Studying the signaling role of 2-oxoglutaric acid using analogs that mimic the ketone and ketal forms of 2-oxoglutaric acid

2-Oxoglutaric acid (2-OG), a Krebs cycle intermediate, is a signaling molecule in many organisms. To determine which form of 2-OG, the ketone or the ketal form, is responsible for its signaling function, we have synthesized and characterized various 2-OG analogs. Only 2-methylenepentanedioic acid (2-MPA), which resembles closely the ketone form of 2-OG, is able to elicit cell responses in the cyanobacterium Anabaena by inducing nitrogen-fixing cells called heterocysts. None of the analogs mimicking the ketal form of 2-OG are able to induce heterocysts because none of them are able to interact with NtcA, a 2-OG sensor. NtcA interacts with 2-MPA and 2-OG in a similar manner, and it is necessary for heterocyst differentiation induced by 2-MPA. Therefore, it is primarily the ketone form that is responsible for the signaling role of 2-OG in Anabaena.     

Evidence from ESR studies for [Co(eta-C2H4)3] produced at 77 K in a rotating cryostat

Co atoms were reacted with ethene at 77 K and the paramagnetic products studied by electron spin resonance (ESR) at X- and K-bands. The ESR spectra of the major product at both frequencies showed eight cobalt multiplets (ICo=7/2) indicating a mono-cobalt complex. The spectra have orthorhombic g and cobalt hyperfine tensors and were simulated by the parameters; g1=2.284, g2=2.0027, g3=2.1527; A1<-25 MHz, A2=-109 MHz, A3=-198 MHz. Proton and 13C (1% natural abundance) hyperfine couplings were lower than the line widths (<2 MHz) indicating less than 0.5 spin transfer to the ethene ligands. We assigned the spectrum to a Jahn-Teller-distorted planar trigonal mono-cobalt tris-ethene [Co(eta-C2H4)3] complex in C2v symmetry. The SOMO is either a 3dx2-y2 (2a1) orbital in a T-geometry or a 3dxy (b1) orbital in a Y-geometry but there is only a spin density, a2, of 0.30 in these d orbitals. The spin deficiency of 0.70 is attributed to two factors; spin transfer from the Co to ethene pi/pi* orbitals and a 4p orbital contribution, b2, to the SOMO. Calculations of a2 and b2 have been made at three levels of spin transfer, theta. At theta=0.00a2 is 0.23 and b2 is 0.78, at theta=0.25a2 is 0.25 and b2 is 0.52 and at theta=0.50a2 is 0.28 and b2 is 0.23. The other possible assignment to a mono-cobalt bis-ethene complex [Co(eta-C2H4)2] cannot be discounted from the ESR data alone but is considered unlikely on other grounds. The complex is stable up to approximately 220 K indicating a barrier to decomposition of approximately 50 kJ Mol-1     

Oxygen measurement via phosphorescence: reaction of sodium dithionite with dissolved oxygen

A homemade instrument for the measurement of oxygen concentration in aqueous solutions measures the decay rate of the phosphorescence of a Pd-porphyrin complex (phosphor) dissolved in the solution, which is flashed every 0.1 s with 630 nm light. The concentration of O2 is a linear function of the decay rate. The instrument is used to study the reaction of dithionite (S2O42-) with O2 at 25 degrees C and 37 degrees C. It is found that the ratio of dithionite to oxygen consumed in the reaction is 1.2 +/- 0.2 at 25 degrees C and 1.7 +/- 0.1 at 37 degrees C, suggesting a temperature-dependent stoichiometry. At both temperatures, the initial rate of O2 consumption, -d[O2]/dt, is found to be 1/2 order in S2O42- and first order in O2. This finding is consistent with a previously proposed mechanism: S2O42- <--> 2SO2- comes to a rapid equilibrium, and SO2- reacts with O2 in the rate-determining step.     

