Study of slabstock flexible polyurethane foams based on varied toluene diisocyanate isomer ratios

The morphological features of three flexible slabstock polyurethane foams based on varied contents of 2,4 and 2,6 toluene diisocyanate (TDI) isomers are investigated. The three commercially available TDI mixtures, that is, 65:35 2,4/2,6 TDI, 80:20 2,4/2,6 TDI, and 100:0 2,4/2,6 TDI were used. The foams were characterized at different length scales with several techniques. Differences in the cellular structure of the foams were noted with scanning electron microscopy. Small‐angle X‐ray scattering was used to demonstrate that all three foams were microphase‐separated and possessed similar interdomain spacings. Transmission electron microscopy revealed that the aggregation of the urea phase into large urea‐rich regions decreased systematically on increasing the asymmetric TDI isomer content. Fourier transform infrared spectroscopy showed that the level of bidentate hydrogen bonding of the hard segments increased with the 2,6 TDI isomer content. Differential scanning calorimetry and dynamic mechanical analysis (DMA) were used to note changes in the soft‐segment glass‐transition temperature of the foams on varying the diisocyanate ratios and suggested that the perfection of microphase separation was enhanced on increasing the 2,6 TDI isomer content. The preceding observations were used to explain why the foam containing the highest content of the symmetric 2,6 TDI isomer exhibited the highest rubbery storage modulus, as measured by DMA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 258–268, 2003     

Nonadiabatic electron dynamics in the exit channel of Na-molecule optical collisions

We study optical collisions of Na atoms with N(2), CO, C(2)H(2), and CO(2) molecules in a crossed-beam experiment. Excited electronic states of the collision complex are selectively populated during the collision. We measure the relative population of the Na(3p) fine-structure levels after the collision and observe in this way the nonadiabatic transitions occuring in the final phase of the collision process. For the NaCO, NaC(2)H(2), and NaCO(2) systems new ab initio potential surfaces were generated. The theoretical analysis of the nonadiabatic electron dynamics on the excited potential surfaces is made within the classical-path formalism. The results are in good qualitative agreement with the experimental data and provide insight into the nonadiabatic mechanisms prevailing during the evolution in the upper 3p manifold. The differences between the different collisional systems are related to the presence and system-specific locations of conical intersections and avoided crossing seams in the excited potential surfaces.     

Isomeric yield ratios of fission products in proton-induced fission of232Th

Isomeric yield ratios of 11 fission products were measured in the system of 13 MeV proton-induced fission of²³²Th by an on-line ion-guide isotope separator. It was found that the closed shell structures of primary fragments and their complementary fragments affect the isomeric yield ratios. Isomeric yield ratios of¹²¹Cd (11/2⁻, 3/2⁺) and¹³⁵Xe (11/2⁻, 3/2⁺) were measured precisely in the proton energy range of 13 to 26 MeV to investigate their energy dependence. It was found that the isomeric yield ratios increased slightly with proton energy. The results were discussed in connection with the deformation of fission fragments and fission modes.     

Studies on antineoplastic effect by adjusting ratios of targeted-ligand and antitumor drug

A series of drug delivery systems based on a sodium alginate derivative were prepared by mixing glycyrrhetinic acid(GA) and doxorubicin(DOX) conjugates at different ratios. GA(a liver-targeting ligand) and DOX(an antitumor drug) were both conjugated to oligomeric glycol monomethyl ether-modified sodium alginate(ALG-mOEG) for prolonged duration of action. These NP-based delivery systems exhibited active cell uptake and cytotoxicity in vitro and liver-targeted distribution and anti-tumor activity in vivo. In addition, nanoparticles with a 1:1(W:W) ratio of GA-ALG-mOEG and DOXALG-mOEG(NPs-3) showed the highest cellular uptake and cytotoxicity in vitro and liver-targeted distribution and antitumor activity in vivo. Specifically, when mixed nanoparticles defined as NPs-3 were injected in mice, liver DOX concentration reached 61.9 μg/g 3 h after injection, and AUC0-∞ and t1/2 of DOX in liver reached 4744.9 μg·h/g and 49.5 h, respectively. In addition, mice receiving a single injection of NPs-3 exhibited much slower tumor growth(88.37% reduction in tumor weight) 16 days after injection compared with placebo. These results indicate that effective cancer treatment may be developed using mixed NP delivery systems with appropriate ratio of targeted ligand and drug.     

Nonadiabatic transitions in the exit channel of atom-molecule collisions: fine-structure branching in Na+N2

We study Na+N(2) collisions by laser excitation of the collision complex in a differential scattering experiment. The measured relative population of the Na(3p) fine-structure levels reflects the nonadiabatic transitions occurring in the exit channel of the collision. Theoretical results obtained with a classical-path formalism and accurate quantum chemical data for NaN(2) are found to be in good agreement. The presence of a conical intersection for the T-shaped geometry has a profound influence on the observed fine-structure branching.     

