Rapid Volumetric Optoacoustic Tracking of Individual Microparticles In Vivo Enabled by a NIR-Absorbing Gold-Carbon Shell

Rapid volumetric in vivo visualization of circulating microparticles can facilitate new biomedical applications, such as blood flow characterization or targeted drug delivery. However, existing imaging modalities generally lack the sensitivity to detect the weak signals generated by individual micrometer-sized particles distributed across millimeter- to centimeter-scale depths in living mammalian tissues. Also, the temporal resolution is typically insufficient to track the particles in an entire three-dimensional region. Herein, we introduce a new type of monodisperse (4 μm) silica-core microparticle coated with a shell formed by a multilayered structure of carbon nanotubes (CNT) and gold nanoparticles (AuNP) to provide strong optoacoustic (OA) absorption-based contrast. We capitalize on the unique advantages of a state-of-the-art high-frame-rate OA tomography system to visualize and track the motion of these core-shell particles individually and volumetrically as they flow throughout the mouse brain vasculature. The feasibility of localizing individual solid particles smaller than red blood cells opens new opportunities for mapping the blood flow velocity, enhancing the resolution and visibility of OA images, and developing new biosensing assays.

Dye-Loaded Quatsomes Exhibiting FRET as Nanoprobes for Bioimaging

Fluorescent organic nanoparticles (FONs) are emerging as an attractive alternative to the well-established fluorescent inorganic nanoparticles or small organic dyes. Their proper design allows one to obtain biocompatible probes with superior brightness and high photostability, although usually affected by low colloidal stability. Herein, we present a type of FONs with outstanding photophysical and physicochemical properties in-line with the stringent requirements for biomedical applications. These FONs are based on quatsome (QS) nanovesicles containing a pair of fluorescent carbocyanine molecules that give rise to Förster resonance energy transfer (FRET). Structural homogeneity, high brightness, photostability, and high FRET efficiency make these FONs a promising class of optical bioprobes. Loaded QSs have been used for in vitro bioimaging, demonstrating the nanovesicle membrane integrity after cell internalization, and the possibility to monitor the intracellular vesicle fate. Taken together, the proposed QSs loaded with a FRET pair constitute a promising platform for bioimaging and theranostics.

Novel Light-Responsive Hydrogels with Antimicrobial and Antifouling Capabilities

Smart materials with both bactericidal and bacteria-resistant functions are promising for combating the infection concern of medical devices. Current work mostly utilizes hydrolysis to switch materials from antimicrobial to antifouling forms by incubating materials in aqueous solutions for hours to days. In this work, a new photoresponsive poly[2-((4,5-dimethoxy-2-nitrobenzyl)oxy)- N-(2-(methacryloyloxy)ethyl)- N, N-dimethyl-2-oxoethan-1-aminium] (polyCBNA) hydrogel was developed, incorporating the photolabile 4,5-dimethoxy-2-nitrobenzyl and cationic quaternary ammonium groups. The photolabile groups were readily cleaved from the hydrogel shortly upon UV irradiation at 365 nm (a long wavelength widely used for biomedical applications), leading to polymer surface charge switching from cationic to zwitterionic form. Protein adsorbed significantly on polyCBNA but easily desorbed from surfaces after UV irradiation. The cationic hydrogel as a precursor was shown to effectively kill the attached bacteria, and then quickly switched to zwitterionic antifouling form via photolysis, which released the attached bacteria from surfaces and prevented further bacterial attachment. Moreover, the adhered endothelial cells were easily detached from polyCBNA surfaces triggered by light, providing a facile and less destructive nonenzymatic approach to harvest cells. This smart photoresponsive polyCBNA polymer, with integrated antimicrobial and antifouling properties, holds great potential in biomedical applications such as self-sterilizing and self-cleaning coatings for implants, cell harvesting, and cell patterning.

