Light-matter interaction in the strong coupling regime: configurations, conditions, and applications.

Resonance interaction between a molecular transition and a confined electromagnetic field can reach the coupling regime where coherent exchange of energy between light and matter becomes reversible. In this case, two new hybrid states separated in energy are formed instead of independent eigenstates, which is known as Rabi splitting. This modification of the energy spectra of the system offers new possibilities for controlled impact on various fundamental properties of coupled matter (such as the rate of chemical reactions and the conductivity of organic semiconductors). To date, the strong coupling regime has been demonstrated in many configurations under different ambient conditions. However, there is still no comprehensive approach to determining parameters for achieving the strong coupling regime for a wide range of practical applications. In this review, a detailed analysis of various systems and corresponding conditions for reaching strong coupling is carried out and their advantages and disadvantages, as well as the prospects for application, are considered. The review also summarizes recent experiments in which the strong coupling regime has led to new interesting results, such as the possibility of collective strong coupling between X-rays and matter excitation in a periodic array of Fe isotopes, which extends the applications of quantum optics; a strong amplification of the Raman scattering signal from a coupled system, which can be used in surface-enhanced and tip-enhanced Raman spectroscopy; and more efficient second-harmonic generation from the low polaritonic state, which is promising for nonlinear optics. The results reviewed demonstrate great potential for further practical applications of strong coupling in the fields of photonics (low-threshold lasers), quantum communications (switches), and biophysics (molecular fingerprinting).

[Kinetics of the lactone-carboxylate transition of hybrid camptothecin-netropsin molecules]. / Kinetika lakton/karboksilatnogo perekhoda gibridnoi molekuly kamptotetsin-netropsin.

The kinetics of the hydrolysis of the lactone ring of a hybrid molecule containing the molecules of the antitumor drug camptothecin and a derivative of the antibiotic netropsines, which is highly affine and specific to the DNA A-T sequences was investigated. It was shown that intramolecular interaction significantly slows down the rate of hydrolysis but does not change the equilibrium ratio of concentrations of the lactone and carboxylate forms of the camptothecin fragment of the hybrid molecule, which corresponds to the pH value. The use of intramolecular interaction for controlling the kinetics of the lactone/carboxylate transition makes it possible to create the drugs of the camptothecin family, which preserve the biologically active lactone form under the physiological conditions for a longer time and, therefore, are more effective as anticancer agents.

[Study of P-glycoprotein effect on the lipid monolayer properties by the Langmuir-Blodgett technique]. / Issledovanie metodom Lengmiura-Blodzhett vliianiia P-glikoproteina na svoistva lipidnykh monosloev.

Expression of the P-glycoprotein (Pgp) is proved to be one of the main reasons for the development of the multidrug resistance (MDR) phenotype by cancer cells. The effect of Pgp on the properties of lipid monolayers was studied using membrane fractions of sensitive and Pgp over-expressing multidrug resistance cancer cells containing 11, 24 or 32% of Pgp relative to the total content of membrane proteins. The effect of the Pgp membrane concentration on the properties of monolayers prepared from the membrane fractions was analyzed by the Langmuir-Blodgett method. The subphase composition was found to play a critical role in the stability of monolayers at any Pgp concentration. The optimal subphase comprised 10 mM tris-HCl buffer, pH 6.5, which made it possible to create very stable monolayer films with the pressure of collapse of about 30-40 mN/m. Monolayers prepared from membrane fractions of sensitive cells and cells containing the maximum (32%) amount of Pgp were found to be much more stable compared with fractions comprising 11 or 24% of Pgp. The analysis of monolayer compression dynamics revealed three distinct stages: (1) the self-organization of lipid molecules, which is characterized by an abrupt change of surface potential; (2) the compression of Pgp molecules at the constant potential of monolayers; and (3) the compression of lipid molecules, which is characterized by a quasilinear increase of both pressure and surface potential. It was shown that the specific surface areas of monolayers formed from sensitive and Pgp-enriched membranes containing 11 or 24% of Pgp are very similar, whereas the surface area of the monolayer formed from membranes containing 32% of Pgp is nearly 1.5-fold greater. This fact may reflect the effect of the threshold rearrangement of the structure of lipid molecules or cooperative modifications of lipid-Pgp interactions induced by the increase in the Pgp content from 24 to 32%. The effect of verapamil, a well-known Pgp modulator, on the properties of monolayers was studied. It was show that verapamil is able to induce changes of the surface of Pgp-containing monolayers, and these modifications are maximal at the Pgp:verapamil 1:1 molar ratio. The data present the first experimental evidence for the possible intervention of Pgp modulator into the processes of lipid-lipid or lipid-Pgp cooperative interactions within Pgp-enriched membranes.

Mixed mode of ligand-DNA binding results in S-shaped binding curves.

