The Teacher Academy in the Natural Sciences (TANS) provided middle school (U.S. Grades 6-8) teachers (N581) with intensive professional development (PD) in chemistry, geosciences, and physics, with teachers enrolled in one scientific discipline per year. Because some teachers were retained and rotated into different disciplines, the TANS program investigated retention of science content 1-2 years beyond an instructional year. All teacher participants exhibited significant gains (p<.001), in chemistry, geosciences, or physics content, between their incoming knowledge and the 10-day summer academy's conclusion. Chemistry and geosciences content were retained until the end of the PD year. Physics participants reported a significant loss (p<. 001), although gains from teachers' incoming knowledge were still significant. When retention was measured beyond the instructional year, only the geosciences content was retained. Chemistry and physics gains were not retained, with no significant differences between incoming teachers' knowledge and content 1-2 years post instruction. Our research indicates that science content support is needed after PD programs, and importantly, that the support differs between scientific disciplines.

The Teacher Academy in the Natural Sciences (TANS) provided middle school (U.S. Grades 6-8) teachers (N = 81) with intensive professional development in chemistry, geosciences, and physics through 13 days of face-to-face instruction that was extended with 2 online science modules per discipline. Because we administered online module assessments before the summer academy (pretest), after the summer academy (Post 1), and after the online module was assigned (Post 2), we were able to analyze via dependent t tests the learning components contributed by the online module. Only 1 geosciences module resulted in significant gains after it was assigned. Other modules (2 physics, 1 geosciences) resulted in gains before module assignments, at the end of the 10-day summer academy. Although the 2 chemistry modules exhibited positive score increases, no significant gains were made. Calculated Pearson correlation coefficients revealed no association between participants' online access times and science content gains. This research documents benefits of hybrid teacher professional development programs and offers recommendations for their optimized effectiveness, including more consistent instructor/participant online access.

Para-aryl-dithiols (PADTs, HS-(C6H4)(n)-SH, n = 1, 2, and 3) have been used extensively in molecular electronics, surface-enhanced Raman spectroscopy (SERS), and quantum electron tunneling between two gold or silver nanoparticles (AuNPs and AgNPs). One popular belief is that these dithiols cross-link noble metal nanoparticles (NPs) as monolayer dithiolate spacers. Reported herein is our finding that PADTs predominantly exist as monothiolate forms on AuNPs or AgNPs. No PADT-induced NP cross-linking was observed regardless of the NP/PADT concentration ratios. Moreover, only one PADT thiol can be deprotonated even when PADTs are treated with concentrated NaOH or AgNO3 solutions. In contrast, 1,4-benzenedimethanethiol (HS-CH2-(C6H4)(1)-CH2-SH) and alkyl dithiol 1,2-ethanedithiol can be dithiolated on AuNPs and AgNPs, and in excess NaOH and AgNO3 solutions. This study should be of broad importance for plasmonic NP research given the popularity of PADTs in molecular electronics and SERS applications.

A computational study of dimers of heterosubstituted sumanenes has been carried out using a dispersion-corrected density functional theory method. In the heterosubstituted systems, the three bridging CH2 groups of sumanene have been replaced by O, NH, and S. For each dimer system, two motifs, staggered and eclipsed forms, were considered. The most stable geometry was the staggered stacked concave–convex motif where one monomer was rotated by 60° from the eclipsed configuration. The calculated binding energies and equilibrium distances of the staggered concave–convex dimers are predicted to be 20.1 kcal/mol and 3.7 Å for the parent sumanene molecule, 17.4 kcal/mol and 3.8 Å, 12.3 kcal/mol and 3.7 Å, and 16.6 kcal/mol and 3.7 Å for the NH-, O-, and S-substituted analogs, respectively. The binding energies of the dimers have been analyzed in terms of dipole–dipole contributions, dispersion contributions, and C–H···π interactions.

A series of neutral and protonated five-membered ring cyclic ketene acetals have been examined computationally for any trends in nucleophilicity in the exocyclic methylene and for their ground state geometries. A total of 58 different species were examined, 29 neutral molecules and the corresponding 29 protonated species. The heteroatoms that were used in the heterocyclic ring were a combination of nitrogen, phosphorus, and arsenic from the pnictogen family and oxygen, sulfur, and selenium from the chalcogen family. All geometries were initially optimized at using density functional theory and all stationary points were confirmed to be either minima or transition states through vibrational analysis. All the geometries were consequentially optimized using Møller–Plesset second order perturbation theory with a polarized triple zeta basis set. The main focus of the study was the nucleophilicity of the exocyclic methylene carbon atom and its dependence on heteroatom substitution. As probes for nucleophilicity, the proton affinities of the neutral species, the bond lengths of the exocyclic double bond, and atomic charges were used. The study also resulted in some interesting molecular geometries.

