Degradation of cellulose in historic paper by iron gall ink is a synergistic process of both, acid hydrolysis caused by acidic
ink ingredients and oxidation catalyzed by free iron and/or copper ions. The interplay of both reactions was studied according
to the CCOA method on historic paper samples. Only minute amounts (few mg) of the samples were required to obtain profiles
of naturally present and oxidatively introduced carbonyl groups, which was done by group-selective fluorescence labeling in
combination with determination of the molecular weight distribution by GPC-MALLS. In the present study naturally occurring
degradation pathways in historic sample papers have been investigated. Different extents of oxidatitive degradation were shown
for paper with and without ink. A typical pattern of the molecular weight distribution in naturally aged papers was identified,
the peculiar feature being a distinctive shoulder in the region of low molecular weight, roughly between 25,000 and 5,000 g/mol
corresponding to a DP between 150 and 30. This pattern was a typical attribute of degraded natural samples: any artificial
aging procedures aimed at modeling natural aging processes must thus attempt to reproduce this feature. Although the historic
samples had been more severely oxidized than model papers, the inhibition of further oxidation and hydrolysis by the calcium
phytate/hydrogen carbonate treatment was evident and could be proven for the first time on the molecular level. Also on plain
paper without ink application the oxidation was suppressed and the molecular weight was stabilized on a high level. 相似文献
Cellulose in historic paper documents is often damaged by the writing media used, especially iron gall ink or copper pigments.
Degradation induced by iron gall ink is suggested to be a synergistic process comprising both hydrolytic and oxidative reactions.
These processes were studied on very low sample amounts according to the CCOA and FDAM method, i.e. by fluorescence labeling
of carbonyl and carboxyl groups in combination with GPC-MALLS, respectively. This study focused on preventive means to stop
the deterioration induced by iron gall ink of cellulose and to prevent further damage, keeping in mind that a suitable conservation
treatment has to hinder both, hydrolytic and oxidative processes, at the same time. A combination of the complexing agent
calcium phytate and calcium hydrogencarbonate in aqueous solution was proved to give optimum results. To gain insight into
long term stability, an aging step was performed after treatment and different ink modifications were tested. Recording the
molecular weight distributions and the carbonyl group content over time GPC analysis verified for the first time the preventive
effect of this treatment. This effect was not only seen for the ink-covered areas, but extended also to areas remote from
the ink lines. Ink containing copper ions responded equally positively to the calcium phytate/hydrogencarbonate treatment
as the iron gall ink papers did. Gelatine, sometimes used in a similar way due to an alleged cellulose-stabilizing effect
did not have a beneficial influence on cellulose integrity when metal ions were present. 相似文献
The deeper understanding of metastasis phenomenon and detection of drug targets could be a potential approach to minimize cancer mortality. In this study, attempts were taken to unmask novel therapeutics to prevent metastasis and cancer progression. Initially, we explored the physiochemical, structural and functional insights of three metastasis tumor antigens (MTAs) and evaluated some plant-based bioactive compounds as potent MTA inhibitors. From 50 plant metabolites screened, isoflavone, gingerol, citronellal and asiatic acid showed maximum binding affinity with all three MTA proteins. The ADME analysis detected no undesirable toxicity that could reduce the drug likeness properties of top plant metabolites. Moreover, molecular dynamics studies revealed that the complexes were stable and showed minimum fluctuation at molecular level. We further performed ligand-based virtual screening to identify similar drug molecules using a large collection of 376,342 compounds from DrugBank. The results suggested that several structural analogs (e.g., tramadol, nabumetone, DGLA and hydrocortisone) may act as agonist to block the MTA proteins and inhibit cancer progression at early stage. The study could be useful to develop effective medications against cancer metastasis in future. Due to encouraging results, we highly recommend further in vitro and in vivo trials for the experimental validation of the findings.
This communication reports the investigation of the pH effects on the interaction of a well-known lung surfactant, Dipalmitoylphosphatidylcholine (DPPC) with water soluble highly fluorescent dye Rhodamine B (RhB) in complex Langmuir monolayers at the air–water interface. The ionic nature of DPPC changes with the pH of the subphase in the Langmuir trough. At sufficiently low pH it becomes cationic whereas at higher pH it can be presented with a negative net charge and at normal pH it is zwitterionic. Being zwitterionic, RhB molecules can interact with DPPC at normal and higher pH, whereas at lower pH the interaction becomes less probable. This has been investigated in details at the air–water interface in Langmuir trough as well as in Langmuir Blodgett (LB) film by employing surface pressure versus area per molecule (π–A) isotherms, compressibility study, in-situ Fluorescence Imaging Microscopy (FIM), UV-vis absorption spectroscopy and Atomic Force Microscopy (AFM) study. 相似文献
Summary: Copper corrosion on paper works of art is commonly explained by copper ion-catalysed cellulose oxidation, usually reflected by discoloration of pigment and surrounding paper as well as by loss of mechanical strength. In this study, model paper and historic paper samples, both containing copper pigments, were compared using fluorescence labelling of carbonyl groups and subsequent GPC analysis. The historic paper samples did not show any typical sign of copper pigment induced discoloration, but high brittleness. In artificially copper-corroded paper samples the distribution of carbonyl groups in combination with the molecular weight distribution of cellulose clearly indicated the occurrence of oxidative processes. In contrast, only insignificant oxidative damage was detected in the case of the paper fragments from an original work of art, a codex from the 15th century. Here, mostly degradation by hydrolytic action was revealed. There was no introduction of carbonyl groups into the bulk section of the molecular weight distribution, and the gain in new carbonyl groups corresponded to the number of reducing end groups newly generated by hydrolysis. 相似文献
We consider a finite-buffer single-server queue with renewal input where the service is provided in batches of random size
according to batch Markovian service process (BMSP). Steady-state distribution of number of customers in the system at pre-arrival and arbitrary epochs have been obtained along
with some important performance measures. The model has potential applications in the areas of computer networks, telecommunication
systems, and manufacturing systems, etc.
相似文献
Highly functionalized bicyclo[3.2.1]-octanone derivatives have been prepared by metal catalyzed decompostion of diazoketones through a net retention of configuration at the benzylic center. 相似文献
Glycosylation of racemic and optically active α-hydroxy β-lactams by reaction with a few glycal derivatives in the presence of catalytic amounts of iodine has provided stereospecific formation of α-glycosides. This method has been extended for the preparation of optically active hydroxy β-lactams in excellent yields. The stereochemistry and nature of the glycals as well as the stereochemistry of the β-lactam ring has a profound influence for effective glycosylation. 相似文献