Preferential Population Research Articles

Optical rotamers of substituted simple alkanes induced by macroscopic translation-rotational motions

Four substituted simple alkanes – 1-bromo-2-chloroethane, 1-chloropropane, 1,1-dichloropropane, and 1,1,2-trichlorotrifluoroethane – can exist in gauche positive (G), gauche negative (G′), and trans (T) conformers. The G and G′ conformers are optical rotamers, while the T conformer is achiral. Here, the first observation of the preferential population of the optical rotamers in these alkanes induced by the molecular flow through molecular drag pumps is reported. The molecular mechanism of the observed enantiomeric excess of the studied alkanes is rationalized in the general framework of the molecular chirality generated through oriented collisions involving flowing molecules in macroscopic translation-rotational motions induced by a rotating surface.

Clinical benefits TH-302, a tumor-selective, hypoxia-activated prodrug, and gemcitabine in first-line pancreatic cancer (PanC).

265 Background: Gemcitabine (G) is the standard treatment for first- line PanC. PanC is one of the most hypoxic solid tumors. TH-302 is an inert prodrug of brominated isophosphoramide mustard and undergoes selective activation in deep hypoxia. As a single agent, tumor responses were reported in patients (pts) with metastatic melanoma, SCLC, and head/neck cancer at TH-302 weekly doses of 480-575 mg/m2. Methods: Eligible pts for the PanC expansion of this phase I/II study ( NCT00743379 ) had ECOG <1, locally advanced or metastatic PanC previously untreated with systemic chemotherapy other than adjuvant G, 5FU, and/or radiation. IV TH-302 was dosed at 240-575 mg/m2 (240 or 340 in expansion) with standard dose G (1000 mg/m2) on days 1, 8 and 15 of a 28-day cycle. Serum protein and microRNA hypoxia biomarkers were analyzed at baseline, start of cycle 3 and end of study. Results: 46 PanC subjects (12 locally advanced, 34 distant mets); median age: 63 (range 41-83); 24 male; ECOG 0/1 in 29/17 pts; RECIST response rate (RR) of 21%, median PFS of 6.1 mo (95%CI 4.8, 7.7) and median survival of 11.4 mo (95%CI 6.0, not reached) were observed. RR was 23% with median survival of 7.4 mo in pts with distant mets. 52% of pts had a >50% decrease in CA19-9. Common adverse events were skin or mucosal toxicity, nausea, fatigue and vomiting; most grade 1/2. Grade 3/4 neutropenia, thrombocytopenia and anemia in 68%, 64%, and 20% of pts respectively. The dose intensities at 240 mg/m2 and 340 mg/m2 were similar and related to hematologic toxicities. Skin toxicities were less common at 240 mg/m2. A TH-302 dose response was present with higher RR and PFS at 340 mg/m2. Initial serum hypoxia biomarkers did not identify a preferential pt population. Conclusions: The activity and clinical benefits of the combination of TH-302 with G in first line PanC are promising as compared to previous studies of G alone. TH-302 adds to the hematologic toxicity of G, but the regimen is well tolerated. The safety and activity provided rationale for comparing TH-302 plus G versus G alone in a randomized phase II trial ( NCT01144455 ) and indicate TH-302 may complement G by penetrating into the hypoxic regions of the PanC tumors where activation induces cytotoxicity. No significant financial relationships to disclose.

Linear polarization of photon emissions from reflected neutrals of atomic hydrogen at high-Z first wall surfaces

This paper presents theoretical results for linear polarization of 2p–1s and 3d–2p line emission following single electron capture by a proton to excited levels above a W surface. The polarization degrees are evaluated for photons from H outgoing along surface normal with translation velocities of 0.44–2.2×106m/s (corresponding to 1–25keV kinetic energy of H). Negative polarization degrees are obtained for electric-dipole photons emitted at 90° to the surface normal due to preferential population in large m levels of each sub-shell.

Asymmetry and Electronegativity in the Electron Capture Activation of the Se-Se Bond: σ*(Se-Se) vs σ*(Se-X).

