Polyacrylamide cryogels by photoinitiated free radical polymerization

A novel method for the preparation of poly(acrylamide) cryogels by photoinitiated polymerization of monomeric precursors was described. A series of poly(acrylamide) cryogels were easily prepared by irradiating aqueous solutions containing acrylamide and N,N′‐methylene(bis)acrylamide as monomer and cross‐linker, respectively, in the presence of 1‐[4‐(2‐hydroxyethoxy)phenyl]‐2‐hydroxy‐2‐methyl‐1‐propane‐1‐one (Irgacure 2959) as water‐soluble photoinitiator with the help of freezing–thawing procedures. Photolysis was conducted at ?13 °C isothermally through specially designed cryostat‐integrated Rayonet merry‐go‐round photoreactor. On comparing the described photochemical method with the conventional redox counter part, the polymerization is initiated, and gelation proceeds only on external stimulation by light. This way, concomitant hydrogel formation usually observed with the redox process as a result of premature polymerization during the cooling process was prevented. The obtained cryogels exhibited superfast swelling behavior. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Synthesis and evaluation of new dental monomers with both phosphonic and carboxylic acid functional groups

Novel dental monomers containing both phosphonic and carboxylic acid functional groups were prepared. The monomers were based on t‐butyl α‐bromomethacrylate (t‐BuBMA) and synthesized in three steps: The reaction of o‐hydroxyaryl phosphonates [diethyl (2‐hydroxyphenyl) phosphonate, tetraethyl (2,5‐dihydroxy‐1,4‐phenylene) diphosphonate and tetraethyl 5,5′‐(propane‐2,2‐diyl)bis(2‐hydroxy‐5,1‐ phenylene) diphosphonate] with t‐BuBMA, the hydrolysis of phosphonate groups to phosphonic acid using trimethyl silylbromide, and the hydrolysis of the t‐butyl groups to carboxylic acid with trifluoroacetic acid. The monomers were solids and soluble in water and ethanol. The structures of the monomers were determined by Fourier transform infrared (FTIR), ¹H, ¹³C, and ³¹P nuclear magnetic resonance (NMR) spectroscopy. The copolymerization behaviors of the synthesized monomers with glycerol dimethacrylate were first investigated in bulk using photodifferential scanning calorimetry at 40 °C with 2,2′‐dimethoxy‐2‐phenyl acetophenone as photoinitiator. Then, the solution copolymerization of the monomers with acrylamide in ethanol and water was studied, indicating that the synthesized monomers are incorporated into the copolymers. The acidic nature of the aqueous solutions of these monomers (pH values 1.72–1.87) is expected to give them etching properties important for dental applications. The interaction of the monomers with hydroxyapatite was investigated using ¹³C NMR and FTIR techniques. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1953–1965, 2009     

In vitro evaluation of mucoadhesive vaginal tablets of antifungal drugs prepared with thiolated polymer and development of a new dissolution technique for vaginal formulations

The main objective of this work was to develop antifungal matrix tablet for vaginal applications using mucoadhesive thiolated polymer. Econazole nitrate (EN) and miconazole nitrate (MN) were used as antifungal drugs to prepare the vaginal tablet formulations. Thiolated poly(acrylic acid)-cysteine (PAA-Cys) conjugate was synthesized by the covalent attachment of L-cysteine to PAA with the formation of amide bonds between the primary amino group of L-cysteine and the carboxylic acid group of the polymer. Vaginal mucoadhesive matrix tablets were prepared by direct compression technique. The investigation focused on the influence of modified polymer on water uptake behavior, mucoadhesive property and release rate of drug. Thiolated polymer increased the water uptake ratio and mucoadhesive property of the formulations. A new simple dissolution technique was developed to simulate the vaginal environment for the evaluation of release behavior of vaginal tablets. In this technique, daily production amount and rate of the vaginal fluid was used without any rotational movement. The drug release was found to be slower from PAA-Cys compared to that from PAA formulations. The similarity study results confirmed that the difference in particle size of EN and MN did not affect their release profile. The release process was described by plotting the fraction released drug versus time and n fitting data to the simple exponential model: M(t)/M(∞)=kt(n). The release kinetics were determined as Super Case II for all the formulations prepared with PAA or PAA-Cys. According to these results the mucoadhesive vaginal tablet formulations prepared with PAA-Cys represent good example for delivery systems which prolong the residence time of drugs at the vaginal mucosal surface.     

On the interaction between retrials and sizing of call centers

This paper models a call center as a Markovian queue with multiple servers, where customer impatience, and retrials are modeled explicitly. The model is analyzed as a continuous time Markov chain. The retrial phenomenon is explored numerically using a real example, to demonstrate the magnitude it can take and to understand its sensitivity to various system parameters. The model is then used to assess the impact of disregarding existing retrials in the staffing of a call center. It is shown that ignoring retrials can lead to under-staffing or over-staffing with respect to the optimal, depending on the forecasting assumptions being made.     