Co—MgO催化剂上NO—程序升温表面反应和NO—CH4反应

ＮＯ，程序升温表面反应（ＴＰＳＲ），ＮＯ－ＣＨ４反应，Ｃｏ－ＭｇＯ     

Completion of the series of M2(hpp)4Cl2 compounds from W to Pt: the W, Os, and Pt compounds

The series of M2(hpp)4Cl2 complexes (hpp is the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine) from M = W to M = Pt has been completed by the preparation and characterization of those with M = W, Os, and Pt. W(hpp)4Cl2 (1) has a W-W distance of 2.250(2) A, is diamagnetic, and can be assigned a W-W triple bond based on a sigma 2 pi 4 electron configuration. Os2(hpp)4Cl2 (2) has an Os-Os distance of 2.379(2) A and displays a temperature-independent paramagnetism. It can be assigned a sigma 2 pi 4 delta 2 delta*2 configuration. Pt2(hpp)4Cl2 has a Pt-Pt distance of 2.440(1) A and is diamagnetic. A bond order of 1, based on a configuration in which only the sigma* orbital is empty, is consistent with these data.     

A family of vanadate esters of monoionized and diionized aromatic 1,2-diols: synthesis,structure, and redox activity

The concerned diols (general abbreviation, H(2)L) are catechol (H(2)L(1)) and its 3,5-Bu(t)(2) derivative (H(2)L(2)). Esters of the type VO(xsal)(HL), 2, are obtained by reacting H(2)L with VO(xsal)(H(2)O) or VO(xsal)(OMe)(HOMe), where xsal(2-) is the diionized salicylaldimine of glycine (x = g), L-alanine (x = a), or L-valine (x = v). The reaction of VO(acac)(2) with H(2)L and the salicylaldimine (Hpsal) of 2-picolylamine has furnished VO(psal)(L), 3. In the structures of VO(gsal)(HL(1)), 2a, and VO(vsal)(HL(2)), 2f, the HL(-) ligand is O,O-chelated, the phenolic oxygen lying trans to the oxo oxygen atom. The xsal(2-) coligand has a folded structure and the conformation of 2f is exclusively endo. In both 2a and 2f the phenolic oxygen atom is strongly hydrogen bonded (O...O, 2.60 A) to a carboxylic oxygen atom of a neighboring molecule. In VO(psal)(L(2)).H(2)O, 3b, the diionized diol is O,O-chelated to the metal and the water molecule is hydrogen bonded to a phenoxidic oxygen atom (O.O, 2.84 A). The C-O and C-C distances in the V(diol) fragment reveal that 2 is a pure catecholate and 3 is a catecholate-semiquinonate hybrid. In solution each ester gives rise to a single (51)V NMR signal (no diastereoisomers), which generally shifts downfield with a decrease in the ester LMCT band energy. The V(V)/V(IV) and catecholate-semiquinonate reduction potentials lie near -0.75 and 0.35, and 1.10 and 0.70 V vs SCE for 2 and 3, respectively. Molecular oxygen reacts smoothly with 2 quantitatively furnishing the corresponding o-quinone, and in the presence of H(2)L the reaction becomes catalytic. In contrast, type 3 esters are inert to oxygen. The initial binding of O(2) to 2 is proposed to occur via hydrogen bonding with chelated HL(-).     

Interaction of diatomic germanium with lithium atoms: electronic structure and stability

Quantum chemical calculations were applied to investigate the electronic structure of mono-, di-, and trilithiated digermanium (Ge2Lin) and their cations (n=0-3). Computations using a multiconfigurational quasidegenerate perturbation approach based on complete active space self-consistent-field wave functions, and density functional theory reveal that Ge2Li has a 2B1 ground state with a doublet-quartet energy gap of 33 kcal/mol. Ge2Li2 has a singlet ground state with a 3Au-1A1 gap of 29 kcal/mol, and Ge2Li3 a doublet ground state with a 4B2-2A2 separation of 22 kcal/mol. The cation Ge2Li+ has a 3B1 ground state, being 13 kcal/mol below the open-shell 1B1 state. The computed electron affinities for diatomic germanium are EA(1)=1.9 eV, EA(2)=-2.5 eV, and EA(3)=-6.0 eV, for Ge2-, Ge2 (2-), and Ge2 (3-), respectively, indicating that only the monoanion is stable with respect to electron detachment, in such a way that Ge2Li is composed by Ge2-Li+ ions. An "atoms-in-molecules" analysis shows the absence of a ring critical point in Ge(2)Li. An electron localization function analysis on Ge2Li supports the view that the Ge-Li bond is predominantly ionic; however, a small covalent character could be anticipated from the analysis of the Laplacian at the Ge-Li bond critical point. The ionic picture of the Ge-Li bond is further supported by a natural-bond-order analysis and the Laplacian of the electron density. The calculated Li affinity value for Ge2 is 2.08 eV, while the Li+ cation affinity value for Ge2- is 5.7 eV. The larger Li+ cation affinity value of Ge2- suggests a Ge2-Li+ interaction and thus supports the ionic nature of Ge-Li bond. In GeLi4 and Ge2Li, the presence of trisynaptic basins indicates a three-center bond connecting the germanium and lithium atoms.     

