Dynamics and fragmentation of van der Waals clusters: (H2O)n, (CH3OH)n, and (NH3)n upon ionization by a 26.5 eV soft x-ray laser

A tabletop soft x-ray laser is applied for the first time as a high energy photon source for chemical dynamics experiments in the study of water, methanol, and ammonia clusters through time of flight mass spectroscopy. The 26.5 eV/photon laser (pulse time duration of approximately 1 ns) is employed as a single photon ionization source for the detection of these clusters. Only a small fraction of the photon energy is deposited in the cluster for metastable dissociation of cluster ions, and most of it is removed by the ejected electron. Protonated water, methanol, and ammonia clusters dominate the cluster mass spectra. Unprotonated ammonia clusters are observed in the protonated cluster ion size range 2< or =n< or =22. The unimolecular dissociation rate constants for reactions involving loss of one neutral molecule are calculated to be (0.6-2.7)x10(4), (3.6-6.0)x10(3), and (0.8-2.0)x10(4) s(-1) for the protonated water (9< or =n< or =24), methanol (5< or =n< or =10), and ammonia (5< or =n< or =18) clusters, respectively. The temperatures of the neutral clusters are estimated to be between 40 and 200 K for water clusters (10< or =n< or =21), and 50-100 K for methanol clusters (6< or =n< or =10). Products with losses of up to five H atoms are observed in the mass spectrum of the neutral ammonia dimer. Large ammonia clusters (NH(3))(n) (n>3) do not lose more than three H atoms in the photoionization/photodissociation process. For all three cluster systems studied, single photon ionization with a 26.5 eV photon yields near threshold ionization. The temperature of these three cluster systems increases with increasing cluster size over the above-indicated ranges.     

Radiation-induced cationic dimerization and polymerization of styrene in methylene chloride solution. I

Radiation-induced polymerization of styrene in methylene chloride solution or bulk system was investigated to explain the initiation mechanism of cationic polymerization. It was found that high energy radiation produces polymers and dimers. The main dimers were identified as trans-1,2-diphenylcyclobutane, 1-phenyl-1,2,3,4-tetrahydronaphthalene, and 1-phenyl-1,2-dihydronaphthalene. The dimerization procedure was cationic in a pattern similar to that obtained in photoexcited EDA systems. It was shown clearly by product analysis that the bonded dimer cation radical intermediate, which was assumed to be an initiating species of the cationic polymerization, was produced in a radiation-induced polymerization system. The observed polymerization was composed of two types; cationic and radical, the latter initiated by radical species.     

Infrared plus vacuum ultraviolet spectroscopy of neutral and ionic methanol monomers and clusters: new experimental results

We present new observations of the infrared (IR) spectrum of neutral methanol and neutral and protonated methanol clusters employing IR plus vacuum ultraviolet (vuv) spectroscopic techniques. The tunable IR light covers the energy ranges of 2500-4500 cm(-1) and 5000-7500 cm(-1). The CH and OH fundamental stretch modes, the OH overtone mode, and combination bands are identified in the vibrational spectrum of supersonic expansion cooled methanol (2500-7500 cm(-1)). Cluster size selected IR plus vuv nonresonant infrared ion-dip infrared spectra of neutral methanol clusters, (CH(3)OH)(n) (n=2,[ellipsis (horizontal)],8), demonstrate that the methanol dimer has free and bonded OH stretch features, while clusters larger than the dimer display only hydrogen bonded OH stretch features. CH stretch mode spectra do not change with cluster size. These results suggest that all clusters larger than the dimer have a cyclic structure with OH groups involved in hydrogen bonding. CH groups are apparently not part of this cyclic binding network. Studies of protonated methanol cluster ions (CH(3)OH)(n)H(+) n=1,[ellipsis (horizontal)],7 are performed by size selected vuv plus IR photodissociation spectroscopy in the OH and CH stretch regions. Energies of the free and hydrogen bonded OH stretches exhibit blueshifts with increasing n, and these two modes converge to approximately 3670 and 3400 cm(-1) at cluster size n=7, respectively.     

