Asynchronous Orthogonal Sample Design Research Articles

Patterns of Cross-Peaks in Two-Dimensional Correlation Spectra to Probe Intermolecular Interactions Described by Two Reversible Reactions.

Two-dimensional correlation spectroscopy is used to investigate the intermolecular interaction between two substances dissolved in the same solutions, where the intermolecular interaction is described by two reversible reactions producing two supramolecular aggregates. The severe overlappings expected among the characteristic peaks of the original solute and aggregates make conventional one-dimensional spectra difficult to accurately reflect the physiochemical nature of the intermolecular interaction. The double asynchronous orthogonal sample design (DAOSD) approach is utilized to analyze the simulated data for proof-of-principle demonstration. The patterns of cross-peaks are much more complex compared with the intermolecular interaction described by only a single reaction. Four major groups of cross-peaks with characteristic patterns observed in the pair of DAOSD asynchronous spectra are systematically analyzed and classified. Further analysis of the spectral feature of the cross-peaks of the DAOSD asynchronous spectra is helpful to exact additional information concerning the variation of the peak position and peak width of the aggregates compared with those of the original solute. The result is important to reveal the physicochemical nature of intermolecular interaction between the solutes (e.g., changes in conformation, dynamical behavior, etc.). The pattern of cross-peaks in the corresponding 2D asynchronous spectra may become rather complex when the peak position, peak width, and peak intensity of two supramolecular aggregates change simultaneously. Further work using artificial intelligence techniques to interpret the complex cross-peaks is still being carried out.

Robust Approach to Estimating the Stoichiometric Ratio of Supramolecular Complexes Using the Volume of Cross-Peaks in 2D Asynchronous Spectra and the Jonckheere-Terpstra Test.

Estimation of the stoichiometric ratio of a supramolecular aggregate formed by different compounds is very important in elucidating the structure and function of the aggregate. Many spectroscopic methods used to estimate the stoichiometric ratios of coordination complexes become invalid when characteristic peaks of the aggregate overlap with peaks of compounds that form the aggregate. Previously, we combined the asynchronous orthogonal sample design with Job's method to address the abovementioned problem. However, the interference of noise may lead to incorrect results. Herein, a new method has been developed. In the generation of corresponding Job's curve, the intensity of a cross peak at a single apex is replaced by the volume of the cross peak. Since most noise is canceled in the calculation of the volume of the cross peak, resultant Job's curve is robust to noise. Moreover, the Jonckheere-Terpstra statistical test, a famous nonparametric method to detect whether the data has an upward or downward trend, could further reduce the risk of yielding incorrect results caused by noise. We have applied this approach to two real-world examples (resveratrol/β-Cyclodextrin (β-CD) and N, N-diethyl-N'-benzoylthiourea (DEBT)/Cu2+) with satisfactory results. The method described in this paper provides a robust way to measure the stoichiometric ratio in supramolecular systems.

Investigation on the luminescence behavior of terbium acetylsalicylate/bilirubin system via 2D-COS approaches

Terbium acetylsalicylate has been prepared, and the ethanol solution of the complex exhibits strong luminescence under the excitation of ultraviolet radiation. When a small amount of bilirubin solution is introduced into the solution containing a high concentration of terbium acetylsalicylate, a remarkable diminution of the luminescence of the terbium complex was observed. Investigations on the behavior and life-time of luminescence indicate that the quenching is not caused by forming a stable non-luminescent product via a reaction between terbium acetylsalicylate and bilirubin. A π-π interaction between the chromophore of bilirubin and the aromatic moiety of ligand was revealed via the pattern of cross peaks in the 2D asynchronous spectrum generated using the DAOSD (double asynchronous orthogonal sample design) approach. Such an interaction paves a route for energy transfer in the quenching process. The combination of a high concentration of the terbium complex and a long life-time of luminescence in the lanthanide complex/bilirubin system forms a special scenario: a bilirubin molecule by diffusion may visit and deactivate dozens of excited terbium complexes within the half-life period of the lanthanide complex. This is why a small amount of bilirubin can bring about the significant reduction of luminescence on the solution containing a high concentration of the terbium complex.

