A Large Conformational Change of a Bridged β-Cyclodextrin Dimer in Aqueous Solution

A novel bridged β-CD dimer in which two β-cyclodextrins were linked by a naphthalene at positions 2 and 7 has been synthesized. 1H and 13CNMR measurements showed that a large change in the conformation of the dimer occurred in aqueous solution. The dimer interacted with methyl and ethyl orange to form stable inclusion complexes via "induced fit" mechanism.     

Selective Transport of Saccharides Through a Liquid Membrane Using Cyclodextrin Dimer

A new effective transport system for saccharides through a liquid membranewas constructed. The transport rate of d-ribose in the condition of theliquid membrane with cyclodextrin dimer (2) as a transporter is 2.5 timerlarger than that without the transporter, whereas the transport rate of d-ribosein the condition of the liquid membrane with cyclodextrin monomer (1) isalmost the same as that without the transporter. The transport rate of methyld-glucoside by 2 is over twice than that by 1. The transport rate of d-deoxyribose by 2 is larger than that by 1.     

Conformational Change of Spermidine upon Interaction with Adenosine Triphosphate in Aqueous Solution

A complex rotation : The solution conformation of spermidine (SPD) was elucidated by using diastereospecifically deuterated and ¹³C‐labeled derivatives to diagnose the orientation of seven conformationally relevant bonds. NMR coupling constants were determined for a complex formed from spermidine and adenosine triphosphate (ATP; see figure).

     

Conformational Control of a Polyether-Linked Porphyrin Dimer Induced by Complexation with a Sodium Cation

Abstract

A porphyrin dimer with a polyether linkage was newly synthesized and its conformational change triggered by complexation with an sodium cation was examined. It was confirmed by ¹H NMR titration experiments that the dimer bearing a pentaoxyehtylene linkage (1b) was effectively formed a 1:1 complex with a sodium perchlorate. A detailed investigation of the CIS values for the protons confirmed that the complex of 1b?Na⁺ adopts a slipped face-to-face conformation.     

A Study of b-Cyclodextrin Inclusion Complexes with Progesterone and Hydrocortisone Using Rotating Frame Overhauser Spectroscopy

Summary.  Inclusion complexes of β-cyclodextrin with two steroid derivatives, progesterone (pregn-4-ene-3,20-dione) and hydrocortisone (11,17,21-trihydroxy-pregn-4-ene-3,20-dione), were studied in the liquid state by NMR spectroscopy. The complex formation process was monitored by intermolecular dipolar interactions between ¹H signals in the hydrophobic β-cyclodextrin cavity (H-3 and H-5 of the α-glucose units) and the steroid moiety in ROESY spectra. The data revealed that progesterone is fully immersed in the β-cyclodextrin cavity; however, complete inclusion of the hydrocortisone molecule was prevented by the polar hydroxyl groups on its surface. Received April 26, 2001. Accepted (revised) May 18, 2001     

水溶液中降冰片二烯衍生物敏化光异构化反应

研究了水溶液中双环[2.2.1]-2,5-庚二烯-2,3-二羧酸在吖啶黄(AY)和吖啶橙(AO)的敏化作用下的光诱导价键异构化反应。量子效率分别为0.33(AY)和0.31(AO).采用安全廉价的水为反应介质,通过荧光猝灭和热力学讨论提出了电子转移反应机理。     

Enhancement of Photocurrent Generation of a Novel Stilbazolium Dye Dimer in LB Monolayer Films

A novel dye dimer,bis-{[1-(N-hexadecyl-4-pyridinium)-2-(4-N,N-dimethylaminopheyl)] ethenyl} methane diiodide (C16BP) was synthesized,and the photoelectrochemistry of the dye Langmuir-Blodgett monolayer modified ITO electrode was investigated.For comparison,the photoelectrochemistry of the monomer (E)-N-hexadexyl-4-[2-(4-N,N-dimethylaminophenyl) ethenyl] pyridinium iodide (C16P) was also measured.The results show that the photocurrent generation property of the dimer is enhanced.The photocurrent generation quantum yield is 0.38% for C16BP,while that for C16P is 0.23%.     

均苯三酰胺桥联三环糊精/Zn2+/金刚烷衍生物三元超分子体系的合成及其羧肽酶A模拟研究

本文合成了一种均苯三酰胺基桥联三(b-环糊精) 1及其锌(II)配合物 2, 进而通过与金刚烷衍生物的包结配位作用制备了三种均苯三酰胺桥联三环糊精/Zn2+/金刚烷衍生物4-6. 利用茚三酮显色实验和圆二色谱研究了其作为羧肽酶A模拟物对牛血清白蛋白水解反应的酶促性能和不同pH下的变构能力, 推测了可能的酶促反应机理. 结果表明1/Zn2+/金刚烷-1-乙酸三元超分子体系在中性条件显示出高达10.43 U·mg-1的酶活力     