Pulse radiolysis study on the initial processes of radiation-induced cationic polymerization of styrene and α-methylstyrene

Initial processes of radiation-induced cationic polymerization of styrene and α-methylstyrene have been studied by means of microsecond pulse radiolysis. For styrene, absorption bands caused by the monomer cation radical St⁺? appear at 630 and 350 nm in a mixture of isopentane and n-butyl chloride at about ?165°C. In parallel with the decay of St⁺?, three absorption bands appear in the near-infrared (IR) region, and at 600 and 450 nm. The IR and 600 nm bands are assigned to the associated dimer cation radical St₂⁺?, and the 450 nm band to the bonded dimer cation radical St-St⁺?. The kinetic behavior of these species shows that reaction of St⁺? with styrene monomer forms both St₂⁺? and St-St⁺?. With the decay of St-St⁺?, another absorption band appears at 340 nm, and the lifetime of this band is relatively long. The 340 nm band may be due to carbonium ions of the growing polystyrene. For α-methylstyrene, the monomer cation radical (at 690 and 350 nm), the associated dimer cation radical (in the near-IR region and at 620 nm) and the bonded dimer cation radical (at 480 nm) behave in a manner similar to that of the corresponding styrene species. The absorption band caused by carbonium ions of growing poly(α-methylstyrene) appears at 340 nm.     

Size-restricted proton transfer within toluene-methanol cluster ions

To understand the interaction between toluene and methanol, the chemical reactivity of [(C6H5CH3)(CH3OH) n=1-7](+) cluster ions has been investigated via tandem quadrupole mass spectrometry and through calculations. Collision Induced Dissociation (CID) experiments show that the dissociated intracluster proton transfer reaction from the toluene cation to methanol clusters, forming protonated methanol clusters, only occurs for n = 2-4. For n = 5-7, CID spectra reveal that these larger clusters have to sequentially lose methanol monomers until they reach n = 4 to initiate the deprotonation of the toluene cation. Metastable decay data indicate that for n = 3 and n = 4 (CH3OH)3H(+) is the preferred fragment ion. The calculational results reveal that both the gross proton affinity of the methanol subcluster and the structure of the cluster itself play an important role in driving this proton transfer reaction. When n = 3, the cooperative effect of the methanols in the subcluster provides the most important contribution to allow the intracluster proton transfer reaction to occur with little or no energy barrier. As n >or= 4, the methanol subcluster is able to form ring structures to stabilize the cluster structures so that direct proton transfer is not a favored process. The preferred reaction product, the (CH3OH)3H(+) cluster ion, indicates that this size-restricted reaction is driven by both the proton affinity and the enhanced stability of the resulting product.     

The exchange coupling in Cr3On (n = 0-3) clusters

The structures of neutral and cationic Cr3On0,+ (n = 0-3) clusters are calculated with density functional theory employing the BLYP and BP86 functionals. Gas-phase CrnOm clusters are produced by laser vaporization and characterized with time-of-flight mass spectrometry. The ionization energies of Cr3On (n = 0-2) are determined with threshold photoionization spectroscopy using tunable laser light in the 4.5-5.60 eV range. On the basis of a comparison between experimental and calculated ionization energies, ground-state structures were assigned. The influence of sequential addition of oxygen on the exchange coupling between the chromium atoms is investigated providing evidence for enhanced ferromagnetic coupling of chromium atoms in both the neutral and cationic Cr3On0,+ clusters. This evidence of superexchange interaction through oxygen extends earlier ideas to control the magnetic interactions in the chromium dimer via chemical reactions with oxygen toward larger chromium clusters.     

Compatibility between methanol and water in the three-dimensional cage formation of large-sized protonated methanol-water mixed clusters

Infrared spectra of large-sized protonated methanol-water mixed clusters, H(+)(MeOH)(m)(H(2)O)(n) (m=1-4, n=4-22), were measured in the OH stretch region. The free OH stretch bands of the water moiety converged to a single peak due to the three-coordinated sites at the sizes of m+n=21, which is the magic number of the protonated water cluster. This is a spectroscopic signature for the formation of the three-dimensional cage structure in the mixed cluster, and it demonstrates the compatibility of a small number of methanol molecules with water in the hydrogen-bonded cage formation. Density functional theory calculations were carried out to examine the relative stability and structures of selected isomers of the mixed clusters. The calculation results supported the microscopic compatibility of methanol and water in the hydrogen-bonded cage development. The authors also found that in the magic number clusters, the surface protonated sites are energetically favored over their internal counterparts and the excess proton prefers to take the form of H(3)O(+) despite the fact that the proton affinity of methanol is greater than that of water.     

