3D optical coherence tomography as new tool for microscopic investigations of nucleate boiling on heated surfaces

Boiling phenomena are an important aspect in security and efficiency for technical applications with high heat flux like nuclear reactors. This study presents optical coherence tomography (OCT) as a novel modality for three-dimensional and two-dimensional time resolved imaging of nucleate boiling on heated surfaces on a microscopic scale with high spatial (<10 μm) and temporal (>25 frames per second) resolution. Within this study, a borosilicate glass plate coated with an optically transparent and electrically conductive indium tin oxide (ITO) layer with a thickness of approximately 100 nm was used as heating surface. The combination of these two properties allows optical inspection of the nucleate boiling from the backside by OCT focused on the formation, growth and detachment of single bubbles. We demonstrated for the first time that OCT is an excellent tool to acquire two-dimensional and three-dimensional images of the base of vapor bubbles from the backside of the heated surface. The acquired images allow for instance the temporally resolved measurement of the bubble diameter, diameter of the bubble base and the contact angle. Exploiting the phase information of the acquired OCT signal stacks allows imaging the movement of the bubble surrounding fluid. We think that OCT will provide many new insights into the boiling phenomena at the bubble base. The recent enhancement of the acquisition rates of OCT systems will facilitate four-dimensional imaging of single bubble evaporation procedures in the nearer future.     

Asymmetric hybrid silica nanomotors for capture and cargo transport: towards a novel motion-based DNA sensor

An innovative self-propelled nanodevice able to perform motion, cargo transport, and target recognition is presented. The system is based on a mesoporous motor particle, which is asymmetrically functionalized by the attachment of single-stranded DNA onto one of its faces, while catalase is immobilized on the other face. This enzyme allows catalytic decomposition of hydrogen peroxide to oxygen and water, giving rise to the driving force for the motion of the whole system. Moreover the motor particles are able to capture and transport cargo particles functionalized with a noncomplementary single-stranded DNA molecule, only if a specific oligonucleotide sequence is present in the media. Functionalization with characteristic oligonucleotide sequences in the system implies a potential for further developments for lab-on-chip devices with applications in biomedical applications.     

Wild Lactobacillus strains: Technological characterisation and design of Coalho cheese lactic culture

To design a specific lactic culture for the controlled manufacture of coalho cheese, 13 Lactobacillus rhamnosus, two Lactobacillus fermentum and one Lactobacillus plantarum strains isolated from artisanal coalho cheeses were identified and characterised. Two Lb. rhamnosus, one Lb. plantarum and one Lb. fermentum were selected and grouped in pairs designing four different culture formulations that demonstrated a good performance in cheesemaking experiments at pilot scale. Further studies to adjust the balance of strains used are necessary to attain adequate sensorial and technological attributes as expected for artisanal cheeses.     

Analysis of nitrosamines in wastewater: exploring the trace level quantification capabilities of a hybrid linear ion trap/orbitrap mass spectrometer

A method was developed to determine nine N-nitrosamines in wastewater on the basis of solid-phase extraction and liquid chromatography mass spectrometry using a linear ion trap-orbitrap hybrid instrument at high mass resolution. Analytes and five deuterated internal standards were preconcentrated by solid-phase extraction. Positive electrospray ionization resulted in protonated molecular ions of all nitrosamines. One to three product ions were formed by collision-induced dissociation or higher energy C-trap dissociation. The signal intensity of the product ions differed up to a factor of 3 between the two techniques. The molecular ions were usually used for quantification, because of the better sensitivity, and the product ions for confirmation. An actual mass resolving power of 25 000-40 000 ensured a sufficient selectivity to distinguish all molecular and product ions from interfering background ions. Only for N-nitrosomorpholine was a coeluting isobaric molecular ion detected in wastewater samples, which, however, formed different product ions. The mass accuracy was between -12 ppm at m/z 55 and 0 ppm at m/z 205 and did not change for more than 5 ppm over a sample sequence of 20 h analysis time. The optimized method allowed quantifying nine N-nitrosamines in drinking water and wastewater samples down to method detection limits of 0.3-3.9 ng/L at instrumental detection limits of 2-14 pg on column. Recoveries over the whole method were between 75 and 125% for six compounds, but considerably lower for three compounds, probably due to strong matrix effects causing a signal suppression of up to 95% in wastewater samples. N-Nitrosodimethylamine and N-nitrosomorpholine were the most abundant compounds (3-22 ng/L) in samples from two wastewater treatment plants, another four nitrosamines (N-nitrosopyrrolidone, -piperidine, -diethylamine, and -dibutylamine) were also detected. Our study demonstrates that the LTQ Orbitrap is a powerful instrument to quantify low molecular weight compounds at the picogram level in complex matrixes with both a high sensitivity and selectivity.     

