Labile Structures Research Articles

Role of Carbonaceous Fragments on the Functionalization and Electrochemistry of Carbon Materials

AbstractCarbonaceous fragments (CF) formed by acid treatment of carbon materials have important properties that are not completely understood. In this work, CF were produced by oxidation of CNT by using mineral acid followed by treatment with NaOH. The role of CF on CNT voltammetric properties was studied by using different materials: oxidized CNT (a‐CNT), a‐CNT refluxed in NaOH and neutralized with HCl (b‐CNT), pristine CNT exposed to a CF suspension (c‐CNT), and b‐CNT exposed to a CF suspension (r‐CNT). The extension of functionalization of these materials was evaluated by thermogravimetric analysis (TGA). The spectroscopic characterization (UV/Vis, fluorescence, FTIR, Raman and NMR) of CF indicates the presence of graphene‐type conjugated aromatic rings with highly oxidized moieties. In this work we demonstrate that CF are responsible for the ameliorated voltammetric properties of oxidized CNT. Adsorption of CF on oxidized and non‐oxidized CNT showed that CF provide active sites for hydroquinone (HQ) adsorption, enhancing current responses. The interaction of CF with carbon materials depended on both the surface oxidation degree and the surface roughness. Voltammograms from CF adsorbed on oxidized CNT indicate the presence of labile supramolecular structures with a voltammetric response typical of quinoid units. Carbon materials functionalized with CF displayed lower peak potentials and higher currents (30 to 180 %) than the unmodified electrodes, demonstrating that CF is a promising material for sensors design.

Fire effects in the molecular structure of soil organic matter fractions under Quercus suber cover

Forest fires cause immediate and lasting environmental impacts in soil organic matter (SOM) by modifying existing chemical structures, forming new ones, or adding/removing materials such as fresh or charred biomass. In this paper, the information provided by analytical pyrolysis (Py-GC/MS) of whole soil samples and two particle-size fractions (coarse and fine) is analysed in a sandy soil from a typical Mediterranean oak forest close to Doñana National Park (Southwest Spain) that was affected by a severe wildfire. The pyrograms from unburnt whole soil samples show a prevalence of compounds derived from polysaccharides, proteins and lignin, whereas in pyrograms from burnt soils lignin markers prevail followed by proteins, alkylaromatic and polycyclic aromatic hydrocarbons. In fact, it seems clear that fire preferentially removes thermolabile biogenic materials with a concomitant selective preservation of lignin. Concerning particle size fractions, SOM in the unburnt coarse fraction had a major impact on vegetation, whereas the fine fraction consisted of comparatively humified SOM with lignin degradation and microbial-derived compounds. The pyrolysis products from the burnt soil coarse fraction revealed post-fire litter inputs from stressed vegetation, whereas the fine fraction shares chemical characteristics with those from the unburnt soil, with additional signs of fire alteration (less labile carbohydrate structures and higher relative abundance of PAHs). Alkane changes observed in the carbon preference index indicate that fire affected SOM mostly in the fine fraction, whereas the short/long chain ratio points to the cracking of long-chain alkanes. In addition, when plotting O/C and H/C values in a Van Krevelen diagram, additional information about the main chemical modifications produced by fire in SOM are described, including condensation (oxidation and hydrogenation paralleling) and dealkylation (associated with oxidation and dehydrogenation) processes. This is the first time that Py-GC/MS molecular information from soil samples is analysed using a Van Krevelen graphical approach and together with other classic geochemical proxies it proves to be a valuable and intuitive tool in facilitating the interpretation of complex geochemical data.

Selective forces and mutational biases drive stop codon usage in the human genome: a comparison with sense codon usage.

