MO LCAO calculation of the chemical and physical properties of α-pyrone derivatives

The molecules of -pyrone, coumarin, 2, 3: 7, 6-furocoumarin (psoralene), 2, 3: 7, 8-furocoumarin (isopsoralene), and 3, 4-benzocoumarin were the object of MO LCAO calculations. It is shown that these compounds do not obey the Hückel rule and that they form closed electron shells in the presence of 8, 12, and 16 electrons. In most cases, the obtained values of the characteristics of the electronic structure of the compounds studied are in good agreement with the chemical properties of these compounds. It follows from a comparison between the proton chemical shifts in NMR spectra and the values of the -electron density at the corresponding carbon atoms calculated by the MO method that the current of the benzene ring exerts the greatest effect on the protons, whereas a lesser effect is exerted by the furan ring and, finally, the least effect is exerted by the current of the -pyrone ring.     

Correlation effects in calculation of electronic states for model molecular systems

Multiply excited configurations have been taken into account in evaluation of singlet, triplet and quinlet state energies and the relevant intensities of electronic transitions for model molecular systems. The results of calculation point out the essential role of interelectron, for (Π,Π^*) triplets and quintets in particular.     

A correlation energy calculation of the 1s hole state in neon

The Bethe-Goldstone formalism for calculating correlation energy has been applied to the 1s hole state in neon. The binding energy of the 1s electron is computed to be 870.0 eV which is in excellent agreement with experiment.     

Correlation between chemical and physical surface properties and blood compatibility of PPE/EVA-blends

The chemical and physical surface properties of a biomaterial are of high importance for the blood compatibility of an implant. Blends of poly(propylene-co-ethylene) with various amounts of poly(ethylene-co-vinyl acetate) (PPE/EVA-blends) were examined because of the varying surface hydrophilicity. Surface characterizations were performed by means of X-ray Photoelectron Spectroscopy (XPS), Infrared Spectroscopy in Attenuated Totalreflexion Mode (IR-ATR) in relation to dynamic contact angle and zeta potential measurements. The examination of the blood compatibility of the polymer surfaces was carried out in vitro in a modified BOWRY blood chamber with native whole human blood. A balanced ratio of polar and dispersive surface free energy and a zeta potential of −4 mV are the conditions for a good blood compatibility of the investigated PPE/EVA-blends.     

A CNDO calculation of electron and hole defects in a mixed halide alkaline earth crystal

The CNDO method representing a large cluster embedded in the point charges of the surrounding lattice has been applied to trapped electron and hole species in BaFBr. F centers are more stable on the F^- lattice site while V_K or H centers are more stable on Br^- lattice sites. The relative energy levels show the unpaired electron 1–2 eV above the valence band edge for V_K and H centers and 5–6 eV above the valence band edge for F centers. The results are qualitatively in agreement with physical expectations in this system. Relative strengths and weaknesses of this type of calculation are     

Correlation hole for an exactly solvable problem

The probability distribution of the interparticle distance is obtained for the N-body boson problem where the potential is an attractive delta function. This is done for both the exact wave function and the Hartree wave function allowing the calculation of the correlation hole.     

Dynamics of adsorption: A model calculation for HD activated adsorption

We have recently developed a model potential for the interaction of a diatomic molecule with a rigid solid surface. In this note, we report some results of classical trajectory studies designed to simulate the adsorption of a diatomic molecule. Model potentials with different barrier heights are used and a variety of different initial conditions for the incident molecule are studied. In common with gas-phase results, we find that translational energy is most effective in surmounting early barriers and enhancing adsorption.     

