Confocal microscopy on the beamline: novel three-dimensional imaging and sample positioning.

Confocal microscopy, a technique that has been extensively applied in cellular biological studies, may also be applied to the visualization and three-dimensional imaging of protein crystals at high resolution on synchrotron beamlines. Protein crystal samples are examined using a commercially available confocal microscope adapted for cryogenic use. A preliminary test using a custom confocal design adapted for beamline use is also presented. The confocal optics configuration is compatible with nonlinear imaging techniques such as two-photon excited fluorescence imaging and second harmonic generation. The possibilities of this method are explored using two modes: fluorescence and reflection confocal. In fluorescence mode, small amounts of dye are introduced into the crystal through soaking or growth conditions. Under such conditions, protein crystals are easily resolved from salts and amorphous precipitates, which do not generally take up dye. Reflection mode, which does not require dye, still exhibits greater resolution and sensitivity to surface detail than conventional wide-field microscopy as a result of the confocal optics configuration. The inherent three-dimensional nature of the method means that on-axis sample views (along the direction of the X-ray beam) can be reconstructed from an off-axis configuration, simplifying the beamline setup and providing uniquely detailed views of cryogenically cooled crystals.

Polyhedral-based nonlinear optical materials. 3. Synthetic studies of cyclopentadiene- and cycloheptatriene-substituted polyhedral compounds: synthesis of 1,12-[C(7)H(7)C(2)B(10)H(10)(C(5)H(3)Me(2))] and related species.

The synthesis and characterization of a series of new olefin-substituted closo-1,12-[C(2)B(10)H(12)] compounds is described. The reaction of deprotonated closo-1,12-dicarbadodecaborane with 7-methoxycycloheptatriene yields the cycloheptatriene-substituted carborane compound, closo-[1-(1-C(7)H(7))-12-(H)-C(2)B(10)H(10)] (3). Deprotonation of 3 with butyllithium and subsequent reaction with 3,4-dimethyl-2-cyclopenten-1-one was found to yield the bis-olefin-substituted carbinol compound [1-(1-C(7)H(7))-12-(C(5)H(4)-1-(OH)-3,4-(CH(3))(2))-C(2)B(10)H(10)] (5) in good yield. Acidic dehydration of 5 quantitatively converted it into the simple bis-olefin cage compound [1-(1-C(7)H(7))-12-(C(5)H(3)-3,4-(CH(3))(2))-C(2)B(10)H(10)] (6). Finally, thermal treatment of 6 in refluxing toluene was employed to prepare the isomerized cycloheptatriene compound [1-(4-C(7)H(7))-12-(C(5)H(3)-3,4-(CH(3))(2))-C(2)B(10)H(10)] (7) in high yield. These compounds represent the first metal-free cyclopentadiene and bis-olefin large cluster species reported in which the C(5) ring is attached directly to the cage. The complete characterization of products by multinuclear NMR ((1)H, (11)B, and (13)C), infrared, UV-visible, and mass spectroscopic analyses is presented. The X-ray crystal structures of 3 and 7 are also reported. X-ray data for 3: triclinic system, space group P&onemacr; with cell constants a = 6.6807(3) A, b = 10.2939(3) A, c = 10.3962(4) A, alpha = 89.342(2) degrees, beta = 74.610(2) degrees, gamma = 83.373(2) degrees, Z = 2, R1 = 0.0487 (wR2 (all data) = 0.1272). X-ray data for 7: monoclinic system, space group P2(1)/c with cell constants a = 7.7207(7) A, b = 15.8730(14) A, c = 15.5493(13) A, beta = 99.146(2) degrees, Z = 4, R1 = 0.0761 (wR2 (all data) = 0.2050).

Interaction of Rh(I) with meso-arylsapphyrins and -rubyrins: first structural characterization of bimetallic hetero-rubyrin complex.