BackgroundThe three stop codons UAA, UAG, and UGA signal the termination of mRNA translation. As a result of a mechanism that is not adequately understood, they are normally used with unequal frequencies.ResultsIn this work, we showed that selective forces and mutational biases drive stop codon usage in the human genome. We found that, in respect to sense codons, stop codon usage was affected by stronger selective forces but was less influenced by neutral mutational biases. UGA is the most frequent termination codon in human genome. However, UAA was the preferred stop codon in genes with high breadth of expression, high level of expression, AT-rich coding sequences, housekeeping functions, and in gene ontology categories with the largest deviation from expected stop codon usage. Selective forces associated with the breadth and the level of expression favoured AT-rich sequences in the mRNA region including the stop site and its proximal 3’-UTR, but acted with scarce effects on sense codons, generating two regions, upstream and downstream of the stop codon, with strongly different base composition. By favouring low levels of GC-content, selection promoted labile local secondary structures at the stop site and its proximal 3’-UTR. The compositional and structural context favoured by selection was surprisingly emphasized in the class of ribosomal proteins and was consistent with sequence elements that increase the efficiency of translational termination. Stop codons were also heterogeneously distributed among chromosomes by a mechanism that was strongly correlated with the GC-content of coding sequences.ConclusionsIn human genome, the nucleotide composition and the thermodynamic stability of stop codon site and its proximal 3’-UTR are correlated with the GC-content of coding sequences and with the breadth and the level of gene expression. In highly expressed genes stop codon usage is compositionally and structurally consistent with highly efficient translation termination signals.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2692-4) contains supplementary material, which is available to authorized users.

Quantification of perflutren microsphere contrast destruction during transit through an ex vivo extracorporeal membrane oxygenation circuit.

BackgroundEchocardiography is a key investigation in the management of patients on extracorporeal membrane oxygenation (ECMO). However, echocardiographic images are often non-diagnostic in this patient population. Contrast-enhanced echocardiography may overcome many of these limitations but contrast microspheres are hydrodynamically labile structures prone to destruction from shear forces and turbulent flow, which may exist within an ECMO circuit. This study sought to evaluate microsphere destruction (utilising signal intensity as a marker of contrast concentration) during transit through an ECMO circuit.MethodsActivated Definity® contrast was diluted to 50 ml with normal saline and infused into a crystalloid primed ex vivo ECMO with a Quadrox oxygenator at 150 ml/h. Imaging was performed on pre- and post-pump head/oxygenator sections of the circuit using a Philips iE33 scanner and S5-1 transducer. Five-millimetre regions of interest were placed in the centre of the ultrasound field. Average signal intensity (decibels) was calculated at speeds of 1000, 2000, 3000 and 4000 rpm and then repeated with an infusion rate of 300 ml/h. The oxygenator was then spliced out of the circuit and the measures repeated.ResultsThere was a significant reduction in contrast concentration during passage through the ECMO circuit at all speeds (with higher pump head speeds resulting in greater microsphere destruction). In a circuit with an oxygenator, relative decrease in signal intensity was 21.4 versus 5.2 % without an oxygenator. There was significant destruction of contrast microspheres during passage through the ECMO circuit at all pump head speeds. An oxygenator contributed to microsphere destruction at a significantly greater level than the pump head alone. There was no significant difference in mean signal intensity reduction in the circuit between an infusion of 150 or 300 ml/h (3.5 ± 3.2 versus 3.6 ± 2.5 dB, respectively, p = 0.79).ConclusionsFlow of contrast through an ECMO circuit results in significant destruction of microspheres. Circuits with an oxygenator result in significantly greater levels of contrast destruction than by the pump head alone. Clinicians should be cognisant of the relationship between ECMO circuit configurations, pump head speed and contrast destruction when performing a contrast-enhanced echocardiogram in patients supported with ECMO.Electronic supplementary materialThe online version of this article (doi:10.1186/s40635-016-0079-0) contains supplementary material, which is available to authorized users.

Structure-Property-Function Relationship in Humic Substances to Explain the Biological Activity in Plants.

