Luminescent Amphiphilic Aminoglycoside Probes to Study Transfection

We report the characterization of amphiphilic aminoglycoside conjugates containing luminophores with aggregation-induced emission properties as transfection reagents. These inherently luminescent transfection vectors are capable of binding plasmid DNA through electrostatic interactions; this binding results in an emission “on” signal due to restriction of intramolecular motion of the luminophore core. The luminescent cationic amphiphiles effectively transferred plasmid DNA into mammalian cells (HeLa, HEK 293T), as proven by expression of a red fluorescent protein marker. The morphologies of the aggregates were investigated by microscopy as well as ζ-potential and dynamic light-scattering measurements. The transfection efficiencies using luminescent cationic amphiphiles were similar to that of the gold-standard transfection reagent Lipofectamine® 2000.     

CYP154C5 Regioselectivity in Steroid Hydroxylation Explored by Substrate Modifications and Protein Engineering**

CYP154C5 from Nocardia farcinica is a P450 monooxygenase able to hydroxylate a range of steroids with high regio- and stereoselectivity at the 16α-position. Using protein engineering and substrate modifications based on the crystal structure of CYP154C5, an altered regioselectivity of the enzyme in steroid hydroxylation had been achieved. Thus, conversion of progesterone by mutant CYP154C5 F92A resulted in formation of the corresponding 21-hydroxylated product 11-deoxycorticosterone in addition to 16α-hydroxylation. Using MD simulation, this altered regioselectivity appeared to result from an alternative binding mode of the steroid in the active site of mutant F92A. MD simulation further suggested that the entrance of water to the active site caused higher uncoupling in this mutant. Moreover, exclusive 15α-hydroxylation was observed for wild-type CYP154C5 in the conversion of 5α-androstan-3-one, lacking an oxy-functional group at C17. Overall, our data give valuable insight into the structure–function relationship of this cytochrome P450 monooxygenase for steroid hydroxylation.     

Estimation in Random Coefficient Autoregressive Models

Abstract. We propose the quasi‐maximum likelihood method to estimate the parameters of an RCA(1) process, i.e. a random coefficient autoregressive time series of order 1. The strong consistency and the asymptotic normality of the estimators are derived under optimal conditions.     

A novel technique for the preparation of secondary fatty amides

A technique for the synthesis of monosubstituted fatty amides at low temperature and ambient pressure was developed. This method involved the condensation of an amine with a triacylglycerol. The primary amine (ethyl,n-butyl,n-hexyl andn-octyl were tested) acted as reagent and solvent for the fatty substrates. No additional organic solvent or catalyst was added. Tallow, vegetable oils and fish oil all served well as substrates, as did pure tripalmitin. The rate of amidation was dependent upon temperature and the ratio of fat to amine. In a series of experiments conducted with tallow andn-butylamine at a fat:amine molar ratio of 1:16, amidation could be carried out at 20°C, producingn-butyltallowamide in 83% yield in 24 hr. When the fat:amine molar ratio was reduced to 1:8, and the temperature raised to 45°C, the amide yield was 87.6% in 24 hr. When the reaction was carried out at the boiling point ofn-butylamine (78°C) and at a fat:amine ratio of 1:8, the amide yield was 93.2% in 4 hr. The reaction progressed more rapidly with higher molecular weight amines. The identity and purity of the amides was assessed by thin-layer chromatography and confirmed by elemental analyses and infrared and C¹³ nuclear magnetic resonance spectroscopy.     

Preparation and characterization of surfactant‐free stimuli‐sensitive microgel dispersions

A surfactant‐free method to produce responsive polymer microgels is introduced. As an example, poly(methacrylic acid) hydrogels with varying crosslinking density have been synthesized in bulk and then chopped using a high shear mechanical cutter to form microgel particles dispersed in water. The mechanical cutting technique enables the concentration and particle size distribution of the microgel suspensions to be easily controlled, therefore making the rheology of the suspensions tuneable. The particle size distribution of the dispersions, characterized using light scattering, was dependent on the speed and duration of mechanical cutting. The particle size distribution also depended on the degree of crosslinking of the hydrogel. The higher the crosslinking density, the lower the average mean diameter of the resulting microgel particles. The lower the crosslinking density of the hydrogel, the larger the difference between the maximum and minimum particle size. The time to complete swelling of the particles upon change in pH was measured to be up to 45 s, depending on the particle size. The rheology of the resulting suspensions as a function of pH was investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 104: 1912–1919, 2007     

Geschäftsmodelle

The business model concept, although a relatively new topic for research, has garnered growing attention over the past decade. Whilst it has been robustly defined, the concept has so far attracted very little substantive research. In the context of the wide-spread digitization of businesses and society at large, the logic inherent in a business model has become critical for business success and, hence, a focus for academic inquiry. The business model concept is identified as the missing link between business strategy, processes, and Information Technology (IT). The authors argue that the BISE community offers distinct and unique competencies (e.g., translating business strategies into IT systems, managing business and IT processes, etc.) that can be harnessed for significant research contributions to this field. Within this research gap three distinct streams are delineated, namely, business models in IT industries, IT enabled or digital business models, and IT support for developing and managing business models. For these streams, the current state of the art, suggest critical research questions, and suitable research methodologies are outlined.     