Oxidative degradation of tetramethylammonium hydroxide (TMAH) by UV/persulfate and associated acute toxicity assessment

Tetramethylammonium hydroxide (TMAH) is widely used in high-tech industries as a developing agent. Ultraviolet (UV) light-activated persulfate (PS, S₂O₈^2-) can be used to generate strongly oxidative sulfate radicals, and it also exhibits the potential to treat TMAH-containing wastewater. This study initially investigated the effect of S₂O₈^2- concentration and UV strength on the UV/S₂O₈^2- process for the degradation of TMAH in a batch reactor. The results suggested that 15 watts (W) of UV-activated S₂O₈^2- at concentrations of 10 or 50 mM resulted in pseudo-first-order TMAH degradation rate constants of 3.1-4.2 × 10^-2 min^-1, which was adopted for determining the hydraulic retention time (HRT) in a continuous stirred tank reactor (CSTR). The operating conditions (15 W UV/10 mM S₂O₈^2-) with a HRT of 129 min resulted in stable residual concentrations of S₂O₈^2- and TMAH at approximately 2.6 mM and 20 mg L^-1 in effluent, respectively. Several TMAH degradation intermediates including trimethylamine, dimethylamine, and methylamine were also detected. The effluent was adjusted to a neutral pH and evaluated for its biological acute toxicity using Cyprinus carpio as a bioassay organism. The "bio-acute toxicity unit" (TU_a) was determined to be 1.41, which indicated that the effluent was acceptable for being discharged into an aquatic ecosystem.

Titania/CnTAB Nanoskeleton as adsorbent and photocatalyst for removal of alkylphenols dissolved in water

We report here on the removal of alkylphenols (phenol, 4-n-propylphenol, 4-n-heptylphenol and 4-nonylphenol) dissolved in water using the composite particles of nanocrystalline titania and alkyltrimethylammonium bromide (CnH2n+1N(CH3)3Br, CnTAB; n=12, 14, 16 and 18) (named as TiO2/CnTAB Nanoskeleton) as adsorbents and photocatalysts. In particular, the adsorption of alkylphenols onto TiO2/CnTAB Nanoskeleton in water was investigated in terms of hydrophobic interaction between alkylphenols and CnTAB, surface area, pore structure and crystal size of TiO2/CnTAB Nanoskeleton. We revealed that CnTAB incorporated in the TiO2/CnTAB Nanoskeleton promotes the adsorption of alkylphenols onto TiO2/CnTAB Nanoskeleton due to the hydrophobic interaction between alkylphenols and CnTAB. On the other hand, the surface area, pore structure and crystal size of TiO2/CnTAB Nanoskeleton did not affect the adsorption of alkylphenols onto TiO2/CnTAB Nanoskeleton. We also found that the alkylphenols dissolved in water were completely removed by the combination of adsorption and photocatalytic degradation by the TiO2/CnTAB Nanoskeleton under UV irradiation. These results prove that the TiO2/CnTAB Nanoskeleton acts as in tandem an adsorbent and a photocatalyst for removal of alkylphenols dissolved in water.

Facile synthesis of TiO2 nanocrystals using NH4F as morphology-controlling agent and its influences on photocatalytic activity

Controllable synthesis of nanomaterials with different morphologies can significantly affect their properties. Here we report that the morphology and facet orientation of TiO2 nanocrystals can be readily modulated via a hydrothermal method using a simple morphology-controlling agent of NH4F. The photocatalytic activity of resultant TiO2 has been evaluated by photodegradation of methyl orange. The results indicate that the introduction of NH4F can be used to modulate the mophology and, thereby, the photocatalytic activity of TiO2. The obtained TiO2 with high-energy facet, small size, and large surface area can exhibit an improved photocatalytic efficiency, which may be promising for real application.