Knowledge of the structure-property-function relationship of humic substances (HSs) is key for understanding their role in soil. Despite progress, studies on this topic are still under discussion. We analyzed 37 humic fractions with respect to their isotopic composition, structural characteristics, and properties responsible for stimulating plant root parameters. We showed that regardless of the source of origin of the carbon (C3 or C4), soil-extracted HSs and humic acids (HAs) are structurally similar to each other. The more labile and functionalized HS fraction is responsible for root emission, whereas the more recalcitrant and less functionalized HA fraction is related to root growth. Labile structures promote root stimulation at lower concentrations, while recalcitrant structures require higher concentrations to promote a similar stimulus. These findings show that lability and recalcitrance, which are derived properties of humic fractions, are related to the type and intensity of their bioactivity. In summary, the comparison of humic fractions allowed a better understanding of the relationship between the source of origin of plant carbon and the structure, properties, and type and intensity of the bioactivity of HSs in plants. In this study, scientific concepts are unified and the basis for the agronomic use of HSs is established.

Field-scale fluorescence fingerprinting of biochar-borne dissolved organic carbon

Biochar continues to receive worldwide enthusiasm as means of augmenting recalcitrant organic carbon in agricultural soils. Realistic biochar amendment rate (typically less than 1 wt%) in the field scale, and subsequent loss by sizing, rain, and other transport events demand reliable methods to quantify the remaining portions of amended biochar. This study employed fluorescence excitation-emission (EEM) spectrophotometry and parallel factor analysis (PARAFAC) to specifically target pyrogenic dissolved organic carbon (DOC) released by amended biochar during the course of a field trial at Bowling Green, KY experimental site. Toluene/methanol (1:6 v/v) extracts of surface (0–15 cm) soils amended with 21.28 t ha−1 fast pyrolysis biochar afforded PARAFAC fingerprints representing different degrees of aromaticity. Compared to the control without treatments, biochar treatment (with and without poultry manure or chemical fertilizer) increased the relative contribution of PARAFAC fingerprint attributable to labile polyaromatic DOC structures. Poultry manure or chemical fertilizer alone (without biochar) did not influence the amounts of polyaromatic DOC structures. Existence of biochar could be further validated by the changes in %DOC (relative to the total carbon), fixed C content, and UV absorbance (360 nm), whereas FTIR, %O, and sorption of model agrochemical (deisopropylatrazine) did not reflect the presence of biochar in the soil samples. Developed toluene/methanol-based EEM-PARAFAC technique will provide a sensitive, rapid, and cost-competitive method to validate the long-term carbon sequestration by the biochar soil amendment.

Supporting data for the characterization of PNA-DNA four-way junctions.

Holliday or DNA four-way junctions (4WJs) are cruciform/bent structures composed of four DNA duplexes. 4WJs are key intermediates in homologous genetic recombination and double-strand break repair. To investigate 4WJs in vitro, junctions are assembled using four asymmetric DNA strands. The presence of four asymmetric strands about the junction branch point eliminates branch migration, and effectively immobilizes the resulting 4WJ. The purpose of these experiments is to show that immobile 4WJs composed of DNA and peptide nucleic acids (PNAs) can be distinguished from contaminating labile nucleic acid structures. These data compare the electrophoretic mobility of hybrid PNA–DNA junctions vs. i) a classic immobile DNA 4WJ, J1 and ii) contaminating nucleic acid structures.

Precision Burn Trauma Medicine: Application for Molecular Engineering Science

range, the kinetic energy of the molecules in the cell plasma membrane exceeds the hydration energy barrier that holds phospholipids in the membrane as a supramolecular assembly [4, 5]. In effect, the heated membrane forms defects and becomes indiscriminately permeable, or “porous” to ions. Once permeabilized, the cell attempts to maintain the transmembrane ionic gradients by increasing the activity of cellular energy pumps, resulting in the rapid depletion of cellular energy charge. Unless the membrane defects are sealed before the degradation processes exceed certain limits, the permeabilized cell will lose viability. Because the cell plasma membrane is one of the most thermally labile cell structures, yet is critical for cell viability, tissue loss from thermal injury is heavily mediated by cell membrane disruption [4]. Protein structure tends to be more stable against thermal fluctuation than the lipid assembly in the cell plasma membrane due to stronger bonding forces. The melting temperatures of common structural proteins actin (intracellular) and collagen (extracellular), measured by near-equilibrium healing kinetics, have been reported at 67 °C and 58 °C respectively, well above the melting temperature of the cell plasma membrane. However, the melting temperature of protein denaturation is highly dependent on tissue density, macromolecular crowding, and the temperature history. Once thermal denaturation occurs, the exposed hydrophobic regions interact, resulting in biomolecular aggregation and alteration of both cell water structure and metabolic dynamics. Unless corrected, cell death followed by tissue necrosis will inexorably occur.