Pathway for the stereocontrolled Z and E production of alpha,alpha-difluorine-substituted phenyl butenoates

An efficient preparation of pure ethyl Z- and E-alpha,alpha-difluoro-4-phenyl-3-butenoate 1a and 1b together with the corresponding acids 2a and 2b is described. The procedures involve stereocontrolled additions of *CF2CO2Et to phenylacetylene or beta-bromostyrene. Compound 1a is easily obtained by addition of *CF2CO2Et to phenylacetylene via a mechanism where the stereochemistry is controlled by an electron-transfer process to produce predominantly the Z vinyl anion. The product 1b is obtained by *CF2CO2Et addition-elimination to Z- or E-beta-bromostyrenes via a mechanism where the stereochemistry is controlled by steric factors in the conformational equilibration of the intermediates.     

8-Hydroxyquinoline derivative as a fluorescent chemosensor for zinc ion.

8-Hydroxyquinoline derivative 1 as a fluorescent chemosensor for Zn2+ was synthesized. Because Cd2+ is often found with Zn2+ in the environment and can form fluorescent complexes with chelating fluorophores, a potentially important property of chemosensors for Zn2+ is their selectivity for Zn2+ over Cd2+. The Zn2+ or Cd2+ complexes of 1 gave an emission band from the 1:1 complex, but the fluorescence intensity for Cd2+ was a half of that for Zn2+. Ligand 1 is suited for use as a fluorescent chemosensor for Zn2+.     

Chemical understanding of carbide cluster metallofullerenes: a case study on Sc2C2@C2v(5)-C80 with complete X-ray crystallographic characterizations

Little is known about the chemical properties of carbide cluster metallofullerenes (CCMFs). Here we report the photochemical reaction of a newly assigned CCMF Sc(2)C(2)@C(2v)(5)-C(80) with 2-adamantane-2,3-[3H]-diazirine (AdN(2), 1), which provides a carbene reagent under irradiation. Five monoadduct isomers (2a-2e), with respective abundances of 20%, 40%, 25%, 5%, and 10%, were isolated and characterized with a combination of experimental techniques including unambiguous single-crystal X-ray crystallography. Results show that the two Sc atoms of the bent Sc(2)C(2) cluster tend to move in most cases, whereas the C(2)-unit is almost fixed. Accordingly, it is difficult to explain the addition patterns by considering the strain and charge density on the cage with a fixed cluster, and thus a moving cluster may account for the addition patterns. These results show that the situation of CCMFs is more complicated than those in other metallofullerenes. Furthermore, a thermal isomerization process from 2b to 2c was observed, confirming that the most abundant isomer 2b is a kinetically favored adduct. Finally, it is revealed that the electronic and electrochemical properties of pristine Sc(2)C(2)@C(2v)(5)-C(80) have been markedly altered by exohedral modification.     

Electrochemical and chemical formation of [Mn4(IV)O5(terpy)4(H2O)2]6+, in relation with the photosystem II oxygen-evolving center model [Mn2(III,IV)O2(terpy)2(H2O)2]3+

To examine the real ability of the binuclear di-mu-oxo complex [Mn2(III,IV)O2(terpy)2(H2O)2]3+ (2) to act as a catalyst for water oxidation, we have investigated in detail its redox properties and that of its mononuclear precursor complex [Mn(II)(terpy)2]2+ (1) in aqueous solution. It appears that electrochemical oxidation of 1 allows the quantitative formation of 2 and, most importantly, that electrochemical oxidation of 2 quantitatively yields the stable tetranuclear Mn(IV) complex, [Mn4(IV)O5(terpy)4(H2O)2]6+ (4), having a linear mono-mu-oxo{Mn2(mu-oxo)2}2 core. Therefore, these results show that the electrochemical oxidation of 2 in aqueous solution is only a one-electron process leading to 4 via the formation of a mono-mu-oxo bridge between two oxidized [Mn2(IV,IV)O2(terpy)2(H2O)2]4+ species. 4 is also quantitatively formed by dissolution of the binuclear complex [Mn2(IV,IV)O2(terpy)2(SO4)2] (3) in aqueous solutions. Evidence of this work is that 4 is stable in aqueous solutions, and even if it is a good synthetic analogue of the "dimers-of-dimers" model compound of the OEC in PSII, this complex is not able to oxidize water. As a consequence, since 4 results from an one-electron oxidation of 2, 2 cannot act as an efficient homogeneous electrocatalyst for water oxidation. This work demonstrates that a simple oxidation of 2 cannot produce molecular oxygen without the help of an oxygen donor.     

