Anthracene Based Bulky Diol Hosts. Crystal Structures of a Free Host and of Inclusion Compounds with Dipolar Guests

X-ray crystal structures are reported of a free host compound 1, comprising two diphenylmethanol terminal groups attached to a central 9,10-ethynyl substituted anthracene unit, and of three inclusion compounds of a fluoren-9-ol substituted analogous host 2 with acetone, dimethyl sulphoxide (DMSO) and dimethylformamide (DMF) as guest, respectively. Despite the presence of two hydroxyl groups in 1, there is no O–H...O hydrogen bond between the molecules in the guest free crystal – only weaker C–H...O interactions and van der Waals' type connections. In the inclusion compounds of 2, H-bonded 1:2 host–guest associates are formed, where each of the host hydroxyl groups binds to a guest oxygen atom. The orientations of the host–guest connections in these complexes vary, being E for acetone and Z for both DMSO and DMF guests, relative to the host anthracene unit. The DMSO and DMF inclusion compounds of 2 proved to be isostructural.     

Dissociation of sulfur dioxide by ultraviolet multiphoton absorption between 224 and 232 nm

Multiphoton excitation and dissociation of SO(2) have been investigated in the wavelength range from 224 to 232 nm. Strong evidence is found for two-photon excitation to the H Rydberg state, followed by dissociation to SO + O and ionization of the SO product by absorption of a third photon. The two-photon excitation is resonantly enhanced via the C (1)B(2) intermediate state, and the two-photon yield spectrum thus bears a strong resemblance to the spectrum of this intermediate. Imaging of the O((3)P(2)), S((1)D(2)), and SO products suggests that, following dissociation of SO(2) from the H state, SO is produced in the A and B electronic states. S((1)D(2)) is produced both from two-photon dissociation of SO(2) to give S((1)D(2)) + O(2) and by single-photon dissociation of SO(+). In the former process, the O(2) is likely formed in all of its lowest three electronic states.     

Aziridinomitosenes by anionic cyclization: deuterium as a removable blocking group

Treatment of 11a with methyllithium affords the destannylated product 12 together with a small amount of tetracyclic product derived from intramolecular Michael addition. The same procedure from the deuterated analogue 11b gives the tetracyclic 18 as the major product, the result of a substantial kinetic deuterium isotope effect that favors formation of 16 and 17 by suppressing indole ring lithiation to the undesired 15. When the product mixture is quenched with phenylselenenyl chloride, 17 is converted into the aziridinomitosene 19 in 80% yield. Conversion into the aziridinomitosene alcohol 21 and the deprotected aziridine 20 is also demonstrated.     

Studies on Radical Cations,III. The Type C Valence-Isomeric System Quadricyclane Radical Cation/Norbornadiene Radical Cation

The previously discussed principles involved in electrocyclic reactions of openshell ions are exemplified for a type C system, the radical cation couple quadricyclane⁺ ( Q ⁺)/norbornadiene⁺ ( NBD ⁺). Exhaustive calculations (MINDO/3) for the various states of the ions support the general predictions for such types of systems. The barrier of interconversion Q ⁺ → NBD ⁺ is estimated to be significantly lower than that for the corresponding neutrals. Experimental support to this prediction is obtained by γ-irradiation of Q or NBD in an electron scavenging matrix. In both cases only NBD ⁺ is observed, indicating that Q ⁺ is not stable at 77 K. Previous observations and propositions referring to the system Q ⁺/ NBD ⁺ are discussed in view of the present findings.     

