Anna Orlova

The mechanism of propagation of variation potentials in wheat leaves

Here we examined the mechanism of propagation of variation potential (VP) induced by burning in wheat leaves. Participation of hydraulic and chemical mechanisms in VP transmission was analyzed by optical coherent tomography and a radioactive tracer method, respectively. The speed of the hydraulic signal considerably exceeded the VP velocity. Investigation of a chemical substance spreading from the zone of local wounding was based on experimental data for radioactive marker transmission derived with a one-dimensional diffusion equation. The speed of the marker transmission was in accordance with VP velocity. The elimination of the potential transmission of a chemical signal by a timed severing of the leaf between the burn site and the recorded site blocked VP propagation. We suggest that a VP is formed by the transmission of a wound substance, the velocity of which is likely increased by hydraulic wave propagation.

Simultaneous photoacoustic and optically mediated ultrasound microscopy: phantom study.

An experimental setup for combined photoacoustic (PA) and optically mediated ultrasound (US) microscopy is presented. A spherically focused 35 MHz polyvinylidene fluoride (PVDF) ultrasonic detector with a numerical aperture of 0.28, a focal distance of 9 mm, and a bandwidth (-6 dB level) of 24 MHz was used to obtain PA and US data with a 3 mm imaging depth. A fiber-optic system was employed to deliver laser excitation pulses from a tunable laser to the studied medium. A single optical pulse was used to form both PA and US A-scans. The probing US pulses were generated thermoelastically due to absorption of backscattered laser radiation by the metalized surface of a PVDF film.

Simultaneous photoacoustic and optically mediated ultrasound microscopy: an in vivo study.

We propose the use of thermoelastic (TE) excitation of an ultrasonic (US) detector by backscattered laser radiation as a means of upgrading a single-modality photoacoustic (PA) microscope to dual-modality PA/US imaging at minimal cost. The upgraded scanning head of our dual-modality microscope consists of a fiber bundle with 14 output arms and a 32MHz polyvinylidene difluoride (PVDF) detector with a 34 MHz bandwidth (-6 dB level), 12.7 mm focal length, and a 0.25 numerical aperture. A single optical pulse delivered through the fiber bundle to the biotissue being investigated, in combination with a metalized surface on the PVDF detector allows us to obtain both PA and US A-scans. To demonstrate the in vivo capabilities of the proposed method we present the results of bimodal imaging of the brain of a newborn rat, a mouse tail and a mouse tumor.

Polarimetry as a Tool for the Study of Solutions of Chiral Solutes

Optical rotation of aqueous solutions of D-levoglucosan was studied experimentally in the 0.03-4.0 mol L(-1) concentration range and a nonlinear concentration dependence of specific optical rotation (SR) was revealed. Discontinuities observed in the concentration plot of SR (at 0.1, 0.3, 0.5, 1.0, and 2.0 mol L(-1)) are well correlated with those found by static and dynamic light scattering and identify concentration ranges in which different solution domains (supramers) may exist. The average SR experimental value for a D-levoglucosan aqueous solution ([α]D(28) -58.5±8.7 deg dm(-1) cm(-3) g(-1)) was found to be in good agreement with values obtained by theoretical calculation (TD-DFT/GIAO) of SR for 15 different conformers revealed by conformational sampling at the PCM/B3LYP/6-311++G(2d,2p)//B3LYP/6-31+G(d,p) level, which were shown to be strongly affected by the solvation microenvironment (0, 1, 2, and 3 explicit solvent molecules considered) due to local geometrical changes induced in the solute molecule. This exceptionally high sensitivity of SR makes polarimetry a unique method capable of sensing changes in the structure of supramers detected in this study.

In vivo study of photosensitizer pharmacokinetics by fluorescence transillumination imaging

The possibility of in vivo investigation of the pharmacokinetics of photosensitizers by means of fluorescence transillumination imaging is demonstrated. An animal is scanned in the transilluminative configuration by a single source and detector pair. Transillumination is chosen as an alternative approach to reflection imaging. In comparison with the traditional back-reflection technique, transillumination is preferable for photosensitizer detection due to its higher sensitivity to deep-seated fluorophores. The experiments are performed on transplantable mouse cervical carcinomas using three drugs: photosens, alasens, and fotoditazin. For quantitative evaluation of the photosensitizer concentration in tumor tissue the fluorescence signal is calibrated using tissue phantoms. We show that the kinetics of photosensitizer tumor uptake obtained by transillumination imaging in vivo agree with data of standard ex vivo methods. The described approach enables rapid and cost-effective study of newly developed photosensitizers in small animals.

A universal approach to the synthesis of carbohydrate conjugates of polyhedral boron compounds as potential agents for boron neutron capture therapy

A universal approach to the synthesis of carbohydrate conjugates with polyhedral boron compounds (PBCs) was developed. Oligosaccharide derivatives with amino group in aglycone moiety can be conjugated with PBC carboxy derivatives using N-methyl-N-(4,6-dimethoxy-1,3,5-triazin-2-yl)morpholinium chloride as a condensing agent. Both N-and O-glycosides differing in the conformation mobility around the glycoside bond were shown to be useful as oligosaccharides with a functional group in the aglycone moiety. This allows the application of this approach to the synthesis of PBC conjugates with a wide range of oligosaccharides isolated from natural sources can be transformed into N-glycosides with a functional group in aglycone. The approach was tested by conjugation of the carboxy derivatives of ortho-carborane and dodecaborate anion with lactose as a model oligosaccharide. Lactose, an easily available disaccharide, is a ligand of lectins expressed on the surface of melanoma cells. The approach suggested is the first example of the synthesis of such conjugates that does not require protective groups for the carbohydrate residue. It is especially important for obtaining dodecaborate-carbohydrate conjugates for which the removal of protective groups is often a non-trivial task.

