Retention of lysozyme activity by physical immobilization in nanocellulose aerogels and antibacterial effects

Aerogels prepared from aqueous dispersions of anionic and cationic cellulose nanofibrils (CNFs) were investigated as solid supports for enzymes and silver nanoparticles and to elicit a sustained antibacterial effect. The imparted stabilization in dry conditions was studied with aerogels that were cast after mixing the enzymes with CNFs followed by dehydration (freeze-drying). The activity of lysozyme immobilized in the given CNF system was analyzed upon storage in liquid and air media. In contrast with aqueous solutions of free, unbound enzyme, which lost activity after the first day, the enzyme immobilized physically in unmodified and cationic CNF presented better stability (activity for a longer time). However, the enzyme activity was reduced in the case of anionic CNF, which was prepared by TEMPO-mediated oxidation (TO-CNF). Both humidity and temperature reduced the stability of the enzyme immobilized in the respective CNF aerogel. The antibacterial activity of CNF aerogels carrying lysozyme was also tested against gram-negative and gram-positive bacteria. The results were compared with those obtained from CNF systems loaded with silver nanoparticles (AgNP) after in situ synthesis via UV reduction. Storage in cold or dry conditions preserved the activity and antibacterial performance of enzyme-loaded CNF aerogels. As expected, the lysozyme-containing aerogels showed lower inhibition than the AgNP-containing aerogel. In this latter case, the antibacterial activity depended on the concentration and size of the nanoparticles. Compared to unmodified CNF and TO-CNF, the aerogels prepared with cationic CNF, loaded with either lysozyme or AgNPs, showed remarkably better antibacterial activity. Similar experiments were conducted with horseradish peroxidase, which confirmed, to different degrees, the observations derived from the lysozyme systems. Overall, the results indicate that non-toxic and biodegradable CNF is a suitable support for bio-active materials and is effective in protecting and retaining enzymatic and antibacterial activities.     

Kinetic and mechanistic study of the reactions of atomic chlorine with CH3CH2Br, CH3CH2CH2Br, and CH2BrCH2Br

A laser flash photolysis-resonance fluorescence technique has been employed to investigate the reactions of atomic chlorine with three alkyl bromides (R-Br) that have been identified as short-lived atmospheric constituents with significant ozone depletion potentials (ODPs). Kinetic data are obtained through time-resolved observation of the appearance of atomic bromine that is formed by rapid unimolecular decomposition of radicals generated via abstraction of a β-hydrogen atom. The following Arrhenius expressions are excellent representations of the temperature dependence of rate coefficients measured for the reactions Cl + CH(3)CH(2)Br (eq 1 ) and Cl + CH(3)CH(2)CH(2)Br (eq 2 ) over the temperature range 221-436 K (units are 10(-11) cm(3) molecule(-1) s(-1)): k(1)(T) = 3.73?exp(-378/T) and k(2)(T) = 5.14?exp(+21/T). The accuracy (2σ) of rate coefficients obtained from the above expressions is estimated to be ±15% for k(2)(T) and +15/-25% for k(1)(T) independent of T. For the relatively slow reaction Cl + CH(2)BrCH(2)Br (eq 3 ), a nonlinear ln k(3) vs 1/T dependence is observed and contributions to observed kinetics from impurity reactions cannot be ruled out; the following modified Arrhenius expression represents the temperature dependence (244-569 K) of upper-limit rate coefficients that are consistent with the data: k(3)(T) ≤ 3.2 × 10(-17)T(2)?exp(-184/T) cm(3) molecule(-1) s(-1). Comparison of Br fluorescence signal strengths obtained when Cl removal is dominated by reaction with R-Br with those obtained when Cl removal is dominated by reaction with Br(2) (unit yield calibration) allows branching ratios for β-hydrogen abstraction (k(ia)/k(i), i = 1,2) to be evaluated. The following Arrhenius-type expressions are excellent representations of the observed temperature dependences: k(1a)/k(1) = 0.85?exp(-230/T) and k(2a)/k(2) = 0.40 exp(+181/T). The accuracy (2σ) of branching ratios obtained from the above expressions is estimated to be ±35% for reaction 1 and ±25% for reaction 2 independent of T. It appears likely that reactions 1 and 2 play a significant role in limiting the tropospheric lifetime and, therefore, the ODP of CH(3)CH(2)Br and CH(3)CH(2)CH(2)Br, respectively.     

MRI of intracranial sinovenous thrombosis: the role of phase imaging

Conventional spin-echo magnetic resonance (MR) imaging of venous thrombosis is complicated by the variable appearance produced by the stage of blood clot degradation and velocity of blood flow. Phase MR imaging is a simple method based primarily on whether protons are stationary or moving. A case of superior sagittal sinus thrombosis demonstrates the utility of phase imaging.     

Carbon-13 spectral analysis,tautomeric structures and conformations of four two-ring methylene-bridged phloroglucinol derivatives

The ¹³C NMR spectra of phloropyron BB, desaspidin BB, albaspidin BB and margaspidin BB were recorded and the structures of the compounds investigated with the aid of chemical shifts and CH coupling constants. The filicinic acid ring of the first three compounds appeared to have a monoketonic structure with the carbonyl group in position 2 (acyl group in position 3). The pyronone ring of phloropyron BB also has a monoketonic structure, with the carbonyl function adjacent to the ring oxygen. The two rings of the first three compounds attain a conformation where a stabilizing hydrogen bond(s) is (are) formed between the two rings, as shown by the observed CH couplings to some of the hydroxyl protons. The spectrum of margaspidin BB, whichconsists of two aromatic acyl phloroglucinol rings, indicates less inter-ring hydrogen bonding interactions.     

A tensile testing machine for a scanning electron microscope; Its structure,properties and applications

This work introduces a micro tensile testing machine built in to an ISI 40 SEM scanning electron microscope. With additional accessories (an anticontamination system and a Robinson detector), the machine is suitable for studying non-conductive materials, such as polymers, plastics and non-metallic composites, without coating, during tension or compression.With regard to its properties, the micro tensile testing machine developed in this context can structurally be compared in all aspects to normal mechanical universal tensile testing machines. The difference is that in this case, in addition to the conventional information (force, deformation), a continuing picture of the surface of test materials can be recorded from the area where the most interesting changes are happening. With the micro tensile testing machine it has been possible to retain all movements of the specimen stage, which enables the efficient observation of the specimen in a scanning electron microscope.The examples of applications presented in this paper show that the tensile machine is suitable and useful in studies of plastics and plastic-based composites in a very wide area.     

Hydrodesulfurization activity and transformations of nickel molybdate hydrate

Nickel molybdate hydrate has been found to be an effective precursor catalyst for the hydrodesulfurization of thiophene. Calcination of the hydrate at 300°C and presulfidation with H₂S are favorable treatments for higher activity.

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