锂参与合成MOF-5用于CO2/CH4混合气体分离

利用溶剂热法合成了不同锂含量的MOF-5(xLi-MOF-5, x=0, 1, 3, 5).在MOF-5结晶过程中,锂离子被合并入其骨架结构中.实验表明,合并入骨架的锂能够改变MOF-5的结构和表面化学性质.不同的xLi-MOF-5能够不同程度降低骨架相互穿插的程度从而导致其吸附分离能力的大幅改变.其中,3Li-MOF-5具有最高的二氧化碳捕获能力(5.47 mmol·g^-1),对40% CO₂/60% CH₄混合气体具有最优吸附选择性.     

meso-去甲二氢愈创木酸和Machilin A的合成

报道了一条合成内消旋去甲二氢愈创木酸(meso-NDGA)和Machilin A的新路线. 此路线通过两次Stobbe缩合构建木脂素结构骨架, 经官能团转换, 合成了meso-NDGA和Machilin A. 该路线操作简便、实用性强.     

三苯三戊并烯及其衍生物的合成研究进展

三苯三戊并烯类化合物含三个相互稠合的茚满单元具有独特的刚性骨架, C_3v对称性, 凹凸杯状结构. 该类化合物的合成研究具有重要的理论意义和应用前景. 结合自己的研究工作综述了近年来三苯三戊并烯类化合物的合成进展.     

立方介孔相含钕氧化硅的合成与表征

以十六烷基三甲基溴化铵为结构导向剂，通过水热法合成了具有立方结构的含钕Nd-MCM-48介孔分子筛材料。XRD和TEM测试表明当n_Nd/n_Si<0.05时可以获得典型的长程有序介孔立方结构相，随n_Nd/n_Si比的增加，晶胞参数的增大和红外吸收光谱(FT-IR)的变化为Nd进入介孔分子筛骨架中提供了有力证据。N₂吸附-脱附实验给出了其BET表面积为1 195 m²·g^-1，BJH平均孔径为3.6 nm。紫外-可见漫反射光谱(UV-Vis)证明钕氧形成一种八面体结构。X射线光电子能谱(XPS)进一步证明钕主要以三价形式存在于立方介孔分子筛骨架中。     

三维开放骨架结构混配型铜羟亚乙基二膦酸化合物的合成、结构和磁性研究

采用水热方法合成了一个具有新型三维骨架结构的混配型铜羟亚乙基二膦酸化合物Na₂Cu₃(hedp)₂(pz)(H₂O)₂(hedp=1-羟亚乙基二膦酸)，并对其进行了初步表征。X-射线单晶结构分析表明它属于三斜晶系，空间群为P1，晶胞参数为a=6.2435(17)?，b=7.100(2)?，c=11.998(3)?，α=84.400(4)°，β     

苯并螺环β-溴代酮Wagner-Meerwein重排反应研究及其在(±)-Colchicine形式合成中的应用

报道了在AgBF₄促进下苯并螺环β-溴代酮的Wagner-Meerwein重排反应, 从而发展了一条简捷新颖的构筑天然产物中广泛存在的n,7,6-三环骨架的方法. 作为该反应的应用, 合成了(±)-colchicine的7,7,6-三环母核, 完成了(±)-colchicine的形式合成.     

二(咪唑基)苯及戊二酸根构筑的三维镉配位聚合物的合成、晶体结构与荧光性质

用水热法合成了一个新的镉配位聚合物[Cd(BIMB)_0.5(glu)]_n(BIMB=1, 4-二(咪唑基)苯, H₂glu=戊二酸), 用红外, 元素分析进行了表征。X射线单晶衍射分析表明配位聚合物属于单斜晶系, P2₁/c空间群, a=0.822 06(5) nm, b=0.774 38(5) nm, c=1.877 93(10) nm, β=107.966°, V=1.137 nm³, Z=4, F(000)=684。在配合物中, 相邻的镉原子通过2个戊二酸连接成一维链状结构, 链状结构通过另一戊二酸拓展成二维层状结构, 相邻二维层状结构进一步由BIMB配体拓展成三维骨架结构。热重分析表明配合物具有较好的稳定性, 荧光光谱分析表明配合物具有较好的荧光性质。     

