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Lysozyme adsorption complexes with graphene oxide (GO) and reduced GO were studied by means of radiotracer method using tritium as a label. The experiment includes adsorption study, with amount and...

A study of ion-molecular reactions of fluoro-substituted phenyl cations with benzopyridine derivatives demonstrated the following: (a) at present only the nuclear-chemical method enables the reaction of a direct phenylation of the nitrogen atom in benzopyridine derivatives, which makes it possible to obtain previously unknown quaternized structures, and (b) generation of nucleogenic phenyl cations with various substituents leads to a simultaneous introduction of the required substituents into the aromatic ring at the nitrogen heteroatom. Quantum-chemical calculations additionally confirmed the assumption about the pathways of the ion-molecular reactions with nucleogenic phenyl cations.

Chitosan adsorption complexes were obtained with nanodiamonds possess negative as well as positive zeta-potential in the aqueous suspensions. The application of tritium labeled chitosan all...

Nanodiamond-chitosan composites of definite composition were prepared to modify heart valve biological prostheses materials. The final material is characterized by higher failure stress and...

Graphene oxide was reduced by aspartic acid, β-mercaptoethanol in the acidic mixture, hydrothermal method and by atomic hydrogen (deuterium and tritium). Raman spectroscopy and FTIR indicat...

Quinazoline derivatives are well known to have a diverse array of therapeutic activities. Unfortunately, “classic” chemical synthesis does not provide an opportunity for the formation of N-phenyl quaternary 1,3-diazinium compounds. A devised nuclear-chemical method of synthesis based on chemical effects of nuclear transformations enables a new way of the direct nitrogen atom phenylation by the nucleogenic (generated by tritium β-decay) phenyl cations in 1,3-diazines, furnishing, based on our prediction, formation of previously unknown derivatives with N-phenyl quaternary quinazolinium scaffold.

The efficiency of tritium labeling of salts of pantothenic (HO–R–COOH), hopantenic (HO–R–CH2–COOH), and 4-D-phosphopantothenic [(HO)2P(=O)–O–R–COOH] acids [R = CH2C(CH3)2CHOH–CONH(CH2)2] with thermal activation of tritium at target temperatures of 77 and 295 K was studied. The phosphate group inhibits the isotope exchange. The tritium-labeled compounds were used for studying the adsorption of pantothenic acid derivatives from aqueous solutions and in the presence of 0.9% NaCl at 297 ± 3 K onto nanodiamonds prepared by detonation synthesis (NDs). Preparation of stable ND suspensions in advance enhances the ability of NDs to adsorb the compounds studied. The parameters of the equation describing the sorption isotherms at different ionic strengths of the solution were calculated. The strength of the adsorbate retention in contact with water, 0.9% NaCl solution, 0.01 M HCl solution, and 40 g L−1 bovine serum albumin (BSA) solution was determined. The data obtained allow two mechanisms of the adsorbate retention on the ND surface to be considered: reversible adsorption due to ionic interactions and irreversible binding due to hydrophobic interactions. The strongly bound molecules undergo slow desorption in the presence of BSA. The revealed trends confirm high potential of NDs as a drug delivery platform.

The paper studies the combined effects of beta-emitting radionuclide tritium and Humic Substances (HS) on the marine unicellular microorganism—luminous bacteria—under conditions of low-dose radiation exposures (&lt, 0.04 Gy). Tritium was used as a component of tritiated water. Bacterial luminescence intensity was considered as a tested physiological parameter. The bioluminescence response of the marine bacteria to tritium corresponded to the “hormesis” model: it included stages of bioluminescence inhibition and activation, as well as the absence of the effect. HS were shown to decrease the inhibition and activation effects of tritium, similar to those of americium-241, alpha-emitting radionuclide, studied earlier. Correlations between the bioluminescence intensity and the content of Reactive Oxygen Species (ROS) were found in the radioactive bacterial suspensions. The results demonstrate an important role of HS in natural processes in the regions of low radioactive contamination: HS can mitigate radiotoxic effects and adaptive response of microorganisms to low-dose radioactive exposures. The involvement of ROS in these processes was demonstrated.

