A Simple Design for Production of a Chopped Laser Output with a Reference Wave for a Lock-In Amplifier

Abstract

A chopper was constructed to modulate the output of an infrared Helium-Neon laser at 3.39 microns. The chopper was constructed to fit onto a previously constructed optical bench which houses the laser. The chopper also encompasses a number of inexpensive electrical components including an LED (the source) and a phototransistor (the detector) and the accompanying electronics to power the components and provides a reference wave of the characteristics required for the reference input of the PAR model 5101 Lock-In Amplifier.     

Development of a biosensor for caffeine

We have utilized a microbe, which can degrade caffeine to develop an Amperometric biosensor for determination of caffeine in solutions. Whole cells of Pseudomonas alcaligenes MTCC 5264 having the capability to degrade caffeine were immobilized on a cellophane membrane with a molecular weight cut off (MWCO) of 3000-6000 by covalent crosslinking method using glutaraledhyde as the bifunctional crosslinking agent and gelatin as the protein based stabilizing agent (PBSA). The biosensor system was able to detect caffeine in solution over a concentration range of 0.1 to 1 mg mL⁻¹. With read-times as short as 3 min, this caffeine biosensor acts as a rapid analysis system for caffeine in solutions. Interestingly, successful isolation and immobilization of caffeine degrading bacteria for the analysis of caffeine described here was enabled by a novel selection strategy that incorporated isolation of caffeine degrading bacteria capable of utilizing caffeine as the sole source of carbon and nitrogen from soils and induction of caffeine degrading capacity in bacteria for the development of the biosensor. This biosensor is highly specific for caffeine and response to interfering compounds such as theophylline, theobromine, paraxanthine, other methyl xanthines and sugars was found to be negligible.Although a few biosensing methods for caffeine are reported, they have limitations in application for commercial samples. The development and application of new caffeine detection methods remains an active area of investigation, particularly in food and clinical chemistry. The optimum pH and temperature of measurement were 6.8 and 30 ± 2 °C, respectively. Interference in analysis of caffeine due to different substrates was observed but was not considerable. Caffeine content of commercial samples of instant tea and coffee was analyzed by the biosensor and the results compared well with HPLC analysis.     

Characterizing a source of fission fragments for a gas jet

A model for the rate at which various primary fission products stop in the gas of the source chamber of a gas jet has been constructed. It describes the absorption of fission fragments in Al foils placed between the²³⁵U deposit and the gas chamber as well as the penetration of fragments through the gas. The model is based on reported ranges (mean values as a function of A and the dispersion in ranges) and measured activities of Kr and Xe.     

Use of a chiral surfactant for enantioselective reduction of a ketone

The influence of a chiral surfactant and a polymer-supported chiral additive on reduction of ketones using sodium borohydride will be described. Initial preparations involved methylation of (S)-leucinol to give (2S)-N , N-dimethyl-2-amino-4-methyl-1-pentanol (1) (67%). The chiral surfactant (2) was synthesized by reacting (1) with bromohexadecane (71%). The functionalized styrene for the polymer-supported chiral additive (5) was synthesized by reacting (1) with 4-vinylbenzyl chloride. Polymerization was carried out with 10% of the functionalized monomer (4), 5% cross-linking agent divinylbenzene, and 85% styrene with AIBN as the initiator. The activity of the chiral surfactant and polymeric additive were examined by using them as additives in a standard reduction of 2-pentanone with sodium borohydride to yield (R)- and (S)-2-pentanol (3) (20%). The resulting alcohol was analyzed by polarimetry (ee 9.5%) and also esterified with (2S)-methylbutyric acid prior to characterization by NMR. 13C NMR indicated an enantiomeric excess of 5.2% when the chiral surfactant was used, and 7% when the polymeric additive was used.     

