Quantum cross-linking

Alternatively, proton double quantum (DQ) NMR, based on a combined DQ excitation and a reconversion block of the pulse sequence, has been utilized to gain direct access to residual DCCs for cross-linked systems.69,83-89 For this purpose, double-quantum buildup curves are obtained with use of a well-defined double-quantum Hamiltonian along with a specific normalization approach. Residual interactions are directly proportional to a dynamic order parameter Sb of the polymer backbone,87... 

By application of proton multiple quantum (MQ) NMR experiments, information about the segmental order parameter, which is directly related to the restrictions on chain motion (cross-links) formed upon gelation of PVA, is obtained.103The quantitative study of rigid phase... 

Owing to their unique (tunable-electronic) properties, semiconductor (quantum dots) nanocrystals have generated considerable interest for optical DNA detection [12], Recent activity has demonstrated the utility of quantum dot nanoparticles for enhanced electrical DNA detection [33, 34, 50], Willner et al. reported on a photoelectrochemical transduction of DNA sensing events in connection with DNA cross-linked CdS nanoparticle arrays [50], The electrostatic binding of the Ru(NH3)63+ electron acceptor to the dsDNA... 

Acid generation in photoresist films add photogeneration vs. dose, 3233/ acid present after irradiation, 32,34r add present before irradiation, 32 quantum yield, 3234 Acid hardening resin resists cross-linking adivation energy determination, 87,89 cross-linking chemistry, 87 determination of acid generated, 87-88 effect of postexposure bake temperature and time, 87... 

Overall, this work highlights how quantum chemical methods can be used to study tribochemical reactions within chemically complex lubricant systems. The results shed light on processes that are responsible for the conversion of loosely connected ZP molecules derived from anti-wear additives into stiff, highly connected anti-wear films, which is consistent with experiments. Additionally, the results explain why these films inhibit wear of hard surfaces, such as iron, yet do not protect soft surface such as aluminum. The simulations also explained a large number of other experimental observations pertaining to ZDDP anti-wear films and additives.103 Perhaps most importantly, the simulations demonstrate the importance of cross-linking within the films, which may aid in the development of new anti-wear additives. 

QUANTUM YIELD PHOTOCHROMISM PHOTO-CROSS-LINKING PHOTOAFFINITY LABELING PHOTODIMERIZATION PHOTOISOMERIZATION PHOTOLYSIS FLASH PHOTOLYSIS... 

Under UV-laser irradiation, photosensitive multifunctional acrylate resins become rapidly cross-linked and completely insoluble. The extent of the reaction was followed continuously by both UV and IR spectroscopy in order to evaluate the rate and quantum yield of the laser-induced polymerization of these photoresist systems. Two basic types of lasers emitting in the UV range were employed, either a continuous wave (C.W.) argon-ion laser, or a pulsed nitrogen laser. 

The radiation chemical yields are expressed in terms of G-values. G(scission), G(s), equals the number of main chain scissions produced per 100 eV of energy absorbed and G (cross-linking), G(x), the number of crosslinks formed per 100 eV absorbed. The G-value is a structure dependent constant similar to quantum efficiency in photochemistry. 

Figure 26-15 Larger CdSe quantum dots are eluted before smaller quantum dots by 0.1 M trioctylphosphine in toluene at 1.0 mL/min in size exclusion chromatography on a 7.5 x 300 mm cross-linked polystyrene column of 100-nm pore size Polymer Labs PLgel 5 (im. Triangles are CdSe and squares are polystyrene calibration standards. The size of the CdSe core was measured with a transmission electron microscope and the length of 1-dodecanethiol endcaps (0.123 nm) was added to the radius. [Data from K. M. Krueger. A. M. Al-Somall, J. C. Falkner, and V. L. Colvin, "Characterization of Nanocrystalline CdSe by Size Exclusion Chromatography," Anal. Chem. 2005, 77,3511.]...

Tissue also contains some endogenous species that exhibit fluorescence, such as aromatic amino acids present in proteins (phenylalanine, tyrosine, and tryptophan), pyridine nucleotide enzyme cofactors (e.g., oxidized nicotinamide adenine dinucleotide, NADH pyridoxal phosphate flavin adenine dinucleotide, FAD), and cross-links between the collagen and the elastin in extracellular matrix.100 These typically possess excitation maxima in the ultraviolet, short natural lifetimes, and low quantum yields (see Table 10.1 for examples), but their characteristics strongly depend on whether they are bound to proteins. Excitation of these molecules would elicit background emission that would contaminate the emission due to implanted sensors, resulting in baseline offsets or even major spectral shifts in extreme cases therefore, it is necessary to carefully select fluorophores for implants. It is also noteworthy that the lifetimes are fairly short, such that use of longer lifetime emitters in sensors would allow lifetime-resolved measurements to extract sensor emission from overriding tissue fluorescence. 

In these equations, and are the initial molecular weights, 4>(s) and 4>(x) are the quantum yields for the scissioning and cross-linking reactions, respectively D is absorbed dose and is Avogadro s number. The slopes of the respective plots of I/M and I/M versus dose produce two simultaneous equations, the solution of which yields values for 4>(s) and 4>(x). We (60) have analyzed the data obtained for a number of polysilane derivatives by GPC (gel permeation chromatography) to evaluate the respective molecular weights and distributions (Table III). Polystyrene standards were used for molecular weight calibration. 

To study the structural sensitivity of poly silanes to ionizing radiation, a number of samples were irradiated with a calibrated Co source, and the degraded materials were analyzed by GPC in a manner similar to that described for the determination of photochemical quantum yields (59). In radiation processes, the slopes of the plots of molecular weight versus absorbed dose yield the G values for scissioning, G(s), and cross-linking, G(x), rather than the respective quantum yields. These values, which represent the number of chain breaks or cross-links per 100 eV of absorbed dose, are indicative of the relative radiation sensitivity of the material. The data for a number of polysilanes are given in Table IV. Also included in Table IV for comparison is the value for a commercial sample of poly(methyl methacrylate) run under the same conditions. The G(s) value of this sample compares favorably with that reported in the literature (83). 

MODEL Molecular Descriptor Lab (MODEL) (http //jing.cz3.nus.edu.sg/ cgi-bin/model/model.cgi) is a free Web-based server for computing a comprehensive set of 3778 molecular descriptors, which can be divided into 6 classes constitutional descriptors, electronic descriptors, physical chemistry properties, topological indexes, geometrical molecular descriptors, and quantum chemistry descriptors [73], Compounds can be provided to the server in various molecular formats such as PDB, MDL, MOL2, and COR, and the computed molecular descriptors are displayed in a few seconds or less. Cross-links to the relevant sections of the reference manual page are also provided for some of the descriptors and descriptor classes. 

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