二维含镧链异核金属化合物的合成、结构和磁性研究

水热法合成了3个层状异核金属化合物[Ln(idaH)M(ida)₂]_n·0.5nH₂O,(H₂ida=亚氨基二乙酸,Ln=Nd,M=Co (1);Ln=La,M=Co (2);Ln=La,M=Ni (3))。进行了晶体结构测定,红外光谱分析、能谱分析与磁性能分析。3个化合物除金属原子不同外具有相同的结构,其晶体都属于单斜晶系,C2/c空间群。单晶结构表明该结构含有由十配位的Ln通过羧基氧连接而成的链,六配位的3d金属(Co、Ni)交替地处在链的两边,形成了带状结构,带状链通过配体连成二维结构,通过氢键形成三维骨架。     

3-(4-氯苯基)-6-取代苯氧乙酰氨基均三唑并[3,4-b]-1,3,4-噻二唑类化合物的合成

将取代苯氧乙酰氨基引入到3,6-二取代均三唑并噻二唑的分子骨架中, 设计合成了8个未见文献报道的3-(4-氯苯基)-6-取代苯氧乙酰氨基均三唑并[3,4-b]-1,3,4-噻二唑类化合物5a～5h, 结构经元素分析、IR和¹H NMR等测试得到确证.     

肽核酸骨架分子键联卟啉的合成及结构表征

以5,10,15-三苯基-20-(4-羧基苯基)卟啉和5,10,15-三苯基-20-(4-羟基苯基)卟啉为原料, 分别与N-(Boc-氨乙基)甘氨酸乙酯(3)及其衍生物4作用, 得到了两种肽核酸骨架分子键联卟啉化合物6和8. 中间体和目标化合物均由紫外-可见光谱、红外光谱、核磁共振光谱、质谱及元素分析所确证. 目标化合物的荧光光谱测试结果表明, 肽核酸单元分子的链接对卟啉分子的荧光波长和强度影响不大.     

Crystal structure of a partly self-complementary peptide nucleic acid (PNA) oligomer showing a duplex-triplex network

The X-ray structure of a partly self-complementary peptide nucleic acid (PNA) decamer (H-GTAGATCACT-l-Lys-NH(2)) to 2.60 A resolution is reported. The structure is mainly controlled by the canonical Watson-Crick base pairs formed by the self-complementary stretch of four bases in the middle of the decamer (G(4)A(5)T(6)C(7)). One right- and one left-handed Watson-Crick duplex are formed. The two PNA units C(9)T(10) change helical handedness, so that each PNA strand contains both a right- and a left-handed section. The changed handedness in C(9)T(10) allows formation of Hoogsteen hydrogen bonding between C(9)T(10) and G(4)A(5) of a PNA strand in an adjacent Watson-Crick double helix of the same handedness. Thereby, a PNA-PNA-PNA triplex is formed. The PNA unit A(3) forms a noncanonical base pair with A(8) in a symmetry-related strand of opposite handedness; the base pair is of the A-A reverse Hoogsteen type. The structural diversity of this PNA demonstrates how the PNA backbone is able to adapt to structures governed by the stacking and hydrogen-bonding interactions between the nucleobases. The crystal structure further shows how PNA oligomers containing limited sequence complementarity may form complex hydrogen-bonding networks.     

