Showing papers by "Moscow State University published in 2000"

The heck reaction as a sharpening stone of palladium catalysis.

Abstract: s, or keywords if they used Heck-type chemistry in their syntheses, because it became one of basic tools of organic preparations, a natural way to

Efficient algorithms for solving overdefined systems of multivariate polynomial equations

Abstract: The security of many recently proposed cryptosystems is based on the difficulty of solving large systems of quadratic multivariate polynomial equations. This problem is NP-hard over any field. When the number of equations m is the same as the number of unknowns n the best known algorithms are exhaustive search for small fields, and a Grobner base algorithm for large fields. Grobner base algorithms have large exponential complexity and cannot solve in practice systems with n ≥ 15. Kipnis and Shamir [9] have recently introduced a new algorithm called "relinearization". The exact complexity of this algorithm is not known, but for sufficiently overdefined systems it was expected to run in polynomial time. In this paper we analyze the theoretical and practical aspects of relinearization. We ran a large number of experiments for various values of n and m, and analysed which systems of equations were actually solvable. We show that many of the equations generated by relinearization are linearly dependent, and thus relinearization is less efficient that one could expect. We then develop an improved algorithm called XL which is both simpler and more powerful than relinearization. For all 0 < ∈ ≤ 1/2, and m ≥ ∈n2, XL and relinearization are expected to run in polynomial time of approximately nO(1/√Ɛ). Moreover, we provide strong evidence that relinearization and XL can solve randomly generated systems of polynomial equations in subexponential time when m exceeds n by a number that increases slowly with n.

Organic solvent dispersions of single-walled carbon nanotubes: Toward solutions of pristine nanotubes

Abstract: A systematic study has been performed in order to find an appropriate medium for solubilization/dispersion of pristine single-walled carbon nanotubes (SWCNTs). Five solvents, all featuring high electron pair donicity (β) and low hydrogen bond parameter (α) have demonstrated the ability to readily form stable dispersions. The best dispersions have been characterized by UV/visible-NIR spectra, ESR spectra, and atomic force microscopy (AFM).

The development of dielectric barrier discharges in gas gaps and on surfaces

Abstract: Dielectric barrier discharges (DBDs) occur in configurations which are characterized by a dielectric layer between conducting electrodes. Two basic configurations can be distinguished: a volume discharge (VD) arrangement with a gas gap; and a surface discharge (SD) arrangement with surface electrode(s) on a dielectric layer and an extensive counter electrode on its reverse side. At atmospheric pressure the DBD consists of numerous microdischarges (VD) and discharge steps (SD), respectively, their number being proportional to the amplitude of the voltage. These events have a short duration in the range of some 10 ns transferring a certain amount of charge within the discharge region. The total transferred charge determines the current and hence the volt-ampere characteristic of each arrangement. The microdischarges (discharge steps) have a complicated spatial structure. The discharge patterns on the dielectric surface depend on the polarity and amplitude of the applied voltage as well as on the specific capacity of the dielectric. Experimental findings on DBDs in air and oxygen are presented and discussed. On the basis of a self-consistent two-dimensional modelling the temporal and spatial development of a microdischarge and discharge step are investigated numerically. The results lead to an understanding of the dynamics of DBDs. Although in VD arrangements cathode-directed streamers appear especially in electronegative gases, their appearance is rather unlikely in SD arrangements. The application of DBDs for plasma-chemical reactions is determined by the productivity, with which the energy of the electric field can be converted into internal states of atoms and/or molecules. Depending on the desired product it could be both the generation of internal electronic states of molecules or atoms and dissociation products of molecules. The discharge current and current density of DBDs in both the SD and VD arrangements as well as the energy release and energy density distribution in the discharge region are presented. As an example the effectiveness of the energy conversion into ozone production is detailed. Some peculiarities of the discharge parameters, for instance the correlation between discharge patterns (microdischarges or discharge steps) and surface charge density, are discussed.