Sumanene, C21H12, the second smallest “buckybowl,” is a bowl-shaped fragment of buckminsterfullerene, C60. It can be described as a slice of buckminsterfullerene with 21 carbon atoms with all vacant valences terminated by hydrogens. A computational study of dimers of the sumanene molecule has been carried out. The concave–convex surface arrangement is the most favorable arrangement, and the binding energy and the equilibrium distance for the most stable conformation of the sumanene dimer are predicted to be 19.3 kcal/mol and 3.7 Å, respectively. The most stable geometry was the staggered stacked concave–convex motif, where one monomer was rotated by 60° from the eclipsed conformation. The binding energy of the eclipsed concave–convex dimer is predicted to be 16.7 kcal/mol with an equilibrium distance between the monomer units of 3.8 Å. At the MP2 level, the basis set superposition errors are quite large, 3–5 kcal/mol at the equilibrium distance depending on the basis set. The basis set superposition errors are smaller for dispersion-corrected density functional methods.

The potential energy surfaces of both singlet and triplet B 2 N 2 have been investigated computationally at the coupled-cluster level with a polarized triple zeta basis set augmented with diffuse functions. Calculated vibrational frequencies and intensities are also reported. The triplet species are consistently more stable than their singlet analogs and the stabilities of the linear B 2 N 2 isomers increase with increasing number of B–N bonds. The most stable isomer is the linear triplet BNBN isomer with a rhombic form with a short diagonal BB distance close in energy. Our results are consistent with the results of the matrix IR studies of Andrews et al. nucleus-independent chemical shift (NICS) values were calculated for the singlet D 2h rhombic form and its C 2v dication, and these were compared to those of the D 2h cyclobutadiene and its D 2d dication, respectively. Electron density plots for the linear and rhombic B 2 N 2 minima showed similar distributions for the singlet and triplet states. These plots confirmed weak BB bonding interactions in both rhombic forms but larger BN bond orders.

Coupled-cluster investigations (CCSD/cc-pVDZ and CCSD/cc-pVQZ//CCSD/cc-pVDZ) of singlet cyclobutadiene and fifteen-substituted analogs were conducted. A local minimum with a square frame does not exist on their potential surfaces. The well-known rectangular D2h minimum, the square D4h transition state, and two additional stationary points were found on cyclobutadiene’s potential surface. This included a transition state with a rhombic carbon ring and C2h symmetry, separating two equivalent puckered C2v local minima. The predicted barriers were 19.7 and 19.8 kcal/mol at the CCSD/cc-pVDZ and CCSD/cc-pVQZ//CCSD/cc-pVDZ levels, respectively. The relative strain energies of rectangular D2h cyclobutadiene and all fifteen-substituted analogs were obtained from isodesmic reactions. Progressive substitution with methyl or BH2 groups continuously lowers ring strain while increasing substitution with fluorines or trifluoromethyl groups steadily increases ring strain. C4(BH2)4 is 16.6 and 13.3 kcal/mol less strained than cyclobutadiene while C4F4 is 17.7 and 21.5 kcal/mol more strained at the levels above. Cyclobutadiene is more strained than both cyclopropene and cyclobutene by 12.2 and 37.0 kcal/mol, respectively. Electron density contours indicate that fluorine substitution raised the electron density especially in the short C=C ring bonds above/below the ring plane (π-electrons) but not in the ring plane (σ-electrons). BH2-substitutions lower the ring π-electron density with little effect in the ring plane. Methyl substituents have little effect on electron densities. All rings retain a strong bond alternation tendency (rectangular) whether substituted with electron-donating or -attracting groups. One-bond coupling constants and the percent p-character in ring C-to-C and C-to-substituent bonds are described.