水溶液中降冰片二烯衍生物敏化学异构化反应

研究了水溶液中双环［２，２，１］－２，５庚二烯－２，３－二羧酸在吖和吖啶橙的敏化作用下的光诱导价键异构化反应。量子效率分别为０，３３（ＡＹ）和０，３１（ＡＯ）。     

Conformational selection of protein kinase A revealed by flexible-ligand flexible-protein docking

Protein kinases have high structural plasticity: their structure can change significantly, depending on what ligands are bound to them. Rigid-protein docking methods are not capable of describing such effects. Here, we present a new flexible-ligand flexible-protein docking model in which the protein can adopt conformations between two extremes observed experimentally. The model utilized a molecular dynamics-based simulated annealing cycling protocol and a distance-dependent dielectric model to perform docking. By testing this model on docking four diverse ligands to protein kinase A, we found that the ligands were able to dock successfully to the protein with the proper conformations of the protein induced. By imposing relatively soft conformational restraints to the protein during docking, this model reduced computational costs yet permitted essential conformational changes that were essential for these inhibitors to dock properly to the protein. For example, without adequate movement of the glycine-rich loop, it was difficult for the ligands to move from the surface of the protein to the binding site. In addition, these simulations called for better ways to compare simulation results with experiment other than using the popular root-mean-square deviation between the structure of a ligand in a docking pose and that in experiment because the structure of the protein also changed. In this work, we also calculated the correlation coefficient between protein-ligand/protein-protein distances in the docking structure and those in the crystal structure to check how well a ligand docked into the binding site of the protein and whether the proper conformation of the protein was induced.     

Oxidative Splitting of a Pyrimidine Cyclobutane Dimer:A Pulse Radiolysis Study

The oxidative splitting process of cis-syn 1,3-dimethyluracil cyclobutane dimer(DMUD) in aqueous solution was investigated using pulse radiolysis technique.The results indicated that DMUD can be splitted into 1,3-dimethyluracil(DMU) by OH radicals(OH) and Br2 radical anions(Br2^-),but not by azide radicals(N3^).The oxidative mechanisms that an H-abstracted from DMUD for OH oxidative splitting and an electron transfer from DMUD to Br2-,were suggested.Related kinetic parameters were determined.     

NMR研究水溶液中L-精氨酸与磷酸腺苷的相互作用及其构象变化

利用核磁共振(NMR)方法,研究了水溶液中L-精氨酸分别与一磷酸腺苷、三磷酸腺苷的相互作用及其构象变化.通过测定L-精氨酸分别与一磷酸腺苷、三磷酸腺苷混合后体系的1H、13C NMR,对混合前后L-精氨酸1H及13C化学位移变化情况进行了分析,发现L-精氨酸与一磷酸腺苷、三磷酸腺苷存在氢键和静电作用,并且这种相互作用会导致L-精氨酸构象产生变化,即由作用之前的伸展型转变为作用后的弯曲型.     

Dimer of calcein used as fluorescence probe in the determination of proteins

In the presence of appropriate amounts of the cationic surfactant cetyl trimethyl ammonium bromide (CTMAB), the anionic dye calcein dimerizes. The weak fluorescence intensity of the dimer is enhanced by adding proteins at pH 6–8. The interaction between calcein-CTMAB and proteins was studied on the basis of this behavior and a new method was developed for determining proteins. Under optimal conditions, the enhanced fluorescence intensity is proportional to the concentration of proteins in the range 0.4–8 μg mL⁻¹ for human serum albumin (HSA) and 0.8–10 μg mL⁻¹ for bovine serum albumin (BSA), with detection limits of 0.034 μg mL⁻¹ and 0.032 μg mL⁻¹, respectively. Three samples were determined by using this method satisfactorily with relative standard deviations (RSD) of 1.1–3.1%.     

Gnetupendin C, a New Stilbene Dimer from the Lianas of Gnetum Pendulum

Continuous investigation on stilbenoids from the lianas of Gnetum pendulum1 resulted in the isolation of a new dimer, Gnetupendin C (1), a cis-2, 3-dihydrobenzofuran dimer of resveratrol and oxyresveratrol.Gnetupendin C (1) was obtained as yellowish amorphous power, [(] -220.0 (c 0.100, MeOH). UV (c 0.02, MeOH) (max (log (): 222 (4.5), 288 (sh), 310 (sh), 327 (4.4) nm. The high resolution EIMS, m/z 470.1344, agreed with a molecular formula of C28H22O7 (requires 470.1366) and the 1H NM…     

Syntheses of imidazolium-bridged cyclodextrin dimers and their catalytic properties in the hydrolytic cleavage of p-nitrophenyl alkanoates

Two imidazolium-bridged cyclodextrin dimers 3a and 3b were prepared by reacting 6-deoxy-6-N-imidazolyl-β-CD (2) with bis(bromomethyl)benzene. The catalytic properties of 2, 3a and 3b in the hydrolytic cleavage of p-nitrophenyl alkanoates, in the form of acetate (PNPA) , butanoate (PNPB) , hexanoate (PNPH) and octanoate (PNPO), were examined. CD dimeis showed middling rate enhancements around neutrality. Catalytic rate constants ( kc) in the presence of 3a or 3b did not vary much with chain length of esters. In contrast, dissociation constants ( Kd) and selectivity factors (kc/Kd) for "long-chain" esters were much smaller and significantly larger than those for short-chain ones respectively, indicating CD dimers 3a and 3b have good dimensional recognition ability and substrate selectivity in the hydrolytic cleavage of p-nitrophenyl alkanoates . Their kinetic consequences are briefly interpreted.     