Enzymatic formation of styrene during wheat beer fermentation is dependent on pitching rate and cinnamic acid content

Styrene is formed by the thermal decarboxylation of cinnamic acid during wort boiling or by enzymatic decarboxylation during fermentation. The enzymatic reaction processes simultaneously to the decarboxylation of ferulic‐ and p‐cumaric acid to clove‐like 4‐vinylguaiacol and phenolic 4‐vinylphenol by the same PAD1 and FDC1 decarboxylase enzymes. However, the formation of styrene occurs much faster within the first hours of fermentation. In addition, the conversion of cinnamic acid starts immediately after pitching without an adaption of yeast on the new medium. Only after 120 min does the level of transposition decrease. Moreover, high cinnamic acid content in pitching wort, in combination with an open fermentation management, causes faster and higher styrene formation during this period. In contrast to the formation of 4‐vinylguaiacol, a correlation between pitching rate and styrene formation during open fermentation could be shown. The resulting time interval between styrene and 4‐vinylguaiacol formation provides scope for minimization strategies for styrene, while maintaining the typical wheat beer flavours. Copyright © 2012 The Institute of Brewing & Distilling     

Reactions of a sulfonamide antimicrobial with model humic constituents: assessing pathways and stability of covalent bonding

The mechanism of covalent bond formation of the model sulfonamide sulfathiazole (STZ) and the stronger nucleophile para-ethoxyaniline was studied in reactions with model humic acid constituents (quinones and other carbonyl compounds) in the absence and presence of laccase. As revealed by high resolution mass spectrometry, the initial bonding of STZ occurred by 1,2- and 1,4-nucleophilic additions of the aromatic amino group to quinones resulting in imine and anilinoquinone formation, respectively. Experiments using the radical scavenger tert-butyl-alcohol provided the same products and similar formation rates as those without scavenger indicating that probably not radical coupling reactions were responsible for the initial covalent bond formation. No addition with nonquinone carbonyl compounds occurred within 76 days except for a slow 1,4-addition to the β-unsaturated carbonyl 1-penten-3-one. The stability of covalent bonds against desorption and pressurized liquid extraction (PLE) was assessed. The recovery rates showed no systematic differences in STZ extractability between the two product types. This suggests that the strength of bonding is not controlled by the initial type of bond, but by the extent of subsequent incorporation of the reaction product into the formed polymer. This incorporation was monitored for (15)N aniline by (1)H-(15)N HMBC NMR spectroscopy. The initial 1,2- and 1,4-addition bonds were replaced by stronger heterocyclic forms with increasing incubation time. These processes could also hold true for soils, and a slow nonextractable residue formation with time could be related to a slow increase of the amount of covalently bound sulfonamide and the strength of bonding.     

Nucleic acid delivery: the missing pieces of the puzzle?

