REFINED CRYSTAL STRUCTURE OF INSULIN AT 1.8A RESOLUTION——CRYST

The structure of insulin has been refined by difference Fourier method at 1.8A resolu-tion. A set of computer programs calculating the mF_o-nF_c Fourier synthesis and the cor-rections of parameters automatically has been set up. With the programs to refine theinsulin model obtained from MIR map at 1.8A resolution for 11 cycles, the R index(R=∑|KF_o- F_c|/∑KF_o) is reduced to 0.210 from the initial value of 0.388. Duringthe refinement the stereochemistry of the insulin molecules is constantly detected andadjusted to fit the reasonable geometry. The refinement has greatly improved the structuremodel of insulin and provided more detailed structure information. On the basis of this thesystems of hydrogen bond in an insulin dimer are determined and the interaction betweenwater and insulin molecules in the crystal is investigated.     

CLOUD POINT CURVES OF POLY(ETHYLENE GLYCOL)/POLY(PROPYLENE GLYCOL) MIXTURES AND THEIR THERMODYNAMIC EXPLANATION

In the study of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) mixtures not only a bimodal shape but also a reverse trend of the dependence on molecular weight of the cloud point curves were observed.This trend indicates that the miscibility of the studied mixtures decreases as the molecular weight of one component decreases. The excess volumes of the mixtures show that the interaction parameter between two components decreases at first and increases after passing a minimum as the concentration of one component increases. This supports the explanation of Koningsveld on the bimodal shape of cloud point curves. Based on a binary interaction model a formula was derived revealing that the interaction between PPG and the end group of PEG and the hydrogen bonding interaction between ether and hydroxy end group inner or inter PEG molecules are not favorable for mixing. The latter interaction is an "attractive" force in PEG molecules. The two interactions are responsible for the observed abnormal dependence.     

Determination of the Flavonoids from Ginkgo Biloba Extract by High Performance Liquid Chromatography

Today Ginkgo biloba extract (GBE) is one of the most widely used food supplements and herbal medicines. The amounts of flavone glycosides, one of the key active components in GBE, vary according to the source of the ginkgo leaves and the extraction and enrichment procedures used to prepare the extract. A typical GBE contains from 22% to 27% of flavone glycosides. Ginkgo flavone glycosides are a group of small complex molecules that can be hydrolyzed to give kaempferol, quercetin and isor…     

INTERACTION OF POLY(SODIUM SULFODECYL METHACRYLATE)WITH CETYLTRIMETHYL AMMONIUM BROMIDE IN AQUEOUS SOLUTION

The interaction of poly(sodium sulfodecyl methacrylate) (PSSM) with cetyltrimethyl ammonium bromide (CTAB)was studied. It was found that the precipitate formed from PSSM and CTAB will be dissolved by excessive CTAB, resultingin the appearance of two maxima of the solution viscosity at the molar ratio (CTAB/-SO_3~-) of≈ 0.68 and≈1.30,respectively. The first one is related closely to the aggregation of polymer chains via CTAB molecules and the second oneshould be ascribed to the formation of the mixed micelles comprising surfactant and the polymer's hydrophobic chains. Theeffect of NaCl on the viscosity, the transmittance of the aqueous solution and the solubility of oil-soluble dye (dimethyl yellow) in the mixed system were also investigated.     

PRELIMINARY CRYSTALLOGRAPHIC STUDIES ON BACTERIOFERRITIN FROM AZOTOBACTER VINELANDII

Bacteriofcrritin-eytochrome from Azotobacter vinelandii is an unusual protein containinghaem groups as well as iron core like other ferritin. This paper reports tile purification of bacterioferritin by affinity chromatography and theformation of brick-red crystals from a solution containing MgCl_2. The crystals are opticalisotropic with maximum dimensions of 0.4×0.4×0.1 mm~3. The preliminary X-ray crystallo-graphic studies have boca performed. 1.5°unscreened precession photographs show that thecrystals of bacterioferritin belong to the cubic system, space group I432, with. cell dimen-sion 230 A. There arc probably 8 molecules in one cubic unit cell and the molecule might have 32symmetry. A molecular diameter of 115 A is derived from the packing of the molecules auda molecular weight of 826,000 is estimated for baeterioferritin.     