Molecular analysis of Neanderthal DNA from the northern Caucasus

Abstract: The expansion of premodern humans into western and eastern Europe ∼40,000 years before the present led to the eventual replacement of the Neanderthals by modern humans ∼28,000 years ago1. Here we report the second mitochondrial DNA (mtDNA) analysis of a Neanderthal, and the first such analysis on clearly dated Neanderthal remains. The specimen is from one of the eastern-most Neanderthal populations, recovered from Mezmaiskaya Cave in the northern Caucasus2. Radiocarbon dating estimated the specimen to be ∼29,000 years old and therefore from one of the latest living Neanderthals3. The sequence shows 3.48% divergence from the Feldhofer Neanderthal4. Phylogenetic analysis places the two Neanderthals from the Caucasus and western Germany together in a clade that is distinct from modern humans, suggesting that their mtDNA types have not contributed to the modern human mtDNA pool. Comparison with modern populations provides no evidence for the multiregional hypothesis of modern human evolution.

Rayleigh scattering in high-Q microspheres

Abstract: The Rayleigh scattering has to be largely suppressed in high-Q whispering-gallery modes in microspheres because of restrictions imposed on scattering angles by cavity confinement. Earlier estimates of the fundamental limit for the quality factor in fused-silica microspheres are revisited, and Q≃1012 is predicted in few-millimeter-size fused-silica spheres, if the surface hydration problem is ovecome. Particular effects of surface scattering losses are analyzed, and the manifestation of scattering in the form of intermode coupling is calculated. The predominant effect of counterpropagating mode coupling (intracavity backscattering) is analyzed in the presence of a mode-matched traveling-wave coupler. As much as 100% resonance reflection regime is shown to be feasible.

Amperometric biosensor for glutamate using prussian blue-based "artificial peroxidase" as a transducer for hydrogen peroxide.

Abstract: The specially deposited Prussian Blue denoted as “artificial peroxidase” was used as a transducer for hydrogen peroxide. The electrocatalyst was stable, highly active, and selective to hydrogen peroxide reduction in the presence of oxygen, which allowed sensing of H2O2 around 0.0 V (Ag/AgCl). Glutamate oxidase was immobilized on the surface of the Prussian Blue-modified electrode in a Nafion layer using a nonaqueous enzymology approach. The calibration range for glutamate in flow injection system was 1 × 10-7−1 × 10-4 M. The lowest concentration of glutamate detected (1 × 10-7 M) and the highest sensitivity in the linear range of 0.21 A M-1 cm-2 were achieved. The influence of reductants was practically avoided using the low potential of an indicator electrode (0.0 V Ag/AgCl). The attractive performance characteristics of the glutamate biosensor illustrate the advantages of Prussian Blue-based “artificial peroxidase” as transducer for hydrogen peroxide detection.

Optimal Control of Distributed Systems: Theory and Applications

Abstract: The existence of solutions to optimal control problems Optimality system for optimal control problems The solvability of boundary value problems for a dense set of data The problem of work minimization in accelerating still fluid to a prescribed velocity Optimal boundary control for nonstationary problems of fluid flow and nonhomogeneous boundary value problems for the Navier-Stokes equations The Cauchy problem for elliptic equations in a conditionally well-posed formulation The local exact controllability of the flow of incompressible viscous fluid Bibliography Index.

Last glacial maximum biomes reconstructed from pollen and plant macrofossil data from northern Eurasia

