Biomedical subjects

Jussi Valkonen

Publications and source records attributed to Jussi Valkonen.

11 recordsLinked to original sources

PubMed2005

Electronic structures and molecular properties of chalcogen nitrides Se2N2 and SeSN2.

The electronic structures and molecular properties of S2N2 as well as the currently unknown chalcogen nitrides Se2N2 and SeSN2 have been studied using various ab initio and density functional methods. All molecules share a qualitatively similar electronic structure and can be primarily described as 2pi-electron aromatics having minor singlet diradical character of 6-8% that can be attributed solely to the nitrogen atoms. This diradical character is manifested in the prediction of their molecular properties, in which coupled cluster and multiconfigurational approaches, as well as density functional methods, show the best performance. The conventional ab initio methods RHF and MP2 completely fail to describe these systems. Predictions for the vibrational frequencies, IR intensities, Raman activities, and 14N, 15N, and 77Se chemical shifts, as well as singlet excitation energies of Se2N2 and SeSN2, have been made. The computed high-level spectroscopic data will be of considerable value in future efforts aimed at the preparation of the conducting polymers (SeN)x and (SeNSN)x.

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PubMed2005

A computational and experimental study of the structures and Raman and 77Se NMR spectra of SeX3+ and SeX2 (X = Cl, Br, I): FT-Raman spectrum of (SeI3)[AsF6].

The ability of MP2, B3PW91 and PBE0 methods to produce reliable predictions in structural and spectroscopic properties of small selenium-halogen molecules and cations has been demonstrated by using 6-311G(d) and cc-pVTZ basis sets. Optimized structures and vibrational frequencies agree closely with the experimental information, where available. Raman intensities are also well reproduced at all levels of theory. Calculated GIAO isotropic shielding tensors yield a reasonable linear correlation with the experimental chemical shift data at each level of theory. The largest deviations between calculated and experimental chemical shifts are found for selenium-iodine species. The agreement between observed and calculated chemical shifts for selenium-iodine species can be improved by inclusion of relativistic effects using the ZORA method. The best results are achieved by adding spin-orbit correction terms from ZORA calculations to nonrelativistic GIAO isotropic shielding tensors. The calculated isotropic shielding tensors can be utilized in the spectroscopic assignment of the 77Se chemical shifts of novel selenium-halogen molecules and cations. The experimental FT-Raman spectra of (SeI3)[AsF6] in the solid state and in SO2(l) solution are also reported.

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PubMed2005

Experimental and theoretical investigations of tellurium(IV) diimides and imidotelluroxanes: X-ray structures of B(C6F5)3 adducts of OTe(mu-NtBu)2TeNtBu, [OTe(mu-NtBu)2Te(mu-O)]2 and tBuNH2.

The hydrolysis of (t)BuNTe(mu-N(t)Bu)(2)TeN(t)Bu (1) with 1 or 2 equiv of (C(6)F(5))(3)B.H(2)O results in the successive replacement of terminal imido groups by oxo ligands to give the telluroxane-Lewis acid adducts (C(6)F(5))(3)B.OTe(mu-N(t)Bu)(2)TeN(t)Bu (2) and [(C(6)F(5))(3)B.OTe(mu-N(t)Bu)(2)Te(mu-O)](2) (3), which were characterized by multinuclear NMR spectroscopy and X-ray crystallography. The Te=O distance in 2 is 1.870(2) A. The di-adduct 3 involves the association of four (t)()BuNTeO monomers to give a tetramer in which both terminal Te=O groups [d(TeO) = 1.866(3) A] are coordinated to B(C(6)F(5))(3). The central Te(2)O(2) ring in 3 is distinctly unsymmetrical [d(TeO) = 1.912(3) and 2.088(2) A]. The X-ray structure of (C(6)F(5))(3)B.NH(2)(t)()Bu (4), the byproduct of these hydrolysis reactions, is also reported. The geometries and energies of tellurium(IV) diimides and imido telluroxanes were determined using quantum chemical calculations. The calculated energies for the reactions E(NR)(2) + Te(NR)(2) (E = S, Se, Te; R = H, Me, (t)Bu, SiMe(3)) confirm that cyclodimerization of tellurium(IV) diimides is strongly exothermic. In the mixed-chalcogen systems, the cycloaddition is energetically favorable for the Se/Te combination. The calculated energies for the further oligomerization of the dimers XE(mu-NMe)(2)EX (E = Se, Te; X = NMe, O) indicate that the formation of tetramers is strongly exothermic for the tellurium systems but endothermic (X = NMe) or thermoneutral (X = O) for the selenium systems, consistent with experimental observations.

