Sub-100-ps structural dynamics of horse heart myoglobin probed by time-resolved X-ray solution scattering

Oang, K.Y.,Kim, K.H.,Jo, J.,Kim, Y.,Kim, J.G.,Kim, T.W.,Jun, S.,Kim, J.,Ihee, H. Elsevier Science Publishers [etc.] 2014 Chemical physics Vol.442 No.-

Here we report sub-100-ps structural dynamics of horse heart myoglobin revealed by time-resolved X-ray solution scattering. By applying the time-slicing scheme to the measurement and subsequent deconvolution, we investigate the protein structural dynamics that occur faster than the X-ray temporal pulse width of synchrotrons (~100ps). The singular value decomposition analysis of the experimental data suggests that two structurally distinguishable intermediates are formed within 100ps. In particular, the global structural change occurring on the time scale of 70ps is identified.

Ultrafast X-Ray Crystallography and Liquidography

Ki, Hosung,Oang, Key Young,Kim, Jeongho,Ihee, Hyotcherl Annual Reviews 2017 Annual review of physical chemistry Vol.68 No.-

<P>Time-resolved X-ray diffraction provides direct information on three-dimensional structures of reacting molecules and thus can be used to elucidate structural dynamics of chemical and biological reactions. In this review, we discuss time-resolved X-ray diffraction on small molecules and proteins with particular emphasis on its application to crystalline (crystallography) and liquid-solution (liquidography) samples. Time-resolved X-ray diffraction has been used to study picosecond and slower dynamics at synchrotrons and can now access even femtosecond dynamics with the recent arrival of X-ray free-electron lasers.</P>

Direct observation of myoglobin structural dynamics from 100 picoseconds to 1 microsecond with picosecond X-ray solution scattering

Kim, Kyung Hwan,Oang, Key Young,Kim, Jeongho,Lee, Jae Hyuk,Kim, Youngmin,Ihee, Hyotcherl Royal Society of Chemistry 2011 Chemical communications Vol.47 No.1

<P>Here we report structural dynamics of equine myoglobin (Mb) in response to the CO photodissociation visualized by picosecond time-resolved X-ray solution scattering. The data clearly reveal new structural dynamics that occur in the timescale of ∼360 picoseconds (ps) and ∼9 nanoseconds (ns), which have not been clearly detected in previous studies.</P> <P>Graphic Abstract</P><P>Picosecond pump-probe X-ray solution scattering reveals structural dynamics of equine myoglobin in response to the CO photodissociation. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cc01817a'> </P>

Charge Transfer-Induced Torsional Dynamics in the Excited State of 2,6-Bis(diphenylamino)anthraquinone

Choi, Jungkweon,Ahn, Doo-Sik,Oang, Key Young,Cho, Dae Won,Ihee, Hyotcherl American Chemical Society 2017 The Journal of Physical Chemistry Part C Vol.121 No.43

<P>Intramolecular charge transfer (ICT) in a multibranched pushpull chromophore is a key photophysical process which is attracting attention due to its relevance to the development of highly efficient organic light-emitting diodes, but the excited-state dynamics of multibranched pushpull chromophores is still unclear. Here, using femtosecond transient absorption spectroscopy and singular value decomposition analysis, we studied the excited state dynamics of 2,6-bis(diphenylamino)anthraquinone (DPA-AQ-DPA), which contains two diphenylamino (DPA) groups as electron-donors (D) and anthraquinone (AQ) as an electron-acceptor (A) and is a candidate for an efficient red TADF (thermally activated delayed fluorescence) emitter. The emission of DPA-AQ-DPA exhibits large Stokes shifts with increasing solvent polarity, indicating that the emission can be attributed to an ICT process. The charge separated (CS) state formed by ICT undergoes torsional dynamics, involving twisting between D and A, resulting in the formation of a twisted charge separated state (CStwisting). This twisting reaction between D and A is accelerated in high-polarity solvents compared with that in low-polarity solvents. Such faster CT-induced torsional dynamics in high-polarity solvents is explained in terms of the localization of ICT on one of two ICT branches, suggesting that DPA-AQ-DPA in localized CStwisting formed in high-polarity solvents has two different dihedral angles between a single A group and two D groups. On the other hand, with increasing solvent polarity, the CS and CStwisting states of DPA-AQ-DPA become stabilized, making their energy levels considerably lower than that of (3)(pi,pi*), consequently blocking the formation of the triplet excited state and TADF in a high-polarity solvent such as acetonitrile. By contrast, the energy levels of CS and CStwisting states in a low-polarity solvent, such as diethyl ether, are higher than that of (3)(pi,pi*), allowing for deactivation into (3)DPA-AQ-DPA* through intersystem crossing. This result indicates that the energy levels of CS and CStwisting states can be adjusted by controlling aspects of the local environment, such as solvents, so that intersystem crossing can be either inhibited or promoted. In other words, the energy gap (Delta E-ST) between the lowest singlet and triplet excited states for DPA-AQ-DPA can be regulated by changing the solvent polarity.</P>

