AKD-Modification of bacterial cellulose aerogels in supercritical CO2

Different approaches towards hydrophobic modification of bacterial cellulose aerogels with the alkyl ketene dimer (AKD) reagent are presented. If AKD modification was performed in supercritical CO₂, an unexpectedly high degree of loading was observed. About 15 % of the AKD was bound covalently to the cellulose matrix, while the other part consisted of re-extractable AKD-carbonate oligomers, which are novel chemical structures described for the first time. These oligomers contain up to six AKD and CO₂ moieties linked by enolcarbonate structures. The humidity uptake from environments with different relative humidity by samples equipped with up to 30 % AKD is strongly reduced, as expected due to the hydrophobization effect. Samples above 30 % AKD, and especially at very high loading between 100 and 250 %, showed the peculiar effect of increased humidity uptake which even exceeded the value of unmodified bacterial cellulose aerogels.     

Observation of content and heterogeneity of poly-β-hydroxybutyric acid (PHB) in Legionella bozemanii by vibrational spectroscopy

Information on how cells respond to their environment, interact with each other, or undergo complex processes such as cellular differentiation or gene expression has been obtained mostly by interference from population-level data. Individual microorganisms, even those on supposedly "clonal" populations, may differ widely from each other in terms of their genetic composition, physiology, biochemistry, or behaviours. This genetic and phenotypic heterogeneity has important practical consequences for a number of relevant interests, including antibiotic or biocide resistance, the productivity and stability of industrial fermentations, the efficacy of food preservatives, and the potential of pathogens to cause disease. Here we introduce vibrational spectroscopy to characterize Legionella bozemanii with respect to its content of poly-hydroxybutyric acid (PHB) and its distribution on both the population level and the single cell level.     

Total Synthesis of the Hypermodified RNA Bases Wybutosine and Hydroxywybutosine and Their Quantification Together with Other Modified RNA Bases in Plant Materials

We report an efficient synthesis of the hypermodified natural tRNA modifications wybutosine (yW) and hydroxywybutosine (OHyW). We also describe the preparation of isotopically labeled analogues for precise quantification of yW and OHyW in different tissues including plant materials. The synthesis involved the formation of the unusual tricyclic ring structure of the bases by using a catalytic, intramolecular hydroamination reaction. The basis for the synthesis is also a stereoselective coupling reaction that allows the introduction of the fully substituted side chains to the tricyclic core structure. The isotopologues of yW and OHyW, together with other isotopically labeled tRNA modifications, were ultimately used in LC‐MS quantification experiments to investigate the role of the modified bases in the translational process. Quantification was performed in the plant species Arabidopsis thaliana.     

Development of an Improved Rhodium Catalyst for Z‐Selective Anti‐Markovnikov Addition of Carboxylic Acids to Terminal Alkynes

To develop more active catalysts for the rhodium‐catalyzed addition of carboxylic acids to terminal alkynes furnishing anti‐Markovnikov Z enol esters, a thorough study of the rhodium complexes involved was performed. A number of rhodium complexes were characterized by NMR, ESI‐MS, and X‐ray analysis and applied as catalysts for the title reaction. The systematic investigations revealed that the presence of chloride ions decreased the catalyst activity. Conversely, generating and applying a mixture of two rhodium species, namely, [Rh(DPPMP)₂][H(benzoate)₂] (DPPMP=diphenylphosphinomethylpyridine) and [{Rh(COD)(μ₂‐benzoate)}₂], provided a significantly more active catalyst. Furthermore, the addition of a catalytic amount of base (Cs₂CO₃) had an additional accelerating effect. This higher catalyst activity allowed the reaction time to be reduced from 16 to 1–4 h while maintaining high selectivity. Studies on the substrate scope revealed that the new catalysts have greater functional‐group compatibility.     

Superior performance of liposomes over enzymatic amplification in a high-throughput assay for myoglobin in human serum

Myoglobin is one of several cardiac markers which become elevated in the blood following an acute myocardial infarction and can aid in the diagnosis of a heart attack. Here, a sandwich immunoassay for myoglobin was developed, including a thorough optimization of fluorescent dye-encapsulating liposomes versus enzymatic amplification (alkaline phosphatase and horseradish peroxidase) at each step. The optimized microtiter plate-based assay was capable of detecting as low as 11.3 pg/mL myoglobin and was successfully applied for the quantification of myoglobin in human serum. In comparison to enzymatic approaches, the liposomes demonstrated lower limits of detection, significantly reduced limits of quantification, improved signal discrimination through substantial signal enhancement, and reduced assay time. Liposomes were stable and functional at ambient temperatures for over 400 days. Finally, ease of use was greater due to lack of reliance on additional reagents, non-time-based signal enhancement, and excellent photostability. Optimal conditions identified for enzymatic approaches can also be used for liposome amplification, which makes substitution of these liposomes into existing assays straightforward. Thus, the extensive studies carried out here suggest that liposomes may be incorporated into formats currently utilizing enzymatic enhanced fluorescence with a potential for increased performance on various levels.

Chromophores in cellulosics,XI: isolation and identification of residual chromophores from bacterial cellulose

In the present work, bacterial cellulose (BC) was analyzed for its chromophore content with the chromophore release and identification (CRI) method. In aged BC, seven chromophores were unambiguously identified, despite their very low (ppb) presence. The compounds contain 2-hydroxy-[1,4]benzoquinone, 2-hydroxyacetophenone and 5,8-dihydroxy-naphthoquinone moieties. These three classes of key chromophores had also been found in other celluloses such as bleached pulp, fiber and derivatives. The detection of chromophores in lignin-free BC confirms that the chromophores are formed from oxidized and degraded carbohydrate material rather than lignin fragments. Samples that were insufficiently purified before the aging step also yielded three N-heterocyclic compounds. They originated from tryptophan moieties in residual adhering protein and protein degradation products. N-Heteropentacycles 9 and 10 showed strong adsorption onto cellulosic surfaces, and that adsorption aided oxidation of cyclohexadiene derivative 9 into the corresponding aromatic and intensely yellow system 10, consistent with the strain-induced bond localization theory. In purified fresh BC, no chromophores were detectable by the CRI method. The present contribution is the first report on defined chromophoric structures isolated from BC.     

Adjoint concepts for the optimal control of Burgers equation

Adjoint techniques are a common tool in the numerical treatment of optimal control problems. They are used for efficient evaluations of the gradient of the objective in gradient-based optimization algorithms. Different adjoint techniques for the optimal control of Burgers equation with Neumann boundary control are studied. The methods differ in the point in the numerical algorithm at which the adjoints are incorporated. Discretization methods for the continuous adjoint are discussed and compared with methods applying the application of the discrete adjoint. At the example of the implicit Euler method and the Crank Nicolson method it is shown that a discretization for the adjoint problem that is adjoint to the discretized optimal control problem avoids additional errors in gradient-based optimization algorithms. The approach of discrete adjoints coincides with that of automatic differentiation tools (AD) which provide exact gradient calculations on the discrete level.