Fast and Ultrafast Dynamics in Cyclodextrin Nanostructures (original) (raw)
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Ultrafast Dynamics in Biological Systems and in Nano-Confined Environments
Bulletin of The Chemical Society of Japan, 2007
Ultrafast chemical dynamics in a nano-confined system is very different from that in a bulk liquid. In this account, we give an overview on recent femtosecond study on dynamics of ultrafast chemical processes in the nanocavity of a biological system. Dynamics in a biological system crucially depends on the location of the fluorescent probe. We show that one can study solvation dynamics in different regions (i.e. spatially resolve) by variation of the excitation wavelength. We discuss two interesting cases of how structure affects dynamics. First, solvation dynamics of two protein folding intermediates of cytochrome c is found to be differ significantly in the ultrafast initial part (<20 ps). Second, methyl substitution of the OH group in a cyclodextrin is shown to slow down the initial part of solvation dynamics quite dramatically. The most interesting observation is the discovery of the ultraslow component of solvation dynamics which is 100-1000 times slower compared to bulk water. The electron-and proton-transfer processes in a nano-confined system are found to be markedly retarded because of slow solvation and structural constraints. Close proximity of the reactants in a confined system is expected to accelerate dynamics of bi-molecular processes. This is illustrated by ultrafast fluorescence resonance energy transfer (FRET) in %1 ps time scale between a donor and an acceptor in a micelle. Finally, it is demonstrated that the decay of fluorescence anisotropy provides structural information (e.g. size of a cyclodextrin inclusion complex) and may be used to detect formation of a nano-aggregate.
Ultrafast chemistry in complex and confined systems
Journal of Chemical Sciences, 2004
Self-organized molecular assemblies play a crucial role in many natural and biological processes. Recent applications of ultrafast laser spectroscopy and computer simulations revealed that chemistry in a confined environment is fundamentally different from that in ordinary solutions. Many recent examples of slow dynamics in constrained environments and their biological implications are discussed.
A Femtosecond Study of Excitation-Wavelength Dependence of Solvation Dynamics in a Vesicle
Chemistry – An Asian Journal, 2006
Solvation dynamics and anisotropy decay of coumarin 480 (C480) in a supramolecular assembly containing a triblock copolymer, PEO 20-PPO 70-PEO 20 (Pluronic P123) and a surfactant, CTAC (cetyl trimethylammonium chloride) are studied by femtosecond up-conversion. In a P123-CTAC complex, C480 displays a significant (22 nm) red edge excitation shift (REES) in the emission maximum as λ ex increases from 335 to 445 nm. This suggests that the P123-CTAC aggregate is quite heterogeneous. The average rotational relaxation time (〈τ rot 〉) of C480 in a P123-CTAC complex decreases by a factor of 2 from 2500 ps at λ ex) 375 nm to 1200 ps at λ ex) 435 nm. For λ ex) 375 nm, the probe molecules in the buried core region of P123-CTAC are excited and the solvation dynamics displays three components, 2, 60, and 4000 ps. It is argued that insertion of CTAC in P123 micelle affects the polymer chain dynamics, and this leads to reduction of the 130 ps component of P123 micelle to 60 ps in P123-CTAC. For λ ex) 435 nm, which selects the peripheral highly polar corona region, solvation dynamics in P123-CTAC and P123 are extremely fast with a major component of <0.3 ps (∼80%) and a 2 ps (∼20%) component.