Abstract: Pollen and plant macrofossil data from northern Eurasia were used to reconstruct the vegetation of the last glacial maximum (LGM: 18,000 ± 2000 14C yr bp) using an objective quantitative method for interpreting pollen data in terms of the biomes they represent ( Prentice et al., 1996 ). The results confirm previous qualitative vegetation reconstructions at the LGM but provide a more comprehensive analysis of the data. Tundra dominated a large area of northern Eurasia (north of 57°N) to the west, south and east of the Scandinavian ice sheet at the LGM. Steppe-like vegetation was reconstructed in the latitudinal band from western Ukraine, where temperate deciduous forests grow today, to western Siberia, where taiga and cold deciduous forests grow today. The reconstruction shows that steppe graded into tundra in Siberia, which is not the case today. Taiga grew on the northern coast of the Sea of Azov, about 1500 km south of its present limit in European Russia. In contrast, taiga was reconstructed only slightly south of its southern limit today in south-western Siberia. Broadleaved trees were confined to small refuges, e.g. on the eastern coast of the Black Sea, where cool mixed forest was reconstructed from the LGM data. Cool conifer forests in western Georgia were reconstructed as growing more than 1000 m lower than they grow today. The few scattered sites with LGM data from the Tien-Shan Mountains and from northern Mongolia yielded biome reconstructions of steppe and taiga, which are the biomes growing there today.

Mechanical buckling instability of thin coatings deposited on soft polymer substrates

Abstract: Deformation of rubber and poly(ethylene terephthalate) coated with a platinum or a gold film was studied. The thickness of the coating film was approximately ten nanometers. The polymer substrates were 104 to 105-fold softer than the coating. Folding of the coating leading to the appearance of a wave-like pattern on an originally smooth surface was observed both in tension and after shrinkage. In tension the wave crests are oriented along the elongation direction. After shrinkage the wave crests are perpendicular to the shrinkage direction. For rubber substrates, the appearance of the wave is explained by a mechanical buckling instability of the coating under compressive force. The length of the surface wave depends on the thickness of the coating layer and the rigidity of the polymer substrate. In addition to folding, regular fragmentation of the coating film on long and comparatively narrow bands is observed. The cracks are perpendicular to the wave crests both in tension and after shrinkage.

Relationship between pluronic block copolymer structure, critical micellization concentration and partitioning coefficients of low molecular mass solutes

Abstract: Using pyrene and homologous alkyl derivatives of fluorescein as fluorescent probes, this work examines the partitioning coefficients of hydrophobic solutes in aqueous dispersions of Pluronic block copolymers (poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide)). An incremental approach is developed, allowing measurement of the free energy of transfer of a methylene group from aqueous media into the micelles. Effects of variation of length of the ethylene oxide (EO) and the propylene oxide (PO) blocks in Pluronic molecules on the partitioning characteristics of the solutes are established. A simple reciprocal relationship between partitioning coefficients of the solute and critical micellization concentration is demonstrated.

Application of high hydrostatic pressure for increasing activity and stability of enzymes.

Abstract: Elevated hydrostatic pressure has been used to increase catalytic activity and thermal stability of alpha-chymotrypsin (CT). For an anilide substrate, characterized by a negative value of the reaction activation volume (DeltaV( not equal)), an increase in pressure at 20 degrees C results in an exponential acceleration of the hydrolysis rate catalyzed by CT reaching a 6.5-fold increase in activity at 4700 atm (4.7 kbar). Due to a strong temperature dependence of DeltaV( not equal), the acceleration effect of high pressure becomes more pronounced at high temperatures. For example, at 50 degrees C, under a pressure of 3.6 kbar, CT shows activity which is more than 30 times higher than the activity at normal conditions (20 degrees C, 1 atm). At pressures of higher than 3.6 kbar, the enzymatic activity is decreased due to a pressure-induced denaturation.Elevated hydrostatic pressure is also efficient for increasing stability of CT against thermal denaturation. For example, at 55 degrees C, CT is almost instantaneously inactivated at atmospheric pressure, whereas under a pressure of 1.8 kbar CT retains its anilide-hydrolyzing activity during several dozen minutes. Additional stabilization can be achieved in the presence of glycerol, which is most effective for protection of CT at an intermediate concentration of 40% (v/v). There has been observed an additivity in stabilization effects of high pressure and glycerol: thermal inactivation of pressure-stabilized CT can be decelerated in a supplementary manner by addition of 40% (v/v) glycerol. The protection effect of glycerol on the catalytic activity and stability of CT becomes especially pronounced when both extreme factors of temperature and pressure reach critical values. For example, at approximately 55 degrees C and 4.7 kbar, enzymatic activity of CT in the presence of 40% (v/v) glycerol is severalfold higher than in aqueous buffer.The results of this study are discussed in terms of the hypotheses which explain the action of external and medium effects on protein structure, such as preferential hydration and osmotic pressure.

