Physicochemical and thermodynamic characterization of hydroxy pentacyclic triterpenoic acid/γ-cyclodextrin inclusion complexes

Hydroxy pentacyclic triterpenoic acids (HPTAs) have been described to exhibit numerous pharmacological properties. They also exhibit poor hydrosolubility, thus affecting their potential clinical interest. The association of these active substances with cyclodextrins could be employed to improve some properties such as bioavailability and activity. 1:1 Inclusion complexes of ursolic, oleanolic and betulinic acids with γ-cyclodextrin were evaluated by DSC and ¹H NMR spectroscopy. The apparent formation constants (K_f) of the formed complexes were determined using RP-HPLC. Thermodynamic parameters ΔGo, ΔHo and ΔSo were calculated with temperatures ranging from 25 to 45?°C to evaluate the complexation process. Finally the influence of γ-CD on the HPTA water solubility was investigated by phase-solubility studies.     

Discovery of bioactive small-molecule inhibitor of poly adp-ribose polymerase: implications for energy-deficient cells

Poly (ADP-ribose) polymerase (PARP1) is a nuclear protein that, when overactivated by oxidative stress-induced DNA damage, ADP ribosylates target proteins leading to dramatic cellular ATP depletion. We have discovered a biologically active small-molecule inhibitor of PARP1. The discovered compound inhibited PARP1 enzymatic activity in vitro and prevented ATP loss and cell death in a surrogate model of oxidative stress in vivo. We also investigated a new use for PARP1 inhibitors in energy-deficient cells by using Huntington's disease as a model. Our results showed that insult with the oxidant hydrogen peroxide depleted cellular ATP in mutant cells below the threshold of viability. The protective role of PARP1 inhibitors against oxidative stress has been shown in this model system.     

Relevance of NH4F in acid digestion before ICP-MS analysis

In order to implement a simpler, less expensive and more safe sample dissolution procedure, we have substituted the HF-HClO₄ mixture by NH₄F. By testing three certified reference materials, lichen 336, basalt BE-N, soil 7, it was found that the three-reagents digestion without HF and HClO₄ (HNO₃ + H₂O₂ + NH₄F was used) was very effective for the pretreatment of ICP-MS measurement. The comparison was based on the measurement results and their uncertainties. All are reference material for amount contents of different trace elements. The accuracy and precision of the developed method were tested by replicate analyses of reference samples of established element contents. The accuracy of the data as well as detection limits (LODs) vary among elements but are usually very good (accuracy better than 8%, LODs usually below 1 μg/g in solids). ICP-MS capabilities enable us to determine routinely 13 and 16 minor and trace elements in basalt and soil.     

Thermal analysis of salts from 4-nitrophenol and aliphatic amines

In this work, the thermodynamic performance of a single slope solar still with cotton cloth energy storage medium was compared with a simple solar still without energy storage. Two solar stills with similar dimensions (one with cotton cloth energy storage and another without energy storage) were fabricated and investigated its performance under the hot humid climatic conditions of Chennai in India during the summer months of 2017. The performance was evaluated in terms of energy and exergy analysis based on first and second law of thermodynamics, respectively, for 2 mm, 4 mm, 6 mm and 8 mm cotton cloth thickness. The results showed that the maximum energy and exergy efficiency of a solar still was observed to be 23.8% and 2.6%, respectively, for 6 mm cotton cloth thickness. The results confirmed that the cotton cloth regenerative medium has enhanced the still productivity by about 24.1% when compared to the solar still without heat storage.

     

Structural isomer differentiation of 1,6-diaza-3,8-dioxabicyclo[4.4.1]undecane and N,N'-methylenebis(oxazolidine) by mass spectrometry

The title compound types are structural isomers. The absence of literature studies dealing with the mass spectrometric gas-phase behavior of such compounds prompted a search for the best conditions for differentiation between the two prototype examples (R,R)-5,10-diphenyl-1,6-diaza-3,8-dioxabi-cyclo[4.4.1]undecane and N,N'-methylenebis[(R)-4-phenyloxazolidine]. Attempts to differentiate between the isomers by NMR were inconclusive and X-ray crystallography had to be used. The best mass spectrometric results were obtained using gas-phase ionization techniques, particularly chemical ionization, whereby protonated molecules were observed. The fragmentation pathways were elucidated from MS/MS studies and from experiments performed on hexadeuterated samples of each compound.     

