Determination of low concentrations of the flotation reagent ethyl xanthate by sampled DC polarography and flow injection with amperometric detection

A polarographic DC(tast) method with the static mercury drop electrode, SMDE, was developed for determination of the flotation collector ethyl xanthate (EtX) in the concentration range from 1x10(-5) to 8x10(-5) M. The potentiality of the method was demonstrated by evaluating the capacity of powdered galena ore (PbS) to adsorb EtX in a titration-like procedure. Sulfide could be determined simultaneously with EtX because in NaOH electrolyte their anodic waves are well separated (E(1/2) congruent with-0.72 and -0.42 V versus Ag/AgCl, respectively). In addition, a new FIA method was developed by adapting a simple device to the tip of the glass capillary of a mercury electrode and doing amperometric detection at a fixed potential of -0.1 V, always in the DC(tast) mode. No oxygen removal was required. Reproducible results were obtained at a frequency of 72 injections per h, with automatic renewal of the SMDE every second. The calibration curve for freshly prepared EtX standards rendered a straight line from 5x10(-6) to 8x10(-5) M with correlation coefficient of 0.997, suitable for real applications in flotation processes and its effluents.     

Reaction of ethyl 3-ethoxymethylene-2,4-dioxovalerate and ethyl ethoxymethyleneoxaloacetate with 3-aminopyrazole analogs. Synthesis and chemistry of 3,6,7-trisubstituted pyrazolo[1,5-a]pyrimidine derivatives

The chemical reactivity of a series of 3-substituted-6-acetyl-7-carbethoxypyrazolo[l,5-a]pyrimidines ( 6a,b,c ) and 3-substituted-6,7-dicarbethoxypyrazolo[1,5-a]pyrimidines ( 7a,b,c ), prepared by the condensations of the 3-aminopyrazole analogs ( 3a,b,c ) with ethyl 3-ethoxymethylene-2,4-dioxovalerate ( 1 ) or ethyl 3-ethoxymethyleneoxaloacetate ( 2 ), was investigated. Catalytic hydrogenation of 6 or 7 afforded 4,7-dihydro derivatives ( 8 or 9 ). Treatment of 6a,b with acetic acid and water underwent ring transformation into 6H-pyrazolo[1,5-a][1,3]diazepin-6-ones ( 17a,b ). By treatment with phenylhydrazine compounds of type 6 underwent cyclization to yield 2H-dipyrazolo[1,5-a:4′,3′-e]pyrimidines ( 18a,b,c ). Compounds 6 or 7 were treated with an excess of diazomethane at room temperature to give 5-methyl-6H-cyclopropa[5a,6a]pyrazolo-[1,5-a]pyrimidines ( 24 and 25 ) in excellent yields. However, when this reaction was carried out under ice cooling, only compounds of type 23 were isolated. Reaction of 6a with ethyl diazoacetate is also described.     

Short chain acyclic crown ethers

A series of short chain acyclic crown ethers such as (1,2), (1,3), (1,4)-phenylenediethers and some symmetric or assymmetrico-substituted phenyl ethers were prepared. The complexation studies of these compounds were carried out by a) direct UV titration method, b) picrate extraction method and c) isolation of crystalline complex.Taken in part from the master's thesis ofMaria Cecilia Bastos Vieira de Souza, Instituto Militar de Engenharia, 1978.     

Synthetic modifications in ethyl 2-amino-4-methylthiazole-5-carboxylate: 3D QSAR analysis and antimicrobial study

Ethyl 2-amino-4-methylthiazole-5-carboxylate (1) is a very substantial derivative of the thiazole group. This derivative has been modified and has been synthesized using readily available materials. The structures of synthesized derivatives were confirmed by IR, ¹H NMR, ¹³C NMR, and mass spectral techniques. The newly prepared compounds (5a–k) were studied for their antimicrobial activities against strains of bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pyogenes) and fungi (Candida albicans, Aspergillus niger, and Aspergillus clavatus) using serial dilution method. Structure-activity relationship was carried out by CoMFA and CoMSIA with the help of 3D-QSAR analysis. As per the database alignment, the CoMFA and CoMSIA models were developed. Information based on these models is useful for structure-activity relationships of the reported molecules.     