Prospects for development of a technology for production of butene-1

Industrial technologies for production of butene-1 are described, including the most promising process for recovery of butene-1 of polymerization purity from C₄ fractions formed in pyrolysis and catalytic cracking of hydrocarbons. It is shown that this technology can be improved and suggested to use as a raw material the recycle butene fraction formed from these C₄ fractions upon isolation of 1,3-butadiene and isobutene. A technological scheme for recovery of butene-1 of polymerization purity is suggested.     

Evaluation of a novel ELISA for serotonin: urinary serotonin as a potential biomarker for depression

Depression is a common disorder with physical and psychological manifestations often associated with low serotonin. Since noninvasive diagnostic tools for depression are sparse, we evaluated the clinical utility of a novel ELISA for the measurement of serotonin in urine from depressed subjects and from subjects under antidepressant therapy. We developed a competitive ELISA for direct measurement of serotonin in derivatized urine samples. Assay performance was evaluated and applied to clinical samples. The analytical range of the assay was from 6.7 to 425 μg serotonin/g creatinine (Cr). The limit of quantification was 4.7 μg/g Cr. The average recovery for spiked urine samples was 104.4%. Average intra-assay variation was 4.4%, and inter-assay variation was <20%. The serotonin analysis was very specific. No significant interferences were observed for 44 structurally and nonstructurally related urinary substances. Very good correlation was observed between urinary serotonin levels measured by ELISA and liquid chromatography tandem mass spectrometry (LC-MS/MS; ELISA = 1.16 × LC-MS/MS − 53.8; r = 0.965; mean % bias = 11%; n = 18). Serotonin was stable in acidified urine for 30 days at room temperature and at −20 °C. The established reference range for serotonin was 54–366 μg/g Cr (n = 64). Serotonin levels detected in depressed patients (87.53 ± 4.89 μg/g Cr; n = 60) were significantly lower (p < 0.001) than in nondepressed subjects (153.38 ± 7.99 μg/g Cr). Urinary excretion of serotonin in depressed individuals significantly increased after antidepressant treatment by 5-hydroxy-tryptophane and/or selective serotonin re-uptake inhibitor (p < 0.01). The present ELISA provides a convenient and robust method for monitoring urinary serotonin. It is suitable to monitor serotonin imbalances and may be particularly helpful in evaluating antidepressant therapies.     

Fluoral-P,a member of a selective family of reagents for aldehydes

The compound 4-amino-3-penten-2-one is introduced as a member of a selective family of reagents for aldehydes. The stability, selectivity and reactivity of the reagent are described and its utility in automatic determinations of formaldehyde is demonstrated. It is shown that the condensation reaction between 4-amino-3-penten-2-one (called Fluoral-P) and formaldehyde gives a product detectable by fluorescence. The flow injection system utilizing this reagent can be used to determine formaldehyde in the lower. nanomole range.     

Evidence of a self-inclusion phenomenon for a new class of mono-substituted alkylammonium-beta-cyclodextrins

A new class of mono-substituted N-alkyl-N,N-dimethylammonium-beta-cyclodextrins has been synthesized in a three step procedure from the native beta-cyclodextrin. The structural analysis of these compounds undertaken by combined use of 1D and 2D NMR spectra indicate that the two methyl groups bound on the nitrogen are magnetically inequivalent due to a self-inclusion phenomenon of the alkyl chain inside the CD cavity. A variable-temperature 1H NMR study showed that these mono-substituted CD derivatives formed temperature-independent intramolecular complexes with their own alkylammonium substituent. The strength of the interaction between the alkyl moiety and the cyclodextrin cavity has been evaluated by a competitive method using an adamantane derivative. Finally, surface tension measurements demonstrated the surface active character of these compounds and confirmed their self-inclusion ability.     

Preparation of a radon-free thoron source for a thoron calibration chamber

Journal of Radioanalytical and Nuclear Chemistry - During long-term radon/thoron surveys, solid-state nuclear track detectors (SSNTDs) are commonly used. For the application of these integral...     

