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1.
The weak inclusion complex of cyclomaltoheptaose (beta-cyclodextrin, betaCD) with p-nitrobenzoic acid was investigated in the solid state. Crystallography shows that two betaCD molecules co-crystallize with two p-nitrobenzoic acids and 28.5 water molecules [2(C(42)H(70)O(35))x2(C(7)H(5)NO(4))x28.5H(2)O] in the triclinic system. 相似文献
2.
The main objective of this work was to increase the solubility of sulfadiazine by formation of inclusion complexes with β-cyclodextrin, and methyl-β-cyclodextrin. The apparent stability constants have been determined by phase solubility studies in water and buffer solutions of pH values of 2 and 8. The stoichiometry of all complexes was found to be 1:1 but different relative affinities were found for each cyclodextrin. It was possible to obtain a greater overall solubility by using a combined approach of pH adjustment and complexation with cyclodextrins. Guest-host interactions have been investigated using nuclear magnetic resonance. Complexes were prepared in solid state by different methods and were characterized using differential scanning calorimetry, thermogravimetric analysis, Fourier-transform infrared spectroscopy, X-ray diffractometry and scanning electron microscopy. The dissolution rate of the drug from the inclusion complex made by freeze-dried was much faster than this of the pure drug. 相似文献
3.
The crystallographic structure of the complex formed by beta-cyclodextrin with 1,10-phenanthroline has been studied by X-ray diffraction. The result shows that the complex adopts an uncommon 2:3 stoichiometry in solid state, that is, every complex unit contains three 1,10-phenanthroline molecules and two beta-cyclodextrin molecules, where two 1,10-phenanthroline molecules individually occupy two cyclodextrin cavities, and the third guest molecule is located in the interstitial space between two head-to-head cyclodextrin molecules. The intermolecular hydrogen bonds between the adjacent complex units further link these individual monomers to a channel-type assembly. Furthermore, 1H and 2D NMR spectroscopy has been employed to investigate the inclusion behavior between the host beta-cyclodextrin and guest 1,10-phenanthroline in aqueous solution. 相似文献
4.
The Raman spectra of three globular proteins, beef pancreas chymotrypsinogen A, beef pancreas ribonuclease, and hen egg white ovalbumin have been obtained in the solid state and aqueous solution. X-ray diffraction and circular dichroism evidence have indicated that these proteins have a low α-helical content and a large fraction of the residues in the unordered and β-sheet conformation. The frequencies and intensities of the amide I and amide III lines are consistent with assignments based on the Raman spectra of polypeptides. The intense amide III lines observed in all the spectra would be expected for proteins with a low fraction of the residues in the α-helical conformation. Several spectra changes occur upon dissolution of the proteins in water and may be associated with further hydration of the proteins. The spectrum of thermally denatured chymotrypsinogen is presented. A 3 cm–1 decrease in the frequency of the amide I line of the protein dissolved in D2O upon heating was observed. This observation is consistent with a denaturation mechanism allowing only slight changes in the secondary structure but an increase in solvent penetration upon going from the native to the reversibly denatured state. 相似文献
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6.
Gisbert Grossmann Kim A. Burkov Lubov A. Myund Claudia Verwey 《Inorganica chimica acta》2004,357(3):797-808
Dissociation and alkali complex formation equilibria of nitrilotris(methylenephosphonic acid) (NTMP, H6L) have been studied by dilatometric, potentiometric and 31P NMR-controlled titrations. Dilatometry indicated the formation of alkali complexes ML (M=Li, Na, K, Rb, Cs) at high pH with a stability decreasing from Li to Cs. An efficient combination of potentiometric and NMR methods confirmed two types of alkali metal complexes MHL and ML. Stability constants for the equilibria following M+ + HL5− ? MHL4− and M+ + L6− ? ML5−, respectively, were determined: logKNaHL=1.08(0.07), logKKHL=0.86(0.08), logKNaL=2.24(0.03). Systematic errors are introduced by using alkali metal hydroxides as titrants for routine potentiometric determinations of dissociation constants pKa5app and pKa6app. Correction formulae were derived to convert actual dissociation constants pKa into apparent dissociation constants pKaapp (or vice versa). The actual dissociation constants were found: pKa5(H2L4− ? H+ + HL5−)=7.47(0.03) and pKa6(HL5− ? H+ + L6−)=14.1(0.1). The anisotropy of 31P chemical shifts of salts MnH6 − nL (M=Li, Na, n=0-5) is more sensitive towards titration (n) than isotropic solution state chemical shifts. 相似文献
7.
