Enzymatic microreactors have been prepared in capillaries and on microfluidic chips by immobilizing trypsin on porous polymer monoliths consisting of 2-vinyl-4,4-dimethylazlactone, ethylene dimethacrylate, and acrylamide or 2-hydroxyethyl methacrylate. The azlactone functionalities react readily with amine and thiol groups of the enzyme to form stable covalent bonds. The optimized porous properties of the monoliths lead to very low back pressures enabling the use of simple mechanical pumping to carry out both the immobilization of the enzyme from its solution and the subsequent analyses of substrate solutions. The Michealis-Menten kinetic characteristics of the reactors were probed using a low molecular weight substrate: N-alpha-benzoyl-L-arginine ethyl ester. The effects of immobilization variables such as the concentration of trypsin in solution and percentage of azlactone functionalities in the monolith, as well as the effect of reaction time on the enzymatic activity, and of process variables such as substrate flow velocity and residence time in the reactor, were studied in detail. The proteolytic activity of the enzymatic microreactor on chip was demonstrated at different flow rates with the cleavage of fluorescently labeled casein used as a substrate. The excellent performance of the monolithic microreactor was also demonstrated with the digestion of myoglobin at the fast flow rate of 0.5 microL/min, which affords a residence time of only 11.7 s. The digest was then characterized using MALDI-TOF MS, and 102 out of 153 possible peptide fragments were identified giving a sequence coverage of 67%.
A novel polymeric imaging material containing polyacetal and photoacid generator has been designed. The polyacetal having acetals in its main chain was prepared by condensation of a monomer containing both a carbonyl and a diol group and also it was reverted to the monomer through an main chain cleavege reaction catalyzed with photogenerated acid.
Amidation of polyethylenes creates a range of amide-containing materials with enhanced properties, but the effect of these functional groups on the microstructure of these new materials is not known. Here we employ solid-state nuclear magnetic resonance (NMR) techniques to analyze the microstructure of amide-modified polyethylenes. While a decrease in crystallinity was observed with increasing amounts of functionalization, we found by measuring the chain mobility of the crystalline, amorphous, and interphasial regions of the polyethylenes with NMR relaxation techniques that the grafted amidyl groups partition into the rigid amorphous fraction (RAF) between the crystalline and amorphous regions. The chemical specificity of these NMR experiments creates precise assessments of the location of functional groups within the materials. Together, these insights into the microstructure and morphology of amide-containing polyethylenes lay a foundation for a deeper understanding of the structure and properties of functional polyolefins.
Supramolecular liquid–crystalline polymeric complexes based on a backbone that contains vinyl pyridine units and azobenzene or biphenyl derivatives that posses alkyl chains terminated by carboxylic acid have been obtained by the formation of intermolecular hydrogen bonds between the carboxylic acid and the pyridyl moieties. The polymeric complexes behave as side-chain liquid–crystalline polymers and exhibit smectic phases. A new type of H-bonded host-guest liquid–crystalline system is also reported. The liquid–crystalline host copolymers contain both mesogenic acrylate and 4-vinylpyridine units. The guest molecule is an azobenzene that has a carboxylic acid moiety at one of its extremities. The H-bonded polymeric host–guest complexes exhibit nematic phases. Sequential UV and visible light irradiation of the polymeric complex causes reversible photochemically induced phase transitions. The isothermal nematic–isotropic and isotropic–nematic transitions result from the trans-cis and cis-trans photoisomerization of the guest azobenzene in the host–guest system. © 1996 John Wiley & Sons, Inc.
Abstract : A novel approach to thermoresponsive polymeric membranes based on molded monolithic sheets of macroporous polymers has been demonstrated. The macroporous sheet prepared from glycidyl methacrylate ethylene dimethacrylate is functionalized either by free-radical grafting of N-isopropylacrylamide, or, better, by copolymerization of N-isopropylacrylamide onto the vinylated surface of the pores of the polymer sheet. The macroporous polymers modified with poly(N-isopropylacrylamide) were shown to be thermoresponsive. Changes in the temperature of a flow system incorporating the modified macroporous material were accompanied by significant changes in the backpressure required to effect flow. This study confirms the feasibility of thermoresponsive membranes for water purification.