Modified asynchronous orthogonal sample design scheme @ Job’s method to determine the stoichiometric ratio in the molecular association system

The determination of the stoichiometric ratio in the molecular association system is of great signification. The asynchronous orthogonal sample design scheme @ Job’s (AOSD@Job’s) method, which was developed in our previous work, had a considerable advantage over the commonly-used Job’s method. However, the AOSD@Job’s method might give incorrect results due to the severe interference of the noise from the spectral measurements. In this paper, a modified AOSD@Job’s (MAOSD@Job’s) method was proposed by introducing the modified reference spectrum into the AOSD@Job’s method. Firstly, mathematical analysis suggested that the MAOSD@Job’s method might be more robust to noise compared with the AOSD@Job’s method. Then, the results of computer simulation showed that the stoichiometric ratios obtained from the MAOSD@Job’s method were all consistent with the set values under the disturbance of noise. However, AOSD@Job’s method produced incorrect stoichiometric ratios in the computer simulation experiments due to the interference of noise. Lastly, the MAOSD@Job’s method was successfully applied on two real chemical systems.

A Novel Approach Based on Two-Dimensional Correlation Spectroscopy to Determine the Stoichiometric Ratio of Two Substances Involved in Intermolecular Interactions.

A novel technique called AOSD@Job's, combining asynchronous orthogonal sample design scheme (AOSD) with Job's method, is proposed to estimate the stoichiometric ratio of two substances that form a supramolecular aggregate under intermolecular interactions. First, a mathematical analysis was performed along with the procedure of the AOSD@Job's method. Then, the validity of the AOSD@Job's method was manifested by computer simulation on two model systems. Finally, the AOSD@Job's method was applied on two real chemical systems. The stoichiometric ratio between the coordination complex of Ni2+ and ethylenediaminetetraacetic acid disodium salt (EDTA) was estimated to be 1.0. Benzyl alcohol (BA) and β-cyclodextrin (β-CD) were determined to form a 1 : 1 host-guest complex. These values were consistent with the values reported in the literature. Compared with the traditional Job's method, the AOSD@Job's method has an evident advantage since it is still valid even if all the peaks of the supramolecular aggregate severely overlap with the peaks of the substances that form the aggregate.

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 XP) dissolved in the same solvent via the near diagonal cross peaks around the coordinate (XP, XP) 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 (XP, XP) 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.

Two-dimensional correlation spectroscopic studies on coordination between organic ligands and Ni2 + ions

3A2g→3T1g(P) transition band of Ni2+ is used to probe the coordination of Ni2+. Two-dimensional asynchronous spectra (2DCOS) are generated using the Double Asynchronous Orthogonal Sample Design (DAOSD), Asynchronous Spectrum with Auxiliary Peaks (ASAP) and Two-Trace Two-Dimensional (2T2D) approaches. Cross peaks relevant to the 3A2g→3T1g(P) transition band of Ni2+ are utilized to probe coordination between Ni2+ and various ligands. We studied the spectral behavior of the 3A2g→3T1g(P) transition band when Ni2+ is coordinated with ethylenediaminetetraacetic acid disodium salt (EDTA). The pattern of cross peaks in 2D asynchronous spectrum demonstrates that coordination brings about significant blue shift of the band. In addition, the absorptivity of the band increases remarkably. The interaction between Ni2+ and galactitol is also investigated. Although no clearly observable change is found on the 3A2g→3T1g(P) transition band when galactitol is introduced, the appearance of cross peak in 2D asynchronous spectrum demonstrates that coordination indeed occurs between Ni2+ and galactitol. Furthermore, the pattern of cross peak indicates that peak position, bandwidth and absorptivity of the 3A2g→3T1g(P) transition band of Ni(galactitol)x2+ is considerably different from those of Ni(H2O)62+. Thus, 2DCOS is helpful to reveal subtle spectral variation, which might be helpful in shedding light on the physical-chemical nature of coordination.

