Dynamical models in the two-dimensional infrared spectroscopy of peptides

A brief description of the signals in multidimensional infrared spectroscopy is given with emphasis on the various types of experiments that can be done, what they measure, and their relationship to other kinds of resonant nonlinear optical experiments. The predictions from Bloch dynamics and responses including spectral diffusion are discussed. Experiments with the amide-I transitions of N-methylacetamide and the alanine dipetide show that Bloch dynamics are inadequate, but for small values of waiting times can give a reasonable description of the 2D spectra. Both single frequency and dual frequency 2D experiments that excite both the amide-I and amide-II modes are reported.open2

Microcloning and characterization of DNA from pericentromeric heterochromatin of Drosophila melanogaster polytene chromosomes

A method of microcloning, which involves microsurgical excision of chromosome fragments, DNA amplification by means of a polymerase chain reaction (PCR), and ligation of amplified products with plasmids, was employed in studying Drosophila polytene chromosomes for the first time. Clones of the DNA library thus obtained contained inserts varying in size from 0.1 to 0.5 kb. DNA sequencing of five clones of the library showed that pericentromeric heterochromatin contained the 176 and 297 retrotransposons; the ninja retrotransposon characteristic of D. simulans; and two Drosophila repetitive elements, ag and a12, the function of which remains unknown

Directing the path of light-induced electron transfer at a molecular fork using vibrational excitation

Ultrafast electron transfer in condensed-phase molecular systems is often strongly coupled to intramolecular vibrations that can promote, suppress and direct electronic processes. Recent experiments exploring this phenomenon proved that light-induced electron transfer can be strongly modulated by vibrational excitation, suggesting a new avenue for active control over molecular function. Here, we achieve the first example of such explicit vibrational control through judicious design of a Pt(II)-acetylide charge-transfer donor–bridge–acceptor–bridge–donor ‘fork’ system: asymmetric 13C isotopic labelling of one of the two –C≡C– bridges makes the two parallel and otherwise identical donor→acceptor electron-transfer pathways structurally distinct, enabling independent vibrational perturbation of either. Applying an ultrafast UVpump(excitation)–IRpump(perturbation)–IRprobe(monitoring) pulse sequence, we show that the pathway that is vibrationally perturbed during UV-induced electron transfer is dramatically slowed down compared to its unperturbed counterpart. One can thus choose the dominant electron transfer pathway. The findings deliver a new opportunity for precise perturbative control of electronic energy propagation in molecular devices