Surface concentration of oxidized nanodiamonds (NDs) and NDs modified with oleylamine in NDs–poly(vinyl alcohol) composite films has been determined by autoradiography using tritium-labeled NDs. It has been demonstrated that oxidized NDs are distributed uniformly in the composite films, and their surface concentration is the same at both sides of the film. After modification with oleylamine, ND concentration at the bottom side of the film exceeds that at the top side approximately tenfold. Zisman critical surface tension of the composite films as well as polar and non-polar contributions to the surface tension has been found. It has been shown that surface tension is determined by the polymer, and the addition of NDs does not affect its value.

Isotope exchange between dalargine applied onto various supports [glass, activated carbon, few-layer graphite (FLG)] and molecular tritium, performed with activation on a tungsten wire and on 5% Pd/C, 10% Pd/C, and 5% Pt/FLG catalysts was studied. Depending on the experiment conditions, the molar radioactivity of [3H]dalargine varied from 0.47 to 31 Ci mmol−1 with activation on a tungsten wire and from 0.63 to 5.5 Ci mmol−1 under the conditions of heating to 335 K in the presence of noble metal catalysts. Significant difference in the tritium distribution between amino acid residues of the peptide depending on the support and on the activation method is observed. Reactions of tritium atoms generated on tungsten led to the tritium incorporation mainly into aliphatic acid residues upon application of the peptide onto glass and into aromatic residues upon application onto activated carbon. The use of FLG as a support influenced the tritium redistribution between aliphatic and aromatic residues to a lesser extent. Upon tritium activation on 5% Pd/C, 10% Pd/C, and 5% Pt/FLD, tritium was mainly incorporated into aromatic residues, which is typical of electrophilic reactions. The study revealed strong effect of the support on the mechanism of the isotope exchange of hydrogen for tritium in dalargine. The intramolecular distribution of tritium in preparation of labeled compounds using thermal activation can be controlled by properly choosing a support onto which the substrate is applied.

The adsorption of lysozyme in the presence of high molecular weight (pluronic P123) and low molecular weight (Brij-35) non-ionic surfactants was studied at liquid-liquid and liquid-air interfaces. Using tritium-labeled compounds and liquid scintillation spectrometry of tritium, we investigated the competitive adsorption of lysozyme-pluronic P123 and lysozyme-Brij-35 at the aqueous-xylene interface. The substitution of protein by both polymer and low molecular weight surfactant was observed, while the presence of lysozyme does not influence the behavior of non-ionic molecules. We found that the ionic strength of the aqueous phase does not influence the strength of the effect, while it has a significant influence on the rate of diffusion and penetration of the adsorption layer by free protein. The thermodynamics of the competitive adsorption was described by the model suggested by Fainerman and co-authors, and the obtained parameters were used to describe the interfacial tension isotherms of the respective mixtures at the aqueous-air interface. Thus, the adsorption of each component of the mixture (protein and non-ionic surfactant) at the aqueous-air interface was revealed.

The kinetics and isotherm of lysozyme adsorption and the strength of lysozyme binding to two carbon materials, activated charcoal and carbon foil, were studied using tritium-labeled lysozyme. Polyethylene films were used as a model nonporous material. The lysozyme adsorption resulted in modification of the surface of the materials, making it more hydrophilic, and the rate at which the adsorption equilibrium was attained depended on the capability of the lysozyme solution to penetrate into pores of carbon materials. The specific coverage of the surface of graphite foil, activated carbon, and polyethylene with lysozyme appeared to be virtually equal when taking into account only pores accessible to the protein. The lysozyme adsorption on the polyethylene surface is reversible, whereas on the surface of activated charcoal and graphite foil it is practically irreversible. The possibility of modification of the carbon foil surface with a lysozyme solution to increase the adsorption zone was confirmed by autoradiography.

