)

Hexavalent chromium (Cr(VI)) pollution is related to human health, and the detection of its concentration has a decisive effect on pollution treatment. In this work, we designed a Cr2O72− sensor P(Fmoc-Osu) and applied it in farmland. In the boron trifluoride diethyl etherate solution, the monomer Fmoc-Osu was electropolymerized and obtained its conjugated polymer P(Fmoc-Osu). The introduction of succinimide and carbonic ester group in side chain enabled it to show high selectivity to Cr2O72− in comparison to anions and twenty amino acids. Furthermore, by taking advantage of the signal amplification effect of a conjugated polymer, P(Fmoc-Osu) could analyze Cr2O72− in trace amounts and the limit of detection was 8.3 fM. For agricultural application, we employed it in farmland water, soil, Chinese cabbage, carrot and the results showed a satisfactory result. All these results showed that P(Fmoc-Osu) is an efficient tool to detect Cr2O72− in practical application.

Preparation for polyacrylic acid modified by ester group in side chain and its application as viscosity enhancing agent in polycarboxylate superplasticizer system

The problem of bleeding and segregation in high fluidity concrete can be eliminated by the addition of viscosity-enhancing agents (VEA). However, the dispersion capacity of PCE would be perturbed by the addition of VEA. In most cases, this negative impact was due to competitive adsorption between VEA and PCE. In order to mitigate the negative impact, ester groups were introduced to reduce the adsorption capacity, and one new kind of viscosity-enhancing agents was designed; the polymers were copolymerized of acrylic acid (AA) and 2-hydroxyethyl acrylate (HEA), with 1:1 and 1:8 M ratios of AA and HEA. And then, the effect of these two VEAs on rheology of cement paste plasticized by PCE at 5 min and 30 min were studied. Adsorption behavior was analyzed by total organic carbon (TOC), and the zeta potential was also measured. The conformation of the polymers in liquid phase were analyzed by dynamic light scattering (DLS). And the decomposition of ester group under alkaline condition was verified by FTIR and 1HNMR. The results indicated that the synthesized VEA could plasticize cement paste, and the reason was that VEA could be adsorbed by cement grains and act as the same role as the first-generation superplasticizer. The plasticizing capacity was increased over time, because the adsorption capacity was enhanced due to the released carboxyl groups from the decomposition of ester groups. Furthermore, from 5 min to 30 min, the decomposition of ester group could increase the conformation size of VEA by producing crosslinking in the presence of Ca2+, and the crosslinking act as positive role in increasing viscosity and resist the bleeding and segregation. Moreover, it was observed that VEA had negative impact on dispersion capacity of PCE, and the higher density of ester group resulted in lower negative impact at the beginning; one reason for this was because the higher density of ester group showed lower competitive adsorption capacity. Such results offered one new type of VEA available for superplasticizer system.

Degradation of polyacrylic elastomers: Theoretical and experimental studies

A series of Reactive Force Field (ReaxFF) molecular dynamics simulation was performed on polyacrylicester terpolymer for the first time to understand its thermal decomposition characteristics. The effects of time and temperature on the evolution of various products were analyzed. Alkyl radicals were discovered as dominant products at low temperature along with carbon dioxide. Additionally, alkenes were also detected in the final products at higher temperature. Other small molecular products including alkoxy radicals and carbon monoxide were also noticed in the end products. Evolution mechanisms of dominant products (alkyls and alkenes) were explored in detail based on the simulation approach. The fracture of ester linkage is the typical initiation step for the formation of alkyl radicals. The pathway for yielding alkenes mainly consists of the β-hydrogen elimination from the side chain ester groups. The products during the thermal decomposition processes of polyacrylicester predicted theoretically were in agreement with the experimental results from thermogravimetry coupled with fourier transform infrared spectroscopy (TGA-FTIR) and simultaneous thermal analysis coupled with gas chromatography and mass spectroscopy (STA-GC-MS). The apparent activation energy for thermal decomposition of polyacrylicester obtained from the ReaxFF simulation was also consistent with the experimental results.

