Finite size effects in the presence of a chemical potential: A study in the classical nonlinear O(2) sigma model

In the presence of a chemical potential, the physics of level crossings leads to singularities at zero temperature, even when the spatial volume is finite. These singularities are smoothed out at a finite temperature but leave behind nontrivial finite size effects which must be understood in order to extract thermodynamic quantities using Monte Carlo methods, particularly close to critical points. We illustrate some of these issues using the classical nonlinear O(2) sigma model with a coupling β and chemical potential μ on a 2+1-dimensional Euclidean lattice. In the conventional formulation this model suffers from a sign problem at nonzero chemical potential and hence cannot be studied with the Wolff cluster algorithm. However, when formulated in terms of the worldline of particles, the sign problem is absent, and the model can be studied efficiently with the "worm algorithm." Using this method we study the finite size effects that arise due to the chemical potential and develop an effective quantum mechanical approach to capture the effects. As a side result we obtain energy levels of up to four particles as a function of the box size and uncover a part of the phase diagram in the (β,μ) plane. © 2010 The American Physical Society.

15N NMR relaxation data reveal significant chemical exchange broadening in the alpha-domain of human α-lactalbumin

Human alpha-lactalbumin (alpha-LA), a 123-residue calcium-binding protein, has been studied using (15)N NMR relaxation methods in order to characterize backbone dynamics of the native state at the level of individual residues. Relaxation data were collected at three magnetic field strengths and analyzed using the model-free formalism of Lipari and Szabo. The order parameters derived from this analysis are generally high, indicating a rigid backbone. A total of 46 residues required an exchange contribution to T(2); 43 of these residues are located in the alpha-domain of the protein. The largest exchange contributions are observed in the A-, B-, D-, and C-terminal 3(10)-helices of the alpha-domain; these residues have been shown previously to form a highly stable core in the alpha-LA molten globule. The observed exchange broadening, along with previous hydrogen/deuterium amide exchange data, suggests that this part of the alpha-domain may undergo a local structural transition between the well-ordered native structure and a less-ordered molten-globule-like structure.

In situ chemical modification of peptide microarrays: application to the study of the antibody responses to methylated antigens.

Peptide microarrays are useful tools for characterizing the humoral response against methylated antigens. They are usually prepared by printing unmodified and methylated peptides on substrates such as functionalized microscope glass slides. The preferential capture of antibodies by methylated peptides suggests the specific recognition of methylated epitopes. However, unmodified peptide epitopes can be masked due to their interaction with the substrate. The accessibility of unmodified peptides and thus the specificity of the recognition of methylated peptide epitopes can be probed using the in situ methylation procedure described here. Alternately, the in situ methylation of peptide microarrays allows probing the presence of antibodies directed toward methylated epitopes starting from easy-to-make and cost-effective unmodified peptide libraries. In situ methylation was performed using formaldehyde in the presence of sodium cyanoborohydride and nickel chloride. This chemical procedure converts lysine residues into mono- or dimethyl lysines.

Treatment of effluents contaminated with prions. Chemical reactor design

The control and elimination of prionic infective agents that may be present in the effluents, turns out to be a complicated mechanism inside a High Containment bological Facility. There are two ways to carry out this neutralization: Installation of thermal systems to ensure achieve a minimum temperature of 134 ° C sterilization plateau for a residence time of 18 minutes, and the use of chemical reactors based on the addition of sodium hypochlorite so the mixture maintained 2% of free chlorine during the reaction period. This study presents the design phases, elements and benefits, of a chemical reactor that allows the treatment of prion effluents in order to serve as a model to biocontainment facilities with areas of animal experimentation, who want to develop their work with prions.