Biodegradation of polyurethanes and nanocomposites to non-cytotoxic degradation products

Polyurethanes with controllable biodegradable properties have been considered for biomedical applications. However, the potential toxicity of their biodegraded by-products is still a concern. In this study, biodegradable polyurethanes based on poly(?-caprolactone) (PCL) and/or poly(ethylene glycol) as soft segments and biodegradable polyurethanes containing montmorillonite nanoparticles were synthesized and were subjected to in vitro biodegradation for 4 months. The post-degraded polyurethanes and nanocomposites were characterized by infrared spectroscopy (FTIR), X-ray diffraction (XRD) and small angle X-ray scattering (SAXS). The toxicity of the biodegradation by-products was evaluated by measuring their effect on the viability of retinal cells. FTIR results indicated that hard segments of the biomaterials were preserved during biodegradation, and suggested that the ester bonds of the PCL incorporated into the soft segments were hydrolytic broken. XRD data indicated also that the soft segments crystallized as a result of the hydrolysis of PCL ester bonds and re-organization of the amorphous phase during annealing at 37 °C. As the biodegradation of the biomaterials induced the formation of soft segment lamella crystals, a complex nanostructure was formed, resulting in the enhancement of the small angle X-ray scattering. The by-products were non-cytotoxic to the retinal cells. These results suggest that the hydrolytic unstable polyurethanes and nanocomposites can be possible candidates for ophthalmological applications.     

N,N′‐Di­methyl‐1,4‐dithiine‐1,2:4,5‐tetracarbox­imide and N,N′‐di­methyl‐1,4‐diselenine‐1,2:4,5‐tetracarbox­imide

The title compounds of sulfur, C₁₀H₆N₂O₄S₂, (I), and selenium, C₁₀H₆N₂O₄Se₂, (II), are isomorphous. The crystallographically centrosymmetric mol­ecules are planar. The bond distances and angles, except for those involving the S and Se atoms, are comparable. The mol­ecules are disposed in layers parallel to the bc plane. The molecular axes differ by 75° for (I) and by 80° for (II) from one layer to the next.     

(2‐Hydro­xy‐5‐methyl­phenyl)­di­phenyl­phosphine oxide

Pairs of individual mol­ecules of the title compound, C₁₉H₁₇O₂P, (I), containing tetrahedrally coordinated P atoms are connected across crystallographic inversion centres via complementary O—H?O=P hydrogen bonds.     

Chlorotris(2,4,6‐trimethylphenyl)tin(IV) and its ethanol hemisolvate

Chloro­tris(2,4,6‐tri­methyl­phenyl)­tin(IV), crystallizes from ethanol as solvent‐free needles, [Sn(C₉H₁₁)₃Cl], (I), and as the hemisolvate, [Sn(C₉H₁₁)₃Cl]·0.5C₂H₆O, (II). The asymmetric unit in (I) has three independent mol­ecules, whereas in (II), there are two [Sn(C₉H₁₁)₃Cl] mol­ecules together with one ethanol molecule. In the unit cell of (II), the ethanol mol­ecules lie in channels between stacks of (Mes)₃SnCl mol­ecules (Mes is 2,4,6‐tri­methyl­phenyl) and each ethanol mol­ecule is disordered (0.50:0.50) over two positions. A comparison of the structures of the title compounds and other (Mes)₃SnX (X = F, Br or I) systems with those of the tri­phenyl­tin analogues shows that the steric requirements of the o‐CH₃ groups are met by a flattening of the SnC₃ skeleton and increases in the average Sn—X and Sn—C values. Comparing Sn—X data for (Mes)₃SnX (X = F, Cl, Br or I) systems with values for the tris(o‐methoxy­phenyl)­tin analogues suggests that the Sn—F distance of 1.961 Å in (Mes)₃SnF may well be characteristic of sterically unhindered four‐coordinate Ar₃SnF systems.     

Synthesis of photocrosslinkable fluorinated polydimethylsiloxanes: Direct introduction of acrylic pendant groups via hydrosilylation

The synthesis of photocrosslinkable fluorinated polydimethylsiloxanes was achieved through direct hydrosilylation with copoly(dimethyl)(methyl‐hydrogen) siloxane. First, the hydrosilylation of a fluorinated olefin allowed the introduction of a fluorinated group onto the polysiloxane. Then, a second hydrosilylation of allyl methyl methacrylate led to the polysiloxane bearing both fluorinated and photocrosslinkable groups. This method, compared with a previous method of copolycondensation, is shown to be easier and more efficient. All the new products synthesized were characterized by IR, ¹H NMR, ¹⁹F NMR, and ²⁹Si NMR. A formulation containing the fluorosilicone was crosslinked after being coated on a mesoporous membrane and was evaluated as a vapor permeation membrane. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3722–3728, 2000