Synthesis,Crystal Structure and Thermal Stability Properties of a Binuclear Copper(Ⅱ) Coordination Polymer {[Cu_2(4,4'-bipy)_2(o-ABA)_4(H_2O)_2][(H_2O)_2]}_n

One-dimensional chain copper(Ⅱ) coordination polymer has been synthesized and characterized in the solvent mixture of water and alcohol with o-acetamidobenzoic acid,4,4'-bipyridine and copper perchlorate.It is of tetragonal,space group P41212 with a=1.57756(10),b= 1.57756(10),c=2.1438(3)nm,V=5.3352(8) nm3,Dc=1.524 g/cm3,Z=4,F(000)=2536,R= 0.0479 and wR=0.0979.The crystal structure shows two coordination modes.The copper(1) is coordinated with two nitrogen atoms of one 4,4'-bipyridine molecule and two oxygen atoms from two o-acetamidobenzoic acid molecules,forming a distorted tetrahedral coordination geometry;the copper(2) is coordinated with two nitrogen atoms of one 4,4'-bipyridine molecule,four oxygen atoms from two o-acetamidobenzoic acid molecules and two water molecules,generating a distorted octahedral coordination geometry.The result of TG analysis shows that the title complex is stable below 180.0 ℃.     

MOLECULAR CHARACTERIZATION OF RICE Wx GENE

The complete nucleotide (nt) sequence of the rice waxy(Wx) gene, which is responsible for the synthesis of amylose in endosperm and pollen, has been determined by a combination of restriction mapping and nt sequence analysis of two overlapping genomic DNA clones. The entire gene is about 5.5 kb in length. The alignment of the nt sequence of the Wx gene from rice with those of maize (Klsgen, R. B. et al.) and barley (Rohde, W. et al.) revealed the presence of thirteen introns and fourteen exons. The full-length of Wx protein in cluding transit peptide is 609 amino acid (aa) residues. The calculated molecular weight of rice Wx preprotein is about 72 kD. There is no significant difference between the similarity scores of the aa sequence deduced from the rice Wx gene compared with those of maize and barley. However, the nt sequences of the 5'-end upstream, 3'-end downstream and introns of the rice Wx gene, as well as the aa sequence of the transit peptide region of the Wx preprotein have low similarity scor     

Probing the effects of external species on poly(acrylate acid) chain dynamics by using cationic AIE-active fluorophore

We report here our results on the investigation of the chain dynamics of poly(acrylic acid) in aqueous solution. The concentration of poly(acrylic acid) was approximately 3.8×10~(-4) mol/L, two orders of magnitude higher than that reported in the literature. The p H value of the solution was 3.9, and the hydrogen bonds between the intrinsic and ionized carboxylic acid groups formed dynamic networks, which captured aggregation-induced emission-active molecules(a tetra-quaternary ammonium modified tetraphenylethene derivative) inside the polymer coils and induced fluorescence emission. The hydrogen bonds can be classified as intra- or intermolecular; both can be probed based on the emission change of the tetra-quaternary ammonium modified tetraphenylethene probes. The effects of different external stimuli on the polymer chain dynamics were investigated using different metal cations(including Na~+, Li~+, Zn~(2+), Ni~(2+), Ca~(2+), and Co~(2+)), different cation concentrations(1×10~(-6) to 4×10~(-4) mol/L), different poly(acrylic acid) molecular weights(5, 240, and 450 k Da), and different copolymers. The experimental results indicate that the long poly(acrylic acid) chains(high molecular weight) tend to form dense globular coils and exclude the probe molecules outside, which are robust and unsusceptible to water-soluble metal cations. However, the shorter poly(acrylic acid) chains tend to form intermolecular hydrogen bonds, which are helpful in capturing more probe molecules inside the networks, thus inducing stronger emission. Because of the dual functions of forming hydrogen bonds with carboxylic groups and acting as an acceptor of protons from the carboxylic acid group to form cationic species, copolymerization with acrylate amide [poly(acrylic acid)-co-poly(acrylamide)] can greatly affect the chain dynamics of poly(acrylic acid) segments, which is reflected by the drastically decreased emission intensity from the fluorescent probes.     