Light-stress-induced pigment changes and evidence for anthocyanin photoprotection in apples.

Abstract: Fruit of two apple (Malus domestica Borkh.) cultivars, differing in their ability to produce anthocyanin pigments when exposed to sunlight, have been studied using reflectance spectroscopy. Comparison of the spectra shows that apple anthocyanins in vivo possess a symmetric absorption band at 500–600 nm with a maximum near 550 nm. Anthocyanins considerably increase light absorption by apples. In on-tree-ripening Zhigulevskoe apples, accumulating high amounts of anthocyanin pigments, chlorophyll contents in sunlit and shaded sides of the fruits are found to be similar. In contrast, frequently considerably lower chlorophyll content is estimated in sunlit compared with shaded sides of Antonovka apples exhibiting low potential for anthocyanin formation. Sunlight also brings about an increase of carotenoid content over that of chlorophylls and accumulation of substances responsible for light absorption in the range 350–400 nm. The rates of high-light-induced chlorophyll bleaching in red zones of fruit containing anthocyanins are considerably lower than those in green zones and decrease with an increase in the pigment content. Anthocyanins show more stability to irradiation than chlorophylls. A protective function of anthocyanins against both light-induced stress in, and damage to, apples is suggested. It is proposed that anthocyanins function as an effective internal light trap filling the chlorophyll absorption gap in the green–orange part of the visible spectrum.

Natural genetic exchanges between vaccine and wild poliovirus strains in humans.

Abstract: In a previous study of poliovirus vaccine-derived strains isolated from patients with vaccine-associated paralytic poliomyelitis (VAPP) (9, 11), we reported that a high proportion (over 50%) of viruses had a recombinant genome. Most were intertypic vaccine/vaccine recombinants. However, some had restriction fragment length polymorphism (RFLP) profiles different from those of poliovirus vaccine strains. We demonstrate here that five such recombinants, of 88 VAPP strains examined, carried sequences of wild (nonvaccine) origin. To identify the parental wild donor of these sequences, we used RFLP profiles and nucleotide sequencing to look for similarity in the 3D polymerase-coding region of 61 wild, cocirculating poliovirus isolates (43 type 1, 16 type 2, and 2 type 3 isolates). In only one case was the donor identified, and it was a wild type 1 poliovirus. For the other four vaccine/wild recombinants, the wild parent could not be identified. The possibility that the wild sequences were of a non-poliovirus-enterovirus origin could not be excluded. Another vaccine/wild recombinant, isolated in Belarus from a VAPP case, indicated that the poliovirus vaccine/wild recombination is not an isolated phenomenon. We also found wild polioviruses (2 of 15) carrying vaccine-derived sequences in the 3′ moiety of their genome. All these results suggest that genetic exchanges with wild poliovirus and perhaps with nonpoliovirus enteroviruses, are also a natural means of evolution for poliovirus vaccine strains.

A new approach to preparative enzymatic synthesis.