Imidazoline derivatives as promising cationic emulsifiers for styrene heterophase polymerization

The colloidochemical properties of new cationic surfactants synthesized from fatty acids of palm oil and diethylenetriamine are first studied. It is found that, at solution pH below 6.0, the examined surfactants exist mainly as salts formed from protonated surfactant molecules and residues of strong acids, e.g., hydrochloric acid. In the pH range above 7.0, the protonated and nonprotonated forms of the surfactants are at equilibrium, which shifts to the nonprotonated form with an increase in pH. The analysis of interfacial tension isotherms shows that the minimum values of the interfacial tension are achieved at pH 7.0 when the concentrations of the protonated and nonprotonated forms of surfactant molecules are equal. New cationic surfactants are used as emulsifiers in emulsion polymerization of styrene. It is found that stable polystyrene latexes with narrow particle size distributions and high positive ζ potentials (as high as +68.4 mV) can be obtained at styrene concentration in an initial emulsion of 25 vol % and surfactant concentration in an aqueous phase of 2 wt %. A hydrogen peroxide-iron(II) salt redox system is used as an initiator of polymerization at component concentrations equal to 5 and 0.05 wt % of the monomer, respectively.     

Vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters

In this work, we report on the vacuum-ultraviolet (VUV) photoionization of small methanol and methanol-water clusters. Clusters of methanol with water are generated via co-expansion of the gas phase constituents in a continuous supersonic jet expansion of methanol and water seeded in Ar. The resulting clusters are investigated by single photon ionization with tunable vacuum-ultraviolet synchrotron radiation and mass analyzed using reflectron mass spectrometry. Protonated methanol clusters of the form (CH3OH)nH(+) (n = 1-12) dominate the mass spectrum below the ionization energy of the methanol monomer. With an increase in water concentration, small amounts of mixed clusters of the form (CH3OH)n(H2O)H(+) (n = 2-11) are detected. The only unprotonated species observed in this work are the methanol monomer and dimer. Appearance energies are obtained from the photoionization efficiency (PIE) curves for CH3OH(+), (CH3OH)2(+), (CH3OH)nH(+) (n = 1-9), and (CH3OH)n(H2O)H(+) (n = 2-9) as a function of photon energy. With an increase in the water content in the molecular beam, there is an enhancement of photoionization intensity for the methanol dimer and protonated methanol monomer at threshold. These results are compared and contrasted to previous experimental observations.     

Production of methyl-oxonium ion and its complexes in the core-excited (HC(O)OCH3)n clusters: H/H+ transfer from the alpha carbonyl

Dissociation of free methyl-formate (MF), HC(O)OCH3, and its clusters (MF)n, (HC(O)OCH3)n, induced by core-level excitation was studied near the oxygen K edge by time-of-flight fragment-mass spectroscopy. Besides the protonated clusters, (MF)nH+ with n < or = 15, we identified the production for another series of (MF)mCH3OH2+ with m < or = 14 as well as methyl-oxonium ion, CH3OH2+, characteristic of hydrogen transfer reactions in the cationic clusters. Here; specifically labeled methyl-formate-d (MFD), DC(O)OCH3 was also used to examine the core-excited dissociation mechanisms. Deuterium-labeled experiments indicated that MFD+ with low internal energies, partially generated after the core excitation, produces CH3OD+ via a site-specific deuterium transfer from the alpha carbonyl in the molecular cation and that CH3OD2+ can be formed via the successive transfer of another deuterium from the neighbor molecule in the clusters. The deuteron (proton) transfer was also found to take place preferentially from the alpha carbonyl of the neighbor molecule for the production of deuteronated (MFD)nD+, (protonated (MF)nH+), clusters. The minimal energy requirement paths were examined for dimer (MF)2+ cation to support the present dissociation mechanisms of core-excited (MF)n clusters using ab initio molecular-orbital calculations.     

Experimental and computational study of the Zn(n)S(n) and Zn(n)S(n)+ clusters

Zinc sulfide clusters produced by direct laser ablation and analyzed in a time-of-flight mass-spectrometer, showed evidence that clusters composed of 3, 6, and 13 monomer units were ultrastable. The geometry and energies of neutral and positively charged Zn(n)S(n) clusters, up to n = 16, were obtained computationally at the B3LYP/6-311+G level of theory with the assistance of an algorithm to generate all possible structures having predefined constraints. Small neutral and positive clusters were found to have planar geometries, neutral three-dimensional clusters have the geometry of closed-cage polyhedra, and cationic three-dimensional clusters have structures with a pair of two-coordinated atoms. Physical properties of the clusters as a function of size are reported. The relative stability of the positive stoichiometric clusters provides a thermodynamic rationale for the experimental results.     