Our aim is to doubly confine a molecule of coumarin C522 in a host–guest supramolecular complex with b-cyclodextrin in a reverse sodium dioctyl sulfosuccinate (AOT) micelle using nonpolar n-heptane and polar water solvents. Varying the volumes of coumarin C522 and b-cyclodextrin dissolved in water allows us to control the water-pool diameters of the reverse micelle in n-heptane with values of w=3, 5, 10, 20, and 40, where w is the ratio of water concentration to AOT concentration in n-heptane. To study the fluorescence dynamics of coumarin C522, the spectral steady-state and time-resolved dependences are compared for the two systems coumarin C522- (water)/AOT(n-heptane), denoted C522/micelle, and coumarin C522/b-cyclodextrin(water)/AOT(n-heptane), referred to as C522/CD/micelle. The formation of the supramolecular host– guest complex CD–C522 is indicated by a blue shift, but in the micelle, the shift is red. However, the values of the fluorescence maxima at 520 and 515 nm are still way below the value of 535 nm representing bulk water. The interpretation of the red shift is based on two complementary processes. The first one is the confinement of CD and C522 by the micelle water pool and the second is the perturbation of the micelle by CD and C522, resulting in an increase of the water polarity. The fluorescence spectra of the C522/micelle and C522/CD/micelle systems have maxima and shoulders. The shoulder intensities at 440 nm, representing the C522 at n-heptane/AOT interface, decrease as the w values decrease. This intensity shift suggests that the small micelle provides a stronger confinement, and the presence of CD shifts the equilibrium from n-heptane towards the water pool even more. The fluorescence emission maxima of the C522/micelle and C522/CD/micelle systems for all w values clearly differentiate two trends for w=3–5, and w=10–40, suggesting different interaction in the small and large micelles. Moreover, these fluorescence maxima result in 7 and 13 nm differences for w=3 and w=5, respectively, and provide the spectral evidence to differentiate the C522 confinement in the C522/micelle and C522/CD/micelle systems as an effect of the CD molecule, which might be interpreted as a double confinement of C522 in CD within the micelle. The ultrafast decay in the case of w=3 ranges from 9.5 to 16 ps, with an average of 12.6 ps, in the case of the C522/micelle system. For C522/CD/micelle, the ultrafast decay at w=3 ranges from 9 to 14.5 ps, with an average of 11.8 ps. Increasing w values (from 10 to 40) result in a decrease of the ultrafast decay values in both cases to an average value of about 6.5 ps. The ultrafast decays of 12.6 and 11.8 ps for C522/micelle and C522/CD/micelle, respectively, are in the agreement with the observed red shift, supporting a double confinement in the C522/CD/micelle(w=3) system. The dynamics in the small and large micelles clearly show two different trends. Two slopes in the data are observed for w values of 3–5 and 10–40 in the steady-state and time-resolved data. The average ultrafast lifetimes are determined to be 12.6 and 6.5 ps for the small (w=3) and the large (w=40) micelles, respectively. To interpret the experimental solvation dynamics, a simplified model is proposed, and although the model involves a number of parameters, it satisfactory fits the dynamics and provides the gradient of permittivity in the ideal micelle for free water located in the centre (60–80) and for bound water (25–60). An attempt to map the fluorescence dynamics of the doubly confined C522/CD/micelle system is presented for the first time.
Industrial & Engineering Chemistry Research, 2011
The structure and dynamics of a charge transfer drug molecule 4,4-diaminodiphenyl sulfone (dapsone) inside the cyclodextrins (R-, β-, γ-CDs) in aqueous solution have been studied using steady state and time-resolved emission spectroscopies. The quantum yields were significantly larger in the presence of βand γ-CDs than in water, wherein the β-CD confinement shows the largest effect. The results reveal that dapsone forms 1:1 complexes with both β-CD and γ-CD. At higher concentrations of β-CD a combination of 1:1 and 1:2 inclusion complexes could be observed. The average lifetime of the probe inside the CD cavity is larger than that observed in water due to hydrophobic and polarity effects of the nanocage. Anisotropy decay has been used to study the rotational dynamics of the molecule inside the cyclodextrin cavity. 1 H NMR data also confirm shallow inclusion of dapsone in β-CD. PM3 semiempirical calculations indicate that for unimolar complex a partial (3.8 Å) encapsulation of the dapsone molecule in β-CD at an angle of 72°with the CD axis. The DFT calculations with solvent effect show that the formation of inclusion is spontaneous and enthalpy driven.
