Effect of β- and γ-cyclodextrins and their methylated derivatives on the degradation rate of benzylpenicillin

Benzylpenicillin is characterized by instability in aqueous media, low oral bioavailability, and short biological half-life. Since their degradation products can cause allergic reactions, β-lactam antibiotics are supplied as a powder for injection and require special precaution when stored and re-constituted in water. An efficient method for β-lactam stabilization in the aqueous environment could reduce allergic side effects and facilitate their handling. Previously we proposed that complexation with cyclodextrins (CDs) is a way to achieve this goal. The purpose of the present study was to investigate the effect of methylation of CD on the chemical stability of benzylpenicillin. Kinetic studies revealed that degree of methylation of the CD molecule determines whether the CD has destabilizing or stabilizing effect on the β-lactam. The fully methylated βCD derivative Trimeb stabilizes benzylpenicillin while partial methylation of βCD only decreases to some extent the catalytic effect of native βCD. The complexes of all investigated CDs were also studied by DSC, FT-IR and NMR spectroscopy.     

8-AminoBODIPYs: cyanines or hemicyanines? The effect of the coplanarity of the amino group on their optical properties

The role of the amino group twisting ability in the BODIPY photophysics for nonsterically hindered and constrained molecular structures was studied. When a coplanar disposition of the amino and the BODIPY core is feasible, a hemicyanine-like delocalized π-system gives rise to novel blue and efficient BODIPY laser dyes. The key role of such rotamer is confirmed by newly synthesized derivatives where the amino and the BODIPY core are electronically decoupled by steric repulsions.     

Binding behaviors of scutellarin with α-, β-, γ-cyclodextrins and their derivatives

A series of cyclodextrin/scutellarin inclusion complexes were prepared from α-cyclodextrin, β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin with scutellarin (SCU), and their inclusion complexation behaviors, such as stoichiometry, complex stability constants and inclusion mode, were investigated by means of UV/Vis spectroscopy, ¹H NMR and 2D NMR. The results showed that the SCU could be efficiently encapsulated in the cyclodextrin cavity in aqueous solution to produce complexes that were more soluble than free SCU. The enhanced binding ability of cyclodextrins towards SCU was discussed from the viewpoint of the size/shape-fit and multiple recognition mechanism between host and guest.     

Effect of γ-irradiation on optical and electrical properties of Se1−xTex

The effect of γ-irradiation on optical and electrical properties of amorphous and polycrystalline Se_1−xTe_x (0.211<x<0.802) thin films of thickness 180 nm were investigated. The analysis of the absorption coefficient data revealed the existence of indirect transition both before and after irradiating. It was observed that the value of the optical energy gap depends on the value of x, decreasing as x increases. It was found also that the optical energy gap decreases with an increase of γ-doses for all compositions. The obtained results for all Se_1−xTe_x, films have been interpreted in terms of density of states model of Mott and Davis. From the experiment of electrical conductivity σ at various temperatures, it was observed that Se_1−xTe_x. films exhibited ln σ versus T⁻¹ relationships at high temperatures and ln σ(T)^1/2 versus T^−1/4 hopping conductivity behaviour at low temperatures. It was found that the thermal activation energies ΔE decrease with increasing Te content and increases with decreasing γ-doses. X-ray diffraction patterns for the as-deposited Se_1−xTe_x, show that polycrystalline films start to appear for x>0.407.     

Influence of degree and patterns of substitution on the inclusion properties of ethylated β-cyclodextrins

Different batches of ethylated derivatives of -cyclodextrins (Et-CD) obtained by various synthetic routes were used as host molecules to prepare inclusion compounds of salbutamol. Previous results showed that these complexes were suitable to achieve variable sustained-release behaviour of salbutamol. The mechanism of sustained-release was related to the inclusion capacity and physicochemical properties of Et-CD. Among the various analytical techniques carried out to characterize them, high resolution NMR afforded relevant information in terms of degree and patterns of subtitution, which could explain the differences observed between CD derivatives.     