Direct Observation of Cooperative Protein Structural Dynamics of Homodimeric Hemoglobin from 100 ps to 10 ms with Pump–Probe X-ray Solution Scattering

Kim, Kyung Hwan,Muniyappan, Srinivasan,Oang, Key Young,Kim, Jong Goo,Nozawa, Shunsuke,Sato, Tokushi,Koshihara, Shin-ya,Henning, Robert,Kosheleva, Irina,Ki, Hosung,Kim, Youngmin,Kim, Tae Wu,Kim, Jeongh American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.16

<P/><P>Proteins serve as molecular machines in performing their biological functions, but the detailed structural transitions are difficult to observe in their native aqueous environments in real time. For example, despite extensive studies, the solution-phase structures of the intermediates along the allosteric pathways for the transitions between the relaxed (R) and tense (T) forms have been elusive. In this work, we employed picosecond X-ray solution scattering and novel structural analysis to track the details of the structural dynamics of wild-type homodimeric hemoglobin (HbI) from the clam <I>Scapharca inaequivalvis</I> and its F97Y mutant over a wide time range from 100 ps to 56.2 ms. From kinetic analysis of the measured time-resolved X-ray solution scattering data, we identified three structurally distinct intermediates (I<SUB>1</SUB>, I<SUB>2</SUB>, and I<SUB>3</SUB>) and their kinetic pathways common for both the wild type and the mutant. The data revealed that the singly liganded and unliganded forms of each intermediate share the same structure, providing direct evidence that the ligand photolysis of only a single subunit induces the same structural change as the complete photolysis of both subunits does. In addition, by applying novel structural analysis to the scattering data, we elucidated the detailed structural changes in the protein, including changes in the heme–heme distance, the quaternary rotation angle of subunits, and interfacial water gain/loss. The earliest, R-like I<SUB>1</SUB> intermediate is generated within 100 ps and transforms to the R-like I<SUB>2</SUB> intermediate with a time constant of 3.2 ± 0.2 ns. Subsequently, the late, T-like I<SUB>3</SUB> intermediate is formed via subunit rotation, a decrease in the heme–heme distance, and substantial gain of interfacial water and exhibits ligation-dependent formation kinetics with time constants of 730 ± 120 ns for the fully photolyzed form and 5.6 ± 0.8 μs for the partially photolyzed form. For the mutant, the overall kinetics are accelerated, and the formation of the T-like I<SUB>3</SUB> intermediate involves interfacial water loss (instead of water entry) and lacks the contraction of the heme–heme distance, thus underscoring the dramatic effect of the F97Y mutation. The ability to keep track of the detailed movements of the protein in aqueous solution in real time provides new insights into the protein structural dynamics.</P>

Global Reaction Pathways in the Photodissociation of I₃⁻ Ions in Solution at 267 and 400 nm Studied by Picosecond X‐ray Liquidography

Kim, Kyung Hwan,Ki, Hosung,Oang, Key Young,Nozawa, Shunsuke,Sato, Tokushi,Kim, Joonghan,Kim, Tae Kyu,Kim, Jeongho,Adachi, Shin‐,ichi,Ihee, Hyotcherl WILEY‐VCH Verlag 2013 Chemphyschem Vol.14 No.16

