Chain Units Research Articles

Analysis of secondary organic aerosols from ozonolysis of isoprene by proton transfer reaction mass spectrometry

To understand the mechanism of formation of the secondary organic aerosols (SOAs) produced by the ozonolysis of isoprene, proton transfer reaction mass spectrometry (PTR-MS) was used to identify the semi-volatile organic compounds (SVOCs) produced in both the gaseous and the aerosol phases and to estimate the gas–aerosol partitioning of each SVOC in chamber experiments. To aid in the identification of the SVOCs, the products were also studied with negative ion-chemical ionization mass spectrometry (NI-CIMS), which can selectively detect carboxylic acids and hydroperoxides. The gaseous products were observed by on-line PTR-MS and NI-CIMS, whereas the SVOCs in SOAs collected on a filter were vaporized by heating the filter and were then analysed by off-line PTR-MS and NI-CIMS. The formation of oligomeric hydroperoxides involving a Criegee intermediate as a chain unit was observed in both the gaseous and the aerosol phases by NI-CIMS. PTR-MS also detected oligomeric hydroperoxides as protonated molecules from which a H2O molecule was eliminated, [M−OH]+. In the aerosol phase, oligomers involving formaldehyde and methacrolein as chain units were observed by PTR-MS in addition to oligomeric hydroperoxides. The gas–aerosol partitioning of each component was calculated from the ion signals in the gaseous and aerosol phases measured by PTR-MS. From the gas–aerosol partitioning, the saturated vapour pressures of the oligomeric hydroperoxides were estimated. Measurements by a fast-mobility-particle-sizer spectrometer revealed that the increase of the number density of the particles was complete within a few hundred seconds from the start of the reaction.

The role of chain structure in the rheological behavior of vinyl acetate-vinyl alcohol copolymers

A comparative study of the viscoelastic properties of melts of vinyl acetate-vinyl alcohol copolymers with equimolar compositions characterized by different statistical distributions of chain units has been performed. It has been shown that the principle of temperature-frequency superposition is obeyed by copolymers close to a random copolymer, but is violated by copolymers with the block distribution of units. Unlike amorphous random copolymers, a multiblock copolymer is characterized by weak crystallinity, the absence of the relaxation flow state, and a more pronounced tendency to form interchain hydrogen bonds both between two hydroxyl groups and between hydroxyl and ester groups.

Rapid structural elucidation of polysaccharides employing predicted functions of glycosyltransferases and NMR data: Application to the O-antigen of Escherichia coli O59

A computerized method that uses predicted functions of glycosyltransferases (GTs) in conjunction with unassigned NMR data has been developed for the structural elucidation of bacterial polysaccharides (PSs). In this approach, information about the action of GTs (consisting of possible sugar residues used as donors and/or acceptors, as well as the anomeric configuration and/or substitution position in the respective glycosidic linkages) is extracted from the Escherichia coli O-antigen database and is submitted, together with the unassigned NMR data, to the CASPER program. This time saving methodology, which alleviates the need for chemical analysis, was successfully implemented in the structural elucidation of the O-antigen PS of E. coli O59. The repeating unit of the O-specific chain was determined using the O-deacylated PS and has a branched structure, namely, →6)[α-d-GalpA3Ac/4Ac-(1 → 3)]-α-d-Manp-(1 → 3)-α-d-Manp-(1 → 3)-β-d-Manp-(1 → 3)-α-d-GlcpNAc-(1→. The identification of the O-acetylation positions was efficiently performed by comparison of the (1)H,(13)C HSQC NMR spectra of the O-deacylated lipopolysaccharide and the lipid-free PS in conjunction with chemical shift predictions made by the CASPER program. The side-chain d-GalpA residue carries one equivalent of O-acetyl groups at the O-3 and O-4 positions distributed in the LPS in a 3:7 ratio, respectively. The presence of O-acetyl groups in the repeating unit of the E. coli O59 PS is consistent with the previously proposed acetyltransferase WclD in the O-antigen gene cluster.