Adsorbing behavior of polycarboxylate superplasticizer in the presence of the ester group in side chain

ABSTRACTThe effect of the ester group in side chain on adsorbing behavior and dispersion of polycarboxylate superplasticizer (PC) was studied by comparing the performance of two types of PC. The fluidity of cement paste was tested to discuss the dispersing ability and dispersing retention ability of PC. The total organic carbon analyzer was used to measure the adsorption amount, and the adsorption layer was obtained by x-ray photoelectron spectroscopy. Fourier-transform infrared spectroscopy, nuclear magnetic resonance, and pH value were used to verify the stability of the ester group, and the electrokinetic properties of cement particle were confirmed using the zeta potential measurement. The results show that the ester group in side chain reduces the initial dispersing ability while it increases the dispersing retention ability. The dispersing retention ability depends on the increase of adsorption amount and adsorption layer in 5–60 minutes, and the greater increase leads to the better dispersing retention ability. The ester group can be decomposed to release carboxyl group to enhance the adsorbing ability of PC under the condition of cement hydration, which is the main reason for the greater increase of adsorption amount and adsorption layer and the improvement in dispersing retention ability. It suggests that grafting the ester group is a good way to enhance the dispersing retention ability.

Benzoxaborole antimalarial agents. Part 4. Discovery of potent 6-(2-(alkoxycarbonyl)pyrazinyl-5-oxy)-1,3-dihydro-1-hydroxy-2,1-benzoxaboroles.

A series of 6-hetaryloxy benzoxaborole compounds was designed and synthesized for a structure–activity relationship (SAR) investigation to assess the changes in antimalarial activity which result from 6-aryloxy structural variation, substituent modification on the pyrazine ring, and optimization of the side chain ester group. This SAR study discovered highly potent 6-(2-(alkoxycarbonyl)pyrazinyl-5-oxy)-1,3-dihydro-1-hydroxy-2,1-benzoxaboroles (9, 27–34) with IC50s = 0.2–22 nM against cultured Plasmodium falciparum W2 and 3D7 strains. Compound 9 also demonstrated excellent in vivo efficacy against P. berghei in infected mice (ED90 = 7.0 mg/kg).

Role of graded length side chains up to 18 carbons in length on the damping behavior of polyurethane/epoxy interpenetrating polymer networks

A series of novel polyurethane (PU)/epoxy resin (EP) graft interpenetrating polymer network (IPN) composites with graded length side chains were prepared from toluene diisocyanate (TDI), polytetrahydrofuran glycol (PTMG), EP, trimethylolpropane (TMP), and diol chain extenders. The effects of the side chain lengths, content, and groups on the damping properties and mechanical properties were investigated. Two damping peaks were observed in the PU/EP IPN system, indicating that the peak damping factor (tanδ) increased with increased side chain length at low temperatures. The introduction of an apolar side chain slightly narrowed the damping range. However, the side chain carrying polar groups broadened the damping temperature range. The strong H-bond interaction between the ester group of side chain and the NH of hard segments in PU was believed to favor microphase separation to form a larger-sized domain and induce the appearance of the relaxation peak at high temperatures. Consequently, the effective damping temperature range was broadened. The side chain content tethered in the hard segment remarkably influenced the damping properties of PU/EP IPNs both at low and high temperatures. The width and intensity of the tanδ peaks of PU/EP IPNs increased with increased side chain content. The mechanical properties (tensile strength and elongation at break) were significantly affected by the side chain content. Thus, an important method of improving the mechanical damping of elastomers by controlling the side chain molecular structure was established.

Enantioselective Synthesis of a (1R,5R,9R)-2-Azabicyclo[3.3.1]nonane-9-carboxylic Acid with an Embedded Morphan Motif: A Multipurpose Product

A convenient asymmetric synthesis of (1<i>R</i>,5<i>R</i>,9<i>R</i>)-2-aza­bicyclo[3.3.1]nonane-9-carboxylic acid is described, starting from (2<i>E</i>,7<i>E</i>)-dimethyl nonadienedioate. The route involves a stereo­selective domino Michael–Dieckman process that furnishes a 1,2,3-trisubstituted cyclohexane derivative bearing three adjacent stereocenters with full stereochemical control. A subsequent chemoselective transformation of one of the side-chain ester groups allows an effective second cyclization leading to the morphan motif. The versatility of this novel amino acid for the generation of molecular complexity was tested by elaborating a tripeptide in homogeneous phase.

