The terpenes α-(+)-pinene, and α-(−)pinene have been radiolyzed at radiation doses of 150, 300 and 600 kGy. The radiolyzed
samples have been analyzed by FT-IR spectroscopy and polarimetry. Both α-(+)-, α-(−)-pinenes show a linear trend to radioracemization
as a function of the radiation dose administered ≈2.5·10−3 [α]D/kGy. The solvent fractionation and the liquid chromatographic analysis (HPLC) of the radiolyzed samples shows that both α-pinene
enantiomers produce ocimene and dipentene together with minor quantities of other products and a resin. The kinetics of α-pinene
decomposition under radiolytic conditions can be described by a pseudofirst order rate constant k∼5.3·10−7s−1 while the radiation chemical yield for the same reaction has a G = 5.0 molecules/100 eV, so that about 30% of the original α-pinene is converted into other products at 600 kGy.
The degradation of a mixture of 18 different polycyclic aromatic hydrocarbons (PAHs) has been studied in acetonitrile solution
by usingg-radiation at radiation doses of 100, 200 and 300 kGy. The mixture of radiolyzed PAHs was analyzed by liquid chromatography
(HPLC) using a diode array detector. Radiolysis at 100 kGy total dose is already sufficient to cause the complete disappearance
of all PAHs with the exception of fluorene and crysene which still survive in small amounts. They are known to be among the
most radiation-resistant PAHs and can be completely eliminated from the radiolyzed solution by a treatment with ozone. Alternatively
higher radiation dose (200 kGy) is needed to eliminate fluorene and crysene completely from the acetonitrile solution. PAHs
can be degraded completely with an excess of ozone but the distribution of products is of course different from that obtained
by radiolysis and radiolysis followed by ozonolysis.
The radiolysis of β(−)pinene has been studied at five different radiation dose, namely at 50, 100, 150, 300 and 600 kGy with
a dose rate of 2.2 kGy/h. At lower radiation dose, β(−)pinene showed a reduction of the optical activity, hence, the expected
radioracemization appeared predominant. At higher radiation dose, an opposite and unexpected trend was observed: the optical
activity increased almost linearly with the radiation dose. The increase of [α]D of radiolyzed β(−)pinene was due to the formation oligomers, mainly a dimer and/or a trimer of β(−)pinene which remain soluble
in the monomer but which displayed a higher optical activity than the starting monomer, contributing to the increase in the
specific optical rotation. Simultaneously to the formation of the dimer/trimer the radiolysis of β(−)pinene induced also its
polymerization into a poly(β(−)pinene) resin which was insoluble in the monomer and which was characterized by a high structural
order and by the preservation of the chiral centers so that it showed an enhanced specific optical rotation which is ≈2 times
that of the monomer. It is shown that poly(β(−)pinene) radiopolymer can be easily racemized in presence of a Friedel-Crafts
catalyst. The kinetics of β(−)pinene radiation-induced oligomerization and polymerization can be described by a pseudofirst
order rate constant k = 1.9·10−7·s−1. The radiation chemical yield for the same reaction is G = 1.93·10−6 mol/J. The work shows that also the radiation-induced polymerization of chiral monomers may be a tool for the preservation
and amplification of the optical activity of the monomer with implications for abiotic mechanisms of chiral amplification.
A relatively heavy petroleum fraction called distillate aromatic extract (DAE) which has been proposed to be the carrier of the emission bands of certain astronomical objects like protoplanetary nebulae (PPNe) and the so-called unidentified infrared bands (UIBs), has been radiolyzed with -radiation to a total dose of 1 MGy. The stability of DAE toward radiation was assessed by FT-IR and electronic spectroscopy. The gases produced during radiolysis have been identified by GC. They were essentially H2 and CH4. A certain degree of crosslinking has been verified on the radiation-processed material by measuring the hexane insoluble fraction of DAE, which increased dramatically after the radiation treatment. Further analyses were conducted using high performance liquid chromatography (HPLC) on the radiation processed sample in comparison to the pristine sample.
Anthracite coal and oil bitumen were submitted to γ-radiation at a total dose of 1 MGy and the radiation-processed samples
were studied by FT-IR spectroscopy, thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The coal samples
were studied also by TGA coupled with FT-IR spectroscopy of the evolved gases. Thermal analysis has revealed a completely
different behavior of the radiolyzed samples in comparison to the unirradiated samples. Both for coal and bitumen significantly
less volatile fraction was released during the TGA and in both cases a significant increase in the amount of carbon coke produced
at 800-900 °C was observed. The radiation processed bitumen increased significantly its ethyl acetate insolubles content.
These results were interpreted in terms of extensive crosslinking and coalification of the samples under the action of γ-radiation.