The crystal structure of the 1:1 complex of beta-cyclodextrin (cyclomaltoheptaose) with trans-cinnamic acid was studied by X-ray diffraction. Two beta-cyclodextrin molecules related by a twofold crystal axis form dimers in the hydrophobic cavity of which, two guest molecules are entirely buried. The complex crystallizes in the monoclinic C2 space group with channel-type molecular packing. The oxygen atoms of the carboxylate group of the trans-cinnamic acid molecule form strong hydrogen bonds with two water molecules lying in the interdimeric space of the hydrophobic channel. 相似文献
8.
An inclusion complex of fenbufen with beta-cyclodextrin (beta-CD) in aqueous solution was characterized by (1)H-NMR spectroscopy. The [1:1] stoichiometry was determined and a stability constant of several 1000s (M(-1)) was calculated. The geometry of the inclusion complex was established based on MM(+) molecular mechanics calculations. 相似文献
9.
V Renugopalakrishnan P M Horowitz M J Glimcher 《The Journal of biological chemistry》1985,260(21):11406-11413
Phosvitin, a highly phosphorylated glycoprotein, represents the major fraction of hen egg yolk phosphoproteins. Circular dichroism, Fourier transform infrared spectroscopy, and Fourier transform infrared photoacoustic and fluorescence spectroscopic methods were employed to determine the secondary structure of the protein in both the solid and solution phases. This was supplemented by a Chou-Fasman type of predictive algorithm for the first 25 residues at the N terminus of the dephosphorylated protein. A three-compartment model consisting of alpha-helical, beta-sheet, and beta-turn components with beta-turns occurring at the interface between alpha-helical and beta-sheet regions in the proximity of O-phosphoserine residues is suggested from the combined analyses. Beta-sheets appear to be the dominant secondary structural component in phosvitin in the solid and solution phases. The suggested model bears many similarities to other phosphoproteins reported in the literature. The secondary structure of phosvitin is observed to be sensitive to environmental factors as previously reported although the present studies differ in some respects from earlier results. Preliminary results suggest that Ca2+ ions trigger a decrease in beta-sheet structure at pH 2. 相似文献
10.
The molecular recognition of caffeine in both solution and solid state is important to understand different enzymatic reactions i.e., enzyme–substrate interactions, immunological reactions in vivo, selective host–guest complexation and catalytic reactions in bio-mimetic chemistry. The weak intermolecular forces in recognition system direct the molecules toward self-linking in supramolecular engineering in the chemistry of life and material science. In this contribution, it has been illustrated the immense variety of receptors that have been designed for caffeine recognition in both solid and solution phase. The binding studies for the recognition of caffeine are reported by different research groups including our group. It is important to understand the goal of developing artificial molecular receptors, capable of binding very efficiently and very selectively with caffeine which is described elaborately in this context. The modern bioorganic chemistry concerns the design of synthetic molecules that mimic various aspects of enzyme chemistry and to understand their essential roles in biological systems. The stimulating effect of caffeine is not only exploited in nutrient technology but also in cosmetics and pharmaceuticals, which accounts for the economic importance of this particular additive. Although caffeine was first time isolated by Ferdinand Runge from coffee beans almost 200 years ago, it still has some surprise in hoard. 相似文献
11.
J. Abrahamsson S. Abrahamsson B. Hellqvist K. Larsson I. Pascher S. Sundell 《Chemistry and physics of lipids》1977,19(3):213-222
Cholesteryl sodium sulphate (CS) crystallizes as the dihydrate, the crystal structure of which is known. On heating the dihydrate, solid state phase transitions are observed at 65°C and 95°C and melting occurs at 165°C. The structure of the high temperature phases has not been determined. Cholesteryl dihydrogen phosphate (CP) is not isostructural with any phases of CS. It undergoes a phase transition at 50°C and melts at 190°C. In systems with water CS is unstable whereas it was possible to determine the phase diagram of CP. In most of the composition range a crystalline hydrate is in equilibrium with a gel-phase. The latter has remarkable properties in that lamellar order exists with the 46 Å lipid bilayer interleaved with water layers up to 1000 Å. The monofilm behaviour of CS and CP at different pH levels is also reported. 相似文献
12.