Films of poly-e-caproamide (PA), polyethylene (PE), and polyethylene terephthalate (PET) were used for detection of hydrogen spillover through the gas phase. The hydrogen used in the experiments contained tritium activated by two procedures (W wire, 2000 K; 5% Pd/C, 335 K). The radioactivity of the films was recorded by classical and digital autoradiography and by liquid scintillation counting. Under the action of “hot” atoms generated on a W wire, the maximal specific radioactivity of the films, equal to 420, 415, and 330 mCi cm–2 for PA, PE, and PET, respectively, was reached in 100 s. Preliminary thermalization of the atoms to a temperature of 77–335 K influenced the decrease in the film radioactivity differently. The effective activation energy of the reaction in the range 298–318 K was 21, 30, and 12.5 kJ mol–1 for PA. PE, and PET, respectively. Under the conditions of heating 5% Pd/C to 335 K for 25 min, the radioactivity of PA, PE, and PET was 1.6, 0.05, and 0.15 μCi cm–2, respectively. The revealed difference in the radioactivity of the films suggests different mechanisms of the interaction of tritium with organic molecules at different activation methods.

An experimental study of protein-peptide binding was performed by means of radiochemical and spectroscopic methods. Lysozyme and dalargin were chosen due to their biological and physiological importance. By means of tensiometry and radiochemical assays, it was found that dalargin possesses rather high surface activity at the aqueous-air and aqueous-p-xylene interfaces to be substituted by protein. Dalargin forms a hydrophobic complex with lysozyme in which the secondary structure of lysozyme is preserved. When lysozyme forms a mixed adsorption layer with dalargin at the aqueous-air surface, the peptide prevents protein from concentrating in the subsurface monolayer. In the presence of p-xylene protein in the interface, reorganization occurs quickly, so there is no lag in the interfacial tension time dependence. The interfacial tension in this case is controlled by protein and/or protein-peptide complexes. An increase in the enzymatic activity of lysozyme in the presence of dalargin was confirmed by a docking model that suggests the formation of hydrogen bonds between dalargin and amino acid residues in the active site.

The degree of adsorption of chitosan on the collagen matrices of bovine pericardium upon deposition from solutions in the two-phase H2O/CO2 system was studied as a function of pressure.

The effect adsorption layers of nonionic surfactant (pluronic P123) have on the distribution of nanodiamonds (NDs) between aqueous and organic phases is studied with radioactive tracers using compounds labeled with tritium. The values of reversible and irreversible adsorptions of P123 on NDs are determined. It is shown that the distribution coefficients of NDs modified by irreversibly adsorbed layers of P123 are several times higher than those of raw nanodiamonds. This result is explained by the hydrophobization of an ND’s surface, as is shown by data obtained via interfacial tensiometry and wetting.

Carbon-based nanomaterials have piqued the interest of several researchers. At the same time, radioactive labeling is a powerful tool for studying processes in different systems, including biological and organic; however, the introduction of radioactive isotopes into carbon-based nanomaterial remains a great challenge. We have used the Langmuir hydrogen dissociation method to introduce tritium in single-walled carbon nanotubes and graphene oxide. The technique allows us to achieve a specific radioactivity of 107 and 27 Ci/g for single-layer graphene oxide and single-walled carbon nanotubes, respectively. Based on the analysis of characteristic Raman modes at 1350 and 1580 cm−1, a minimal amount of structural changes to the nanomaterials due to radiolabeling was observed. The availability of a simple, nondestructive, and economic technique for the introduction of radiolabels to single-walled carbon nanotubes and graphene oxide will ultimately expand the applicability of these materials.

Tritium was introduced by the thermal activation method into samples of single-walled carbon nanotubes modified with diaminotriethylene glycol. Chemical linking of the modifier considerably increased the specific radioactivity of the product. The maximal specific radioactivity was reached when “hot” (2000 K) tritium atoms acted on targets of modified nanotubes kept at 295 K. The main pharmacokinetic parameters of tritium-labeled modified carbon nanotubes upon intravenous administration into mongrel rats chosen as a model were determined.

