Quantitative millimetre wavelength spectrometry at pressures approaching atmospheric: II. Determination of oxygen at atmospheric pressure

A millimetre wavelength (MMW) Fabry-Perot cavity spectrometer described in earlier work has been applied to the measurement of oxygen absorption at 60 GHz and atmospheric pressure in a gas matrix of nitrogen. The spectrometer has also been modified such that the MMW source is stabilised by a sub-harmonic microwave signal transmitted by an infrared carrier on a single mode telecommunications fibre optic. This is a step towards developing an instrument comprising minimal electronic components that can perform MMW spectrometry remotely. Oxygen determinations were achieved by monitoring the change in the quality factor (Q) of a resonant Fabry-Perot cavity due to the presence of an absorbing sample. The MMW absorption of the sample was determined by incrementing the frequency modulation (FM) deviation of the source frequency scanning the cavity resonance profile. The response curve of absorption signal versus fraction of oxygen in nitrogen was found to be linear throughout the working range of 1-100% O₂ (v/v) in N₂ with a slope of (1.407±0.007)×10⁻⁴ m⁻¹ (% O₂)⁻¹. The detection limit (3× standard deviation of the background) was found to be ∼0.8% (v/v). The MMW technique employed is advantageous since, unlike common MMW techniques, there is no vacuum requirement. Application of this method, to the monitoring of oxygen in gas mixtures of practical importance, is proposed. Values of the oxygen spectral absorption coefficients of lines between 55 and 60 GHz were measured at reduced pressure and found to be within ±2% of previous literature values. A pressure correction coefficient for O₂ absorption at 60 GHz in the 45-121 kPa range was obtained and found to be (1.354±0.014)×10⁻⁴ m⁻¹ kPa⁻¹.     

An algorithm for the location of branching points on reaction paths

A branching point is a point on a reaction path leading from reactants to products (via a transition state) at which it is energetically favorable for the system to break symmetry. Such a point can be defined in terms of normal modes along the reaction path and corresponds to zero curvature (a zero Hessian eigenvalue) along a symmetry-breaking mode. An effective method for the location of such points is presented and realized in an efficient, practical algorithm designed for use in the ab initio program package Gaussian 82.     

Effects of Poly(ethylene glycol) Doping on the Behavior of Pyrene, Rhodamine 6G, and Acrylodan-Labeled Bovine Serum Albumin Sequestered within Tetramethylorthosilane-Derived Sol-Gel-Processed Composites

We investigate the effects of controlled poly(ethylene glycol) (PEG) doping on the behavior of pyrene, rhodamine 6G (R6G), and acrylodan-labeled bovine serum albumin (BSA-Ac) sequestered within tetramethylorthosilicate (TMOS)-derived sol-gel-processed materials. To probe the dipolarity of the local environment within the composite we performed static fluorescence measurements on pyrene as the composites aged. We found that small levels of PEG loading effected significant enhancements in the local dipolarity surrounding the average pyrene molecule. Time-resolved fluorescence anisotropy measurements were used to follow the rotational reorientation dynamics of R6G as the composites aged. As the PEG loading increased, the R6G reorientational mobility increased. Nitrogen adsorption techniques were used to quantify the effects of PEG doping level on the surface area and final xerogel pore features. A large reduction in surface area was observed with PEG doping, but no detectable change in pore size was noted. The effects of PEG doping on a biomolecule were probed by following the time-resolved fluorescence anisotropy decay of BSA-Ac. These results showed that PEG doping resulted in increased biomolecule dynamics relative to that found for a neat, undoped TMOS-derived composites. Together these results show that PEG doping can be used to tune the sol-gel-processed composite dipolarity, alter the mobility of dopants sequestered within the composite, control analyte acessibility to the sensing chemistry, and modulate the internal dynamics within a biodopant.     

Mass spectrometry of pancuronium bromide and related quaternary ammonium steroids using the moving belt LC/MS interface

Pancuronium and vecuronium are members of a series of quaternary ammonium steroids used as neuromuscular blocking agents in anesthesiology. In this study the mass spectrometric properties of these bromide salts are examined and spectral features which permit their differentiation are evaluated. The relative merits of chemical ionization and fast atom bombardment using the moving belt liquid chromatography/mass spectrometry interface have been investigated. Fragmentation pathways for both ionization methods were determined with deuterium labeling and linked-scan techniques. Cleaner spectra can be obtained via the matrix-free belt introduction system as compared to conventional fast atom bombardment.     

5′-substituted-5′-deoxy nucleosides

The methyl esters of the uronic acids derived from uridine, 5-fluorodeoxyuridine, 6-aza-2′-deoxyuridine and 2′,3′-o-isopropylideneadenosine were converted to the amides with aqueous d0·88 ammonia. After protection of the sugar hydroxyls each 5′-carboxamide was dehydrated with phosphoryl chloride at ?5° to yield, after deprotection, the respective novel 5′-nitrile nucleosides. Treatment of the protected 5′-nitrile nucleosides with ammonium azide in DMF gave, after deprotection, the novel 5′-C-tetrazole nucleosides.     

