Spectroscopy alkane chains

Deuterium NMR spectroscopy has been employed to probe the interaction between perdeuteriated n-alkanes and host molecules such as liquid crystals, urea crystals, lipid bilayers or zeolites. In general, the temperature-dependent quadrupolar splitting of the deuterium signals is interpreted in terms of conformation and ordering of the alkane chains. For lipid bilayers these studies are of interest in connection with the anaesthetic properties of alkanes. Phospatidylcholine bilayer membranes were chosen as a model. The solubilities of n-alkanes as determined by NMR were found to be dependent on both the membrane- and alkane-chain length ". The complex signal patterns which show the dynamic processes of perdeuteriated hexane in a multilayer is reproduced in Figure 3 ... 

The polyethers containing three, five and seven methylene units were analyzed by 200 MHz spectroscopy. The last two polymers present bromo-alkane chain ends only. A typical NMR spectrum is shown in Figure 2 together with its proton assignments. The polyethers of 1,3-dibromopropane and HMS present both bromopropane and allyl ether chain ends. A typical spectrum is given in Figure 3. The ratio between allyl ether and bromopropane chain ends depends on the reaction conditions used. If a small... 

The recrystallization of S-layer proteins at phosphoethanolamine monolayers on aqueous subphases has been also studied on a mesoscopic scale by dual label fluorescence microscopy andFourier transform infrared spectroscopy (FTIR) [110]. It has been shown that the phase state of the lipid exerts a marked influence on the protein crystallization. When the surface monolayer is in the phase separated state between fluid and crystalline phase, the S-layer protein is preferentially adsorbed at the boundary line between the two coexisting phases and crystallization proceeded underneath the crystalline phase. Crystal growth is much slower under the fluid lipid and the entire interface is overgrown only after prolonged protein incubation. In turn, as indicated by characteristic frequency shifts of the methylene stretch vibrations on the lipids, protein crystallization affects the order of the alkane chains and drives the fluid lipid into a state of higher order. However, the protein does not interpenetrate the lipid monolayer as confirmed by x-ray reflectivity studies [105-107]. 

According to Raman spectroscopy the chains in the hexagonal form are confor-mationally disordered with an appreciable concentration of gauche bonds.(276,277) These results are consistent with the interpretation of the wide-angle diffraction pattern of this phase which requires an element of conformational disorder.(278,279) The gauche content of the pure melt of low molecular weight alkanes is known to increase with increasing applied hydrostatic pressure. 

Gao et al. used [bmim][BFJ to prepare nonaqueous [bmim][BFJ-benzene-TX-100 [26] and [bmim][BFJ-cyclohexane-TX-100 [30] microemulsions. Tliey reported the phase behavior of IL-oil microemulsion and found physicochemical properties similar to those of water-oil microemulsions [26]. The microstructure was investigated by SANS [28], electron microscopy [30], DLS, UV-Vis, FTIR, and H-NMR spectroscopy [26]. An in-depth phase diagram study of EAN-n-alkane-CiEj surfactant systems was reported by Atkin and Warr, where the influence of the n-alkane chain length and of the surfactant structure on the efficiency was highlighted [29]. 

Figure 6.2. Polarized reflection infrared spectroscopy to determine structure and order in alkane thiol SAMs (a) comparison of theoretical and experimental C-H stretching IR spectra for octadecyl thiol adsorbed on to gold (b) effect of temperature on increasing the disorder in the alkane chain...

Abstract. In this contribution some recent developments in the area of intramolecular excited state interactions will be discussed. In a first part the power of global compartmental analysis of fluorescence decays of intramolecular exciplex forming systems is exemplified. In a second part the use of photoacoustic spectroscopy in the study of intramolecular back electron transfer is illustrated and in a last part the alternative linking of a donor and an acceptor with a flexible silane chain will be compared with a similar donor and acceptor linked by an alkane chain. 

Figure 13.18. Experimental (left) and calculated (right) reflection spectra of an ODS monolayer on silicon for (a) 5-polarized radiation, and (b) p-polarized radiation at different incidence angles. A uniform tilt angle of 10° of the alkane chain in the monolayer film was assumed for the simulated spectra. (Reproduced from [12], by permission of the Society for Applied Spectroscopy copyright 1997.)...

Polarized infrared external reflection spectroscopy (PIERS) has been very useful in determining the structural details of these SAMs (11,15,20,21). PIERS results show that SAMs of alkanethiolates on gold are nearly analogs of two-dimensional crystalline alkanes. The alkane chains are predominantiy in a trans zig-zag conformation the few gauche conformations are concentrated near the ends of the chains (15,18,23). The alkane chains are tilted 26° relative to the surface normal. This tilt, which allows the chains to be close-packed, is a direct result of the lattice spacing of the sulfur atoms. 

The FT-IR and Raman spectra of 1-decylphosphonic acid, its ammonium, ethylenediaminium and calcium salts, have each been assigned in the 4000-500 cm range, all revealing trans conformation of the alkane chain. Also, a series of new piperazine phosphoramide derivatives of 4-hydroxycoumarin have been characterized using a combination of IR and NMR spectroscopy, electrospray ionization (ESI-MS)- and high-resolution MS (HR-MS). ... 

One of the initial spectroscopic methods applied to stationary-phase characterization was Fourier transform infrared spectroscopy (FTIR). This originated from several important studies of phase conformational order in crystalline n-alkanes conducted in the late 1960s and early 1980s by Snyder, Maroncelli, and coworkers [111-114], In this work, assignments of C—H bond wagging modes were associated with chain... 

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