Picosecond dynamics of iron proteins

The excitation of hemoproteins containing either Fe(2+) or Fe(3+) with a picosecond light pulse resulted in the bleaching and recovery of the iron absorbance bands within 6 psec. A new absorbance band also was observed whose formation and decay rate of less than 6 psec suggests that it is probably due to S(1)-->S(n) absorbance. The Soret band relaxation time is deduced to be approximately 0.5 psec whereas the free base hemoprotein does not show any of the above fast-decay characteristics. Therefore, there is a strong influence of the metal on the energy dissipation process.

Photolysis of CBr4 and Its Transient Solvent Stabilized (CBr3+//Br-)Solv Ion Pair

In this paper we describe the mechanism of the photodissociation of CBr4 in various solvents. We have monitored and identified the intermediate species and determined the growth and decay rates of the excited states and metastable species formed during the photodissociation process by means of ultrafast time-resolved spectroscopy. On the basis of the experimental data presented in this paper, the observed transient spectra and species have been assigned to the stabilized solvated ion pair (CBr3+//Br-)solv.

Nonvolatile read-out molecular memory

A versatile molecule is described that performs as a nondestructible read-out optical-storage molecular memory. This molecular memory is composed of two distinct molecules that are chemically bonded to each other to form a single molecule with unique properties. One component is a photochromic fulgimide, and the other is a strongly fluorescing oxazine dye. This composite molecule was specifically designed and synthesized to display, under specific conditions, both the photochromic functions of the first component and the fluorescence properties of the dye. To store information, the polar, closed form of the photochromic component is illuminated with 530-nm light, which converts it to the open, nonpolar form. The information is accessed by excitation at the 650-nm band of the oxazine dye component, causing the dye to fluoresce. However, the dye emits intense fluorescence under a nonpolar environment, which is attained only when the fulgimide component is in its open, nonpolar structure. The ultrafast kinetics, spectroscopy, and mechanism of the photoreaction of this molecule and its photoinduced intermediates have been measured, and fluorescence quantum yields and cross sections were determined.

Structures of bromoalkanes' photodissociation in solution by means of ultrafast extended x-ray absorption fine-structure spectroscopy

The structures of initial and final products of bromoalkanes' photodisociation reaction in cyclohexane solution have been measured with a bond length accuracy of 0.02 A by means of ultrafast time-resolved extended x-ray absorption fine structure spectroscopy. The photoredaction mechanism is also discussed.

Dynamical principles in biological processes: a model of charge migration in proteins and DNA

The generalized master equations (GMEs) that contain multiple time scales have been derived quantum mechanically. The GME method has then been applied to a model of charge migration in proteins that invokes the hole hopping between local amino acid sites driven by the torsional motions of the floppy backbones. This model is then applied to analyze the experimental results for sequence-dependent long-range hole transport in DNA reported by Meggers et al. [Meggers, E., Michel-Beyerle, M. E., & Giese, B. (1998) J. Am. Chem. Soc. 120, 12950-12955]. The model has also been applied to analyze the experimental results of femtosecond dynamics of DNA-mediated electron transfer reported by Zewail and co-workers [Wan, C., Fiebig, T., Kelley, S. O., Treadway, C. R., Barton, J. K. & Zewail, A. H. (1999) Proc. Natl. Acad. Sci. USA 96, 6014-6019]. The initial events in the dynamics of protein folding have begun to attract attention. The GME obtained in this paper will be applicable to this problem.

Laser-induced transient structure and stress in a platinum(111) crystal studied by time-resolved X-ray diffraction

Nanosecond time-resolved X-ray diffraction has been employed to study the transient structure deformation of a Pt(111) crystal induced by laser pulse heating. A direct-imaging X-ray CCD system with high spatial resolution allowed the detection of structural changes of the order of 10−3 Å. The time evolution of lattice strain was measured with 12 ns resolution. The lattice spacings were found to suffer a transient change from 2.2653 to 2.2695 (10) Å, and the strain reached its maximum value 10 ns after laser irradiation.

Dynamical principles in biological processes

The purpose of this paper is to propose certain dynamical principles in biological systems, which can be used to explain the effectiveness of charge transfer or excitation transfer in biological systems. Some of these systems are accessible experimentally.

Experimental characterization of a two-photon memory

We demonstrate the recording of 100 planes of digital images in a page-oriented two-photon memory and characterize the images in terms of signal-to-noise ratio and bit error rate. Possible error sources in the recording are discussed, and methods for compensating for some of these effects are presented. Looking at the distributions of the normalized bit intensities, we are able to estimate the minimum achievable bit error rate for this system.