Polarization Dependence of a Hydrophobized Electrode for Electrosynthesis of a Soluble Product

An equation for a polarization curve of a hydrophobized electrode is proposed for electrosynthesis of a soluble electroactive product in an inner-kinetic mode. The equation contains the concentration of the target product (TP) in an explicit form. The shape of the curve depends on the biquadratic root of the TP concentration and the square root of the ratio between exchange currents of the side and target reactions.     

加热毛细管作为飞行时间质谱仪真空接口的研究

介绍了一种自制的毛细管真空接口,用于连接电喷雾离子源(electrospray ionization,ESI)与自制高分辨率垂直引入式飞行时间质谱仪,初步研究了该接口对仪器灵敏度的影响.结果表明,毛细管接口在有效提高离子传输效率的同时也提高了质谱仪真空系统的性能.加热毛细管的最优加热温度为125 ℃,仪器最低检测灵敏度为1.6 amol.该文还介绍了该接口与自制大气压基体辅助激光解析离子源(atmospheric pressure ma-trix-assisted laseT desorption/ionization,AP-MALD15)联用的实验结果,仪器与该离子源联用的最低检测灵敏度为25 fmol.     

Change of mechanism with a change of substituents for a Zincke reaction

The reaction between N-(2,4-dinitrophenyl)-4-(4-pyridyl)pyridinium chloride and 4-aminothiophenol led to an unexpected displacement of the 2,4-dinitrophenyl group, in contrast with the normal Zincke product formed with other nucleophilic 4-substituted anilines. Evidence for a SET process was obtained from EPR spectra of the reaction mixture.     

Investigation of a novel thermogelling hydrogel for a versatility of drugs delivery

The P(CL-PDO)-PEG-(P(CL-PDO)(PECP) copolymer hydrogel is an attractive thermogelling material for practical applications due to the fast dissolution of the copolymer in water and good stability of the resultant sol solution that is beneficial for guest matter mixing. In this paper, the degradation properties and drug release behavior of the hydrogel loaded with various types of drugs were evaluated. The integrity of the PECP hydrogel could preserve for 2?weeks and became viscous liquid after degradation time of 21?weeks. With the degradation time, both the molecular weight and weight loss of the hydrogel decreased gradually. NMR analysis of the degraded products indicated that the chain breaking of the copolymer mainly occurred within the sequence structures of PDO-PDO or PDO-PCL, implying the acceleration effect of PDO unit to the degradation of hydrogel. Three distinct types of drugs including small molecular hydrophobic, small molecular hydrophilic and hydrophilic macromolecular drugs were loaded into the PECP hydrogel to evaluate their release profiles. The result showed that the releasing periods for macromolecular protein or hydrophobic drug were extended to more than one month. Since these two types of drugs are loaded within different regions of the hydrogel due to their different hydrophobic/hydrophilic nature, the PECP hydrogel is expected to develop injectable system loaded with a versatility of drugs or guest matter for synergetic effect.     

Synthesis of a novel pentagastrin-drug conjugate for a targeted tumor therapy

The synthesis of the novel pentagastrin seco-CBI conjugate 3, which is based on the highly cytotoxic antitumor antibiotic (+)-duocarmycin SA (1), is reported. A key step in the synthesis is the palladium-catalyzed carbonylation of aryl bromide 7 to give the benzyl ester 16, which is transformed into the new seco-CBI derivative 21 bearing a carboxylic acid ester moiety. Subsequent transformation of 21 into an activated ester followed by the introduction of beta-alanine and tetragastrin led to the new pentagastrin drug 3 that contains a peptide moiety for targeting cancer cells expressing CCK-B/gastrin receptors.     

