"Alpha"-, "beta"- and "delta"-anhydrodigitoxigenin

The syntheses of 3β-hydroxy-5β-carda-14, 20:22-dienolide (= «β»-anhydro-), 3β-hydroxy-5β-carda-8:14, 20:22-dienolide (= «α»-anhydro-) and «δ»-anhydro-digitoxigenin (= probably 3β-hydroxy-5β, 14β-carda-8, 20:22-dienolide) by the best ways known to date, have been described. «δ»-Anhydro-digitoxigenin represents the thermodynamically most stable isomer. In this isomer the double bond in position 8 is unaffected by hydrogenation with Pt in acetic acid; with perbenzoic acid an epoxide results from which, on hydrogenation, the double bond can be regenerated in its original position. Analogous reactions are known to occur in the 8:14-epoxides.     

Making "wheels" and "cubes" from triangles

[Mn(IV)Mn(II)3] triangular units directed by the presence of tripodal alcohols self-assemble in the presence of azide and acetate ligands to form either a [Mn24] "wheel" or a [Mn32] "cube".     

营养化学课程翻转课堂的探索与实践

With its tailored learning content, flexible learning environment and directed teacher guidance, the flipped classroom in "nutrition chemistry" has effectively solved the problems of students' specialty, large number and limited time in the course of elective course. The teaching mode based on the cultivation of students' ability and the core of improving scientific literacy was constructed.     

Size evolution study of "molecular" and "atom-in-cluster" polarizabilities of medium-size gold clusters

A study on static polarizabilities for a family of gold clusters (Au(n), n = 6, 12, 20, 34, 54) is presented. For each cluster, a density functional theory perturbation theory calculation was performed to compute the cluster polarizability and the polarizability of each atom in the cluster using Bader's "quantum theory of atoms in molecules" formalism. The cluster polarizability tensor, α(cluster), is expressed as a sum of the atom-in-molecule tensors, α(cluster)=∑(Ω)α(Ω). A strong quadratic correlation (R(2) = 0.98) in the isotropic polarizability of atoms in the cluster and their distance to the cluster center of mass was observed. The cluster polarizabilities are in agreement with previous calculations.     

Fabrication of "roll-off" and "sticky" superhydrophobic cellulose surfaces via plasma processing

Most of the artificial superhydrophobic surfaces that have been fabricated to date are not biodegradable, renewable, or mechanically flexible and are often expensive, which limits their potential applications. In contrast, cellulose, a biodegradable, renewable, flexible, inexpensive, biopolymer which is abundantly present in nature, satisfies all the above requirements, but it is not superhydrophobic. Superhydrophobicity on cellulose paper was obtained by domain-selective etching of amorphous portions of the cellulose in an oxygen plasma and subsequently coating the etched surface with a thin fluorocarbon film deposited via plasma-enhanced chemical vapor deposition using pentafluoroethane as a precursor. Variation of plasma treatment yielded two types of superhydrophobicity : "roll-off" (contact angle (CA), 166.7 degrees +/- 0.9 degrees ; CA hysteresis, 3.4 degrees +/- 0.1 degrees ) and "sticky" (CA, 144.8 degrees +/- 5.7 degrees ; CA hysteresis, 79.1 degrees +/- 15.8 degrees ) near superhydrophobicity. The nanometer scale roughness obtained by delineating the internal roughness of each fiber and the micrometer scale roughness which is inherent to a cellulose paper surface are robust when compared to roughened structures created by traditional polymer grafting, nanoparticle deposition, or other artificial means.     

Switching "on" and "off" the expression of chirality in peptide rotaxanes

The hydrogen-bond-directed synthesis, X-ray crystal structures, and optical properties of the first chiral peptide rotaxanes are reported. Collectively these systems provide the first examples of single molecular species where the expression of chirality in the form of a circular dichroism (CD) response can selectively be switched "on" or "off", and its magnitude altered, through controlling the interactions between mechanically interlocked submolecular components. The switching is achievable both thermally and through changes in the nature of the environment. Peptido[2]rotaxanes consisting of an intrinsically achiral benzylic amide macrocycle locked onto various chiral dipeptide (Gly-L-Ala, Gly-L-Leu, Gly-L-Met, Gly-L-Phe, and Gly-L-Pro) threads exhibit strong (10-20k deg cm(2) dmol(-1)) negative induced CD (theta;) values in nonpolar solvents (e.g. CHCl(3)), where the intramolecular hydrogen bonding between thread and macrocycle is maximized. In polar solvents (e.g., MeOH), where the intercomponent hydrogen bonding is weakened, or switched off completely, the elliptical polarization falls close to zero in some cases and can even be switched to large positive values in others. Importantly, the mechanism of generating the switchable CD response in the chiral peptide rotaxanes is also determined: a combination of semiempirical calculations and geometrical modeling using the continuous chirality measure (CCM) shows that the chirality is transmitted from the amino acid asymmetric center on the thread via the macrocycle to the C-terminal stopper of the rotaxane. This understanding could have important implications for other areas where chiral transmission from one chemical entity to another underpins a physical or chemical response, such as the seeding of supertwisted nematic liquid crystalline phases or asymmetric synthesis.     

