Raman and Infrared Studies of Platinum-Based Drugs: Cisplatin, Carboplatin, Oxaliplatin, Nedaplatin, and Heptaplatin.

This study reports the optimized structures and lowest-energy conformations/stereochemistry of five currently used platinum-based drugs: cisplatin, carboplatin, nedaplatin, oxaliplatin, and heptaplatin. Normal Raman and IR spectra of each drug are experimentally obtained and have been compared to various levels of density functional theory (DFT). Although some combination of structure, reactivity, or spectroscopy for these drugs has been studied by various groups, there are no known experimental normal Raman and IR spectra for nedaplatin, oxaliplatin, and heptaplatin in the literature. The detailed structural and vibration findings of these drugs are very important to understanding platinum behavior and drug dynamics. The following work explores the vibrational frequencies of these drugs particularly by focusing on the low-energy modes between 200 and 600 cm-1, where anharmonicity effects will have less influence on the accuracy of computed frequencies. Ideally, the Pt-N stretching modes provide vibrational diagnostics for each drug. Interestingly, a vibrational energy decomposition analysis (VEDA) suggests that oxaliplatin and heptaplatin Pt-N stretching modes are not Raman or IR active. Instead, C-C and Pt-O stretching frequencies in the various bidentate dioxo ligands might be more useful in characterizing new cisplatin derivatives. Analysis of anharmonicity effects was compared against (and in tandem with) dimer computations of four of the five drugs. Harmonic vibrational computations of the dimeric cisplatin derivatives provided greater qualitative improvement than that of the monomeric derivatives. Satisfying agreement with experimental Raman spectra was obtained, even without resorting to linear scale factors for the harmonic dimer frequencies.

Cooperative bi-exponential decay of dye emission coupled via plasmons.

Bi-exponential decay of dye fluorescence near the surface of plasmonic metamaterials and core-shell nanoparticles is shown to be an intrinsic property of the coupled system. Indeed, the Dicke, cooperative states involve two groups of transitions: super-radiant, from the most excited to the ground states and sub-radiant, which cannot reach the ground state. The relaxation in the sub-radiant system occurs mainly due to the interaction with the plasmon modes. Our theory shows that the relaxation leads to the population of the sub-radiant states by dephasing the super-radiant Dicke states giving rise to the bi-exponential decay in agreement with the experiments. We use a set of metamaterial samples consisting of gratings of paired silver nanostrips coated with Rh800 dye molecules, having resonances in the same spectral range. The bi-exponential decay is demonstrated for Au\SiO2\ATTO655 core-shell nanoparticles as well, which persists even when averaging over a broad range of the coupling parameter.

Publisher's Note: Coherence-Driven Topological Transition in Quantum Metamaterials [Phys. Rev. Lett. 116, 165502 (2016)].

This corrects the article DOI: 10.1103/PhysRevLett.116.165502.

Coherence-Driven Topological Transition in Quantum Metamaterials.

We introduce and theoretically demonstrate a quantum metamaterial made of dense ultracold neutral atoms loaded into an inherently defect-free artificial crystal of light, immune to well-known critical challenges inevitable in conventional solid-state platforms. We demonstrate an all-optical control, on ultrafast time scales, over the photonic topological transition of the isofrequency contour from an open to closed topology at the same frequency. This atomic lattice quantum metamaterial enables a dynamic manipulation of the decay rate branching ratio of a probe quantum emitter by more than an order of magnitude. Our proposal may lead to practically lossless, tunable, and topologically reconfigurable quantum metamaterials, for single or few-photon-level applications as varied as quantum sensing, quantum information processing, and quantum simulations using metamaterials.

Stimulated Raman spectroscopy with 0π pulses.

We developed a new variant of stimulated Raman spectroscopy with shaped short pulses, applicable to multiscattering media. The technique is based on the spectral modulation of the laser pulse due to the Raman scattering and may have a broad range of applications from spectroscopy and pathogen detection to microscopy.

Carrier-envelope phase effect on atomic excitation by few-cycle rf pulses.

We present an experimental and theoretical study of the carrier-envelope phase effects on population transfer between two bound atomic states interacting with intense ultrashort pulses. Radio frequency pulses are used to transfer population among the ground state hyperfine levels in rubidium atoms. These pulses are only a few cycles in duration and have Rabi frequencies of the order of the carrier frequency. The phase difference between the carrier and the envelope of the pulses has a significant effect on the excitation of atomic coherence and population transfer. We provide a theoretical description of this phenomenon using density matrix equations. We discuss the implications and possible applications of our results.

Optimizing the laser-pulse configuration for coherent Raman spectroscopy.

We introduce a hybrid technique that combines the robustness of frequency-resolved coherent anti-Stokes Raman scattering (CARS) with the advantages of time-resolved CARS spectroscopy. Instantaneous coherent broadband excitation of several characteristic molecular vibrations and the subsequent probing of these vibrations by an optimally shaped time-delayed narrowband laser pulse help to suppress the nonresonant background and to retrieve the species-specific signal. We used this technique for coherent Raman spectroscopy of sodium dipicolinate powder, which is similar to calcium dipicolinate (a marker molecule for bacterial endospores, such as Bacillus subtilis and Bacillus anthracis), and we demonstrated a rapid and highly specific detection scheme that works even in the presence of multiple scattering.

Electromagnetically induced coherent backscattering.

We demonstrate a strong coherent backward wave oscillation using forward propagating fields only. This is achieved by applying laser fields to an ultradispersive medium with proper chosen detunings to excite a molecular vibrational coherence that corresponds to a backward propagating wave. The physics then has much in common with the propagation of ultraslow light. Applications to coherent scattering and remote sensing are discussed.

Efficient generation of short terahertz pulses via stimulated Raman adiabatic passage.

We have analyzed the efficiency of coherent scattering of infrared radiation in molecular gases for the production of intense, short terahertz (THz) pulses by using stimulated Raman adiabatic passage for the preparation of coherence. We show that coherently driven molecular media potentially yield strong, controllable, short pulses of THz radiation. The pulses have energies ranging from several nanojoules to microjoules and time durations from several femtoseconds to nanoseconds at room temperature.

Visible and UV coherent Raman spectroscopy of dipicolinic acid.

We use time-resolved coherent Raman spectroscopy to obtain molecule-specific signals from dipicolinic acid (DPA), which is a marker molecule for bacterial spores. We use femtosecond laser pulses in both visible and UV spectral regions and compare experimental results with theoretical predictions. By exciting vibrational coherence on more than one mode simultaneously, we observe a quantum beat signal that can be used to extract the parameters of molecular motion in DPA. The signal is enhanced when an UV probe pulse is used, because its frequency is near-resonant to the first excited electronic state of the molecule. The capability for unambiguous identification of DPA molecules will lead to a technique for real-time detection of spores.