Modification of Microbial Polymalic Acid With Hydrophobic Amino Acids for Drug‐Releasing Nanoparticles

Microbial poly(β, l-malic acid) was modified with either l-leucine ethyl ester (L) or l-phenylalanine methyl ester (F) to produce amphiphylic copolymers. The degradation of these copolymers in aqueous buffer took place under physiological conditions in a few weeks by hydrolysis of the side chain ester group followed by cleavage of the main chain. Spherical nanoparticles with diameters ranging between 70 and 230 nm were prepared from these copolymers by the dialysis-precipitation method. No alteration of the cell viability was observed after incubation of these nanoparticles in different cell lines. Anticancer drugs temozolomide and doxorubicin were encapsulated in the nanoparticles. Temozolomide was released within several hours whereas doxorubicin took several weeks to be completely liberated.

Rac-Methyl 2-(2-formyl-4-nitrophenoxy)hexanoate

In the racemic title compound, C14H17NO6, the plane of the ester group of the methyl hexa­noate side chain makes a dihedral angle of 80.0 (2)° with the benzene ring, while the nitro group is approximately coplanar with the benzene ring [dihedral angle = 10.3 (2)°]. In the crystal, mol­ecules form weak aromatic C—H⋯Onitro hydrogen-bonding inter­actions, giving inversion dimers [graph set R 2 2(8)].

Diastereoisomeric β-ethyl aspartate–cobalt(III) complexes: Λ(+)578- and Δ(−)578-bis(ethane-1,2-diamine)[β-ethyl (S)-aspartato]cobalt(III) bis(perchlorate) monohydrate

The structures of the diastereoisomers Λ(+)(578)-, (I), and Δ(-)(578)-bis(ethane-1,2-diamine)[β-ethyl (S)-aspartato-κ(2)N,O(1)]cobalt(III) bis(perchlorate) monohydrate, (II), both [Co(C(6)H(10)N(2)O(4))(C(2)H(8)N(2))(2)](ClO(4))(2)·H(2)O, are compared. In both structures, the ester group of the amino acid side chain is engaged only in intramolecular hydrogen bonding to coordinated amine groups. This interaction is stronger in (I) and correlates with previously observed diastereoisomeric equilibrium ratios for related metal complex systems in aqueous media. The two perchlorate anions of (II) are located on twofold axes. Both perchlorates in (I) and one of the perchlorates in (II) are affected by disorder. Both structures exhibit extensive three-dimensional hydrogen-bonding networks.

Degradation of Aliphatic Polyesters by Vacuum Ultraviolet Irradiation

The photon energy of vacuum ultraviolet (VUV) light is higher than the binding energy of some chemical bonds in organic molecules, such as C–C, C–H, or C–O. Therefore, VUV light is able to cause the scission of various bonds in polymer molecules, which can lead to the decomposition of the polymeric molecules. Degradation of polymers by VUV has been studied with the purpose of investigating damage to polymeric materials by VUV, developing new photoresist materials, revealing the degradation mechanism, and modifying polymer surfaces, etc. The degradation mechanism of poly(methyl methacrylate) (PMMA) has been extensively studied for evaluation as a new photoresist material. It was found that the side chain ester group is decomposed by VUV irradiation, leading to a polymer containing carboncarbon double bonds. In addition, scission of the main chain also occurred. If an ester group is easily cleaved by VUV, it may be expected that aliphatic polyesters, which contain ester groups in the main chain, will be degraded to small volatile molecules and may function as good photoresist materials. Aliphatic polyesters are soluble in common organic solvents, which enables good thin films to be easily formed. It is well known that aliphatic polyesters are easily degraded by biological reactions, and although many studies have been performed regarding the biodegradation of aliphatic polyesters, only a few studies have investigated degradation by irradiation with UV or VUV light. In this report, the degradation of aliphatic polyesters by VUV was investigated and compared with that of PMMA. The study concentrated on the reaction mechanism, the effect of oxygen and application of an external electric field during irradiation. EXPERIMENTAL