Read moreWe investigate the design of new photoprecursors of organic bases and the steric and electronic factors that control their photocleavage to give free amines. The design strategy involves the protection of an amine with novel [(benzoinyl)oxy]carbonyl groups and substituted analogs. The resulting masked amines owe their photosensitivity to the rich photochemistry of the benzoinyl chromophore. The photochemistry of this chromophore allows for the clean photogeneration of free amine upon irradiation with UV light below 400 nm in both the solid state and in solution. The structure of the benzoinyl chromophore was varied to determine the optimal chromophore design. By varying the chromophore design, the influence of various steric and electronic effects on the photoliberation of free amines from α-keto carbamates could be gauged. Structural modification of the aryl rings was intended to probe the electronic factors of the photocyclization. Substitution at the 2 position was varied to investigate the steric factors involved in photocyclization. The practical potential of these photoactive carbamates as organic sources of photogenerated base was demonstrated spectroscopically (UV, IR, and NMR). GC-MS product studies also proved diagnostic in identifying photogenerated base. The thermal properties of this class of base photogenerators were also determined. α-Keto carbamates derived from 3',5'-dimethoxybenzoin and its substituted analogs appear particularly attractive. These carbamates undergo near quantitative photocleavage to give free amine along with the corresponding substituted benzo[b]furan photocyclization product. Preliminary evaluation of the solid state quantum yield for cyclohexylamine photogeneration from 3,3',5,5'-tetramethoxybenzoin cyclohexyl carbamate ranged from 0.03 to 0.08 depending on the exposure wavelength. The variation in photoefficiency correlates with the UV absorbance of the keto chromophore indicating direct excitation of the carbonyl group is the preferred pathway for photocleavage.
Read moreThe synthesis of functional aromatic bis(sulfonyl chlorides) containing an acetophenone and two sulfonyl chloride groups, i.e., 3,5-bis[4-(chlorosulfonyl)phenyl]-1-acetophenone (16), 3,5-bis(chlorosulfonyl)-1-acetophenone (17), and 3,5-bis(4-(chlorosulfonyl)phenyloxy)-1-acetophenone (18) via a sequence of reactions, involving in the last step the quantitative oxidative chlorination of S-(aryl)- N,N'-diethylthiocarbamate, alkyl- or benzyl thiophenyl groups as masked nonreactive precursors to sulfonyl chlorides is described. A related sequence of reactions was used for the synthesis of the aromatic trisulfonyl chloride 1,1,1-tris(4-chlorosulfonylphenyl)ethane (24). 4-(Chlorosulfonyl)phenoxyacetic acid, 2,2-bis[[[4-(chlorosulfonyl)phenoxyacetyl]oxy]methyl]-1,3-propanediyl ester (27), 5,11,17,23-tetrakis(chlorosulfonyl)-25,26,27,28-tetrakis(ethoxycarbonylmethoxy)calix[4]arene (38), 5,11,17,23,29,35-hexakis(chlorosulfonyl)-37,38,39,40,41,42-hexakis(ethoxycarbonylmethoxy)calix[6]arene (39), 5,11,17,23,29,35,41,47-octakis(chlorosulfonyl)-49,50,51,52,53,54,55,56-octakis(ethoxycarbonylmethoxy)calix[8]arene (40), 5,11,17,23-tetrakis(tert-butyl)-25,26,27,28-tetrakis(chlorosulfonyl phenoxyacetoxy)calix[4]arene (44), 5,11,17,23,29,35-hexakis(tert-butyl)-37,38,39,40,41,42-hexakis(chlorosulfonylphenoxyacetoxy)calix[6]arene (45), and 5,11,17,23,29,35,41,47-octakis(tert-butyl)-49,40,51,52,53,54,55,56-octakis(chlorosulfonylphenoxyacetoxy)calix[8]arene (46) were synthesized by two different multistep reaction procedures, the last step of both methods consisting of the chlorosulfonation of compounds containing suitable activated aromatic positions. 2,4,6-Tris(chlorosulfonyl)aniline (47) was obtained by the chlorosulfonation of aniline. The conformation of two series of multisulfonyl chlorides i.e., 38, 39, 40 and 44, 45, 46, was investigated by (1)H NMR spectroscopy. The masked nonreactive precursor states of the functional aromatic multisulfonyl chlorides and the aromatic multisulfonyl chlorides reported here represent the main starting building blocks required in a new synthetic strategy elaborated for the preparation of dendritic and other complex organic molecules.
Read moreAbstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Read morePhotoinduced crosslinking of polymers through electrophilic aromatic substitution has been achieved with a family of styrenic polymers or copolymers containing both latent electrophiles and activated aromatic groups. These polymers can be used in combination with a photoacid generator to design a non-swelling negative multipurpose resist which can be used for deep-UV, X-ray or E-beam imaging and has a very high sensitivity. For example, in the deep-UV, sensitivities of less than 1 mJ/cm2 are obtained with very high contrasts. Irradiation of the two-component resists results in the generation of strong acid which, upon baking, activates the latent electrophile to a carbocationic species that couples to neighboring activated aromatic moieties in a crosslinking process. Vinyl-phenol units are incorporated in the copolymer formulation to provide activated aromatic sites, solubility of the resist in aqueous base, and lack of swelling during image development. Alternate three-component formulations in which the latent electrophile is separate from the activated aromatic moiety are also suitable.