Glucuronoarabinoxylan from coconut palm gum exudate: Chemical structure and gastroprotective effect

A glucuronoarabinoxylan (CNAL) was extracted with 1% aq. KOH (25°C) from Cocos nucifera gum exudate. It had a homogeneous profile on HPSEC-MALLS-RI (Mw 4.6×104g/mol) and was composed of Fuc, Ara, Xyl, GlcpA (and 4-O-GlcpA) in a 7:28:62:3 molar ratio. Methylation data showed a branched structure with 39% of non-reducing end units, 3-O-substituted Araf (8%), 3,4-di-O- (15%), 2,4-di-O- (5%) and 2,3,4-tri-O-substituted Xylp units (17%). The anomeric region of CNAL 13C NMR spectrum contained 9 signals, indicating a complex structure. The main chain of CNAL was characterized by analysis of a Smith-degraded polysaccharide. Its 13C NMR spectrum showed 5 main signals at δ 101.6, δ 75.5, δ 73.9, δ 72.5, and δ 63.1 that were attributed to C-1, C-4, C-3, C-2 and C-5 of (1→4)-linked β-Xylp-main chain units, respectively. CNAL exhibited gastroprotective effect, by reducing gastric hemorrhagic lesions, when orally administered (1 and 3mg/kg) to rats prior to ethanol administration.

Reversible cross-linking reactions of alkoxyamine-appended polymers under bulk conditions for transition between flow and rubber-like states

Reversible cross-linking reactions of alkoxyamine-appended polymers with low glass transition temperature (Tg) were successfully carried out under bulk conditions. The low-Tg polymers with alkoxyamine units in the side chains were synthesised by radical copolymerisation of 2-ethylhexyl acrylate and two kinds of alkoxyamine-containing acrylate monomers. By heating the low-Tg polymers under bulk conditions at 100 °C, cross-linked polymers were formed by radical exchange reactions between alkoxyamine units, and a transition from a liquid-like flowable polymer state to a rubber-like polymer state was confirmed. A de-cross-linking reaction was also accomplished by radical exchange reactions between the cross-linked polymers and an added alkoxyamine-containing small molecule or stable nitroxyl radical, which resulted in transition to the flowable state again. The structural transition between low-Tg linear polymers and cross-linked polymers were characterised by 1H and 13C NMR spectroscopy, Fourier transform infrared spectroscopy, rheology measurement, swelling experiment, and gel permeation chromatography measurement.

Development of a new micro reaction sampler for pyrolysis-GC/MS system facilitating on-line analytical chemolysis of intractable condensation polymers

A new micro reaction sampler is developed to facilitate the thermally assisted hydrolysis and methylation (THM) reaction of intractable condensation polymers, at an elevated temperature in a sealed glass capsule under high pressure. The sampler is integrated with a glass capsule and a crushing metal rod, and it is air-tightly mounted inside a vertical micro-furnace pyrolyzer of a pyrolysis (Py)-GC/MS system. The developed sampler is firstly applied for THM-GC/MS measurements of polycarbonate (PC) whose structural characterization using tetramethylammonium hydroxide (TMAH) as a reagent has been reported in detail previously, to confirm the applicability of the developed sampler. Two peaks are clearly observed in the pyrogram and they are assigned to methyl derivatives of a main chain unit (bisphenol A) and a terminal group (tert-butyl phenol) which are the THM reaction products of PC. The area ratio of these two peaks is almost the same as that obtained by the conventional THM-GC/MS, suggesting the effectiveness of the developed reaction sampler. Further, the developed sampler is applied for THM of nylon 6.6 which has been hardly analyzed by conventional THM-GC/MS using TMAH as a reagent in the open system where samples are exposed to the ambient gas in a pyrolyzer. Using the developed method, measured pyrogram clearly shows several peaks with fairly high yields that are assigned to methyl derivatives of monomer units of nylon 6.6, that is, adipic acid and hexamethylenediamine, and a hybrid dimer of each monomer. Therefore, it can be said that the developed sampler based on the closed system, sealed glass capsule, is quite useful for the pyrolysis analysis of intractable condensation polymers such as nylon 6.6, compared to the conventional THM-GC/MS using the open system.