<P><B>Abstract</B></P><P>The mechanism of a photochemical reaction involves the formation and dissociation of various short‐lived species on ultrafast timescales and therefore its characterization requires detailed structural information on the transient species. By making use of a structurally sensitive X‐ray probe, time‐resolved X‐ray liquidography (TRXL) can directly elucidate the structures of reacting molecules in the solution phase and thus determine the comprehensive reaction mechanism with high accuracy. In this work, by performing TRXL measurements at two different wavelengths (400 and 267 nm), the reaction mechanism of I<SUB>3</SUB><SUP>−</SUP> photolysis, which changes subtly depending on the excitation wavelength, is elucidated. Upon 400 nm photoexcitation, the I<SUB>3</SUB><SUP>−</SUP> ion dissociates into I<SUB>2</SUB><SUP>−</SUP> and I. By contrast, upon 267 nm photoexcitation, the I<SUB>3</SUB><SUP>−</SUP> ion undergoes both two‐body dissociation (I<SUB>2</SUB><SUP>−</SUP>+I) and three‐body dissociation (I<SUP>−</SUP>+2I) with 7:3 molar ratio. At both excitation wavelengths, all the transient species ultimately disappear in 80 ns by recombining to form the I<SUB>3</SUB><SUP>−</SUP> ion nongeminately. In addition to the reaction dynamics of solute species, the results reveal the transient structure of the solute/solvent cage and the changes in solvent density and temperature as a function of time.</P>

Ultrafast Electron Diffraction Technology for Exploring Dynamics of Molecules

Kyu Ha Jang,Key Young Oang,In-Hyung Baek,Sadiq Setiniyaz,Ki-TaeLee,Young Uk Jeong,Hyunwoo Kim 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.4

With the recent successful development of X-ray free electron lasers (X-FELs), it became possible to explore sub-nano structure dynamics of materials with 100-fs temporal accuracy. Ultrafast electron diffraction (UED) can achieve similar performance at a much lower cost and on a smaller scale by using ultrashort and low-energy electron beams. The UEDs are suitable for studying thin films, surfaces, and gas samples that are difficult to study with the X-FELs. Starting from non-relativistic UEDs using low-energy electron beams of less than 100 keV, it led to the development of relativistic UEDs using a-few-MeV electron beams. These efforts have contributed to the identification of the unexplored mechanism of matter by observing the dynamics of atoms with higher temporal accuracy. Electron beam is easier to handle than X-rays, and various technologies are being developed to improve the performance of UED. We review UEDs historically based on the development of core technologies. And application researches with the UEDs will be outlined in this paper.

Tracking reaction dynamics in solution by pump–probe X-ray absorption spectroscopy and X-ray liquidography (solution scattering)

Kim, Jeongho,Kim, Kyung Hwan,Oang, Key Young,Lee, Jae Hyuk,Hong, Kiryong,Cho, Hana,Huse, Nils,Schoenlein, Robert W.,Kim, Tae Kyu,Ihee, Hyotcherl The Royal Society of Chemistry 2016 Chemical communications Vol.52 No.19

<P>Characterization of transient molecular structures formed during chemical and biological processes is essential for understanding their mechanisms and functions. Over the last decade, time-resolved X-ray liquidography (TRXL) and time-resolved X-ray absorption spectroscopy (TRXAS) have emerged as powerful techniques for molecular and electronic structural analysis of photoinduced reactions in the solution phase. Both techniques make use of a pump-probe scheme that consists of (1) an optical pump pulse to initiate a photoinduced process and (2) an X-ray probe pulse to monitor changes in the molecular structure as a function of time delay between pump and probe pulses. TRXL is sensitive to changes in the global molecular structure and therefore can be used to elucidate structural changes of reacting solute molecules as well as the collective response of solvent molecules. On the other hand, TRXAS can be used to probe changes in both local geometrical and electronic structures of specific X-ray-absorbing atoms due to the element-specific nature of core-level transitions. These techniques are complementary to each other and a combination of the two methods will enhance the capability of accurately obtaining structural changes induced by photoexcitation. Here we review the principles of TRXL and TRXAS and present recent application examples of the two methods for studying chemical and biological processes in solution. Furthermore, we briefly discuss the prospect of using X-ray free electron lasers for the two techniques, which will allow us to keep track of structural dynamics on femtosecond time scales in various solution-phase molecular reactions.</P>

