用多维NMR谱和圆二色CD光谱研究蛋白质亲环素A的结构稳定性

The structural stability of cyclophilin A （CypA） was investigated using H/D exchange and temperature coefficients of chemical shifts of amide protons, monitored by 213 heteronuclear NMR spectroscopy. Amide proton exchange rates were measured by H/D exchange experiments for slow-exchange protons and measured by SEA （Solvent Exposed Amides）-HSQC experiments for fast-exchange protons. Temperature coefficients of chemical shifts and hydrogen exchange rates of amide protons show reasonably good correlation with the protein structure. Totally, 44 out of 153 non-proline assigned residues still exist in 86 d of hydrogen-deuterium exchange at 4 ℃, suggesting that CypA structure should be highly stable. Residues in secondary structures of α2, β1, β2, β5, β6 and β7 might constitute the hydrophobic core of the protein. The change in free energy of unfolding （ △Gu^H2O ） of CypA was estimated to be （21.99± 1.53） kJ·mol^-1 by circular dichroism （CD）. The large free energy change is also an indicator of the high structural stability.     

Clean SEA-TROSY Experiments to Map Solvent Exposed Amides in Large Proteins

It is well known that the SEA-TROSY experiment could alleviate some of the problems of resonance overlap in ^15N/^2H labeled proteins as it was designed to selectively map solvent exposed amide protons. However, SEATROSY spectra may be contaminated with exchange-relayed NOE contributions from fast exchanged hydroxyl or amine protons and contributions from longitudinal relaxation. Also, perdeuteration of the protein sample is a prerequisite for this experiment. In this communication, a modified version, clean SEA-TROSY, was proposed to eliminate these artifacts and to allow the experiment to be applied to protonated or partially deuterated proteins and protein complexes.     

~1H NMR INVESTIGATION OF THE BINDING OF METHYL-β-D-GALACTOSES WITH SIALIC ACID RESIDUES ON HEPATIC BINDING PROTEIN——THE EFFECT OF DIVALENT CALCIUM ION

The present study is a proton NMR investigation of the influence of Ca~(2+) on the interaction between the intact sialic acid residues on HBP (Hepatic Binding Protein) and methyl-β-D-galactoses. The proton NMR spectra of HBP and methyl-β-D-galactose mixing solution at different Ca~(2+) concentratiou have been measured. The analysis of the experimental results indicates that Ca~(2+) participates in the binding of sialic acid residues on HBP with methyl-β-D-galactoses and this enables the galactose molecules to, be in stable bound state. The proton NMR spectra of the samples containing EDTA have confirmed this conclusion.     

Design and Synthesis of a Highly Stable Six-hydrogen-bonded Serfassembly Yellowish Green Electroluminescent Molecular Duplex

This paper describes the design, synthesis and characterization of a hydrogen-bonded molecular duplex with 1,8-naphthalimide fluorescent pendants. The two oligoamide molecular strands, with complementary hydrogen bond sequences of DDADAA and AADADD, can form an ultra stable self-assembly duplex. Its molecular structure was confu-med by ^1H NMR and ESI-MS, and its photoluminescence properties were determined. The resulting duplex exhibited a dramatically enhanced photoluminescence （PL） quantum efficiency of 63.7% compared to the corresponding 1,8-naphthalimide segment （32.4%）, suggesting that the formation of the duplex with larger molecular weight could successfully inhibit the quenching of the fluorescent pendant. This novel duplex is a prospective candidate for new electroluminescent emitter.     

Substituent Effect on Proton Affinity of Imidazole in Cu,Zn-Superoxide Dismutase

To investigate whether the proton-accepting ability of imidazole in Cu,Zn-superoxide dismutase （SOD） was possibly modulated by Zn（Ⅱ） or not, the proton affinity （Ap） of N^3 in imidazole group was calculated by density functional theory （DFT） with B3LYP functional. It was found that Zn（Ⅱ） attenuates the Ap, because of its electron-withdrawing effect, while the three ligands connected with Zn（Ⅱ） （residues of two His and one Asp） exert an opposite effect, owing to their electron-donating ability. This finding suggested that the three ligands should play a role in the normal function of Cu,Zn-SOD and should be taken into consideration in the future study.     

Relative Stability of the Key Enamine,Oxazolidinone, and Imine Intermediates in Some Proline-catalyzed Asymmetric Reactions

Many proline-catalyzed asymmetric addition reactions with ketones as substrates were assumed to involve a key intermediate, an enamine, produced by the condensation of proline and ketone. In this paper, the key intermediate enamines derived from L-proline and cyclohexanone （or acetone） as well as the corresponding oxazolidinone and imine tautomers have been investigated by means of density functional calculations at the B3LYP/6-311＋G^＊＊ level. The predicted order of stability for these tautomers is oxazolidinones 〉 enamines 〉 imines in gas phase and oxazolidinones 〉 imines 〉 enamines in aprotic THF solvent. This prediction explains why enamine intermediate can not be observed experimentally. The predicted energy/enthalpy difference between the formal oxazolidinone structure and the zwitterionic imine structures is very small in THF solvent, suggesting the oxazolidinone-to-imine tautomerization can be readily induced in solvent. ^13C NMR chemical shifts of the oxazolidinone and imine structures have been computed and used to explain the experimental NMR spectra observed in oxazolidinone-to-imine tautomerization induced by protic solvent.     

