Calorimeters for biotechnology

The isothermal and temperature scanning calorimeters manufactured by Calorimetry Sciences Corporation are briefly described. Applications of calorimetry to determine thermodynamics and kinetics of reactions of interest in biotechnology are described with illustrative examples.     

Synthesis of a transition metal-dithionite complex, (η5-C5H5)(CO)2FeS(O)2S(O)2Fe(CO)2(η5-C5H5)

The reaction of Na[η⁵-C₅H₅Fe(CO)₂] with large excess of SO₂ in THF at ?78°C followed by warming to room temperature affords an iron—dithionite complex, (η⁵-C₅H₅)(CO)₂FeS(O)₂S(O)₂Fe(CO)₂(η⁵-C₅H₅).     

Excess heat capacities and orientational order in systems containing hexadecane isomers of different molecular structure

Using the Picker flow microcalorimeter, excess heat capacities have been obtained at 25°C throughout the concentration range for 2,2-dimethylbutane,n-hexane, and cyclohexane each mixed with a series of hexadecane isomers of increasing degrees of orientational order, as determined by depolarized Rayleigh scattering. The isomers are 2,2,4,4,6,8,8-heptamethylnonane, 6-, 4-, and 2-methylpentadecane, andn-hexadecane. Thec _p ^E values are negative, increasing rapidly in magnitude with increase of orientational order, and are not predicted by the Prigogine—Flory theory which neglects order. Values ofc _p ^E are obtained at 10, 25, and 55°C for cyclohexane +6-, 4-, and 2-methylpentadecane which with other literature data lead to the temperature dependence of the thermodynamic excess functions for cyclohexane solutions of the five C₁₆ isomers. The excess enthalpy and entropy vary with the C₁₆ isomer and with temperature, but the corresponding variation of the excess free energy is small, indicating a high degree of enthalpy-entropy compensation. This is consistent with a rapid decrease with temperature of orientational order in the C₁₆ isomers.     

Synthesis and in Vitro Evaluation of N-[[4-[2-(Carboxyl)-1-Cycloalken-1-yl]Phenyl]Methyl]Imidazoles as Nonpeptide Angiotensin II Receptor Antagonists

A series of nonpeptide angiotensin II receptor antagonists was synthesized via palladium-assisted cross coupling of aryl stannane and cycloalkenyl triflates and subsequent alkylation of silyl-protected imidazole. Our compounds, which have a terminal five- to seven-membered cycloalkenyl ring, are compared to DuPont EXP7711, an N-[(2′-carboxybiphenylyl)methyl]imidazole, which has a terminal phenyl moiety. Physicochemical properties of the compounds, such as lipophilicity, steric bulk, conformation, and the relative spatial proximity of the 2-carboxyl and the middle phenyl, are quantitated by computational chemistry. Potency in terms of binding affinity to AT₁ receptors in rat adrenal glomerulosa and rabbit aorta is maximized when the terminal ring is aromatic.     

Effects of molecular weight distribution in drag reduction and shear degradation

A reduction of frictional drag in turbulent flow was obtained in benzene by using three monodisperse polystyrene samples having weight-average molecular weights of 1.8, 4.1 and 7.1 × 10⁶. By testing these polymers individually and in mixtures, data were obtained for samples with known molecular weight distributions. The drag reduction of these samples was studied as a function of polymer concentration and flow rate so that a generalized picture of the effects of polydispersity could be obtained. These results are used to help explain much of the behavior that was observed for polystyrene and other polymers. This includes the fact that the polystyrene samples exhibit a remarkably high resistance to the loss of drag reduction via degradation in turbulent flow. Such experiments indicate that drag reduction and degradation depend strongly on molecular weight distribution. Thus a molecular level interpretation of experimental results cannot be made unless the effects of the distribution are considered.     

