Stationary points in the temperature dependence of electron transfer rates

The temperature dependence of the rate of electron transfer is analyzed in the framework of a molecular theory presented recently, characterized by decoupling the total solvent reorganization energy into two contributions featuring reorganizations of permanent dipoles as well as solvent density. The inclusion of the temperature dependence of liquid density reorganization can give rise to a maximum in the Arrhenius coordinates for electron transfer in the inverted region and for exothermic reactions with small activation barriers as well.     

Metal complexes with an aminosubstituted tricarbollide ligand

The reaction of the tricarbollide salt Tl[7-tBuNH-7,8,9-C₃B₈H₁₀] (Tl1) with [(cod)Rh(THF)_x]⁺ gives the rhodium complex [1-(cod)-12-tBuNH-1,2,4,12-RhC₃B₈H₁₀] in almost quantitative yield. Analogous reactions of Tl1 with [(ring)M(THF)_x]²⁺ ((ring)M = Cp*Rh and (1,3,5-C₆H₃Me₃)Ru) afford the corresponding metallatricarbollides [1-(ring)-12-tBuNH-1,2,4,12-MC₃B₈H₁₀] in ca. 50% yield. Refluxing Tl1 with [Mn(CO)₃(MeCN)₃]⁺ in THF give the tricarbollide analogue of cymantrene, [1,1,1-(CO)₃-12-tBuNH-1,2,4,12-MnC₃B₈H₁₀], the structure of which was determined by single-crystal X-ray diffraction analysis. In all cases, the formation of the metallatricarbollide complexes is accompanied by polyhedral rearrangement leading to the maximum separation of the cage carbon atoms.     

A very large diversity space of synthetically accessible compounds for use with drug design programs

We have constructed a very large virtual diversity space containing more than 10¹³ chemical compounds. The diversity space is built from about 400 combinatorial libraries, which have been expanded by choosing sizeable collections of suitable R-groups that can be attached to each link point of their scaffolds. These R-group collections have been created by selecting reagents that have drug-like properties from catalogs of available chemicals. As members of known combinatorial libraries, the compounds in the diversity space are in general synthetically accessible and useful as potential drug leads. Hence, the diversity space can be used as a vast source of compounds by a de novo drug design program. For example, we have used such a program to generate inhibitors of HIV integrase enzyme that exhibited activity in the micromolar range.     

Water-soluble meroterpenes containing an aminoglyceride fragment with geraniol residues: synthesis and membranotropic properties

1. Download high-res image (189KB)
2. Download full-size image

     

Characteristic frequencies in the infrared spectra of pyrazolines

Pyrazolines are characterized by valence vibrations at the following frequencies: C=N (1580–1627 cm^–1), H-C³=N (3040–3063 cm^–1), H-N (3270–3305 cm^–1) and CH₃-N (2780–2805 cm^–1). Lowering of the frequencies of the valence vibrations of C=N in pyrazolines, when compared with the magnitudes characteristic of alkyledene amines and oximes, is regarded as a consequence of coupling with the unshared electron pair of the neighboring nitrogen atom. By means of the IR spectra, it is possible to determine the position of the double bonds in the pyrazoline ring, to distinguish between pyrazolines substituted and nonsubstituted in positions 1 and 3, and to establish the presence of geminate (twin) methyl groups and methyl groups in position 1.     

对一个大单轴磁各向异性镍(Ⅱ)配合物中的磁跃迁的直接观察

最近Ruamps和同事发现三角双锥构型的Ni（Ⅱ）配合物[Ni（Me₆tren）Cl]ClO₄（1，Me₆tren=tris（2-（dimethylamino）ethyl）amine）具有大的单轴磁各向异性（J.Am.Chem.Soc.，2013，135：3017-3026）。他们利用HF-EPR研究获得横向零场分裂（ZFS）参数E=1.56（5）cm^-1但未能确定轴向零场分裂参数D。在本工作中，我们利用0~17.5 T和5 K的变磁场远红外光谱（FIRMS）来检测自旋基态S=1中的M_S=±1和M_S=0态之间的磁跃迁。在FIRMS中直接观察到Zeeman分裂态之间的跃迁，得出轴向ZFS参数D=-110.7（3）cm^-1。我们对1的晶体结构进行了Hirshfeld表面分析，揭示了1分子中的阳离子与阴离子之间以及分子之间的相互作用。     

Total stepwise solid-phase synthesis of oligonucleotide-(3'-->N)-peptide conjugates

[structure: see text] An efficient total stepwise solid-phase synthesis of oligonucleotide-(3'-->N)-peptide conjugates is described that makes use of either a controlled pore glass support or macroporous polystyrene beads. Extending our previous homoserine linker approach, we prepared a range of conjugates containing one of four different cell or nuclear penetration peptides together with oligonucleotides containing 2'-deoxynucleoside or 2'-O-methylribonucleoside phosphodiesters, or gapmers containing 2'-deoxyphosphorothioates. The route also allows incorporation of a fluorescent label within the conjugate for cell uptake studies.     

A convenient route to 1-(2-oxiranyl)-1,4-diketones and their application to the synthesis of endo-brevicomin, endo-isobrevicomin, frontalin and related compounds via alkylated 6,8-dioxabicyclo[3.2.1]octan-2-ones

1-(2-Oxiranyl)-1,4-alkanediones were prepared from the ethylene acetals of ethyl 4-oxoalkanoates via the oxidation of the intermediate 1,2-dialkylcyclopropanols having a protected carbonyl group in an aliphatic chain. Intramolecular acetalization of these epoxy dicarbonyl compounds gave alkylated 6,8-dioxabicyclo[3.2.1]octan-2-ones in good yields. The latter were found suitable to be precursors for (±)-endo-brevicomin and its 2-hydroxy derivative, as well as (±)-endo-isobrevicomin and (±)-frontalin.     

Dichloro[N,N‐dimethyl‐1‐(1‐methyl‐1H‐tetrazol‐5‐yl‐κN4)methanamine‐κN]copper(II)

The title compound, [CuCl₂(C₅H₁₁N₅)], is the first structurally characterized molecular chelate complex involving an α‐­amino­alkyl­tetrazole. There are two complex mol­ecules in the asymmetric unit. The ligand mol­ecules are bidentate. Both Cu atoms reveal rather distorted square‐planar coordinations. The complex mol­ecules are linked together by van der Waals interactions only.     

Iron(III) dihydrogenphosphate(I)

The structure of rhombohedral (R) iron(III) tris­[di­hydrogen­phosphate(I)] or iron(III) hypophosphite, Fe(H₂PO₂)₃, has been determined by single‐crystal X‐ray diffraction. The structure consists of [001] chains of Fe³⁺ cations in octa­hedral sites with symmetry bridged by bidentate hypophosphite anions.