Identifying the major intermediate species by combining time-resolved X-ray solution scattering and X-ray absorption spectroscopy

Kim, Kyung Hwan,Kim, Jeongho,Oang, Key Young,Lee, Jae Hyuk,Grolimund, Daniel,Milne, Christopher J.,Penfold, Thomas J.,Johnson, Steven L.,Galler, Andreas,Kim, Tae Wu,Kim, Jong Goo,Suh, Deokbeom,Moon, J The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.36

<P>Identifying the intermediate species along a reaction pathway is a first step towards a complete understanding of the reaction mechanism, but often this task is not trivial. There has been a strong on-going debate: which of the three intermediates, the CHI<SUB>2</SUB> radical, the CHI<SUB>2</SUB>–I isomer, and the CHI<SUB>2</SUB><SUP>+</SUP> ion, is the dominant intermediate species formed in the photolysis of iodoform (CHI<SUB>3</SUB>)? Herein, by combining time-resolved X-ray liquidography (TRXL) and time-resolved X-ray absorption spectroscopy (TR-XAS), we present strong evidence that the CHI<SUB>2</SUB> radical is dominantly formed from the photolysis of CHI<SUB>3</SUB> in methanol at 267 nm within the available time resolution of the techniques (∼20 ps for TRXL and ∼100 ps for TR-XAS). The TRXL measurement, conducted using the time-slicing scheme, detected no CHI<SUB>2</SUB>–I isomer within our signal-to-noise ratio, indicating that, if formed, the CHI<SUB>2</SUB>–I isomer must be a minor intermediate. The TR-XAS transient spectra measured at the iodine L<SUB>1</SUB> and L<SUB>3</SUB> edges support the same conclusion. The present work demonstrates that the application of these two complementary time-resolved X-ray methods to the same system can provide a detailed understanding of the reaction mechanism.</P> <P>Graphic Abstract</P><P>We identify a major transient species formed in the photolysis of CHI<SUB>3</SUB> by combining time-resolved X-ray liquidography (TRXL) and time-resolved X-ray absorption spectroscopy (TR-XAS). <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5cp03686k'> </P>

Direct observation of bond formation in solution with femtosecond X-ray scattering

Kim, Kyung Hwan,Kim, Jong Goo,Nozawa, Shunsuke,Sato, Tokushi,Oang, Key Young,Kim, Tae Wu,Ki, Hosung,Jo, Junbeom,Park, Sungjun,Song, Changyong,Sato, Takahiro,Ogawa, Kanade,Togashi, Tadashi,Tono, Kensuk Nature Publishing Group, a division of Macmillan P 2015 Nature Vol.518 No.7539

The making and breaking of atomic bonds are essential processes in chemical reactions. Although the ultrafast dynamics of bond breaking have been studied intensively using time-resolved techniques, it is very difficult to study the structural dynamics of bond making, mainly because of its bimolecular nature. It is especially difficult to initiate and follow diffusion-limited bond formation in solution with ultrahigh time resolution. Here we use femtosecond time-resolved X-ray solution scattering to visualize the formation of a gold trimer complex, [Au(CN)<SUB>2</SUB><SUP>–</SUP>]<SUB>3</SUB> in real time without the limitation imposed by slow diffusion. This photoexcited gold trimer, which has weakly bound gold atoms in the ground state, undergoes a sequence of structural changes, and our experiments probe the dynamics of individual reaction steps, including covalent bond formation, the bent-to-linear transition, bond contraction and tetramer formation with a time resolution of ∼500 femtoseconds. We also determined the three-dimensional structures of reaction intermediates with sub-ångström spatial resolution. This work demonstrates that it is possible to track in detail and in real time the structural changes that occur during a chemical reaction in solution using X-ray free-electron lasers and advanced analysis of time-resolved solution scattering data.