Many-body calculation of the core hole spectra of PdCO

To investigate the dependence of ligand (adsorbate) core hole spectra on the electronic structure of the metal substrate, we performed ab initio 2h1p and 2h2p/3h2p CI calculations of the core hole spectra of the linear PdCO molecule using an extended basis set. The main line is the one-hole state and takes a much larger intensity than for NiCO and NiN₂ but still smaller than for free CO. As in the case of NiCO and NiN₂, also for PdCO the π charge transfer (CT) shakeup satellite of a small intensity is obtained near the main line peak. The most striking spectral feature of PdCO which differs from NiCO and NiN₂ is the absence of the 5 eV giant σ shakeup satellite in the carbon spectrum. In the oxygen spectrum the corresponding satellite of a small satellite intensity, is shifted toward the higher energy (around 8 eV). However, with an increase of the bond length this satellite also disappears. As in the case of NiCO, the π to π^* shakeup satellites are obtained around 9 eV for both carbon and oxygen spectra. These dramatic spectral feature changes are explained in terms of the different degree of the dσ-s hybridization and s-dσ promotion in the local metal configuration in the ground and ionized states. We point out the possibility that the DES spectrum becomes similar to the AES spectrum in the spectator Auger decay energy region even when initial core hole state differs.     

Correlation between physical properties and conformational rigidity of some aromatic polyimides having pendant phenolic groups

Soluble polyimides based on an aromatic diamine containing pendant phenolic group and four different dianhydrides have been synthesized by two-step polycondensation reaction in solution. The polyimides were easily soluble in polar organic solvents and even in less polar solvents and showed high thermal stability, with initial decomposition temperature being above 420 °C. Monte Carlo method was used to calculate conformational rigidity parameters of these polyimides. Some physical properties such as solubility, glass transition temperature and initial decomposition temperature were investigated and compared with those of related polyimides which did not contain any pendant groups based on the same dianhydrides and a diamine without pendant phenolic group. All data were discussed in relation to the rigidity of the chain.

     

A model study on effect of glucose on the basic characteristics and physical properties of natural rubber

Glucose at various concentrations was incorporated into sugar free purified natural rubber (PNR) latex to model the effect of carbohydrate on the basic characteristics and physical properties of natural rubber (NR). PNR samples treated with various concentrations of glucose were characterized for the basic properties of unvulcanized NR, i.e., gel content, molecular weight distribution and Mooney viscosity to evaluate the effect of sugar on these parameters. In addition, the effect of glucose on the physical properties of vulcanizates derived using sulfur and peroxide vulcanization was investigated. Glucose was shown to affect the viscosity of unvulcanized NR and the discoloration of vulcanized NR. Moreover, glucose was found to have a strong effect on crosslink density, as well as tensile and dynamic properties of sulfur vulcanizates, while those properties of peroxide vulcanizates was not much affected by glucose.     

A model calculation of protonic mobility in ice

The protonic conductivity in ice crystals is considered within the framework of strong coupling developed earlier by the present authors for semiconductors with narrow bands and strong coupling of electrons with phonons. The generalization for a two-band model is developed. The model used is the one described by Gosar and Pintar, the principal feature of which is the concept of the protonic conduction bands. The analytical expression for the protonic mobility is given. The results of the theory are in qualitative agreement with the experimental data.     

Polyynes as a model for carbyne: synthesis, physical properties, and nonlinear optical response

With the Fritsch-Buttenberg-Wiechell rearrangement as a primary synthetic route, a series of conjugated, triisopropylsilyl end-capped polyynes containing 2-10 acetylene units has been assembled. In a few steps, significant quantities of the polyynes are made available, which allow for a thorough analysis of their structural, physical, and optical properties. Molecules in the series have been characterized in detail using (13)C NMR spectroscopy, differential scanning calorimetry, mass spectrometry, and, for four derivatives including octayne 6, X-ray crystallography. UV-vis spectroscopy of the polyynes 1-7 shows a consistent lowering of the HOMO-LUMO gap (E(g)) as a function of the number of acetylene units (n), fitting a power-law relationship of E(g) approximately n(-)(0.379)(+/-)(0.002). The third-order nonlinear optical (NLO) properties of the polyyne series have been examined, and the nonresonant molecular second hyperpolarizabilities (gamma) increase as a function of length according to the power-law gamma approximately n(4.28)(+/-)(0.13). This result exhibits an exponent that is larger than theoretically predicted for polyynes and higher than is observed for polyenes and polyenynes. The combined linear and nonlinear optical results confirm recent theoretical studies that suggest polyynes as model 1-D conjugated systems. On the basis of UV-vis spectroscopic analysis, the effective conjugation length for this series of polyynes is estimated to be ca. n = 32, providing insight into characteristics of carbyne.     

