Inclusion Complexation of Carbaryl and β-Cyclodextrin in Solution and in the Solid State

This study was carried out with the aim ofinvestigating the interactions between-cyclodextrin and carbaryl, a carbamatepesticide, and their effect on some physico-chemicalproperties of carbaryl, such as aqueous solubility andlipophilicity. The interactions between carbaryl and-cyclodextrin were thoroughly investigated bothin solution and in the solid state. The effect of-cyclodextrin on the aqueous solubility ofcarbaryl was evaluated by the phase solubility method.The amount of carbaryl dissolved increased linearlywith the addition of -cyclodextrin according toan A_L type plot and without precipitation of thecomplex. The apparent stability constant of thecomplex was 289 ± 21 M^-1, assuming a 1 : 1stoichiometry; this value was confirmed by a methodbased on circular dichroism measurements.Equimolar carbaryl/-cyclodextrin solid systemswere prepared by physical-mixing and freeze-drying,and fully characterised by Differential ScanningCalorimetry, X-ray powder diffractometry and FourierTransform Infra-Red analysis. The results of the solidstate study demonstrated that the freeze-drying methodyields a system with a high degree of amorphisationand yields an inclusion complex.The dissolution profile of the pesticide was affectedby the physico-chemical properties of each solidsystem, the freeze-dried form dissolving more rapidly. However, the physical association of-cyclodextrin and carbaryl enhanced the aqueoussolubility of the insecticide as well.     

Interaction of Naproxen with Crystalline and Amorphous Methylated β-Cyclodextrin in the Liquid and Solid State

Abstract

Interactions of naproxen (NAP) with amorphous, randomly methylated β-cyclodextrin at a degree of substitution per anhydroglucose unit of 1.8 (RAMEB) and with crystalline heptakis-(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) were studied in aqueous solution and in the solid state using, respectively, phase-solubility analysis (at 25 °C, 37 °C and 47 °C) and differential scanning calorimetry (DSC) supported by X-ray powder diffractometry. RAMEB and DIMEB displayed similar solubilizing and complexing abilities towards NAP, suggesting analogous inclusion modes of the drug in the host cavity in aqueous solution. Differences were instead observed in interactions in the solid state, where the amorphizing capacity of RAMEB toward NAP (evaluated by DSC) was about twice that of DIMEB at each drug-to-carrier ratio. Assuming that inclusion complexation is also involved in solid-state interactions, molecular modelling accounted for the experimental results in terms of structural features of DIMEB, i.e. the particular inwards orientation of O-6-C-8 groups of three alternate glucoses on the primary hydroxyl side which hampers a deep penetration of NAP in the DIMEB cavity in the solid state. On the contrary, no obstruction of the cavity apparently occurs with RAMEB due its noncrystalline state. The aqueous dissolution rate of NAP from NAP-RAMEB and NAP-DIMEB blends containing 0.59, 0.73, 0.85, and 0.92 mass fraction of carrier linearly increased at decreasing drug-to-carrier ratios. The improvement was 5 to 20 times (from powders) and 50 to 200 times (from discs) the dissolution rate of NAP alone for both carrier. Therefore the choice of the amorphous RAMEB in pharmaceutical formulations can be recommended mainly for economic reasons, though the anhydrous and non-hygroscopic nature of crystalline DIMEB might be of particular advantage in case of moisture sensitive formulations.     