Fluorescent boronic acid polymer grafted on silica particles for affinity separation of saccharides.

Boronic acid affinity gels are important for effective separation of biological active cis-diols, and are finding applications both in biotech industry and in biomedical research areas. To increase the efficacy of boronate affinity separation, it is interesting to introduce repeating boronic acid units in flexible polymer chains attached on solid materials. In this work, we synthesize polymer brushes containing boronic acid repeating units on silica gels using surface-initiated atom transfer radical polymerization (ATRP). A fluorescent boronic acid monomer is first prepared from an azide-tagged fluorogenic boronic acid and an alkyne-containing acrylate by Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction (the CuAAC click chemistry). The boronic acid monomer is then grafted to the surface of silica gel modified with an ATRP initiator. The obtained composite material contains boronic acid polymer brushes on surface and shows favorable saccharide binding capability under physiological pH conditions, and displays interesting fluorescence intensity change upon binding fructose and glucose. In addition to saccharide binding, the flexible polymer brushes on silica also enable fast separation of a model glycoprotein based on selective boronate affinity interaction. The synthetic approach and the composite functional material developed in this work should open new opportunities for high efficiency detection, separation, and analysis of not only simple saccharides, but also glycopeptides and large glycoproteins.

Conductivity scaling and thermoelectric properties of polyaniline hydrochloride

We report on the thermoelectric properties of the polyaniline hydrochloride as a function of the temperature. In order to stress the influences of both the synthesis and the samples preparation on the thermoelectric efficiency, we have systematically measured the electrical conductivity, the thermopower, and the thermal conductivity. We show that several parameters such as the polymerization temperature and the pressure used to compress powders are crucial in order to optimize the thermoelectric performance. The microscopic origins of the transport coefficients are also discussed. In particular, the overall dataset of the measured electrical conductivity is found to scale onto a master curve involving a unique microscopic length, which coincides with the total bond length of the repeating unit of the polymeric chain. We believe that the drawn conclusions can hold for most of the conducting polymers and are thus potentially generic.

Dual pH-and Thermo-Responsive Self-Assembly of the P(NIPAM-<em>co</em>-AA) Hydrophilic Random Copolymer in Pure Aqueous Solution

从N-异丙基丙烯酰胺（NIPAM）和丙烯酸（AA）单体合成了一种全亲水无规共聚物P（NIPAM-co-AA），实验发现该聚合物在水相中可以产生pH或温度双重刺激响应性自组装。采用透射电子显微镜（TEM）观察了自组装体的形貌，采用动态光散射（DLS）和静态光散射（SLS）观察了其粒径及粒径分布。测定了该聚合物水溶液的最低临界溶解温度（LCST）及其zeta电位随pH的变化，通过分析NIPAM和AA两种链节的质子化状态随温度和pH变化的趋势，阐释了其在水相中产生双重响应性自组装的推动力；并结合傅里叶红外（FT-IR）光谱测定自组装体表面富集基团的结果，进一步阐释了不同环境下自组装体的微结构。这类全亲水无规共聚物的合成方法简单，具有pH和温度双重响应性，其全水相中的刺激响应性自组装行为在药物释放等方面具有潜在的应用价值。

Exploring the solid state properties of enzymatic poly(amine-co-ester) terpolymers to expand their applications in gene transfection

