Strongly orthogonal geminals: size-extensive and variational reference states

Properties and some applications of strongly orthogonal geminals (APSG) are reviewed emphasizing the motivations for their use and their shortcomings. An overview presents some techniques capable of improving the APSG function.     

Chromatographic effects of residual amino groups on liquid chromatographic stationary phases derived from aminopropyl-silica gel

Low-capacity phenylazo-8-quinolinol-silica gel (QSG) stationary phases were made by two different procedures. The first began with an aminopropyl-silica gel (APSG), which was converted to nitrobenzamide-silica gel (NBSG) by amidization with p-nitrobenzoyl chloride. The second began with the direct preparation of the NBSG using nitrobenzamidesilane. Retention data for several organic analytes were obtained on APSG and on the NBSG and QSG phases made by both procedures. Anomalously high capacity factors were obtained for p-nitrobenzoic acid on the NBSG material obtained from APSG, indicating the presence of unreacted aminopropyl anion-exchange sites. Only after reamidization of the NBSG using more vigorous conditions did the retention data approach that on the NBSG made by the second method. Even then, the opposite order of elution of p-nitrobenzoic and benzoic acids on the two NBSG and QSG phases indicated that vestiges of amino groups remained on the materials made from the APSG. Several chromatographic and chemical characterization methods confirmed the presence of residual aminopropyl groups.     

Some acid—base and complexation properties of silica-bound ligands

Several aspects of the acid-base properties of aminopropyl, aminoethylaminopropyl-, and 8-quinolinol silica gel (APSG, EDSG, and QSG, respectively) are considered. Acid wash of APSG and EDSG reduces the metal-uptake capacity to nearly zero. Following a base wash, most of this capacity is restored. Effective basicity of each silica gel is found to be significantly less than that of the free base analog for APSG and EDSG, but only slightly less for QSG. Hydrogen bonding of the γ-amine group to residual silanols is postulated as at least one cause of lower base-strengths, although dependence of pK_b on the degree of neutralization is also a possibility. Solution equilibrium is reached very slowly in potentiometric pH titrations of the three modified silica gels, possibly because of diffusion or other kinetic phenomena. The bound amines possess 2:1 ligand-to-copper(II) stoichiometry. The bound 8-quinolinol exhibits a 1:1 ratio. A lower surface density and steric constraints of bound groups on QSG are possible reasons for the difference between 8-quinolinol and the amines.     

A stationary property of the APSG wave function

The method of antisymmetrized product of strongly orthogonal geminals (APSG) emerges by optimizing the one-electron functions used to construct two-electron functions (geminals), the latter being expanded (with coefficients selected variationally) in mutually exclusive subspaces of the former ones. Accordingly, E _APSG is stationary with respect to the expansion coefficients and to unitary transformations of the one-electron orbitals. We show that the APSG energy is also stationary to the unitary transformation of identical geminals. For non-identical geminals, this statement holds only approximately.     

Stabilization of <Emphasis Type="Italic">n</Emphasis>-aminopropyl silica gel against hydrolysis by blocking silanol groups with TiO<Subscript>2</Subscript> or ZrO<Subscript>2</Subscript>

Silanol groups of n-aminopropyl silica gel (APSG) were blocked with TiO₂ or ZrO₂ to produce Ti-APSG and Zr-APSG, respectively. The silica materials were characterized by infrared, Raman spectra, thermogravimetric, elemental analyses, magic angle spinning ¹³C-nuclear magnetic resonance, specific surface area measurements, pH-metric titration and inductively coupled plasma—optical emission spectrometry—monitored silica hydrolysis. The stability of APSG against hydrolysis was found to be mainly affected by the specific surface area and the basicity of the n-aminopropyl groups which acquire additional strength from their intramolecular interaction with the silanol groups. The hydrolysis of silica in Ti-APSG and Zr-APSG remarkably decreased in the range of pH 1.0–9.1 due to the interruption of that intramolecular interaction. The hydrolyzed silica of Ti-APSG and Zr-APSG was decreased to 22.7 and 29.9%, respectively, of that of APSG at pH 4.5. Capacity and stability of Ti-APSG and Zr-APSG were improved in comparison with APSG upon application in the extraction of Cu²⁺ for 20 cycles of extraction and regeneration.     

