The impact of antibiotics on bacterial cellulose in vivo

This study investigated how antibiotics, to which Gluconacetobacter hansenii is naturally resistant, impact cellulose crystallinity, allomorph, aggregation into bundles and layers, cellulose yield, and cell morphology. G. hansenii was exposed to 100 μg/mL ampicillin, chloramphenicol, and kanamycin for 7 days, and cellulose structure was analyzed using scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Biomass and cellulose weights were also assessed. Ampicillin increased bundle thickness, and the bundles also showed nodular deposits indicative of non-cellulosic exopolysaccharide deposition. Ampicillin also yielded the lowest amount of cellulose per gram of biomass (p < 0.01) and induced significant filamentation behavior. Chloramphenicol inhibited biomass production (p < 0.01), increased the I-α allomorph content (p < 0.01), and also induced filamentation, though not as profusely as ampicillin. We hypothesize that defects in the peptidoglycan layer and in protein production lowered cellulose yield and promoted cells to undergo filamentation as a survival tactic. Additionally, we hypothesize that antibiotic stress caused additional exopolysaccharides to be produced and that they likely enhanced glucan chain aggregation into higher-order structures. Our findings have significant implications for downstream applications such as genetically engineering G. hansenii to produce bacterial cellulose with modified properties.     

Cigarette smoke exacerbates ventricular remodeling and dysfunction in the volume overloaded heart

Cigarette smoking is an independent risk factor for heart disease and is linked to sudden cardiac death. In this study, we examined the effects of cigarette smoke (CS) on the volume overload stressed heart. Our hypothesis was that CS exacerbates volume overload (VO)-induced cardiac dysfunction by accelerating ventricular remodeling. VO stress was surgically induced in male Sprague-Dawley rats by abdominal aortocaval fistula (ACF). Rats, with and without ACF, were exposed to either room air or CS (6 cigarettes/day) for 6 weeks. Temporal echocardiogram measurements indicated that CS significantly increased VO-induced left ventricular dilatation, prevented compensatory wall thickening, and depressed fractional shortening. Morphological analysis of ventricular collagen revealed that CS blunted compensatory collagen expression (45% decrease versus ACF alone). CS exacerbated the VO-induced increase of MMP-9 and TIMP-1 expression in the heart. CS also blocked the compensatory increases of HIF-1α, VEGF, and TGF-β in the VO-stressed heart. These data indicate that CS worsens VO remodeling by disrupting compensatory mechanisms, thereby promoting eccentric dilation and dysfunction.     

Controlling the self-assembly structure of magnetic nanoparticles and amphiphilic block-copolymers: from micelles to vesicles

We report how to control the self-assembly of magnetic nanoparticles and a prototypical amphiphilic block-copolymer composed of poly(acrylic acid) and polystyrene (PAA-b-PS). Three distinct structures were obtained by controlling the solvent-nanoparticle and polymer-nanoparticle interactions: (1) polymersomes densely packed with nanoparticles (magneto-polymersomes), (2) core-shell type polymer assemblies where nanoparticles are radially arranged at the interface between the polymer core and the shell (magneto-core shell), and (3) polymer micelles where nanoparticles are homogeneously incorporated (magneto-micelles). Importantly, we show that the incorporation of nanoparticles drastically affects the self-assembly structure of block-copolymers by modifying the relative volume ratio between the hydrophobic block and the hydrophilic block. As a consequence, the self-assembly of micelle-forming block-copolymers typically produces magneto-polymersomes instead of magneto-micelles. On the other hand, vesicle-forming polymers tend to form magneto-micelles due to the solubilization of nanoparticles in polymer assemblies. The nanoparticle-polymer interaction also controls the nanoparticle arrangement in the polymer matrix. In N,N-dimethylformamide (DMF) where PS is not well-solvated, nanoparticles segregate from PS and form unique radial assemblies. In tetrahydrofuran (THF), which is a good solvent for both nanoparticles and PS, nanoparticles are homogeneously distributed in the polymer matrix. Furthermore, we demonstrated that the morphology of nanoparticle-encapsulating polymer assemblies significantly affects their magnetic relaxation properties, emphasizing the importance of the self-assembly structure and nanoparticle arrangement as well as the size of the assemblies.     