Determination of the types of nitrogen in steels containing aluminium or titanium by an extraction method with hydrogen

The extraction method with hydrogen, hitherto used to determine mobile nitrogen in steels over the temperature range 350–450°C, has been employed at higher temperatures to determine nitrogen bound as aluminium nitride, or as titanium nitride or carbonitride. In steels containing only silicon and titanium as deoxidizers, the nitrogen remaining after passage of hydrogen at 600 or 750°C is present as titanium nitride or carbonitride and can be determined by difference. In steels containing only silicon and aluminium as deoxidizers, the nitrogen remaining after passage of hydrogen at 600°C is present as aluminium nitride and can also be determined by difference. This was verified by determining the aluminium nitride indirectly. The nitrogen released from both the aluminium and titanium steels in hydrogen at 600°C probably results from dissociation of submicroscopic particles of manganese silicon nitride.     

OptiDock: virtual HTS of combinatorial libraries by efficient sampling of binding modes in product space

Products from combinatorial libraries generally share a common core structure that can be exploited to improve the efficiency of virtual high-throughput screening (vHTS). In general, it is more efficient to find a method that scales with the total number of reagents (Sigma growth) rather with the number of products (Pi growth). The OptiDock methodology described herein entails selecting a diverse but representative subset of compounds that span the structural space encompassed by the full library. These compounds are docked individually using the FlexX program (Rarey, M.; Kramer, B.; Lengauer, T.; Klebe, G. J. Mol. Biol. 1995, 251, 470-489) to define distinct docking modes in terms of reference placements for combinatorial core atoms. Thereafter, substituents in R-cores (consisting of the core structure substituted at a single variation site) are docked, keeping the core atoms fixed at the coordinates dictated by each reference placement. Interaction energies are calculated for each docked R-core with respect to the target protein, and energies for whole compounds are calculated by finding the reference core placement for which the sum of corresponding R-core energies is most negative. The use of diverse whole compounds to define binding modes is a key advantage of the protocol over other combinatorial docking programs. As a result, OptiDock returns better-scoring conformers than does serially applied FlexX. OptiDock is also better able to find a viable docked pose for each library member than are other combinatorial approaches.     

PHOTOINHIBITION OF PHOTOSYNTHESIS IN NATURAL WATERS*

Abstract— A quantitative analysis of the wavelength-dependent influence of solar irradiance on natural phytoplankton photosynthesis has been made. The effect on productivity due to several different UV radiation regimes has been measured. In the course of this analysis, it has been shown that the biological weighting function for photoinhibition of chloroplasts (Jones and Kok, 1966) allows the calculation of a biologically effective dose which is consistent with the measured photoinhibition in natural phytoplankton populations. The ecological implications of a change in available UV radiation, possibly due to anthropogenic altering of the ozone layer, are explored and it is found that the present static bottle ^l4C technique of measuring in situ phytoplankton productivity does not lend itself to assessing accurately the potential ecological consequences of possible increased MUV (middle ultraviolet radiation in the 280–340 nm region) on phytoplankton populations. A small change in MUV has a relatively minor effect on photoinhibition dose rates whereas it has a large potential effect on DNA dose rates.     

Irreversible enzyme inhibitors. CXI. Candidate active-site-directed irreversible inhibitors of dihydrofolic reductase derived from 4,6-diamino-1,2-dihydro-l-phenyl-s-triazines. V.

Condensation of 5-(p-nitrophenyl)-2-pentanone with phenylbiguanide hydrochloride (V) gave a 2-methyl-2-(p-nitrophenylpropyl)-1,2-dihydro-s-triazine (IX); hydrogenation of the nitro group to amino followed by bromoacetylation afforded the candidate irreversible inhibitor of dihydrofolic reductase, namely, 2-(p-bromoacetamidophenylpropyl)-4,6-diamino-1,2-dihydro-2-methyl-s-triazine hydrochloride (VIII). Similarly, the o, m, and p-isomers of 5-nitrophenoxy-2-pentanone were converted to the corresponding 2-(bromoacetamidophenoxypropyl)-1,2-dihydro-s-triazines (XI). The four candidate irreversible inhibitors were evaluated on the dihydrofolic reductases from pigeon liver, Walker-256 rat tumor, and L-1210/FR8 mouse leukemia. Only VIII was an irreversible inhibitor; VIII slowly inactivated the L-121-/FR8 mouse leukemia enzyme with a half-life of 2–3 hours at 37°, but VIII showed no inactivation of the other two dihydrofolic reductases—a species specific inactivation.