Elimination mechanisms of Br(2)+ and Br+ in photodissociation of 1,1- and 1,2-dibromoethylenes using velocity imaging technique

Elimination pathways of the Br(2)(+) and Br(+) ionic fragments in photodissociation of 1,2- and 1,1-dibromoethylenes (C(2)H(2)Br(2)) at 233 nm are investigated using time-of-flight mass spectrometer equipped with velocity ion imaging. The Br(2)(+) fragments are verified not to stem from ionization of neutral Br(2), that is a dissociation channel of dibromoethylenes reported previously. Instead, they are produced from dissociative ionization of dibromoethylene isomers. That is, C(2)H(2)Br(2) is first ionized by absorbing two photons, followed by the dissociation scheme, C(2)H(2)Br(2)(+) + hv→Br(2)(+) + C(2)H(2). 1,2-C(2)H(2)Br(2) gives rise to a bright Br(2)(+) image with anisotropy parameter of -0.5 ± 0.1; the fragment may recoil at an angle of ～66° with respect to the C=C bond axis. However, this channel is relatively slow in 1,1-C(2)H(2)Br(2) such that a weak Br(2)(+) image is acquired with anisotropy parameter equal to zero, indicative of an isotropic recoil fragment distribution. It is more complicated to understand the formation mechanisms of Br(+). Three routes are proposed for dissociation of 1,2-C(2)H(2)Br(2), including (a) ionization of Br that is eliminated from C(2)H(2)Br(2) by absorbing one photon, (b) dissociation from C(2)H(2)Br(2)(+) by absorbing two more photons, and (c) dissociation of Br(2)(+). Each pathway requires four photons to release one Br(+), in contrast to the Br(2)(+) formation that involves a three-photon process. As for 1,1-C(2)H(2)Br(2), the first two pathways are the same, but the third one is too weak to be detected.     

Reaction of silanes in supercritical CO2 with TiO2 and Al2O3

Infrared spectroscopy was used to investigate the reaction of silanes with TiO2 and Al2O3 using supercritical CO2 (Sc-CO2) as a solvent. It was found that contact of Sc-CO2 with TiO2 leads to partial removal of the water layer and to the formation of carbonate, bicarbonate, and carboxylate species on the surface. Although these carbonate species are weakly bound to the TiO2 surface and can be removed by a N2 purge, they poison the surface, resulting in a lower level of reaction of silanes with TiO2. Specifically, the amount of hexamethyldisilazane adsorbed on TiO2 is about 10% of the value obtained when the reaction is performed from the gas phase. This is not unique to TiO2, as the formation of carbonate species also occurs upon contact of Al2O3 with Sc-CO2 and this leads to a lower level of reaction with hexamethyldisilazane. This is in contrast to reactions of silanes on SiO2 where Sc-CO2 has several advantages over conventional gaseous or nonaqueous methods. As a result, caution needs to be applied when using Sc-CO2 as a solvent for silanization reactions on oxides other than SiO2.     

CO为还原剂同时还原SO2和NO的SnO2-TiO2固溶体催化剂Ⅱ.催化剂的物理化学性质

 用XRD, XPS, CO-TPR, NH3-TPD, SO2-TPD和IR等方法表征了SnO2-TiO2固溶体催化剂的物理化学性质. 不同配比的SnO2和TiO2均可形成均一的具有金红石结构的连续固溶体,其晶粒度比单纯的SnO2或TiO2的晶粒度小. SnO2-TiO2固溶体的比表面积随SnO2含量的增大呈火山形变化,说明在SnO2-TiO2固溶体中SnO2可阻止TiO2由锐钛矿型变为金红石型过程中比表面积的减小,而TiO2则提供了维持大表面的结构框架. SnO2倾向于在固溶体表面偏析,固溶体的表面氧含量高于单纯SnO2的表面氧含量而低于单纯TiO2的表面氧含量. SnO2, TiO2和SnO2-TiO2表面含有能被CO还原的吸附氧和晶格氧,被还原的SnO2, TiO2和SnO2-TiO2的表面晶格氧的数量仅占所有晶格氧的0.001%, 说明CO只使部分晶格氧还原并生成氧阴离子空穴. TiO2表面没有酸性, SnO2和SnO2-TiO2呈微弱酸性. 经CO还原的SnO2-TiO2上存在大量的强碱中心,说明SnO2和TiO2之间发生了协同作用. SnO2-TiO2固溶体的这些物化性质均十分有利于SO2+NO+CO的氧化还原反应.     