The results of this study have been applied to the carbonization process of terrestrial sedimentary organic matter which is
commonly attributed to the action of heat flux from the depth of the Earth but which may be also due to the action of natural
radiation. Other application of the results of the present study is to the complex organic matter present on the surfaces
of comets and meteorites. This complex matter was formed by exposure of simple precursors to a field of high energy radiation
for millions or billions of years and is consequently transformed into coal-like and bitumen-like matter. The same arguments
apply to the carbon grains present in the interstellar and circumstellar medium.
Three isomeric chiral terpenes, R(+)-limonene, S(-)-limonene and R(-)-a-phellandrene were γ-radiolyzed in sealed vials at
room temperature with a total radiation dose of 317 kGy. The radiolyzed samples were analyzed by FT-IR, electronic absorption
spectroscopy, liquid chromatography using a diode-array detector (HPLC-DAD) and by polarimetry. Despite a relatively high
radiation dose used, all the chiral molecules selected have shown a low radioracemization rate. This fact and the role played
by the impurities in the selective radio-degradation of one of the two enantiomers has been discussed in the context of the
origin of chirality in prebiotic molecules and the chirality enhancement in a prebiotic world. The results were also discussed
in the frame of the radiosterilization technique of chiral drugs, perfumes and food components.
Triazines are a class of molecules which have been found in meteorites such as Orgueil meteorite. Despite their poor resistance
to UV radiation, these molecules survived millions of years inside a meteorite. The present work is dedicated to the examination
of the radiation resistance of the simplest sym-triazine: 1,3,5-triazine. The crystals of this molecule have been irradiated
with γ-radiation at 50 and 350 kGy and were studied by electronic absorption spectroscopy, liquid chromatography, FT-IR spectroscopy
and differential scanning calorimetry (DSC). All the data suggest the relatively low stability of this molecule to high energy
radiation. The resulting products from radiolysis are formamidine together with triazine dimers and oligomers. Other radiolysis
products are H2, CH4, HCN and other gases.
Isoprene polymerizes under the action of γ-radiation from a 60Co source yielding a low molecular weight polyisoprene which remains soluble in the unreacted monomer. The electronic absorption
spectrum of polyisoprene oligomer in isoprene monomer has been explained using squalene, a polyisoprene hexamer, as model
compound. The radiation chemical yield for polyisoprene formation has been estimated from both gravimetric and spectrophotometric
data pertaining the amount of polymer formed. An average G value of 35 molecules/100 eV has been determined suggesting that the polymerization mechanism involves free radicals. The
chemical structure of the resulting polyisoprene radio-oligomer has been determined by FT-IR spectroscopy and found identical
to that of a reference polyisoprene sample prepared by a chemically-initiated free radical polymerization process. The structure
determination by FT-IR spectroscopy has been reported in detail.
Authors:F. Cataldo, O. Ursini, P. Ragni, and A. Rosati
Poly(dimethylbutadiene) (PDMB) was synthesized through the inclusion polymerization technique, by γ-irradiation of a clathrate
of 2,3-dimethyl-1,3-butadiene in deoxycholic acid (DOCA) at 75, 150, 320 and 430 kGy. The resulting inclusion complexes PDMB@DOCA
were studied by FTIR spectroscopy and by thermal analysis (DTA, TGA and DTG). Pure PDMB was isolated by extracting the complex
PDMB@DOCA with ethanol. The best sample in terms of purity was that prepared at 75 kGy, while the other samples prepared at
higher doses suffered of DOCA grafting on PDMB chains. Pure PDMB isolated from PDMB@DOCA complex was studied by FT-IR spectroscopy
and by thermal analysis in comparison to a reference highly crystalline and ≈=100% trans-1,4-PDMB prepared by inclusion polymerization
in thiourea and in comparison to PDMB prepared by emulsion polymerization. A lower degree of regularity and crystallinity
has been found on the PDMB sample prepared as inclusion compound in DOCA in comparison to the reference PDMB obtained by inclusion
polymerization in thiourea.
Authors:F. Cataldo, E. Lilla, O. Ursini, and G. Angelini
C60 fullerene was radiolyzed in toluene solution both in presence of air and in vacuum at four different radiation doses 12,
24, 36, 48 and 96 kGy. Clear evidences of the addition of benzyl radicals to the fullerene cage derive from FT-IR and C13-NMR spectra of the reaction product. In presence of air the interference of oxygen is evident in the FT-IR spectra and from
the elemental analysis. A detailed analysis of the kinetics of the multiple addition of benzyl radicals to the fullerene cage
was made spectrophotometrically with the determination of the addition rate constants at the each addition step and the average
number of benzyl groups added to the fullerene cage as function of the radiation dose.