The delivery of genes or RNA interference (RNAi) agents can increase or decrease the expression of virtually any protein in a cell, and this process opens the path for cures to most diseases that afflict humans. However, the high molecular weight, anionic nature, and instability of nucleic acids in the presence of enzymes pose major obstacles to their delivery and frustrates their use as human therapies. This Account describes current ideas about the mechanisms in nonviral nucleic acid delivery and how lipidic and polymeric carriers can overcome some of the critical barriers to delivery. Over the last 20 years, researchers have developed a multitude of polymeric and lipidic vectors, but only a small fraction of these have progressed into clinical trials. None of these vectors has received FDA approval, which indicates that the current vectors do not yet have suitable properties for effective in vivo nucleic acid delivery. Nucleic acid delivery is a multistep process and inefficiencies at any stage result in a dramatic decrease in gene delivery or gene silencing. However, the majority of studies investigating synthetic vectors focus solely on optimization of endosomal escape. A small number of studies address how to improve uptake via targeted delivery, and an even smaller fraction examine the intracellular fate of the delivery systems and nucleic acid cargo. The internalization of genes into the cell nucleus remains an inefficient and mysterious process. In the case of DNA delivery, strategies are needed to increase and accelerate the migration of DNA through the cytoplasm and transport it through the nuclear membrane. siRNA delivery involves fewer barriers. siRNA is more readily released from the carrier and more resistant to enzymatic degradation, and its target is in the cytoplasm; hence, siRNA delivery systems are becoming a clinical reality. With regard to siRNA therapy, the exact cytoplasmic location of RNA-induced silencing complex (RISC) formation and activity is unknown, which makes specific targeting of the RISC for more efficient delivery difficult. Furthermore, we would like to identify the factors that favor the binding of siRNA to Ago-2. If we could understand how the half-life of siRNA and Ago-2/siRNA complex in the cytoplasm can be modulated without interfering with RISC functions that are essential for normal cell activity, we could increase siRNA delivery efficiency. In this Account, we review the current synthetic vectors and propose alternative strategies in a few cases. We also suggest how certain cellular mechanisms might be exploited to improve gene transfection and silencing. Finally, we discuss whether some carriers that deliver the siRNA to cells could also repackage the siRNA into exosomes. The exosomes would then transport the siRNA into a subsequent population of cells that manifest the siRNA effect. This piggy-back mechanism may be responsible for reported deep tissue siRNA effects using certain carriers.     

Levels of PCDD/Fs, PCBs, and PCNs in soils and vegetation in an area with chemical and petrochemical industries

The concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDFs), polychlorinated biphenyls (PCBs), and polychlorinated naphthalenes (PCNs) have been determined in soil and wild chard samples collected in an area of Tarragona County (Catalonia, Spain) with an important number of chemical and petrochemical industries. Samples were also collected in urban/residential zones, as well as in presumably unpolluted sites. In soils, the levels of PCDD/Fs ranged from 0.16 ng I-TEQ/kg (unpolluted sampling points) to 2.65 ng I-TEQ/kg (industrial zone), and those of sigmaPCBs ranged from 657 to 12038 ng/ kg in these same zones. In turn, sigmaPCNs ranged from 32 (unpolluted sites) to 180 ng/kg (residential/urban sites). In contrast to soil concentrations, there were not significant differences among collection zones in the levels of PCDD/Fs, PCBs, and PCNs found in chard. However, PCB and PCN concentrations in chard samples collected at the unpolluted sampling points were higher than the respective concentrations in soils. In general terms, the current concentrations of the organic pollutants analyzed in this study are similar or lower than data from previous reports in other countries.     

Study of Thermal Degradation Kinetics of Elastomeric Powder (Ground Tire Rubber)

This paper investigates the use of thermogravimetric analysis to study the kinetics of thermal degradation of ground tire rubber (GTR) obtained from reclaimed tires. We analyzed the composition of GTR and determined the content percentage of its components (volatile compounds, rubber, and ash) using thermogravimetric analysis (TGA). T ₁ and T ₂ temperature peaks corresponding to the maximum normalized weight loss rate (NWLR) of the two main rubber components of tires NR (natural rubber) and a BR/SBR (butadiene/styrene-butadiene rubber blend) using the Gaussian deconvolution method has been determined. The influence of GTR particle size and heating rate on reaction rates (dx/dt) and on degradation time during the degradation process has been analyzed.