S-shaped binding curves often characterize interactions of ligands with nucleic acid molecules as analyzed by different physico-chemical and biophysical techniques. S-shaped experimental binding curves are usually interpreted as indicative of the positive cooperative interactions between the bound ligand molecules. This paper demonstrates that S-shaped binding curves may occur as a result of the "mixed mode" of DNA binding by the same ligand molecule. Mixed mode of the ligand-DNA binding can occur, for example, due to 1) isomerization or dimerization of the ligands in solution or on the DNA lattice, 2) their ability to intercalate the DNA and to bind it within the minor groove in different orientations. DNA-ligand complexes are characterized by the length of the ligand binding site on the DNA lattice (so-called "multiple-contact" model). We show here that if two or more complexes with different lengths of the ligand binding sites could be produced by the same ligand, the dependence of the concentration of the complex with the shorter length of binding site on the total concentration of ligand should be S-shaped. Our theoretical model is confirmed by comparison of the calculated and experimental CD binding curves for bis-netropsin binding to poly(dA-dT) poly(dA-dT). Bis-netropsin forms two types of DNA complexes due to its ability to interact with the DNA as monomers and trimers. Experimental S-shaped bis-netropsin-DNA binding curve is shown to be in good correlation with those calculated on the basis of our theoretical model. The present work provides new insight into the analysis of ligand-DNA binding curves.

[Surface enhanced Raman spectroscopy for characterization of structural characteristics of carbon chains in alpha1-acid glycoprotein and pseudoglycoproteins]. / Osobennosti strukturnoi organizatsii uglevodnykh tsepei v alfa1- kislom glikoproteine i psevdoglikoproteinakh po dannym spektroskopii gigantskogo kombinatsionnogo rasseianiia.

Surface-enhanced Raman scattering (SERS) spectroscopy was used to study the structure of carbohydrate chains in glycosylated forms of alpha 1-acid glycoprotein (AGP) and in pseudoglycoproteins obtained by transferring the carbohydrate chains of AGP to a polyacrylamide carrier. It was found that AGP-D glycoform and pseudoglycoproteins containing three or more glycans per molecule, which possess high immunomodulating activity, have a specific spatial organization of carbohydrate chains. This organization is maintained by the interaction of neighboring glycans with each other and does not depend on the nature of the carrier (whether it is polypeptide or polyacrylamide).

[Study of sialated neoglycoconjugates by surface enhanced Raman scattering spectroscopy]. / Issledovanie sialirovannykh neoglikokon''iugatov metodom spektroskopii gigantskogo kombinatsionnogo rasseianiia.

Neoglycoconjugates based on polyacrylamide and sialic acid with N-acetylneuraminic acid or sialooligosaccharides as side chains were studied by surface-enhanced Raman scattering (SERS) spectroscopy. It had previously been found that these polymers can effectively inhibit influenza virus adhesion. This study revealed the possibility to evaluate, based on the intensity of SERS signals, the overall availability for interaction and the conformational freedom of sialic acid residues in glycoconjugates. The dependence of these two factors on the structure and density of sialylated side chains was studied. The uniformity of distribution of sialylated side chains in conjugates was shown. Comparison of the results of the SERS spectroscopic study of the conjugates and the data on their inhibitory effect on the adhesion of specific strains of influenza virus allowed the identification of the conjugates for which the availability and conformational freedom of sialic acid are the main factors determining their inhibitory properties. A conclusion was also reached about the predominance of one of the mechanisms (competitive inhibition or steric stabilization) in the inhibitory properties of the specific conjugates.

DNA topoisomerase I changes the mode of interaction between camptothecin drugs and DNA as probed by UV-resonance Raman spectroscopy.

Pronounced differences of interactions of camptothecin (CPT) and its derivative 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT11), inhibitors of DNA topoisomerase I, with oligonucleotides were found using UV resonance Raman spectroscopy. 30-mer oligonucleotides were derived from the sequences of the topoisomerase I-induced and CPT-enhanced cleavage sites in SV40 DNA. CPT induces well-defined alterations of the oligo structure, whereas CPT11 interacts with oligonucleotides more weakly and in another manner than CPT. Formation of cleavable ternary complexes between CPT11, topoisomerase I and oligonucleotides causes CPT11 to interact with oligonucleotides in the same fashion as was found for its parent compound CPT, and enhances this interaction as compared to CPT-oligonucleotide complexes. The data present evidence of molecular interactions of CPT11 with both other partners (topoisomerase I and oligonucleotide) of the ternary cleavable complex at the oligonucleotide-enzyme interface.

Selective analysis of antitumor drug interaction with living cancer cells as probed by surface-enhanced Raman spectroscopy.

A new technique for the selective measurement of small amounts of antitumor drugs in the nucleus and cytoplasm of a living cancer cell, based on surface-enhanced Raman spectroscopy (SERS), is proposed. The ability to detect SERS signals from very dilute (up to 10(-10) M) solutions of doxorubicin or adriamycin (DOX), and 4'O-tetrahydropyranyl-adriamycin (THP-ADM), as well as from their complexes with targets in vitro and in vivo, has been demonstrated. SERS spectra were obtained from a population as well as from single living erythroleukaemic K562 cells treated with DOX. The results of the measurements on the population of cells containing DOX in nuclei or in the cytoplasm are well correlated with the microscopic SERS measurements on the single cells treated with DOX, obtained by selectively recording signals from the living cell nucleus or from the cytoplasm. Possibilities for the application of this new technique in different aspects of cancer research are discussed.