Comparative study of amidase production by free and immobilized Escherichia coli cells

Escherichia coli NCIM 2569 was evaluated for its potential for amidase production under submerged fermentation. Among the various amide compounds screened, maximum substrate specificity and enzyme yield (8.1 U/mL) were obtained by using 1% acetamide. Fermentation was carried out at 30°C in shake-flask culture under optimized process conditions. A maximum of 0.52 U/mL of intracellular amidase activity was also obtained from cells incubated for 24 h. Studies were also performed to elucidate the optimal conditions (gel concentration, initial biomass, curing period of beads, and calcium ion concentration in the production medium) for immobilization of whole cells. By using E. coli cells entrapped in alginate, a maximum of 6.2 U/mL of enzyme activity was obtained after 12 h of incubation under optimized conditions. Using the immobilized cells, three repeated batches were carried out successfully, and 85% of the initial enzyme activity was retained in the second and third batches. The study indicated that the immobilized E. coli cells offered certain advantages such as less time for maximum enzyme production, more stability in the enzyme production rate, and repeated use of the biocatalyst.     

Effect of lignocellulosic degradation compounds from steam explosion pretreatment on ethanol fermentation by thermotolerant yeast Kluyveromyces marxianus

The filtrate from steam-pretreated poplar was analyzed to identify degradation compounds. The effect of selected compounds on growth and ethanolic fermentation of the thermotolerant yeast strain Kluyveromyces marxianus CECT 10875 was tested. Several fermentations on glucose medium, containing individual inhibitory compounds found in the hydrolysate, were carried out. The degree of inhibition on yeast strain growth and ethanolic fermentation was determined. At concentrations found in the prehy-drolysate, none of the individual compounds significantly affected the fermentation. For all tested compounds, growth was inhibited to a lesser extent than ethanol production. Lower concentrations of catechol (0.96 g/L) and 4-hydroxybenzaldehyde (1.02 g/L) were required to produce the 50% reduction in cell mass in comparison to other tested compounds.     

Molecular structure and Bader's theory

 It is shown that a supposed catastrophe of Bader's theory of atoms in molecules, suggested by Cassam-chena? and Jayatilaka [Theor Chem Acc (2001) 105: 213] is merely a consequence of the approximate character of the adiabatic Born–Oppenheimer theory of molecular structure, and that nonadiabatic approaches could be in accordance with Bader's ideas. Received: 4 April 2001 / Accepted: 5 September 2001 / Published online: 3 June 2002     

N- and O-Alkylation of 3-indolylcyclopropylacetic acid derivatives

2,2-Dimethyl-3-(2-methyl-3-indolyl)cyclopropylacetic acid, its amide and esters, and the corresponding alcohol, viz., the product of ester reduction by LiAlH₄, were synthesized. The chemoselectivity of N- and O-alkylation of these compounds was studied. Selective monoalkylation at the nitrogen atom of the heterocycle, O-alkylation to the side chain, or dialkylation at both nucleophilic sites can be carried out under conditions of phase-transfer catalysis. The N-acylation at the indole fragment of nitrile of this acid occurs only under the Vilsmeier—Haak formylation conditions.     

Radical polymerization of muconic acid and ethyl muconate

Muconic acid (Mu-acid) was found to polymerize to trans-1,4-poly(Mu-acid) with the use of azobisisobutyronitrile (AIBN) as an initiator. Similarly, a muconic acid derivative, ethyl muconate (EMu), was readily polymerized through a trans-1,4 addition mechanism by the use of a radical or anionic catalyst, but did not polymerize when a cationic catalyst such as boron trifluoride etherate was used. Moreover, the copolymerization of Mu-acid and EMu with various comonomers such as styrene, acryronitrile, and 2-vinylpyridine was carried out and Q–e values of Mu-acid and EMu are discussed. These substituted diene monomers always polymerized through trans-1,4 addition with all catalysts and any comonomers.     

Inelastic neutron scattering and vibrational spectra of 2-(N-methyl-α-iminoethyl)-phenol and 2-(N-methyliminoethyl)-phenol: Experimental and theoretical approach

The infrared, Raman, and inelastic neutron scattering (INS) spectra of two ortho-hydroxy aryl Schiff’s bases, 2-(N-methyliminoethyl)-phenol and 2-(N-methyl-α-iminoethyl)-phenol, were recorded. Ab initio molecular orbital calculations employing the DFT (B3LYP) method with the 6-31G** basis set for both compounds were done. Assignments of vibrational modes within the 3500–50 cm⁻¹ spectral region were carried out. On the basis of the DFT calculations, four rotomers of 2-(N-methyl-α-iminoethyl)-phenol were analysed.     