Polymers bearing amino functional groups are an important class of materials capable of serving as non-viral carriers for DNA delivery to living cells. In this work biodegradable poly(amine-co-ester) terpolymers were synthesized via ring-opening and polycondensation copolymerization of lactone (ε-caprolactone (CL), ω-dodecalactone, ω-pentadecalactone (PDL), and ω-hexadecalactone) with diethyl sebacate (DES) and N-methyldiethanolamine (MDEA) in diphenyl ether, catalyzed by Candida antarctica lipase B (CALB). All lactone-DES-MDEA terpolymers had random distributions of lactone, sebacate, MDEA repeat units in the polymer chains. PDL-DES-MDEA terpolymers were studied in the composition range from 21 mol% to 90 mol% PDL whereas the terpolymers with other lactones were investigated at a single composition (80 mol% lactone). DSC and WAXS analyses showed that all investigated terpolymers crystallize in their respective homopolylactone crystal lattice. Terpolymers with large lactones and a high lactone content melt well above room temperature and are hard solids, whereas terpolymers with small lactones (e.g. CL) or with a low lactone content melt below/around ambient temperature and are waxy/gluey materials. Given the importance of hydrophobicity in influencing gene delivery, water contact angle measurements were carried out on lactone-DES-MDEA terpolymers showing that it is possible to tune the hydrophilic-to-hydrophobic balance by varying polymer composition and size of lactone units. To demonstrate the feasibility of using solid terpolymers as nanocarriers for DNA delivery, PDL-DES-MDEA copolymers with 65-90% PDL were successfully transformed into free-standing nanoparticles with average particle size ranging from 163 to 175 nm. Our preliminary results showed that LucDNA-loaded nanoparticles of the terpolymer with 65% PDL were effective for luciferase gene transfection of HEK293 cells.

Chemical Polymerization Kinetics of Poly-O-Phenylenediamine and Characterization of the Obtained Polymer in Aqueous Hydrochloric Acid Solution Using K2Cr2O7as Oxidizing Agent

The oxidative chemical polymerization of o-phenylenediamine (OPDA) was studied in hydrochloric acid solution using potassium dichromate as oxidant at 5°C. The effects of potassium dichromate, hydrochloric acid, and monomer concentrations on the polymerization reaction were investigated. The order of reaction with respect to potassium dichromate, hydrochloric acid, and monomer concentration was found to be 1.011, 0.954, and 1.045, respectively. Also, the effect of temperature on the polymerization rate was studied and the apparent activation energy of the polymerization reaction was found to be 63.658 kJ/mol. The obtained polymer was characterized using XPS, IR, UV-visible, and elemental analysis. The surface morphology of the obtained polymers was characterized by X-ray diffraction and transmission electron microscopy (TEM). The TGA analysis was used to confirm the proposed structure and number of water molecules in each polymeric chain unit. The ac conductivity(σac)of (POPDA) was investigated as a function of frequency and temperature. The ac conductivity was interpreted as a power law of frequency. The frequency exponent (s) was found to be less than unity and decreased with the increase of temperature, which confirms that the correlated barrier hopping model was the dominant charge transport mechanism.

Enhancing Photovoltaic Performance of Copolymers Containing Thiophene Unit with D–A Conjugated Side Chain by Rational Molecular Design

Rational molecular design of conjugated polymers and cautious optimization of morphologies of the active layer are critical for developing high performance polymer solar cells (PSCs). In this work, we designed and synthesized a new thiophene monomer TBTF attaching donor–acceptor (D–A) conjugated side chain with fluorinated 4,7-dithien-5-yl-2,1,3-benzodiathiazole (BTF) as acceptor unit, and synthesized two new two-dimension-conjugated (2D-conjugated) copolymers, P(BDT-TBTF) and P(BDT-TBTF/DPP), for the application as donor materials in PSCs. P(BDT-TBTF) is a new side chain D–A copolymer of benzodithiophene (BDT) and TBTF units, and P(BDT-TBTF/DPP) is a ternary D–A copolymer of BDT, TBTF and pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) units. The introduction of TBTF unit with D–A conjugated side chain and DPP unit forming the ternary copolymer provides the opportunity to tune the optoelectronic properties of the resulting polymers. As expected, the binary copolymer P(BDT-TBTF) shows an enhanced absorption coeffic...