Coordination-driven inversion of handedness in ligand-modified PNA

Peptide nucleic acid (PNA) is a synthetic analogue of DNA, which has the same nucleobases as DNA but typically has a backbone based on aminoethyl glycine (Aeg). PNA forms duplexes by Watson Crick hybridization. The Aeg-based PNA duplexes adopt a chiral helical structure but do not have a preferred handedness because they do not contain a chiral center. An L-lysine situated at the C-end of one or both strands of a PNA duplex causes the duplex to preferably adopt a left-handed structure. We have introduced into the PNA duplexes both a C-terminal L-lysine and one or two PNA monomers that have a γ-(S)-methyl-aminoethyl glycine backbone, which is known to induce a preference for a right-handed structure. Indeed, we found that in these duplexes the γ-methyl monomer exerts the dominant chiral induction effect causing the duplexes to adopt a right-handed structure. The chiral PNA monomer had a 2,2':6',2'-terpyridine (Tpy) ligand instead of a nucleobase and PNA duplexes that contained one or two Tpys formed [Cu(Tpy)(2)](2+) complexes in the presence of Cu(2+). The CD spectroscopy studies showed that these metal-coordinated duplexes were right-handed due to the chiral induction effect exerted by the S-Tpy PNA monomer(s) except for the cases when the [Cu(Tpy)(2)](2+) complex was formed with Tpy ligands from two different PNA duplexes. In the latter case, the metal complex bridged the two PNA duplexes and the duplexes were left-handed. The results of this study show that the preferred handedness of a ligand-modified PNA can be switched as a consequence of metal coordination to the ligand. This finding could be used as a tool in the design of functional nucleic-acid based nanostructures.     

PNA/dsDNA complexes: site specific binding and dsDNA biosensor applications

The ability of peptide nucleic acids (PNA) to form specific higher-order (i.e., three- and four-stranded) complexes with DNA makes it an ideal structural probe for designing strand-specific dsDNA biosensors. Higher-order complexes are formed between a dye-labeled charge-neutral PNA probe and complementary dsDNA. Addition of a light-harvesting cationic conjugated polymer (CCP) yields supramolecular structures held together by electrostatic forces that incorporate the CCP and the dye-labeled PNA/DNA complexes. Optimization of optical properties allows for excitation of the CCP and subsequent fluorescence resonance energy transfer (FRET) to the PNA-bound dye. In the case of noncomplementary dsDNA, complexation between the probe and target does not occur, and dye emission is weak. The binding between PNA and noncomplementary and complementary dsDNA was examined by several methods. Gel electrophoresis confirms specificity of binding and the formation of higher-order complexes. Nano-electrospray mass spectrometry gives insight into the stoichiometric composition, including PNA/DNA, PNA(2)/DNA, PNA/DNA(2), and PNA(2)/DNA(2) complexes. Finally, structural characteristics and binding-site specificity were examined using ion mobility mass spectrometry in conjunction with molecular dynamics. These results give possible conformations for each of the higher-order complexes formed and show exclusive binding of PNA to the complementary stretch of DNA for all PNA/DNA complexes. Overall, the capability and specificity of binding indicates that the CCP/PNA assay is a feasible detection method for dsDNA and eliminates the need for thermal denaturing steps typically required for DNA hybridization probe assays.     

Real Time Electrochemical Monitoring of DNA/PNA Dissociation by Melting Curve Analysis

An immobilization‐free electrochemical method is reported for real‐time monitoring of the DNA hybrid dissociation between a ferrocene labeled peptide nucleic acid (PNA) and a fully‐complementary or single‐base‐mismatched DNA. This method takes advantages of electrostatic charge characteristics and interactions among the neutrally charged PNA, the negatively charged DNA and the negatively charged electrode surface made of indium tin oxide (ITO). When a ferrocene labeled PNA (Fc‐PNA) sequence is hybridized to a complementary DNA strand, electrostatic repulsion between the negatively charged PNA/DNA hybrid and the negative ITO surface retards the diffusion of the electroactive Fc to the electrode, resulting in a much reduced electrochemical signal. On the other hand, when the Fc‐PNA is dissociated from the hybrid at elevated temperatures, the neutrally charged Fc‐PNA easily diffuses to the electrode with an enhanced electrochemical signal. Therefore, an electrochemical melting curve of the Fc‐PNA/DNA hybrid can be obtained by measuring the Fc signal with the increasing temperature. This strategy allows monitoring of the dissociation of the DNA hybrid in real time, which might lead to a simple detection method for single nucleotide polymorphism (SNP) analysis.     