PRODUCTION OF LIGHT OLEFINS FROM CO2 HYDROGENATION OVER Fe/SILICALITE-2 CATALYST. I.CATALYTIC REACTIVI-FY AND REACTION MECHANISM

K-Fe-MnO/Silicalite-2 is a desirable catalyst for the production of light olefins from CO2 hydrogenation The activity can be improved greatly with increasing the Fe loading, and the selectivities to hydrocarbons rise with Fe loading increase However, an ambiguous effect of Fe loading on the selectivity of light olefin in hydrocarbon products is observed. The CO2 hydrogenation containing a two-step mechanism CO2+H2=CO+H2O, a reversible water gas shift reaction, and CO+(m/2n+1)H2 =1/nCnHm+H2O2, a Frscher-Tropsch reaction, is suggested by the results of CO2-TPD and CO2/H2-TPSR as well as CO/H2-TPSR characterizations.     

Distillation and detection of SO2 using a microfluidic chip

A miniaturized distillation system is presented for separating sulfurous acid (H(2)SO(3)) into sulfur dioxide (SO(2)) and water (H(2)O). The major components of the proposed system include a microfluidic distillation chip, a power control module, and a carrier gas pressure control module. The microfluidic chip is patterned using a commercial CO(2) laser and comprises a serpentine channel, a heating zone, a buffer zone, a cooling zone, and a collection tank. In the proposed device, the H(2)SO(3) solution is injected into the microfluidic chip and is separated into SO(2) and H(2)O via an appropriate control of the distillation time and temperature. The gaseous SO(2) is then transported into the collection chamber by the carrier gas and is mixed with DI water. Finally, the SO(2) concentration is deduced from the absorbance measurements obtained using a spectrophotometer. The experimental results show that a correlation coefficient of R(2) = 0.9981 and a distillation efficiency as high as 94.6% are obtained for H(2)SO(3) solutions with SO(2) concentrations in the range of 100-500 ppm. The SO(2) concentrations of two commercial red wines are successfully detected using the developed device. Overall, the results presented in this study show that the proposed system provides a compact and reliable tool for SO(2) concentration measurement purposes.     

Theoretical studies to understand surface chemistry on carbon anodes for lithium-ion batteries: reduction mechanisms of ethylene carbonate.

Reductive decomposition mechanisms for ethylene carbonate (EC) molecule in electrolyte solutions for lithium-ion batteries are comprehensively investigated using density functional theory. In gas phase the reduction of EC is thermodynamically forbidden, whereas in bulk solvent it is likely to undergo one- as well as two-electron reduction processes. The presence of Li cation considerably stabilizes the EC reduction intermediates. The adiabatic electron affinities of the supermolecule Li(+)(EC)n (n = 1-4) successively decrease with the number of EC molecules, independently of EC or Li(+) being reduced. Regarding the reductive decomposition mechanism, Li(+)(EC)n is initially reduced to an ion-pair intermediate that will undergo homolytic C-O bond cleavage via an approximately 11.0 kcal/mol barrier, bringing up a radical anion coordinated with Li(+). Among the possible termination pathways of the radical anion, thermodynamically the most favorable is the formation of lithium butylene dicarbonate, (CH2CH2OCO2Li)2, followed by the formation of one O-Li bond compound containing an ester group, LiO(CH2)2CO2(CH2)2OCO2Li, then two very competitive reactions of the further reduction of the radical anion and the formation of lithium ethylene dicarbonate, (CH2OCO2Li)2, and the least favorable is the formation of a C-Li bond compound (Li carbides), Li(CH2)2OCO2Li. The products show a weak EC concentration dependence as has also been revealed for the reactions of LiCO3(-) with Li(+)(EC)n; that is, the formation of Li2CO3 is slightly more favorable at low EC concentrations, whereas (CH2OCO2Li)2 is favored at high EC concentrations. On the basis of the results presented here, in line with some experimental findings, we find that a two-electron reduction process indeed takes place by a stepwise path. Regarding the composition of the surface films resulting from solvent reduction, for which experiments usually indicate that (CH2OCO2Li)2 is a dominant component, we conclude that they comprise two leading lithium alkyl bicarbonates, (CH2CH2OCO2Li)2 and (CH2OCO2Li)2, together with LiO(CH2)2CO2(CH2)2OCO2Li, Li(CH2)2OCO2Li and Li2CO3.     