Sh. N. Khattab A. El-Faham A. M. El-Massry E. M. E. Mansour M. M. Abd El-Rahman 《Letters in Peptide Science》2000,7(6):331-345
The IR studies for the preactivation step of N-protected iminodiacetic acid with different coupling reagents (TCFH,TFFH, HATU, HBTU, HSTU) were reported here and showed theformation of an anhydride as an active intermediate in caseof TCFH and TFFH. The formation of a mixture of an anhydrideand an active ester (–OBt, –OAt or –OSu) were observed forHBTU, HATU or HSTU coupling reagent. Dependent on the couplingconditions, acylation of N-protected iminodiacetic acid with amino acid ester or amide derivatives in solution phase gavemono- or di-substituted iminodiacetic acid derivatives. Couplingof N-protected iminodiacetic acid with an amino acid or peptideattached to a solid support (PAL-PEG-PS or Wang resin) gave onlythe monosubstituted iminodiacetic acid derivatives. 相似文献
13.
Khattab Sh. N. El-Faham A. El-Massry A. M. Mansour E. M. E. Abd El-Rahman M. M. 《International journal of peptide research and therapeutics》2000,7(6):331-345
Summary The IR studies for the preactivation step of N-protected iminodiacetic acid with different coupling reagents (TCFH, TFFH,
HATU, HBTU, HSTU) were reported here and showed the formation of an anhydride as an active intermediate in case of TCFH and
TFFH. The formation of a mixture of an anhydride and an active ester (-OBt,-OAt or-OSu) were observed for HBTU, HATU or HSTU
coupling reagent. Dependent on the coupling conditions, acylation of N-protected iminodiacetic acid with amino acid ester
or amide derivatives in solution phase gave monoor di-substituted iminodiacetic acid derivatives. Coupling of N-protected
iminodiacetic acid with an amino acid or peptide attached to a solid support (PAL-PEG-PS or Wang resin) gave only the monosubstituted
iminodiacetic acid derivatives.
Abbreviations: HBTU, N-[(1H-benzotriazol-1-yl)(dimethylamino)methylene]-N-methylmethanaminium hexafluorophosphate N-oxide; Boc,t-butyloxycarbonyl; DCC, N,N′-dicyclohexylcarbodiimide; DIC, N,N′-diisopropylcarbodiimide; DIEA, diisopropylethylamine; HATU,
N-[(dimethylamino)-1H-1,2,3,-triazolo[4,5-b]pyridin-1-yl-methylene]-N-methylmethanaminium hexafluorophosphate N-oxide; DMF,
N,N-dimethylformamide; Bsmoc, 1,1-dioxobenzo[b]thiophene-2-ylmethoxycarbonyl; Fmoc, 9-fluorenylmethyloxycarbonyl; HOAt, l-hydroxy-7-azabenzotriazole;
HOBt, l-hydroxybenzotriazol; IDA, iminodiacetic acid; HSTU, O-(succinimidyl)-tetramethyluronium hexafluorophosphate; TCFH;
1,1,3,3-tetramethyl-2-chloroformamidinium hexafluorophosphate; TFFH, 1,1,3,3-tetramethyl-2-fluoroformamidinium hexafluorophosphate;
TMS-Cl, trimethylchlorosilane. Amino acids and peptides are abbreviated and designated following the rules of the IUPAC-IUB
Commission of Biochemical Nomenclature (J. Biol. Chem., 247 (1972) 997). 相似文献
14.