Rational design of a dual-mode optical and chemical prodrug

Purpose. The purpose of this study is to demonstrate the rational design and behaviour of the first dual mode optical and chemical prodrug, exemplified by an acetyl salicylic acid-based system. Methods. A cyclic 1,4-benzodioxinone prodrug was synthesised by reaction of 3,5-dimethoxybenzoin and acetyl salicoyl chloride with pyridine. After purification by column chromatography and recrystallization, characterization was achieved using infrared and NMR spectroscopies, mass spectrometry, elemental analysis and single crystal X-ray diffraction. Light-triggered drug liberation was characterised via UV-visible spectroscopy following low-power 365 nm irradiation for controlled times. Chemical drug liberation was characterised via UV-visible spectroscopy in pH 5.5 solution. Results. The synthetic method yielded pure prodrug, with full supporting characterisation. Light-triggered drug liberation proceeded at a rate of 8.30 10j2 sj1, while chemical, hydrolytic liberation proceeded independently at 1.89 10j3 sj1. The photochemical and hydrolytic reactions were both quantitative. Conclusions. This study demonstrates the first rational dual-mode optical and chemical prodrug, using acetyl salicylic acid as a model, acting as a paradigm for future dual-mode systems. Photochemical drug liberation proceeds 44 times faster than chemical liberation, suggesting potential use in drug-eluting medical devices where an additional burst of drug is required at the onset of infection.

Chemical composition of B-type supergiants in the OB 8, OB 10, OB 48, OB 78 associations of M 31

Absolute and differential chemical abundances are presented for the largest group of massive stars in M31 studied to date. These results were derived from intermediate resolution spectra of seven B-type supergiants, lying within four OB associations covering a galactocentric distance of 5-12 kpc. The results are mainly based on an LTE analysis, and we additionally present a full non-LTE, unified model atmosphere analysis of one star (OB 78-277) to demonstrate the reliability of the differential LTE technique. A comparison of the stellar oxygen abundance with that of previous nebular results shows that there is an off set of between similar to0.15-0.4 dex between the two methods which is critically dependent on the empirical calibration adopted for the R 23 parameter with [O/H]. However within the typical errors of the stellar and nebular analyses (and given the strength of dependence of the nebular results on the calibration used) the oxygen abundances determined in each method are fairly consistent. We determine the radial oxygen abundance gradient from these stars, and do not detect any systematic gradient across this galactocentric range. We find that the inner regions of M31 are not, as previously thought, very "metal rich". Our abundances of C, N, O, Mg, Si, Al, S and Fe in the M31 supergiants are very similar to those of massive stars in the solar neighbourhood.

Recent applications of Chemical Imaging to pharmaceutical process monitoring and quality control

Chemical Imaging (CI) is an emerging platform technology that integrates conventional imaging and spectroscopy to attain both spatial and spectral information from an object. Vibrational spectroscopic methods, such as Near Infrared (NIR) and Raman spectroscopy, combined with imaging are particularly useful for analysis of biological/pharmaceutical forms. The rapid, non-destructive and non-invasive features of CI mark its potential suitability as a process analytical tool for the pharmaceutical industry, for both process monitoring and quality control in the many stages of drug production. This paper provides an overview of CI principles, instrumentation and analysis. Recent applications of Raman and NIR-CI to pharmaceutical quality and process control are presented; challenges facing Cl implementation and likely future developments in the technology are also discussed. (C) 2007 Elsevier B.V. All rights reserved.

Effects of Accretion Flow on the Chemical Structure in the Inner Regions of Protoplanetary Disks

Aims. We study the dependence of the profiles of molecular abundances and line emission on the accretion flow in the hot (100 K) inner region of protoplanetary disks.
Methods. The gas-phase reactions initiated by evaporation of the ice mantle on dust grains are calculated along the accretion flow. We focus on methanol, a molecule that is formed predominantly by the evaporation of warm ice mantles, to demonstrate how its abundance profile and line emission depend on the accretion flow.
Results. Our results indicate that some evaporated molecules retain high abundances only when the accretion velocity is sufficiently high, and that methanol could be useful as a diagnostic of the accretion flow by means of ALMA observations at the disk radius of 10 AU.