Investigation on the relationship between solubility of artemisinin and polyvinylpyrroli done addition by using DAOSD approach

In this work, we investigated the influence of polyvinylpyrrolidone (PVP) on the solubility of artemisinin in aqueous solution by using quantitative 1H NMR. Experimental results demonstrate that about 4 times of incremental increase occurs on the solubility of artemisinin upon introducing PVP. In addition, dipole-dipole interaction between the ester group of artemisinin and the amide group of N-methylpyrrolidone (NMP), a model compound of PVP, is characterized by two-dimensional (2D) correlation FTIR spectroscopy with the DAOSD (Double Asynchronous Orthogonal Sample Design) approach developed in our previous work. The observation of cross peaks in a pair of 2D asynchronous spectra suggests that dipole-dipole interaction indeed occurs between the ester group of artemisinin and amide group of NMP. Moreover, the pattern of cross peaks indicates that the carbonyl band of artemisinin undergoes blue-shift while the bandwidth and absorptivity increases via interaction with NMP, and the amide band of NMP undergoes blue-shift while the absorptivity increases via interaction with artemisinin. Dipole-dipole interaction, as one of the strongest intermolecular interaction between artemisinin and excipient, may play an important role in the enhancement of the solubility of artemisinin in aqueous solution.

Investigation on intermolecular interaction between two solutes where one solute occurs in two states

The spectral behavior of a pair of 2D asynchronous spectra generated by using the double asynchronous orthogonal sample design (DAOSD) approach on a chemical system is investigated. Two solutes (P and Q) are dissolved in the solution and intermolecular interaction between P and Q is characterized. In this particular system, P occurs in two exchangeable states when it is dissolved in the solutions. Results on mathematical analysis and computer simulation demonstrated that interference unrelated to the intermolecular interaction can be completely removed. Hence the resultant 2D asynchronous spectra generated by using the DAOSD approach can reflect intermolecular interaction reliably. Moreover, properties of cross peaks in different regions of the pair of asynchronous spectra are discussed. In our previous works, cross peaks generated by using the DAOSD and relevant techniques reflect variations on peak position, bandwidth or absorptivity of the characteristic peaks of solutes caused by intermolecular interaction. However, we find that cross peak can still be produced even if intermolecular interaction do not bring about any changes on the characteristic peaks of solutes. Mathematical analysis demonstrates that cross peaks are related to the variations of chemical systems caused by intermolecular interaction at a network level.

Investigation on the intermolecular interaction between diethyl ether and dichloromethane in gaseous phase by using the DAOSD approach

Intermolecular interaction between diethyl ether and dichloromethane was investigated by using double asynchronous orthogonal sample design (DAOSD) scheme. FT-IR spectra of the two compounds were measured in the gas phase. A gas cell that satisfied the requirement of the DAOSD approach was designed, fabricated and utilized. The appearance of cross peaks in a pair of asynchronous spectra demonstrated that intermolecular interaction occurred between two compounds. Interference from the spectra of solvent can be avoided by measuring the samples in gas phase, thereby extending the application range of DAOSD and relevant approaches.

Characterization of the coordination between Nd3+ and ester groups by using double asynchronous orthogonal sample design approach

We applied a newly developed technique of DAOSD (double asynchronous orthogonal sample design) approach to probe weak coordination between Nd3+ ions and ethyl acetate. Cross peaks from the 2D asynchronous spectra are successfully used to reveal subtle spectral variation on carbonyl band of ethyl acetate and f–f transition peak of Nd3+, which is relevant to the coordination between Nd3+ and the ester group of ethyl acetate. In addition, we also use 13C NMR spectra to investigate the Nd3+/ethyl acetate system. The appearance of new weak carbonyl peak around 177.8ppm provides alternative evidence of the weak coordination between Nd3+ and ester group of ethyl acetate.