信息技术与“教学评”一体化深度融合的教学实践*——以“有机合成”为例

以建构有机合成中的顺推法和逆合成分析法思维模型为载体,通过设置驱动任务,将信息技术和“教学评”一体化深度融合,促进学生结构观、发展观和转化观的形成,理解有机化学的社会价值,培养学生的宏微结合、变化观念、科学态度和社会责任等化学学科核心素养。     

Design and synthesis of "dumb-bell" and "triangular" inorganic-organic hybrid nanopolyoxometalate clusters and their characterisation through ESI-MS analyses

A series of tris(hydroxymethyl)aminomethane (TRIS)‐based linear (bis(TRIS)) and triangular (tris(TRIS)) ligands has been synthesised and were covalently attached to the Wells–Dawson type cluster [P₂V₃W₁₅O₆₂]^9? to generate a series of nanometer‐sized inorganic–organic hybrid polyoxometalate clusters. These huge hybrids, with a molecular mass similar to that of small proteins in the range of ≈10–16 kDa, were unambiguously characterised by using high‐resolution ESI‐MS. The ESI‐MS spectra of these compounds revealed, in negative ion mode, a characteristic pattern showing distinct groups of peaks corresponding to different anionic charge states ranging from 3^? to 8^? for the hybrids. Each peak in these individual groups could be unambiguously assigned to the corresponding hybrid cluster anion with varying combinations of tetrabutylammonium (TBA) and other cations. This study therefore highlights the prowess of the high‐resolution ESI‐MS for the unambiguous characterisation of large, nanoscale, inorganic–organic hybrid clusters that have huge mass, of the order of 10–16 kDa. Also, the designed synthesis of these compounds points to the fact that we were able to achieve a great deal of structural pre‐design in the synthesis of these inorganic–organic hybrid polyoxometalates (POMs) by means of a ligand design route, which is often not possible in traditional “one‐pot” POM synthesis.     

基于现代信息技术的结构化学一维势箱理论和HMO法“翻转课堂”教学设计

In the article, we presented an instructional design of "Particle in One-Dimensional Box Theory" and "HMO Theory" application based on flipped classroom teaching. The students are instructed to use both "Particle in One-Dimensional Box Theory" and "HMO Theory" to solve the electronic structure of olefins and enhance their understanding of quantum mechanics theory via comparison of "Particle in One-Dimensional Box Theory" and "HMO Theory".     

Synthesis of "solid solution" and "core-shell" type cobalt--platinum magnetic nanoparticles via transmetalation reactions

In this article, we report the synthesis of "solid solution" and "core-shell" types of well-defined Co--Pt nanoalloys smaller than 10 nm. The formation of these alloys is driven by redox transmetalation reactions between the reagents without the need for any additional reductants. Also the reaction proceeds selectively as long as the redox potential between the two metals is favorable. The reaction between Co(2)(CO)(8) and Pt(hfac)(2) (hfac = hexafluoroacetylacetonate) results in the formation of "solid solution" type alloys such as CoPt(3) nanoparticles. On the other hand, the reaction of Co nanoparticles with Pt(hfac)(2) in solution results in "Co(core)Pt(shell)" type nanoalloys. Nanoparticles synthesized by both reactions are moderately monodispersed (sigma < 10%) without any further size selection processes. The composition of the alloys can also be tuned by adjusting the ratio of reactants. The magnetic and structural properties of the obtained nanoparticles and reaction byproducts are characterized by TEM, SQUID, UV/vis, IR, EDAX, and XRD.     