The molecule [1.1.1]propellane and its neutral boron, nitrogen, oxygen, sulphur, S–O, and SO2 analogs as well as the methyl, hexafluoro, and tri-carbonyl substituted derivatives have been investigated by theoretical calculations at the coupled-cluster singles and doubles level with an augmented polarized double zeta basis set. The geometries were optimized and vibrational analysis was carried out for each species. The main objective of this study was to determine the relative strain in these systems, which in turn is a predictor of stability and reactivity providing valuable information about potentially viable synthetic targets. The systems with the least strain are the nitrogen, boron and the S–O analogs, whereas the SO2 substituted molecule and the hexafluoride and tricarbonyl substituted analogs exhibited the largest amount of strain. Geometrical features are also investigated and it is demonstrated that non-bonded repulsive interactions contribute significantly to the strain in some of the systems since cage-like structures force relatively short non-bonded distances.

A systematic computational study of four-membered cyclic ketene – O,O – , – O,S – , – O,N – , – S,N – and – N,N -acetals as well as their protonated analogs have been performed at the second order Möller Plesset level with a polarized triple zeta basis set. The main purpose of this study was to make predictions about the nucleophilicity of these systems and the variations in nucleophilicity with the hetero atoms. Our calculations suggest that all six target molecules are good nucleophiles, and that the N,N analog is the strongest and the S,S analog the weakest nucleophile. Our results include molecular geometries, bond lengths, proton affinities, vibrational frequencies, and calculated charges.

High level ab initio calculations on the eclipsed concave–convex corannulene dimer yielded a binding energy of 15.5 kcal/mol with a monomer–monomer distance of 3.69 Å at the (extrapolated) counterpoise corrected QCISD(T)/aug-cc-pVTZ level. Single point calculations at the CCSD(T) level demonstrated that CCSD(T) and QCISD(T) results for the binding energy are virtually identical. Dispersion corrected DFT functionals (B97-D, M06-2X and ωB97X-D) combined with the cc-pVQZ basis set gave reasonable estimations of the binding energies and minimum energy separation of the monomers. Studies of several other motifs of the corannulene dimer were also carried out at the B97-D/cc-pVQZ level.

All traditional methods for electron correlation share a steep power law dependence on the molecular size. This high scaling prohibits the use of these methods to large systems in spite of the very impressive advances in computer technology over the past decades. Clearly, this problem cannot be solved with improvements of computers alone, and new methods reducing the power law scaling to one or near one must be developed. In this chapter some linear of low scaling methods for electron correlation will be reviewed. The focus will be on the linear scaling MP2 methods, but other more accurate correlation methods will also be briefly discussed. In addition, the very efficient R1-MP2 will be discussed even though the high power law scaling of conventional MP2 has not been reduced. A discussion of the R1-MP2 method has been included since it is perhaps an order of magnitude more efficient than other efficient MP2 methods. The RI or density fitting approach has now been combined with the local correlation method, and the R1-LMP2 method exhibits linear scaling with the size of the system. Most of the methods discussed herein are based on the local correlation method introduced by Pulay and Saebo in the early eighties and developed further by Schutz, Werner and co-workers. The topic was reviewed in 2002 and this review will focus on the more recent advances in this field. A new linearly scaling LMP2 approach yielding essentially identical results to conventional canonical MP2 will be described, and MP2 calculations with around 5,000 contracted basis functions have been performed without density fitting using this approach.

Malondialdehyde (MDA) is a biomarker of lipid peroxidation that has been widely associated with food rancidity as well as many human diseases. Most current MDA detection methods involve MDA reaction with thiobarbituric acid (TBA), followed by UV–visible and/or fluorescence detection of high-performance liquid chromatography (HPLC)-separated TBA–MDA. Herein, we report the first proof-of-concept study of surface-enhanced Raman detection of a TBA–MDA adduct using silver nanoparticles as the SERS substrate and the 632.8 nm HeNe laser as a Raman excitation source. Current SERS detection limit of TBA–MDA is 0.45 nM, ~100 times higher than the 36 nM fluorescence sensitivity recently reported with the HPLC-purified TBA–MDA. Molecular specificity of the SERS technique was studied by comparing the SERS spectrum of TBA–MDA with those acquired with TBA adducts of other TBA-reactive compounds (TBARCs) that includes formaldehyde, acetaldehyde, butyraldehyde, trans-2-hexenal, and pyrimidine. Compared to TBA and TBA adducts with those TBARCs, the SERS activity of TBA–MDA adduct is significantly higher. The possibility of direct SERS detection of TBA–MDA in a reaction mixture (without HPLC separation) has also been investigated.