Pseudorotaxanes of β-Cyclodextrin with Diamino End-functionalized Oligo-phenyl and -benzyl Compounds in Solution and in the Solid State

-Cyclodextrin forms a 1:1 host:guest inclusion complex ([2]pseudorotaxane) with 4-[2-(4-aminophenyl)ethyl]-benzenamine (1) in water as determined by 1D and 2D NMRexperiments. In the crystalline state, the structure of the complex has revealed a 2:2 stoichiometry, with two CD molecules forming head-to-head dimers byH-bonds between the secondary O3 hydroxyl groups and enclosing two molecules of the guest. The packing mode of the present complex is encountered for the first time, since it does not belong to any of the four known packing types of the dimeric CD inclusion complexes. On the other hand,N ¹,N ⁴-bis(4-aminophenyl)-1,4-benzenedimethanamine 2), which is longer than 1 by a phenylene diamine unit, has not afforded any crystals, at present, however it threads into CD in aqueous solution forming most probably [2]- and [3]pseudorotaxanes. The solution structures and the equilibria in this system are investigated.     

Solid State Photochemistry of Nitrobenzaldehydes

The photochemical reaction of nilrobenzaldehyde with indole and antipyrine was investigated in solid state.The structures of the new products were identified by means of IR,MS,'H NMR and elemental analysis,and the crystal structure of audition product 2c was determined by X-ray diffraction analysis.The mechanism of this reaction was also proposed.     

Conformational Stability of 2,2′-Dialkoxybenzpinacols in Solid State

Abstract

X-ray analyses of the 2,2′-dialkoxybenzpinacols have established that the previously tentative assignment of configuration is incorrect. For example, the dl-and meso-isomer of 2,2′-dimethoxy-, 2,2′-diethoxy-, and 2,2′-dibutoxybenzpinacols proved to have a rigid conformation (1aα, 1bα, 1eα) and (1aβ, 1bβ, 1cα) where hydroxy groups are always in an anti fashion, in the solid state, respectively. MM2 and semi-empirical molecular orbital calculations for possible conformations were performed, suggesting that the conformational stability of the present pinacols is controlled by repulsive gauche interactions between aryl groups associated with intramolecular hydrogen bondings.     

Stability of Mefenamic Acid in the Inclusion Complex with β-Cyclodextrin in the Solid Phase

The inclusion complex of mefenamic acid with -cyclodextrin was obtained by the method of coprecipitation from diethyl ether. The product was identified by the thermogravimetric and X-ray methods. The complex stability constants were determined by the potentiometric method. The effect of -CD on the solubility and stability of mefenamic acid was analysed.     

Stepwise Self-assembly of a Tripeptide from Molecular Dimers to Supramolecular β-sheets in Crystals and Amyloid-like Fibrils in the Solid State

The terminally protected tripeptide Boc–Ala(1)–Leu(2)–Ala(3)–OMe 1 forms antiparallel hydrogen-bonded dimers of two different conformers in the asymmetric unit and the individual dimers then self-associate to form supramolecular β-sheet structures in crystals and amyloid-like fibrils in the solid state.     

Study of the Solid—Liquid Equilibrium in Mixed Alkaline Earth Fluorohalides

We have studied the solid-liquid equilibrium of the system Sr_1–yBa_yFCl_1–xBr_x using DTA and X-ray diffraction techniques. The entire composition range in this system yields solid solutions which crystallize in the PbFCl (Matlockite) structure type. The melting points of the entire composition range have been parametrized (within 5°C rms error) using a biquadratic fit of the available data obtained by experiment and from the literature.This revised version was published online in November 2005 with corrections to the Cover Date.     

Free-Radical Reaction Routes in γ-Irradiated β-D-Fructose

-Irradiated -D-fructose was studied over a wide temperature range (77–380 K) using EPR spectroscopy. A plausible scheme of the radiation-induced degradation of -D-fructose is proposed.     