Abstract: A new approach to preparative organic synthesis in aqueous–organic systems is suggested. It is based on the idea that the enzymatic process is carried out in a biphasic system “water–water-immiscible organic solvent.” Thereby the enzyme is localized in the aqueous phase—this eliminates the traditional problem of stabilizing the enzymes against inactivation by a nonaqueous solvent. Hence, in contrast to the commonly used combinations “water–water-miscible organic solvent,” in the suggested system the content of water may be infinitely low. This allows one to dramatically shift the equilibrium of the reactions forming water as a reaction product (synthesis of esters and amides, polymerization of amino acids, sugars and nucleotides, dehydration reactions, etc.) toward the products. The fact that the system consists of two phases provides another very important sources for an equilibrium shift, i.e., free energies of the transfer of a reagent from one phase to the other. Equations are derived describing the dependence of the equilibrium constant in a biphasic system on the ratio of the volumes of the aqueous and nonaqueous phases and the partition coefficients of the reagents between the phases. The approach has been experimentally verified with the systhesis of N-acetyl-L-tryptophan ethyl ester from the respective alcohol and acid. Porous glass was impregnated with aqueous buffer solution of chymotrypsin and suspended in chloroform containing N-acetyl-L-tryptophan and ethanol. In water (no organic phase) the yield of the ester is about 0.01%, whereas in this biphasic system it is practically 100%. The idea is applicable to a great number of preparative enzymatic reactions.

Oriented immobilization of antibodies onto the gold surfaces via their native thiol groups.

Abstract: The general approach for site-oriented immobilization of antibodies onto gold supports is reported. The immobilization is carried out using the native sulfide groups of immunoglobulin (IgG). To liberate the thiol groups, the intact IgG was split into two half-IgG fragments without destruction of the binding site of the antibody. The immobilization of half-IgG fragments on the gold surface was carried out by simple adsorption. The antigen binding capacity of the half-IgG modified gold supports is similar to that of the gold surfaces with the traditionally linked antibodies and is much higher than for nonspecifically adsorbed intact IgGs. The immobilized antibodies, according to the proposed approach, maintain high antigen binding constants. The immobilization procedure provides orientation of IgG fragments in terms of the similar distance between the binding site of the antibody and the surface of the gold support, which does not cause the distribution of the apparent affinity constants. The high operational stability of half-IgG modified gold electrodes makes them applicable for analytical applications.

Physical Association of Eukaryotic Initiation Factor 4G (eIF4G) with eIF4A Strongly Enhances Binding of eIF4G to the Internal Ribosomal Entry Site of Encephalomyocarditis Virus and Is Required for Internal Initiation of Translation