Trifluoperazine (TFP) has been widely studied in relation to its mode of binding and its inactivation of calmodulin (CaM). Most studies in solution have indicated that CaM has two high-affinity binding sites for TFP. The crystal structure of the 1:4 CaM-TFP complex (CaM-4TFP) shows that three TFP molecules bind to the C-domain of CaM, and that one TFP molecule binds to the N-domain. In contrast, the crystal structure of the 1:1 CaM-TFP complex (CaM-1TFP) shows that one TFP molecule binds to the C-domain. It has been thought that the binding of one TFP molecule to the C-domain is followed by binding to the N-domain. The crystal structure of the 1:2 CaM-TFP complex (CaM-2TFP), moreover, has recently been determined, showing that two TFP molecules bind to the C-domain. In order to determine the structure of the CaM-TFP complex and to clarify the interaction between CaM and TFP in solution, we performed a molecular dynamics simulation of the CaM-TFP complex in aqueous solution starting from the CaM-4TFP crystal structure. The obtained solution structure is very similar to the CaM-2TFP crystal structure. The computer simulation showed that the binding ability of the secondary binding site of the C-domain is higher than that of the primary binding site of the N-domain. 相似文献
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16.
Complex formation of poly(glutumic acid) with cupric ions in aqueous solution was investigated by three different methods: optical spectroscopy, optical rotatory dispersion, and electron spin resonance. Formation of a characteristic complex was found to occur in a pH region suitable for the helix-coil transition. An analysis of the ESH spectrum of the complex is given, and the results of calculation of bonding parameters suggest that the bond between copper and nitrogen atoms had an appreciably covalent character. The change in the secondary structure of the polymer as a result of complex formation is discussed. 相似文献
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18.
Kurtán T Pescitelli G Salvadori P Kenéz A Antus S Szilágyi L Illyés TZ Szabó I 《Chirality》2008,20(3-4):379-385
Solution and solid-state CD spectra of nine peracetylated and deacetalyted diglycosyl disulfides were measured to study the relationship between the low-energy CD transitions (n1-->sigma*(S--S) and n2-->sigma*(S--S)) and helicity of the inherently chiral disulfide chromophore as perturbed by chiral carbohydrate moieties. The solid-state CD spectra were directly correlated with the reported X-ray structures of Ac4GlcSSGlcAc4 and Ac4GlcSSGalAc4, and the CD data revealed that all the disulfides have M helicity with C1--S--S--C1' dihedral angles -90 degrees < phi < 0 degrees both in solution and in the solid state. A TDDFT CD study was carried out on dimethyl diselenide which confirmed that the same quadrant rule is relevant between the signs of the low-energy CD transitions and the diselenide torsional angle as formulated previously for the disulfide chromophore. The CD spectra of Ac4GlcSeSeGlcAc4 measured in solution and in the solid state were correlated with its X-ray structure and reproduced well by TDDFT CD calculations performed on its tetra-O-acetyl derivative. 相似文献
19.
The crystal and molecular structure of the 1:1 inclusion complex of beta-cyclodextrin (cyclomaltoheptaose) with squaric acid (3,4-dihydroxycyclobutene-1,2-dione) was determined by X-ray diffraction. The complex crystallizes in the monoclinic P2(1) space group and belongs to the monomeric cage-type, characterized by a herringbone-like packing motif. Co-crystallized water molecules are present on seven sites, of which six are fully occupied. The guest molecule is placed inside the beta-cyclodextrin cavity, perpendicular to the plane defined by the glycosidic O-4n atoms, and held in place by direct and water-mediated hydrogen bonds mainly involving symmetry-related beta-cyclodextrin molecules. The accommodation of the planar guest molecule into the beta-cyclodextrin cavity determines a significant distortion of the latter from the sevenfold symmetry. 相似文献
20.
Kealley CS Rout MK Dezfouli MR Strounina E Whittaker AK Appelqvist IA Lillford PJ Gilbert EP Gidley MJ 《Biomacromolecules》2008,9(10):2937-2946
We report a multitechnique study of structural organization and molecular mobility for soy glycinin at a low moisture content (<30% w/w) and relate these to its glass-to-rubber transition. Small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy are used to probe structure and mobility on different length and time scales. NMR (approximately 10(-6) to 10(-3) s) reveals transitions at a higher moisture content (>17%) than DSC or SAXS, which sample for much longer times (approximately 10 to 10(3) s) and where changes are detected at >13% water content at 20 degrees C. The mobility transitions are accompanied by small changes in unit-cell parameters and IR band intensities and are associated with the enhanced motion of the polypeptide backbone. This study shows how characteristic features of the ordered regions of the protein (probed by SAXS and FTIR) and mobile segments (probed by NMR and DSC) can be separately monitored and integrated within a mobility transformation framework. 相似文献