The present study considers a possible role of enzymatic reactions in the adaptive response of cells to the beta-emitting radionuclide tritium under conditions of low-dose exposures. Effects of tritiated water (HTO) on the reactions of bacterial luciferase and NAD(P)H:FMN-oxidoreductase, as well as a coupled system of these two reactions, were studied at radioactivity concentrations &le, 200 MBq/L. Additionally, one of the simplest enzymatic reactions, photobiochemical proton transfer in Coelenteramide-containing Fluorescent Protein (CLM-FP), was also investigated. We found that HTO increased the activity of NAD(P)H:FMN-oxidoreductase at the initial stage of its reaction (by up to 230%), however, a rise of luciferase activity was moderate (&lt, 20%). The CLM-FP samples did not show any increase in the rate of the photobiochemical proton transfer under the exposure to HTO. The responses of the enzyme systems were compared to the &lsquo, hormetic&rsquo, response of luminous marine bacterial cells studied earlier. We conclude that (1) the oxidoreductase reaction contributes significantly to the activation of the coupled enzyme system and bacterial cells by tritium, and (2) an increase in the organization level of biological systems promotes the hormesis phenomenon.

Adsorption of alkyltrimethylammonium bromides (DTAB, TTAB and CTAB) on detonation nanodiamonds was studied. Nanodiamonds of positive and negative zeta potentials in aqueous suspensions were used. The amount of the compound on nanodiamond surface was determined using tritium labeled surfactants. Our results suggested the same mechanism of the adsorption complex formation for nanodiamonds of total positive and negative charge.

It has been shown that when a mixture of sodium 4-phenylbenzoate and 5% Pd/C preliminarily exposed to a molecular tritium atmosphere at 333 K for 25 min is treated with atomic protium, tritium is incorporated into sodium 4-phenylbenzoate molecules. The resulting molar radioactivity of this compound is as high as 0.8 ± 0.2 Ci/mmol, and the molar radioactivity of 4-cyclohexylbenzoic acid turns out to be fourto-five times higher than that of labeled sodium 4-phenylbenzoate. It has been suggested that the interaction of protium atoms with (3H+)(ē) clusters formed on the support surface upon tritium spillover can initiate isotope exchange and hydrogenation reactions.

The efficiency of the protium–tritium isotope exchange in the sodium 4-phenylbenzoate (PBNa) molecule on activating the reaction on a tungsten filament at 1940 K (target temperature 77 and 295 K) and on heating the substrate supported on 5% Pd/C in the presence of gaseous tritium is compared. It is shown that the reaction mechanism is laregly determined by the properties of the material on which this reaction occurs and not only by the method of generation of activated tritium species. In the reaction of tritium atom with PBNa deposited on glass walls of the reaction vessel, the isotope substitution of tritium for protium occurred by the radical mechanism, leading to the formation of [3H]PBNa and hydrogenation products. It is assumed that the spillover of tritium atom over the support (carbon) surface is accompanied by polarization of the electronic shell and formation of the cluster (3 +)( $$\bar e$$ ), which leads to changes in the composition of the reaction products. The combined treatment of PBNa on 5% Pd/C allows estimation of the concentration of clusters on the carbon surface, which reaches 10.9 particles per 100 nm2 (9.2 nm2 per cluster).

Tritium labeling was introduced into detonation nanodiamonds (ND) through the tritium thermal activation method. Two target preparation techniques were developed to increase the radioactivity and the specific radioactivity of the labeled product: the desiccation of the waterless solvent suspension and the lyophilization of the hydrosol. The specific radioactivity of the labeled product was shown to correlate with the hydrogen content in the starting material and to achieve 2.6 TBq/g.

The scintillation phase method, interfacial tensiometry, and dynamic light scattering have been employed to study the behavior of mixtures composed of a globular protein, lysozyme, and a zwitterionic surfactant, cocoamidopropyl betaine, in a water/octane system. The comparison between the absorption values of the components, interfacial tensions, component concentrations, and aggregate sizes in the phases that are in contact, together with the analysis of the interaction between the components and the structure and surface activity of resulting aggregates, has made it possible to propose a mechanism for the behavior of the proteinzwitterionic surfactant mixture in the two-phase system.