Density-functional study of small neutral and cationic bismuth clusters Bi(n) and Bi(n) (+)(n=2-24)

Density-functional theory with scalar-relativistic pseudopotential and a generalized gradient correction is used to calculate the neutral and cationic Bi(n) clusters (2< or =n< or =24), with the aim to elucidate their structural evolution, relative stability, and magnetic property. The structures of neutral Bi clusters are found to be similar to that of other group-V elemental clusters, with the extensively studied sizes of n=4 and 8 having a tetrahedron and wedgelike structure, respectively. Generally, larger Bi clusters consist of a combination of several stable units of Bi(4), Bi(6), and Bi(8), and they have a tendency to form an amorphous structure with the increase of cluster sizes. The curves of second order energy difference exhibit strong odd-even alternations for both neutral and cationic Bi clusters, indicating that even-atom (odd-atom) sizes are relatively stable in neutral clusters (cationic clusters). The calculated magnetic moments are 1micro (B) for odd-atom clusters and zero for even-atom clusters. We propose that the difference in magnetism between experiment and theory can be greatly improved by considering the orbital contribution. The calculated fragmentation behavior agrees well with the experiment, and for each cationic cluster the dissociation into Bi(4) or Bi(7) (+) subclusters confirms the special stability of Bi(4) and Bi(7) (+). Moreover, the bond orders and the gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital show that small Bi clusters would prefer semiconductor characters to metallicity.     

Theoretical study of mixed silicon-lithium clusters Si(n)Li(p)(+) (n=1-6, p=1-2)

Theoretical study on the structures of neutral and singly charged Si(n)Li(p)((+)) (n=1-6, p=1-2) clusters have been carried out in the framework of the density functional theory (DFT) with the B3LYP functional. The structures of the neutral Si(n)Li(p) and cationic Si(n)Li(p)(+) clusters are found to keep the frame of the corresponding Si(n), Li species being adsorbed at the surface. The localization of the lithium cation is not the same one as that of the neutral atom. The Li(+) ion is preferentially located on a Si atom, while the Li atom is preferentially attached at a bridge site. A clear parallelism between the structures of Si(n)Na(p) and those of Si(n)Li(p) appears. The population analysis show that the electronic structure of Si(n)Li(p) can be described as Si(n)(p)(-)+pLi(+) for the small sizes considered. Vertical and adiabatic ionization potentials, adsorption energies, as well as electric dipole moments and static dipolar polarizabilities, are calculated for each considered isomer of neutral species.     

Vacuum ultraviolet (VUV) photoionization of small water clusters

Tunable vacuum ultraviolet (VUV) photoionization studies of water clusters are performed using 10-14 eV synchrotron radiation and analyzed by reflectron time-of-flight (TOF) mass spectrometry. Photoionization efficiency (PIE) curves for protonated water clusters (H2O)(n)H+ are measured with 50 meV energy resolution. The appearance energies of a series of protonated water clusters are determined from the photoionization threshold for clusters composed of up to 79 molecules. These appearance energies represent an upper limit of the adiabatic ionization energy of the corresponding parent neutral water cluster in the supersonic molecular beam. The experimental results show a sharp drop in the appearance energy for the small neutral water clusters (from 12.62 +/- 0.05 to 10.94 +/- 0.06 eV, for H2O and (H2O)4, respectively), followed by a gradual decrease for clusters up to (H2O)23 converging to a value of 10.6 eV (+/-0.2 eV). The dissociation energy to remove a water molecule from the corresponding neutral water cluster is derived through thermodynamic cycles utilizing the dissociation energies of protonated water clusters reported previously in the literature. The experimental results show a gradual decrease of the dissociation energy for removal of one water molecule for small neutral water clusters (3 相似文献   

Size resolved infrared spectroscopy of Na(CH3OH)n (n = 4-7) clusters in the OH stretching region: unravelling the interaction of methanol clusters with a sodium atom and the emergence of the solvated electron

