The influence of different heat shielding constructions on the distribution of temperature and thermoelastic and residual
stresses in growing basal-plane-faceted sapphire ribbons (Al2O3) is studied. It is shown that inclined shields decrease thermoelastic stresses owing to the redistribution of heat fluxes
from a heater to a ribbon, which allows growing block-free basal-plane-faceted sapphire ribbons. 相似文献
The ways in which a block structure is formed in shaped sapphire single crystals grown from melt by the Stepanov method are
considered. The measured temperature distributions and results of a mathematical modeling of the heat exchange in the growth
zones, as well as the calculated thermoelastic fields and measured residual stresses, are reported. The possibility of effectively
controlling the thermal fields and growth of block-free crystals by choosing optimal screening is shown for single crystals
in the form of tubes and basal-plane-faceted ribbons. 相似文献
5-(Ethylamino)-9-diethylaminobenzo[a]phenothiazinium chloride (EtNBS) is a photosensitizer (PS) with broad antimicrobial photodynamic activity. The objective of this study was to determine the antimicrobial photodynamic effect of side chain/end group modifications of EtNBS on two representative bacterial Gram-type-specific strains. Two EtNBS derivatives were synthesized, each functionalized with a different side-chain end-group, alcohol or carboxylic acid. In solution, both exhibited photochemical properties consistent with those of the EtNBS parent molecule. In vitro photodynamic therapy experiments revealed an initial Gram-type-specificity with two representative strains; both derivatives were phototoxic to Staphylococcus aureus 29,213 but the carboxylic acid derivative was nontoxic to Escherichia coli 25,922. This difference in photodynamic efficacy was not due to a difference in the binding of the two molecules to the bacteria as the amount of both derivatives bound by bacteria was identical. Interestingly, the carboxylic acid derivative produced no fluorescence emission when observed in cultures of E. coli via fluorescence microscopy. These early findings suggest that the addition of small functional groups could achieve Gram-type-specific phototoxicity through altering the photodynamic activity of PSs and deserve further exploration in a larger number of representative strains of each Gram type. 相似文献
A cunning and dangerous plan foiled! An enzyme‐specific molecular construct exploits the overexpression of β‐lactamase in several drug‐resistant bacteria. Specific photodynamic toxicity was detected towards β‐lactam‐resistant methicillin‐resistant Staphylococcus aureus (MRSA), whereby the usual mechanism for antibiotic resistance (cleavage of the β‐lactam ring) releases the phototoxic component from the prodrug (see picture; Q=quencher).
The functional definition of extended-spectrum β-lactamase (ESBL) activity is a clinical challenge. Here we report a rapid and convenient assay of β-lactamase activity through the competitive inhibition of fluorescent substrate hydrolysis that provides a read-out nearly 40× more rapidly than conventional techniques for functional definition. A panel of β-lactam antibiotics was used for competition against β-lactamase enzyme-activated photosensitizer (β-LEAP) yielding a competitive index (Ci) in 30 min. Significant differences in the relative Ci values of the panel of β-lactams were determined in vitro for Bacillus cereus penicillinase. Additionally, the relative Ci values for whole bacterial cell suspensions of B. cereus 5/β were compared with the relative minimal inhibitory concentration (MIC) values and a correlation coefficient of 0.899 was determined. We further demonstrated the ability of β-LEAP to probe the capacity of ceftazidime to inhibit the enzyme activity of a panel of ESBL-producing Escherichia coli. The bacteria were assayed for susceptibility to ceftazidime and the relative MIC values were compared with the relative Ci values for ceftazidime yielding a correlation coefficient of 0.984. This work demonstrates for the first time the whole cell assay of the competitive inhibition of β-lactamase enzyme activity and derivation of associated constants. 相似文献