Correlated spectroscopy principle

Ozaki, Y. and Wang, Y., Two-dimensional near-infrared correlation spectroscopy principle and its applications, J. Near-Infrared Spectrosc., 6(1-4), 19-31, 1998. 

Y. Ozaki, S. Sasic, T. Tanaka, I. Noda. Two-Dimensional Correlation Spectroscopy Principle and Recent Theoretical Development RuH Chem Soc Jpn 74 1-17. 2001. 

Various techniques and equipment are available for the measurement of particle size, shape, and volume. These include for microscopy, sieve analysis, sedimentation methods, photon correlation spectroscopy, and the Coulter counter or other electrical sensing devices. The specific surface area of original drug powders can also be assessed using gas adsorption or gas permeability techniques. It should be noted that most particle size measurements are not truly direct. Because the type of equipment used yields different equivalent spherical diameter, which are based on totally different principles, the particle size obtained from one method may or may not be compared with those obtained from other methods. 

J.M. Chalmers, Spectra-structure correlations Polymer spectra. In N.J. Everall, J.M. Chalmers and P.R. Griffiths (Eds.), Vibrational Spectroscopy Principles and Practice, Wiley, Chichester, 2007, pp. 69-112. 

In fluorescence correlation spectroscopy (FCS), the temporal fluctuations of the fluorescence intensity are recorded and analyzed in order to determine physical or chemical parameters such as translational diffusion coefficients, flow rates, chemical kinetic rate constants, rotational diffusion coefficients, molecular weights and aggregation. The principles of FCS for the determination of translational and rotational diffusion and chemical reactions were first described in the early 1970s. But it is only in the early 1990s that progress in instrumentation (confocal excitation, photon detection and correlation) generated renewed interest in FCS. 

Reports on the application of pulsed field gradient (PFG) assisted pulse schemes for two-dimensional X/Y correlation spectroscopy focused mainly on the adaptation of HSQC sequences which seemed to perform better than HMQC experiments under these conditions.21 Although the generalisation of standard pulse sequences for / C correlation spectroscopy should in principle be straightforward, large spectral ranges and short relaxation... 

Beyond imaging, CARS microscopy offers the possibility for spatially resolved vibrational spectroscopy [16], providing a wealth of chemical and physical structure information of molecular specimens inside a sub-femtoliter probe volume. As such, multiplex CARS microspectroscopy allows the chemical identification of molecules on the basis of their characteristic Raman spectra and the extraction of their physical properties, e.g., their thermodynamic state. In the time domain, time-resolved CARS microscopy allows recording of ultrafast Raman free induction decays (RFIDs). CARS correlation spectroscopy can probe three-dimensional diffusion dynamics with chemical selectivity. We next discuss the basic principles and exemplifying applications of the different CARS microspectroscopies. 

This section contains a general description of the principles by which the Coulter Model N4 Sub-Micron Particle Analyzer, used in this study to characterize artificial gas-in-water emulsions (see Section 10.4), determines sample particle size. The measuring principles are based on the theory of Brownian motion and photon correlation spectroscopy (ref. 464,465 see also Sections 10.2 and 10.4). 

Dynamic light scattering (DLS), also called photon correlation spectroscopy (PCS) or laser light scattering (LLS) is a technique based on the principle that moving objects cause a frequency shift due to the Doppler effect. If a solution of macromolecules with random Brownian motion is illuminated with monochromatic laser light, the scattered light should contain a distribution of frequencies about the incident frequency the spectral line is virtually broadened. The width of the distribution is related to the MMD. 

Coupling FFF with other techniques can enhance measurement capabilities. Here, the possibility of taking fractions after the FFF separation is of great advantage. The use of photon correlation spectroscopy, for example, to determine the size of spheres eluted from sedimentation FFF yields both size and density [75]. Further comparison can be achieved with electron microscopy. In principle, every analytical technique (spectroscopy, microscopy, chemical analysis, etc.) can be performed off-line on fractions from FFF. 

Figure 17.4 Principle of fluorescence correlation spectroscopy the fluorescence intensity temporal fluctuations originating from a well-defined volume are recorded and correlated to estimate the average number of molecules observed and the characteristic fluctuation time. This data is used to compute the average detected fluorescence rate per molecule in the observation volume.

Schwille P, Haustein E. Ruorescence correlation spectroscopy. Biophysical Society, http //www.biophysics.org/education/schwille.pdf. Valeur B, Editor. Molecular Ruorescence Principles and Apphcations. 

Unlike correlation spectroscopy based on spin diffusion, the adiabatic version enables, in principle, almost full exchange of magnetization between the two spins. As a result, the entire signal intensity will reside in the cross-peaks. Violation of the adiabaticity is characterized by the appearance of a diagonal peak and can be expected to occur if the rotation sweep is too fast compared to the interaction between spins. While numerical simulations indicate possible linear dependencies of the polarization transfer coefficient on spin coupling and the rate of the sweep over a range of practical values, the validity of this assumption remains to be tested. Here we present a semi-quantitative example of a relayed polarization transfer process. 

Figure 33.6 Illustration of confocal volume in fluorescence correlation spectroscopy (FCS) describing the experimental principle for evaluation of diffusion coefficients from the fluctuation of photon signals, (a) Fluctuation due to large and less mobile molecules is slow and...

General symmetry principles for rotor-synchronized pulse sequences in MAS solid-state NMR have been presented. The synunetry theory has been extended to the case of generalized Hartmann-Hahn sequences, in which rotor-synchronized r.f. irradiation is applied simultaneously to two isotopic spin species. The symmetry theory has been used to design pulse sequences which implement heteronuclear dipolar recoupling at the same time as decoupling homonuclear spin-spin interactions, and which also suppress CSAs. Experimental demonstrations of heteronuclear 2D correlation spectroscopy, heteronuclear MQ spectroscopy, and the estimation of intemuclear dipolar couplings have been given. 

Even if "X, "Y correlation spectroscopy imposes no principle differences with respect to H, Y correlations, its widespread use was until recently limited by hardware restrictions recording of such spectra under additional H... 

In principle, there is nothing uncommon in performing ID- or 2D-"X,"Y correlation spectroscopy as compared to conventional H,"X heteronuclear... 

NMR has become a standard tool for structure determination and, in particular, for these of Strychnos alkaloids. The last general article in this field was authored by J. Sapi and G. Massiot in 1994 [65] and described the advances in spectroscopic methods applied to these molecules. More recently, strychnine (1) has even been used to illustrate newly introduced experiments [66]. We comment, here, on their advantages and sum up the principles of usual 2D experiments in Fig. (1) and Fig. (2) (COSY Correlation SpectroscopY, TOCSY TOtal Correlation SpectroscopY, NOESY Nuclear Overhauser Enhancement SpectroscopY, ROESY Rotating frame Overhauser Enhancement SpectroscopY, HMQC Heteronuclear Multiple Quantum Coherrence, HMBC Heteronuclear Multiple Bond Correlation). This section updates two areas of research in the field new H and 13C NMR experiments with gradient selection or/and selective pulses, 15N NMR, and microspectroscopy. To take these data into account, another section comments on the structure elucidation of new compounds isolated from Strychnos. It covers the literature from 1994 to early 2000. 

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