The bilayer lipid membrane as a basis for a selective sensor for ammonia

The development of an electrochemical method for the selective sensing of ammonia gas, based on a modified bilayer lipid membrane, is described. Membrane selectivity for ammonium ion is achieved through incorporation of the antibiotic nonactin as ion-carrier. The detection limits compare favourably with those for conventional ammonia gas-sensing electrodes, but the selectivity is much superior. Theoretical evaluation of the potential sensitivity of the new gas-sensor with respect to design parameters is described.     

Single-Molecule Study of a Plasmon-Induced Reaction for a Strongly Chemisorbed Molecule

Chemical reactions induced by plasmons achieve effective solar-to-chemical energy conversion. However, the mechanism of these reactions, which generate a strong electric field, hot carriers, and heat through the excitation and decay processes, is still controversial. In addition, it is not fully understood which factor governs the mechanism. To obtain mechanistic knowledge, we investigated the plasmon-induced dissociation of a single-molecule strongly chemisorbed on a metal surface, two O₂ species chemisorbed on Ag(110) with different orientations and electronic structures, using a scanning tunneling microscope (STM) combined with light irradiation at 5 K. A combination of quantitative analysis by the STM and density functional theory calculations revealed that the hot carriers are transferred to the antibonding (π*) orbitals of O₂ strongly hybridized with the metal states and that the dominant pathway and reaction yield are determined by the electronic structures formed by the molecule–metal chemical interaction.     

Toward a magnetostructural correlation for a family of Mn6 SMMs

We have structurally and magnetically characterized a total of 12 complexes based on the Single-Molecule Magnet (SMM) [MnIII6O2(sao)6(O2CH)2(MeOH) 4] (1) (where sao2- is the dianion of salicylaldoxime or 2-hydroxybenzaldeyhyde oxime) that display analogous structural cores but remarkably different magnetic behaviors. Via the use of derivatized oxime ligands and bulky carboxylates we show that it is possible to deliberately increase the value of the spin ground state of the complexes [Mn6O2(Me-sao)6(O2CCPh3)2(EtOH)4] (2), [Mn6O2(Et-sao)6(O2CCMe3)2(EtOH)5] (3), [Mn6O2(Et-sao)6(O2CPh2OPh)2(EtOH)4] (4), [Mn6O2(Et-sao)6(O2CPh4OPh)2(EtOH)4(H2O)2] (5), [Mn6O2(Me-sao)6(O2CPhBr)2(EtOH)6] (6), [Mn6O2(Et-sao)6(O2CPh)2(EtOH)4(H2O)2] (7), [Mn6O2(Et-sao)6{O2CPh(Me)2}2(EtOH)6] (8), [Mn6O2(Et-sao)6(O2C11H15)2(EtOH)6] (9), [Mn6O2(Me-sao)6(O2C-th)2(EtOH)4(H2O)2] (10), [Mn6O2(Et-sao)6(O2CPhMe)2(EtOH)4(H2O)2] (11), and [Mn6O2(Et-sao)6(O2C12H17)2(EtOH)4(H2O)2] (12) (Et-saoH2 = 2-hydroxypropiophenone oxime, Me-saoH2 = 2-hydroxyethanone oxime, HO2CCPh3 = triphenylacetic acid, HO2CCMe3 = pivalic acid, HO2CPh2OPh = 2-phenoxybenzoic acid, HO2CPh4OPh = 4-phenoxybenzoic acid, HO2CPhBr = 4-bromobenzoic acid, HO2CPh(Me)2 = 3,5-dimethylbenzoic acid, HO2C11H15 = adamantane carboxylic acid, HO2C-th = 3-thiophene carboxylic acid, HO2CPhMe = 4-methylbenzoic acid, and HO2C12H17 = adamantane acetic acid) in a stepwise fashion from S = 4 to S = 12 and, in-so-doing, enhance the energy barrier for magnetization reorientation to record levels. The change from antiferromagnetic to ferromagnetic exchange stems from the "twisting" or "puckering" of the (-Mn-N-O-)3 ring, as evidenced by the changes in the Mn-N-O-Mn torsion angles.