The ligational behavior of meso-arylsapphyrins and rubyrins toward Rh(I) is investigated. Sapphyrins form monometallic complexes with coordination of one imine and amine type nitrogens of the bipyrrole unit in an eta2 fashion. The Rh(I) coordination is completed by the presence of two ancillary carbon monoxide ligands. Rubyrins form both monometallic and bimetallic complexes. Two types of bimetallic complexes have been isolated. In the first type, both rhodium atoms are projected above the mean rubyrin plane, while in the second type, one rhodium atom is projected above and the other below the mean plane. Detailed 1H and 2D NMR spectral analyses along with IR and UV-visible spectra of the complexes confirm the proposed binding modes for the rhodium complexes. Furthermore, the single-crystal X-ray analysis of one of the bimetallic complexes of rubyrin shows a bowl-shaped symmetric structure where both Rh(I) atoms are projected above the mean rubyrin plane at an angle of 71.73 degrees. The geometry around each rhodium center is approximately square planar [N1-Rh1-N2, 80.38(9) degrees; C15-Rh1-C16, 86.95(14) degrees; N1-Rh1-C15, 97.13(12) degrees; and N2-RH1-C16, 94.97(12) degrees ]. The omicronbserved distance of 4.313 A between the two rhodium centers reveals very little interaction between the two rhodium atoms. This type of metal binding is accompanied by a 180 degrees ring flip of the heterocyclic ring connecting the two bipyrrole units. In dioxarubyrin, where one of the pyrrole rings of the bipyrrole unit is inverted, Rh(I) binds at the periphery to the pyrrole nitrogen, leaving the rubyrin cavity empty. The absence of one amino and one imino nitrogen on the dipyrromethene subunits in the sapphyrins and rubyrins described here forces Rh(I) to bind to bipyrrole nitrogens.

Core modified meso-aryl corrole: first examples of CuII, NiII, CoII and RhI complexes.

A variety of metal complexes of 5,10,15-triphenyl-21-monooxa-corrole 4 have been investigated. This monooxa corrole, where one of the pyrrole ring is replaced by a furan moiety, is synthesized by the alpha-alpha coupling reaction of 16-oxa tripyrrane and dipyrromethane. The single crystal X-ray structure of 4 indicates only small deviation of the inner-core heteroatoms from planarity and this macrocycle arrange themselves into a columnar structure. Insertion of metals further flattens the corrole framework. Specifically, oxacorrole 4 binds to Nil(II), Cu(II), and Co(II) with the participation of all heteroatoms in the coordination. However, Rh(I) ion binds to only one imino and one amino nitrogen of the macrocycle. The bond angles at the metal center in the Ni(II) and Rh(I) complexes reveal square planar geometry completed by two CO molecules for Rh(I). The EPR spectra of the paramagnetic that Cu(II) and Col(II) complexes display significant decreases in the metal hyperfine couplings compared with the corresponding porphyrin complexes. The presence of superhyperfine coupling in the Cu(II) complex suggests delocalization of unpaired electron density into the ligand orbitals. Electrochemical studies reveal easier oxidations and harder reductions relative to the corresponding porphyrin derivatives while, the metallated derivatives did not show their characteristic metal reductions due to the high energy of their LUMO.

Barium thiolates and selenolates: syntheses and structural principles.

The synthesis and structural characterization of a family of barium thiolates and selenolates is described. The thiolates were synthesized by metallation of thiols, the selenolates by reductive insertion of the metal into the selenium-selenium bond of diorganodiselenides. Both reaction sequences were carried out by using barium metal dissolved in ammonia; this afforded barium thiolates and selenolates in good yield and purity. The structural principles displayed in the target compounds span a wide range of solid-state formulations, including monomeric and dimeric species, and separated ion triples, namely [Ba(thf)4(SMes*)2] (1; Mes* = 2,4,6-tBU3C6H2), [Ba(thf)4(SeMes*)2] (2), [Ba([18]crown-6)(hmpa)2][(SeMes*)2] (3), the dimeric [(Ba(py)3(thf)(SeTrip)2)2] (4; py = pyridine, Trip = 2,4.6-iPr3C6H2), and [Ba([18]crown-6)(SeTrip)2] (5). The full range of association modes is completed by [Ba([18]crown-6)(hmpa)SMes*][SMes*] (6) communicated earlier by this group. In the solid state, this compound displays an intermediate ion coordination mode: one anion is bound to the metal, while the second one is unassociated. Together these compounds provide structural information about all three different association modes for alkaline earth metal derivatives. This collection of structural data allows important conclusions about the influence of solvation and ligation on structural trends.

Syntheses, structures, and reactivities of heteroleptic magnesium amide thiolates.