Iodine Supported on 3-Aminopropyl Silica Gel as Efficient Catalyst for Acetylation of Alcohols under Solvent-free Conditions

3-Aminopropyl silica gel (I2/APSG) was found to catalyze the acetylation of alcohols and phenols efficiently with acetic anhydride. The reaction is mild and selective with high yields. A wide variety of alcohols and phenols are selectively converted into the corresponding acetates using I2/APSG under solvent-free conditions at room temperature.     

Die horizontale Korrelation in π-Elektronensystemen und ihre Beschreibung durch Elektronenpaarfunktionen

Different types of pair functions (geminal products and their linear combinations) are tested with respect to their ability to describe the “horizontal correlation” of the π-electrons of butadiene. The validity of the π-electron approximation is not discussed and “full configuration interaction” within the limited LCAO basis is used as the standard to which the model calculations are referred. An APSG-function (APSG = antisymmetrized product of strongly orthogonal geminals) built up from equivalent (localized) geminals, which contains only one variational parameter is able to account for about 90% of the “horizontal correlation energy”. Both APSG and APIG functions constructed from delocalized geminals, are much less favorable. Criteria of the goodness of an approximate wave function are a) the energy b) comparison of its one- and two-particle density matrices with those obtained from “full CI”. The good results with the localized APSG function are related to the fact that electron correlation between electrons of opposite spin is (in this molecule) essential only within either of the “double bonds” of the “canonical structure”. The pertinent results are quite insensitive to different parametrization of the integrals.     

Synthesis of dimethyl acetals. diethyl acetals. and cyclic acetals catalyzed by aminopropylated silica gel hydrochloride (APSG-HCL)

The aminopropylated Silica-Gel hydrochloride (APSG.HCl) proved to be an efficient catalyst for the rapid conversion of carbonyl compounds in the corresponding acetals with high yields and in mild and selective conditions. In addition to the obvious advantages offered by heterogeneous catalysis, the present method results very useful when the presence of a weakly-acidic function chemically bonded on the catalyst surface (alkyl ammonium salt). is necessary (compounds which contains functions unstable in acidic media).     

Computation scheme for optimizing multiconfigurational wave-functions

A computation scheme is proposed to determine the wave-functions of molecular systems within the framework of the CMC SCF theory and the APSG SCF approach. The orbital optimization is carried out by the refined first-order one-electron Hamiltonian method. Explicit expressions of the first and second energy derivatives are obtained. In the suggested scheme all the calculations are based on using the matrices of the “partial” Coulomb and the exchange operators constructed over the orbitals at the current iteration cycle.     

Role of electron correlation in the quantum-mechanical calculations of the coulomb interaction energy in the DNA base pairs

The intermolecular electronic correlation contributions to the Coulomb component of the nucleic acid base interaction energy are estimated. The Coulomb energy is evaluated with the use of atomic monopoles, which are determined from the π-electronic densities calculated by the SCF method and by employing partially or completely optimized APSG wave functions. When the correlation is thus taken into account, a systematic decrease in atomic charges occurs; this effect is considerable only if an optimized orbital set is used. As a result, the Coulomb interaction energy due to the π-electronic atoms decreases from ?1.13 to ?0.85 kcal/mol for the AT pair and from ?7.15 to ?4.61 kcal/mol for the GC pair.     

价键结构函数与键数Ⅰ.理论处理及甲烷的应用实例

采用键函数形式对键表进行逐级展开,其中荚函数的强正交积作为零级函数,进而构造了各级校正函数以描述多对键之间的相关作用,同时采用Heitler-london 函数作为键函数,对甲烷进行离键表计算,结果表明CH~4中一.二.三级校正能近似有4:2:-1的关系,即校正函数的收敛性能较好.     