Spontaneous alternating copolymerization of N-phenylmaleimide with ethyl α-phenylacrylate

The spontaneous copolymerization of N-phenylmaleimide (NPMI) (M₁) with ethyl α-phenylacrylate (EPA)(M₂) were carried out in dioxane at 85°C. A high alternating tendency was observed. The monomer reactivity ratios were r₁ = 0.07 ±0.01 and r₂ = 0.09 ± 0.02. The maximum copolymerization rate and molecular weight occurs at 70–80 mol% (M₁) in feed ratio. The spontaneous alternating copolymerization is considered to be carried out via a contact-type charge transfer complex (CTC) formed between the monomers. Thermogravimetric analyses (TGA) indicate the resulting copolymers have high thermal stability. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2927–2931, 1998     

Biotransformation of Valdecoxib by Plant Cell Cultures

Valdecoxib is a new anti-inflammatory drug that is highly selective for inhibition of the inducible form of cyclooxygenase (COX-2). In the present study, biotransformation of valdecoxib was investigated in cell cultures of five medicinal plants, viz., Catharanthus roseus, Azadirachta indica, Capsicum annuum, Ervatamia heyneana, and Nicotiana tabacum. Identification of the biotransformed products was carried out by using high-performance liquid chromatography coupled with diode array detection and liquid chromatography–tandem mass spectrometry analysis. All the cultures transformed valdecoxib into more polar compounds, and C. roseus also produced one unknown compound that is less polar than the substrate. The reactions performed by these plant cell cultures include hydroxylation, methylation, and demethylation. Optimization studies were performed to investigate the effect of the day of extraction and substrate concentration on biotransformation.     

Thermal Study of [Pd(2-Phpy)Cl(L)] Complexes (L=pyridines and amines)

The complex [Pd(2-Phpy)(μ-Cl)]₂ reacts with pyridines (L=pyridine, α-picoline and γ-picoline), amines (L=isopropylamine, tert-butylamine) and ammonia to form the corresponding ortho-palladatedderivatives [Pd(2-Phpy)ClL]. The compounds have been characterized by C, H and Nanalyses and spectroscopic methods (IR and ¹H and ¹³C NMR).TG, DTG and DSC studies of the complexes were carried out in dynamic nitrogen atmosphere. From DSC analyses the heats of decomposition were calculated. The kinetics ofthe first step of thermal decomposition were evaluated from TG data by isothermal methods for L=pyridine and isopropylamine. The activation energies obtained are in the range 90–100 kJ mol^-1. The best fitting for data was observed for R2 and A1.5 kinetic models. This revised version was published online in August 2006 with corrections to the Cover Date.     

Two new lanostane triterpenoids from Abies sachalinensis

The continuous chemical investigation on the ethyl acetate （EtOAc） soluble fraction of the MeOH extract afforded two new lanostane triterpenoid derivatives including one with a rearranged lanostane skeleton. They were identified as 3,4-seco-8-（14→13R）abeo-17,13-friedo-9β-lanosta-4（28）, 7,14（30）,24-tetraen-26,23-olide-23-hydroxy-3-oic acid （1） and 7,14-mariesa- dien-3oL-hydroxy-25-methoxy-26-oic acid （2）. Structural determination of these compounds were carried out by the spectral studies especially by the two digital （2D）-NMR and high-resolution MS experiences.     

Amino Acid Derivatives,IV [1]: Synthesis and Antiviral Evaluation of New α-Amino Acid Esters Bearing Methyl β-<Emphasis Type="SmallCaps">d</Emphasis>-Ribofuranoside Side Chain

Summary. Methyl 2,3-O-isopropylidene-β-d-ribofuranoside was synthesized and oxidized with HIO₄ to afford the corresponding carboxylic acid. The latter was coupled with the appropriate acylated amino acids in the presence of HOBt and DDC as coupling reagents to give the corresponding amides. The methyl acetate derivative was hydrolyzed with 2 N KOH/MeOH to the corresponding carboxylic acid, which was coupled with l-glycine methyl ester to furnish the amide. Deprotection was carried out with 70% AcOH at reflux temperature. The prepared glycopeptides were tested for antiviral activity against Herpes Simplex virus type-1 (HSV-1) and hepatitis-A virus (HAV). The plaque reduction infectivity assay was used to determine virus count reduction as a result of treatment with tested compounds.     

Preparation ofN-chloroacetyl-N′-arylsulfonylureas and the crystal structure ofN-chloroacetyl-N′-(4-methylphenylsulfonyl)urea

Novel arylsulfonylureas were prepared by the reaction of chloroacetyl isocyanate with arylsulfamides. The structures of the compounds synthesized were determined by IR and¹H NMR spectra. An X-ray structural analysis ofN-chloroacetyl-N-(4-methylphenylsulfonyl)urea was carried out. It was found that the molecule has theanti-syn conformation stabilized by an intramolecular H-bond. In the crystal, the molecules are combined into centrosymmetrical dimers by intermolecular hydrogen bonds. The compounds considered exhibit moderate fungicide activity.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1786–1788, October, 1994.     