Abstract: The initiation phase of translation in eukaryotes is the process leading to assembly of a translation-competent 80S ribosome at the initiation codon of an mRNA. The canonical initiation process involves more than 10 initiation factors (6, 27, 38). The first stage in the initiation process is the binding of a eukaryotic initiation factor 2 (eIF2)-GTP-initiator tRNA complex, eIF1A, and eIF3 to the 40S ribosomal subunit to form a 43S complex. The second stage involves the binding of mRNA to this ribosomal complex and involves eIF3, eIF4A, eIF4B, eIF4F, and the poly(A)-binding protein (PABP). All nonorganellar cellular mRNAs have a 5′-terminal m7G cap structure that is recognized by the eIF4E (cap-binding) subunit of eIF4F. Mammalian eIF4F also contains eIF4G and eIF4A subunits. eIF4A is an RNA-dependent ATPase and RNA helicase. After binding of eIF4F to the 5′ end of an mRNA, eIF4A and eIF4B melt the RNA structure in its 5′-nontranslated region, which facilitates binding of the 43S complex to the 5′ end of the mRNA. Ribosomal binding is thought to be mediated through interactions of eIF4G and eIF4B with ribosome-bound eIF3 (22, 29). The ribosomal complex then scans to the initiating AUG codon (35). Finally, eIF5 and eIF5B mediate the displacement of factors from the 40S subunit and joining of the 60S subunit to form an active 80S ribosome (40). eIF4G is a large adapter protein with a modular structure that plays a key coordinating role in the early stages of initiation (19, 31). Two related eIF4G proteins (eIF4GI and eIF4GII) encoded by two different genes exist in yeast and mammals (8, 9, 15, 19). Mammalian eIF4G can be divided into three distinct functional domains. The N-terminal third (amino acids [aa] 1 to 612) contains the eIF4E and PABP binding sites (15, 24); the middle third (aa 613 to 1090) binds eIF3, eIF4A, and RNA (3, 14, 22, 30, 41); and the C-terminal third (aa 1091 to 1560) contains a second eIF4A binding site (14, 22, 30) and a binding site for the protein kinase Mnk1 (43). eIF4G therefore acts as a platform for the assembly of a multiprotein-RNA complex to recruit the ribosome to a mRNA. Consistent with its central role in initiation, eIF4G is also an important target in the regulation of protein synthesis. The 4E binding proteins (4E-BPs) act as general inhibitors of cap-dependent translation by binding eIF4E and sequestering it from the rest of the eIF4F complex (6). Biochemical and structural studies have established that the 4E-BPs are molecular mimics of eIF4G and compete for the same binding site on the dorsal surface of eIF4E (11, 25). eIF4G is also a direct target for regulation by phosphorylation (44) and by proteolysis, both during apoptosis (26) and during infection by some picornaviruses such as poliovirus (10, 21, 22). Proteases encoded by these picornaviruses cleave eIF4G specifically, separating the eIF4E-PABP binding domain from the eIF4A and eIF3 binding sites. In contrast, other picornaviruses such as encephalomyocarditis virus (EMCV) inhibit cellular translation by dephosphorylating 4E-BP1 and thereby disrupting the eIF4E-eIF4G interaction (7). Both strategies abrogate the activity of eIF4F in initiation on capped mRNAs and thus lead to a shutoff of host cell translation. Initiation of translation of picornavirus mRNAs occurs by a noncanonical cap-independent mechanism of internal initiation that is mediated by a ∼400-nucleotide (nt) highly structured internal ribosomal entry site (IRES) that lies immediately upstream of the initiation codon (16). The EMCV IRES epitomizes those of a large group of picornaviruses, including all members of the Aphthovirus, Cardiovirus, and Parechovirus genera. We reconstituted EMCV IRES-mediated initiation in vitro using purified translation components and found that this process is ATP dependent and utilizes the same set of canonical eIFs as does cap-mediated initiation except for eIF1, eIF1A, eIF4E, PABP, and the amino-terminal third of eIF4G, to which the last two bind (37, 39, 40). The essential region of eIF4G corresponds to the carboxy-terminal proteolytic cleavage product that is generated during poliovirus infection. It binds specifically to the J-K domain of the IRES, in close proximity to the initiation codon, and recruits eIF4A and eIF4B to the IRES (20, 41). Its interaction with the IRES is essential for 48S complex formation, and its role in IRES-mediated initiation may be analogous to that of the eIF4E-eIF4G complex in initiation on capped mRNAs, i.e., recruiting factors and promoting ribosomal attachment at a defined location on the mRNA. The requirement for eIF4G and its specific binding to the J-K domain is a general characteristic of the mechanism of initiation on all EMCV-like picornavirus IRESs, such as those of foot-and-mouth disease virus, human parechovirus 1, and Theiler's murine encephalomyelitis virus (41a; V. G. Kolupaeva, unpublished data). In this article we define the minimum region of eIF4GI required for its specific interaction with the EMCV IRES and for support of 48S complex formation on this RNA. Our data provide evidence that the specific interaction of eIF4A with eIF4G significantly enhances its affinity for the IRES and indicate that the interaction of eIF4A and eIF4G is required to yield an active complex in IRES-mediated initiation.

Measuring Russian Culture using Hofstede’s Dimensions

Abstract: On analyse dans cet article les reponses de 250 Russes sur les cinq dimensions culturelles d'Hofstede. Les scores sont ventiles par sous-groupes selon l'âge, l'experience professionnelle, le metier, le nombre de subordonnes et la region. En moyenne, il apparait que la culture russe du milieu des annees 90 est moderee en individualisme, masculinite et distance hierarchique, et assez haute en paternalisme et controle de l'incertitude. La jeune generation qui parvint a l'adolescence lors de la perestroika (autour de 1990) a les plus hauts scores en masculinite et les plus faibles en paternalisme. Les individus du monde des affaires presentent un plus fort controle de l'incertitude que ceux du secteur universitaire.

