Crosslinking of PVA and glutaraldehyde in water monitored by viscosity and pulse field gradient NMR: a comparative study

The crosslinking of poly(vinyl alcohol) (PVA) with glutaraldehyde at 80 °C was characterized by viscosity and pulse field gradient (PFG) nuclear magnetic resonance (NMR) techniques. NMR signified an initial dormant period of approximately 6 hr, in which the self‐diffusion coefficient of PVA was found to be constant and independent of time. During the next 7 hr (the “primary” gel period), this induction period was succeeded by a fast decay of the self‐diffusion coefficient of rate (9.13 ± 0.45) × 10⁻⁵ sec⁻¹ followed by a slower decay rate of (3.22 ± 0.30) × 10⁻⁵ sec⁻¹ (the “secondary” gel period). The viscosity of the solution showed the same time behavior, i.e. an initial dormant period (∼ 6 hrs), followed by a fast increase of the viscosity for the next 7 –8 hr. During the “secondary” gel regime, the viscosity became too large to be reliably determined. However, within the time regime where both techniques produced reliable data, they gave identical information regarding the kinetics of the gel process, suggesting that PFG NMR enables in situ monitoring of gelation within porous materials (for instance sandstone). Copyright © 2000 John Wiley & Sons, Ltd.     

Open- and closed-loop aberration correction by use of a quadrature interferometric wave-front sensor

Experimental results are presented for an adaptive optics system based on a quadrature Twyman-Green interferometric wave-front sensor. The system uses a circularly polarized reference beam to form two interferograms with a pi/2 phase shift. The experiments conducted used Kolmogorov phase screens to simulate atmospheric phase distortions. Strehl ratio improvements by a factor of 8, to an absolute value of 0.45, are demonstrated.     

Pyridazines. Part 37: Facile solution phase combinatorial synthesis of highly substituted pyridazin-3-ones

Arrays of polysubstituted pyridazinones were prepared through three- or four-component transformations starting from the readily accessible ene-adducts 2.     

Differential synthetic aperture ladar

We report a differential synthetic aperture ladar concept that relaxes platform and laser requirements compared with those for conventional synthetic aperture ladar. Line-of-sight translation-vibration constraints are reduced by several orders of magnitude, while laser frequency stability is typically relaxed by an order of magnitude. The technique is most advantageous for shorter laser wavelengths, ultraviolet to mid-infrared. Analytical and modeling results, including the effect of speckle and atmospheric turbulence, are presented.     

Analysis of DNA-phosphate adducts in vitro using miniaturized LC-ESI-MS/MS and column switching: Phosphotriesters and alkyl cobalamins

DNA-phosphate adducts are known to be formed by a variety of alkylating agents. Due to little or no repair of DNA-phosphate adducts, these adducts may offer increased possibilities of both identifying and quantifying DNA adducts. The formation of DNA-phosphate adducts leads to a complete esterification of the phosphate group giving rise to a phosphotriester configuration. This work consists of the characterization of ethyl phosphotriesters (Ethyl PTE) using miniaturized LC-ESI-MS/MS and column switching in enzymatic hydrolysate of DNA treated in vitro with the model compound N-ethyl-N-nitrosourea (ENU). In vitro ENU-treated DNA was enzymatically degraded using nuclease P1, phosphodiesterase, and alkaline phosphatase. The use of column switch allowed for large-volume injections, where unmodified nucleosides were discarded in the loading step. The analytes were forward flushed to the analytical column in the eluting step and separated using a linear gradient. Ten different ethyl PTEs (dGpEtdG, dApEtdA, dCpEtdC, TpEtT, dGpEtdA, dGpEtdC, dGpEtT, dApEtdC, dApEtT, and dCpEtT) were characterized by their masses and CAD product ion spectra. Measurements of accurate masses were carried out yielding experimental masses within 5 ppm of the calculated masses for 9 of the 10 ethyl PTEs. For comparison, the enzymatic hydrolysate of ENU-treated DNA was subjected to transalkylation of the DNA-phosphate adducts by cob(I)alamin. Formed ethyl-cobalamins were analyzed according to earlier developed methods. The limit of detection of an alkyl-cobalamin standard and an alkyl PTE standard was 2 fmol and 5 fmol, respectively.     

Potentiometric discrimination of neutral forms of nitrophenol isomers by liquid membrane electrodes incorporated with corroles

The results of studies on the use of corrole derivatives as a host ligand in the PVC liquid membrane electrodes and their ability for the potentiometric high-throughput discrimination of nitrophenol guests have been presented. The significance of parameters which govern the mechanism of generation of potentiometric signals such as the attachment of substituents in the corrole structure, acidity and lipophilicity of the guests, and pH of the aqueous solutions has been discussed in details. Supramolecular recognition processes between corroles and para-nitrophenol molecules have been confirmed by independent NMR measurements.