AN INVESTIGATION ON THE ab initio CALCULATION OF INTERMOLECULAR INTERACTION——NON-BONDED INTERACTION IN THE HYDROGEN BOND COMPLEX (HF)_2

An ab initio calculation of the hydrogen bond complex (HF)_2 is given with the 6-311 G~(**) basis set, according to which the potential surface around the balance point of the distancès and the orientations between two HF molecules is obtained. The atomic charges in the system are calculated with the PD/LSF method (potential-derived/least-square-fitting method) and then an analysis of the hydrogen bond interaction between two HF molecules is given with the (exp-6-1) potential function, by means of which it is shown that the main interaction between them is not an electro-static but a charge transfer one. The potential curve between two HF molecules is like a Morse function.     

REFINED CRYSTAL STRUCTURE OF INSULIN AT 1.8A RESOLUTION——HYDROGEN BONDS AND BOUND WATER

The hydrogen bonds in insulin fall into three cases: the helical hydrogen bonds in α- or 3_(10)helices, the non-helical one formed by polar groups of insulin itself, and the hydrogen bondsformed between insulin and water. By using the information obtained, the results of a seriesof biochemical investigations on insulin analogs related to B-chain C-terminal peptide can beinterpreted and it can also be inferred that the complex behaviours of the aggregation ofinsulin may play a protective role for the unique conformation of the molecule. Water structure also appears in the refined model. About one third of the water in anasymmetric unit is hydrogen-bonded to insulin molecules or each other, which are referred toas bound water. The polar and charged groups of insulin all show the tendencies to bind towater molecules as many as possible, which is a significant factor for the stabilization of theunique conformation of the molecule. The binding way of water molecules to insulin mole-cules is also analysed.     

Periodic tables of diatomic and triatomic molecules

The Mendeleev periodic table of atoms is one of the most important principles in natural science. However, there is shortage of analog for molecules. Here we propose two periodic tables, one for diatomic molecules and one for triatomic molecules. The form of the molecular periodic tables is analogous to that of Mendeleev periodic table of atoms. In the table, molecules are classified and arranged by their group number G, which is the number of valence electrons, and the periodic number P, which represents the size of the molecules. The basic molecular properties, including bond length, binding energy, force constant, ionization potential, spin multiplicity, chemical reactivity, and bond angle, change periodically within the tables. The periodicities of diatomic and triatomic molecules are thus revealed. We also demonstrate that the periodicity originates from the shell-like electronic configurations of the molecules. The periodic tables not only contain free molecules, but also the "virtual" molecules present in polyatomic molecules. The periodic tables can be used to classify molecules, to predict unknown molecular properties, to understand the role of virtual molecules in polyatomic molecules, and to initiate new research fields, such as the periodicities of aromatic species, clusters, or nanoparticles. The tables should be of interest not only to scientists in a variety of disciplines, but also to undergraduates studying natural sciences.     

A simulation of thermal characteristic parameters with an inverse "S" type curve

A synthetical equation is proposed to characterize the essential features of the inverse "S" type curve on the oasis of summing-up simulation approach of "S" type curve.The two physical variables in the model obtained are discussed and the detailed method used to determine the parameters is given.The model is then presented to describe the crystallization of poly(caryleher ether ketone) (PEEK) and thermal decomposition of poly (amide-imide) (PAl) respectively.It is found that some thermal characteristic parameters can be well estimated from the model simulated in computer.     