Photoelectron anisotropy and channel branching ratios in the detachment of solvated iodide cluster anions

Photoelectron spectra and angular distributions in 267 nm detachment of the I(-)Ar, I(-)H(2)O, I(-)CH(3)I, and I(-)CH(3)CN cluster anions are examined in comparison with bare I(-) using velocity-map photoelectron imaging. In all cases, features are observed that correlate to two channels producing either I((2)P(3/2)) or I((2)P(1/2)). In the photodetachment of I(-) and I(-)Ar, the branching ratios of the (2)P(1/2) and (2)P(3/2) channels are observed to be approximately 0.4, in both cases falling short of the statistical ratio of 0.5. For I(-)H(2)O and I(-)CH(3)I, the (2)P(1/2) to (2)P(3/2) branching ratios are greater by a factor of 1.6 compared to the bare iodide case. The relative enhancement of the (2)P(1/2) channel is attributed to dipole effects on the final-state continuum wave function in the presence of polar solvents. For I(-)CH(3)CN the (2)P(1/2) to (2)P(3/2) ratio falls again, most likely due to the proximity of the detachment threshold in the excited spin-orbit channel. The photoelectron angular distributions in the photodetachment of I(-), I(-)Ar, I(-)H(2)O, and I(-)CH(3)CN are understood within the framework of direct detachment from I(-). Hence, the corresponding anisotropy parameters are modeled using variants of the Cooper-Zare central-potential model for atomic-anion photodetachment. In contrast, I(-)CH(3)I yields nearly isotropic photoelectron angular distributions in both detachment channels. The implications of this anomalous behavior are discussed with reference to alternative mechanisms, affording the solvent molecule an active role in the electron ejection process.     

Parametric investigation on the effect of channel topologies on electrophoretic separations

This paper presents a systematic study that illustrates the importance of the topologies of microchannels on electrokinetically based separation. Using theoretical and numerical analyses, we designed and showed that topologies that significantly increased the surface-to-volume ratio of the channel can provide dramatic improvement in the ability of the channel both to dissipate the heat generated by Joule heating and to reduce the axial dispersion associated with the siphoning effect. The incremental benefit and tradeoff of geometric complexity was also evaluated. The improvement offered by topographically patterned channels, such as finned structures, is especially pertinent in the development of preparative or semi-preparative scale electrokinetically driven separations, such as capillary electrophoresis and capillary electrochromatography, in which large cross sections of channels are required to achieve the needed volumetric throughput.     

Characterization of aminophenol isomer adsorption on silver nanostructures

Surface-enhanced infrared absorption (SEIRA), temperature-programmed desorption, and density functional theory calculations were used to explore the adsorption of aminophenol isomers on vacuum deposited silver films and silver powder. Salts of the aminophenolate ions were synthesized to aid in vibrational spectral interpretation. No evidence for dissociation of any of the aminophenols into aminophenolate ions in the monolayer or multilayer was found when adsorbed on silver nanostructures (SNS). SEIRA demonstrated additional hydrogen-bonding interactions in a multilayer of 2-aminophenol and 3-aminophenol adsorbed on SNS beyond what is present in the aminophenol powders. Surface-enhanced Raman spectroscopy (SERS) experiments also showed that a 2-aminophenol monolayer adsorbed on SNS is photolytically oxidized to either 3-aminophenoxazone or 2,2′-dihydroxyazobenzene, while neither 3-aminophenol nor 4-aminophenol showed any SERS activity. This work is expected to have a significant impact in a range of environmental, biochemical, and industrial applications where phenol chemistry is important.     

Possible effect of source backing on the backscatter peak in gamma spectra

Backscattering peak is one of the main features of the pulse height spectrum from a gamma ray detector. This arises mainly from materials outside the detector like source backing, photo multiplier tube housing, shielding etc. We have studied the effect of source backing on the relative importance of the back scattered peak for a NaI(I) scintillation detector. Gamma energies in the range from 60 to 1333 keV have been used. The measurements have been carried out for various backing thicknesses and differing source to detector distances. The details of the measurements and the results are presented.     

Counter-ion perturbation of the fragmentation pathways of multiply charged anions: evidence for exit channel complexes on the fragmentation potential energy surfaces

We report the first low-energy collisional excitation measurements and density functional theory calculations to characterize the ground state potential energy surfaces of contact ion-pair complexes that contain multiply charged anions (MCAs). Excitation of K+.Pt(CN)(4) (2-) and K+.Pt(CN)(6) (2-) result in fragmentation products associated with decay of the isolated constituent dianions, revealing that the ground state ion-pair surfaces are dominated by the intrinsic characteristics of the MCA. This observation is important since it indicates that counter-ion complexation only weakly perturbs the electronic structure of an MCA. For K+.Pt(CN)(4) (2-), where the Pt(CN)(4) (2-) dianion decays with production of two ionic fragments, we observe evidence for the existence of a novel exit-channel complex corresponding to a polar KCN salt unit bound to the Pt(CN)(3) (-) anion. The results described provide a basis for understanding the potential energy surfaces and fragmentation characteristics of other ion-pair complexes that involve MCAs.     