Thermochemistry of Ionic Liquid-Catalyzed Reactions. Experimental and Theoretical Study of Chemical Equilibria of Isomerization and Transalkylation of tert-Butylbenzenes

The chemical equilibrium of mutual interconversions of tert-butylbenzenes was studied in the temperature range 286 to 423 K using chloroaluminate ionic liquids as a catalyst. Enthalpies of five reactions of isomerization and transalkylation of tert-butylbenzenes were obtained from temperature dependences of the corresponding equilibrium constants in the liquid phase. Molar enthalpies of vaporization of methyl-tert-butylbenzenes and 1,4-ditert-butylbenzene were obtained by the transpiration method and were used for a recalculation of enthalpies of reactions and equilibrium constants into the gaseous phase. Using these experimental results, ab initio methods (B3LYP and G3MP2) have been tested for prediction thermodynamic functions of the five reactions under study successfully. Thermochemical investigations of tert-butyl benzenes available in the literature combined with experimental results have helped to resolve contradictions in the available thermochemical data for tert-butylbenzene and to recommend consistent and reliable enthalpies of formation for this compound in the liquid and the gaseous state.

Comparison of a novel spray congealing procedure with emulsion-based methods for the micro-encapsulation of water-soluble drugs in low melting point triglycerides

The particle size characteristics and encapsulation efficiency of microparticles prepared using triglyceride materials and loaded with two model water-soluble drugs were evaluated. Two emulsification procedures based on o/w and w/o/w methodologies were compared to a novel spray congealing procedure. After extensive modification of both emulsification methods, encapsulation efficiencies of 13.04% tetracycline HCl and 11.27% lidocaine HCl were achievable in a Witepsol (R)-based microparticle. This compares to much improved encapsulation efficiencies close to 100% for the spray congealing method, which was shown to produce spherical particles of similar to 58 mu m. Drug release studies from a Witepsol (R) formulation loaded with lidocaine HCl showed a temperature-dependent release mechanism, which displayed diffusion-controlled kinetics at temperatures similar to 25 degrees C, but exhibited almost immediate release when triggered using temperatures close to that of skin. Therefore, such a system may find application in topical semi-solid formulations, where a temperature-induced burst release is preferred.

Synthesis of the alkaloids hopromine, hoprominol and hopromalinol, using transamidation methods.

Synthesis of the unsym. Homalium alkaloids hopromine (I, R = H, R1 = pentyl), hoprominol (I, R = OH, R1 = pentyl) and hopramalinol (I, R = OH, R1 = Ph), in diastereoisomeric mixt. form, is reported. The component eight-membered azalactams are first prepd. N-(3-halogenopropyl)-4-pentyl- and 4-heptylazetidin-2-ones are aminated and ring expanded in liq. ammonia to give, after reductive methylation, the corresponding 4-alkyl-5-methyl-1,5-diazacyclooctan-2-ones. Synthesis of the 4-(2-hydroxyheptyl)-5-methyl-1,5-diazacyclooctan-2-one required for hoprominol and hopromalinol is carried out via 4-allyl ?-lactam ring expansion to the eight-membered 4-allylazalactam, followed by methylation, epoxidn. and epoxide opening with lithium dibutylcuprate. A similar epoxidn.-cuprate sequence was carried out on the epoxypropyl ?-lactam, as its N-tert-butyldimethylsilyl deriv., and led to a convenient copper-catalyzed N- to O-migration of the protection; this migration is examd. Alkylation gave O-tert-butyldimethylsilyl-protected N-(3-chloropropyl)-4-(2-hydroxyheptyl)azetidin-2-one which could be aminated and transamidated in excellent yield, to give, after methylation, a superior sequence to the required eight-membered hydroxy azalactam. Although satisfactory for attachment of the first azalactam unit, a dibromobutane coupling system proved unreactive for the second. Couplings with unmethylated, methylated, and benzyloxycabronyl-protected azalactams were examd. using (E)-1,4-dibromobutene and (Z)-1,4-dichlorobutene as the bridging unit. Employing the latter, coupling the first N-methylated azalactam with potassium bis(trimethylsilyl)amide as the base, and then the second with bis(trimethylsilyl)amide-sodium hydride as the base system, provided a satisfactory synthetic outcome. Hydrogenation under acidic conditions gave the unsym. structures hopromine, hoprominol and hopromalinol, as well as the more simple and sym. alkaloid, homaline.