A Novel Three-dimensional Mn(Ⅱ) Coordination Polymer Constructed from Biphenyl-3,3?,5,5?-tetracarboxylic Acid and Water

The title Mn(Ⅱ) coordination polymer,poly{[heptaaqua-(μ4-bi-phenyl-3,3?,5,5?-tetracarboxylate)-bimanganese(Ⅱ)] pentahydrate},[Mn_2(bpta)(H_2O)_7]_n·5n H_2O(I),is crystallized from a mixture of biphenyl-3,3?,5,5?-tetracarboxylic acid(H_4bpta) and MnCl_2·4H_2O in waterethanol under room temperature. Its asymmetric unit consists of one and two halves of crystallographically independent Mn(Ⅱ) cations,one fully deprotonated H4 bpta ligand,seven coordinated water molecules and five solvent water as guest molecules. In I,each Mn(Ⅱ) atom is octahedrally coordinated by six oxygen atoms from bpta~(4-) anions and coordinated water molecules. In the Mn(Ⅱ) cations,one half Mn(Ⅱ) ion of them located at a 2-fold axis generating a trinuclear [Mn_3(H_2O)_2(RCOO)_2] linker by μ1,1-O(water) and μ1,3-O,O?(carboxylate) bridges and another half Mn(Ⅱ) ion with an inversion is a mononuclear linker. These neighbouring trinuclear and mononuclear Mn(Ⅱ) cations are linked together by biphenyl-3,3?,5,5?-tetracarboxylates to form a three-dimensional framework with a(42.84) topology of a(4,4)-connected net,in which the positions of the trinuclear [Mn_3(H_2O)_2(R-COO)_2] linker as a 4-connector linking four bpta~(4-) ligands in I reproduce an eagle-shaped arrangement. The polymeric structure exhibits a water channel with an accessible void of 797.1 ?~3,amounting to 15.7% of the total unit-cell volume. Each of the cavities in the network is occupied by solvent water molecules.     

Prevalent intrinsic emission from nonaromatic amino acids and poly(amino acids)

Nonaromatic amino acids are generally believed to be nonemissive, owing to their lack of apparently remarkable conjugation within individual molecules. Here we report the intrinsic visible emission of nonaromatic amino acids and poly(amino acids) in concentrated solutions and solid powders. This unique and widespread luminescent characteristic can be well rationalized by the clustering-triggered emission(CTE) mechanism, namely the clustering of nonconventional chromophores(i.e. amino, carbonyl,and hydroxyl) and subsequent electron cloud overlap with simultaneous conformation rigidification. Such CTE mechanism is further supported by the single crystal structure analysis, from which 3 D through space electronic communications are uncovered.Besides prompt fluorescence, room temperature phosphorescence(RTP) is also detected from the solids. Moreover, persistent RTP is observed in the powders of exampled poly(amino acids) of ε-poly-L-lysine(.-PLL) after ceasing UV irradiation. These results not only illustrate the feasibility of employing the building blocks of nonaromatic amino acids in the exploration of new luminescent biomolecules, but also provide significant implications for the emissions of peptides and proteins at aggregated or crystalline states. Meanwhile, they may also shed lights on further understanding of autofluorescence from biological systems.     

SYNTHESIS OF THE 3'-HALF MOLECULE OF YEAST ALANINE tRNA

This paper deals with the synthesis of the 3'-half molecule of yeast alanine transfer RNA (tRNA_y~(Ala)) by ligation with T_4 RNA ligase of three component oligonucleotide fragments corresponding to nucleotides 36-45(Ⅰ), 46-57(Ⅱ) and 58-76(Ⅲ) in succession extending from the 3'-end to the 5'-end. First, in a ratio of acceptor to donor at 1.5 to 1, we adopted a method of three successive reactions, namely, the 5'-phosphorylation of the nonadecamer (Ⅲ), ligation with the dodecamer(Ⅱ) and the 5'-phosphorylation of the ligation product formed; with one isolation step and obtained the 5'-phosphorylated 31mer(46-76) (Ⅳ) in an overall yield of 70%. Then the 31met(Ⅵ) as a donor was ligated with 3 times of decamer(Ⅰ) to form the 41met(36-76) (Ⅴ), the 3'-half molecule of tRNA_y~(Ala)). The yield was 67%. After 5'-phosphorylation, (Ⅴ) was ligated with the natural 5'-half molecule to form the semi-synthetic tRNA_y~(Ala)), which was biologically active, i. e. accepting and transferring (~3H)-alanine into p     

Methane—the Promising Career of a Humble Molecule

Methane, CH4, here represents natural gas (NG) of which it is the main constituent. Routes ofchemical utilisation of NG — as opposed to energy usage — are discussed. A main step is the conversion of NG to synthesis gas, a mixture of CO and H2. Simple molecules derived from synthesis gas, like methanol,can be further reacted to longer-chained hydrocarbons like propylene and other olefins and even to gasoline and diesel.     

