Influence of (hydroxy)alkylamino substituents on enantioseparation ability of single-isomer amino-beta-cyclodextrin derivatives in chiral capillary electrophoresis

A family of single-isomer amino-beta-cyclodextrin (amino-beta-CD) derivatives containing an amino or (hydroxy)alkylamino group in one of the primary positions has been synthesized. The steric effect and hydrogen bond forming ability of the different substituents on enantioseparation of acidic enantiomers has been studied by capillary electrophoresis (CE). Three enantiomeric model compounds (mandelic acid, cis-permethrinic acid, and cis-deltamethrinic acid) having significantly different apparent complex stability constants with beta-CD were applied in the experiments. Dependence of separation selectivity, resolution as well as mobility difference on chiral selector concentration (0.1-20 mM, pH 6.0) was investigated. Each amino-beta-CD showed higher enantioselectivity than the native beta-CD. One hydroxyalkyl group attached to the primary amino N-atom significantly increased both the enantioselectivity and the resolution compared to the primary amino-beta-CD, while two hydroxyalkyl moieties decreased them due to the predominance of steric hindrance. The value of the apparent complex stability constants obtained suited well the mobility difference model (by Wren). On the other hand, the optimum selector concentrations calculated according to the model were slightly lower than the experienced concentrations giving the maximum enantioresolution of enantiomers.     

Controlling Light-Induced Proton Transfer from the GFP Chromophore

Green Fluorescent Protein (GFP) is known to undergo excited-state proton transfer (ESPT). Formation of a short H-bond favors ultrafast ESPT in GFP-like proteins, such as the GFP S65T/H148D mutant, but the detailed mechanism and its quantum nature remain to be resolved. Here we study in vacuo, light-induced proton transfer from the GFP chromophore in hydrogen-bonded complexes with two anionic proton acceptors, I⁻ and deprotonated trichloroacetic acid (TCA⁻). We address the role of the strong H-bond and the quantum mechanical proton-density distribution in the excited state, which determines the proton-transfer probability. Our study shows that chemical modifications to the molecular network drastically change the proton-transfer probability and it can become strongly wavelength dependent. The proton-transfer branching ratio is found to be 60 % for the TCA complex and 10 % for the iodide complex, being highly dependent on the photon energy in the latter case. Using high-level ab initio calculations, we show that light-induced proton transfer takes place in S₁, revealing intrinsic photoacid properties of the isolated GFP chromophore in strongly bound H-bonded complexes. ESPT is found to be very sensitive to the topography of the highly anharmonic potential in S₁, depending on the quantum-density distribution upon vibrational excitation. We also show that the S₁ potential-energy surface, and hence excited-state proton transfer, can be controlled by altering the chromophore microenvironment.     

Li2B12Si2: the first ternary compound in the system Li/B/Si: synthesis, crystal structure, hardness, spectroscopic investigations, and electronic structure

We present the synthesis, crystal structure, hardness, IR/Raman and UV/Vis spectra, and FP-LAPW calculations of the electronic structure of Li(2)B(12)Si(2), the first ternary compound in the system Li/B/Si. Yellow, transparent single crystals were synthesized from the elements in tin as solvent at 1500 degrees C in h-BN crucibles in arc-welded Ta ampoules. Li(2)B(12)Si(2) crystallizes orthorhombic in the space group Cmce (no. 64) with a=6.1060(6), b=10.9794(14), c=8.4050(8) A, and Z=4. The crystal structure is characterized by a covalent network of B(12) icosahedra connected by Si atoms and Li atoms located in interstitial spaces. The structure is closely related to that of MgB(12)Si(2) and fulfils the electron-counting rules of Wade and Longuet-Higgins. Measurements of Vickers (H(V)=20.3 GPa) and Knoop microhardness (H(K)=20.4 GPa) revealed that Li(2)B(12)Si(2) is a hard material. The band gap was determined experimentally and calculated by theoretical means. UV/Vis spectra revealed a band gap of 2.27 eV, with which the calculated value of 2.1 eV agrees well. The IR and Raman spectra show the expected oscillations of icosahedral networks. Theoretical investigations of bonding in this structure were carried out with the FP-LAPW method. The results confirm the applicability of simple electron-counting rules and enable some structural specialties to be explained in more detail.     

Hydrothermal synthesis of a mixed-valence hexamolybdate cluster: crystal structure of [HN(CH2CH2)3N]2[HMoVMoVI5O19]·[N(CH2CH2)3N]

The hydrothermal reaction of MoO₃, V, Na₂WO₄· 2H₂O, [N(CH₂CH₂)₃N](1,4-diazabicyclo[2.2.2] octane), and H₂O at 160°C for 90h gave dark-brown crystals of [HN(CH₂CH₂)₃N]₂[HMo^VMo^VI ₅O¹⁹]·[N(CH₂CH₂)₃N], (1), in 40% yield. Complex (1) is the first one-electron reduced mixed-valence hexamolybdate to be crystallized and structurally characterized. The crystal structure of (1) consists of discrete [HMo^VMo^VI ₅O₁₉]^2– anions, [HN-(CH₂CH₂)₃N]⁺ cations, and neutral [N(CH₂CH₂)₃N] molecules of crystallization.     

The life and work of Sophie Germain

We discuss the life of Sophie Germain, her struggle to educate herself and to win acceptance within the French mathematical community, and her contributions to number theory and to the theory of elasticity.     

A Synthetic Glycopeptide Vaccine for the Induction of a Monoclonal Antibody that Differentiates between Normal and Tumor Mammary Cells and Enables the Diagnosis of Human Pancreatic Cancer

In studies within the realm of cancer immunotherapy, the synthesis of exactly specified tumor‐associated glycopeptide antigens is shown to be a key strategy for obtaining a highly selective biological reagent, that is, a monoclonal antibody that completely differentiates between tumor and normal epithelial cells and specifically marks the tumor cells in pancreas tumors. Mucin MUC1, which is overexpressed in many prevalent cancers, was identified as a promising target for this strategy. Tumor‐associated MUC1 differs significantly from that expressed by normal cells, in particular by altered glycosylation. Structurally defined tumor‐associated MUC1 cannot be isolated from tumor cells. We synthesized MUC1–glycopeptide vaccines and analyzed their structure–activity relationships in immunizations; a monoclonal antibody that specifically distinguishes between human normal and tumor epithelial cells was thus generated.