The effects of electron capture on the structure of XSeSeX' diselenide derivatives in which the substituents attached to the selenium atoms have different electronegativities have been investigated at different levels of theory, namely, DFT, MP2, CCSD, G2, and CASSCF/CASPT2. An analysis of the bonding changes upon electron attachment shows that when the diselenides bear low-electronegativity substituents, the Se-Se bond becomes activated upon electron capture, as previous studies have shown. However, this is no longer the case for very electronegative substituents, where this bond remains practically unaltered and is the Se-X bond the one which becomes strongly activated through a preferential population of the σ*(Se-X) antibonding orbital rather than the σ*(Se-Se) one. When this is the case, several anionic species are also encountered, namely, stretched, bent, and book structures. The present findings are similar to those obtained for a series of analogous disulfide compounds, which points out that these results are not unique and could be extrapolated to a wider range of compounds than the ones covered here. The Se-Se (Se-X) linkage in CH3SeSeOH, CH3SeSeF, FSeSeOH, and FSeSeF bears some of the characteristics of the so-called charge-shift bonds, with a clear charge fluctuation between both selenium atoms. This is more evident in their anions where the bonding reflects the important contribution of the ionic resonant forms Se-Se(-) ↔ (-)Se-Se vs the covalent component Se∴Se. This resonance changes with the nature of the substituents but also depends on the asymmetry of the substitution.

Scanning probe microscopy study of height-selected Ag/Ge(111) nanomesas driven by quantum size effects

We present scanning tunnel microscope, noncontact atomic force microscopy, Kelvin probe force microscopy, and low-energy electron diffraction study of the morphological evolution of Ag ultrathin films (0.5--6 ML) grown at 150 K on $\text{Ge}(111)\text{\ensuremath{-}}c(2\ifmmode\times\else\texttimes\fi{}8)$ substrate. Although the system has been widely studied in the context of quantum confinement effects in the electronic structure of these films, no real-space imaging has been reported so far. Our results demonstrate that upon annealing to room temperature, the Ag film adopts a (111) epitaxy on top of a wetting layer. It has been found that the Ag film adopts a metastable morphology which is determined by a delicate interplay between thermodynamics and the kinetics of interlayer mass transport. The preferential population of a discrete set of the deposit heights at 6, 10, and 12 ML suggests that quantum size effects are indeed active for the Ag/Ge system. Kelvin probe force microscopy indicates that the surface potential depends monotonically on the film thickness and does not show any oscillatory behavior in correspondence to the height changes.

Comparative vibrational study on alkali coadsorption with CO and O on Ni(111) andCu(111)

High-resolution electron energy loss spectroscopy was used to investigate alkali (Na, K)coadsorption with CO and O on Cu(111) and Ni(111). Measurements providednew insights in these systems. A CO-induced weakening of the alkali–substratebond was revealed on both substrates. The effect is more pronounced for theNa+CO/Ni(111) system. Submonolayers of alkalis were found to promote the preferential population of thesubsurface site for O/Cu(111) but not for O/Ni(111).

Internal Energy Distributions of OH Products in the Reaction of O(3PJ) with HSiCl3

The OH(X 2 II, υ=0, 1) internal state distributions from the reaction of electronically ground state oxygen atoms with HSiCl 3 were measured using laser-induced fluorescence. The ground-state 0( 3 Pi) atoms with kinetic energies above the reaction barrier were produced by photolysis of NO 2 at 355 nm. The OH product revealed strong vibrational population inversion, P(υ=1)/Pυ=0) = 4.0 ± 0.6, and rotational distributions in both vibrational states exhibit substantial rotational excitations to the limit of total available energy. However, no preferential populations in either of the two A doublet states were observed from the micropopulations, which supports a mechanism involving a direct abstraction of hydrogen by the atomic oxygen. It was also found that the collision energy between O and HSiCl 3 is effectively coupled into the excitation of the internal degrees of freedom of the OH product ( = 0.62, and = 0.20). The dynamics appear consistent with expectations for the kinematically constrained reaction which supports the reaction type, heavy + light-heavy → heavy-light + heavy (H + LH'→ HL + H'). The dynamics of oxygen atom collision with HSiCl 3 are discussed in comparison to those with SiH 4 .