Synthesis of a C-linked glycosylated thymine-based PNA monomer and its incorporation into a PNA oligomer

Backbone modification of peptide nucleic acids (PNAs) by glycosylation has been shown to enhance selective biodistribution and cellular targeting of PNA oligomers based on sugar and cell surface lectin interactions. Here we report the synthesis of a new backbone-glycosylated thymine-based PNA monomer (T(gal)). The sugar residue was attached to the backbone of PNA via a stable carbon-carbon linkage between the sugar and the PNA monomers. Also, incorporation of the modified monomer into a PNA decamer (H-Ala(gal)-G-G-G-T(gal)-C-A-G-C-T(gal)-T-Lys-NH2) was successfully performed. Melting temperature (UV-Tm) of the modified PNA against the complementary DNA was only slightly lower than unmodified PNA.     

End-labeling of peptide nucleic acid with osmium complex. Voltammetry at carbon and mercury electrodes

Peptide nucleic acid (PNA), the DNA mimic with electrically neutral pseudopeptide backbone, is intensively used in biotechnologies and particularly in single-base mismatch detection in DNA hybridization sensors. We propose a simple method of covalent end-labeling of PNA with osmium tetroxide, 2,2′-bipyridine (Os,bipy). Os,bipy-modified PNA (PNA–Os,bipy) produces voltammetric stripping peaks at carbon and mercury electrodes. Peak potential (E_p) of one of the anodic peaks of PNA–Os,bipy at the pyrolytic graphite electrode (PGE) differs from E_p of the reagent, allowing PNA–Os,bipy analysis directly in the reaction mixture. At the hanging mercury drop electrode (HMDE) the PNA–Os,bipy yields a catalytic peak Cat_p, in addition to the redox couples. Using Cat_p it is possible to detect purified PNA–Os,bipy down to 1 pM concentration at accumulation time 60 s. To our knowledge this is the highest sensitivity of the electrochemical detection of PNA.     

Nucleic acid sensor for M. tuberculosis detection based on surface plasmon resonance

Cysteine modified NH(2)-end peptide nucleic acid (PNA) (24-mer) probe and 5'-thiol end labeled deoxyribonucleic acid (DNA) probes specific to Mycobacterium tuberculosis have been immobilized onto BK-7 gold coated glass plates for the detection of complementary, one-base mismatch, non-complementary targets and complementary target sequence in genomic DNA of Mycobacterium tuberculosis using a surface plasmon resonance (SPR) technique. The DNA/Au and PNA/Au bio-electrodes have been characterized using contact angle, atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetric (CV) techniques, respectively. It is revealed that there is a 252 millidegrees SPR angle change in the case of PNA immobilization and 205 millidegrees for DNA immobilization, indicating increased amount of immobilized PNA molecules. Hybridization studies reveal that there is no binding of the non-complementary target to DNA/Au and PNA/Au electrode. Compared to the DNA/Au bioelectrode, PNA/Au electrode has been found to be more efficient for detection of one-base mismatch sequence. The PNA/Au bioelectrode shows better detection limit (1.0 ng ml(-1)) over the DNA-Au bioelectrode (3.0 ng ml(-1)). The values of the association (k(a)) and dissociation rate constant (k(d)) for the complementary sequence in case of the PNA/Au bioelectrode have been estimated as 8.5 x 10(4) m(-1) s(-1) and 3.6 x 10(-3) s(-1), respectively.     

Electrochemiluminescent monomers for solid support syntheses of Ru(II)-PNA bioconjugates: multimodal biosensing tools with enhanced duplex stability