We present a research program that uses the unique characteristics of the LCLS to investigate the response and evolution of reactants during the early chemical events that are initiated by photon-induced electronic redistributions. We intend to explore ultrafast events coupled to chemical reactivity in systems ranging in complexity from diatomic molecules in the gas phase to nanocrystalline materials in the condensed phase. A full experimental, theoretical, and instrumentation program will be developed that puts minimum demands on the exact x-ray energy delivered by the beam line by using non-resonant spectroscopic and scattering techniques. A maximum amount of information will be gathered by simultaneously utilizing final-state x-ray fluorescence spectroscopy and wide angle x-ray scattering with the full intensity of the FEL photon output.
Journal of Colloid and Interface Science, 2005
In this contribution we report studies of the nature of solvation and resonance energy transfer processes in a reverse micelle (RM) upon encapsulation of a digestive enzyme, α-chymotrypsin (CHT). We have used one donor, Coumarin 500 (C500), and three acceptors Rhodamine 123 (R123, cationic), ethidium bromide (EtBr, cationic), and Merocyanine 540 (MC540, anionic). By selectively exciting the donor at the surface of the RM with a proper excitation wavelength we have examined solvation dynamics in the microenvironment. The solvation correlation function in the RM without CHT exhibits single-exponential decay with time constant ∼660 ps, which is similar to that of the CHT-included RM. However, in the case of CHT-included RM (w 0 = 10), the time-resolved anisotropy and spectral linewidth analysis of the surface-bound donor reveal the existence of an annular aqueous channel of thickness ∼2.5 Å between the enzyme surface and the inner surface of the RM. The aqueous channel is a potential host for the water-soluble substrate and also is involved in maintaining the proper functionality of RM encapsulated CHT. The studies use both steady-state and time-resolved fluorescence resonance energy transfer (FRET) techniques to measure donor-acceptor distances in the RM and also emphasize the danger of using steady-state fluorescence quenching as a method in careful estimation of the distances. The local geometrical restriction on the donor and acceptor molecules was estimated from time-resolved polarization (anisotropy) measurements. The time-resolved anisotropy of the donor and acceptor molecules also revealed significant randomization of the relative orientation of transition dipoles of the donor and acceptor, justifying the use of 2/3 as the value of the orientation factor κ 2. These studies attempt to elucidate the excellence of the RM as a nanohost of biological macromolecules.
Journal of Molecular Structure, 2000
The experimental set-up for time dependent transient absorption/gain measurements with femtosecond time resolution is presented. Using pump-probe spectroscopy technique with femtosecond pulses from Ti:Sapphire laser system (Spectra Physics), the optical density of transient absorption and transient gain in the spectral range of 330-700 nm, time resolution of 120 fs, can be measured with the precision of up to 0.005. Knowing the real time resolution and "zero time" dispersion of the system from two-photon absorption measurements, we performed femto-and picosecond study of electronically excited DCM molecule in c-C 6 H 12 and MeOH solution. The emission decay of the DCM molecule in the locally excited singlet state, S 1 -LE, was measured with picosecond time resolution using TCSPC set-up (Time Correlated Single Photon Counting). The steadystate and time resolved measurements permitted the determination of the properties of this locally excited singlet S 1 -LE state and the pathways of its deactivation. ᭧
A steady-state and time-resolved photophysical study of CdTe quantum dots in water
Photochem. Photobiol. Sci., 2015
The exciton generation and recombination dynamics in semiconductor nanocrystals are very sensitive to small variations in dimensions, shape and surface capping. In the present work CdTe quantum dots are synthesized in water using 3-mercaptopropionic acid and 1-thioglycerol as stabilizers. Nanocrystals with an average dimension of 4.0 ± 1.0 and 3.7 ± 0.9 nm were obtained, when 3-mercaptopropionic acid or 1-thioglycerol, respectively, was used as a capping agent. The steady-state characterization shows that the two types of colloids have different luminescence behavior. In order to investigate the electronic structure and the dynamics of the exciton state, a combined study in the time domain has been carried out by using fluorescence time-correlated single photon counting and femtosecond transient absorption techniques. The electron-hole radiative recombination follows the non-exponential decay law for both colloids, which results in different average decay time values (of the order of tens of nanoseconds) for the two samples. The data demonstrate that the process is slower for 1-thioglycerol-stabilized colloids.