The structures of endohedral complexes of the polyhedral oligomeric silsesquioxane (POSS) cage molecule (HSiO3/2)12, with both D 2d and D 6h starting cage symmetries, containing the atomic or ionic species: Li0, Li+, Li−, Na0, Na+, Na−, K0, K+, K−, F−, Cl−, Br−, He, Ne, Ar were optimized by density functional theory using B3LYP and the 6-311G(d,p) and 6-311 ++G(2d,2p) basis sets. The exohedral Li+, Na+, K+, K−, F−, Cl−, Br−, He, Ne, Ar complexes, were also optimized. The properties of these complexes depend on the nature of the species encapsulated in, or bound to, the (HSiO3/2)12 cage. Noble gas (He, Ne and Ar) encapsulation in (HSiO3/2)12 has almost no effect on the cage geometry. Alkali metal cation encapsulation, in contrast, exhibits attractive interactions with cage oxygen atoms, leading to cage shrinkage. Halide ion encapsulation expands the cage. The endohedral X@(HSiO3/2)12 (X = Li+, Na+, K+, F−, Cl−, Br−, He and Ne) complexes form exothermically from the isolated species. The very low ionization potentials of endohedral Li0, Na0, K0 complexes suggest that they behave like “superalkalis”. Several endohedral complexes with small guests appear to be viable synthetic targets. The D 2d symmetry of the empty cage was the minimum energy structure in accord with experiment. An exohedral fluoride penetrates the D 6h cage to form the endohedral complex without a barrier.

This article describes the capabilities and performance of the latest release (version 4.0) of the Parallel Quantum Solutions (PQS) ab initio program package. The program was first released in 1998 and evolved from the TEXAS program package developed by Pulay and coworkers in the late 1970s. PQS was designed from the start to run on Linux-based clusters (which at the time were just becoming popular) with all major functionality being (a) fully parallel; and (b) capable of carrying out calculations on large-by ab initio standards-molecules, our initial aim being at least 100 atoms and 1000 basis functions with only modest memory requirements. With modern hardware and recent algorithmic developments, full accuracy, high-level calculations (DFT, MP2, CI, and Coupled-Cluster) can be performed on systems with up to several thousand basis functions on small (4-32 node) Linux clusters. We have also developed a graphical user interface with a model builder, job input preparation, parallel job submission, and post-job visualization and display.

Dimers of corannulene, a curved, saucer shaped molecule, were Studied by theoretical calculations using second order Moller-Plesset perturbation theory and a large polarized triple zeta basis set. Three dimer motifs were investigated: the "native" dimer is the concave-convex stacking of two monomers with the geometries of both monomers conserved; the "planar" motif with both monomers forced to be planar; and the "C-60-like" dimer where the outer monomer has the native geometry while the inner one has the curvature of buckminsterfullerene C-60. Both staggered and eclipsed conformations of the dimers were investigated. Our calculations show that the binding energy of the native concave-convex corannulene dimer is quite substantial (17.2 kcal/mole at the "best" SCS-MP2/cc-pvtz level of theory) with ail equilibrium distance of about 3.64 angstrom. Surprisingly, there are only minor differences in both binding energies and equilibrium distances between the three different dimer motifs. This Suggests that the curvature of the conjugated carbon networks does not disable their ability to form pi-pi stacked assemblies similar to the planar systems. However, in contrast to the planar systems, at least part of the binding energies in the stacked curved systems can be attributed to attractive electrostatic dipole-dipole contributions since buckybowls exhibit significant dipole moments. For the "planar" dimer, a staggered arrangement of the two monomers is preferred, while eclipsed conformations are the most stable for all Curved dimers. For all systems, the basis set superposition errors are large (ca. 7 kcal/mol) at the equilibrium distance even with Our largest basis sets. (C) 2008 Wiley Periodicals, Inc. Int J Quantum Chem 109: 65-72, 2009

Cyclic ketene acetals are a class of organic molecules characterized by a nucleophilic exo-methylene carbon attached to a carbon with two adjacent O, N, or S atoms. We have carried out a systematic computational study of a series of five-membered cyclic acetals like 2-methylene-1,3-dioxolane and its OS, SS, NO, NS, and NN analogs as well as all the protonated species. The calculations were performed at the MP2 level using a triple zeta plus polarization basis set. The nucleophilicity was discussed in terms of geometrical factors, calculated atomic charges, calculated chemical shifts, and proton affinities. All the six neutral species were strong nucleophiles. The NN analog was predicted to be the strongest and the SS analog the weakest nucleophile.

