Investigation on the Behavior of Noise in Asynchronous Spectra in Generalized Two-Dimensional (2D) Correlation Spectroscopy and Application of Butterworth Filter in the Improvement of Signal-to-Noise Ratio of 2D Asynchronous Spectra

The behavior of noise in asynchronous spectrum in generalized two-dimensional (2D) correlation spectroscopy is investigated. Mathematical analysis on the noise of 2D spectra and computer simulation on a model system show that the fluctuation of noise in a 2D asynchronous spectrum can be characterized by the standard deviation of noise in 1D spectra. Furthermore, a new approach to improve a signal-to-noise ratio of 2D asynchronous spectrum by a Butterworth filter is developed. A strategy to determine the optimal conditions is proposed. Computer simulation on a model system indicates that the noise of 2D asynchronous spectrum can be significantly suppressed using the Butterworth filtering. In addition, we have tested the approach to a real chemical system where interaction between berberine and β-cyclodextrin is investigated using 2D UV–vis asynchronous spectra. When artificial noise is added, cross peaks that reflect intermolecular interaction between berberine and β-cyclodextrin are completely masked by noise. After the method described in this article is utilized, noise is effectively suppressed, and cross peaks are faithfully recovered. The above result demonstrates that the approach described in this article is applicable in real chemical systems

Novel Method of Constructing Two-Dimensional Correlation Spectroscopy without Subtracting a Reference Spectrum

In this study, we propose a new approach to generate two-dimension spectra to enhance the intensity of cross peaks relevant to intermolecular interaction. We investigate intermolecular interaction between two solutes (denoted as P and Q, where P has a characteristic peak at <i>X</i>_P) dissolved in the same solvent via the near diagonal cross peaks around the coordinate (<i>X</i>_P, <i>X</i>_P) in a two-dimensional (2D) asynchronous spectrum of generalized spectroscopy. Because of physical constrains in many cases, the variation ranges of the initial concentrations of P or Q must be kept very narrow, leading to very weak cross peak intensities. The weak cross peaks vulnerable to noise bring about difficulty in the investigation of subtle intermolecular interaction. Herein, we propose a new of way constructing a 2D asynchronous spectrum without the subtraction of the average spectrum often used as a reference spectrum. Mathematical analysis and computer simulation demonstrate that the near diagonal cross peaks around the coordinate (<i>X</i>_P, <i>X</i>_P) in the 2D asynchronous spectrum using the new approach possess two characteristics: (1) they can still reflect an intermolecular interaction reliably; 2) the absolute intensities of the cross peaks are significantly stronger than those generated by the conventional method. We incorporate the novel method with the DAOSD (double asynchronous orthogonal sample design scheme) approach and applied the modified DAOSD approach to study hydrogen bonding behavior in diethyl either/methanol/THF system. The new approach made the weak cross peaks, which are not observable in 2D asynchronous spectrum generated using conventional approach, become observable. The appearance of the cross peak demonstrate that When a small amount of THF is introduced into diethyl solution containing low amount of methanol, THF breaks the methanol–diethyl ether complex and forms methanol-THF complex via new hydrogen bond. This process takes place in spite of the fact that the content of diethyl ether is overwhelmingly larger than that of THF. The above result demonstrates that the new approach described in this article is applicable to enhance intensity of cross peaks in real chemical systems

Double Asynchronous Orthogonal Sample Design Scheme for Probing Intermolecular Interactions

This paper introduces a new approach called double asynchronous orthogonal sample design (DAOSD) to probe intermolecular interactions. A specifically designed concentration series is selected according to the mathematical analysis to generate useful 2D correlated spectra. As a result, the interfering portions are completely removed and a pair of complementary sub-2D asynchronous spectra can be obtained. A computer simulation is applied on a model system with two solutes to study the spectral behavior of cross peaks in 2D asynchronous spectra generated by using the DAOSD approach. Variations on different spectral parameters, such as peak position, bandwidth, and absorptivity, caused by intermolecular interactions can be estimated by the characteristic spectral patterns of cross peaks in the pair of complementary sub-2D asynchronous spectra. Intermolecular interactions between benzene and iodine in CCl₄ solutions were investigated using the DAOSD approach to prove the applicability of the DAOSD method in real chemical system

