Octa-O-propanoyl-beta-maltose: crystal structure, acyl stacking, related structures, and conformational analysis

The crystal structure of beta-maltose octapropanoate (1) was solved to improve understanding of di-, oligo-, and polysaccharide conformations. The O6 and O6' atoms are in gg and gt orientations, respectively. Extrapolation of the coordinates of the non-reducing residue and observed linkage bond and torsion angles of 1 [Formula: see text] yields a left-handed helix similar to amylose triacetate I. The phi and psi values of 1 are also similar to those of other crystalline, acylated maltose compounds as well as some hydroxyl-bearing molecules. Acylated maltose moieties are often stabilized by stacking of the carbonyl groups and alpha-carbons on O3 and O2' as well as by the exo-anomeric effect. The conformation of 1 is within the 1-kcal/mol contour on a hybrid energy map built with a dielectric constant of 7.5, but corresponds to higher energies on maps made with lower dielectric constants. In one region of phi,psi space, both hydroxyl-bearing and derivatized maltose moieties are found but no inter-residue, intramolecular hydrogen-bonding occurs. In another region, only hydroxyl-bearing molecules crystallize and O2'...O3 hydrogen bonds are always found. In agreement with the energy surfaces, amylose helices extrapolated from available linkage geometries were almost all left-handed.     

Production of cross-reactive peptide antibodies against viral capsid proteins of human enterovirus B to apply diagnostic reagent

The coxsackievirus group B (CVB) of the genus Enterovirus and the species human enterovirus B is a nonenveloped virus containing a single-stranded positive-sense RNA genome. Coxsackievirus has icosahedral symmetry and four capsid proteins, VP1, VP2, VP3, and VP4. Specific antibodies against each viral protein are prerequisites for various studies. In this study, we developed seven peptide-derived antibodies directed against coxsackievirus VP1 (NO1-NO5), VP2 (B3), and VP3 (GL3). We developed a type-specific antibody (NO1) and broadly cross-reactive antibodies (NO3 and NO5) to VP1. Anti-VP2 and anti-VP3 antibodies (B3 and GL3, respectively) are also cross-reactive to human enterovirus B such as CVB and echoviruses. Their sensitivities and reactivities are likely to be better than those of the commercial VP1 monoclonal antibody (MAb). The dot-blot analysis also showed that NO5 against VP1 is able to detect less than 1 microg [2x10(6) plaque-forming unit (pfu) of CVB3] of viruses, suggesting that it could be used to develop a diagnostic kit that can directly detect human enterovirus B. The antibodies produced here may allow us to undertake several studies, such as those involving viral trafficking, expression kinetics, and the roles of viral proteins in infection, and the development of diagnostic kits.     

Influence of the nature of quantum dot surface cations on interactions with DNA

Quantum dots are semiconductor nanoparticles that are approximately 1-10nm in diameter, similar to small proteins, and their photoluminescence is sensitive to the presence and nature of adsorbates. We have deployed these nanomaterials as luminescent probes of DNA structure. Sequence dependent conformational flexibility of DNA is of great interest due to its implications for drug-DNA and DNA-protein interactions. The counterion atmosphere surrounding DNA plays an important role in its structure, dynamics, and packaging. In this paper, we investigate the effect that various monovalent and divalent cations have on the binding of 4.5 nm CdS quantum dots to oligonucleotides that have sequence-directed intrinsic structure.     

Cation radicals of xanthophylls

Carotenes and xanthophylls are well known to act as electron donors in redox processes. This ability is thought to be associated with the inhibition of oxidative reactions in reaction centers and light-harvesting pigment–protein complexes of photosystem II (PSII). In this work, cation radicals of neoxanthin, violaxanthin, lutein, zeaxanthin, β-cryptoxanthin, β-carotene, and lycopene were generated in solution using ferric chloride as an oxidant and then studied by absorption spectroscopy. The investigation provides a view toward understanding the molecular features that determine the spectral properties of cation radicals of carotenoids. The absorption spectral data reveal a shift to longer wavelength with increasing π-chain length. However, zeaxanthin and β-cryptoxanthin exhibit cation radical spectra blue-shifted compared to that of β-carotene, despite all of these molecules having 11 conjugated carbon–carbon double bonds. CIS molecular orbital theory quantum computations interpret this effect as due to the hydroxyl groups in the terminal rings selectively stabilizing the highest occupied molecular orbitals of preferentially populated s-trans-isomers. The data are expected to be useful in the analysis of spectral results from PSII pigment–protein complexes seeking to understand the role of carotene and xanthophyll cation radicals in regulating excited state energy flow, in protecting PSII reaction centers against photoinhibition, and in dissipating excess light energy absorbed by photosynthetic organisms but not used for photosynthesis.     

A hot start alternative for high-fidelity DNA polymerase amplification mediated by quantum dots

Quantum dots （QDs） are of great interest due to their unique chemical and physical properties. Recently, a hot start （HS） polymerase chain reaction （PCR） amplification performance based on QDs with a high-fidelity Pfu DNA polymerase has been reported. However, whether QDs can trigger HS effects with other high-fidelity or conventional DNA polymerases is yet to be understood. In the present study, we studied the QD-triggered HS effects with four high-fidelity and three conventional DNA polymerases, and the HS effect comparisons among them were also made. It was found that QDs could trigger a distinct HS PCR amplification performance with all the four tested high,fidelity DNA polymerases, and specific target DNA could be well amplified even if the PCR mixture was preincubated for 2 h at 50℃. On the contrary, the HS effects were not prominent with all the three conventional Taq DNA polymerases. Specifically, the fidelity of Pfu is not sacrificed in the presence of QDs, even after a 1 h pre-incu- bation at 50℃ before PCR. Furthermore, the electrophoresis results preliminarily demonstrated that QDs prefer to adsorb high-fidelity polymerases rather than conventional ones, which might result in the QD-triggered HS effects on PCR performance by using high-fidelity DNA poly- merases.     