The feasibility of devising a solid support mediated approach to multimodal Ru(II)-peptide nucleic acid (PNA) oligomers is explored. Three Ru(II)-PNA-like monomers, [Ru(bpy)(2)(Cpp-L-PNA-OH)](2+) (M1), [Ru(phen)(2)(Cpp-L-PNA-OH)](2+) (M2), and [Ru(dppz)(2)(Cpp-L-PNA-OH)](2+) (M3) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, dppz = dipyrido[3,2-a:2',3'-c]phenazine, Cpp-L-PNA-OH = [2-(N-9-fluorenylmethoxycarbonyl)aminoethyl]-N-[6-(2-(pyridin-2yl)pyrimidine-4-carboxamido)hexanoyl]-glycine), have been synthesized as building blocks for Ru(II)-PNA oligomers and characterized by IR and (1)H NMR spectroscopy, mass spectrometry, electrochemistry and elemental analysis. As a proof of principle, M1 was incorporated on the solid phase within the PNA sequences H-g-c-a-a-t-a-a-a-a-Lys-NH(2) (PNA1) and H-P-K-K-K-R-K-V-g-c-a-a-t-a-a-a-a-lys-NH(2) (PNA4) to give PNA2 (H-g-c-a-a-t-a-a-a-a-M1-lys-NH(2)) and PNA3 (H-P-K-K-K-R-K-V-g-c-a-a-t-a-a-a-a-M1-lys-NH(2)), respectively. The two Ru(II)-PNA oligomers, PNA2 and PNA3, displayed a metal to ligand charge transfer (MLCT) transition band centered around 445 nm and an emission maximum at about 680 nm following 450 nm excitation in aqueous solutions (10 mM PBS, pH 7.4). The absorption and emission response of the duplexes formed with the cDNA strand (DNA: 5'-T-T-T-T-T-T-T-A-T-T-G-C-T-T-T-3') showed no major variations, suggesting that the electronic properties of the Ru(II) complexes are largely unaffected by hybridization. The thermal stability of the PNA·DNA duplexes, as evaluated from UV melting experiments, is enhanced compared to the corresponding nonmetalated duplexes. The melting temperature (T(m)) was almost 8 °C higher for PNA2·DNA duplex, and 4 °C for PNA3·DNA duplex, with the stabilization attributed to the electrostatic interaction between the cationic residues (Ru(II) unit and positively charged lysine/arginine) and the polyanionic DNA backbone. In presence of tripropylamine (TPA) as co-reactant, PNA2, PNA3, PNA2·DNA and PNA3·DNA displayed strong electrochemiluminescence (ECL) signals even at submicromolar concentrations. Importantly, the combination of spectrochemical, thermal and ECL properties possessed by the Ru(II)-PNA sequences offer an elegant approach for the design of highly sensitive multimodal biosensing tools.     

Enhanced stability of G-quadruplexes from conformationally constrained aep-PNA backbone

Nucleic (DNA) acids having contiguous stretch of G sequence form quadruplex structure, which is very critical to control cell division. Recently the existence of G-quadruplex in RNA is also reported in presence of monovalent metal ion. PNA is a promising DNA analogue which binds strongly to DNA to form PNA:DNA duplex or PNA(2):DNA triplex. PNA also forms quadruplexes such G-quadruplex and i-motif in G and C-rich sequences respectively. aep-PNA containing a prolyl ring is one of several PNA analogues that provide rigidity and chirality in backbone and has binding affinity to natural DNA which is higher than that of PNA. Here we examine the ability of aep-PNA-G to form a quadruplex by UV, CD and mass spectroscopic techniques.     

Synthesis and evaluation of (1S,2R/1R,2S)-aminocyclohexylglycyl PNAs as conformationally preorganized PNA analogues for DNA/RNA recognition

Conformationally constrained cis-aminocyclohexylglycyl PNAs have been designed on the basis of stereospecific imposition of 1,2-cis-cyclohexyl moieties on the aminoethyl segment of aminoethylglycyl PNA (aegPNA). The introduction of the cis-cyclohexyl ring may allow the restriction of the torsion angle beta in the ethylenediamine segment to 60-70 degrees that is prevalent in PNA(2):DNA and PNA:RNA complexes. The synthesis of the optically pure monomers (10a and 10b) is achieved by stereoselective enzymatic hydrolysis of an intermediate ester 2. The chiral PNA oligomers were synthesized with (1S,2R/1R,2S)-aminocyclohexylglycyl thymine monomers in the center and N-terminus of aegPNA. Differential gel shift retardation with one or more units of modified monomer units was observed as a result of hybridization of PNA sequences with complementary DNA sequences. Hybridization studies with complementary DNA and RNA sequences using UV-T(m) measurements indicate that PNA with (1S,2R)-cyclohexyl stereochemistry enhances selective binding with RNA over DNA as compared to control aegPNA and PNA with the other (1R,2S) isomer.