Solid-phase extraction of trace Cu(II) Fe(III) and Zn(II) with silica gel modified with curcumin from biological and natural water samples by ICP-OES

Silica gel was firstly functionalized with aminopropyltrimethoxysilane obtaining the aminopropylsilica gel (APSG). The APSG was reacted subsequently with curcumin yielding curcumin-bonded silica gel (curcumin-APSG). This new bonded silica gel was used for separation, pre-concentration and determination of Cu(II), Fe(III), Zn(II) in biological and natural water samples by inductively coupled plasma optical emission spectrometry (ICP-OES). Experimental conditions for effective adsorption of trace levels of metal ions were optimized with respect to different experimental parameters using batch and column procedures in detail. The optimum pH value for the separation of metal ions simultaneously on the newly sorbent was 4.0. Complete elution of the adsorbed metal ions from the sorbent surface was carried out using 2.0 mL of 0.1 mol L^− 1 of HCl. Common coexisting ions did not interfere with the separation and determination at pH 4.0. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 0.63, 0.46 and 0.37 mmol g^− 1 for Cu(II), Fe(III) and Zn(II) respectively. The time for 95% sorption for Cu(II) Fe(III) and Zn(II) was less than 2 min. The detection limits of the method defined by IUPAC was found to be 0.12, 0.15 and 0.40 ng mL^− 1 for Cu(II), Fe(III) and Zn(II), respectively. The relative standard deviation (RSD) of the method under optimum conditions was lower 3.0% (n = 5). The procedure was validated by analyzing the certified reference river sediment material (GBW 08301, China), the results obtained were in good agreement with standard values. This sorbent was successfully employed in the separation and pre-concentration of trace Cu(II), Fe(III) and Zn(II) from the biological and natural water samples yielding 75-fold concentration factor.     

Preparation of poly(propyleneimine) dendrimer immobilized silica gel and its application as novel microcolumn packing for the on-line FI preconcentration and separation of platinum

A G4.0 poly(propyleneimine) dendrimer immobilized silica gel (PPID-SG) was prepared with a divergent approach from gamma-aminopropyl silica gel (APSG) by repeating the reactions: 1) cyanoethylation of -NH2 and 2) reduction of -CN. Then it was successfully applied as the microcolumn packing for the on-line flow-injection (FI) preconcentration and separation and flame atomic absorption spectrometry (FAAS) determination of Pt. A limit of detection (LOD) of 0.014 microg/mL was obtained when 0.5 microg/mL Pt in chloride acid of PH = 3 was preconcentrated with a sample flow rate of 4.6 mL/min for 60s and the relative standard deviation (RSD) was 2.65%. Coexisting metal ions with concentration of 5.0 mg/mL and anion ions of 20.0 mg/ml have no interference in the determination of Pt. The proposed method was successfully applied to the determination of Pt in nickel alloy and anode slime samples.     

Synthesis and characterisation of morin-functionalised silica gel for the enrichment of some precious metal ions

Silica gel was firstly functionalised with aminopropyltrimethoxysilane obtaining the aminopropylsilica gel (APSG). The APSG was reacted subsequently with morin yielding morin-bonded silica gel (morin-APSG). The structure was investigated and confirmed by elemental and thermogravimetric analyses, IR and (13)C NMR spectral studies. Morin-APSG was found to be highly stable in common organic solvents, acidic medium (<2molL(-1) HCl, HNO(3)) or alkaline medium up to pH 8. The separation and preconcentration of Ag(I), Au(III), Pd(II), Pt(II) and Rh(III) from aqueous medium using morin-APSG was studied. The optimum pH values for the separation of Ag(I), Au(III), Pd(II), Pt(II) and Rh(III) on the sorbent are 5.7, 2.2, 3.7, 3.7 and 6.8, giving rise to separation efficiencies of 43.9, 85.9, 97.7, 60.9 and 91.0%, respectively, where the activity was found to be >90% in the presence of acetate ion. The ion sorption capacity of morin-APSG towards Cu(II) at pH 5.5 was found to be 0.249mmolg(-1) where the sorption capacities of Ag(I) and Pd(II) were 0.087 and 0.121mmolg(-1) and 0.222 and 0.241mmolg(-1) at pH 2.2 and 5.7, respectively. This indicates a 1:1 and 1:2 morin/metal ratios at pH 2.2 and 5.7, respectively. Complete elution of the sorbed metal ions was carried out using 10mL (0.5molL(-1) HCl+0.01molL(-1) thiourea) in case of Au(III), Pd(II), Pt(II) and Rh(III) and 10mL 0.5molL(-1) HNO(3) in case of Ag(I). Morin-APSG was successfully employed in the separation and preconcentration of the investigated precious metal ions from some spiking water samples yielding 100-folds concentration factor. The relative standard deviation (R.S.D.) and the T-test (|t|(1)) were calculated.     

