A convenient and water‐based approach is described for the synthesis of an l ‐lysine‐based zwitterionic polymer, poly(ε−l ‐lysinyl acrylamide) (PLAM), without using protecting group chemistry, chromatographic purifications, and organic solvents as the reaction media. PLAM contains both amine and carboxylic acid groups in each repeating unit, which can either be protonated or deprotonated just by altering the pH of the solution to obtain overall positive or negative charge. PLAM is tested for its applicability as a zwitterionic polymeric buffer in water. Cu(II) ion‐induced aggregation of PLAM as a function of solution pH is studied. Spherical nanogel aggregates are formed at pH 9.5 due to aggregation of PLAM through its complexation with Cu(II) ion. Spherical aggregates appear to dissociate via breaking of the complexation at a pH < 5.5 resulting in molecular dissolution of PLAM. This aggregation process is pH reversible. The Cu(II)–PLAM aggregates are used as a template for fabrication of CuO and CuS nanoparticles.
A novel pH‐switchable macroscopic assembly is reported using alginate‐based hydrogels functionalized with host (α‐cyclodextrin, αCD) and guest (diethylenetriamine, DETA) moieties. Since the interaction of αCD and DETA is pH sensitive, the host hydrogel and guest hydrogel could adhere together when the pH is 11.5 and separate when the pH is 7.0. Furthermore, this pH‐controlled adhesion and dissociation shows a good reversibility. The host and guest polymers have good biocompatibility; therefore, this pH‐sensitive macroscopic assembly shows great potential in biotechnological and biomedical applications.
The infrared spectra of 3mM solutions of horse heart cytochrome c were recorded as a function of pD(corresponding to acid high spin form, acidic low spin form, native form, lysine form, the so-termed “strained lysine form” as well as the so-termed “A state” of cytochrome c). An analysis of the pH-induced changes in the secondary structure was performed based on changes in the conformation-sensitive amide I bands of this protein. In lysine and strained lysine forms, the contents of random structure increase at the expense of α-helix. In acidic low. spin form (pH4–2.5), cytochrome c was almost unfolded. The proportion of α-helix had a substantial decrease while the contents of both random structure and 310-helices got a rise. In acidic high spin form (when pH is below 2.5), a further decrease of pD gave no rise to a continued unfolding in cytochrome c but made it refold to the “A state” with properties similar to those of a molten globular state. Adding enough KC1 to the cytochrome c solution(pD2.2 with 0.5MKC1 and pD3.0 with 1.5 MKCl) in which cytochrome c was nearly fully unfolded also led to the formation of A state of cytochrome c. The compositions of all types of secondary structures in A state were evaluated. The behavior of 310-helices in acidic high/low spin form indicated they might be intermediates between α-helices and random structure in acidic solution as proposed by Miick et al. 相似文献
It has been described in the literature1 that the protonation of the nitrogen in 1-benzyl-1,2,3,4-tetraisoquinoline derivatives does not affect the sign of the ORD spectra. We have recently observed2 that in the case of several (R) and (S) N-methyl-4-phenyl-1,2,3,4-tetrahydroisoquinol ine derivatives this is true only for the three Cotton effects below 300 nm (the 1Lb, 1La and 1B electronic transitions3 of the aromatic moiety), although appreciable variations in intensity and slight shifts in the positions of the extrema were also noticed. On the other hand, the sign of the rotation in the visible spectral range was reversed upon protonation in 0.1N methanolic HCl (or hydrochloride of 1 in methanol). 相似文献
Abstract A scheme for the simultaneous determination of temperature and analyte concentration for application in luminescence-based chemical sensors is proposed. This scheme is applied to an optical oxygen sensor, which is based on the quenching of the fluorescence of a ruthenium complex. Temperature measurement is performed using the excitation radiation and an absorption long-pass filter. Preliminary results are presented that show the viability of an oxygen measurement that is independent of temperature and optical power level. The possibility of self-referenced temperature measurements with semiconductor nanoparticles is also investigated. In order to optimize the sensor design, several different optical fiber probe geometries for oxygen sensing are tested and compared, including different methods of coupling radiation into the optical fiber system. Polyvinyl alcohol (PVA) and polyacrylamide membranes are tested as supports for sensor immobilization in fiber-optical pH sensing devices in aqueous solution. Some results are presented that show the feasibility of using fiber-optical pH indicators for remote monitoring. 相似文献
The new enhancement in the determination of pH using optical fiber system is described here. This work uses the membrane made of cellulose acetate membrane for reagent immobilization and congo red (pKa 3.7) and neutral red (pKa 7.2) as pH indicators. An effective covalent chemical binding procedure is used to immobilize the indicators. The response time, reversibility, linear range, reproducibility, and long-term stability of fiber optic sensor with congo red as well as neutral red have been determined. The linear range measured for the sensor based on the congo red and neutral red is 4.2–6.3 and 4.1–9.0, respectively. The response time of sensor membrane is measured by varying the substance pH values between 11.0 and 2.0. 相似文献
The objective of this study was to investigate the viability of Escherichia coli and Staphylococcus aureus in apple juice after treatment with high pressure at sub-zero temperature and during subsequent storage at 5 and 20 °C. The viability of E. coli and S. aureus cells suspended in the apple juice with a pH of 3.8 did not decrease considerably after pressure treatment at 193 MPa and?20 °C. However, viability losses occurred during storage of samples after pressure treatment. Living cells of both strains were not detected in pressurized samples of apple juice stored for 10 days at 20°C. The lethal effect was lower when the samples after pressure treatment were incubated at refrigerated temperature; the number of E. coli and S. aureus decreased by 6 log cycles when the juice was stored for 10 days at 5 °C. 相似文献