Control of H‐ and J‐Type π Stacking by Peripheral Alkyl Chains and Self‐Sorting Phenomena in Perylene Bisimide Homo‐ and Heteroaggregates

The synthesis, self-assembly, and gelation ability of a series of organogelators based on perylene bisimide (PBI) dyes containing amide groups at imide positions are reported. The synergetic effect of intermolecular hydrogen bonding among the amide functionalities and pi-pi stacking between the PBI units directs the formation of the self-assembled structure in solution, which beyond a certain concentration results in gelation. Effects of different peripheral alkyl substituents on the self-assembly were studied by solvent- and temperature-dependent UV-visible and circular dichroism (CD) spectroscopy. PBI derivatives containing linear alkyl side chains in the periphery formed H-type pi stacks and red gels, whereas by introducing branched alkyl chains the formation of J-type pi stacks and green gels could be achieved. Sterically demanding substituents, in particular, the 2-ethylhexyl group completely suppressed the pi stacking. Coaggregation studies with H- and J-aggregating chromophores revealed the formation of solely H-type pi stacks containing both precursor molecules at a lower mole fraction of J-aggregating chromophore. Beyond a critical composition of the two chromophores, mixed H-aggregate and J-aggregate were formed simultaneously, which points to a self-sorting process. The versatility of the gelators is strongly dependent on the length and nature of the peripheral alkyl substituents. CD spectroscopic studies revealed a preferential helicity of the aggregates of PBI building blocks bearing chiral side chains. Even for achiral PBI derivatives, the utilization of chiral solvents such as (R)- or (S)-limonene was effective in preferential population of one-handed helical fibers. AFM studies revealed the formation of helical fibers from all the present PBI gelators, irrespective of the presence of chiral or achiral side chains. Furthermore, vortex flow was found to be effective in macroscopic orientation of the aggregates as evidenced from the origin of CD signals from aggregates of achiral PBI molecules.

The dynamics of OH channel in the 266 and 355 nm photodissociation of 2-nitrophenol

Photodissociation of gaseous 2-nitrophenol at 266 and 355 nm was investigated by probing the nascent OH products with the laser-induced-fluorescence (LIF) technique. Rotational state distributions of the OH photofragments were measured and characterized by Boltzmann temperatures of 900 ± 40 K and 1070 ± 80 K at 266 and 355 nm, respectively. The OH photoproducts were found to be vibrationally cold at both photolysis wavelengths. Preferential populations of the OH F 1 (Π 3/2) spin–orbit state and Π + Λ-doublet state were observed at both photolysis wavelengths. We have proposed a mechanism for OH production involving the photoisomerization to form aci-nitro isomers, which then dissociate into OH fragments.

Magnetic and crystal structure in connection with ferroelectric properties of multiferroicRMn2O5

metal-organic frameworks (MOFs), however, the NTE mechanism in these structurally complicated compounds still eludes in-depth understanding. Here we use X-ray diffraction techniques to elucidate the nature of the isotropic NTE mechanism in the cubic metal-organic framework Zn4O(BDC)3 (BDC = benzenedicarboxylate), also known as MOF-5 or IRMOF-1. Variable temperature synchrotron radiation powder X-ray diffraction data reveal almost linear NTE behaviour in the measured temperature range from 80-500 K with α =dl/ldT=-11.2 ×10 K. Variable temperature single crystal X-ray diffraction (SCXRD) measurement over a broad temperature range has been used to probe the changes in atomic coordinates and vibrational modes causing the NTE behaviour in the framework. The results suggest population of transverse vibrations, similar to the findings in the metal cyanide frameworks [2], with preferential population of vibrational modes out-of-plane of the BDC oxygen atoms and of the BDC aromatic ring. [1] Evans, J. Chem. Soc., Dalton Trans. (1999) 3317 [2] Chapman et al., J. Am. Chem. Soc. (2005) 127, 15630

Photodissociation dynamics of nitrotoluene at 193 and 248 nm: Direct observation of OH formation

The photodissociation of nitrotoluenes at 193 and 248 nm was investigated, employing laser photolysis–laser induced fluorescence technique. OH was observed as a photoproduct on photodissociation of only o-nitrotoluene. At both the wavelengths of photolysis, OH was formed in both vibrationally ground state, v″ = 0, and the excited state, v″ = 1. The energy partitioned as translational energy of the photofragment, on photolysis at 193 and 248 nm, was found to be 15.2 ± 4.0 and 16.0 ± 3.5 kcal/mol, respectively. No preferential population of spin orbit states was observed at both the wavelengths. However, Λ-doublet states show non-statistical distribution at 248 nm photolysis. Various channels of dissociation leading to OH are examined. Based on partitioning of translational energy and Λ-doublet states ratios, OH formation is attributed to different isomers at two wavelengths.