β-环糊精调控水溶液中Cu2+的辐射还原

在β-环糊精(β-CD)水溶液的安全吸收剂量范围内, 利用β-CD来调控Cu2+的辐射还原. 随着β-CD的加入, 硝酸铜的辐射还原产物从Cu2O 逐渐转变为Cu. 当β-CD浓度增大至8.0 mmol·L-1时, 辐射还原产物主要为Cu纳米粒子. 在辐照过程中, Cu2+的还原没有经历Cu2O的中间过程. 这是由于β-CD对·OH的清除减少了·OH与水化电子(e-aq)的反应, 增大了e-aq的产额, 从而有利于Cu的生成. 另外, β-CD通过羟基在Cu纳米粒子表面的吸附可增强Cu纳米粒子在水溶液中的稳定性. 用紫外-可见(UV-Vis)吸收光谱、粉末X射线衍射(XRD)和选区电子衍射(SAED)对Cu2+辐射还原产物进行了表征.     

Characterization of an Inclusion Complex of 5,10,15,20-Tetrakis(4-sulfonatophenyl)-porphinato Iron and an O-Methylated β-Cyclodextrin Dimer Having a Pyridine Linker and Its Related Complexes in Aqueous Solution

The structure of a carbon monoxide adduct (CO-hemoCD) of a 1:1 complex of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphinato iron(II) (Fe(II)TPPS) and an O-methylated β-cyclodextrin dimer having a pyridine linker (1) has been determined by means of NMR spectroscopy and molecular mechanics (MM) calculation. The results indicate the structure as that the sulfonatophenyl groups at the 5- and 15-positions of Fe(II)TPPS are incorporated into two cyclodextrin cavities of 1 to form a 1:1 inclusion complex (hemoCD), whose Fe(II) center is coordinated by a carbon monoxide (CO) molecule. CO-hemoCD possesses a C _2v symmetrical nature that is supported by MM calculation. The energy minimized structure of CO-hemoCD suggests that the CO–Fe(II) part is significantly covered by two cyclodextrin moieties resulting in a cage effect in CO binding phenomenon. Other spectroscopic results of relating complexes also support the structure of hemoCD deduced from the results concerning CO-hemoCD.     

A Visible‐Light‐Triggered Conformational Diastereomer Photoswitch in a Bridged Azobenzene

Ketal‐substituted bridged azobenzenes have been synthesized; these display a symmetrical boat conformation with the ketal in pseudo‐equatorial positions. These bridged Z‐azobenzenes (Z₁) readily photoisomerize to the E‐isomer as well as another Z‐conformer (Z₂) with ketal function on the pseudo‐axial position upon irradiation at 406 nm. The two diastereomeric conformers display distinct physicochemical characteristics. Spectroscopic and NMR investigations supported that interconversion of two conformers occurs via the E‐isomer, with good photochemical quantum yield (Φ =0.45±0.03, Φ =0.33±0.05, Φ =0.37±0.06 and Φ =0.36±0.04). The system shows high photostability and no thermal equilibrium between the two stable Z₁ and Z₂ conformers.     

Conformational Analysis of a Branched Sugar in Aqueous Solution Based on Molecular Mechanics and 1H-NMR Studies

MM2 and AMBER force fields in both vacuum and GB/SA solvation model were examined to find the most effective method for elucidating the conformational properties of the trisaccharide 2, which is essential to the elicitor activity of hexa-β-D-glucopyranosyl-D-glucitol (1). The NMR studies reveal that the combination of AMBER force field and GB/SA solvation treatment is quite effective in analyzing the conformation of oliosaccharide in water.     

Chemical Oxidative Degradation of Acridine Orange Dye in Aqueous Solution by Fenton's Reagent

Degradation of acridine orange (AO) in aqueous solution by Fenton's reagent (Fe²⁺ and H₂O₂) was investigated. The effects of different reaction parameters such as initial AO concentration, pH value of solution, ferrous concentration, hydrogen peroxide concentration, and the presence of chloride ion on the oxidative degradation of AO were investigated. Under optimum conditions, 2 mM H₂O₂, 0.4 mM Fe²⁺ and pH 3.0, the initial 0.2 mM AO solution was reduced by 95.8% within 10 min. The primary intermediates of the degradation reaction of AO were identified. The analytical results indicated that the N‐de‐methylation degradation of AO dye took place in a stepwise manner to yield mono‐, di‐, tri‐, and tetra‐N‐de‐methylated AO species generated during the Fenton process. The probable degradation pathways were proposed and discussed.