The effect of the linking group on mesogenic properties of three‐ring derivatives of p‐carborane and biphenyl

Four series of mesogenic derivatives of p‐carborane (series A[0] and A[1]) and their benzene analogues (series B[0] and B[1]) with variable linking groups were prepared and investigated for phase behaviour. The data allowed a comparison of the effect of the group on the mesophase stability as a function of the adjacent ring (carborane or benzene), the variable central ring (carborane or benzene), and the presence of an oxygen atom in the terminal chain. The results showed that substitution of carborane for a benzene ring in B[m] depresses the clearing point by 50 K to 208 K and eliminates all smectic behaviour in A[m]. The carborane derivatives A[m] are weakly dependent (effectiveness of : –CH = CHCOO–～–COO–～–CH = CH–>–CH = N–～–CH₂CH₂–>–CONH–), whereas the benzene analogues B[m] are strongly dependent (effectiveness of : –CONH–>–CH = CH–>–CH = N–～–CH = CHCOO–>–COO–>–CH₂CH₂–) on the structure of the linking group . The difference in the effectiveness of the amide group on mesophase stability (ΔT _I = 208 K) has been attributed to the stabilizing intermolecular H‐bonding in B[m], which is prevented in A[m] by steric and electronic effects of the carborane cage on the carbonyl group.     

On the preparation of bilirubins of the natural α series substituted with a propionic acid residue and a hydroxypropyl group

Summary The reduction of mesobiliverdin XIII propan-1,3-diyl diester with NaBH₄ affords mesobilirubin XIII propan-1,3-diyl diester. The same reduction of mesobiliverdin XIII methylen diester. The same reduction of mesobiliverdin XIII methylen diester affords 8-(2-carboxyethyl)-3,17-diethyl-12-(3-hydroxypropyl)-2,7,13,17-tetramethylbiladien-ac-1,19-(21H, 24H)-dione (MBR-mc). The UV/Vis and¹H NMR spectra ofMBR-mc show that its structure in solution is similar to that of the natural bilirubins of the series.

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Zur Herstellung von Bilirubinen der natürlichen -Reihe mit Propionsäure- und Hydroxypropylsubstituenten

Zusammenfassung Reduktion von Mesobiliverdin-XIII-propan-1,3-diyl-diester mit NaBH₄ liefert Mesobilirubin-XIII-propan-1,4-diyl-diester. Die analoge Reaktion des Mesobiliverdin-XIII-methylen-diesters führt zu 8-(2-Carboxyäthyl)-3,17-diäthyl-12-(3-hydroxypropyl)-2,7,13,17-tetramethylbiladien-ac-1,19-(21H,24H)-dion (MBR-mc).MBR-mc weist in Lösung (UV/Vis und 1H-NMR Spektren) eine ähnliche Struktur auf wie die der natürlichen Bilirubine der -Serie.

     

Thermodynamic study on salt effects on complex formation of α-, β- and γ-cyclodextrins with p-aminobenzoic acid

The aim of this work was to gain a deeper understanding of salt effects in the inclusion complex formation of cyclodextrins. For this purpose, thermodynamic study of complex formation of α-, β- and γ-cyclodextrins with p-aminobenzoic acid was carried out in water and solutions of KCl, KBr, KH₂PO₄ and K₂SO₄ (0.2 mol/kg). Stability constants were calculated from the binding isotherms obtained on the basis of ¹H NMR measurements. Enthalpy and entropy of complex formation were estimated from the van’t Hoff plots. It was found that effects of KCl, KH₂PO₄ and K₂SO₄ are insignificant, while the influence of KBr on complex formation of cyclodextrins with p-aminobenzoic acid is more pronounced and results in a decrease of the stability constants. Specific action of Br⁻ is caused by the ability of these anions to penetrate into macrocyclic cavity. Coexistence of two complexation equilibria in KBr solution is accompanied by significant solvent reorganization originated from more intensive dehydration of the interacting species. This results in an increase of the enthalpy and entropy of complex formation. Manifestation of Br⁻ effect was found to be the same in the binding of p-aminobenzoic acid with α-, β- and γ-cyclodextrins.     