Chemical composition of organic matter in a deep soil changed with a positive priming effect due to glucose addition as investigated by 13C NMR spectroscopy

Fresh organic carbon becomes more accessible to deep soil following losses of surface soil and deep intentional incorporation of crop residues, which can cause the priming effect and influence the quality and quantity of SOC in deep soil. This study determined the priming effect due to addition of water-dissolved 13C-labeled glucose (0.4 g C kg−1 soil) to a soil taken from 1.00 to 1.20 m depth. The changes in chemical compositions of SOC in soils without (G0) and with (G0.4) glucose addition during a 31-d incubation were investigated with solid-state 13C cross polarization/total sideband suppression (13C-CP/TOSS) and CP/TOSS with dipolar dephasing nuclear magnetic resonance (NMR) techniques. No glucose remained in the soil after 21 days of incubation, with 48% being completely mineralized into CO2 emission and 52% being incorporated into SOC. The native SOC was decomposed by 0.23% more in G0.4 than in G0. The NMR spectra demonstrated that both labile and recalcitrant organic compounds in SOC changed during the incubation, but in different manners in G0 and G0.4. During the incubation, the -(CH2)n-abundance in G0 did not change over time, but in G0.4 it decreased from Day 0 to Day 21 and then increased from Day 21 to Day 31, suggesting shifts of soil microbial communities only in G0.4. After the incubation, in G0 the abundances of ketones/aldehydes and nonpolar alkyl C increased, but those of aromatic C–C and protonated O-alkyl C (OCH) decreased; In G0.4, the abundances of NCH and protonated O-alkyl C (OCH) increased, but those of nonpolar alkyl C and nonprotonated aromatic C–O and ketones/aldehydes decreased. Such inconsistent changes in recalcitrant compounds between G0 and G0.4 indicated that glucose addition likely primed the decomposition of aromatic C–O and suppressed the formation of ketones/aldehydes. We have demonstrated for the first time that the priming effect of SOC decomposition in the deep soil was involved with larger notable changes in both labile and recalcitrant structures of native SOC due to glucose addition compared with that without glucose addition.

Fragmentation behavior of poly(methyl methacrylate) during matrix-assisted laser desorption/ionization.

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been widely utilized for the structural characterization of various synthetic polymers. However, polymer sample molecules can occasionally decompose even in the MALDI process depending on the measurement conditions. In this work, the fragmentation behavior of radically polymerized poly(methyl methacrylate) (PMMA) during laser irradiation in MALDI was investigated in detail. Two types of PMMA samples with oligomeric molar mass were examined: Sample A was synthesized with an excess content of a chain transfer reagent to form simple molecules with less labile structures. Sample B was polymerized with a greater amount of a peroxide initiator without any chain transfer reagent, which resulted in the formation of various terminal and chain structures including relatively labile ones. The original components and fragment ions for the PMMA samples were precisely assigned using a high-resolution MALDI spiral time-of-flight MS system. Electrospray ionization MS measurements were also performed for comparison. The PMMA chains underwent fragmentation during the MALDI process with high laser intensity even for the relatively stable sample A. The fragmentation reactions proceeded mainly through 1,5-hydrogen rearrangements via a six-membered intermediate structure. Furthermore, PMMA molecules formed via recombination termination in sample B selectively decomposed during the MALDI-MS measurements even with low laser intensity. It was observed that the fragmentation reactions in the PMMA chains in MALDI with high laser power were generally the same as those in the post-source decay or collision-induced dissociation in MALDI-MS/MS measurements. Even with low laser intensity, less stable structures in the PMMA chain, especially head-to-head linkages, were readily decomposed during the MALDI process. Possible fragmentation, therefore, should be considered in the structural characterization of synthetic polymer samples by MALDI-MS.