The competitive adsorption and distribution in the bulk of the aqueous solution/p-xylene system was studied, using tritium labeling and the scintillation phase method, for human serum albumin (HSA) and ionic surfactants: dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulfate (SDS). Tritiumlabeled HSA, DTAB, and SDS of high specific radioactivity were obtained by the tritium thermal activation method and were purified by chromatography. Physicochemical studies were performed with HSA-SDS and HSA-DTAB mixtures at a protein concentration of 0.06 g l−1 and varied surfactant concentrations from 0.3 to 8.0 μM. The distribution ratio and the adsorption isotherm were obtained for each component of the mixture by the scintillation phase method. The effect of ultralow concentrations of surfactants on the competitive adsorption in mixtures with HSA and on the bulk distribution of the substances in the two-phase system was found. The parameters of intermolecular interaction in the adsorption layer were calculated, and a mechanism of formation of the adsorption layer was suggested.

The scintillation phase and tensiometry methods were used to study the mutual influence of dodecyl ether of poly(23)ethylene glycol (Brij-35) with sodium dodecyl sulfate and Brij-35 with dodecyltrimethylammonium bromide on the distribution in the water/octane system and adsorption at the liquid/liquid interface. The composition of mixed adsorption layers was determined and interaction parameters between molecules were calculated according to the Rosen model.

A method of tritium introduction into different types of organic molecules that is based on the interaction of atomic tritium with solid organic target is described. Tritium atoms are formed on the hot W-wire, which is heated by the electric current. Such an approach is called “tritium thermal activation method”. Here we summarize the results of labeling globular proteins (lysozyme, human and bovine serum albumins); derivatives of pantothenic acid and amino acids; ionic surfactants (sodium dodecylsulfate and alkyltrimethylammonium bromides) and nonionic high-molecular weight surfactants – pluronics. For the first time it is observed that if the target-compound is fixed and its radicals are stable the specific radioactivity of the labeled product can be drastically increased (up to 400 times) when the target temperature is ca. 295 K compared with the results obtained at 77 K. The influence of labeling parameters as tritium gas pressure, exposure time and W-wire temperature was tested for each target temperature that results in the optimum labeling conditions with high specific radioactivity and chemical yield of the resulting compound.

The capability of atomic tritium to penetrate deep into anhydrous targets of complex composition was examined. Amino acids coated with cetylamine were used as targets. With an increase in the cetylamine layer thickness, the yield of labeled amino acids drastically decreased, whereas the yield of labeled by-products increased. Measurements of the radioactivity of the amino acids allowed evaluation of the capability of cetylamine layers to transmit tritium atoms, which was characterized by gravimetric attenuation coefficients. The attenuation coefficient depends on particular amino acid used as indicator and on the cetylamine layer thickness. The most accurate values of the attenuation factors were obtained from the radioactivity of all the reaction products, taking into account the nonuniformity of cetylamine application onto the target. A decrease in the attenuation coefficient in thick cetylamine coatings was attributed to the open-work (porous) structure of these layers.

Diagnostics of nanoagglomerates of hydroxyapatite Ca10(PO4)6(OH)2 and of hierarchic structures based on them by the method of adsorption of tritium-labeled sodium succinate is made. The adsorption kinetics is one-step in the case of hydroxyapatite nanocrystals and two-step in the case of textured hydroxyapatite. The parameters of the S-shaped sorption isotherms are calculated; they are described by the Guggenheim-Fowler-Frumkin equation. The specific surface area of hydroxyapatite nanoagglomerates is 650–700 m2 g−1, which is close to the theoretical density of individual nanocrystals (900 m2 g−1), and the specific surface area of textured hydroxyapatite (macrospheroids) is 250–300 m2 g−1. Adsorption of succinate ions on the surface of hydroxyapatite nanocrystals leads to the formation of a tightly bound monolayer, which may lead to structural rearrangement of the sorbent.

The distribution of Triton X-100 nonionic surfactant in the water-cyclohexane system was investigated by the scintillating phase method. It was shown that an increase in the distribution coefficient as the volume ratio between the aqueous and organic phases grew was explained by the presence in Triton X-100 of homologues with different numbers of ethoxyethyl groups and with the distribution coefficients between the phases different by many times. For the real composition of Triton X-100, distribution coefficients of components of the surfactant were estimated, and the behavior of the surfactant in the system under consideration was simulated; the results were in close agreement with the experimental data.