Structural optimization of cyclic sulfonamide based novel HIV-1 protease inhibitors to picomolar affinities guided by X-ray crystallographic analysis

Synthesis and HIV-1 protease inhibitory activity of compound 5 based on the structure of a novel cyclic sulfonamide pharmacophore has been recently disclosed from our group. X-ray crystallographic structure of 5 when bound to the HIV-1 protease defined its binding mode. The importance of the geometry of the substitution at C4–Me (S configuration) was emphasized. In the present paper we wish to disclose the design of novel inhibitors 47 and 48 based on the X-ray structure of compound 5 bound to the HIV-1 protease, their synthesis and activity against HIV-1 protease. By making changes at the C4 position and the carbamate linkage the above compounds 47 and 48 were found to be approximately one hundred fold more active compared to 5 and their K_i values are in the picomolar range. An unusual observation regarding the activity and geometry was made with compounds 51 and 52. X-ray results demonstrate that 48 and 52 bind to the same binding pocket with simultaneous change in the conformation of the cyclic sulfonamide ring.     

Inverse scattering transform for the defocusing Ablowitz–Ladik system with arbitrarily large nonzero background

In this work we develop the inverse scattering transform (IST) for the defocusing Ablowitz–Ladik (AL) equation with arbitrarily a large nonzero background at space infinity. The IST was developed in previous works under the assumption that the amplitude of the background satisfies a “small norm” condition . On the other hand, Ohta and Yang recently showed that the defocusing AL system, which is modulationally stable for , becomes unstable if , and exhibits discrete rogue wave solutions, some of which are regular for all times. Here, we construct the IST for the defocusing AL with , analyze the spectrum, and characterize the soliton and rational solutions from a spectral point of view. We formulate the direct and inverse problems by using a suitable uniformization variable, and pose the inverse problem as an RHP across a simple contour in the complex plane of the uniform variable. As a by‐product of the IST, we also obtain explicit soliton solutions, which are the discrete analog of the celebrated Kuznetsov–Ma, Akhmediev, Peregrine solutions, and which mimic the corresponding solutions for the focusing AL equation. Soliton solutions that are the analog of the dark soliton solutions of the defocusing AL equation in the case are also presented.     

The use of tunable diode laser absorption spectroscopy for rapid measurements of the δ13C of animal breath for physiological and ecological studies

In this study we introduce the use of tunable diode laser absorption spectroscopy (TDLAS) as a technique for making measurements of the δ¹³C of animal ‘breath’ in near real time. The carbon isotope ratios (δ¹³C) of breath CO₂ trace the carbon source of the materials being metabolized, which can provide insight into the use of specific food resources, e.g. those derived from plants using C₃ versus C₄ or CAM photosynthetic pathways. For physiological studies, labeled substrates and breath analyses provide direct evidence of specific physiological (e.g. fermentative digestion) or enzymatic (e.g. sucrase activity) processes. Although potentially very informative, this approach has rarely been taken in animal physiological or ecological research. In this study we quantify the utilization of different plant resources (photosynthetic types – C₃ or C₄) in arthropod herbivores by measuring the δ¹³C of their ‘breath’ and comparing it with bulk tissue values. We show that breath δ¹³C values are highly correlated with bulk tissues and for insect herbivores reflect their dietary guild, in our case C₃‐specialists, C₄‐specialists, or generalists. TDLAS has a number of advantages that will make it an important tool for physiologists, ecologists and behaviorists: it is non‐invasive, fast, very sensitive, accurate, works on animals of a wide range of body sizes, per‐sample costs are small, and it is potentially field‐deployable. Copyright © 2009 John Wiley & Sons, Ltd.     

A simple borohydride-based method for selective 1,4-conjugate reduction of α,β-unsaturated carbonyl compounds

Sodium borohydride is used in combination with a heterogeneous palladium catalyst and acetic acid to selectively reduce the carbon-carbon double bonds of various α,β-unsaturated ketones and related compounds. This simple method is most selective when non-polar solvents such as toluene are used. We observed nearly complete conversion and high selectivities using moderate catalyst loadings. The reactions were typically complete in less than 2 h.     

A contrathermodynamic epimerization of a 2,3-trans-disubstituted butyrolactone: intermediates for chiral polypropionate units.

A method is described which produces the less thermodynamically stable cis-2,3-disubstituted lactone $\text{8}$ From its mole stable epimer $\text{6}$. These substances are complementary to aldol and crotyl organometallics in the construction of chiral polypropionate residues.