Sugar–Metal Ion Interactions: The Complicated Coordination Structures of Cesium Ion with d‑Ribose and <i>myo</i>-Inositol

The novel cesium chloride–d-ribose complex (CsCl·C₅H₁₀O₅; Cs-R) and cesium chloride–<i>myo</i>-inositol complex (CsCl·C₆H₁₂O₆; Cs-I) have been synthesized and characterized using X-ray diffraction and FTIR, FIR, THz, and Raman spectroscopy. Cs⁺ is eight-coordinated to three chloride ions, O1 and O2 from one d-ribose molecule, O1 from another d-ribose molecule, and O4 and O5 from the third d-ribose molecule in Cs-R. For one d-ribose molecule, the oxygen atom O1 in the ring is coordinated to two cesium ions as an oxygen bridge, O2 is cocoordinated with O1 to one of the two cesium ions, and O4 and O5 are coordinated to the third cesium ion, respectively. O3 does not coordinate to metal ions and only takes part in forming hydrogen bonds. One chloride ion is connected to three cesium ions. Thus, a complicated structure of Cs–d-ribose forms. For Cs-I, Cs⁺ is 10-coordinated to three chloride ions, O1 and O2 from one <i>myo</i>-inositol molecule, O3 and O4 from another <i>myo</i>-inositol molecule, O5 and O6 from the third <i>myo</i>-inositol molecule, and O6 from the fourth <i>myo</i>-inositol molecule. One metal ion is connected to four ligands, and one <i>myo</i>-inositol is coordinated to four Cs⁺ ions, which is also a complicated coordination structure. Crystal structure results, FTIR, FIR, THz, and Raman spectra provide detailed information on the structure and coordination of hydroxyl groups to metal ions in the cesium chloride–d-ribose and cesium chloride–<i>myo</i>-inositol complexes

Sugar–Metal Ion Interactions: The Complicated Coordination Structures of Cesium Ion with d‑Ribose and <i>myo</i>-Inositol

The novel cesium chloride–d-ribose complex (CsCl·C₅H₁₀O₅; Cs-R) and cesium chloride–<i>myo</i>-inositol complex (CsCl·C₆H₁₂O₆; Cs-I) have been synthesized and characterized using X-ray diffraction and FTIR, FIR, THz, and Raman spectroscopy. Cs⁺ is eight-coordinated to three chloride ions, O1 and O2 from one d-ribose molecule, O1 from another d-ribose molecule, and O4 and O5 from the third d-ribose molecule in Cs-R. For one d-ribose molecule, the oxygen atom O1 in the ring is coordinated to two cesium ions as an oxygen bridge, O2 is cocoordinated with O1 to one of the two cesium ions, and O4 and O5 are coordinated to the third cesium ion, respectively. O3 does not coordinate to metal ions and only takes part in forming hydrogen bonds. One chloride ion is connected to three cesium ions. Thus, a complicated structure of Cs–d-ribose forms. For Cs-I, Cs⁺ is 10-coordinated to three chloride ions, O1 and O2 from one <i>myo</i>-inositol molecule, O3 and O4 from another <i>myo</i>-inositol molecule, O5 and O6 from the third <i>myo</i>-inositol molecule, and O6 from the fourth <i>myo</i>-inositol molecule. One metal ion is connected to four ligands, and one <i>myo</i>-inositol is coordinated to four Cs⁺ ions, which is also a complicated coordination structure. Crystal structure results, FTIR, FIR, THz, and Raman spectra provide detailed information on the structure and coordination of hydroxyl groups to metal ions in the cesium chloride–d-ribose and cesium chloride–<i>myo</i>-inositol complexes