Study of ATP binding in the active site of Na+,K(+)-ATPase as probed by ultraviolet resonance Raman spectroscopy.

The ultraviolet resonance Raman (UV RR) spectra of functional ATP/membrane-bound Na+,K+-ATPase complexes have been obtained. The substrate binding in the enzyme active site has been shown to be accompanied with significant changes in the electronic vibrational structure of the adenine ring. From the spectral analysis of ATP, 8-Br-ATP and 6-NHMe-adenine at various pH values the conclusion was made that N1 and the NH2 group and, probably, N7 of the substrate adenine part, interact with the protein surroundings via hydrogen bonds.

Binding of monovalent cations induces large changes in the secondary structure of Na+,K+-ATPase as probed by Raman spectroscopy.

Raman spectra of active Na+,K+-ATPase from pig kidney in media containing Na+ (E1), K+ (E2) or without exogenous ions (E1 conformation) were recorded in order to calculate the changes in the enzyme's secondary structure induced by binding of monovalent cations. It is demonstrated that: (i) K+ binding to the E1 form of the enzyme leads to conversion of approximately 100 peptide groups from the beta-structure to alpha-helical conformation; (ii) the transition is reversible and fully reproducible in the E1----E2----E1 and E2----E1----E2 experimental schemes. Predictional calculations revealed polypeptide chain segments involved in the alpha----beta transformations. These segments reside mainly in the two highly conserved regions of the alpha-subunit in the cytoplasmic domain of Na+,K+-ATPase. A possible role for the beta-subunit is discussed.

Differentiated analysis of the secondary structure of hydrophilic and hydrophobic regions in alpha- and beta-subunits of Na+,K+-ATPase by Raman spectroscopy.

Raman spectra of active Na+,K+-ATPase from pig kidney and membrane-bound products of its two-stage trypsinolysis, including alpha-subunit hydrophobic regions as well as the intact beta-subunit and hydrophobic regions of alpha- and beta-subunits, were measured to calculate the secondary structure of hydrophilic and hydrophobic regions of the enzyme. Consequent comparison demonstrated unambiguously that (i) membrane-bound hydrophobic parts of polypeptide chains of Na+,K+-ATPase subunits are in the alpha-helical conformation; (ii) essential contents of the alpha-helix as well as beta-sheet are estimated to form the hydrophilic (mainly cytoplasmic) domain of the Na+,K+-ATPase alpha-subunit; (iii) the exoplasmic hydrophilic domain of the beta-subunit is shown to include several antiparallel beta-pleated sheets and a small amount of the alpha-helix and unordered conformations. The model of the secondary structure organization of hydrophilic domains as well as 8 hydrophobic transmembrane segments of the enzyme molecule was proposed on the basis of experimental results and predictional calculations.

Retinal Schiff base position relative to the surfaces of photoreceptor disk.

Surface-enhanced Raman spectra of native and photobleached bovine rod outer segment disks as well as inside-out (inverted) photoreceptor disks adsorbed on silver hydrosol have been analyzed. Surface-enhanced spectra of inverted disks and disk-monoclonal antibody complexes reveal the short-range mechanism of enhancement. The distance between retinal Schiff base and the cytoplasmic side of native disk has been shown to be 5-10 A.

[Surface-enhanced Raman spectroscopy of biopolymers: membrane proteins, bacteriorhodopsin and rhodopsin adsorbed on silver electrodes and silver hydrosols]. / Spektroskopiia gigantskogo kombinatsionnogo rasseianiia biopolimerov: membrannye belki, bakteriorodopsin i rodopsin, adsorbirovannye na serebrianykh élektrodakh i gidrozoliakh serebra.

Surface-enhanced Raman (SER) spectra of purple membranes of Halobacterium halobium and photoreceptor disks of the rod outer segments adsorbed on silver hydrosols were analysed. It has been shown that the intensity of SER spectra of bacterial and visual rhodopsins increases 5 X 10(4) times at adsorption. Concentration relationship of the signal intensity of SER spectra has the maximum at bacteriorhodopsin concentration about 2 X 10(-7) M. It has been shown that adsorption on silver hydrosol leads to fixation of light-induced photochemical transformations in bacterial and visual rhodopsins. Adsorption on the "smooth" electrodes at the potential of the zero charge of silver does not affect the photocycle of bacteriorhodopsin. An increase or decrease of the electrode potential relative to the zero charge point of silver leads to the accumulation of kinetic intermediate K610 and a decrease of the concentration of the form BRh570. It has been shown that on the "smooth" electrode primarily the long-range component of the SER mechanism is realized. Bands corresponding to the vibrations of the atom groups directly contacting with the metal are mainly intensified after redox cycle which increases the concentration of chemosorption centres. A conclusion is drawn that the method of SER spectroscopy of biomolecules adsorbed on "smooth" electrodes, permits obtaining information similar to that obtained from the analysis of Raman spectra of unadsorbed molecules, but at concentrations by two orders less. Adsorption on the electrodes treated with the help of redox cycle permits to obtain highly oriented preparations and to study topography of biopolymers in water solutions and suspensions.