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PubMed2004

Ca[Ag2(SCN)4].2H2O.

Calcium tetrathiocyanatodiargentate(I) dihydrate, Ca[Ag(2)(SCN)(4)].2H(2)O, contains eight-membered Ag(4)S(4) rings bonded together through shared atoms to form layers parallel to (100). The thiocyanate groups link the layers to Ca-O chains running parallel to the c axis. The Ca atom is located on a twofold rotation axis parallel to b and is surrounded by four water molecules of crystallization and four thiocyanate N atoms in a distorted square antiprism.

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PubMed2004

Experimental and theoretical investigations of structural trends for selenium(IV) imides and oxides: X-ray structure of Se3(NAd)2.

The thermal decomposition of Se(NAd)(2) (Ad = 1-adamantyl) in THF was monitored by (77)Se NMR and shown to give the novel cyclic selenium imide Se(3)(NAd)(2) as one of the products. An X-ray structural determination showed that Se(3)(NAd)(2) is a puckered five-membered ring with d(Se-Se) = 2.404(1) A and |d(Se-N)| = 1.873(4) A. On the basis of (77)Se NMR data, other decomposition products include the six-membered ring Se(3)(NAd)(3), and the four-membered rings AdNSe(micro-NAd)(2)SeO and OSe(micro-NAd)(2)SeO. The energies for the cyclodimerization of E(NR)(2) and RNEO (E = S, Se; R = H, Me, (t)Bu, SiMe(3)), and the cycloaddition reactions of RNSeO with E(NR)(2), RNSO(2) with Se(NR)(2), and S(NR)(2) with Se(NR)(2) have been calculated at MP2, CCSD, and CCSD(T) levels of theory using the cc-pVDZ basis sets and B3PW91/6-31G* optimized geometries. Sulfur(IV) and selenium(IV) diimide monomers are predicted to be stable, the sole exception being Se(NSiMe(3))(2) that shows a tendency toward cyclodimerization. The cyclodimerization energy for RNSeO and the cycloaddition reaction energies of RNSeO with Se(NR)(2) as well as that of RNSO(2) with Se(NR)(2) are negative, consistent with the observed formation of OSe(micro-N(t)Bu)(2)SeO, OSe(micro-N(t)Bu)(2)SeN(t)Bu, and O(2)S(micro-N(t)Bu)(2)SeN(t)Bu, respectively. Cycloaddition is unlikely when one of the reactants is a sulfur(IV) diimide.

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PubMed2002

Polymorphism in Cs[AgZn(NCS)4].

The title compound, caesium silver zinc tetrathiocyanate, crystallizes in two polymorphic forms, in space groups P2(1)/n and C2/c. Both structures form a continuous three-dimensional network. The structure in C2/c contains a delocalized Ag atom in a binuclear-like anion, where two [Ag(NCS)(4)] units (delocalized Ag as an average) share two common NCS(-) ligands.

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PubMed2002

Cs[Ag4Zn2(SCN)9].

Caesium tetrasilver dizinc nonathiocyanate, Cs[Ag(4)Zn(2)(SCN)(9)], forms a continuous structure, where the Ag atoms and the S atoms of the thiocyanate groups form chains which run along [101]. These chains are bonded together through the Cs and Zn atoms. It is not possible to distinguish between space groups P1 and P-1, but, if the latter space group is correct, the structure contains a thiocyanate group disordered across a centre of inversion. The structure is described in space group P-1, in which the Cs atom also lies on a centre of inversion.

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PubMed2002

Preparation and structural characterization of (Me(3)SiNSN)(2)Se, a new synthon for sulfur-selenium nitrides.

The reaction of (Me(3)SiN)(2)S with SeCl(2) (2:1 ratio) in CH(2)Cl(2) at -70 degrees C provides a route to the novel mixed selenium-sulfur-nitrogen compound (Me(3)SiNSN)(2)Se (1). Crystals of 1 are monoclinic and belong the space group P2(1)/c, with a = 7.236(1) A, b = 19.260(4) A, c = 11.436(2) A, beta = 92.05(3) degrees, V = 1592.7(5) A(3), Z = 4, and T = -155(2) degrees C. The NSNSeNSN chain in 1 consists of Se-N single bonds (1.844(3) A) and S=N double bonds (1.521(3)-1.548(3) A) with syn and anti geometry at the N=S=N units. The N-Se-N bond angle is 91.8(1) degrees. The EI mass spectrum shows a molecular ion with good agreement between the observed and calculated isotopic distributions. The (14)N NMR spectrum exhibits two resonances at -65 and -77 ppm. Both (13)C and (77)Se NMR spectra show single resonances at 0.83 and 1433 ppm, respectively. The reaction of 1 with an equimolar amount of SeCl(2) produces 1,5-Se(2)S(2)N(4) (2) in a good yield, and that of (Me(3)SiNSN)(2)S with SCl(2) affords S(4)N(4) (3), but the reactions of (Me(3)SiNSN)(2)Se with SCl(2) and (Me(3)SiNSN)(2)S with SeCl(2) result in the formation of a mixture of 2 and 3. A likely reaction pathway involves the intermediate formation of E(2)N(2) fragments (E = S, Se).