The role of photoionization in positive streamer dynamics

Abstract: The results of two-dimensional modelling of positive streamer dynamics in 2 cm point-to-plane gap are presented, including the process of photoionization in a gas volume. The model of photoionization in air, developed by Zhelezniak, Mnatsakanian and Sizykh is considered in detail and a comparison with the experimental data of Penney and Hummert is presented. The model of photoionization in nitrogen, based on the data of Penney and Hummert is described. The simulations of streamers were performed for air and nitrogen-like gas. It is shown, that fundamental space scale of streamer - the width of space charge layer lρ (ionization domain) around its head is defined by the length of absorption of photoionizing radiation la. This length defines all other parameters: electron density, radius of streamer channel etc, so one may speak about standard streamer in air, whose properties depend only on pressure. Based on simulation results one may assume that streamer branching occurs in high field, when lρ exceeds la. The process of branching may be interpreted as an instability which transforms the non-standard streamer into a number of standard ones.

Spectroscopic study of pressure-polymerized phases of C 60

Abstract: Comparative studies of the infrared (IR) and Raman spectra of the orthorhombic, tetragonal, and rhombohedral pressure-polymerized phases of ${\mathrm{C}}_{60}$ as well as the pressure-dimerized state have been performed at ambient conditions. The tentative assignment of the vibrational spectra of different phases has shown that they could be perfectly described by the molecular symmetry of the ${\mathrm{C}}_{60}$ polymers which are the structure-forming elements of crystalline polymerized phases. This allowed one to consider the IR and Raman spectra of the crystalline polymerized phases as characteristic of those of the appropriate one- and two-dimensional ${\mathrm{C}}_{60}$ polymers and to use them for molecular fractional analysis of polymerization products.

Targeted intracellular delivery of photosensitizers to enhance photodynamic efficiency.

Abstract: Photodynamic therapy (PDT) is a novel treatment, used mainly for anticancer therapy, that depends on the retention of photosensitizers (PS) in tumour cells and irradiation of the tumour with appropriate wavelength light. Photosensitizers are molecules such as porphyrins and chlorins that, on photoactivation, effect strongly localized oxidative damage within target cells. The PS used for PDT localize in various cytoplasmic membranous structures, but are not found in the most vulnerable intracellular sites for reactive oxygen species, such as the cell nucleus. The experimental approaches discussed in the present paper indicate that it is possible to design highly efficient molecular constructs, PS carriers, with specific modules conferring cell-specific targeting, internalization, escape from intracellular vesicles and targeting to the most vulnerable intracellular compartments, such as the nucleus. Nuclear targeting of these PS-carrying constructs results in enhanced photodynamic activity, maximally about 2500-fold that of free PS. Future work is intended to optimize this approach to the point at which tumour cells can be killed rapidly and efficiently, while minimizing normal cell and tissue damage.

The time-dependent process of oxidation of the surface of Bi2Te3 studied by x-ray photoelectron spectroscopy

Abstract: The process of oxidation of the Bi2Te3 surface was investigated by x-ray photoelectron spectroscopy (XPS). The oxidized surface layer was found to have a definite thickness, with configurations where O is bonded with Bi and Te, and Bi and Te are bonded with three and four oxygens, respectively. The oxidation time dependence of the oxidized layer thickness d(t) estimated from the XPS behaved as (t-t0)1/2 when d(t) was smaller than the thickness of a single oxidized quintuple atomic layer in our oxide model and behaved as t-t1 when it was larger than that. Experimental data were compared to our oxidation process model for the layered structure with the van der Waals gap and very good agreement was found.