Size resolved IR action spectra of neutral sodium doped methanol clusters have been measured using IR excitation modulated photoionisation mass spectroscopy. The Na(CH(3)OH)(n) clusters were generated in a supersonic He seeded expansion of methanol by subsequent Na doping in a pick-up cell. A combined analysis of IR action spectra, IP evolutions and harmonic predictions of IR spectra (using density functional theory) of the most stable structures revealed that for n = 4, 5 structures with an exterior Na atom showing high ionisation potentials (IPs) of ~4 eV dominate, while for n = 6, 7 clusters with lower IPs (~3.2 eV) featuring fully solvated Na atoms and solvated electrons emerge and dominate the IR action spectra. For n = 4 simulations of photoionisation spectra using an ab initio MD approach confirm the dominance of exterior structures and explain the previously reported appearance IP of 3.48 eV by small fractions of clusters with partly solvated Na atoms. Only for this cluster size a shift in the isomer composition with cluster temperature has been observed, which may be related to kinetic stabilisation of less Na solvated clusters at low temperatures. Features of slow fragmentation dynamics of cationic Na(+)(CH(3)OH)(6) clusters have been observed for the photoionisation near the adiabatic limit. This finding points to the relevance of previously proposed non-vertical photoionisation dynamics of this system.     

Experimental and theoretical study of the microsolvation of sodium atoms in methanol clusters: differences and similarities to sodium-water and sodium-ammonia

Methanol clusters are generated in a continuous He-seeded supersonic expansion and doped with sodium atoms in a pick-up cell. By this method, clusters of the type Na(CH(3)OH)(n) are formed and subsequently photoionized by applying a tunable dye-laser system. The microsolvation process of the Na 3s electron is studied by determining the ionization potentials (IPs) of these clusters size-selectively for n = 2-40. A decrease is found from n = 2 to 6 and a constant value of 3.19 +/- 0.07 eV for n = 6-40. The experimentally-determined ionization potentials are compared with ionization potentials derived from quantum-chemical calculations, assuming limiting vertical and adiabatic processes. In the first case, energy differences are calculated between the neutral and the ionized cationic clusters of the same geometry. In the second case, the ionized clusters are used in their optimized relaxed geometry. These energy differences and relative stabilities of isomeric clusters vary significantly with the applied quantum-chemical method (B3LYP or MP2). The comparison with the experiment for n = 2-7 reveals strong variations of the ionization potential with the cluster structure indicating that structural diversity and non-vertical pathways give significant signal contributions at the threshold. Based on these findings, a possible explanation for the remarkable difference in IP evolutions of methanol or water and ammonia is presented: for methanol and water a rather localized surface or semi-internal Na 3s electron is excited to either high Rydberg or more localized states below the vertical ionization threshold. This excitation is followed by a local structural relaxation that couples to an autoionization process. For small clusters with n < 6 for methanol and n < 4 for water the addition of solvent molecules leads to larger solvent-metal-ion interaction energies, which consequently lead to lower ionization thresholds. For n = 6 (methanol) and n = 4 (water) this effect comes to a halt, which may be connected with the completion of the first cationic solvation shell limiting the release of local relaxation energy. For Na(NH(3))(n), a largely delocalized and internal electron is excited to autoionizing electronic states, a process that is no longer local and consequently may depend on cluster size up to very large n.     

Differences in structure, energy, and spectrum between neutral, protonated, and deprotonated phenol dimers: comparison of various density functionals with ab initio theory

We have carried out extensive calculations for neutral, cationic protonated, anionic deprotonated phenol dimers. The structures and energetics of this system are determined by the delicate competition between H-bonding, H-π interaction and π-π interaction. Thus, the structures, binding energies and frequencies of the dimers are studied by using a variety of functionals of density functional theory (DFT) and M?ller-Plesset second order perturbation theory (MP2) with medium and extended basis sets. The binding energies are compared with those of highly reliable coupled cluster theory with single, double, and perturbative triple excitations (CCSD(T)) at the complete basis set (CBS) limit. The neutral phenol dimer is unique in the sense that its experimental rotational constants have been measured. The geometry of the neutral phenol dimer is governed by the hydrogen bond formed by two hydroxyl groups and the H-π interaction between two aromatic rings, while the structure of the protonated/deprotonated phenol dimers is additionally governed by the electrostatic and induction effects due to the short strong hydrogen bond (SSHB) and the charges populated in the aromatic rings in the ionic systems. Our salient finding is the substantial differences in structure between neutral, protonated, and deprotonated phenol dimers. This is because the neutral dimer involves in both H(π)···O and H(π)···π interactions, the protonated dimer involves in H(π)···π interactions, and the deprotonated dimer involves in a strong H(π)···O interaction. It is important to compare the reliability of diverse computational approaches employed in quantum chemistry on the basis of the calculational results of this system. MP2 calculations using a small cc-pVDZ basis set give reasonable structures, but those using extended basis sets predict wrong π-stacked structures due to the overestimation of the dispersion energies of the π-π interactions. A few new DFT functionals with the empirical dispersion give reliable results consistent with the CCSD(T)/CBS results. The binding energies of the neutral, cationic protonated, and anionic deprotonated phenol dimers are estimated to be more than 28.5, 118.2, and 118.3 kJ mol(-1), respectively. The energy components of the intermolecular interactions for the neutral, protonated and deprotonated dimers are analyzed.     