Mercury-free sono-electroanalytical detection of lead in human blood by use of bismuth-film-modified boron-doped diamond electrodes

We report the electroanalytical determination of lead by anodic stripping voltammetry at in-situ-formed, bismuth-film-modified, boron-doped diamond electrodes. Detection limits in 0.1 mol L^–1 nitric acid solution of 9.6x10^–8 mol L^–1 (0.2 ppb) and 1.1x10^–8 mol L^–1 (2.3 ppb) were obtained after 60 and 300 s deposition times, respectively. An acoustically assisted deposition procedure was also investigated and found to result in improved limits of detection of 2.6×10^–8 mol L^–1 (5.4 ppb) and 8.5×10^–10 mol L^–1 (0.18 ppb) for 60 and 300 s accumulation times, respectively. Furthermore, the sensitivity obtained under quiescent and insonated conditions increased from 5.5 (quiescent) to 76.7 A mol^–1 L (insonated) for 60 s accumulation and from 25.8 (quiescent) to 317.6 A mol^–1 L (insonated) for 300 s accumulation. Investigation of the use of ultrasound with diluted blood revealed detection limits of the order of 10^–8 mol L^–1 were achievable with excellent inter- and intra-reproducibility and sensitivity of 411.9 A mol^–1 L . For the first time, electroanalytical detection of lead in diluted blood is shown to be possible by use of insonated in-situ-formed bismuth-film-modified boron-doped diamond electrodes. This method is a rapid, sensitive, and non-toxic means of clinical sensing of lead in whole human blood.     

Spherically symmetric axial Gaussian lobe 3d and 4f orbitals

The axial Gaussian lobe orbital (AGLO ) representations of 3d and 4f orbitals proposed by LeRouzo and Silvi have been angularly optimized to ensure spherical symmetry of filled 3d and 4f shells. The functions have been tested on the hydrogen atom in the presence of high quality s and p basis sets and found to provide excellent minimal Gaussian representations of polarization functions. Exact orbital degeneracy is not obtained within each shell, however. Tabulated values are given to allow arbitrary scaling of the 3d and 4f lobe mimic orbitals.     

Chiroptical properties of α-substituted succinic acids : Conformation and absolute configuration

The effect of conformational preference on the chiroptical properties of α-substituted succinic acids and esters 2 has been investigated using variable-temperature CD in solvents of different polarity. All available evidence indicates that when R' in 2 is alkyl or halogen, the preferred conformation is 1e with the -CH₂COOR group eclipsed by the CO bond, while when R' in 2 is hydroxy, methoxy or amino, the major conformer is 1d in which the heteroatom is eclipsed by the CO bond. In both cases, conformation 1f appears to be the least favored, mainly on steric grounds. The results when R' = chloro or bromo do not support previously proposed conclusions and an alternative explanation is advanced. In the resultant octant projection (Fig, 2) it is shown that the sign of the Cotton effect for 1 will be determined by the position of the groups X and Y in the back octants, and since one of these is always H in the two favored conformations, the sign is actually determined by the position of the other group. This octant projection predicts successfully the sign of the ellipticity of the n→π^* transition for any α-substituted succinic acid or ester with the appropriate substituent R', and appears to apply also to simple alkanoic acids and esters with the same substituents.     

DNA-templated assembly of nanoscale wires and protein-functionalized nanogap contacts

The use of DNA to template the assembly of nanoscale wires and protein-functionalized nanogap contacts is described: Specifically, the use of DNA to template the assembly of gold nanowires between conventionally patterned gold contacts on a silicon wafer substrate. Also described is the use of DNA to template the assembly of protein-functionalized nanogap gold contacts on a silicon wafer substrate. Of particular significance is the finding that suitably modified gold nanoparticles recognize and bind selectively the protein-functionalized nanogap and are localized there.     

Time-dependent pump-probe spectra of NeBr2

Time- and frequency-resolved pump-probe measurements on NeBr2 have been performed to better characterize its fragmentation dynamics on the B electronic state for vibrational levels in the energy region of the transition from direct vibrational predissociation to intramolecular vibrational relaxation dynamics. Above nu'=20 of the Br2 stretching mode, it was observed that the dependence of lifetime on the vibrational quantum number deviates from the energy-gap law by leveling off in the range of 10 psE transitions of the complex. These transitions are shifted 20 cm(-1) to lower energy from the free Br2 resonances, indicating an E state Ne-Br2 bond energy of 82 cm(-1). Measurements of NeBr2 vibrational predissociation via the delta nu=-2 channel were also performed for nu'=27, 28, and 29. The closing of the delta nu=-1 channel leads to an increase in the lifetimes of these vibrational levels. A new Nd:yttrium aluminum garnet pumped dual optical parametric oscillator/optical parametric amplifier system is described that allows us to conveniently record time-delayed pump-probe spectra with 2-cm(-1) spectral resolution and 15-ps time resolution.