The advancing and receding contact angles in the tetradecyltrimethylammonium bromide aqueous solution-p-xylene-glass system are determined. The adsorption of surfactant at the water-p-xylene interface is studied by the scintillating phase method and the assumption of the possible formation of microemulsion phase at the interface is made. Surfactant distribution over a solid surface in selective wetting is investigated by autoradiography. It is established that selective wetting differs substantiallyfrom wetting in air; possible reasons for the observed differences are discussed.

The permeability for atomic tritium of adsorption layers of aqueous solutio ns of alkyltrimethylammonium bromides RN(CH3)3Br differing in the length of the hydrocarbon radical R (C12H25, C14H29, C16H33) was studied. The change in the radioactivity of alanine present in the examined solutions was used as the measure of the attenuation of the flow of reactive tritium atoms. The formation of an adsorption monolayer of surfactant molecules on the liquid-gas phase boundary caused the radioactivity of alanine to decrease by a factor of 6.5 (R = C12H25) to 8 (R = C16H33) relative to the experiment with a straight alanine solution. A correlation between the structure of the adsorbed layers of alkyltrimethylammonium bromides and their permeability to atomic tritium is discussed.

The behavior of binary mixtures composed of a nonionic surfactant Triton X-100 (TX-100) and monomeric dodecyltrimethylammonium bromide (DTAB) or gemini N,N’-bis(N-dodecyl-N,N-dimethyl)-1,2-diammonium ethane dibromide (DDAB) cationic surfactants is studied upon micellization, wetting of Teflon and adsorption at the solution-air and solution-Teflon interfaces. The compositions of mixed micelles and adsorption layers, as well as the parameters of interaction between the surfactants (mixture components), were calculated using the Rubingh-Rosen model. For both mixtures, the interaction parameters are negative, and their absolute values increase in the following order: mixed micelles ≈ adsorption layers at the solution-air interface < adsorption layers at the solution-Teflon interface. The absolute values of the interaction parameters for TX-100-DDAB mixtures are larger than those for TX-100-DTAB mixtures. The adsorption of both mixtures on Teflon demonstrates synergistic effects. In case of TX-100-DDAB mixtures, the synergistic effects are also observed upon micellization, reduction of the surface tension, and wetting of Teflon.

The scintillation phase procedure based on measuring the counting rate of compounds labeled with tritium in a two-layer scintillation cocktail-aqueous solution system was modified. Previously this procedure was used primarily for studying sorption of proteins at the phase boundary. After certain modification, it became applicable to studying the kinetics of sorption and the equilibrium sorption of various compounds at the organic scintillation cocktail-aqueous solution boundary and to evaluating the distribution coefficients of compounds in this system. Two experimental modes are proposed: common two-layer system and drop system. The suitability of these procedures for determining the surface activity and hydrophobicity of organic compounds and for studying the permeability of the molecular layers adsorbed at the phase boundary is discussed.

The feasibility of the labeling procedure involving thermal activation (TA) of tritium was examined with the substrates that are commonly labeled by solid-phase catalytic hydrogenation (SCH) with tritium. Comparative characteristics of SCH and TA as procedures for tritium labeling of sugars and diazines were obtained. These two methods ensure comparable rates of tritium incorporation into purine and pyrimidine bases. The SCH allows preparation of tritium-labeled compounds with the maximum possible molar radioactivity. The molar radioactivity of the same compounds labeled using TA did not exceed 37 TBq mol−1, because only a small fraction of the substrate could react with atomic tritium. Longer reaction times and increased amounts of tritium taken into the reaction resulted in stronger degradation of the substrates. On the assumption that the reactive tritium atoms penetrate into the target to a depth of 0.5 nm, the actual specific radioactivity of the labeled compound in the zone accessible for atomic tritium reaches 0.2–2 PBq mol−1. Ways are suggested to increase the molar radioactivity of compounds labeled using thermal activation of tritium.

Surfactant adsorption on quartz and wetting of glass by aqueous solutions of tetradecyltrimethylammonium bromide, Triton X-100, and their mixtures are studied. It is shown that synergistic adsorption of surfactants from mixed solutions occurs in the region of low concentrations. In the region of high concentrations, mixed molecular aggregates of the cationic and nonionic surfactants are formed on the surface. The structure of the mixed adsorption layers is discussed.