A 1H NMR assay for measuring the photostationary States of photoswitchable ligands

Incorporation of photoisomerizable chromophores into small molecule ligands represents a general approach for reversibly controlling protein function with light. Illumination at different wavelengths produces photostationary states (PSSs) consisting of different ratios of photoisomers. Thus optimal implementation of photoswitchable ligands requires knowledge of their wavelength sensitivity. Using an azobenzene-based ion channel blocker as an example, this protocol describes a (1)H NMR assay that can be used to precisely determine the isomeric content of photostationary states (PSSs) as a function of illumination wavelength. Samples of the photoswitchable ligand are dissolved in deuterated water and analyzed by UV/VIS spectroscopy to identify the range of illumination wavelengths that produce PSSs. The PSSs produced by these wavelengths are quantified using (1)H NMR spectroscopy under continuous irradiation through a monochromator-coupled fiber-optic cable. Because aromatic protons of azobenzene trans and cis isomers exhibit sufficiently different chemical shifts, their relative abundances at each PSS can be readily determined by peak integration. Constant illumination during spectrum acquisition is essential to accurately determine PSSs from molecules that thermally relax on the timescale of minutes or faster. This general protocol can be readily applied to any photoswitch that exhibits distinct (1)H NMR signals in each photoisomeric state.

Characterization and detoxification of a mature landfill leachate using a combined coagulation-flocculation/photo Fenton treatment

The aim of the present work was to characterize and treat a mature landfill leachate using a coagulation/flocculation process followed by a photo-Fenton oxidation treatment. The leachate was obtained from a landfill in Tetlama, Morelos (Mexico) during the drought season and was characterized in terms of its major pollutants. Considerable levels of chemical oxygen demand (COD), total carbon (TC) and NH4+ were identified, as well as high concentrations of Hg, Pb, and As. Other heavy metals such as Ni, Co, Zn, Cd, and Mn were detected at trace levels. The lethal concentration (LC50) of the leachate, evaluated on Artemia salina, was 12,161±11 mg/L of COD, demonstrating an antagonistic interaction among the leachate's components. The treatment of this effluent consisted of a coagulation-flocculation process using an optimal dose of FeCl3 · 6H2O of 300 mg/L. The supernatant was treated using a photo-Fenton process mediated with FeCl2 · 4H2O and H2O2 in a compound parabolic concentrator (CPC) photo-reactor operating in batch mode using an R ratio (R=[H2O2]/[Fe2+]) of 114. The global removal efficiencies after treatment were 56% for the COD, 95% for TC, and 64% for NH4+. The removal efficiencies for As, Hg, and Pb were 46%, 9%, and 85%, respectively.

NH4+-NH3 removal from simulated wastewater using UV-TiO2 photocatalysis: effect of co-pollutants and pH

The main objective of the present study was to investigate the efficiency of titanium dioxide (TiO2) assisted photocatalytic degradation (PCD) process for the removal of ammonium-ammonia (NH4(+)-NH3) from the aqueous phase and in the presence of co-pollutants thiosulfate (S2O3(2-)) and p-cresol (C6H4CH3OH) under varying mixed conditions. For the NH4(+)-NH3 only PCD experiments, results showed higher NH4 -NH3 removal at pH 12 compared to pH 7 and 10. For the binary NH4(+)-NH3/S2O3(2-) studies the respective results indicated a significant lowering in NH4(+)-NH3 PCD in the presence of S2O32- at pH 7/12 whereas at pH 10 a marked increase in NH4(+)-NH3 removal transpired. A similar trend was noted for the p-cresol/NH4(+)-NH3 binary system. Comparing findings from the binary (NH4(+)-NH3/S2O3(2-) and p-cresol/NH4(+)-NH3) and tertiary (NH4(+)-NH3/S2O3(2-)/p-cresol) systems, at pH 10, showed fastest NH4(+)-NH3 removal transpiring for the tertiary system as compared to the binary systems, whereas both the binary systems indicated comparable NH4(+)-NH3 removal trends. The respective details have been discussed.