Tetraaminoperylenes: their efficient synthesis and physical properties

Trimethylsilylation of 1,8-diaminonaphthalene gave 1,8-bis(trimethylsilylamino)naphthalene (1 a), which was in turn lithiated with two molar equivalents of n-butyllithium to give the tris(thf)-solvated dilithium diamide [1,8-[(Me(3)SiN)Li(thf)](2)C(10)H(6)](thf) (2 a). Metal exchange of 2 a with TlCl was carried out in two steps, via the previously characterized mixed-metal amide [1-[(Me(3)SiN)Li(thf)(2)]-8-[(Me(3)SiN)Tl]C(10)H(6)], to give the dithallium diamide [1,8-[(Me(3)SiN)Tl](2)C(10)H(6)] (3 a). Thermolysis of 3 a cleanly gave a 1:1 mixture of the 4,9-bis(trimethylsilylamino)perylenequinone-3,10-bis(trimethylsilylimine) (4 a) and 1 a. By this route, a whole series of silylated homologues of 4 a was obtained in good yields, while the same method proved to be inefficient for the synthesis of the alkyl-substituted analogues. Compound 4 a and its tert-butyldimethylsilyl derivative 4 d were reduced with sodium amalgam to give, after protonation, the corresponding 3,4,9,10-tetraaminoperylenes 7 a and 7 d. Cyclic voltammetry showed two reversible, closely spaced reduction waves (E(red 1)=-1.39, E(red 2)=-1.59 V versus SCE) corresponding to this conversion. The perylenes 7 a and 7 d are thought to be the primary products in the reaction cascade leading to the perylene derivatives, involving the thermal demetalation of the thallium amides, possibly via Tl(II)bond;Tl(II) intermediates, first to give 7 a and its analogues. The final oxidation of the tetraaminoperylenes by one molar equivalent of 3 a and analogous thallium amides gave the quinoidal derivatives such as 4 a and 4 d, a step that could be studied by direct reaction of the isolated species. The UV/Vis absorption spectra of the 4,9-bis(silylamino)perylenequinone-3,10-bis(silylimines) are characterized by a long-wavelength absorption band with a pronounced vibrational structure (lambda(max)=639 nm, lg epsilon =4.53) attributed to a pi*<--pi and a pi*<--n absorption band at 454 nm (lg epsilon 4.83), along with intense absorption in the UV region. A weak red emission with a rather low quantum yield (Phi(fl)=0.001, lambda(max)=660 nm) is observed upon irradiation of a sample; the lifetime of the emission is only 66 ps. The low emission quantum yield is attributed to the *pi<--n transition of the amino perylene, which induces strong spin-orbit coupling, leading to a large triplet yield. The triplet state was probed by transient absorption spectroscopy and found to have a lifetime of 200 ns in air, and 1100 ns in argon-flushed solution. Treatment of 4 a with a stoichiometric amount of KF in methanol/water under phase-transfer conditions (with the cryptand [C 222]) gave an almost quantitative yield of the parent compound 4,9-diaminoperylenequinone-3,10-diimine (8). Treatment of 8 with two molar equivalents of the ruthenium complex [Ru(bpy)(2)(acetone)(2)](PF(6))(2), generated in situ, yielded the blue dinuclear ruthenium complex [(bpy)(4)Ru(2)[mu(2)-N,N':N",N"'-[[4,9-(NH(2))(2)-3,10-(NH)(2)]C(20)H(8)]]](PF(6))(4) (9), the redox properties of which were studied by cyclic voltammetry. The difference in the potentials of the two one-electron redox steps (225 mV) indicates strong coupling of the metal centers through the 4,9-diaminoperylenquinone-3,10-dimine bridging ligand and corresponds to a comproportionation constant K(c) of 6.3 x 10(3). The UV/Vis absorption spectrum of the mixed valent form, which is stable in air, has a characteristic intervalence charge-transfer (IVCT) band in the near infrared at 930 nm (lg epsilon =3.95), from which an electronic coupling parameter J of 760 cm(-1) could be estimated, placing compound 9 at the borderline between the class II and class III cases in the Robin-Day classification.     

