Short sidechain

Table V illustrates the carbon-number distribution in selected series. Similar trends were observed in most others. With one exception, the homolog present in the largest concentration within a series has three to four carbon atoms more than the first member of the series. This could indicate short sidechains or, possibly, the appearance of isomeric naphthenoaromatic series...

Flliott and Paddison (2007) used the ONIOM method of QM/MM calculations (Vreven et al., 2003) to understand the effects of hydration on the local structure of PFSA membranes. Calculations were performed on fragments of a short sidechain (SSC) PFSA ionomer with three sidechains affixed to the backbone. Full optimizations of the oligomeric fragment was carried out with six to nine water molecules added. The lowest energetic state was found with six water molecules. Upon addition of further water molecules, the energetic preference for uniform hydration of sidechains via interconnected water clusters disappeared. The optimized structures of a system of two oligomeric fragments at X = 2.5 showed that the structure with... 

DPD simulations have been analyzed in view of the microsegregated structure of hydrated Nafion at various X (Hayashi et al., 2003 Vishnyakov and Neimark, 2005 Yamamoto and Hyodo, 2003). A typical structure is depicted in Figure 2.11. Size and separation distance of ionic clusters were found to increase approximately linearly with X. Upon increasing X, the membrane undergoes a percolation transition from isolated hydrophilic clusters to a 3D network of randomly interconnected water channels. Wu et al. (2008) applied extensive DPD simulations to compare the morphologies of Nafion, short sidechain (SSC) PFSA PEMs of Solvay-Solexis, and 3M... 

Branching m (1) The growth of a new polymer chain from an active site on an established chain, in a direction difierent from that of the original chain. Branching occurs as a result of chain-transfer processes or from the polymerization of difunctional monomers, and is an important factor influencing polymer properties. (2) Two-dimensional polymers having relatively short sidechains branching from the main backbone. (Odian GC, (2004) Principles of polymerization, WUey, New York). 

Silk fibroin (SF) polymers consist of repetitive protein sequences and provide structural roles in cocoon formation, nest building, traps, web formation and egg protection. Silks are generally composted of P-sheet structures due to the dominance of hydrophobic domains consisting of short sidechain amino acids in the primary sequence. Silk is biocompatible, degradable and shows superior mechanical properties. Silk materials are amenable to aqueous or organic solvent processing and can be chemically modified to suit a wide range of biomedical applications [249-251]. 

Figure 8 X-ray diffraction patterns of PaAA-n fibers (a) short sidechain (PaAA-3) (b) medium sidechain (PaAA-6) (c) long sidechain (PaAA-18).

Returning to the photosynthetic system it now seems plausible that the explanation for the short charge-separation times in the primary steps must be found in the nature of the medium between the redox-sites involved. In this connection it is interesting to note that saturated hydrocarbon chains (i.e. phytyl sidechains) extend from the special pair and from the menaquinone towards the intermediate bacteriopheophytin (see Fig.l). At this moment it is not clear, however, whether in rhodopseudomonas viridis any of these phytyl sidechains plays the role of a molecular wire (see also Kuhn, 1986) that we attribute to the hydrocarbon bridges in l(n). For rhodopseudomonas sphaeroides a fivefold decrease in the rate of the reverse electron transfer from the quinone (ubiquinone) to the bacteriopheophytin was recently reported to result upon removal of the isoprenoid sidechain from the quinone (Gunner et al., 1986). 

The pentacyclic component at m/e 412 resembles the spectrum of oleanane (structure shown) or gammacerane. It is also similar to that of lupane (13, 15) but lacks the M-43 (369) fragment indicative of any isopropyl sidechain. Therefore, ring E is probably 6-member-ed, not 5-membered as in lupane or the hopanes. Although the mass spectrum is a slightly better match to gammacerane, the short GC retention time probably rules out gammacerane but not oleanane (13). 

In summary, it appears from spectroscopic studies such as neutron scattering or NMR relaxation measurements which probe rotational water motions on a short time scale, 10 -10 s, and thus over a short distance range that, at the highest water contents, water mobility within the pore of an ionomeric membrane is not drastically different than bulk water mobility. However, as the water content of the membrane decreases, its mobility is increasingly hindered. The nanopore liquid in the membrane is essentially a concentrated acid solution and ion-water (as well as ion-ion) interactions will have significant influences on water motion. Intrusions of sidechains... 

Fig. 4 Molecular structure of diblock copolymers and side-chain modified lipopolymers whose pressure-area isotherms are presented in Figs. 6 and 7, respectively. Diblock copolymers are poly(2-n-nonyl)-poly(2-methyl or 2-ethyl-2-oxazoline) (NxEy and NxMj,), where x and y denote the block sizes of the hydrophobic nonyl and hydrophilic oxazoline blocks. Side-chain modified lipopolymers, which contain short oligo-EG sidechains in each monomer of the lipopolymer to create a bottle-brush-like structure, are di-octadecanoyl-glycerol 2-(3 -methoxymonoethylene glycol)propyl-2-oxazoline (DiCigMEGOxn) and di-octadecanoyl-glycerol 2-(3 -methoxytiiethyleneglycol)propyl-2-oxazoline (DiCisTEGOxn) (adapted from [7,8])...

For some problems, such as the motion of heavy particles in aqueous solvent (e.g., conformational transitions of exposed amino acid sidechains, the diffusional encounter of an enzyme-substrate pair), either inertial effects are unimportant or specific details of the dynamics are not of interest e.g., the solvent damping is so large that inertial memory is lost in a very short time. The relevant approximate equation of motion that is applicable to these cases is called the Brownian equation of motion,... 

In coals, the alkyl sidechains are short, as are the bridges between rings and so there is less opportunity to form long-chain paraffinic products. Instead, more hydrogen atoms per carbon are required to cap radicals and to remove a smaller number of carbons in the gas and liquid products. The net effect is an inefficient use of hydrogen that results in aromatization of a significant fraction of the aliphatic carbons. 

Fig.1 Possible types of cages where the strings represent the backbones or their bundles, that can provide a short-range-ordered system of fourfold coordinated inverted micelles composed of hydrated sidechains (not shown) pointing from the strings towards the interior of the cages [31]. These micelles keep water droplets (not shown) with protons of dissociation encapsulated inside the cage. The channels, when they form, bridge water droplets, through the windows in the cages...

Numerous multipulse and two dimensional experiments are used to identify unknown (co)polymers and these experiments are most useful in analyzing differences between copolymers or impurities in production problems. The Distortionless Enhancement via Polarization Transfer (DEPT) pulse sequence is frequently used to determine the carbon multiplicity (CH vs. CHj vs. CH3) of a carbon spectrum. Newmark showed excellent DEPT spectra could be obtained on sidechain groups in vinyl polymers or in typical polyesters and polyurethanes, but that it was difficult to observe good DEPT spectra (at 200 MHz) on backbone carbons, such as the ring carbons in cellulose acetate butyrate (CAB) with very short carbon spin-spin relaxation times (Tj) (8). 

---