On the Embedding Problem for Discrete-Time Markov Chains

When a discrete-time homogenous Markov chain is observed at time intervals that correspond to its time unit, then the transition probabilities of the chain can be estimated using known maximum likelihood estimators. In this paper we consider a situation when a Markov chain is observed on time intervals with length equal to twice the time unit of the Markov chain. The issue then arises of characterizing probability matrices whose square root(s) are also probability matrices. This characterization is referred to in the literature as the embedding problem for discrete time Markov chains. The probability matrix which has probability root(s) is called embeddable. In this paper for two-state Markov chains, necessary and sufficient conditions for embeddability are formulated and the probability square roots of the transition matrix are presented in analytic form. In finding conditions for the existence of probability square roots for (k x k) transition matrices, properties of row-normalized matrices are examined. Besides the existence of probability square roots, the uniqueness of these solutions is discussed: In the case of nonuniqueness, a procedure is introduced to identify a transition matrix that takes into account the specificity of the concrete context. In the case of nonexistence of a probability root, the concept of an approximate probability root is introduced as a solution of an optimization problem related to approximate nonnegative matrix factorization.

On the Embedding Problem for Discrete-Time Markov Chains

When a discrete-time homogenous Markov chain is observed at time intervals that correspond to its time unit, then the transition probabilities of the chain can be estimated using known maximum likelihood estimators. In this paper we consider a situation when a Markov chain is observed on time intervals with length equal to twice the time unit of the Markov chain. The issue then arises of characterizing probability matrices whose square root(s) are also probability matrices. This characterization is referred to in the literature as the embedding problem for discrete time Markov chains. The probability matrix which has probability root(s) is called embeddable.In this paper for two-state Markov chains, necessary and sufficient conditions for embeddability are formulated and the probability square roots of the transition matrix are presented in analytic form. In finding conditions for the existence of probability square roots for (kxk) transition matrices, properties of row-normalized matrices are examined. Besides the existence of probability square roots, the uniqueness of these solutions is discussed: In the case of nonuniqueness, a procedure is introduced to identify a transition matrix that takes into account the specificity of the concrete context. In the case of nonexistence of a probability root, the concept of an approximate probability root is introduced as a solution of an optimization problem related to approximate nonnegative matrix factorization.

Oligomerization Reaction of the Criegee Intermediate Leads to Secondary Organic Aerosol Formation in Ethylene Ozonolysis

Ethylene ozonolysis was investigated in laboratory experiments using a Teflon bag reactor. A negative ion chemical ionization mass spectrometer (NI-CIMS) using SO2Cl(-) and Cl(-) as reagent ions was used for product analysis. In addition to the expected gas-phase products, such as formic acid and hydroperoxymethyl formate, oligomeric hydroperoxides composed of the Criegee intermediate (CH2OO) as a chain unit were observed. Furthermore, we observed secondary organic aerosol (SOA) formation from the ethylene ozonolysis, and the particle-phase products were also analyzed by NI-CIMS. The CH2OO oligomers were also observed as particle-phase components, suggesting that the oligomeric hydroperoxides formed in the gas phase partition into the particle phase. By adding methanol as a stabilized Criegee intermediate scavenger, both the gas-phase oligomer formation and SOA formation were strongly suppressed. This indicates that CH2OO plays a critical role in the formation of oligomeric hydroperoxides followed by SOA formation in ethylene ozonolysis. A new formation mechanism for the oligomeric hydroperoxides, which includes sequential addition of CH2OO to hydroperoxides, is proposed.

Simplified Deoxypropionate Acyl Chains for Mycobacterium tuberculosis Sulfoglycolipid Analogues: Chain Length is Essential for High Antigenicity

The longer, the better: Increasing the lengths of the 1,3-methyl-branched fatty acyl chain units in mycobacterial diacylated sulfoglycolipid (Acyl2 SGL) analogues led to dramatic improvements in their antigenic properties and gave products more potent than the natural antigen Acyl2 SGLs.