Photodissociation dynamics of n-butyl nitrite at 266 nm: Internal state distributions of nascent NO fragments

Measurements of the nascent NO fragments from the photodissociation of gaseous n-butyl nitrite at 266 nm were performed using the one-photon excited laser induced fluorescence technique. The rotational state distributions of the photofragment NO are found to be well characterized by a Gaussian distribution, which indicates that the photolysis process in the S 2 state is a direct and fast dissociation. The measured relative population of NO v″ = 0:1:2:3 is 0.65:0.19:0.11:0.05, respectively. Preferential populations of the NO Π + Λ-doublet state and F 1( 2Π 1/2) spin-orbit state are observed. The TD-DFT calculations of n-butyl nitrite are in good agreement with the experimental results.

Photodissociation Dynamics of Nitromethane and Nitroethane at 266 nm

Measurements of the nascent OH product from photodissociation of gaseous nitromethane and nitroethane at 266 nm were performed using the single-photon laser induced fluorescence technique. The OH fragment is found to be vibrationally cold for both systems. The rotational state distribution of nitromethane are Boltzmann, with rotational temperature of Trot=2045150 and 1923150 K for both 23/2 and 21/2 states, respectively. For nitroethane, the rotational state distribution shows none Boltzmann and cannot be well characterized by a rotational temperature, which indicates the different mechanisms in producing OH radicals from photodissociation of nitromethane and nitroethane. The rotational energy is calculated as 14.360.8 and 4.980.8 kJ/mol for nitromethane and nitroethane, respectively. A preferential population of the low spin-orbit component (23/2) is observed for both nitromethane and nitroethane. The dominant population of + state in two -doublet states is also observed for both nitromethane and nitroethane, which indicates that the unpaired lobe of the OH fragment is parallel to the plane of rotation.

Neutron scattering studies of hydrogen in potassium–graphite intercalates: Towards tunable graphite intercalates for hydrogen storage

Low-temperature neutron scattering studies on the ternary graphite intercalation compounds KC 24 ( H 2 ) x , x = 1 , 1.5 show low-energy excitations analogous to those seen in CsC 24 ( H 2 ) x and RbC 24 ( H 2 ) x , attributable to the rotational mode of the H 2 split due to the crystal field of the graphene sheets. As in the Cs and Rb-doped systems the hydrogen in KC 24 ( H 2 ) x also occupies two sites. But no preferential population of sites was observed, implying that both sites fill at lower H 2 concentration than in the Cs and Rb systems. Increasing c-lattice spacing by doping with deuterated ammonia has the effect of hindering the H 2 adsorption, underlining the importance of an optimised graphite-charging regime to maximise hydrogen storage capability in these systems.

Measurement of the optically induced spin polarisation of N-V centres in diamond

The nitrogen-vacancy (N-V) colour centre in diamond has an electronic ground state with spin S = 1. The axial crystal field lifts the degeneracy of the spin triplet and the ground state consists of a spin singlet ( S z = 0) and a spin doublet ( S z = ± 1) separated by 2.88 GHz at zero field. Preferential population of the S z = 0 state results when the centre is optically excited from the ground state. Using EPR spectroscopy at low temperature with laser illumination of the sample, we have quantified the degree of spin polarisation. The relevance of these measurements to proposed quantum computing applications of the N-V centre are discussed.

Thermal stability and siting of aluminum in isostructural ZSM-22 and Theta-1 zeolites

Conventional 29Si and 27Al MAS NMR techniques and 27Al two-dimensional Multiple Quantum Magic Angle Spinning (2D MQMAS) NMR technique were used to characterize two isostructural TON type zeolites (Theta-1, ZSM-22). Nonuniform distribution of framework aluminum and the preferential population of T3 and T4 sites by the aluminum atoms in the TON material were established. The aluminum sites of Theta-1 sample showed higher thermal stability compared to ZSM-22 sample, despite of the higher aluminum content and higher calcination temperature. It was shown that 27Al 2D MQMAS NMR technique can be used for monitoring the minute differences in the surrounding of aluminum T sites, caused by the different templates and the post-synthesis treatments.