Assessment of cationic surfactants mineralization by ozonation and photo-Fenton process

Aqueous solutions of two important quaternary ammonium compounds--16-BAC (benzyl-dimethyl-hexadecylammonium-chloride) and 18-BAC (benzyl-dimethyl-stearylammonium-chloride)--were treated by the ozonation and photo-Fenton processes at different ozone doses and hydrogen peroxide concentrations, respectively. During the photo-Fenton experiments, two different types of lamps were used--a UV mercury vapor medium pressure lamp and a xenon lamp, which simulates solar radiation. The total organic carbon removal was monitored to follow the mineralization of the surfactants. According to the experimental results, after 90 minutes of treatment, the photo-Fenton process achieved up to 80% of mineralization when the UV lamp was used. The efficiency of the photo-Fenton with the xenon lamp was lower. The ozonation process reached, at most, 50% mineralization at the used conditions (ozone dose = 7.57 g/h).

Effect of light on self-assembly of aqueous mixtures of sodium dodecyl sulfate and a cationic, bolaform surfactant containing azobenzene

We report light and small-angle neutron scattering measurements that characterize microstructures formed in aqueous surfactant solutions (up to 1.0 wt % surfactant) containing mixtures of sodium dodecyl sulfate (SDS) and the light-sensitive bolaform surfactant, bis(trimethylammoniumhexyloxy)azobenzene dibromide (BTHA) as a function of composition, equilibration time, and photostationary state (i.e., solutions rich in cis-BTHA or trans-BTHA). We observed formation of vesicles in both SDS-rich and trans-BTHA-rich regions of the microstructure diagram, with vesicles present over a particularly broad range of compositions for trans-BTHA-rich solutions. Illumination of mixtures of BTHA and SDS with a broadband UV light source leads to formation of photostationary states where the fraction of BTHA present as cis isomer (75-80% cis-BTHA) is largely independent of the mixing ratio of SDS and BTHA. For a relatively limited set of mixing ratios of SDS and BTHA, we observed UV illumination of SDS-rich vesicles to result in the reversible transformation of the vesicles to micellar aggregates and UV illumination of BTHA-rich vesicles to result in irreversible precipitation. Surprisingly, however, for many mixtures of trans-BTHA and SDS that formed solutions containing vesicles, illumination with UV light (which was confirmed to lead to photoisomerization of BTHA) resulted in only a small decrease in the number of vesicles in solution, relatively little change in the sizes of the remaining vesicles, and coexistance of the vesicles with micelles. These observations are consistent with a physical model in which the trans and cis isomers of BTHA present at the photostationary state tend to segregate between the different microstructures coexisting in solution (e.g., vesicles rich in trans-BTHA and SDS coexist with micelles rich in cis-BTHA and SDS). The results presented in this paper provide guidance for the design of light-tunable surfactants systems.

Encoding light intensity by the cone photoreceptor synapse

How cone synapses encode light intensity determines the precision of information transmission at the first synapse on the visual pathway. Although it is known that cone photoreceptors hyperpolarize to light over 4-5 log units of intensity, the relationship between light intensity and transmitter release at the cone synapse has not been determined. Here, we use two-photon microscopy to visualize release of the synaptic vesicle dye FM1-43 from cone terminals in the intact lizard retina, in response to different stimulus light intensities. We then employ electron microscopy to translate these measurements into vesicle release rates. We find that from darkness to bright light, release decreases from 49 to approximately 2 vesicles per 200 ms; therefore, cones compress their 10,000-fold operating range for phototransduction into a 25-fold range for synaptic vesicle release. Tonic release encodes ten distinguishable intensity levels, skewed to most finely represent bright light, assuming release obeys Poisson statistics.