Simultaneous Reduction of Aldehyde Group to Hydroxymethyl Group in Palladium-catalyzed Suzuki Cross-coupling Reaction

The authors presented an efficient method for the palladium-catalyzed Suzuki cross-coupling reaction with the simultaneous reduction of the aldehyde to a hydroxymethyl group.This method allows halide substituted aryl aldehydes to readily react with arylboronic acids,producing polycyclic aromatic alcohols in moderate to good yields.The reaction was catalyzed by Pd（OAc）2（3％,molar fraction） at 150 ℃ in the presence of 6％（molar fraction）1,4-diazabicyclo[2.2.2]octane（DABCO） and 3 times the molecular weight of K2CO3 in the mixture solvent of N,N-dimethylformamide（DMF）/H2O [V（DMF）∶ V（H2O）=5∶1].     

Spectral and chemical monitoring of cyclo-addition reaction of CO2 with poly(MMA-co-GMA) copolymers

This paper deals with the monitoring cyclo-addition of CO₂ to methyl methacrylate（MMA）-glycidyl methacrylate （GMA） copolymers using spectral（¹H-NMR and FTIR） and chemical（elemental analysis and titration） methods.Thus, poly（MMA-co-GMA）,was first prepared via solution polymerization.The copolymer was then treated with CO₂ gas flow in the presence of cetyltrimethyl ammoniumbromide as a catalyst.In terms of the carbonation reaction time,the terpolymer poly（MMA-co-GMA-co-2-oxo-l,3-dioxolane-4-yl-methyl methacrylate） was prepared in various yield of CO₂ fixation （>90%）.The peak intensity changes in the ¹H-NMR and FTIR spectra provided excellent demonstrative techniques to monitor the carbonation reaction progression.In a comparative analytical viewpoint,the NMR and elemental analysis were recognized to be the most accurate ways to follow the cyclo-addition reaction progression.However,titration was recognized to be the most preferred method,because it is a very inexpensive,facile and available method with a reasonable costaccuracy balance.     

Theoretical Investigation on the Absorption and Emission Properties of the Three Isomers of Bis（thiocyanato）（2,2^1-bipyridyl）platinum（ll）

This paper presents a Density Functional or Time Dependent Density Functional （DFT/TDDFT） study of the molecular and electronic structures, optical absorption and emission spectra of three linkage isomers： bis（isothiocyanato-S）（2,2^1-bipyridyl） platinum（II） （[Pt（SCN）2（bpy）]）, （isothiocyanato-S）（thiocyanato-N）-（2,2^1-bipy- ridyl） platinum（II） （[Pt（SCN）（NCS）（bpy）]）, and bis（thiocyanato-N）（2,2^1）-bipyridyl）platinum（II） （[Pt（NCS）2（bpy）]）, in which different coordination ligands based on the N- and S-coordination of the thiocyanato ligands control the luminescent color. The electronic structures were studied using the B3LYP functional. Optimized geometries Were compared to the experimentally observed structures. TDDFT calculation was carded out to investigate the excited singlet and triplet states. Calculations have been performed both in vacuo and in solvents, using a polarized continuum model （PCM） to account for solute-solvent interactions. Inclusion of the solvent led to a significant energy change, and as a consequence, the computed spectrum calculated in the presence of the solvent was in good agree- ment with the experimental determinations. The first two absorptions were found to originate from mixed plati- num-SCN （or NSC） to bipyridyl-n＊ transitions rather than pure metal-to-ligand-charge-transfer （MLCT） transitions, whereas the higher-energy bands arose from intraligand n→π＊ transitions. The stretching frequencies of C≡N have been calculated both in the ground and excited states, which are relative to the charge transition during the excitation. In addition, different sizes of basis sets were also discussed in this paper.     

Computational Characterization of Reactive Intermediates of Carbon Monoxide Dehydrogenase

The catalytic oxidation of CO to CO2 by carbon monoxide dehydrogenases has been explored theoretically, and a large C-cluster model including the metal core [Ni-4Fe-4S] and surrounding residues and crystal water molecules was used in density functional calculations. The key species involved in the oxidation of CO at the C-cluster, Cred1, Cred2 and Cint, have been elucidated. On the basis of computational results, the plausible enzymatic mechanism for the CO oxidation was proposed. In the catalytic reaction, the first proton abstraction from the Fe（1）-bound water leads to a precursor to accommodate CO binding and the subsequently consecutive proton transfers from the metal-bound carboxylate to the amino acid residues facilitate the release of CO2. The hydrogen-bond network around the C-cluster formed by conserved residues His93, His96, Glu299, Lys563, and four water molecules in the active domain plays an important role in proton transfer and intermediate stabilization. Predicted geometries of key species show good agreement with the reported crystal structures.     