Dimers of corannulene, a curved, saucer shaped molecule, were studied by theoretical calculations using second order Møller‐Plesset perturbation theory and a large polarized triple zeta basis set. Three dimer motifs were investigated: the “native” dimer is the concave‐convex stacking of two monomers with the geometries of both monomers conserved; the “planar” motif with both monomers forced to be planar; and the “C 60 ‐like” dimer where the outer monomer has the native geometry while the inner one has the curvature of buckminsterfullerene C 60 . Both staggered and eclipsed conformations of the dimers were investigated. Our calculations show that the binding energy of the native concave‐convex corannulene dimer is quite substantial (17.2 kcal/mole at the “best” SCS‐MP2/cc‐pvtz level of theory) with an equilibrium distance of about 3.64 Å. Surprisingly, there are only minor differences in both binding energies and equilibrium distances between the three different dimer motifs. This suggests that the curvature of the conjugated carbon networks does not disable their ability to form π‐π stacked assemblies similar to the planar systems. However, in contrast to the planar systems, at least part of the binding energies in the stacked curved systems can be attributed to attractive electrostatic dipole‐dipole contributions since buckybowls exhibit significant dipole moments. For the “planar” dimer, a staggered arrangement of the two monomers is preferred, while eclipsed conformations are the most stable for all curved dimers. For all systems, the basis set superposition errors are large (ca. 7 kcal/mol) at the equilibrium distance even with our largest basis sets. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

The geometries of the polyhedral oligomeric silsesquioxane (T12-POSS) cage, (HSiO3/2)12, containing the endohedral transition metal atoms or ions: Sc0,+1,+,2, Ti0,+2, Cr0,+1,+2, Mn0,+1,+2 Fe0,+1,+2, Co0,+1+,2, Ni0,+1,+2, Cu0,+1,+2, Zn0,+1,+2 Mo0 and W0,+1,+2 have been optimized at the B3LYP/6-311G(d,p) level of theory. The density functional theory (DFT) calculations predict that all these transition metal species form endohedral complexes within the T12-POSS cage. The inclusion energies, electronic properties, the HOMO–LUMO gaps, and ionization potentials of these endohedral transition metal T12-POSS complexes and their 31Si and 1H chemical shifts of (SiHO3/2)12 are predicted and discussed.

The equilibrium geometries of the exohedral and endohedral complexes of the polyhedral oligomeric silsesquioxane (POSS) cage (HSiO3/2)(8) containing the transition metal atoms or ions Sc-0,Sc-+, Cr-0,Cr-+, Fe-0,Fe-+, Co-0,Co-+, Ni-0,Ni-+, Cu-0,Cu-+, Zn0.+, Mo-0,Mo-+, W-0,W-+, Ru-0,Ru-+, Os-0,Os-+ have been investigated at the B3LYP/LanL2DZ levels. All these species form endohedral complexes with the T-8-POSS cage except Sc-0,Sc-+, Mo-0, and W-0,W-+. The Mo-0 and W-0,W-+ species as well as Cr-0,Cr-+, Fe-0,Fe-+, Co-0,Co-+, Ni-0,Ni-+, Cu+, Zn+, Ru-0,Ru-+, Os-0 form stable exohedral complexes. Geometries, electronic properties and ionization potentials were computed. The Si-O and Si-H bond lengths in the cationic endohedral complexes are shorter than in the corresponding complexes of neutral transition metal atoms. The zero-point corrected inclusion energies of the endohedral species X@(SiHO3/2)(8) (X = Fe+, Co+, Nil, Cu+, Os+) are all negative, suggesting that these complexes are more stable than their isolated components. All exohedral complexes have energies that are lower than their corresponding endohedral analogs. Transition metal atom encapsulation raised the HOMO and lowered the LUMO energies, reducing the HOMO-LUMO gaps of every complex compared to that of the pure cage. The HOMO-LUMO gap of the empty cage is 8.1 eV while the endohedral complexes exhibit gaps between 1.2 and 4.96 eV. Insertion of Cr, Fe, Co, Ni, Cu, or Zn into the POSS cage is more favorable in water than in the gas phase. However, insertion of Co+, Ni+, Cu+, or Zn+ into the POSS cage is less favorable in water than in the gas phase. Overall, both the neutral and ionic endohedral transition metal complexes, X@(SiHO3/2)(10). (X = Cr0.+, Fe-0,Fe-+, Co-0,Co-+, Ni-0,Ni-+, Cu-0,Cu-+, Zn-0,Zn-+, Ru-0,Ru-+, Os-0,Os-+) appear to be viable synthetic targets.