The capability of tritium atoms to penetrate deep into solids was used for revealing nonuniformity of coating of polymeric [polyethylene, poly(ethylene terephthalate)] supports by adsorption layers of a nonionic surfactant Brij-35, formed by adsorption from aqueous solutions. The permeability to atomic tritium of Brij-35 adsorption layers on polyethylene appeared to be close to that obtained for hydrocarbon fragments of cationic surfactants in adsorption layers on the water/air boundary. A decrease in the coefficients of attenuation of the tritium atom flow at formation of adsorption polylayers was revealed. This decrease suggests less ordered structure of the polylayers relative to the monolayer. The developed approach involving preparation of adsorption coatings of tritium-labeled surfactants, their treatment with tritium atoms, and subsequent removal of the surfactant from the support, with the autoradiographic detection of tritium distribution on the plate in all the steps of the work, can be used for studying the structure of surfactant adsorption layers on flat solid surfaces.

Reaction of amino acids (glycine and serine) and amino sugar (glucosamine) with atomic tritium generated by thermal dissociation of molecular tritium on a tungsten filament was studied. A frozen aqueous solutions and a freeze-dried mixture of these compounds was bombarded with tritium atoms is a special vacuum unit. The relative yield of the labeled compounds was determined as influenced by the reaction conditions (residual pressure in the system and bombardment time) and target type (frozen solution and freeze-dried mixture). Formation of labeled products is almost independent of the tritium pressure. The ratio of the formation rates of labeled serine and glycine in the frozen solution and freeze-dried mixture bombarded with atomic tritium for 45–270 s was 1.66±0.15 and 1.44±0.13, respectively. At shorter reaction time (15 s), the ratio increases to 3.5±0.2 and 2.0±0.4, respectively. The formation rate of [3H]glucosamine in the mixture is higher at a shorter bombardment time. The radioactivity ratio of labeled glucosamine and glycine formed in frozen solutions and freeze-dried mixture in 15 s was 26.0±2.3 and 6.8±0.6, respectively. At longer reaction time, the relative yield of [3H]glucosamine sharply decreases owing to stronger radiolysis of labeled glucosamine on exposure to tritium beam.

The possibility of measuring a flow of reactive tritium atoms falling on a target during thermal activation using polyethylene (PE) films was studied. Procedures were developed for pretreatment of PE films before experiment, their subsequent treatment, and radioactivity measurements. The distribution of the flow of tritium atoms in a common reactor as influenced by various modes of atomizer arrangement and different experimental conditions was studied with PE films. The rate of formation of the labeled compound was maximal when the product of the tritium pressure in the system (Pa) by the distance from the atomizer to the target (cm) was 2.

Humic substances (HS) of different origins have been labeled with tritium by the thermal activation method. Specific radioactivity of labeled HS ( 3 H-HS) was sufficiently high and varied from 0.14 to 0.6 TBq/g. Parent HS and 3 H-HS were analyzed by size exclusion chromatography with radioactivity and UV detection. The results allowed concluding that (1) neither partial decomposition nor polymerization of HS occurred during labeling and (2) tritium labeled molecules have a regular distribution among HS fractions of different molecular weights. The performed correlation analysis revealed that there was no significant relationship between HS properties and specific radioactivity of the obtained 3 H-HS. Thus universality of the developed technique for radioactive labeling of HS with tritium could be demonstrated.

The topography of bacteriorhodopsin (bR) in situ was earlier studied by using the tritium bombardment approach [Eur. J. Biochem. 178 (1988) 123]. Now, having the X-ray crystallography data of bR at atom resolution [Proc. Natl. Acad. Sci. 95 (1998) 11673], we estimated the influence of membrane environment (lipid and protein) on tritium incorporation into amino acid residues forming transmembrane helices. We have determined the tritium flux attenuation coefficients for residues 10–29 of helix A. They turned out to be low (0.04±0.02 A −1 ) for residues adjacent to the lipid matrix, and almost fourfold higher (0.15±0.05 A −1 ) for those oriented to the neighboring transmembrane helices. We believe that tritium incorporation data could help modeling transmembrane segment arrangement in the membrane.