Chemical processes in protoplanetary disks. II. On the importance of photochemistry and X-ray ionization

We investigate the impact of photochemistry and X-ray ionization on the molecular composition of, and ionization fraction in, a protoplanetary disk surrounding a typical T Tauri star. We use a sophisticated physical model, which includes a robust treatment of the radiative transfer of UV and X-ray radiation, and calculate the time-dependent chemical structure using a comprehensive chemical network. In previous work, we approximated the photochemistry and X-ray ionization; here, we recalculate the photoreaction rates using the explicit UV wavelength spectrum and wavelength-dependent reaction cross sections. We recalculate the X-ray ionization rate using our explicit elemental composition and X-ray energy spectrum. We find that photochemistry has a larger influence on the molecular composition than X-ray ionization. Observable molecules sensitive to the photorates include OH, HCO+, N2H+, H2O, CO2, and CH3OH. The only molecule significantly affected by the X-ray ionization is N2H+, indicating that it is safe to adopt existing approximations of the X-ray ionization rate in typical T Tauri star-disk systems. The recalculation of the photorates increases the abundances of neutral molecules in the outer disk, highlighting the importance of taking into account the shape of the UV spectrum in protoplanetary disks. A recalculation of the photoreaction rates also affects the gas-phase chemistry due to the adjustment of the H/H2 and C+/C ratios. The disk ionization fraction is not significantly affected by the methods adopted to calculate the photochemistry and X-ray ionization. We determine that there is a probable "dead zone" where accretion is suppressed, present in a layer, Z/R lsim 0.1-0.2, in the disk midplane, within R ˜ 200 AU.

Current and possible future methods of assessing the activities of photocatalyst films

The continuing interest in semiconductor photochemistry, SPC, and the emergence of commercial products that utilise films of photocatalyst materials, has created an urgent need to agree a set of methods for assessing photocatalytic activity and international committees are now meeting to address this issue. This article provides a brief overview of two of the most popular current methods employed by researchers for assessing SPC activity. and one which has been published just recently and might gain popularity in the future, given its ease of use. These tests are: the stearic acid (SA) test, the methylene blue (MB) test and the resazurin (Rz) ink test, respectively. The basic photochemical and chemical processes that underpin each of these tests are described, along with typical results for laboratory made sol-gel titania films and a commercial form of self-cleaning glass, Activ (TM). The pros and cons of their future use as possible standard assessment techniques are considered. (C) 2007 Elsevier B.V. All rights reserved.

Comparison of the efficiences of enzymatic and chemical hydrolysis of (nortestosterone and diethylstilboestrol) glucuronides in bovine urine

Residues of 19-nortestosterone (19-NT) and diethylstilboestrol (DES) are excreted in bovine urine, mainly conjugated to glucuronic acid. Prior to quantification, urine must be deconjugated, which is commonly performed by enzymatic or chemical hydrolysis. The efficiencies of two enzymatic and two chemical deconjugation methods were studied. The range of efficiencies obtained for DES were 51.8% (beta -glucuronidase, incubation at 37 degreesC overnight) and 2.7% (methanolic HCl), respectively. Similarly, efficiencies for NT ranged from 43.1% (beta -glucuronidase, incubation at 55 degreesC for 2 h) to 12.7% (methanolic HCl). The results highlight that within control laboratories significant underestimation of drug residue content in samples may occur, due to poor deconjugation. (C) 2001 Elsevier Science B.V. All rights reserved.