Theoretical study of rhenium dinuclear complexes: Re-Re bonding nature and electronic structure

Four dinuclear rhenium complexes, [Re2Cl8](2-) (1), [Re2(mu-Cl)3Cl6](2-) (2a), [Re2(mu-Cl)3Cl6](-) (2b), and [Re2(mu-Cl)2Cl8](2-) (3), were theoretically investigated by the CASSCF, MRMP2, SA-CASSCF, and MCQDPT methods. Interesting differences in electronic structure and Re-Re bonding nature among these complexes are clearly reported here, as follows: In 1, the ground state is the 1A1g state. The approximate stabilization energies by the sigma, pi, and delta bonding interactions are evaluated to be 4.36, 2.89, and 0.52 eV, respectively, by the MRMP2 method. In 2a, the ground state is the 2E" state. The approximate stabilization energy by two degenerate delta bonding interactions is estimated to be 0.36 eV by the MCQDPT method. One delta bonding interaction of 2a is much weaker than that of 1, which is discussed in terms of the Re-Re distance and the Re oxidation state. In 2b, the ground state is the 1A1' state, of which multiconfigurational nature is extremely large unlike that of the 2E" ground state of 2a despite similarities between 2a and 2b. In 3, the sigma, pi, and delta bonding interactions are not effectively formed between two Re centers. As a result, the 1Ag, 3B1u, 5Ag, and 7B1u states are in almost the same energy within 0.03 eV. This result is consistent with the paramagnetism of 3 experimentally reported.     

Nitrogen-ligated iron complexes: photolytic approach to the FeN+ moiety

The synthesis of (PNP)FeCl, (PNP)Fe[NH(xylyl)], and (PNP)FeN3 are reported(PNP = (tBu2PCH2SiMe2)2N-). While the azide is thermally stable, it is photosensitive to lose N2 and form [(PNPN)Fe]2,in which the nitride ligand has formed a double bond to one phosphorus, and this N bridges to a second iron to form a 2-fold symmetric dimer. The reaction energy to form the (undetected) monomeric [eta3- tBu2PCH2SiMe2NSiMe2CH2PtBu2N]Fe is -15.9 kcal/mol, so this PIII --> PV oxidation is favorable. The eta2 version of this same species is less stable by 23.7 kcal/mol, which shows that the loss of one P--> Fe bond is caused by dimerization, and therefore, it does not precede and cause dimerization. A comparison is made to Ru analogs.     

Exploring the actinide-actinide bond: theoretical studies of the chemical bond in Ac2, Th2, Pa2, and U2

Multiconfigurational quantum chemical methods (CASSCF/CASPT2) have been used to study the chemical bond in the actinide diatoms Ac2, Th2, Pa2, and U2. Scalar relativistic effects and spin-orbit coupling have been included in the calculations. In the Ac2 and Th2 diatoms the atomic 6d, 7s, and 7p orbitals are the significant contributors to the bond, while for the two heavier diatoms, the 5f orbitals become increasingly important. Ac2 is characterized by a double bond with a 3Sigmag-(0g+) ground state, a bond distance of 3.64. A, and a bond energy of 1.19 eV. Th2 has quadruple bond character with a 3Dg(1g) ground state. The bond distance is 2.76 A and the bond energy (D0) 3.28 eV. Pa2 is characterized by a quintuple bond with a 3Sigmag-(0g+) ground state. The bond distance is 2.37 A and the bond energy 4.00 eV. The uranium diatom has also a quintuple bond with a 7Og (8g) ground state, a bond distance of 2.43 A, and a bond energy of 1.15 eV. It is concluded that the strongest bound actinide diatom is Pa2, characterized by a well-developed quintuple bond.