Study of the cholesterol extraction capacity of β-cyclodextrin and its derivatives, relationships with their effects on endothelial cell viability and on membrane models

Endothelial cells (HUVEC) were treated with β-cyclodextrin and hydroxypropylated or methylated derivatives solutions in order to quantify their cholesterol extraction capacity. Non-toxic concentrations of cyclodextrins (CDs) were determined following methyl thiazol tetrazolium (MTT) assays, total protein measurements, morphological observations and trypan blue assays. The residual cholesterol content of cells was measured and the extraction power of CDs compared to results obtained by phase solubility diagrams. Cholesterol was extracted with a dose-response relationship, the lowest residual cholesterol content being obtained with β-CD at 10 mM. Low substituted derivatives (Crysmeb^® and hydroxypropyl-β-CD) maintained liposomes integrity (as shown before), were the less cytotoxic and presented the lowest affinity for cholesterol contrary to methylated derivatives with degrees of substitution around 2.     

A study of salt effects on the complexation between β-cyclodextrins and bile salts based on the Hofmeister series

The Hofmeister series is the ranking of ions according to their ability to strengthen (kosmotropic ions) or weaken (chaotropic ions) hydrophobic interactions. Such ions are therefore expected to affect the strength of cyclodextrin (CD) inclusion complexes and may thereby affect the release of CD bound drug molecules. The influence of Hofmeister ions on the binding constants of complexes between CDs (β-CD and hydroxypropylated β-CD) and bile salts (glycocholate and glycochenodeoxycholate) were examined by isothermal titration calorimetry. The chaotropic anions tended to weaken these inclusion complexes. Conversely, kosmotropic ions increased the binding strength and this effect scaled with the buried hydrophobic surface area. Both effects are relatively weak at physiological ion concentrations and may be neglected for most pharmaceutical purposes.     

Quantum chemical studies on the structures, properties and decomposition of the azido derivatives of trinitrobenzenes

The geometries,heats of formation and electronic structures of 15 azido-derivatives of 1,2,3-TNB (Ⅰ),1,2,4-TNB (Ⅱ) and 1,3,5-TNB (Ⅲ) have been studied using quantum chemical AMI method at HF level.The effect of azido substitution on the structures and properties of TNBs has been discussed and the relative stability of the title compounds has been established.The processes of the decomposition of the title compounds by breaking C-NO2,C-N3 and CN-N2 bonds are investigated at UHF-AM1 level.It is shown that the decomposition of the title compounds may be initiated by the cleavage of both C-NO2 and N-N2 bonds.     

Effect of glycerol on the optical and physical properties of sol–gel glass matrices

Glass samples are prepared with different amount of glycerol as drying control chemical additive (DCCA) via acid catalysed sol–gel method. These samples are given solvent treatment namely rinse and dip with methanol while drying of the sample. In rinse treatment solid sample is rinsed with small amount of methanol while in dip treatment sample is dipped for 5 h in methanol. Comparative studies of these treated samples containing varied DCCA concentration are carried out by measuring optical transmission, mechanical strength and bulk density. Various instrumental techniques used for analysis are FTIR, DTA-TGA, XRD, SEM and TEM. The untreated samples take long time to dry up and to come out of the cuvette and show very less transmission in UV region which is much enhanced by solvent treatment. On the basis of this study, the solvent treated glass samples with DCCA amount 8 ml in the composition used are found to have the maximum UV transmission, good mechanical strength and may be useful as silica gel host matrices for solid state dye lasers and other applications. The UV transmission reported in the present studies is 90% in 337 nm region, which is the wavelength of N₂ laser pumping.     

Studies on the formation and properties of polypyrrole doped with ionised β-cyclodextrins: influence of the anionic pendants

Journal of Solid State Electrochemistry - Polypyrrole films doped with sulfonated β-cyclodextrin (PPy/sβ-CD) and carboxymethyl β-cyclodextrin (PPy/CMβ-CD) were formed on...     