Reduced-density-matrix theory: The electron-pair approximation

The form of the K-space representation, , of the 2-matrix for electronic wave functions, which depends strongly on the form of the wave function, is discussed. For Hartree-Fock functions is diagonal, for antisymmetrized products of strongly orthogonal geminal (APSG) functions has N/2 idempotent blocks plus diagonal terms, and for configuration interactions functions is generally non-diagonal. A new proof of the special properties of for APSG functions is given. The 2-matrix of the truncated natural orbital expansion of the Boys ¹ S Be function is presented and discussed in view of the electron-pair approximation. The natural 3-state functions needed in the 1–3 natural expansion of Be are also presented.

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Zusammenfassung Die Form der K-Raum-Darstellung, , der Zweiermatrix für Elektronenwellenfunktionen, die stark von der Form der Wellenfunktion abhängt, wird diskutiert. Für Hartree-Fock-Funktionen ist diagonal, für antisymmetriesierte Produkte von streng orthogonalen Geminalen (APSG) besteht aus N/2 idempotenten Blöcken plus Diagonaltermen, und für Konfigurationswechselwirkungsfunktionen ist allgemein nicht-diagonal. Für die speziellen Eigenschaften von für APSG's wird ein neuer Beweis gegeben. Die Zweiermatrix der abgebrochenen Entwicklung natürlicher Orbitale der Boys'schen ¹ S-Be-Funktionen wird angegeben und im Hinblick auf die Elektronenpaarapproximation diskutiert. Die in der natürlichen 1–3-Entwicklung von Be benötigten 3-Elektronen-Funktionen werden gleichfalls angegeben.

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Résumé On discute la forme de la représentation dans l'espace K, de la matricedensité du second ordre pour des fonctions d'onde électroniques; elle dépend fortement de la forme de la fonction d'onde. Pour des fonctions de Hartree-Fook est diagonal, pour des produits antisymétrisés de fonctions géminales fortement orthogonales (APSG) a N/2 blocs idempotents et des termes diagonaux, pour des fonctions d'interaction de configuration est généralement non-diagonal. Une nouvelle preuve des propriétés spéciales de pour les fonctions APSG est donnée. La matrice du second-ordre du développement tronqué de Boys en orbitales naturelles pour ¹ S Be est présentée et discutée du point de vue de l'approximation par paires. Les fonctions naturelles a 3 états nécessaires au développement naturel 1–3 de Be sont aussi données.

     

On the validity of the electron pair approximation for the Beryllium ground state

The Watson-wave function for the Be ground stats is used to check the necessary conditions — derived previously — for the validity of the antisymmetrized product of strongly orthogonal geminal (APSG) approximation. The agreement between the actual properties of the numerical 1^st and 2^nd order density matrices and those predicted from the APSG scheme is satisfactory, whereas the predictions made in the framework of the antisymmetrized product of identical geminals (APIG) scheme are not at all realized. Correlation adapted orbitals and generating geminals are extracted from the given numerical wave function. The former are compared with the Edmiston-Ruedenberg localized orbitals, the latter with the Be⁺⁺ wave functions.