Hydrolytic degradation of ionically cross-linked polyphosphazene microspheres

The hydrolytic degradation of gel microspheres based on calcium cross-linked phosphazene polyelectrolytes, poly[di(carboxylatophenoxy)phosphazene] (PCPP) and poly[(carboxylatophenoxy) (glycinato)phosphazene] (PCGPP), was investigated. These microspheres are of importance as carriers in protein and cell encapsulation. Both PCPP and PCGPP ionotropic polyphosphazene hydrogels are degradable in an aqueous environment (pH 7.4, 37°C). The degradation rates can be increased by incorporation of hydrolysis sensitive glycinato groups as the pendant structures in the polymer (PCGPP). Hydrolysis of these polymer hydrogels led to low molecular weight (<1,000 Da) products. The erosion and molecular weight profiles varied also according to the molecular weight of the polyphosphazene constituting the gel beads. Another approach to affect the degradation rates consists of coating microspheres with poly-L -lysine. Ionotropic polyphosphazene hydrogels have potential as biodegradable devices for controlled drug delivery systems. © 1994 John Wiley & Sons, Inc.     

Melting and reorganization of poly(ethylene terephthalate) on fast heating (1000 K/s)

For poly(ethylene terephthalate) (PET) and other polymers the origin of the multiple melting peaks observed in differential scanning calorimetry (DSC) curves is still controversially discussed. This is due to the difficulty to investigate the melting of the originally formed crystals exclusively. Recrystallization is a fast process and most experimental techniques applied so far do not allow fast heating in order to prevent recrystallization totally. Developments in thin-film (chip) calorimetry allow scanning rates as high as several thousand Kelvin per second. We utilized a chip calorimeter based on a commercially available vacuum gauge, which is operated under non-adiabatic conditions. The calorimeter was used to study the melting of isothermally crystallized PET. Our results on melting at rates as high as 2700 K/s give clear evidence for the validity of a melting-recrystallization-remelting process for PET at low scanning rates (DSC). At isothermal conditions PET forms crystals, which all melt within a few dozens of K slightly above the isothermal crystallization temperature. There is no evidence for the formation of different populations of crystals with significantly different stability (melting temperatures) under isothermal conditions. Superheating of the crystals is of the order of 10 K at 2700 K/s.     

Buckling of jets in electrospinning

Various buckling instabilities of electrospinning jets were observed and compared with the buckling instabilities of uncharged fluid jets. Buckling instability arises due to jet compression at impingement on a collector surface and occurs independently of the electrical bending instability. The velocity, diameter, density and viscosity of the electrospinning jets are the key factors that determine the buckling frequency. The electrically charged jets impinging onto grounded, horizontal or inclined (wedge-like) electrodes moving laterally at a constant velocity are studied experimentally. Straight and bending (electrospinning) jets emerge at short and sufficiently long inter-electrode distances, respectively. The experiments show that both straight segment and bending jets, when impinging onto a counter-electrode, buckled and produced patterns of meandering deposits. In the case of bending electrospun jets these short-length buckling patterns were superimposed on the bending loops found in the deposits. Buckling-related and bending-related morphologies are easily distinguishable. The buckling patterns have frequencies of the order of 10⁵-10⁶ Hz, whereas the bending loops are formed at the frequencies of the order of 10³ Hz. The deposited buckling patterns include sinuous, zigzag-like, figures-of-eight, recurring curves, coiled and other structures that resembled many patterns created by uncharged jets of highly viscous fluids impinging a hard flat surface. In addition, several new morphologies which were not observed before with uncharged jets were found. The experimentally measured frequencies of the buckling patterns were compared to the theoretical predictions and a reasonable agreement was found.     

HDPE/LLDPE reactor blends with bimodal microstructures—part I: mechanical properties

Reactor blends of polyethylene/poly(ethylene-co-1-octene) resins with bimodal molecular weight and bimodal short chain branching distributions were synthesized in a two-step polymerization process. The compositions of these blends range from low molecular weight (LMW) homopolymer to high molecular weight (HMW) copolymer and, vice versa, HMW homopolymer to LMW copolymer. The physical properties of the blends were found to be consistent with the nature of the individual components. For the tensile properties, the stiffness decreases with increasing the fraction of the copolymer, regardless of the molecular weight of the homopolymer fraction. For these blends with bimodal microstructures, it was confirmed that the degree of crystallinity governs the stiffness of the polymer. However, the energy dampening properties of the polymers benefit from the presence of the copolymer. A balance of stiffness and toughness can be obtained by altering the composition of the blends. For some blends, the presence of HMW homopolymer can dominate the tensile properties, showing little variation in the stiffness with increased addition of copolymer. It was also demonstrated that the testing conditions and thermal treatment of the polymer greatly influence the resulting elastic and energy dampening properties. Depending on the desired application, annealing these polymers (especially very low density copolymers) not only increases the crystallinity and stiffness, but also changes the frequency response of the dynamic mechanical properties.