Probing Lysozyme Conformation with Light Reveals a New Folding Intermediate

A means to control lysozyme conformation with light illumination has been developed using the interaction of the protein with a photoresponsive surfactant. Upon exposure to the appropriate wavelength of light, the azobenzene surfactant undergoes a reversible photoisomerization, with the visible-light (trans) form being more hydrophobic than the UV-light (cis) form. As a result, surfactant binding to the protein and, thus, protein unfolding, can be tuned with light. Small-angle neutron scattering (SANS) measurements were used to provide detailed information of the protein conformation in solution. Shape-reconstruction methods applied to the SANS data indicate that under visible light the protein exhibits a native-like form at low surfactant concentrations, a partially swollen form at intermediate concentrations, and a swollen/unfolded form at higher surfactant concentrations. Furthermore, the SANS data combined with FT-IR spectroscopic analysis of the protein secondary structure reveal that unfolding occurs primarily in the alpha domain of lysozyme, while the beta domain remains relatively intact. Thus, the surfactant-unfolded intermediate of lysozyme appears to be a separate structure than the well-known alpha-domain intermediate of lysozyme that contains a folded alpha domain and unfolded beta domain. Because the interactions between the photosurfactant and protein can be tuned with light, illumination with UV light returns the protein to a native-like conformation. Fluorescence emission data of the nonpolar probe Nile red indicate that hydrophobic domains become available for probe partitioning in surfactant-protein solutions under visible light, while the availability of these hydrophobic domains to the probe decrease under UV light. Dynamic light scattering and UV-vis spectroscopic measurements further confirm the shape-reconstruction findings and reveal three discrete conformations of lysozyme. The results clearly demonstrate that visible light causes a greater degree of lysozyme swelling than UV light, thus allowing for the protein conformation to be controlled with light.

Photocontrol of Protein Folding: The Interaction of Photosensitive Surfactants with Bovine Serum Albumin

The photoresponsive interaction of light-sensitive azobenzene surfactants with bovine serum albumin (BSA) at neutral pH has been investigated as a means to control protein folding with light irradiation. The cationic azobenzene surfactant undergoes a reversible photoisomerization upon exposure to the appropriate wavelength of light, with the visible-light (trans) form of the surfactant being more hydrophobic than the UV-light (cis) form. As a consequence, the trans form exhibits enhanced interaction with the protein compared to the cis form of the surfactant, allowing photoreversible control of the protein folding/unfolding phenomena. Small-angle neutron-scattering (SANS) measurements are used to provide detailed information on the protein conformation in solution. A fitting of the protein shape to a low-resolution triaxial ellipsoid model indicates that three discrete forms of the protein exist in solution depending on the surfactant concentration, with lengths of approximately 90, 150, and 250 A, respectively, consistent with additional dynamic light-scattering measurements. In addition, shape-reconstruction methods are applied to the SANS data to obtain relatively high-resolution conformation information. The results confirm that BSA adopts a heart-shaped structure in solution at low surfactant concentration, similar to the well-known X-ray crystallographic structure. At intermediate surfactant concentrations, protein elongation results as a consequence of the C-terminal portion separating from the rest of the molecule. Further increases in the surfactant concentration eventually lead to a highly elongated protein that nonetheless still exhibits some degree of folding that is consistent with the literature observations of a relatively high helical content in denatured BSA. The results clearly demonstrate that the visible-light form of the surfactant causes a greater degree of protein unfolding than the UV-light form, providing a means to control protein folding with light that, within the resolution of SANS, appears to be completely reversible.

Radiation effect on poly(vinylbenzyltrimethylammonium chloride) in aqueous solution: pulse radiolysis and steady-state study