Reduction of substituted spiro[cyclopropane-3-(1-pyrazolines)] to spiro[cyclopropane-3-pyrazolidines] and 1-(2-aminoethyl)cyclopropylamine derivatives

Raney nickel-catalyzed hydrogenation of 5-substituted spiro[cyclopropane-3-(1-pyrazoline)]-5-carboxylates occurs with N—N bond cleavage with simultaneous cyclocondensation to give 3-aminopyrrolidin-2-ones containing a spirocyclopropane fragment. The presence of the second ester group in the pyrazoline side chain, in the position ensuring the formation of a five-membered ring results in 6,11-diazadispiro[2.1.4.2]undecane-7,10-dione, the product of double cyclocondensation of the intermediate diamine. Hydrogenation of the aryl-substituted spiro[cyclopropane-3-(1-pyrazolines)] in the presence of acetone affords hexahydrospiro[cyclopropane-4-pyrimidines], which can be converted into the cyclopropane-containing 1,3-diamines in the individual state or as salts.

Stereochemical influence on lipase-mediated hydrolysis and biological activity of stampidine and other stavudine phosphoramidates

Stampidine and other halogen substituted stavudine phosphoramidates can be activated by lipase-mediated hydrolysis. The target site for the lipase appears to be the methyl ester group of the L-alanine side chain. Accordingly, the D-amino acid substituted isomers {Rp or Sp}are resistant to lipase-mediated hydrolysis and exhibit substantially less anti-HIV activity. Molecular modeling results indicate that the L-amino acid configured isomers {Rp or Sp} are preferred in the lipase binding pocket.

Infrared Ellipsometric Studies of Mixing in a Thin Double Layer of Poly(n-butyl methacrylate)/Poly(vinyl chloride)

Infrared spectroscopic ellipsometry (IRSE), infrared transmission spectroscopy, and the regularized method of deconvolution are applied cooperatively for the analysis of the process of mixing in thin double layers (about 100 nm each) of poly(n-butyl methacrylate) (PnBMA) and poly(vinyl chloride) (PVC) on gold. For the first time thin polymeric double layers in the nanometer range and the annealing induced interactions have been investigated by IRSE. Spectral changes in the ellipsometric spectra of thin films are compared to those observed in the infrared absorbance of 5−10 μm thick films of the same polymers. The stabilization of conformational states of side-chain ester groups has been revealed after the annealing process and cooling to room temperature. The formation of hydrogen-bond-type interactions between the PnBMA carbonyl and PVC methine groups in the annealed double layer is found. With increasing annealing time the PnBMA/PVC sample progressively approaches a mixed homogeneous state.

Diastereoselective synthesis of substituted 2,3,4,5‐tetrahydro‐1H‐1‐benzazepine‐5‐carboxylic esters by a tandem reduction‐reductive animation reaction

AbstractAn efficient, diastereoselective synthesis of substituted and unsubstituted 2,3,4,5‐tetrahydro‐1H‐1‐benzazepine‐5‐carboxylic esters has been developed based on the tandem reduction‐reductive amination reac tion. Catalytic hydrogenation of a series of 2‐(2‐nitrophenyl)‐5‐oxoalkanoic esters initiates a reaction sequence involving (1) reduction of the aromatic nitro group, (2) condensation of the N‐hydroxylamino (or amino) nitrogen with the side chain carbonyl, and (3) reduction of the seven‐membered cyclic imine. Cyclizations that produce 2‐alkyl‐2,3,4,5‐tetrahydro‐1H‐1‐benzazepine‐5‐carboxylic esters are diastereose lective for the product having the C2 alkyl and the C5 ester groups cis. In these reactions, the transannular ester group exerts a strong stereodirecting effect on the reduction of the cyclic imine intermediate, though not as strong as that observed in previous closures of 2‐alkyl‐1,2,3,4‐tetrahydroquinoline‐4‐carboxylic esters. This decrease in diastereoselectivity is attributed to (1) the greater distance between the ester and the imine double bond and (2) the increased conformational mobility of the larger ring, both of which diminish the stereodirecting effect of the ester. Finally, formation of the seven‐membered ring is sufficiently slow that reaction with the side chain ester group competes with heterocycle formation in several of the reactions.