The syntheses and characterizations of a family of novel heteroleptic magnesium amide thiolates are presented. The compounds are synthesized by ligand redistribution chemistry involving reactions of equimolar amounts of magnesium amides and magnesium thiolates. Utilization of the smaller thiolates [Mg(SPh)2]n and [Mg(S-2,4,6-iPr3C6H2)2]n results in the isolation of dimeric species, [Mg(THF)(N(SiMe3)2)(mu-SR)]2 (R = Ph (1), 2,4,6-iPr3C6H2 (2)), with four-coordinate metal centers and bridging thiolate functions. The sterically more encumbered thiolate S-2,4,6-tBu3C6H2 induces the formation of the four-coordinate, monomeric species Mg(THF)2(N(SiMe3)2)(S-2,4,6-tBu3C6H2) (3)). Careful choice of reaction conditions allows the successful syntheses of pure heteroleptic compounds; however, it remains difficult to obtain the compounds in high yields, since a tendency toward product symmetrization and ligand redistribution under re-formation of the starting materials is prevalent. One of these symmetrized products is also included in this report: the dimeric, four-coordinate magnesium thiolate [Mg-(THF)(S-2,4,6-tBu3C6H2)(mu-S-2,4,6-tBu3C6H2)]2 (4), isolated as the product of the reaction between [Mg-(N(SiMe3)2)2]2 and Mg(THF)2(S-2,4,6-tBu3C6H2)2. All compounds were characterized by NMR and IR spectroscopy, elemental analyses, and X-ray crystallography. Crystal data obtained with Mo K alpha (lambda = 0.710 73 A) radiation are as follows. 1: C16H31MgNOSSi2, a = 11.2100(1) A, b = 17.4512(3) A, c = 11.2999(2) A, beta = 97.952(1) degrees, V = 2189.32(6) A3, Z = 4, monoclinic, space group P2(1)/n, R1 (all data) = 0.0934. 2: C25H49MgNOSSi2, a = 11.1691(1) A, b = 11.0578(1) A, c = 26.0671(4) A, beta = 99.906(1) degrees, V = 3171.44(6) A3, Z = 4, monoclinic, space group P2(1)/c, R1 (all data) = 0.0557. 3: C36H71MgNO3SSi2, a = 42.8293(16) A, b = 10.9737(5) A, c = 16.8305(7) A, beta = 98.755(3) degrees, V = 7818.1(6) A3, Z = 8, monoclinic, space group C2/c, R1 (all data) = 0.1331. 4: C80H132Mg2O2S4, a = 18.8806(2) A, b = 19.3850(2) A, c = 27.3012(4) A, beta = 97.250(1) degrees, V = 9912.4(2) A3, Z = 4, monoclinic, space group P2(1)/n, R1 (all data) = 0.1023.

meso-Aryl smaragdyrins: novel anion and metal receptors.

An easy synthesis of core-modified meso-aryl smaragdyrins containing oxygen and sulfur in addition to pyrrole nitrogens has been achieved through an alpha-alpha coupling involving modified tripyrrane and dipyrromethane. The complexation behavior of these macrocycles toward anions (Cl-, F-, AMP-) and metal cations (Rh(I), Ni(II)) is reported. Specifically, it has been shown that the Rh(I) and Ni(II) ions bind to the smaragdyrin skeleton in its free base form. X-ray structural studies of Rh(I) complex 1 indicate an eta 2-type coordination involving only one imino and one amino nitrogen of the dipyrromethane unit. However, all four bipyrrole nitrogens participate in the coordination with the Ni(II) ion. Furthermore, Ni(II) coordination oxidizes the ligand, and the complex is formulated as the pi-cation radical of nickel(II) smaragdyrin. The anion complexation is followed in both the solid and solution phases. Solution studies reveal that the binding constants of the ions with the protonated form of smaragdyrin vary as F- > AMP- > Cl-. The X-ray structure of the chloride anion complex reveals that the chloride ion is bound above the cavity of the smaragdyrin macrocycle through three N-H...Cl hydrogen bonds. Crystal data with Mo K alpha (lambda = 0.710,73 A) are as follows: 1, C41H27N4O3Rh, a = 11.836(8) A, b = 12.495(9) A, c = 12.670(2) A, alpha = 69.09(6) degrees, beta = 78.78(6) degrees, gamma = 77.02(5) degrees, V = 1692.1(17) A3, Z = 2, triclinic, space group P-1, R1 (all data) = 0.0471; 4.HCl, C41H29N4O1Cl, a = 11.878(2) A, b = 17.379(4) A, c = 16.015(3) A, beta = 109.546(10) degrees, V = 3115.47(11) A3, Z = 4, monoclinic, space group P2(1)/c, R1(all data) = 0.0850.