Intensity autocorrelation function for a flexible polymer

An exact expression for the autocorrelation function of the intensity of light scattered from a solution of large, flexible polymers is obtained using a simple “mean-force” model. A Q² dependence of the reciprocal relaxation time is found for both small values of QR_G and also very large values of QR_G. At small QR_G the relaxation time is proportional to the translational diffusion coefficient D of the entire polymer, while at large QR_G the relaxation time is proportional to the sum of D and an effective segment diffusion coefficient kt/f.     

Luminescent logic function of a surfactant-encapsulated polyoxometalate complex

We have fabricated a novel organic/inorganic hybrid material consisting of multifunctional surfactant-encapsulated polyoxometalloeuropate which functions as a luminescent logic gate with dual output operated by light and metal ion as inputs.     

Surface nanobubbles as a function of gas type

We experimentally investigate the nucleation of surface nanobubbles on PFDTS-coated silicon as a function of the specific gas dissolved in water. In each case, we restrict ourselves to equilibrium conditions (c = 100%, T(liquid) = T(substrate)). Not only is nanobubble nucleation a strong function of gas type, but there also exists an optimal system temperature of ～35 -40 °C where nucleation is maximized, which is weakly dependent on gas type. We also find that the contact angle is a function of the nanobubble radius of curvature for all gas types investigated. Fitting this data allows us to describe a line tension that is dependent on the type of gas, indicating that the nanobubbles sit on top of adsorbed gas molecules. The average line tension was τ ≈ -0.8 nN.     

Generalized born model with a simple smoothing function

Based on recent developments in generalized Born (GB) theory that employ rapid volume integration schemes (M. S. Lee, F. R. Salabury, Jr., and C. L. Brooks III, J Chem Phys 2002, 116, 10606) we have recast the calculation of the self-electrostatic solvation energy to utilize a simple smoothing function at the dielectric boundary. The present GB model is formulated in this manner to provide consistency with the Poisson-Boltzmann (PB) theory previously developed to yield numerically stable electrostatic solvation forces based on finite-difference methods (W. Im, D. Beglov, and B. Roux, Comp Phys Commun 1998, 111, 59). Our comparisons show that the present GB model is indeed an efficient and accurate approach to reproduce corresponding PB solvation energies and forces. With only two adjustable parameters--a(0) to modulate the Coulomb field term, and a(1) to include a correction term beyond Coulomb field--the PB solvation energies are reproduced within 1% error on average for a variety of proteins. Detailed analysis shows that the PB energy can be reproduced within 2% absolute error with a confidence of about 95%. In addition, the solvent-exposed surface area of a biomolecule, as commonly used in calculations of the nonpolar solvation energy, can be calculated accurately and efficiently using the simple smoothing function and the volume integration method. Our implicit solvent GB calculations are about 4.5 times slower than the corresponding vacuum calculations. Using the simple smoothing function makes the present GB model roughly three times faster than GB models, which attempt to mimic the Lee-Richards molecular volume.     

The morse curve as a non-bonded potential function

The morse curve has considerable advantages over the exp-6 and 12-6 potentials as a non-bonded potential function. The three potential functions are compared and the equivalent Morse curves of several commonly used steric potentials are given.     

Use of a scientific microwave apparatus for rapid optimization of reaction conditions in a monomode function and then substrate screening in a multimode function

Recently, a new apparatus has become available, which aims to bring together in one unit the advantages of a monomode and a multimode microwave device. We have assessed the applicability of the apparatus toward rapid optimization of reaction conditions in a monomode function and then substrate screening in a multimode function. We have also probed the effects of differences in microwave absorptivity of reaction mixtures on the product conversions in screening multiple substrates simultaneously in a multimode microwave apparatus. We find that when the microwave absorptivity of a reaction mixture is dictated by the solvent, there is little effect on the heating profile of varying the substrate in a screening run. However, this is not the case when reactions involving non-microwave absorbant solvents are used. In this case the characteristics of the substrate can affect significantly the outcome of the reaction.     