Structure and properties of a model of deoxyheme,an ab initio SCF calculation

Ab initio SCF calculations have been used to study the structure and the electronic properties of four- and five-coordinate Fe(II) porphyrins. The following systems have been considered: FeP (P = porphine dianion) (S = 1 and S = 2) and Fe(NH₂)₄ (S = 1) as four-coordinate systems. FePNH₃, Fe(NH₂)₄NH₃ and Fe(NH₂)₄1m as models of the deoxyheme (S = 2). Fe(NH₂)₄SH (S = 2) as a model of the reduced cytochrome P450. The basis sets used are either of the split-valence type or of double-zeta quality. The ground-state electronic configurations have been assigned. The potential energy curve of FePNH₃, as a function of the out-of-plane displacement of the iron atom, has a minimum for a displacement of 0.32 Å. a value significantly smaller than the accepted value of 0.6 Å in human deoxyhemoglobin. The out-of-plane displacement is larger, by ≈ 0.2 Å, when a mercaptide ligand replaces the ammonia or imidazole ligand. The electric field gradient tensor, the quadrupole splitting and the asymmetry parameter have been calculated and compared with the experimental values derived from the ⁵⁷Fe Mössbauer spectra.     

Squaramides: physical properties, synthesis and applications

Squaramides are remarkable four-membered ring systems derived from squaric acid that are able to form up to four hydrogen bonds. A high affinity for hydrogen bonding is driven through a concomitant increase in aromaticity of the ring. This hydrogen bonding and aromatic switching, in combination with structural rigidity, have been exploited in many of the applications of squaramides. Substituted squaramides can be accessed via modular synthesis under relatively mild or aqueous conditions, making them ideal units for bioconjugation and supramolecular chemistry. In this tutorial review the fundamental electronic and structural properties of squaramides are explored to rationalise the geometry, conformation, reactivity and biological activity.     

Free volume hole size of Cyanate ester resin/Epoxy resin interpenetrating networks and its correlations with physical properties

Cyanate ester (CE) resin was blended with epoxy resin (EP) at different mass ratios (CE/EP: 100/0, 90/10, 70/30, 50/50, 30/70, 10/90, and 0/100). The curing process of the blend system was characterized by Fourier transform infrared spectrometry (FTIR) and differential scanning calorimetry (DSC). Examination of the mechanical properties, thermal stability, and morphology of the blend systems showed that addition of epoxy resin resulted in improved toughness but a little sacrifice in thermal stability when compared with neat CE. The free volume size of the blend system determined by positron annihilation lifetime spectroscopy (PALS) decreased with the epoxy resin content, which is consistent with the chemical structure changes for the copolymerization between CE and EP. The crosslinking units of curing products (oxazoline, oxazolidinone, and polyether network) of the blends are all smaller in size than those of triazine ring structure from neat CE. Therefore, the free volume size of the blends decreases with increase of EP content. The correlations between the free volume properties and other physical properties (thermal stability and mechanical properties) have also been discussed.     

General correlation model for some physical properties of saturated pure fluids

In this work, we use a general expression to accurately correlate the liquid density, the vaporization enthalpy, the surface tension, and the isobaric heat capacity of a saturated liquid versus temperature along the whole coexistence curve. The general expression used is the same for the four thermodynamic properties, and uses both critical and triple point values as reference. As representative examples of the use of the model, results are given for a set of 22 pure substances. We find that this general expression correlates the data with smaller or similar overall deviations when compared with other published models whose number of coefficients are the same or greater.