Poly(vinylbenzyltrimethylammonium chloride) (PVBT) has been synthesized by radiation-induced polymerization of Vinylbenzyltrimethylammonium chloride (VBT). The viscosity average molecular weight of synthesized polymer was estimated to be approximately 10(5) by viscosity measurements. The radiation-induced affects on PVBT have been investigated by steady-state and pulse radiolysis (PR) techniques. The reactions of primary radicals (*)OH, e(aq)(-), and H(*) generated by the radiolysis of water with PVBT were studied. The reactions of some other species such as N(3)(*), Cl(2)(*-), Br(2)(*-), SO(4)(*-), and CO(2)(*-) with PVBT were also investigated. The results indicate that the reactivity of these species toward PVBT is lower then that with the monomer VBT. The rate constants for the reactions of OH radical and H atom with PVBT were evaluated both by competition kinetics and by direct observation of the buildup of transient species. The difference in the rate constant values evaluated by the two methods indicated that (*)OH and H(*) react with PVBT to give more than one species. It was observed that the OH radical and H atom react with PVBT in different manners. Near neutral pH, the OH radicals react to form an adduct and to generate a radical by abstracting methylenic H atom. The H atom, however, also abstracts the H atom from the PVBT backbone. The rate constant value for the reaction of hydrated electron with PVBT was found to be 3.1 currency 10(9) dm(3) mol(-1) s(-1). Steady-state irradiation studies of the aqueous PVBT solution indicated that PVBT predominantly undergoes cross-linking on irradiation. Cross-linking is a function of dose rate, concentration, and ambient of irradiation. At concentrations < 2%, only intramolecular cross-linking takes place, whereas beyond this concentration, the intermolecular cross-linking of polymer chains takes place to form a soft gel. The gel dose (D(gel)) is a function of the ambient of irradiation.

Fast-neutron OSL sensitivity of thallium-doped ammonium salts

The main problem in selecting suitable thermoluminescent (TL) materials for fast-neutron dosimetry is finding a material that is both tissue-equivalent and not damaged upon heating. Optically stimulated luminescence (OSL) avoids the need to heat the materials and allows the use of materials with a high content of hydrogen (responsible for 90% of the absorbed dose of fast-neutrons). The choice of studying the ammonium salts for their OSL properties was based on the calculation of their neutron kerma factor. A constant ratio of an ammonium salt's kerma coefficients to the tissue's kerma coefficients (in the fast-neutron range) is a prerequisite for a similar energy response to neutrons, i.e. tissue equivalency. The salts studied are NH4Br and (NH4)2SiF6 both doped with Tl+. This paper describes the OSL properties of Tl(+)-doped NH4Br and (NH4)2SiF6 after exposure to 14.5 MeV neutrons to explore their potential for developing new, tissue-equivalent OSL materials suitable for fast-neutron dosimetry. The relative neutron sensitivity, k, defined as the ratio of the sensitivity of the material to neutrons to its sensitivity to gamma rays, has been determined for 14.5 MeV neutrons and varies between k = 0.15 and k = 0.5. The latter value is a factor 2.5 higher than that found for known TL materials (k < or = 0.2). A drawback of these materials is the fast fading of the OSL signal.

The role of radiolytically generated species in radiation-induced polymerization of vinylbenzyltrimethylammonium chloride (VBT) in aqueous solution: steady-state and pulse radiolysis study

Radiation-induced polymerization of vinylbenzyltrimethylammonium chloride (VBT) in aqueous solution has been investigated by steady-state and pulse radiolysis techniques. The effects of dose, dose rate, monomer concentration, pH, and ambient conditions on steady state polymerization were investigated. The reactions of primary radicals of water radiolysis, such as OH radical, e(-)aq, and H atom, were studied. The reactions of other chemically active species such as O*-, oxidizing radicals such as N3*, Cl2(*-), Br(2*), SO4(*-), and a reducing specie such as CO2(*-) with VBT were also investigated. The reaction of VBT with OH radical and H atom were investigated by formation kinetics and by competition kinetics. The rate constant values for the reaction of OH radical with VBT were 4.7 x 10(9) dm3 mol(-1) s(-1) and 1.7 x 10(10) dm3 mol(-1) s(-1) by formation kinetics and by competition kinetics, respectively. The results indicate that OH radicals undergo electron transfer reactions (resulting in a radical cation) and addition reactions. The hydrated electron reacts with VBT with a rate constant of 1.9 x 10(10) dm3 mol(-1) s(-1) to form an anion. At pH approximately 1, H atom reaction with VBT is diffusion controlled with a rate constant of 5.1 x 10(9) dm3 mol(-1) s(-1) as determined by formation kinetics and 1.7 x 10(10) dm3 mol(-1) s(-1) as determined by competition kinetics. VBT radical anion reacts with VBT at a rate that is almost twice the rate at which VBT radical cation reacts with VBT, indicating anionic initiation of the polymerization of VBT. VBT undergoes very fast steady-state polymerization and dose rate; the presence of efficient radical quenchers such as oxygen and concentration of VBT in the aqueous solution affects the extent of polymerization. Typically, a dose of 4 kGy is sufficient to achieve 80-85% polymerization. The monomer solution shows a drastic increase in the viscosity of the solution, which finally gels to a soft rubbery mass.