Novel triarylamine dendrimers as a hole-transport material with a controlled metal-assembling function

A series of phenylazomethine dendrimers with a triarylamine core (TPA-DPA) were synthesized by dehydration using TiCl4. The complexation of the fourth genereration (G4) TPA-DPA with SnCl2 proceeds in not a random but a stepwise fashion from the core to the terminal imines of the G4 dendrimer. The molecular size of TPA-DPA G4 is larger than that of DPA G4 in THF solution and has a rigid sphere structure like a globular protein. Organic light-emitting diodes (OLEDs) were fabricated, and the EL performances of the devices using the TPA-DPA-metal complexes as the hole-transport materials are drastically increased (ca. 20 times) by metal complexation.     

Structurally characterized acylruthenium organometallics bearing a pendant aldehyde function

By reacting [Ru(RL¹)(PPh₃)₂(CO)Cl], (1) (R = C₆H₄Me, Et) with an excess of CNBu^t in the presence of NH₄PF₆, organometallics of the type [Ru(RL²)(PPh₃)₂(CNBu^t)₂]PF₆, (2) have been isolated in excellent yield [RL¹ = C₆H₂O-2-CHNHR(p)-3-Me-5, RL² = C₆H₂(CO)-O-2-CHNHR(p)-3-Me-5]. These organometallics, on controlled hydrolysis, produce [Ru(L³)(PPh₃)₂(CNBu^t)₂], (3) in very good yield (L³ = C₆H₂(CO)-O-CHO-3-Me-5). In both ([2(C₆H₄Me)] · 2H₂O) and ([3] · 2CH₂Cl₂) the two phosphine ligands lie in trans positions. In ([2(C₆H₄Me)] · 2H₂O) the Ru(C₆H₄MeL²) fragment, excluding the pendant tolyl ring, is a near perfect plane (mean dev ~ 0.02Å) which makes a dihedral angle of 5.2° with the tolyl plane. The acyl chelate ring in ([2(C₆H₄Me)] · 2H₂O) is excellently planar with a mean deviation of 0.006°. In ([3] · 2CH₂Cl₂) the Ru(L³) fragment defines a crystallographic plane of symmetry, the coordinates of the atom being of the type x, 1/4z. The complex ([2C₆H₄Me)] · 2H₂O) displays N–HȮFO (iminium-phenolato) hydrogen bonding while in ([3] · 2CH₂Cl₂) C–H...O hydrogen bonding is present. Characteristic spectral data (u.v.–vis, i.r. and ¹H n.m.r.) of the complexes are reported. A notable feature is that an allowed band near 500 nm due to the t_2g → π^*(azomethine) charge transfer transition, which is diagnostic of the coordinated iminium-phenolato function, is present in (3) but this band is absent in the aldehydic acyl complex (2). In the ¹H n.m.r. spectrum the N⁺–H signal in (2) (near 13.5 ppm) is split into a doublet due to transcoupling with the azomethine proton. The aldehydic proton of (3) resonates as a sharp singlet near 10 ppm. In CH₂Cl₂ solution (2) and (3) display quasireversible a Ru^III/Ru^IIcyclic voltammetric response with E_1/2 near 0.9 and 0.5 V versuss.c.e. The conversion (2) → (3) is accompanied by the nucleophilic attack of water. The complex (3) is also obtained directly from (1) by reaction with CNBu^t in the presence of H₂O. The aldehyde function in (3) is deactivated by the existing acyl moiety; as a result further decarbonylation does not take place.     

Base-promoted cyclization of 1-nitrohydrazones bearing a thioether function

Functionalized 1-nitrohydrazones 5 react with sodium hydride in boiling benzene to afford different types of ring-closed products. The formation of the latter can be ascribed to competitive modes of evolution of first-formed nitrile imines.     

