Dynamic Interaction between Cyclodextrin and Nonelectrolytes in Aqueous Solutions by Ultrasonic Relaxation Method

Specific Alcohol-Responsive Photonic Crystal Sensors Based on Host-Guest Recognition

A photonic crystal material based on β-cyclodextrin (β-CD) with adsorption capacity is reported. The materials ((A-β-CD)-AM PC) consist of 3D poly (methyl methacrylate) (PMMA) colloidal microsphere arrays and hydrogels supplemented with β-cyclodextrin modified by acryloyl chloride. The prepared materials are then utilized for VOCs gas sensing. The 3D O-(A-β-CD)-AM PC was used to detect toluene, xylene, and acetone and the response was seen as the red-shift of the reflection peak. The 3D I-(A-β-CD)-AM PC was used to detect toluene, xylene, and acetone which occurred redshifted, while methanol, ethanol, and propanol and the peaks' red-shifting was observed. However, among these, methanol gave the largest red-shift response The sensor has broad prospects in the detection of alcohol and the detection of alcohol-loaded drug releases in the future.

An in situ and rapid self-healing strategy enabling a stretchable nanocomposite with extremely durable and highly sensitive sensing features

Progress toward the development of wearable electromechanical sensors with durable and reliable sensing performance is critical for emerging wearable integrated electronic applications. However, it remains a long-standing challenge to realize mechanically stretchable sensing materials with extremely durable and high-performing sensing ability due to the fundamental dilemma lying in the sensing mechanism. In this work, we proposed an in situ and rapid self-healing strategy through nano-confining a dynamic host-guest supramolecular polymer network in a graphene-based multilevel nanocomposite matrix to fabricate a mechanically stretchable and structurally healable sensing nanocomposite which is provided with intriguing sensing durability and sensitivity simultaneously. When repeatedly stretching and releasing the nanocomposite sensing film, the fast association kinetics of cyclodextrin and adamantane host-guest inclusion complexes and good polymer chain dynamics in the supramolecular polymer network endowed by the nanoconfinement effect enable autonomous and rapid repair of the micro-cracks in situ generated in the sensing material. As a result, our strain sensing devices can achieve an extremely high durability and retain stable sensing performance even after over 100 000 stretching-releasing cycles at large strain of 50%. Moreover, the brittle nature originated from the inorganically dominated structure in conjunction with the thermodynamically stable host-guest interactions and dynamic hydrogen bonds inside the multilevel nanocomposite allow the sensing material to exhibit an ultrahigh gauge factor over 1500 with a large working strain of 58%. This work presents a reliable approach for the construction of ultradurable and high-performing wearable electronics.

Dynamic characteristic of amitriptyline in water by ultrasonic relaxation method and molecular orbital calculation

Ultrasonic absorption coefficients in the frequency range of 0.8-220 MHz have been measured in aqueous solution of amitriptyline (3-(10,11-dihydro-5H-dibenzo[a,d]cycloheptene-5-ylidene)-N,N-dimethyl-1-propanamine) in the concentration range from 0.20 to 0.60 mol dm(-3) at 25 °C. A single relaxational phenomenon has been observed, and the relaxation frequency is independent of the concentration. It has been also observed that the amplitude of the relaxational absorption increases linearly with the analytical concentration. From these ultrasonic relaxation data, it has been concluded that the relaxation is associated with a unimolecular reaction due to a conformational change of the solute molecule, such as a structural change due to a rotational motion of a group in the solute molecule. Molecular orbital semiempirical methods using AM1 (Austin model 1) and PM3 (modified neglect of diatomic overlap parametric method 3) have been applied to obtain the standard enthalpy of formation for amitriptyline molecule at various dihedral angles around one of the bonds in alkylamine side chain. The results have shown the two clear minimum standard enthalpies of formation for amitriptyline. From the difference of the two values, the standard enthalpy change between the two stable conformers has been calculated be 2.9 kJ mol(-1). On a rough assumption that the standard enthalpy change reflects the standard free energy change, the equilibrium constant for the rotational isomers has been estimated to be 0.31. Combining this value with the experimental ultrasonic relaxation frequency, the backward and forward rate constants have been evaluated. The standard enthalpy change of the reaction has been also estimated from the concentration dependence of the maximum absorption per wavelength, and it has been close to that calculated by the semiempirical methods. The ultrasonic absorption measurements have been also carried out in amitriptyline solution in the presence of β-cyclodextrin. However, the ultrasonic relaxation has not been found in the above frequency range. The result has been discussed in relation to the host-guest complex formation between β-cyclodextrin and amitriptyline.

Inclusion kinetics of a nucleotide into a cyclodextrin cavity by means of ultrasonic relaxation

To examine a dynamic interaction between nucleotide and cyclic oligosaccharide, ultrasonic absorption measurements were carried out in aqueous solution containing beta-cyclodextrin (beta-CD) and adenosine 5'-monophosphate (AMP) in the frequency range of 0.8-95 MHz. A relaxational absorption was observed in the solution, although it was not found in the individual solution of beta-CD or AMP. From the concentration dependences of AMP on the relaxation time and the maximum absorption per wavelength, the cause of the relaxation was attributed to a perturbation of a chemical equilibrium associated with a complex formation between beta-CD (host) and AMP (guest). The rate constants for the formation and breakup processes of the complex were determined. Also, a standard volume change of the reaction was obtained. From comparisons of the obtained rate and thermodynamic parameters with those for beta-CD and various guests, it has been concluded that the adenine moiety is included in the beta-CD cavity and that the hydrogen bonds may play a role in the complex formation.

Kinetic Study for the Inclusion Complex of Carboxylic Acids with Cyclodextrin by the Ultrasonic Relaxation Method

Ultrasonic absorption coefficients in the frequency range of 0.8-95 MHz were measured in aqueous solutions containing both beta-cyclodextrin (beta-CD) (host) and butanoic acid (in its dissociated form and undissociated one) (guest). A single relaxational phenomenon was observed only when the solutes were coexisting, although no relaxation was found in the beta-CD solution or in the acid solutions. The absorption was also measured in a solution of pentanoic acid (dissociated form) with beta-CD, and single relaxation was detected. The ultrasonic relaxation observed in these solutions was due to a perturbation of a chemical equilibrium related to a reaction of an inclusion complex formed by the host and guest. The equilibrium constant was obtained from the dependence of the maximum absorption per wavelength on the guest concentration. The rate constant for the inclusion process of the guest into a cavity of beta-CD and that for the leaving process from the cavity were determined from the obtained relaxation frequency and the equilibrium constant. The standard volume change of the reaction was also computed from the maximum absorption per wavelength. These results were compared with those in solutions containing both beta-CD and different guest molecules. It was found that the hydrophobicity of guest molecules played an important role in the formation of the inclusion complex and also that the charge on the carboxylic group had a considerable effect on the kinetic characteristics of the complexation reaction.