The cooperative effect of a hydroxyl and carboxyl group on the catalytic ability of novel β-homoproline derivatives on direct asymmetric aldol reactions

Novel β-homoproline derivatives, 2-hydroxy-2-(pyrrolidin-2-yl)acetic acids (R,S)- and (S,S)-1a-d, were synthesized. All of the prepared compounds were used as organocatalysts in the direct asymmetric aldol reaction of 4-nitrobenzaldehyde with several ketones. Among these catalysts, (R)-2-hydroxy-2-((S)-pyrrolidin-2-yl)acetic acid (R,S)-1a showed good catalytic ability in the formation of aldol product 13 (up to 69% ee, 95% yield), which was similar to the results catalyzed by l-proline (71% ee, 96% yield). Relatively low yields and low enantioselectivities were observed in aldol reactions catalyzed by (S,S)-1a, for example, 13 was obtained in 55% yield and 13% ee. The aldol reaction catalyzed by the methyl-protected carboxylic acid 1b and esters 1c,d produced much lower chemical yields and enantioselectivities during the formation of 13. The cooperative effect of the (R)-configured hydroxyl group and the carboxyl group was found to play an important role in inducing enantioselectivity in the aldol reaction. Relatively high diastereoselectivities (anti:syn = 85:15) and enantioselectivity (anti, 83% ee) were observed in the aldol reactions of 4-nitrobenzaldehyde with cyclohexanone, which was catalyzed by (R,S)-1a.     

Synthesis and spectroscopic properties of a novel zinc phthalocyanine with four 17-membered crown ether voids

A novel zinc phthalocyanine containing four 17-crown-5 ether voids(17C5ZnPc) has been synthesized and characterized. UV-visible absorption and fluorescence emission spectra and as-sociated photophysical parameters have been determined. In contrast to most of the crown ether substituted phthalocyanines, no cofacial dimer formation is observed in the presence of alkali metal salts. In addition to the fluorescence at 710 nm from S1, a strong upper excited state (Soret 52) emission around 424 nm has been detected for the first time in the phthalocyanine series. Fluorescence decay of S1 and S2 emission can be analyzed by mono- and biexponential fits respectively. X-ray structure analysis showed that the crown ether unit is conformationally deformed and oblate that may account for the unusual spectroscopic properties.     

Solvent effects on the steady state photophysics of estrone and 17β-estradiol

Absorption and emission yields for estrone and 17β-estradiol were measured in a variety of room temperature solvents. Molar extinction coefficients were found to not vary as a function of solvent, while fluorescence yields were found to be significantly affected by the polarity and hydrogen-bond accepting ability of the solvent, with the yield for 17β-estradiol being highest in nonpolar, hydrogen-bond donating solvents, and lowest in the nonpolar, hydrogen-bond accepting solvent ethyl acetate. Estrone's emission yield was found to be a factor of ten smaller than 17β-estradiol's. Strong solvent and excitation wavelength dependences were found for the relative amounts of emission between estrone's two emission bands, with increased relative emission occurring in nonpolar aprotic solvents, and under higher excitation energies. These results are interpreted with the aid of vertical excitation energies from time-dependent density functional calculations using both explicit and implicit solvation models.     

Investigation on the inclusion behaviour of baicalein with β-cyclodextrin and derivatives and their antioxidant ability study

The formation of the complexes of baicalein (Ba) with β-cyclodextrin (β-CD) and β-CD derivatives (HP-β-CD and Me-β-CD) was studied by UV–vis absorption spectroscopy, fluorescence method, nuclear magnetic resonance spectroscopy and phase-solubility measurement. The solid–inclusion complexes of Ba with CDs were synthesised by the co-precipitation method. The characterisations of the solid–inclusion complexes have been proved by infrared spectra and differential scanning calorimetry. Experimental conditions including the concentration of various CDs and media acidity were investigated in detail. The results suggested that the inclusion ratio of HP-β-CD with Ba was the highest among the three kinds of CDs. The binding constants (Ks) of the inclusion complexes were determined by fluorescence method and phase-solubility measurement. Kinetic studies of DPPH√ with Ba and CDs complexes were also done. The results indicated that the Ba/HP-β-CD complex was the most reactive form.