N,N-Diacetylsialyl chloride--a novel readily accessible sialyl donor in reactions with neutral and charged nucleophiles in the absence of a promoter.

N,N-Diacetylneuraminic acid glycosyl chloride was prepared for the first time and made to react with various nucleophiles to give the corresponding alpha-glycosyl phosphate, beta-glycosyl dibenzyl phosphate, alpha-glycosyl azide, alpha-phenyl thioglycoside and alpha-glycosyl xanthate in 65-82% yields and high stereoselectivity while its reactions with simple alcohols were not stereoselective. The new sialyl donor made possible the first stereoselective synthesis of sialic acid glycosyl phosphate with alpha-configuration and highly efficient synthesis of beta-configured sialic acid glycosyl dibenzyl phosphate.

Glycosylation of dibutyl phosphate anion with arabinofuranosyl bromide: unusual influence of concentration of the reagents on the ratio of anomeric glycosyl phosphates formed

Glycosyl phosphates are widely used building blocks in the synthesis of various natural products, for example, nucleoside diphosphates,1—3 proteophosphoglycans,4 and С and О alkyl(aryl) glycosides5,6. Strategies of oligo saccharide synthesis using glycosyl phosphates as glycosyl donors7,8 were developed for various sugars (for example, derivatives of mannose,9 sialic acids10 and arabinofura nose11). Several known methods for the synthesis of the glyco syl phosphates are based on glysosylation reaction as the key step.3,12,13 During the synthesis (Scheme 1) of dibutyl (2,3,5 tri O benzoyl D arabinofuranosyl) phosphate (2) by glycosylation of dibutyl phosphoric acid ((BuO)2P(O)OH) with 2,3,5 tri O benzoyl α D arabinofuranosyl bromide (1)14 in MeCN in the presence of Pr2NEt 15 we found that concentration of the reagents influences the anomeric ratio of glycosyl phosphates 2. A decrease of concentration (c) of glycosyl bromide 1 (while keeping the molar ratio be tween all reagents constant) leads to an increase in the reaction stereoselectivity in favor of the α anomer 2a. A more detailed study of the concentration dependence of the stereoselectivity in a wide range of concentrations of glycosyl bromide 1 (0.001—0.2 mol L–1) revealed that the anomeric ratio of glycosyl phosphates 2 depends on con centration of the reaction mixture in a complex manner (Table 1, Fig. 1). While in the most concentrated solution (с = 0.2 mol L–1) the glycosylation proceeds unselectively (α/β = 1.5 : 1), upon transition to more diluted solutions the share of α anomer 2a increases, reaching a high value (α/β = 20 : 1) at с = 0.01 mol L–1. Upon a further de crease of concentration of glycosyl bromide 1 the stereo selectivity increases sharply (Table 1, Fig. 1) and the reac tion becomes virtually stereospecific (α/β > 50 : 1). A considerable influence of concentration of reagents on the outcome of glycosylation has been reported in sev eral cases,16—20 both the product yield16c,e,f,17,18 and stereoselectivity16e,f,17—20 as well as the reactivity16e,f,17 of the glycosyl donor being affected by dilution of the reac

Trans-illumination fluorescence imaging of deep-seated tumors in small animals

Abstract Background: Fluorescence diffuse tomography (FDT) is the most accurate technique for the imaging of labeled tumors in the small animal body. However, the procedure for reconstruction of the spatial distribution of the fluorophore requires a high signal-to-noise ratio due to the ill-condition of the inverse problem. Therefore, the FDT technique is ineffective for imaging tumors of small size or with dim fluorophores because of the low intensity of their fluorescence compared with the high level of tissue autofluorescence. In these cases, the size and position of a marked tumor in the animal body can be estimated from two-dimensional fluorescence images obtained using trans- or epi-illumination techniques. Material and methods: A versatile system for small animal fluorescence imaging which combines planar epi- and trans-illumination geometries of the light source and of the fluorescence receiver was created and tested. For epi-illumination imaging, light-emitting diode sources were used to provide homogeneous and stable illumination of the experimental animal, in combination with a cooled CCD camera which covers the entire illuminated area. For trans-illumination imaging, mechanical raster-scanning devices modulated at a low frequency were used for the laser source, together with a cooled photomultiplier tube, which provided outstanding sensitivity. Results: Monitoring the orthotopic tumor growth in animal bodies has demonstrated the efficacy of trans-illumination imaging in comparison with the epi-illumination technique. The results obtained also showed that the effective use of the trans-illumination technique requires Born normalization of the fluorescence signal and the exclusion of lateral illumination by surrounding the animal with additional light absorption material using light-absorption pads on both sides of the body.

Simultaneous in vivo imaging of diffuse optical reflectance, optoacoustic pressure and ultrasonic scattering.

We present reflection-mode bioimaging system providing complementary optical, photoacsoutic and acoustic measurements by acoustic detector after each laser pulse. While the photons absorbed within the sample provide optoacoustic (OA) signals, the photons absorbed by the external electrode of a detector provide the measurable diffuse reflectance (DR) from the sample and the probing ultrasonic (US) pulse. To demonstrate the in vivo capabilities of the system we present the results of complementary DR/OA/US imaging of a mouse tumor, head of a newborn rat, and the back of a newborn rat with 3.5mm/50μm/35μm lateral resolution. Trimodal approach allows visualization of mechanical structures in healthy and pathological tissues along with peculiarities of blood supply. The system may be used for diagnostics of diseases accompanied by the defects of vascularization as well as for assessing the mechanisms of vascular changes when monitoring response to therapy.