Prediction of the directional effect of pressure on the reactivity ratios in free-radical copolymerizations

The Q–e concept of the Alfrey and Price¹ has been applied successfully to the prediction of the pressure effect on the individual reactivity ratios in free-radical copolymerizations. Although the Q value of a given monomer is generally little affected by an increase in pressure, the e value is pressure dependent. The knowledge of the Q and e values at high pressures permits the prediction of variations in reactivity ratios with pressure. Some important consequences have been drawn from this concept.     

Nitration of moderately deactivated arenes with nitrogen dioxide and molecular oxygen under neutral conditions. Zeolite-induced enhancement of regioselectivity and reversal of isomer ratios

In the presence of zeolites, moderately deactivated arenes such as 1-nitronaphthalene, naphthonitriles, and methylated benzonitriles can be smoothly nitrated at room temperature by the combined action of nitrogen dioxide and molecular oxygen. The regioselectivity is considerably improved as compared with the conventional nitration methodology based on nitric and sulfuric acids. In some cases, the minor isomer became favoured to a significant extent, resulting in the reversal of ordinary isomer ratios of nitration products.     

Note on the asymptotic isomer count of large fullerenes

The leading term in the large- $N$ asymptotics of the isomer count of fullerenes with $N$ carbon atoms is extracted from the published enumerations for $N\le 400$ with the help of methods of series analysis. The uncovered simple $N^9$ scaling is distinct from isomer counts of most classes of chemical structures that conform to mixed exponential/power-law asymptotics. The second leading asymptotic term is found to be proportional to $N^{25/3}$ . A conjecture concerning isomer counts of the IPR fullerenes is also formulated.     

Quantum-chemical interpretation of the isomer shift on tin compounds

Molecular orbital calculations (EHT, IEHT, IEHT + Madelung correction) have been applied to a series of tin halides. A calculation procedure is described to derive the charge density of the electrons at the nucleus (0). The dependence of the isomer shift on covalency effects is demonstrated. The influence of the outer charge of the molecules on the isomer shift is shown. The relative change of nuclear charge radius R/R is calculated for tin.     

Surface tension effect on transmembrane channel stability in a model membrane

The effect of surface tension on the lipid bilayer membrane is a question that has drawn considerable research effort. This interest has been driven both by the desire to determine the surface tension effects on the lipid bilayer and from the suggestion that adding finite surface tension to a small membrane system may provide more realistic lipid properties in molecular dynamics simulations. Here, the effect of surface tension on a palmitololelylphosphatidylcholine (POPC) bilayer membrane containing a four-helix transmembrane alamethicin peptide bundle is investigated. Simulations of 10 ns were undertaken for two different ensembles, NPT and NP(z)gammaT with a surface tension, gamma, of 20 mN m(-1) per interface, which is near the pore-forming region. The significance of differences between the tension-free and surface tension simulations was determined using nonparametric statistical analysis on replicate simulations with different initial conditions. The results suggest that, when the membrane is under surface tension, the peptide helical structure is perturbed from that in the tension-free state but that the bundle conformation is more stable than that in the tension-free state, with hydrogen bonding playing an important stabilizing role. Surface tension counteracts the influence of the transmembrane helix bundle on nearby lipid order, making the lipid order more uniform throughout the membrane in the tension state. Conversely, the lipid mobility was less uniform in the tension state, with lipids far from the bundle being significantly more mobile than those near the bundle. One general implication of the results is that surface tension can affect the membrane nonuniformly, in that the properties of lipids near the peptide are different from those further away.     

L X-ray production cross sections, average L shell fluorescence yield and intensity ratios in heavy elements

L X-ray fluorescence cross sections, and intensity ratios were measured for elements in the 70￡Z￡92 atomic range at the excitation energy 59.5 keV using a Si(Li) detector. Furthermore, L X-ray fluorescence cross sections and intensity ratios were calculated for elements in the same range. The average L shell fluorescence yields were derived using experimental L X-ray fluorescence cross sections and theoretical photoionization cross sections. The obtained results were compared with other experimental and theoretical values. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of the effect of ion channel modulators on photosynthetic oxygen evolution

Various ion channel activities can be recorded by electrophysiological methods in the outer and inner envelope membranes of chloroplasts as well as in the thylakoid membrane. However, most of these channels are poorly characterized from a pharmacological point of view. Furthermore, the molecular identity has been determined only for a few of them, preventing an understanding of their role in plant physiology. By allowing specific ion fluxes across plastidial membranes, these ion channels may either directly or indirectly regulate photosynthesis, as has been hypothesized earlier. We have determined the effect of various ion channel modulators [indole-3-acetic acid, 5-nitro-2-(3-phenylpropylamino)-benzoate, (-)-epigallocatechin-3-gallate, p-chlorophenoxyacetic acid, Konig's polyanion, Cs+, Gd3+, 4-aminopyridine, tetraethylammonium chloride, charybdotoxin, nimodipine, and cyclosporin A] on the efficiency of photosynthetic oxygen evolution in intact chloroplasts, broken chloroplasts, and isolated thylakoids. The data may improve our understanding of chloroplast ion channels and identifies inhibitors which may be exploited for electrophysiological studies.