Alpha-decay of excited states in 13C and 14C

Measurements of the 14C( 13C, 13C[ 9Be+ α]) and 14C( 13C, 14C[ 10Be+ α]) break-up reactions have been made at beam energies of 77.8, 112.25 and 119.25 MeV. The studies were performed with two charged particle telescopes which measured the energy, mass, charge and emission angle of each detected particle. These data provide evidence for α-decaying states at 13.2(1), (13.6(2)), 14.2(1), 15.0(1) and 16.0(1) MeV in 13C and 14.9(1), 15.9(1), 16.5(1), 18.5(3), (19.1(2)), (19.9(2)) and 21.3(4) MeV in 14C. The 13C angular distributions were analysed and give an indication of the parity of the various states populated. These data are interpreted from the perspective of the α-cluster structure of 13,14C, and indicate the preferential population of oblate type cluster states.

Detection of OH radical in laser induced photodissociation of tetrahydrofuran at 193nm

On excitation at 193 nm, tetrahydrofuran (THF) generates OH as one of the photodissociation products. The nascent energy state distribution of the OH radical was measured employing laser induced fluorescence technique. It is observed that the OH radical is formed mostly in the ground vibrational level, with low rotational excitation (approximately 3%). The rotational distribution of OH (v"=0,J) is characterized by rotational temperature of 1250+/-140 K. Two spin-orbit states, 2Pi3/2 and 2Pi1/2 of OH are populated statistically. But, there is a preferential population in Lambda doublet levels. For all rotational numbers, the 2Pi+(A') levels are preferred to the 2Pi-(A") levels. The relative translational energy associated with the photoproducts in the OH channel is calculated to be 17.4+/-2.2 kcal mol-1, giving an fT value of approximately 36%, and the remaining 61% of the available energy is distributed in the internal modes of the other photofragment, i.e., C4H7. The observed distribution of the available energy agrees well with a hybrid model of energy partitioning, predicting an exit barrier of approximately 16 kcal mol-1. Based on both ab initio molecular orbital calculations and experimental results, a plausible mechanism for OH formation is proposed. The mechanism involves three steps, the C-O bond cleavage of the ring, H atom migration to the O atom, and the C-OH bond scission, in sequence, to generate OH from the ground electronic state of THF. Besides this high energy reaction channel, other photodissociation channels of THF have been identified by detecting the stable products, using Fourier transform infrared and gas chromatography.

Integral Characteristics of Vibronic–Spin–Orbit Interactions in a Phosphorus-Containing Analogue of the Fluorene Molecule

The strengths (P00s)2 and FVSO2 of the transitions from the triplet sublevels s = z, y, and x of the electronic state 3A″ of the phenyldibenzophosphole (DB(P-Ph)) molecule are calculated taking into account the intramolecular spin-orbit (SO) and joint vibronic-spin-orbit (VSO) interactions. The contributions to the vibronic transition strengths from the SO interactions in different structural elements of the molecule (the C atoms of the dibenzene framework, the P atom, and the Ph substituent) are determined. The effect of the nonplanar nuclear configuration of the DB(P-Ph) molecule on the values of FVSOs is investigated. The radiative deactivation rate constants of the krads triplet sublevels Ts are estimated. It is found that the vibrations of the A′(B1) symmetry in the fine-structure phosphorescence spectrum of DB(P-Ph) occur due to both the SO coupling exclusively in the P atom and the Tx → S0 transition (the x axis is perpendicular to the planar dibenzene framework of the molecule) with a high (preferential) population of this triplet sublevel.

Lamellar orientation in human cornea in relation to mechanical properties

We have applied wide-angle X-ray scattering to the human cornea in order to quantify the relative number of stromal collagen fibrils directed along the two preferred corneal lamellar directions: superior–inferior and nasal–temporal. The data suggest that, on average, the two directions are populated in equal proportion at the corneal centre. Here, approximately one-third of the fibrils throughout the stromal depth tend to lie within a 45° sector of the superior–inferior meridian, and similarly for the nasal–temporal direction. However, in some eyes we have measured significant differences between the two preferential fibril populations, with some corneas exhibiting as much as 25% more collagen in one direction than the other. Based on these findings, a mechanical model of the normal cornea may be envisaged, whereby the fibril tension in the underlying “background” of isotropically arranged collagen helps to balance the intraocular pressure; while the extra preferentially aligned fibrils take up the additional tensile stress along the superior–inferior and nasal–temporal meridians exerted by the rectus muscles and the orbicularis. It is possible that, through a direct impact on the elastic modulus of the tissue, an imbalance of superior–inferior and nasal–temporal fibrils in some eyes might affect corneal shape.