Electron paramagnetic resonance evidence of the generation of superoxide (O2.-) and hydroxyl (.OH) radicals by irradiation of a new photodynamic therapy photosensitizer, Victoria Blue BO

Electron paramagnetic resonance (EPR) experiments were performed on Victoria Blue BO, a cationic dye whose photocytotoxicity has been studied against the human leukaemic cell lines K-562 and TF-1. EPR experiments with 2,2,6,6-tetramethyl-4-piperidone and spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide showed that, on illumination in aerated aqueous solution or DL-alpha-dipalmitoylphosphatidylcholine liposomes, photoexcited Victoria Blue BO is unable to generate 1O2, whereas O2.- and .OH are trapped by 5,5-dimethyl-1-pyrroline-N-oxide in the presence or absence of electron donors. The O2.- formed probably leads to the .OH radical, with an efficiency which is increased by electron donors such as FE2+.

Beta irradiation may induce stereoselectivity in the crystallization of optical isomers

A novel approach has been introduced to detect the manifestation of symmetry breaking weak interactions at molecular level. In the racemic conglomerate crystallization of D,L-sodium-ammonium tartrate the effect of 32P irradiation was studied by measuring the weight and optical purity of the crystalline phase as well as the size distribution of the crystallites. The high number of independent experiments (over 1000) permitted statistical analysis of the results. The following observations have been made: 1. Beta irradiation influences the crystallization process, irradiated samples yield more crystalline material. 2. The effect involves presumably crystal seed formation because from the irradiated solutions more and smaller crystallites are formed. 3. The presence of beta particles induces stereoselective crystallization, the crystalline phase shows optical activity characteristic of the "unnatural" L-isomer. 4. The above changes are attributed to the beta irradiation as the magnitude of the effects depends on the amount of added radioactivity. Optically active contaminants are highly unlikely sources of the differences between irradiated and control series. 5. In the absence of 32P the tartrate enantiomers have equal probability to form crystals, i.e., the contribution of mixing of weak interaction into the electromagnetic one is not measurable in this system.

The radiolysis of aqueous ammonium cyanide: compounds of interest to chemical evolution studies

Oxygen-free aqueous solutions of NH4CN (0.1 M, pH9) were exposed to gamma rays from a 60Co source, the mixture of nonvolatile products was fractionated, and the fractions were analyzed. The procedures were chosen to make effective investigations of radiolytic products, and to minimize the contributions of chemical changes which are known to occur in aqueous solution in the absence of ionizing radiation. It has been found that the main constituents are: urea, 25.9%; an oligomer, very likely oligoimine (18.4%); and several fractions (about 50%) which release amino acids on hydrolysis. These fractions differ considerably, as shown by amino acid assay, enzymatic digestion, IR spectra, and biuret reaction. All these tests were found to be positive for two fractions; in two further fractions the enzymatic cleavage was absent, but other tests were positive. Negative enzymatic and biuret tests, and no bands characteristic of amide or peptide, were found for a fraction whose hydrolysate consisted of 55% glycine. Although most of the isolated materials were found to be composite, the results of the analyses were sufficient for getting a reliable over-all picture of the chemical action of the ionizing radiation. The role of free radicals in reactions leading to the formations of radiolytic products was considered.