Vaccinia virus mutations in the L4R gene encoding a virion structural protein produce abnormal mature particles lacking a nucleocapsid.

Electron micrographs from the 1960s revealed the presence of an S-shaped tubular structure in the center of the vaccinia virion core. Recently, we showed that packaging of virus transcription enzymes is necessary for the formation of the tubular structure, suggesting that the structure is equivalent to a nucleocapsid. Based on this study and on what is known about nucleocapsids of other viruses, we hypothesized that in addition to transcription enzymes, the tubular structure also contains the viral DNA and a structural protein as a scaffold. The vaccinia virion structural protein L4 stands out as the best candidate for the role of a nucleocapsid structural protein because it is abundant, it is localized in the center of the virion core, and it binds DNA. In order to gain more insight into the structure and relevance of the nucleocapsid, we analyzed thermosensitive and inducible mutants in the L4R gene. Using a cryo-fixation method for electron microscopy (high-pressure freezing followed by freeze-substitution) to preserve labile structures like the nucleocapsid, we were able to demonstrate that in the absence of functional L4, mature particles with defective internal structures are produced under nonpermissive conditions. These particles do not contain a nucleocapsid. In addition, the core wall of these virions is abnormal. This suggests that the nucleocapsid interacts with the core wall and that the nucleocapsid structure might be more complex than originally assumed. The vaccinia virus nucleocapsid has been neglected since the 1960s due to a lack of electron microscopy techniques to preserve this labile structure. With the advent of cryo-fixation techniques, like high-pressure freezing/freeze-substitution, we are now able to consistently preserve and visualize the nucleocapsid. Because vaccinia virus early transcription is coupled to the viral core structure, detailing the structure of the nucleocapsid is indispensable for determining the mechanisms of vaccinia virus core-directed transcription. The present study represents our second attempt to understand the structure and biological significance of the nucleocapsid. We demonstrate the importance of the protein L4 for the formation of the nucleocapsid and reveal in addition that the nucleocapsid and the core wall may be associated, suggesting a higher level of complexity of the nucleocapsid than predicted. In addition, we prove the utility of high-pressure freezing in preserving the vaccinia virus nucleocapsid.

Feasibility of perflutren microsphere contrast transthoracic echocardiography in the visualization of ventricular endocardium during venovenous extracorporeal membrane oxygenation in a validated ovine model.

Transthoracic echocardiography (TTE) during extra corporeal membrane oxygenation (ECMO) is important but can be technically challenging. Contrast-specific TTE can improve imaging in suboptimal studies. These contrast microspheres are hydrodynamically labile structures. This study assessed the feasibility of contrast echocardiography (CE) during venovenous (VV) ECMO in a validated ovine model. Twenty-four sheep were commenced on VV ECMO. Parasternal long-axis (Plax) and short-axis (Psax) views were obtained pre- and postcontrast while on VV ECMO. Endocardial definition scores (EDS) per segment were graded: 1 = good, 2 = suboptimal 3 = not seen. Endocardial border definition score index (EBDSI) was calculated for each view. Endocardial length (EL) in the Plax view for the left ventricle (LV) and right ventricle (RV) was measured. Summation EDS data for the LV and RV for unenhanced TTE (UE) versus CE TTE imaging: EDS 1 = 289 versus 346, EDS 2 = 38 versus 10, EDS 3 = 33 versus 4, respectively. Wilcoxon matched-pairs rank-sign tests showed a significant ranking difference (improvement) pre- and postcontrast for the LV (P < 0.0001), RV (P < 0.0001) and combined ventricular data (P < 0.0001). EBDSI for CE TTE was significantly lower than UE TTE for the LV (1.05 ± 0.17 vs. 1.22 ± 0.38, P = 0.0004) and RV (1.06 ± 0.22 vs. 1.42 ± 0.47, P = 0.0.0006) respectively. Visualized EL was significantly longer in CE versus UE for both the LV (58.6 ± 11.0 mm vs. 47.4 ± 11.7 mm, P < 0.0001) and the RV (52.3 ± 8.6 mm vs. 36.0 ± 13.1 mm, P < 0.0001), respectively. Despite exposure to destructive hydrodynamic forces, CE is a feasible technique in an ovine ECMO model. CE results in significantly improved EDS and increased EL.