RELATIONSHIPS BETWEEN X—H STRETCHING OVERTONE FREQUENCIES AND BOND LENGTHS/BOND ANGLES

A relationship between the X-H (X = N, O, C, and so on) equilibrium bond length in a Morse oscillator and the X-H stretching overtone frequency shifts is obtained theoretically. We use the equation to discuss the empirical linear relationships that have been proposed for heterocyclics, alkanes and fluorinated benzenes. On the other hand, a unified relationship between the X-H bond angles and the experimental quantities (ω(?) and the coupling strength λ) is also presented for XH2, XH, and XH4 molecules or molecular fragments. Calculations of X-H bond angles for a number of molecules show that the results from our equations are in excellent agreement with the experimental values. Also we can extract the information of relative magnitude of bond coupling force field.     

THEORETICAL STUDY OF REACTION DYNAMICS OF H_2 ■ H+H ON LITHIUM(100) SURFACE

A generalized LEPS potential energy surface of (H_2?H +H)/Li(100) plane systemwas constructed based on the ab initio SCF absorption and surface diffusion of a hydrogenatom on lithium(100) surface, and reaction kinetic behaviour of this system was investigatedby means of QCT method. It was shown from analysis of the feature of this potential energysurface that the activation energy of absorption of H_2 molecules on a lithium(100) planeis unnecessary and the dissociation of H_2 on the Li(100) plane relates closely to the adsorp-tion sites and adsorption fashions, and the horizontal manner of dissociation of H_2 is easierthan the standing one. And it was also shown from the analysis of various collision trajec-tories that the surface recombination probabilities of bi-hydrogen atoms at low covering arevery small, and that the surface dissociation probabilities of H_2 are controlled by its vibra-tional quantum number. The potential energy surface of gas-metal surface interaction systemconstructed here is con     

Increasing the Solubility of a Hydrophobic Molecule with Thymine-like Face by DNA via Supramolecular Interaction

Poor water-solubility of hydrophobic drugs greatly hampers drug design and creats delivery problems.The traditional way to improve the solubility is to add hydrotropes or excipients to supress aggregations.Here,a novel mechanisim has been proposed based on supramolecular interactions and demonstrated with a small molecule,pvromellitic diimide(PD).This compound contains thymine-like ‘face’ and can interact with adenines through Wat-son-Crick and Hoogsteen hydrogen-bonding.Given the high water solubility of poly adenines[poly(A)],it is expectec that poly(A)will greatly increase the PD solubility.Indeed,such an increased solubility was confirmed by ultraviolet-visible spectroscopy(UV-Vis)and polyacrylamide gel electrophoresis(PAGE)analysis.We believe that this strategy could be used to improve the solubility of other similar hydrophobic molecules.     

Probing the pH-dependent chain dynamics of poly(acrylate acid) in concentrated solution by using a cationic AIE fluorophore

We report a novel strategy to study the chain dynamics of poly(acrylic acid) (PAA) in a relative concentrated solution (1.0 g/L). The strategy is based on the fluorescent probe (DCTPE) with unique aggregation-induced emission (AIE) characteristics. Free DCTPE molecules are non-emissive in aqueous solution, but they become highly emissive when trapped in polymer coils. The fluorescence intensity is proportional to the efficiency of trapping DCTPE molecules in polymer coils. By correlation the change of fluorescence intensity with the variation of pH value (from 1.78 to 12.06), the PAA chain’s dynamics in the relatively concentrated solution have been elucidated into three processes. In the pH range from 12.06 to 6.0, PAA chains take an extended and non-folding conformation. Changing pH from 6.0 to 3.86, PAA chains are partially protonated and loosely packed polymer coils are formed. Further lowering the pH value of the solution (from 3.86 to 1.78), protonated segments dominate the PAA chains, and at the same time, the intermolecular hydrogen bonding takes effect, thus the polymer chains posses in the conformation of more compact coils.