Coordination between cobalt (II) ion and carbonyl group in acetone probed by using DAOSD approach

We applied a newly developed technique of the DAOSD (Double Asynchronous Orthogonal Sample Design) approach to probe weak coordination between Co2+ ions and acetone. Subtle spectral variation on the carbonyl band of acetone and d–d transition band are revealed via cross peaks of 2D asynchronous spectra generated by using the DAOSD approach. These results suggest that coordination occur between cobalt ions and the carbonyl group of acetone. To confirm whether coordination occur between cobalt ions and acetone, EXAFS experiments are utilized. The EXAFS results reveal that a Co2+ is coordinated by six methanol molecules in anhydrous CoCl2/methanol solution. Upon addition of acetone in into the anhydrous CoCl2/methanol solution, the coordination number of Co2+ ion becomes four, and one coordinating oxygen atom is replaced by a chlorine atom. We infer that the decrease in coordination number of Co2+ ion is due to the participation of the carbonyl oxygen of acetone in the coordination since the size of acetone is larger than methanol. This result provides an alternative evidence to support the conclusion that Co2+ ions coordinate with acetone, which is separately obtained from the 2D asynchronous spectra generated by using the DAOSD approach.

Investigation on the dipole–dipole interactions between tetramethylurea and acetonitrile by two-dimensional asynchronous spectroscopy

Double Asynchronous Orthogonal Sample Design scheme (DAOSD) proposed in our previous work is used to probe dipole–dipole interaction between CO and CN groups in tetramethylurea/CD3CN systems. The results indicate that the carbonyl band of tetramethylurea undergoes a red shift and the absorptivity of the carbonyl band of tetramethylurea and νCN of CD3CN decreases under intermolecular interaction. Then the interaction between tetramethylurea and CH3CN was also detected. Besides CO and CN groups, the spectral behavior of a combination band (δCH3+νCC) of CH3CN was also investigated. The spectral behavior is somewhat similar to the TMU/CD3CN system. However, a noticeable feature is observed on the relationship between νCN band at 2254cm−1 and the δCH3+νCC band at 2292cm−1 of CH3CN: no cross peak was observed at (2254, 2292) in the 2D asynchronous spectrum. Mathematical analysis indicates that absence of the cross peak can occur only when the variation of the absorptivity of νCN and that of δCH3+νCC band are in the same proportion. Thus, the DAOSD approach reveals an unexpected relationship on the spectral behavior of the νCN and δCH3+νCC band under intermolecular interaction.

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 CCl(4) solutions were investigated using the DAOSD approach to prove the applicability of the DAOSD method in real chemical system.

The influence of changing the sequence of concentration series on the 2D asynchronous spectroscopy generated by the asynchronous orthogonal sample design (AOSD) approach

The influence of the sequence of the concentration series is investigated on the 2D asynchronous spectra generated by the asynchronous orthogonal sample design (AOSD) approach. We prove that the requirement of the AOSD is also satisfied when the sequence of the concentration series changes, if the initial concentration series satisfies the requirement of the AOSD. Changing the sequence of concentration series produces the same absolute intensity of the 2D asynchronous spectra when only three solutions are used. However, different outcomes can be gained when four solutions are adopted. Studies on a real chemical system indicate that the sensitivity of the cross peak from asynchronous spectra can be improved significantly when the suitable sequence of concentration series is adopted.

Asynchronous Orthogonal Sample Design Scheme for TwoDimensional Correlation Spectroscopy (2D-COS) and Its Application in Probing Intermolecular Interactions from Overlapping Infrared (IR) Bands

This paper introduces a new approach to analysis of spectra called asynchronous orthogonal sample design (AOSD). Specifically designed concentration series are selected according to mathematical analysis of orthogonal vectors. Based on the AOSD approach, the interfering portion of the spectra arising strictly from the concentration effect can be completely removed from the asynchronous spectra. Thus, two-dimensional (2D) asynchronous spectra can be used as an effective tool to characterize intermolecular interactions that lead to apparent deviations from the Beer-Lambert law, even if the characteristic peaks of two compounds are substantially overlapped. A model solution with two solutes is used to investigate the behavior of the 2D asynchronous spectra under different extents of overlap of the characteristic peaks. Simulation results demonstrate that the resulting spectral patterns can reflect subtle spectral variations in bandwidths, peak positions, and absorptivities brought about by intermolecular interaction, which are barely visualized in the conventional one-dimensional (1D) spectra. Intermolecular interactions between butanone and dimethyl formamide (DMF) in CCl(4) solutions were investigated using the proposed AOSD approach to prove the applicability of the AOSD method in real chemical systems.