量子点免疫层析快速定量检测HCG

近年来,量子点以其独特的光学性质被广泛应用到医学检测上.血清中人绒毛膜促性腺激素(HCG)的含量是诊断早期妊娠的常用指标,也可用于异常妊娠性疾病的早期发现和鉴别诊断.本文采用超声乳化法制备了高质量的亲水性量子点,并将其与免疫层析试纸条技术相结合,在此基础上自主研发了用于试纸条检测的量子点免疫荧光检测仪,对血清中HCG的含量进行了高灵敏度的快速定量检测.结果表明,对于血清中的HCG含量检测,最优检测条件为加样体积50μl,反应时间15 min,检测的灵敏度达到0.85 U/L,高于商品化的胶体金试纸条.这种检测技术简单、快速、灵敏,有望在其他蛋白质类标志物的检测中得到广泛应用.     

Kelsoenethiol and dikelsoenyl ether,two unique kelsoane-type sesquiterpenes,from the Formosan soft coral Nephthea erecta

Two new kelsoane-type sesquiterpenes, namely kelsoenethiol (1) and dikelsoenyl ether (2), were obtained from the Formosan soft coral Nephthea erecta. Their structures were elucidated through extensive spectroscopic analyses, ESI orbitrap mass and quantum chemical calculations (QCC). The cytotoxicity against A-459 (human lung carcinoma), P-388 (mouse lymphocytic leukemia), and HT-29 (human colon adenocarcinoma) cancer cell lines of 1 and 2 was evaluated in vitro. Compound 1 showed cytotoxicity against P-388 and HT-29 cells with ED_50s of 1.3 and 1.8 μg/mL, respectively.     

Crystal structure of glycoside hydrolase family 127 β-l-arabinofuranosidase from Bifidobacterium longum

Enzymes acting on β-linked arabinofuranosides have been unknown until recently, in spite of wide distribution of β-l-arabinofuranosyl oligosaccharides in plant cells. Recently, a β-l-arabinofuranosidase from the glycoside hydrolase family 127 (HypBA1) was discovered in the newly characterized degradation system of hydroxyproline-linked β-l-arabinooligosaccharides in the bacterium Bifidobacterium longum. Here, we report the crystal structure of HypBA1 in the ligand-free and β-l-arabinofuranose complex forms. The structure of HypBA1 consists of a catalytic barrel domain and two additional β-sandwich domains, with one β-sandwich domain involved in the formation of a dimer. Interestingly, there is an unprecedented metal-binding motif with Zn²⁺ coordinated by glutamate and three cysteines in the active site. The glutamate residue is located far from the anomeric carbon of the β-l-arabinofuranose ligand, but one cysteine residue is appropriately located for nucleophilic attack for glycosidic bond cleavage. The residues around the active site are highly conserved among GH127 members. Based on biochemical experiments and quantum mechanical calculations, a possible reaction mechanism involving cysteine as the nucleophile is proposed.     

Quantum mechanical study of Burkholderia cepacia lipase enantioselectivity

Quantum mechanical, semiempirical (AM1) and ab initio (6-31G*) study of the Burkholderia cepacia lipase (BCL) catalysed reactions of the secondary alcohol esterification and its ester hydrolysis is presented. We have selected BCL for our study because of numerous experimental results available, but also because of its broad selectivity and stability that makes it interesting for industrial use. Previously we developed models for predicting lipase stereo-selectivity towards primary and secondary alcohols according to their structural parameters. In this work we show that not all of the experimentally determined binding modes are catalytically competent and that additional molecular modelling should be accomplished in order to find good starting points to study chemical reactions. The binding modes from which chemical modification of a substrate is possible are the most relevant for understanding enzyme selectivity and for the rational enzyme engineering.

We also investigated the influence of the tetrahedral atom type, C and P, upon the energy barriers in the proton transfer reactions from the catalytic histidine (His286) to either the catalytic serine (Ser87) or the alcohol oxygen of the substrate.     

Synthesis, crystal structure and quantum study of organoammonium polyoxomolybdate with one-dimension chain containing face-shared molybdenum-oxygen octahedra

Organoammoinium polyoxomolybdate [(enH)₂(H₂Mo₆O₂₀)]_∞ was formed in autogeneous pressure at 160 °C for 120 h. The colorless crystals of polyoxomolybdate were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. The crystals are in monoclinic system with a space group P2₁/n and a = 8.0844(16), b = 14.413(3), c = 8.9153(18) Å, β = 98.12(3)°, V = 1013.8(4) ų, Z = 4. The final R = 0.0375, wR = 0.0706 for 2370 reflections [I > σ(I₀)].The crystals are constructed by one-dimension infinite inorganic chains with Mo₆O₂₀ unit as building block and protonated ethylenediamine cations located in between the inorganic chains. There are many hydrogen bonds between the chains and between the chains and the cations. IR spectrum of the title compound exhibited the vibration absorption of MoO, Mo-O-Mo bonds and protonated ethylenediamine cations, and suggests the presence of N-H-O and O-H-O hydrogen bonds. Quantum calculation gives the distribution of charges and the composition of frontier molecular orbits. From the calculation results, it can be inferred that protonation must have occurred on the terminal oxygen atom (O3) due to its smallest charge value and the terminal oxygen atom (O3) forms hydrogen bonds with the O12 atoms of the adjacent chain (2.936 Å); and that Mo1 atom will first receive the reduced electron. The electron transition taking place between HOMO and LUMO belongs basically to O → Mo charge transfer transition.