Study on the Supramolecular Interaction of β-Cyclodextrin with Gemfibrozil by Spectrofluorimetry and Its Analytical Application

The supramolecular interaction of gemfibrozil with β-cyclodextrin （β-CD） was studied by spectrofluorimetry. The mechanism of the inclusion was discussed by spectrofluoremetry, infrared spectrum and ^1H NMR spectrum. The results showed that a 1 ： 1 （β-CD ： gemfibrozil） complex was formed with an apparent association constant of 3.844 × 10^3 L·mol^-1. Based on the enhancement of the fluorescent intensity of gemfibrozil, a spectrofluorimetric method for the determination of gemfibrozil in bulk aqueous solution in the presence of β-CD was developed. The linear range was 3.30 ng·mL^- 1 -6.00 ug·mL^-1 with the detection limit of 0.980 ng·mL^-1. There was no interference from the excipients normally used in tablet composition and the serum main compositions. The proposed method was then successfully applied to the determination of gemfibrozil in capsules and serum.     

Structure of the β-Cyclodextrin·p-Hydroxybenzaldehyde Inclusion Complex in Aqueous Solution and in the Crystalline State

-Cyclodextrin (-CD) and p-hydroxybenzaldehyde (p-HB) were studied by ¹H-NMR in deuterated aqueous solution and the stoichiometry of the resulting complex (1:1) was determined by the continuous variation method. Inclusion of p-HB in -CD was confirmed by the observation of NMR shifts for the inside H5 protons of the -CD cavity. In the solid state X-ray analysis was carried out and revealed the detailed structure of the inclusion complex. Two -CDs cocrystallize with four p-HB and 9.45 water molecules[2(C₆H₁₀O₅)^7·4C₇H₆O_2·9.45H₂O] in the triclinic space group P1 with unit cell parameters: a = 15.262(2), b = 15.728(1), c = 16.350(1) Å, = 92.67(1)°, = 96.97(1)°, = 103.31(1)°. The anisotropic refinement of 1973 atomic parameters converged at an R-factor = 0.066 for 10157 data with F_o ² > 2 (F_o ²). The 2:4 stoichiometry for the -CD inclusion complex with p-HB in the crystalline state is different from that obtained in solution. -CD forms dimers stabilized by direct O2(m)₁O3(m)₁·O2(n)₂O3(n)₂ hydrogen bonds (intradimer) and by indirect O6(m)₁·O6(n)₂ hydrogen bonds with one or two bridging water molecules joined in between (interdimer). These dimers are stacked like coins in a roll constructing infinite channels where the p-HB molecules are included. The p-HB molecules direct their polar CHO and OH groups into the nonpolar -CD cavities and are hydrogen bonded to each other, yielding infinite, antiparallel chains. In addition, crystals of the complex were also investigated with thermogravimetry, vibrational spectroscopy (FTIR), and ¹³C CP-MAS NMR spectroscopy. The results obtained enabled us to structurally characterize the -CD inclusion complex with p-HB.     

Study of the Podophyllotoxin β-Cyclodextrin Inclusion Complex

The structure of the podophyllotoxin (P)/-cyclodextrin(-CD) inclusion complexhas been studied by infrared spectroscopy, UVspectroscopy, NMR spectroscopy and X-raydiffractometry. The association constant is 128 M^-1in water, calculated from thestraight portion of the phase-solubility diagram.     

An ESR and Optical Spectroscopic Study of the Mechanism of Photostimulated Reactions in Hydrogen Cyanide γ-Irradiated at 77 K

Changes in the electronic absorption spectra and ESR spectra in the course of photobleaching of radiolyzed solid HCN with light of different wavelengths (236–600 nm) were studied by ESR and optical spectroscopy. Two bands at 270 and 290 nm in the optical spectrum were attributed to the presence of H₂C=N and HC=NH radicals, respectively (the molar absorption coefficients are k ₂₇₀ 2.7 × 10²l mol^–1cm^–1and k ₂₉₀ 1.5 × 10²l mol^–1cm^–1, respectively). Structureless broad bands with maximums at 313 and 465 nm, which were detected after the exposure of a sample to light with 300 nm, can belong to the cyanide ions (CN^–) and H₂C=N⁺cations (the molar absorption coefficients of the ions are k _ion= (0.4–1.0) × 10²l mol^–1cm^–1). In the photobleaching of -irradiated HCN ( = 236–280 nm), H₂C=N⁺radicals were additionally formed by the photoinduced reaction of electron transfer from the CN^–anion to the H₂C=N⁺cation. The amount of these radicals generated in the course of photobleaching is several times greater than that of the same radicals formed in the radiolysis via hydrogen atom addition to the multiple bond of HCN molecules.     