Lipase-mediated stereoselective hydrolysis of stampidine and other phosphoramidate derivatives of stavudine

Enzymatic hydrolysis of stampidine and other aryl phosphate derivatives of stavudine were investigated using the Candida Antarctica Type B lipase. Modeling studies and comparison of the hydrolysis rate constants revealed a chiral preference of the lipase active site for the putative S-stereoisomer. The in vitro anti-HIV activity of these compounds correlated with their susceptibility to lipase- (but not esterase-) mediated hydrolysis. We propose that stampidine undergoes rapid enzymatic hydrolysis in the presence of lipase according to the following biochemical pathway: During the first step, hydrolysis of the ester group results in the formation of carboxylic acid. Subsequent step involves an intramolecular cyclization at the phosphorous center with simultaneous elimination of the phenoxy group to form a cyclic intermediate. In the presence of water, this intermediate is converted into the active metabolite Ala-d4T-MP. We postulate that the lipase hydrolyzes the methyl ester group of the l-alanine side chain to form the cyclic intermediate in a stereoselective fashion. This hypothesis was supported by experimental data showing that chloroethyl substituted derivatives of stampidine, which possess a chloroethyl linker unit instead of a methyl ester side chain, were resistant to lipase-mediated hydrolysis, which excludes the possibility of a direct hydrolysis of stampidine at the phosphorous center. Thus, our model implies that the lipase-mediated formation of the cyclic intermediate is a key step in metabolism of stampidine and relies on the initial configuration of the stereoisomers.

Computational analysis of side-chain conformations in polyaspartates exhibiting reversible helical sense inversion in the solid state

Poly(β-phenylpropyl l-aspartate), poly(β-phenylbutyl l-aspartate), and poly(β-phenylpentyl l-aspartate) exhibit a reversible transformation from a right-handed α-helix (αR) to a left-handed ω-helix (ωL) in the solid state. During this transition, the infrared (IR) dichroism of the side-chain ester group and the birefringence change drastically, showing that the side-chain conformations are different for these two helices. In the present study, for the purpose of elucidating the preferred side-chain conformation in each helix, we performed the computational analyses. The energy contours, the directions of the IR transition moments and the anisotropies in polarizability as functions of the first two dihedral angles of the side chain, χ1 and χ2 were calculated. Then, comparing them with the experimental IR dichroism and birefringence data, we elucidated the specific side-chain conformation preferred for each αR or ωL skeleton. The preferred values of (χ1, χ2) were found to be (−75, −60°) for αR and (180, 45°) for ωL.

Graft copolymerization of methyl methacrylate onto mercaptochitin and some properties of the resulting hybrid materials.

The graft copolymerization of methyl methacrylate onto mercaptochitin and some properties of the resulting graft copolymers have been studied. Methyl methacrylate was efficiently graft copolymerized onto mercaptochitin in dimethyl sulfoxide, and the grafting percentage reached 1300% under appropriate conditions. Although the side-chain ester groups were resistant to aqueous alkali, hydrolysis could be achieved with a mixture of aqueous sodium hydroxide and dimethyl sulfoxide. Subsequent treatment with acetic anhydride in methanol transformed the sodium carboxylate groups into carboxyl groups. Although the graft copolymers exhibited an improved affinity for organic solvents, those having sodium carboxylate or carboxyl units were characterized by a much more enhanced solubility and were soluble in common solvents. The hygroscopic nature of chitin decreased with an increase in the grafting extent but increased significantly upon hydrolysis of the ester groups. The enzymatic degradability of the graft copolymers, as evaluated with lysozyme, was also dependent on the grafting extent and much higher than that of the original chitin. DSC measurements revealed the presence of a glass transition phenomenon, which could be ascribed to the poly(methyl methacrylate) side chain.