Antifungal evaluation of cholic acid and its derivatives on Candida albicans by microcalorimetry and chemometrics

In the last few years, several fungus infections caused by multidrug-resistant pathogenic agents have got tremendous emergence and prevalence. Screening for novel antifungal agents is in great demand, but traditional microbiological techniques are far from sufficient to meet that requirement. In this study, a non-invasive and non-destructive microcalorimetric method was performed to investigate the antifungal activities of cholic acid (CA) and its derivatives, glycocholic acid (GCA) and taurocholic acid (TCA) on the multiplying and non-multiplying metabolism of Candida albicans. Then, the heat-flow power-time curves of C. albicans growth affected by different concentrations of CA, GCA and TCA were studied by similarity analysis (SA), the quantitative thermokinetic parameters from these curves were analyzed by multivariate analysis of variance (MANOVA) and principal component analysis (PCA). By comparing the values of two main parameters, P₂ (the heat-flow output power of the highest peak) and Q₂ (the heat output of the second exponential growth phase) of C. albicans, it could be found that CA had the strongest antifungal activity among the three steroid compounds, which might be used as a potential antifungal agent in the future. This study provided a useful method and idea of microcalorimetry with chemometrics to efficiently evaluate the antifungal activities of bile acid derivatives, giving some references for screening out new antifungal agents.However, it has to be stressed that all these experiments are carried out in vitro and they still require clinical validation.     

Theoretical study of the gas-phase thermolysis reaction of alkyl (ethyl,isopropyl, and tert-butyl) N,N-dimethylcarbamates and N,N-diethylcarbamates

Theoretical studies on the thermolysis in the gas phase of alkyl N,N-dialkylcarbamates were carried out using ab initio theoretical methods, at the MP2/6-31G(d), MP2/6-31++G(d,p) and MP2/6-311++G(2d,p)//MP2/6-31G(d) levels. The reactions have two steps: the first one corresponds to the formation of an alkene and a neutral dialkylcarbamic acid intermediate via a six-membered cyclic transition state; the second one is the decarboxylation of this intermediate via a four-membered cyclic transition state, leading to carbon dioxide and the corresponding dialkylamine. The progress of the reactions was followed by means of the Wiberg bond indices. The results indicate that the transition states have character intermediate between reactants and products, and the calculated synchronicities show that the reactions are slightly asynchronous. The bond-breaking processes are more advanced than the bond-forming ones, indicating a bond deficiency in the transition states. The rate constants calculated for all the reactions agree very well with the available experimental data.From the Proceedings of the 28th Congreso de Químicos Teóricos de Expresión Latina (QUITEL 2002)     

Tomocomd-Cardd, a novel approach for computer-aided ‘ rational’ drug design: I. Theoretical and experimental assessment of a promising method for computational screening and in silico design of new anthelmintic compounds

Summary In this work, the TOMOCOMD-CARDD approach has been applied to estimate the anthelmintic activity. Total and local (both atom and atom-type) quadratic indices and linear discriminant analysis were used to obtain a quantitative model that discriminates between anthelmintic and non-anthelmintic drug-like compounds. The obtained model correctly classified 90.37% of compounds in the training set. External validation processes to assess the robustness and predictive power of the obtained model were carried out. The QSAR model correctly classified 88.18% of compounds in this external prediction set. A second model was performed to outline some conclusions about the possible modes of action of anthelmintic drugs. This model permits the correct classification of 94.52% of compounds in the training set, and 80.00% of good global classification in the external prediction set. After that, the developed model was used in virtual in silicoscreening and several compounds from the Merck Index, Negwers handbook and Goodman and Gilman were identified by models as anthelmintic. Finally, the experimental assay of one organic chemical (G-1) by an in vivo test coincides fairly well (100) with model predictions. These results suggest that the proposed method will be a good tool for studying the biological properties of drug candidates during the early state of the drug-development process.     

Kinetics of the gas-phase thermal elimination of (β-bromo ethyl)-pyrazole

Pyrazole elimination and vinyl bromide were found as products in the Flash Vacuum Pyrolysis of (β-Bromo ethyl)-pyrazole. To obtain kinetic parameters (E_a) we carried out competitive reactions using (β-chloro ethyl)-pyrazole as an internal standard. A thermochemical study to calculate Δ(ΔH${}_{\text{?}}^{\text{°}}$ ) for this reaction was carried out.