C(methyl)–H ⋅ ⋅ ⋅ π(aryl) Interaction Stabilizing Molecular Conformation. X-Ray Crystal Structure of an Inclusion Compound of a Nonprotic Host with Nitromethane Guest

In the cocrystal formation of a nonprotic polar (host) molecule (1) with nitromethane (guest) several weak, but directional, intermolecular interactions have vital importance. The endo conformation of the (N)-xylene group of the polycyclic succinimide-based host 1 is stabilized by a C_methyl $---$ H ??? π interaction [C ??? π /H ??? π distances are 3.554(7)/2.57 Å, the C $---$ H ??? π angle is 159^○], and the crystal packing is governed by dipole–dipole type interhost (C $ =$ )O ??? C( $ =$ O) connection [C ??? O $ =$ 3.000(5) Å and <C $ =$ O ??? C $ =$ 159.8(3)^○] in conjunction with possible C $---$ H ??? O interactions [with C ??? O distances ranging between 3.20 and 3.50 Å] involving the polar groups of both host and guest. Crystal data: 1 ??? nitromethane (1:1), C₂₆H₂₁O₂ N ? CH₃NO₂, M _w = 440.50, P2 ₁/n, a = 14.143(1), b = 7.973(1), c = 20.291(2) Å, β = 95.183(9)^○, Z = 4, D _c = 1.2840(2) g cm^?3, R = 0.055 for 1709 reflections.     

Electrochemical probing of ground state electronic interactions in polynuclear complexes of a new heteroditopic ligand

The synthesis and electronic properties of dinuclear ([(bipy)2Ru(I)M(terpy)][PF6]4(bipy = 2,2'-bipyridine, terpy = 2,2':6',2'-terpyridine; M = Ru, Os)) and trinuclear ([[(bipy)2Ru(I)]2M][PF6]6 M = Ru, Os, Fe, Co) complexes bridged by 4'-(2,2'-bipyridin-4-yl)-2,2':6',2'-terpyridine (I) have been investigated and are compared with those of mononuclear model complexes. The electrochemical analysis using cyclic voltammetry and differential pulse voltammetry reveals that there are no interactions in the ground state between adjacent metal centres. However, there is strong electronic communication between the 2,2'-bipyridine and 2,2':6',2'-terpyridine components of the bridging ligand. This conclusion is supported by a step-by-step reduction of the dinuclear and trinuclear complexes and the assignment of each electrochemical process to localised ligand sites within the didentate and terdentate domains. The investigation of the electronic absorption and emission spectra reveals an energy transfer in the excited state from the terminating bipy-bound metal centres to the central terpy-bound metal centre. This indicates that the bridge is able to facilitate energy transfer in the excited state between the metal centres despite the lack of interactions in the ground state.     

Nickel-manganese sulfido carbonyl cluster complexes. synthesis, structure, and properties of the unusual paramagnetic complexes Cp2Ni2Mn(CO)3(mu 3-E)2, E = S, Se

The reaction of Mn(2)(CO)(7)(mu-S(2)) with [CpNi(CO)](2) yielded the paramagnetic new compound Cp(2)Ni(2)Mn(CO)(3)(mu(3)-S)(2) (1) and a new hexanuclear metal product Cp(2)Ni(2)Mn(4)(CO)(14)(mu(6)-S(2))(mu(3)-S)(2) (2). Structurally, compound 1 contains two triply bridging sulfido ligands on opposite sides of an open Ni(2)Mn triangular cluster. EPR and temperature-dependent magnetic susceptibility measurements of 1 show that it contains one unpaired electron. The electronic structure of 1 was determined by Fenske-Hall molecular orbital calculations which show that the unpaired electron occupies a low lying antibonding orbital delocalized unequally across the three metal atoms. The selenium homologue Cp(2)Ni(2)Mn(CO)(3)(mu(3)-Se)(2) (3) was obtained from the reaction of a mixture of Mn(2)(CO)(10) and [CpNi(CO)](2) with elemental selenium and Me(3)NO.2H(2)O. It also has one unpaired electron. Compound 1 reacted with elemental sulfur to yield the dinickeldimanganese compound, Cp(2)Ni(2)Mn(2)(CO)(6)(mu(4)-S(2))(mu(4)-S(5)), 4, which can also be made from the reaction of Mn(2)(CO)(7)(mu-S(2)) with [CpNi(CO)](2) and sulfur. Compound 4 was converted back to 1 by sulfur abstraction using PPh(3). The reaction of Mn(2)(CO)(10) with [CpNi(CO)](2) in the presence of thiirane yielded the ethanedithiolato compound CpNiMn(CO)(3)(mu-SCH(2)CH(2)S) (5), which was also obtained from the reaction of Mn(4)(CO)(15)(mu(3)-S(2))(mu(4)-S(2)) with [CpNi(CO)](2) in the presence of thiirane. Compound 5 reacted with additional quantities of thiirane to yield the new compound CpNiMn(CO)(3)[mu-S(CH(2)CH(2)S)(2)], 6, which contains a 3-thiapentanedithiolato ligand that bridges the two metal atoms. Compound 6 was also obtained from the reaction of Mn(2)(CO)(10) with [CpNi(CO)](2) and thiirane. The molecular structures of the new compounds 1-6 were established by single-crystal X-ray diffraction analyses.     

