Macromolecular spectra

Wiithrich et al published a tour de force on the Automated Peak-Picking and Peak Integration in Macromolecular Spectra (AUTOPSY). This work deals primarily with two-dimensional spectra, but the algorithms are equally... 

Fluorescent probes are divided in two categories, i.e., intrinsic and extrinsic probes. Tryptophan is the most widely used intrinsic probe. The absorption spectrum, centered at 280 nm, displays two overlapping absorbance transitions. In contrast, the fluorescence emission spectrum is broad and is characterized by a large Stokes shift, which varies with the polarity of the environment. The fluorescence emission peak is at about 350 nm in water but the peak shifts to about 315 nm in nonpolar media, such as within the hydrophobic core of folded proteins. Vitamin A, located in milk fat globules, may be used as an intrinsic probe to follow, for example, the changes of triglyceride physical state as a function of temperature [20]. Extrinsic probes are used to characterize molecular events when intrinsic fluorophores are absent or are so numerous that the interpretation of the data becomes ambiguous. Extrinsic probes may also be used to obtain additional or complementary information from a specific macromolecular domain or from an oil water interface. 

The simplest fluorescence measurement is that of intensity of emission, and most on-line detectors are restricted to this capability. Fluorescence, however, has been used to measure a number of molecular properties. Shifts in the fluorescence spectrum may indicate changes in the hydrophobicity of the fluorophore environment. The lifetime of a fluorescent state is often related to the mobility of the fluorophore. If a polarized light source is used, the emitted light may retain some degree of polarization. If the molecular rotation is far faster than the lifetime of the excited state, all polarization will be lost. If rotation is slow, however, some polarization may be retained. The polarization can be related to the rate of macromolecular tumbling, which, in turn, is related to the molecular size. Time-resolved and polarized fluorescence detectors require special excitation systems and highly sensitive detection systems and have not been commonly adapted for on-line use. 

Lyotropic polymeric LC, formed by dissolving two aromatic polyamides in concentrated sulphuric acid, have been studied using variable-director 13C NMR experiments.324 The experimental line shapes at different angles w.r.t the external field were used to extract macromolecular order and dynamic in these ordered fluids. An interesting application of lyotropic LC is for the chiral discrimination of R- and S-enantiomers, and has recently been demonstrated by Courtieu and co-workers.325 The idea was to include a chiral compound 1-deutero-l-phenylethanol in a chiral cage (e.g., /1-cyclodextrin) which was dissolved and oriented by the nematic mean field in a cromolyn-water system. Proton-decoupled 2H NMR spectrum clearly showed the quad-rupolar splittings of the R- and S-enantiomers. The technique is applicable to water-soluble solutes. 

Figures 5-7 are the spectra exhibiting the thermally extracted mobile phase components over different temperature intervals. All five coals mentioned in Figures 5-7 show distinct mass spectra in the mobile phase compared to the spectra of the macromolecular structure (25) and contain alkylsubstituted naphthalenes in the mobile phase although their relative amounts are dependent on coal characteristics. In general, (the temperature where the maximum rate occurs) in Py-FIMS was in the range of 430-470 C for bituminous rank coals. Around T, the macromolecular structure of bituminous rank coals is decomposed to yield FI spectrum showing the dominant peaks of alkylsubstituted phenols. Detailed FI spectra of the macromolecular structure for the ANL-PCS coals mentioned in Figures 5-7 are illustrated elsewhere (25).

As an example chosen in the macromolecular field the C NMR spectrum of syndiotactic polypropylene might be mentioned In solution (averaged random coil conformation, molecular model corresponding to 7) it presents three signals in the crystal state, where a chiral rigid conformation exists [(2/1)2 helix], it shows four signals (Figure 17). 

Ciclopirox olamine is a synthetic broad-spectrum antimycotic agent with inhibitory activity against dermatophytes, Candida species, and P orbiculare. This agent appears to inhibit the uptake of precursors of macromolecular synthesis the site of action is probably the fungal cell membrane. 

As is seen from Table 13, cholesteric copolymers display a maximum of selective light reflection ( w) in an IR- or a visible part of the spectrum. By varying the composition of a copolymer, it is possible to vary Xmax, in accordance with the stipulation max = nP, is proportional to the pitch P of the helical structure of a LC polymer (n — is the refractive index). The pitch of the helix in cholesteric copolymers is usually decreased, when the temperature is raised 105) (at temperatures above Tg), which is equally common for low-molecular cholesterics142) (Fig. 23a). The observed fact that the helix pitch for LC copolymers 2.1-2.3 (Table 13, Fig. 23b) is increased, is rather unusual but explicable within the theoretical views regarding vibrational movement of macromolecular fragments and their conformational mobility 60). 

The dependence of rf, rf, G, and G" on frequency reflects the ability of macromolecular systems to flow like Newtonian fluids if the experimental time allowed them, feXp = 1 /< , is very large compared to the time that they require to fully respond macromolecularly. This temperature-dependent, material-characteristic time is commonly called the relaxation time, X, although it is actually a relaxation spectrum (7). Conversely, when /exp is very short, that is, co is very high compared to X, the macromolecular system can only respond like an elastic solid, able only to undergo deformation and not flow. In... 

The possibility of using the electron paramagnetic resonance properties of Gd3+ to probe its environment in and interactions with biological molecules has previously received little attention in the literature (40). However, the possibility exists that Gd2+ will be a sensitive EPR probe for characterizing macromolecular biological systems such as the Ca2+-ATPase. The EPR spectra of Gd3+, which has S = 7/2. in neutral water and in two different buffers are shown in Figure 13A. The linewidths were found to be independent of pH over the usable range of these buffers and independent of temperature between 4 and 30°C, The spectrum of Gd2+ in neutral water is centered around 3248 G, with a linewidth of 530 G. As shown, Gd3+ in Pipes buffer, but not in Tes buffer, yielded a spectrum similar to that of the aqueous Gd2+ solution. On this basis, all of our Gd3+ EPR and NMR studies... 

Such a decrease in the linewidth may result from a decrease in the Gd3+ coordination number upon formation of the macromolecular complex, which could result in greater symmetry and a lower zero-field splitting for the Gd3+ ion. This spectrum is independent of temperature between 4 and 25°C and is independent of the Gd3+/ ATPase ratio up to 2 Gd + ions/ATPase molecule. The peak-to-peak linewidth of 285 G sets a lower limit of 2,3 x 10"10s Qn the electron spin relaxation time of enzyme-bound Gd +t This symmetric, narrow EPR spectrum for the Gd3+-ATPase complex is compared in Figure 13B to that of Gd3+ bound to parvalbumin, a Ca2+-binding protein from carp. In this case, the spectrum is extremely broad and suggests a greatly distorted Gd3+ coordination geometry compared to the Ca2+-ATPase. 

In the two cases, the Ru(II) complexes are six-coordinated, however, the pyridine complex is soluble in water whereas [Ru(Dipy)2L2]Cl2 is insoluble because of a strong intermolecular interaction. The polymeric nature of the ligand manifests itself in a 10 run shift of the adsorption spectrum (in the UV-region) of the macromolecular complex due to lowering its resonance stabilization, differences... 

The macromolecular nature and structural heterogeneity of the polymeric SOs allow the existence of several different binding sites this holds in particular for proteins which are quite heterogeneous by nature. As a consequence they have usually a broad spectrum of applicability, but their or-values are rather mtxlerate and are typically between 1 and 3. In addition, it is difficult to study the mechanism of chiral recognition and to identify the site of chiral recognition. The exact arrangement of the SA in the active chiral recognition site remains still widely unknown. 

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