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PubMed2001

Calcium dicaesium silver thiocyanate dihydrate.

The title compound, CaCs2[Ag2(SCN)6]*2H2O, forms a continuous structure where the Ag atoms form chains with S atoms in the c-axis direction. The chains are bonded together through Cs and Ca atoms. The crystal water of the structure is bonded to the Ca atoms, which lie on centers of symmetry.

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PubMed2001

Dicaesium silver zinc thiocyanate, Cs2[AgZn(SCN)5].

The title compound, dicaesium(I)-mu-thiocyanato-kappa2N:S-zinc(II)-tetra-mu-thiocyanato-kappa2S:N-argentate(I), crystallizes in the orthorhombic space group Pmn2(1) and contains units of composition AgZn(SCN)3 lying on a mirror plane and bonded together through Cs+ ions and thiocyanate groups. The crystal studied contained equal numbers of inversion twins.

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PubMed1996

Alkoxo Bound Monooxo- and Dioxovanadium(V) Complexes: Synthesis, Characterization, X-ray Crystal Structures, and Solution Reactivity Studies.

A large variety of oxovanadium(V) complexes, mononuclear VO(2)(+) and VO(3+) in addition to the dinuclear VO(3+), of the structural type (VOL)(2), (VOHL)(2), VOLHQ, K(VO(2)HL), K(VO(2)H(2)L), or (salampr) (VO(2)L) {where L = Schiff base ligand possessing alkoxo group(s); HQ = 8-hydroxyquinoline; salampr = cation of reduced Schiff base derived from salicylaldehyde and 2-amino-2-methylpropan-1-ol}, bound to alkoxo, phenolate and imine groups have been synthesized in high yields and characterized by several spectral and analytical methods, including single crystal X-ray studies. While the mononuclear VO(2)(+) complexes have been synthesized at alkaline pH, the dinuclear VO(3+) complexes have been synthesized under neutral conditions using alkoxo rich Schiff base ligands. The X-ray structures indicate that the cis-dioxo complexes showed longer V-O(alkoxo) bond lengths compared to the monooxo counterparts. The plot of V-O(phen) bond distances of several VO(3+) complexes vs the lmct showed a near linear correlation with a negative slope. The cyclic voltammograms revealed a reversible V(V)/V(IV) couple with the reduction potentials increasing to more negative ones as the number of alkoxo groups bound to V increases from 1 to 2. Moreover, the cis-dioxo VO(2)(+) complexes are easier to reduce than their monooxo counterparts. The solution stability of these complexes was studied in the presence of added water (1:4, water:solvent), where no decomposition was observed, unlike other Schiff base complexes of V. The conversion of the dioxo complexes to their monooxo counterparts in the presence of catalytic amounts of acid is also demonstrated. The reactivity of alkoxo bound V(V) complexes is also reported. X-ray parameters are as follows. H(4)L(3): monoclinic space group, P2(1)/c; a = 10.480(3), b = 8.719(6), c = 12.954(8) Å; beta = 101.67(4) degrees; V = 1126(1) Å(3); Z = 4; R = 0.060, R(w) = 0.058. Complex 1: monoclinic space group, P2(1)/n; a = 12.988(1), b = 9.306(2), c = 19.730(3) Å; beta = 99.94(1) degrees; V = 2348.9(7) Å(3); Z = 4; R = 0.031, R(w) = 0.027. Complex 2: monoclinic space group, P2(1)/n; a = 12.282(3), b = 11.664(2), c = 12.971(4) Å; beta = 97.89(2) degrees; V = 1840.5(8) Å; Z = 4; R = 0.035, R(w) = 0.038. Complex 5: monoclinic space group, P2(1)/c; a = 17.274(2), b = 6.384(2), c = 16.122(2) Å; beta = 116.67(1) degrees; V = 1588.7(7) Å(3); Z = 4; R = 0.039, R(w) = 0.043. Complex 8: monoclinic space group, P2(1)/c; a = 11.991(1), b = 11.696(4), c = 12.564(3) Å; beta = 110.47(1) degrees; V = 1650.8(8) Å(3); Z = 2; R = 0.045, R(w) = 0.049.

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