Basic concepts of "cation pool" and "cation flow" methods and their applications in conventional and combinatorial organic synthesis

Carbocations have been generally considered to be relatively unstable and transient species. But the "cation pool" method enables the easy accumulation of carbocations in conventional reaction media such as dichloromethane. In the "cation pool" method, carbocations are generated by low-temperature electrochemical oxidation and accumulated in a solution. In the next step, the carbocations thus produced are allowed to react with various nucleophiles. Combinatorial parallel synthesis based upon the "cation pool" method has also been developed. The applicability of the "cation pool" method depends upon the stability of the cation that is accumulated. This problem can be overcome by the "cation flow" method. In the "cation flow" method, carbocations are generated in a microflow electrochemical system. Short residence times and efficient temperature control of the microflow system are advantageous. Combinatorial sequential synthesis has been achieved based on the "cation flow" method.     

Algorithm for coding DNA sequences into "spectrum-like" and "zigzag" representations

An algorithm for encoding long strings of building blocks, like 4 DNA bases (adenine-A, cytosine-C, thymine-T, and guanidine-G), 20 natural amino acids (from Alanine Ala to Valine-Val, plus the stop triplet), or all 64 possible base triplets (from AAA to TTT), into "zigzag" or "spectrum-like" representations is suggested. The new encoding scheme can be derived in the 3-, 2-, or 1-dimensional form depending on the user's wishes. The only information, besides the string for which the "spectrum-like" representation is sought, is the initial positioning of the complete set of units from which the string is composed, i.e., four positions for A, C, G, and T, or 20 positions for natural amino acids plus stop, etc. This initial positioning can be initialized in either the 3-, 2-, or 1-D form. As an illustration of the suggested encoding scheme of the visual and chemometric comparison of the first 10 exon strings of the beta globin gene of 10 different species, each string consisting of about 100 basic amino acids long is shown.     

Synthesis and complexation of multiarmed cycloveratrylene-type ligands: observation of the "boat" and "distorted-cup" conformations of a cyclotetraveratrylene derivative

Investigations of a previously reported ligand, hexakis(2-pyridylmethyl)cyclotricatechylene (1), and a new tetrameric bridging ligand, octakis(2-pyridylmethyl)cyclotetracatechylene (2), the latter constructed on a larger cyclotetraveratrylene (CTTV) scaffold, are described. Variable-temperature NMR studies support a "sofa" conformation for 2, akin to studies on the parent compound. The coordination chemistry of 2 and its smaller trimeric homologue have also been investigated with silver(I), copper(II) and palladium(II) salts. An unexpected chelating mode was observed for 1 in the structure of DMF subset[Pd(3)Cl(6)(1)] x DMF, whereby the palladium cations bridge two veratrole subunits rather than chelating within a single subunit. In the structure of [Ag(4)(2)][Co(C(2)B(9)H(11))(2)](4) x 2.8 CH(3)CN x H(2)O, ligand 2 adopts a "boat" conformation, whereas in [Pd(4)Cl(8)(2)] x 4 H(2)O, (1)H NMR spectroscopic studies and calculations indicate that the ligand is present in a previously unobserved "distorted-cup" conformation. This conformation was calculated to be approximately 90 kJ mol(-1) lower in energy than the alternative "sofa" conformation. Thus, coordination-induced conformational control over CTTV derivatives offers new routes to exploit the host-guest chemistry of these compounds.     

“高分子物理”及“高分子物理实验”2门精品课程的建设

"高分子物理"(在中国科学技术大学叫"高聚物的结构与性能")和"高分子物理实验"课是该校高分子科学与工程系本科生的必修课。为了讲好和全面建设这两门课,作者倡导并积极开展教学研究,发表39篇教学研究论文,作者把这些研究心得和成果及时引入教学中,先后编写和出版了十几本教材及教学参考书,教学质量不断提高,并逐步形成了有鲜明特色的教学,在国内高校产生了很好的影响。通过多方面的建设,2005年"高聚物的结构与性能"被评为国家级精品课程,2006年"高分子物理实验"被评为安徽省精品课程。     

Synthesis and complexation of "back-to-back" capped bis-dioxocyclams

Pyridine-capped 5,12-dioxocyclams were coupled "back-to-back" directly, with one or two intervening phenyl groups, an ethynyl group, or a diazo group via Suzuki, Sonogashira, or reductive coupling of the 4-nitropyridine monocyclam. These bis-dioxocyclams linked through extended pi-conjugated systems were complexed to copper(II) and cobalt(III), producing bis-metal complexes which were characterized spectroscopically and electrochemically. These studies gave little evidence for electronic communication between metal centers across the pi-conjugated linkers.