Read moreADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDirect polarization carbon-13 and proton magic angle spinning NMR in the characterization of solvent-swollen gelsH. D. H. Stover and J. M. J. FrechetCite this: Macromolecules 1989, 22, 4, 1574–1576Publication Date (Print):April 1, 1989Publication History Published online1 May 2002Published inissue 1 April 1989https://pubs.acs.org/doi/10.1021/ma00194a012https://doi.org/10.1021/ma00194a012research-articleACS PublicationsRequest reuse permissionsArticle Views344Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Read moreEfficient blue light generation by SHG for use in optical storage etc. requires materials that display not only a large nonlinear response and but also optical transparency at the wavelengths of both the laser and the blue light. New chromophores containing sulfonamide, sulfonate, or sulfoximide groups are described that come nearer to this ideal. The optical transparency of electron‐donor and electron‐acceptor substituted conjugated π systems studied previously, which was found to be poor owing to a low‐lying charge‐transfer absorption, is shown to improve when the acceptor group is sulfonamide or sulfonate ester.
Read moreADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStabilization of a liquid-crystalline phase through noncovalent interaction with a polymer side chainTakashi Kato and Jean M. J. FrechetCite this: Macromolecules 1989, 22, 9, 3818–3819Publication Date (Print):September 1, 1989Publication History Published online1 May 2002Published inissue 1 September 1989https://pubs.acs.org/doi/10.1021/ma00199a060https://doi.org/10.1021/ma00199a060research-articleACS PublicationsRequest reuse permissionsArticle Views1515Altmetric-Citations368LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Read moreAbstract : The use of base photogenerated in situ within a polymer coating affords attractive possibilities for the imaging or curing or reactive polymeric materials. In the case of resists. photogenerated base may provide access to materials that are more resistant to airborne contaminants than the chemically amplified resists currently available commercially today. We have designed a family of novel copolymers containing benzisoxazole pendant groups that rearrange to cyanophenols in the presence of a catalytic amount of amine. The rearrangement also occurs thermally at elevated temperatures and may be easily followed by DSC. Films of the benzisoxazole-substituted copolymers containing a small amount of photogenerated base may be imaged to afford positive-tone images of the mask as the rearranged polymer is more soluble in aqueous base than the starting copolymer. At the present time the sensitivity of this resist is relatively low (ca. 100mJ/sq cm), but this may be optimized.
Read moreWe have developed a synthetic approach to the self-assembly of [2]-, [3]-, and [4]rotaxanes, incorporating bis-p-phenylene-34-crown-10 as the ring component(s) surrounding bipyridinium-based dumbbell-shaped components bearing dendritic stoppers at both ends. As a result of the hydrophobic dendritic framework, these [n]rotaxanes are soluble in a wide range of organic solvents, despite the polycationic natures of their bipyridinium-based backbones. In all cases, they could be purified by means of column chromatography employing relatively low polar eluants. The molecular shuttling action of the [2]rotaxane containing two bipyridinium units on the rod portion of the dumbbell shaped component has been investigated by variable-temperature 1H-NMR spectroscopy in a range of solvents [CDCl3, CD2Cl2, THF-d8, and (CD3)2CO] for the first time. This investigation reveals a marked dependence of the rate of the shuttling process upon the polarity of the media. On going from CDCl3 to (CD3)2CO, the rate constant increases from ca. 200 to 33000 times per second. Molecular dynamics simulations, performed in CHCl3 and Me2CO on the [2]rotaxane, suggest that significant conformational changes occur upon changing the polarity of the medium resulting in both steric and electronic hindrance of the shuttling process in CHCl3. Three-dimensional representations, as well as the approximate sizes - i.e. overall lengths and molecular volumes which range from 3 to 6 nm and from 4 to 6 nm3, respectively - of these molecular compounds, were obtained by means of molecular modeling studies. Thus, these nanometer-scale dendritic rotaxanes resemble naturally-occurring chemical systems incorporating an active component, in so far as the rotaxane-like core with its distinctive recognition features is surrounded by a molecular shell in the form of the dendritic framework.
Read moreADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTMultisite functionalized dendritic macromolecules prepared via metalation by superbases and reaction with electrophilesL. Lochmann, K. L. Wooley, P. T. Ivanova, and J. M. J. FrechetCite this: J. Am. Chem. Soc. 1993, 115, 15, 7043–7044Publication Date (Print):July 1, 1993Publication History Published online1 May 2002Published inissue 1 July 1993https://pubs.acs.org/doi/10.1021/ja00068a100https://doi.org/10.1021/ja00068a100research-articleACS PublicationsRequest reuse permissionsArticle Views193Altmetric-Citations55LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Read more
.webp){kind=small}