MRI findings of gastric metastases from breast carcinoma

We describe the MR appearance of breast cancer metastases to the stomach. The stomach wall was diffusely thickened with loss of the regular fold pattern best shown on the single shot T2-weighted images and enhanced with moderate mural enhancement on early and late post gadolinium images. The combination of gastric wall thickening and abnormal enhancement should suggest the diagnosis of diffuse mural metastases in a woman with a history of breast cancer.     

Biosynthesis of pentangular polyphenols: deductions from the benastatin and griseorhodin pathways

The benastatins, pradimicins, fredericamycins, and members of the griseorhodin/rubromycin family represent a structurally and functionally diverse group of long-chain polyphenols from actinomycetes. Comparison of their biosynthetic gene clusters (ben, prm, fdm, grh, rub) revealed that all loci harbor genes coding for a similar, yet uncharacterized, type of ketoreductases. In a phylogenetic survey of representative KRs involved in type II PKS systems, we found that it is generally possible to deduce the KR regiospecificity (C-9, C-15, C17) from the amino acid sequence and thus to predict the nature of the aromatic polyketide (e.g., angucycline, anthracycline, benzoisochromanequinones). We hypothezised that the new clade of KRs is characteristic for biosynthesis of polyphenols with an extended angular architecture we termed "pentangular". To test this hypothesis, we demonstrated the biogenetic relationship between benastatin and the structurally unrelated spiro ketal griseorhodin by generating a mutant producing collinone, a pentangular pathway intermediate. The benastatin pathway served as a model to characterize the KR. Gene inactivation of benL resulted in the formation of a series of 19-hydroxy benastatin and bequinostatin derivatives (e.g., benastatin K and benastatin L). These results clearly showed that BenL functions as a C-19 KR in pentangular pathways.     

Neutron Equivalent Dose Rate Measurements of Gypsum-Waste Tire Rubber Layered Structures

The neutron equivalent dose rates (µSv/h) of gypsum, steel-reinforced rubber waste tire, and gypsum-waste tire rubber sandwich composite samples were investigated. Prepared samples were irradiated with ²⁴¹Am-Be neutrons and transmission values were obtained using dose equivalent rates measured with a BF₃ neutron detector. Results were compared to those of concrete, and as a result of neutron shielding, the performance of gypsum, waste tire, and waste tire (steel-reinforced rubber) embedded gypsum samples was higher than that of concrete. This information may be useful for shielding design of nuclear application areas.     

Comparative study of the high-temperature auto-ignition of cyclopentane and tetrahydrofuran

Cyclopentane (C₅H₁₀) and tetrahydrofuran (C₄H₈O) are both five-membered ring compounds. The present study compares the auto-ignition of cyclopentane and tetrahydrofuran in a high-pressure shock-tube (20 atm). Twelve different mixtures were investigated at two different fuel initial mole fractions (1% and 2%): at X_fuel = 1%, three equivalence ratios, kept constant between cyclopentane and tetrahydrofuran, were studied (0.5, 1, and 2), whereas three X_fuel/X_O2 were investigated when X_fuel = 2%. A detailed kinetic mechanism was developed to reproduce cyclopentane and tetrahydrofuran auto-ignition. The agreement between our experimental results and the modeling is very good. This mechanism was used to explain the similarities and differences observed between cyclopentane and tetrahydrofuran auto-ignition.     

Chain Sliding versus β-Sheet Formation upon Shearing Single α-Helical Coiled Coils

Coiled coils (CCs) are key building blocks of biogenic materials and determine their mechanical response to large deformations. Of particular interest is the observation that CC-based materials display a force-induced transition from α-helices to mechanically stronger β-sheets (αβT). Steered molecular dynamics simulations predict that this αβT requires a minimum, pulling speed-dependent CC length. Here, de novo designed CCs with a length between four to seven heptads are utilized to probe if the transition found in natural CCs can be mimicked with synthetic sequences. Using single-molecule force spectroscopy and molecular dynamics simulations, these CCs are mechanically loaded in shear geometry and their rupture forces and structural responses to the applied load are determined. Simulations at the highest pulling speed (0.01 nm ns⁻¹) show the appearance of β-sheet structures for the five- and six-heptad CCs and a concomitant increase in mechanical strength. The αβT is less probable at a lower pulling speed of 0.001 nm ns⁻¹ and is not observed in force spectroscopy experiments. For CCs loaded in shear geometry, the formation of β-sheets competes with interchain sliding. β-sheet formation is only possible in higher-order CC assemblies or in tensile-loading geometries where chain sliding and dissociation are prohibited.