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Zusammenfassung An Watsons Wellenfunktion für den Be Grundzustand werden die notwendigen Bedingungen für die Gültigkeit der APSG-Näherung getestet, die früher abgeleitet worden waren (APSG=Antisymmetrisiertes Produkt stark orthogonaler Geminale). Die Übereinstimmung zwischen dem tatsächlichen Verhalten der numerischen Dichtematrizen 1. und 2. Ordnung und demjenigen, das vom Standpunkt der APSG-Näherung vorausgesagt wird, ist zufriedenstellend. Überhaupt nicht erfüllt werden allerdings die Voraussagen der APIG-Näherung (APIG=Antisymmetrisiertes Produkt identischer Geminale). Die korrelationsadaptierten Orbitale sowie die erzeugenden Geminale werden, ausgehend von der gegebenen Funktion, konstruiert, und erstere mit den Edmiston-Ruedenbergschen lokalisierten Orbitalen verglichen, letztere mit der Wellenfunktion des Be⁺⁺.

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Résumé On se sert de la fonction numérique de Watson pour l'état fondamental de l'atome de Beryllium pour examiner les conditions nécessaires dérivées antérieurement, qui doivent être satisfaites si l'approximation APSG est valable. Dans le cadre de cette approximation la fonction d'onde peut être représentée comme produit antisymmétrique de géminales fortement orthogonales. Les prédictions faites à partir de ce modèle et les propriétés des matrices densité numériques sont en bon accord. Il n'en est pas autant pour l'approximation APIG où l'on choisit les géminales identiques plutôt que fortement orthogonales. On «extrait» les «orbitales adaptées à la corrélation» aussi bien que les «géminales génératrices» de la fonction numérique. Les premières sont comparées aux «orbitales localisées» d'Edmiston et Ruedenberg, les secondes à la fonction d'onde de Be⁺⁺.

     

Preparation of dendrimer-like polyamidoamine immobilized silica gel and its application to online preconcentration and separation palladium prior to FAAS determination

A amino-terminated G 4.0 dendrimer-like polyamidoamine (PAMAM) immobilized silica gel (PAMAMSG) was prepared with a divergent method by repeating two processes: (1) Michael addition of methyl acrylate (MA) to surface amino groups; and (2) amidation of the resulting esters with ethylenediamine (EDA) from γ-aiminopropyl silica gel (APSG) core. It was then used for the first time as microcolumn packing for the flame atomic absorption spectrometry (FAAS) determination of trace or ultra trace Pd(II), after flow injection (FI) online preconcentration and separation process. A limit of detection (LOD) of 3.9 ng ml⁻¹ was achieved when 0.200 μg ml⁻¹ Pd(II) was preconcentrated in 0.2 mol l⁻¹ HCl medium with a sampling flow rate of 6.0 ml min⁻¹ for 60 s and the relative standard deviation (R.S.D.) was 1.7%. The proposed method was successfully used for the determination of Pd in two metallurgical samples.     

Silica Gel Loaded with <Emphasis Type="Italic">o</Emphasis>-Dihydroxybenzene: Design,Metal Sorption Equilibrium Studies and Application to Metal Enrichment Prior to Determination by Flame Atomic Absorption Spectrometry

The aminopropyl silica gel (APSG) prepared by reaction of activated silica gel with 3-aminopropyltriethoxysilane on reaction with 3,4-dihydroxybenzaldehyde has resulted in a new chelating matrix, o-dihydroxybenzene (DHB) anchored silica gel, which is characterized by IR, TGA and elemental analyses. APSG is characterized with ¹³C CPMAS NMR spectroscopy. DHB anchored silica gel sorbs quantitatively (97.4–99.2% recovery) Cu(II), Pb(II), Fe(III), Zn(II), Co(II), Ni(II) and Cd(II) at pH 6.0–7.5, 5.0–7.0, 5.5–7.0, 6.0–8.0, 6.5–8.0, 5.5–7.0 and 6.5–7.5, respectively. The sorption capacity varies from 32 to 348µmolg^–1 and is highest for copper. Desorption was found to be quantitative with 1.0–3.0molL^–1 HCl/HNO₃ (for Pb). The optimum flow rate of the solution for quantitative sorption of metal ions on a column (10cm×10mm) packed with 1g of the modified silica gel is 1.0–4.0mLmin^–1, whereas for desorption it is 2.0 –4.0mLmin^–1. The tolerance limits for NaCl, NaBr, NaI, NaNO₃, Na₂SO₄, Na₃PO₄, humic acid, EDTA, ascorbic acid, citric acid, sodium tartrate, Ca(II) and Mg(II) in the sorption of all the seven metal ions are reported. The preconcentration factors are between 100 and 300 and t_1/2 values 17min. The present matrix coupled with FAAS has been used to enrich and determine the seven metal ions in river and tap water samples (RSD 1.4–7.0%) and in synthetic certified water samples SLRS-4 (NRC, Canada) with an RSD of 2.73–2.83%. The cobalt present in pharmaceutical vitamin tablets and Zn in milk powder was preconcentrated on DHB anchored silica gel and determined by FAAS (RSD of 2.00 to 2.72%).     