Amino acid rejection behaviour as a function of concentration

The solute rejection versus concentration behaviour of five different amino acids has been investigated using a Nitto Denko NTR7450 nanofiltration membrane. The experimental data for amino acid rejection was also compared against a combined steric and charge rejection model. At its isoelectric point, lysine was effectively neutral and its behaviour was well described by the model incorporating a steric function only. For phenylalanine, the combined model was found to fit the data well. In contrast there was poor agreement between the model and rejection data for glutamine, glutamic acid and glycine whose rejection values at first increased with concentration. This result implied that another governing process was in operation. Dimerisation as an explanation for the observed phenomena was also investigated. Size analysis of amino acid molecules as a function of the prevailing concentration using dynamic light scattering was limited but showed no evidence of dimerisation. This data was supported by osmotic pressure measurements which demonstrated no evidence of non-linearity in the relation between osmotic pressure and concentration.     

Drop retention force as a function of resting time

The force, f, required to slide a drop on a surface is shown to be a growing function of the time, t, that the drop waited resting on the surface prior to the commencement of sliding. In this first report on the resting time effect, we demonstrate the existence of this phenomenon in different systems, which suggests that this phenomenon is general. We show that d f/d t is never negative. The shorter the resting times, the higher d f/d t is. As the resting time increases, d f/d t decreases toward zero (plateau) as t --> infinity. The increase in the force, Delta f, due to the resting time effect (i.e., f( t --> infinity) - f( t --> 0)) correlates well with the vertical component of the liquid-vapor surface tension, and we attribute this phenomenon to the corrugation of the surface by the drop due to this unsatisfied normal component of Young's equation.     

Drop retention force as a function of drop size

The force, f, required to slide a drop past a surface is often considered in the literature as linear with the drop width, w, so that f/w = const. Furthermore, according to the Dussan equation for the case that the advancing and receding contact angles are constant with drop size, one can further simplify the above proportionality to f/V(1/3) = const where V is the drop volume. We show, however, that experimentally f/V(1/3) is usually a decaying function of V (rather than constant). The retention force increases with the time the drop rested on the surface prior to sliding. We show that this rested-time effect is similar for different drop sizes, and thus the change of f/V(1/3) with V occurs irrespective of the rested-time effect which suggests that the two effects are induced by different physical phenomena. The time effect is induced by the unsatisfied normal component of the Young equation which slowly deforms the surface with time, while the size effect is induced by time independent properties. According to the Dussan equation, the change of f/V(1/3) with V is also expressed in contact angle variation. Our results, however, show that contact angle variation that is within the scatter suffices to explain the significant force variation. Thus, it is easier to predict contact angle variation based on force variation rather than predicting force variation based on contact angle variation. A decrease of f/V(1/3) with V appears more common in the system studied compared to an increase.     

The true diatomic potential as a perturbed Morse function

The problem of representing a diatomic (true) Rydberg-Klein-Rees potential U^t by an analytical function U^a is discussed. The perturbed Morse function is in the form U^a = U^M + ∑b_nyⁿ, where the Morse potential is U^M = Dy², y = 1 ?exp(?;a(r ? r_e)). The problem is reduced to determination of the coefficients b_n so U^a(r) = U^t(r). A standard least-squares method is used, where the number N of b_n is given and the average discrepancy ΔU = |(U^t ? U^a)/U^t| is observed over the useful range of r. N is varied until ΔU is stable. A numerical application to the carbon monoxide X¹∑ state is presented and compared to the results of Huffaker¹ using the same function with N = 9. The comparison shows that the accuracy obtained by Huffaker is reached in one model with N = 5 only and that the best ΔU is obtained for N = 7 with a gain in accuracy. Computation of the vibrational energy E_v and the rotational constant B_v, for both potentials, shows that the present method gives values of ΔE and ΔB that are smaller than those found by Huffaker. The dissociation energy obtained here is 2.3% from the experimental value, which is an improvement over Huffaker's results. Applications to other molecules and other states show similar results. © 1995 by John Wiley & Sons, Inc.