The complexity of chloroplast chaperonins

Type I chaperonins are large oligomeric protein ensembles that are involved in the folding and assembly of other proteins. Chloroplast chaperonins and co-chaperonins exist in multiple copies of two distinct isoforms that can combine to form a range of labile oligomeric structures. This complex system increases the potential number of chaperonin substrates and possibilities for regulation. The incorporation of unique subunits into the oligomer can modify substrate specificity. Some subunits are upregulated in response to heat shock and some show organ-specific expression, whereas others possess additional functions that are unrelated to their role in protein folding. Accumulating evidence suggests that specific subunits have distinct roles in biogenesis of ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco).

Properties and structure of raised bog peat humic acids

Humic substances form most of the organic components of soil, peat and natural waters, and their structure and properties differ very much depending on their source. The aims of this study are to characterize humic acids (HAs) from raised bog peat, to evaluate the homogeneity of peat HAs within peat profiles, and to study peat humification impact on properties of HAs. A major impact on the structure of peat HAs have lignin-free raised bog biota (dominantly represented by bryophytes of different origin). On diagenesis scale, peat HAs have an intermediate position between the living organic matter and coal organic matter, and their structure is formed in a process in which more labile structures (carbohydrates, amino acids, etc.) are destroyed, while thermodynamically more stable aromatic and polyaromatic structures emerge as a result of abiotic synthesis. However, in comparison with soil, aquatic and other HAs, aromaticity of peat HAs is much lower. Comparatively, the raised bog peat HAs are at the beginning of the transformation process of living organic matter. Concentrations of carboxyl and phenolic hydroxyl groups change depending on the peat age and decomposition degree from where HAs have been isolated, and carboxylic acidity of peat HAs increases with peat depth and humification degree.

Hofmeister Salts Recover a Misfolded Multiprotein Complex for Subsequent Structural Measurements in the Gas Phase

Proteins are the workhorses of the cell, the functions of which are largely predicated on their structures and dynamics. Detailed knowledge of these attributes has enabled countless breakthroughs in human health and disease.[1] Many aspects, however, of protein structure remain poorly understood, including their high-order interactions.[2] This knowledge gap drives the development of new tools capable of protein structure characterization, some of which operate by measuring desolvated protein structure.[3] While desolvation enables the application of powerful analytical techniques that cannot be used in a solvated environment, and recent results indicate that many features of native protein structure survive in the gas-phase,[4] desolvation may also act to obfuscate critical details of protein conformation.8 Recently, multiple strategies have emerged for observing labile protein structures in the absence of bulk water and have proven useful in stabilizing protein-small molecule interactions, globular proteins, and their complexes.[5] Here, we report the first evidence that a misfolded protein complex, which exists both in solution and in the gas-phase, can be recovered back to a ‘native-like’ structure through the addition of salts prior to desorption/ionization. These data represent the first time that such a solution-phase multiprotein folding equilibrium is captured by gas-phase measurements.

Exceptionally well-preserved vegetal remains from the Upper Cretaceous of ‘Lo Hueco’, Cuenca, Spain