A MORPHOLOGICAL STUDY OF POLY（DIVINYLBENZENE-co-ACRYLIC ACID） IN CROSSLINKING PRECIPITATION POLYMERIZATION

Divinylbenzene-80 （DVB-80） and polar monomer acrylic acid （AA） having hydrogen bonding at a total monomer loading of 5 vol% were precipitated-copolymerized in a variety of organic solvents with 2,2＇-azobis（isobutyronitrile） （AIBN） as initiator. The experiments were investigated from a two-dimensional matrix, i.e., the actual crosslinking degree of DVB varying from 0 to 80% and the solvent composition varying from 0 to 100% of toluene mixture with acetonitrile, when the mixture of acetonitrile and toluene was used as the reaction solvent. Under various reaction conditions, six distinct morphologies including soluble polymers, swellable microgels, coagulum, irregular microparticles, and nano-/micrometer microspheres were formed and the structures of these polymer architectures were described. A morphological map was utilized to discuss the effects of both crosslinking degree of DVB and composition of solvent on the transitions between morphology domains. The results demonstrated that the microspheres are formed by an internal contraction due to the marginal solvency of the continuous phase and the crosslinking of the polymer network through the covalent bonding from DVB as well as the interchain hydrogen-bonding between the carboxylic acid units.     

Spectroscopic and Structural Study of the 1：2 Aluminium（Ⅲ） Complex of Quercetin

Complex formation between aluminium and quercetin（Q） in methanol was investigated by means of 27^Al solid-state, 13^C and 1^H NMR and MS（ESI）, UV and IR spectra. Formation of the 1：2 complex was favored in methanol relative to all other solvent and the predominant species observed of Al（Ⅲ） has a 1：2 stoichiometry. The fine structure of 1：2 aluminum complex of quercetin was that the aluminum central atom chelated with two quereetin molecules and two methoxyl groups between two five membered rings, its coordination is six, the chelated site was 3-hydroxy-4-carbonyl.     

Hydrogen Bonded Semi-Rigidified Bispyridyl-Incorporating Aryl Amide Oligomers： Efficient ＂C＂-Styled Receptors for Aliphatic Ammoniums,a Remarkable Protonation Effect and Chiral Induction

The complexing behaviour of two linear compounds 1 and 2 toward the trifluoroacetic acid （TFA） salts of n-dodecylamine, di-n-octylamine, n-dodecyl D- and L-phenylalaninates （3, 4, and D- and L-5） in chloroform has been described. Compounds 1 and 2 consist of two folded amide moieties with two pyridyls at the terminals which are connected directly or with an acetylene linker. The rigidified folded moieties are stabilized by intramolecular hydrogen bonding, while the whole molecules can adopt an ＂S＂- or a ＂C＂-styled conformation depending on the relative orientation of the two rigidified moieties. ^1H NMR, UV-Vis, fluorescent and circular dichroism investigations revealed that 1 and 2 could bind primary and secondary ammonium cations with their ＂C＂-styled conformation. In the presence of 1 equiv, of TFA, the binding stability was increased significantly as a result of promoted formation of the ＂C＂-styled conformation due to the monoprotonation of the peripheral pyridyl units in 1 and 2. In contrast, the addition of 2 equiv, of TFA substantially weakened the binding stability because the ＂S＂-styled conformation was favored as a result of protonation of both of their pyridyl units. Moreover, remarkable induced circular dichroisms were also displayed for the complexes of 1 and 2 with chiral D- and L-5.     

Determination of petroleum sulfonates in crude oil by column-switching anion-exchange chromatography

A column-switching anion-exchange chromatography method was described for the separation and determination of petroleum monosulfonates （PMS） and petroleum disulfonates （PDS） in crude oil that was simply diluted with the dichloromethane/methanol （60/40）. The high performance liquid chromatography （HPLC） system consisted of a clean-up column and an analytical column, which were connected with two six-port switching valves. Detection of petroleum sulfonates was available and repeatable. This method has been successfully applied to determine PMS and PDS in crude oil samples from Shengli oil field.     