Organically modified silica gel and flame atomic absorption spectrometry: employment for separation and preconcentration of nine trace heavy metals for their determination in natural aqueous systems

A 5-formyl-3-(1′-carboxyphenylazo) salicylic acid-bonded silica gel (FCPASASG) chelating adsorbent was synthesized according to a very simple and rapid one step reaction between aminopropyl silica gel (APSG) and 5-formyl-3-(1′-carboxyphenylazo) salicylic acid (FCPASA) and its adsorption characteristics were studied in details. Nine trace metals viz.: Cd(II), Zn(II), Fe(III), Cu(II), Pb(II), Mn(II), Cr(III), Co(II) and Ni(II) can be quantitatively adsorbed by the adsorbent from natural aqueous systems at pH 7.0–8.0. The adsorbed metal ions can be readily desorbed with 1 M HNO₃ or 0.05 M Na₂EDTA. The distribution coefficient, K_d and the percentage concentration of the investigated metal ions on the adsorbent at equilibrium, C_M,_eqm % (Recovery, R%) were studied as a function of experimental parameters. The logarithmic values of the distribution coefficient, logK_d, are 3.7–6.4. Some foreign ions caused little interference in the preconcentration and determination of the investigated nine metals by flame atomic absorption spectrometry (AAS).The adsorption capacity of FCPASASG was 0.32–0.43 meq g⁻¹. C and N elemental analyses of the adsorbent (FCPASASG) allowed us to calculate a surface converge of 0.82 mmol g⁻¹. This value compares well with the best values reported for the azo compounds. The adsorbent and its formed metal chelates were characterized by IR (absorbance and/or reflectance) and UV spectrometry, potentiometric titrations and thermogravimetric analysis (TGA and DTG). The mode of chelation between the FCPASASG adsorbent and the investigated metal ions is proposed to be due to reaction of those metal ions with the salicylic and/or the carboxyphenylazo chelation centers of the FCPASASG adsorbent. Nanogram concentrations (0.07–0.14 ng ml⁻¹) of Cd(II), Zn(II), Fe(III), Pb(II), Cr(III), Mn(II), Cu(II), Co(II) and Ni(II) can be determined reliably with a preconcentration factor of 100.     

间规聚苯乙烯同质多晶现象的研究

间规聚苯乙烯(ｓＰＳ)是由日本出光公司在1985年首先合成,由于其优良的耐热性(熔点高达270℃),立刻被认为有可能或为下一世纪最重要的工程塑料.独特的分子结构,使间规聚苯乙烯具有密度低、尺寸稳定、耐热性、耐溶剂性好等诸多优点,因而引起研究人员的广泛重视.同时,间规聚苯乙烯存在复杂的同质多晶现象,共有α、β、γ和δ四种晶型.以不同的条件从熔体结晶,间规聚苯乙烯可形成平面锯齿结构的α晶和β晶.其中,α晶属六方晶系,晶胞参数为:ａ=263ｎｍ,ｃ=078ｎｍ;β晶是斜方晶,晶胞参数为:ａ=088ｎｍ,ｂ=263ｎｍ,ｃ=078ｎｍ.与传统的全同聚丙烯…