IR plus vacuum ultraviolet spectroscopy of neutral and ionic organic acid monomers and clusters: propanoic acid

The vibrational spectrum of molecular propanoic acid, cooled in a supersonic expansion, in the region of 2500 to 7500 cm(-1) is obtained employing infrared plus vacuum ultraviolet nonresonant ionization detected spectroscopy. The fundamental and first overtone of the CH and OH stretch modes of cold propanoic acid molecules can be identified in the spectrum. Propanoic acid neutral and ionic clusters are also studied employing nonresonant ion dip and photodissociation spectroscopic techniques, respectively. For the neutral dimer, a sequence of features observed at ca. 2500-2700 cm(-1) can be assigned as combination bands of low frequency modes with the COH bending overtone; these features characterize the cyclic dimer ring structure. IR spectra of the larger neutral clusters n=3, 4, 5 indicate that they also have cyclic structures in which the OH groups are engaged in the cluster hydrogen bonding network. The CH groups are not involved in this hydrogen bonding structure. Free OH features are observed for the protonated ion clusters (C(2)H(5)COOH)(n)H(+), n=1,...,5, indicating that at least one OH group of these cluster ions is not involved in the cluster hydrogen bonding network. A comparison of the results for four hydrogen bonding neutral and ionic clusters (CH(3)OH, C(2)H(5)OH, CH(3)COOH, and C(2)H(5)COOH) is presented and discussed.     

Theoretical study of Al(n) and Al(n)O (n = 2-10) clusters

The stable structures, energies, and electronic properties of neutral, cationic, and anionic clusters of Al(n) (n = 2-10) are studied systematically at the B3LYP/6-311G(2d) level. We find that our optimized structures of Al5(+), Al9(+), Al9(-), Al10, Al10(+), and Al10(-) clusters are more stable than the corresponding ones proposed in previous literature reports. For the studied neutral aluminum clusters, our results show that the stability has an odd/even alternation phenomenon. We also find that the Al3, Al7, Al7(+), and Al7(-) structures are more stable than their neighbors according to their binding energies. For Al7(+) with a special stability, the nucleus-independent chemical shifts and resonance energies are calculated to evaluate its aromaticity. In addition, we present results on hardness, ionization potential, and electron detachment energy. On the basis of the stable structures of the neutral Al(n) (n = 2-10) clusters, the Al(n)O (n = 2-10) clusters are further investigated at the B3LYP/6-311G(2d), and the lowest-energy structures are searched. The structures show that oxygen tends to either be absorbed at the surface of the aluminum clusters or be inserted between Al atoms to form an Al(n-1)OAl motif, of which the Al(n-1) part retains the stable structure of pure aluminum clusters.     

Interaction of guanine, its anions, and radicals with lysine in different charge states

Modification in DNA or protein structure can severely affect DNA-protein interactions and the functioning of biological systems. Some new insights into radiation-induced effects of guanine-lysine interactions have been obtained here by theoretical investigations. Geometries of zwitterionic and non-zwitterionic lysine in different charge states (neutral, radical cation, and protonated cation) were optimized employing the B3LYP/6-31G** and B3LYP/AUG-cc-pVDZ levels of hybrid density functional theory (DFT) and using the second-order M?ller-Plesset perturbation theory along with the 6-31G** basis set. In the case of neutral lysine in the gas phase, no zwitterionic structure was obtained. The non-zwitterionic structures of lysine in radical and protonated cationic forms are appreciably more stable than the corresponding zwitterionic structures in the gas phase as obtained at all levels of theory employed here. Binding of guanine and different dehydrogenated guanine radicals with lysine in different charge states was studied at the B3LYP/6-31G** level of DFT. When guanine makes a complex with the lysine radical cation, large amounts of spin and positive charge densities are transferred from the lysine radical cation to guanine and the guanine is thus converted from its normal form to the radical cationic form. Complexation of the lysine radical cation with the H1-hydrogen-abstracted guanine radical leads to CO2 liberation and proton transfer from lysine. These results are compared with the available experimental ones.