Solid Phase Synthesis of β-Carbolines

Much attention has been paid to carbolines in recent years, owing to the wide range of their biological activity 1. Many papers have reported the synthesis and reactivity of carbolines2,3. Generally there are two ways to synthesize carbolines. One is through the Bischler-Napieralski reaction, and the other through Pictet-Spengler reaction. In the former method, the reaction of carboxylic acids with tryptophan using PPE or POCl3 as the condensing agent give dihydro-?-carbolines, which are c…     

A Facile Procedure for the oxidative Coupling of 2-Naphthol and 2-Naphthalenethiol in Solid State

l,lLBi-2-naPhtholshavebeenwidelyappliedasimportantchiralauxiliariesandligands..tinorganicchemistry'.TheconversionofthiolstothecorrespondingdisulphidesisofintCrestbothfromabiological'andpracticalpointofview.ForthesynthesisofbinaPhtholsanddisulphides,theoxidativecouplingofnaphtholsandthiolshaslongbeenarecognisedmethodofchoice.Variousoxidantscanbringaboutthecouplingofnaphthols'andthiols4insolution,buttheyoftenleadtolowyieldsorsufferfromdisadvantagesduetotheinsolubilityofoxidant,naPhthoIandthiol…     

Study of the Supramolecular Inclusion of β-Cyclodextrin with Andrographolide

An inclusion complex of -cyclodextrin with andrographolide (Andro) was prepared by using a convenient new method of microwave irradiation. The structure of the inclusion complex was determined by UV and IR analyses as well as ¹H NMR, ¹³C NMR and two dimensional NOE spectroscopic measurements. The results indicated that the possible stoichiometry of complex formation is 1:1 (guest:host ratio) and the two isomeric 1:1 inclusion complexes are present simultaneously in solution. Thermal studies proved the thermal stability of the inclusion complex.     

Catalyst Kinetics Analytical Method Study of Ruthenium

Color reactions are used to determine ruthenium utilizing spectrophotometer, but the process need high temperature, long time pyrogenation and miscellaneous extraction and it contaminates the enviroment. As the sensitive degree and simple apparatus of catalyst kinetics analytical method, it was extensively attented. The fundmental principle means to determinn a certain chemistry reaction rate accelerated by homogeneous catalyst and determine substantial content using the function of the numeri…     

Ab Initio Study of the Excited State Decomposition Reactions of Monothioformic Acid

IntroductionTherehasbeenconsiderableinterestinrecentyearsinthetheoreticalstudyofthemonothioformicacid1ed.However,mostofthemhaveconcentIatedontheelectronicproperties,isomerizationandintramolecularhydrogenshiftreactionsoftheacid,andstudiesonitschemicalreactionshaverarelybeenrepofted.Recently,wereportedonthetheoreticalstudyofthegroundstateunimolecularpyrolysisofmonothioforndcacid,andtheresultsshowedthathightemperatureisneededforitsgroundstatedecompositionreactions.Asapotentialinterstellarcompoun…     

Conformational Heterogeneity of a Tripeptide in the Solid State and in Solution: Characterization of a γ-Turn Containing Incipient Hairpin in Solution

A terminally blocked tripeptide Boc--Ala-Aib--Ala-OMe 1 with noncoded amino acids forms a novel type of hairpin structure containing a -turn instead of a conventional -turn in the central loop region in solution. This new type structural motif was characterized by NMR and restraint molecular dynamics simulation study. In the solid state peptide 1 adopts an extended backbone conformation and self-assembles to form supramolecular -sheet.