Amide as an efficient ligand in the palladium-catalyzed Suzuki coupling reaction in water/ethanol under aerobic conditions

Amide,which is derived from proline and is inexpensive and air-stable,has been synthesized and characterized by ¹H NMR,¹³C NMR,and MS.It was found to be an efficient ligand in the palladium-catalyzed Suzuki cross-coupling reaction.In the Pd/amide catalytic system,aryl bromides can be coupled with phenylboronic acid in ethanol/water（1:2;v/v） in excellent yields even with a low Pd loading of 0.01 mol%.Moreover,the scope of the reaction is broad,and a wide variety of functional groups are tolerant.     

DNA Binding Properties and Cytotoxic Activities of Two Trinuclear Ruthenium（Ⅱ） Polypyridyl Complexes

The interactions between two trinuclear Ru（II） complexes and calf thymus DNA（CT DNA） were studied via absorption spectroscopy, reverse salt titrations, binding stoichiometry, DNA melting experiments, as well as viscosity measurement. The results indicate that complexes 1 and 2 bind to DNA via the interaction of the planar π-delocalized system of the complexes with intrinsic binding constants of 4.18 × 10^5 and 3.85 × 10^6 L/tool, respectively, and non-electrostatic binding free energy makes a predominant contribution to the binding free energy. The in vitro cytotoxic activity of complexes 1 and 2 was evaluated by the MTT[3-（4,5-dimethylthiazol-2-yl）-2,5-diphenyl- 2H-tetrazolium bromide] method. Complex I shows higher anticancer potency than complex 2 against four tumor cell lines. Further mechanism study indicates that complexes 1 and 2 can cause cell cycle arrest in the G2/M phase.     

Addition Mechanisms of Phenol toward Formaldehyde under Acidic Condition： a Theoretical Investigation

The reaction mechanisms of phenol with formaldehyde in the first and second addition at the ortho- and para-position in acid solution were theoretically investigated at the PW91/DNP level with solvent effects included. The reaction of phenol with protonated methanediol firstly forms an adduct intermediate, via a SN2 mechanism with a water molecule as the leaving group. From the adduct intermediate, there are two reaction channels involving a proton transfer to form the addition products. One is that a proton directly transfers via a four-membered ring transition state with a notable energy barrier (Four-member mechanism). Another mechanism involving a water molecule as catalyst to mediate the proton transfer (WCP mechanism), is a barrierless process, indicating that the formation of the adduct intermediate, the first reaction step, is rate-limiting. The reaction products are free hydroxymethyl phenols and/or hydroxybenzy carbocation (HOC6H4CH2+) which plays an important role in the following formation of methylene and methylene ether linkages. The second addition reactions between formaldehyde and hydroxymethyl phenol at all possible reaction sites of the phenol ring in acid solution were also investigated and discussed.     

A DNP SPECTROMETER AT 1.94 T MAGNETIC FIELD

We describe a home-made dynamic nuclear polarizatioD (DNP) spectrometer at a fieldof 1.94 T, corresponding to Larmor frequencies 83 MHz and 54 GHz for proton and electron,respectively. Its NMR part is a modified Bruker WP--80SY spectrometer. A 6--mm EIO (ex-tended interaction oscillator) Klystron D3070, with a maximum output power of 30W in cwmode, served as the microwave source of ESR. In ~1H and ~(13)C DNP and DNP--CP (crosspolarization) experiments the probe consisted of a horn-antenna, a movable reflector and adouble-tuned circuit for ~1H and ~(13)C. The proton and carbon NMR signals were enhanced byone to two orders of magnitude for typical samples. Some results are presented in thispaper.     

Synthesis of Heterocycle Compounds Containing Two Pyridazinone Units

Four novel compounds containing two pyridazinone units attached to one benzene or pyridine ring, protected and deprotected 1,5-di[3（2H）-pyridazinon-6-yl]benzene and 2,6-di[3（2H）-pyridazinon-6-yl]pyridine were synthesized in eight steps, which provided a useful method for the preparation of pyridazinone derivatives via the Stetter and cyclization reactions. Their structures were characterized by ^1H NMR, ^13C NMR, and HRMS.     

Thickness Uniformity Adjustment of Inkjet Printed Light-emitting Polymer Films by Solvent Mixture

In this paper, thickness uniformity of poly（9,9-di-n-octylfluorene） films patterned by inkjet printing was im- proved by the use of solvent mixtures （a solvent with higher volatility, higher surface energy and lower viscosity, with another solvent with lower volatility, lower surface energy and higher viscosity）. The average thickness of inkjet printed poly（9,9-di-n-octylfluorene） films was increased from ca. 30 nm to ca. 100 nm when solvent mixtures were used instead of pure chlorobenzene. More flat PFO films were formed instead of the original films with con- cave-lens like cross-section formed by coffee ring effect. This improvement was explained by combination of in- tense Marangoni flow at early drying process and weak complementary flow at the later drying process formed in the solvent mixture. Patterned poly（9,9-di-n-octylfluorene） films were used for fabrication of electroluminescence devices with improved electronic property. Array of pixels with about 80% effective light-emitting area was ob- tained.