Syntheses, structural analyses and luminescent property of four alkaline-earth coordination polymers

Four alkaline-earth coordination polymers, [Ba(Pzdc)(H2O)]n (1), [Ba(Pzdc)]n (2), [AgSr(Pzdc)(NO3)(H2O)]n (3), [Ag2Ca(Pzdc)2(H2O)]n (4) (H2Pzdc=2, 3-pyrazinedicarboxylic acid) have been synthesized and characterized by single-crystal X-ray diffraction. Compounds 1 and 2 afford 2D layer networks generated by one-dimensional chains containing the [Ba2O11N] units. Compound 3 is of 2D mixed-metal coordination network formed by one-dimensional chain units, while 4 is of a 3D heterometallic framework. Interestingly, 1 and 2 can undergo reversible SCSC structural transformation upon dehydration/rehydration of coordinated water molecules. In addition, the π–π stacking interactions dominate fluorescent properties of compounds 1 and 2.

Design and synthesis of dual-responsive hydrogels based on N,N-dimethylaminoethyl methacrylate by copolymerization with N-isopropylacrylamide

Copolymeric hydrogels of N,N-dimethylaminoethyl methacrylate (DMAEMA) and N-isopropylacrylamide (NIPA) of various monomer ratios were evaluated as thermo-responsive and pH-responsive systems for the development of controlled-release and targeted-delivery devices. The swelling properties were investigated with different temperature, pH, and monomer feed ratios. The results show that the temperature-dependent and pH-dependent phase transition of poly(N,N-dimethylaminoethyl methacrylate-N-isopropylacrylamide) (P(DMAEMA-NIPA)) copolymeric hydrogels can be controlled by changing the amount of NIPA units in the network chains. In experiments to determine the temperature-dependent swelling of copolymeric hydrogels in water, it was found that the swelling ratio rapidly decreases as the temperature increases between 35 and 70°C. To characterize the network structure of the copolymeric hydrogels corresponding to effective cross-linking density and average network chain length, uniaxial compressive mechanical testing was carried both after the preparation of hydrogels and after their equilibrium swelling in water. The data obtained demonstrates that the resulting copolymeric hydrogels are promising as materials with tunable hydrophilicity-hydrophobicity and swelling behavior responsive to temperature and pH. Open image in new window

A fuzzy c-means based hybrid evolutionary approach to the clustering of supply chain

This paper describes the work that adapts group technology and integrates it with fuzzy c-means, genetic algorithms and the tabu search to realize a fuzzy c-means based hybrid evolutionary approach to the clustering of supply chains. The proposed hybrid approach is able to organise supply chain units, transportation modes and work orders into different unit-transportation-work order families. It can determine the optimal clustering parameter, namely the number of clusters, c, and weighting exponent, m, dynamically, and is able to eliminate the necessity of pre-defining suitable values for these clustering parameters. A new fuzzy c-means validity index that takes into account inter-cluster transportation and group efficiency is formulated. It is employed to determine the promise level that estimates how good a set of clustering parameters is. The capability of the proposed hybrid approach is illustrated using three experiments and the comparative studies. The results show that the proposed hybrid approach is able to suggest suitable clustering parameters and near optimal supply chain clusters can be obtained readily.

2-(2-Methylbenzoyl)benzoic acid: catemeric hydrogen bonding in a γ-keto acid

The crystal structure of the title compound, C15H12O3, displays catemeric aggregation involving O—H⋯O hydrogen bonds progressing from the carboxyl group of one mol­ecule to the ketone O atom of another glide-related neighbor. The mol­ecule is twisted, with the toluene 80.61 (3)° out of plane with respect to the phenyl group of the benzoic acid. The acid group makes a dihedral angle of 13.79 (14)° with the attached phenyl ring. The mol­ecules are achiral, but the space group glide planes create alternating conformational chirality in the chain units. The four hydrogen-bonding chains progress along [001] in an A—A—B—B pattern (right-to-left versus left-to-right), and are related to each other by the center of symmetry at (0.5, 0.5, 0.5) in the chosen cell. There is one close contact (2.54 Å) between a phenyl H atom and the acid carbonyl from a symmetry-related mol­ecule.