Human neural stem cell growth and differentiation in a gradient-generating microfluidic device

This paper describes a gradient-generating microfluidic platform for optimizing proliferation and differentiation of neural stem cells (NSCs) in culture. Microfluidic technology has great potential to improve stem cell (SC) cultures, whose promise in cell-based therapies is limited by the inability to precisely control their behavior in culture. Compared to traditional culture tools, microfluidic platforms should provide much greater control over cell microenvironment and rapid optimization of media composition using relatively small numbers of cells. Our platform exposes cells to a concentration gradient of growth factors under continuous flow, thus minimizing autocrine and paracrine signaling. Human NSCs (hNSCs) from the developing cerebral cortex were cultured for more than 1 week in the microfluidic device while constantly exposed to a continuous gradient of a growth factor (GF) mixture containing epidermal growth factor (EGF), fibroblast growth factor 2 (FGF2) and platelet-derived growth factor (PDGF). Proliferation and differentiation of NSCs into astrocytes were monitored by time-lapse microscopy and immunocytochemistry. The NSCs remained healthy throughout the entire culture period, and importantly, proliferated and differentiated in a graded and proportional fashion that varied directly with GF concentration. These concentration-dependent cellular responses were quantitatively similar to those measured in control chambers built into the device and in parallel cultures using traditional 6-well plates. This gradient-generating microfluidic platform should be useful for a wide range of basic and applied studies on cultured cells, including SCs.     

Advantages and drawbacks of nanospray for studying noncovalent protein-DNA complexes by mass spectrometry

The noncovalent complexes between the BlaI protein dimer (wild-type and GM2 mutant) and its double-stranded DNA operator were studied by nanospray mass spectrometry and tandem mass spectrometry (MS/MS). Reproducibility problems in the nanospray single-stage mass spectra are emphasized. The relative intensities depend greatly on the shape of the capillary tip and on the capillary-cone distance. This results in difficulties in assessing the relative stabilities of the complexes simply from MS(1) spectra of protein-DNA mixtures. Competition experiments using MS/MS are a better approach to determine relative binding affinities. A competition between histidine-tagged BlaIWT (BlaIWTHis) and the GM2 mutant revealed that the two proteins have similar affinities for the DNA operator, and that they co-dimerize to form heterocomplexes. The low sample consumption of nanospray allows MS/MS spectra to be recorded at different collision energies for different charge states with 1 microL of sample. The MS/MS experiments on the dimers reveal that the GM2 dimer is more kinetically stable in the gas phase than the wild-type dimer. The MS/MS experiments on the complexes shows that the two proteins require the same collision energy to dissociate from the complex. This indicates that the rate-limiting step in the monomer loss from the protein-DNA complex arises from the breaking of the protein-DNA interface rather than the protein-protein interface. The dissociation of the protein-DNA complex proceeds by the loss of a highly charged monomer (carrying about two-thirds of the total charge and one-third of the total mass). MS/MS experiments on a heterocomplex also show that the two proteins BlaIWTHis and BlaIGM2 have slightly different charge distributions in the fragments. This emphasizes the need for better understanding the dissociation mechanisms of biomolecular complexes.