[Effect of salts and sole of metal oxides on radiochemical changes in carbohydrates and abiogenic amino acid synthesis]

It has been shown that gamma-irradiation of solutions of carbohydrates in the presence of sulfates and metal oxide sols results in oxidative and destructive processes and leads to formation of carbonile compounds, organic acids, H2CO, and a substance with lambda max= =261 nm. With respect to their catalytic effect on carbohydrate changes, the sulfates and metal oxide sols investigated may be arranged into the following order: CuSO4 > > MnSO4=NiSO4 > ZnSO4 > H2O (salt free glucose solution); MoO3 > V2O5 > Al2O3 > > H2O (glucose solution without metal oxide sol). Radiolysis of glucose, mannose and arabinose is affected by the nature of gas saturating the solutions: O2 > Ar > CO2. Ionizing irradiation of solutions of hexoses and pentoses which contain nitrates as the source of nitrogen, results in the formation of amino acids with the chain length from 2 to 6 atoms of carbon (gly, ser, lys, ala, asp, his, tre, val, glu).

On the physical origin of biological handedness

In the racemic conglomerate crystallization of over 1,000 samples of D,L-sodium-ammonium tartrate the effect of 32P beta irradiation on the weight, optical activity, and crystallite size was measured. Both weight and optical activity showed a statistical dependence on the intensity of beta irradiation. The crystallite size is also affected by the presence of 32P. Asymmetric crystals are suggested to have been potential mediators between asymmetric parity violating forces and molecular asymmetry so that stereo-selective prebiotic chemical reactions involving crystals need not be considered 'chance' processes. No measurable difference in the energy content of optical isomers was found. An upper limit for the direct contribution of weak interactions to electromagnetic ones has been calculated. The mechanism of stereoselective crystal seeding by beta particles is discussed.

[Effect of additives on the amination of 2-oxoglutaric acid by gamma-radiation]

The effect of added substances was studied on the yield of glutamic acid produced by gamma-ray irradiation of 2-oxoglutaric acid and ammonia in aqueous solution. The contents of amino acids in the irradiated solutions were determined with amino acids analyzer. Sodium nitrate, allyl alcohol or sodium formate was used as an added substance. The yield of glutamic acid significantly decreased by the addition of nitrate, and it was little affected by the addition of allyl alcohol. In the presence of formate the yield increased from G = 0.4 (2-oxoglutaric acid 0.05M and ammonium hydroxide 2M) to G = 1.1. As a result, it was found that hydrated electron contributes on the formation of glutamic acid, but hydroxyl radical does not. The yield showed a maximum at ca. 0.1 M ammonium hydroxide concentration. These facts indicate that NH2 radical does not contribute to the formation of glutamic acid. As a reaction mechanism, it can be explained that 2-oxoglutaric acid which had been reduced by hydrated electron reacts with ammonia.

[Photochemical formation of pyruvic acid in a solution of acetaldehyde and ammonium nitrate]

It has been demonstrated that UV irradiation of acetaldehyde (2.5%) and ammonium nitrate (1.5%) solutions results in the synthesis of the pyruvic acid (PA). With the increase in the duration of irradiation, the yield of the produced PA decreases which is associated both with its photolysis and with its further transformations, for instance, into amino acids. The results obtained are discussed in relation to abiogenic synthesis of biologically important compounds in prebiological evolution and to possible development of metabolic pathways which are found in contemporary organisms.

Synthesis of a sulfur-containing amino acid under simulated prebiotic conditions

Ultraviolet irradiation of an aqueous solution of ammonium thiocyanate produces the sulfur-containing amino acid methionine. Synthesis of this class of biocompound fills another important gap in development of an overall picture of how prebiological chemistry may have evolved on primitive Earth.