Vegetal remains are considered labile structures that quickly become decayed in ecosystems. However, certain lignified tissues (woody plants) can largely resist decomposition, becoming sometimes exceptionally well preserved. At the Upper Cretaceous site of ‘Lo Hueco’ (Cuenca, Spain), those woody remains (trunks and branches) with resinous material in the inner tracheids and parenchyma cells that were buried rapidly under anoxic conditions experienced a low degree of maturation, becoming exceptionally well preserved. Those woody remains deposited under oxic conditions (sub-aerial or sub-aquatic exposure) were more intensely biodegraded and subsequently carbonified, partially or completely mineralized in gypsum and covered by a ferruginous crust. These two modes of preservation are scarce, with silicification or carbonification processes much more common, and both can be considered as ‘exceptional preservation’. Other vegetal remains, such as carbonified leaves, stems and roots, were collected in the site. The different modes of preservation depend directly on: depositional micro-environment (sandy distributary channel, muddy flood plain); and type (trunk, branch, stem, leave, root) and state (presence or absence of resinous material) of the material. The great abundance and diversity of fossils in ‘Lo Hueco’ identify it as Konzentrat-Lagerstätten, sequentially formed by alternated events of flooding and drying depositional events, but the exceptional quality and rarity of determinate vegetal macroremains preservation suggest that certain deposits of this site can be considered as conservation deposits.

Scanning electron microscopy.

Scanning electron microscopy (SEM) remains distinct in its ability to allow topographical visualization of structures. Key elements to consider for successful examination of biological specimens include appropriate preparative and imaging techniques. Chemical processing induces structural artifacts during specimen preparation, and several factors need to be considered when selecting fixation protocols to reduce these effects while retaining structures of interest. Particular care for proper dehydration of specimens is essential to minimize shrinkage and is necessary for placement under the high-vacuum environment required for routine operation of standard SEMs. Choice of substrate for mounting and coating specimens can reduce artifacts known as charging, and a basic understanding of microscope settings can optimize parameters to achieve desired results. This unit describes fundamental techniques and tips for routine specimen preparation for a variety of biological specimens, preservation of labile or fragile structures, immune-labeling strategies, and microscope imaging parameters for optimal examination by SEM.

ChemInform Abstract: Iron‐Catalyzed Ring‐Opening of meso‐Aziridines with Amines.

AbstractN‐Arylaziridines are efficient substrates for the formation of vicinal diamines, generally within a short time and including labile structures such as (VIIIc).

Encapsulation of Polyunsaturated Fatty Acid Esters with Solid Lipid Particles

Encapsulation of structurally sensitive compounds within a solid lipid matrix provides a barrier to prooxidant compounds and effectively limits the extent of oxidative degradation. This offers a simple approach to preserve the bioactivity of labile structures. The technology was developed for cosmetic and pharmaceutical products but may be applied to additives used in food and feed formulations. The encapsulation of docosahexaenoic acid (DHA) and α-linolenic acid (ALA) was examined as model compounds of current interest in functional foods and feeds. Solid lipid particles were prepared from triglycerides containing saturated and unsaturated fatty acids and evaluated by differential scanning calorimetry. The thermal characteristics of the lipids used to form the particle were related to molecular structure and could be adjusted by selection of the appropriate component fatty acids. Encapsulation by solid lipid particles provides a method to inhibit oxidation and improve shelf life of products formulated with DHA and ALA.

ヌクレオシド系天然物の全合成を基盤とした抗薬剤耐性菌薬シーズの創製研究

Natural products are a rich source for drug development. However, some biologically relevant natural products possess rather large, complex or labile chemical structures compared to synthetic drugs, which limits chemical modification in a process pursuing a structure-activity relationship. Here we describe the rational simplification of the muraymycins and caprazamycins class of nucleoside natural products to address the issue associated with their molecular complexity. First, the systematic structure-activity relationship (SAR) study of the muraymycins using an Ugi four-component reaction was investigated. Our SAR study of the muraymycins suggests a probable mechanism for inhibition of the MraY. The predicted binding model would provide further direction towards the design of potent MraY inhibitors. Next, function-oriented synthesis (FOS) of caprazamycins was investigated. Based on the conformation-activity relationship study of a series of analogs 36-38, we designed the oxazolidine-containing uridine derivatives 41-44 by restricting the conformation of 36-38. As a result, the tert-butyl ester derivatives 43 were found to be the most active against a range of bacterial strains containing VRE with a similar potency to the parent natural products. These studies provide a novel strategy for the development of a new type of antibacterial agent effective against drug-resistant bacteria.