Ice nucleation by alcohols arranged in monolayers at the surface of water drops

Monolayers of aliphatic long-chain alcohols induced nucleation of ice at temperatures approaching 0 degrees C, in contrast with water-soluble alcohols, which are effective antifreeze agents. The corresponding fatty acids, or alcohols with bulky hydrophobic groups, induce freezing at temperatures as much as 12 degrees C lower. The freezing point induced by the amphiphilic alcohols was sensitive not only to surface area per molecule but, for the aliphatic series (C(n)H(2n + 1)OH), to chain length and parity. The freezing point for chains with n odd reached an asymptotic temperature of 0 degrees C for an upper value of n = 31; for n even the freezing point reached a plateau of -8 degrees C for n in the upper range of 22 to 30. The higher freezing point induced by the aliphatic alcohols is due to formation of ordered clusters in the uncompressed state as detected by grazing incidence synchrotron x-ray diffraction measurements. The diffraction data indicate a close lattice match with the ab layer of hexagonal ice.     

Free energy and temperature dependence of electron transfer at the metal-electrolyte interface

The rate constant of the electron-transfer reaction between a gold electrode and an electroactive ferrocene group has been measured at a structurally well-defined metal-electrolyte interface at temperatures from 1 degrees to 47 degrees C and reaction free energies from -1.0 to +0.8 electron volts (eV). The ferrocene group was positioned a fixed distance from the gold surface by the self-assembly of a mixed thiol monolayer of (eta(5)C(5)H(5))Fe(eta(5)C(5)H(4))CO(2)(CH(2))(16)SH and CH(3)(CH(2))(15)SH. Rate constants from 1 per second (s(-1)) to 2 x 10(4) s(-1) in 1 molar HClO(4) are reasonably fit with a reorganization energy of 0.85 eV and a prefactor for electron tunneling of 7 x 10(4) s(-1) eV(-1). Such self-assembled monolayers can be used to systematically probe the dependence of electron-transfer rates on distance, medium, and spacer structure, and to provide an empirical basis for the construction of interfacial devices such as sensors and transducers that utilize macroscopically directional electron-transfer reactions.     

Molecular recognition by self-assembled monolayers of cavitand receptors

It is shown by angle-resolved x-ray photoelectron spectroscopy that cavitands derived from resorcin[4]arenes provided with four dialkylsulfide chains form stable monolayers on gold surfaces that are well organized by self-assembly. The cavitand headgroups at the surface of the resorcin[4]arene monolayer act as molecular recognition sites for small organic molecules with remarkable selectivity for perchloroethylene (C(2)Cl(4)). Comparative thermal desorption experiments indicate binding sites with high interaction energies of C(2)Cl(4) at the surface of the resorcin[4]arene monolayers. Fast and reversible "host-guest" interactions were found by the monitoring of extremely small mass changes (in the nanogram range) with a quartz microbalance oscillator provided with gold electrodes coated by resorcin[4]arene monolayers.     

Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores

Use of amphiphilic triblock copolymers to direct the organization of polymerizing silica species has resulted in the preparation of well-ordered hexagonal mesoporous silica structures (SBA-15) with uniform pore sizes up to approximately 300 angstroms. The SBA-15 materials are synthesized in acidic media to produce highly ordered, two-dimensional hexagonal (space group p6mm) silica-block copolymer mesophases. Calcination at 500 degrees C gives porous structures with unusually large interlattice d spacings of 74.5 to 320 angstroms between the (100) planes, pore sizes from 46 to 300 angstroms, pore volume fractions up to 0.85, and silica wall thicknesses of 31 to 64 angstroms. SBA-15 can be readily prepared over a wide range of uniform pore sizes and pore wall thicknesses at low temperature (35 degrees to 80 degrees C), using a variety of poly(alkylene oxide) triblock copolymers and by the addition of cosolvent organic molecules. The block copolymer species can be recovered for reuse by solvent extraction with ethanol or removed by heating at 140 degrees C for 3 hours, in both cases, yielding a product that is thermally stable in boiling water.     

Rapid formation of sulfuric acid particles at near-atmospheric conditions

We investigated the formation of new particles in a laboratory study, starting from H2SO4 produced in situ through the reaction of OH radicals with SO2. Newly formed particles were observed for H2SO4 concentrations above 7 x 10(6) per cubic centimeter. At 293 kelvin, a rough estimate yielded a nucleation rate of 0.3 to 0.4 particles per cubic centimeter per second for approximately 10(7) particles per cubic centimeter of H2SO4 (particle size >/= 3 nanometers). These findings are in agreement with observations from the atmosphere. The results demonstrate that under laboratory conditions similar to the atmosphere, particle formation occurs at atmospheric H2SO4 concentration levels.     

Theoretical studies of the energetics and dynamics of chemical reactions

Computational studies of basic chemical processes not only provide numbers for comparison with experiment or for use in modeling complex chemical phenomena such as combustion, but also provide insight into the fundamental factors that govern molecular structure and change which cannot be obtained from experiment alone. We summarize the results of three case studies, on HCO, OH + H(2), and O + C(2)H(2), which illustrate the range of problems that can be addressed by using modern theoretical techniques. In all cases, the potential energy surfaces were characterized by using ab initio electronic structure methods. Collisions between molecules leading to reaction or energy transer were described with quantum dynamical methods (HCO), classical trajectory techniques (HCO and OH + H(2)), and statistical methods (HCO, OH + H(2), and O + C(2)H(2)). We can anticipate dramatic increases in the scope of this work as new generations of computers are introduced and as new chemistry software is developed to exploit these computers.     

Visualization of the molecular Jahn-Teller effect in an insulating K4C60 monolayer

We present a low-temperature scanning tunneling microscopy (STM) study of K(x)C60 monolayers on Au(111) for 3 < or = x < or = 4. The STM spectrum evolves from one that is characteristic of a metal at x = 3 to one that is characteristic of an insulator at x = 4. This electronic transition is accompanied by a dramatic structural rearrangement of the C60 molecules. The Jahn-Teller effect, a charge-induced mechanical deformation of molecular structure, is directly visualized in the K4C60 monolayer at the single-molecule level. These results, along with theoretical analyses, provide strong evidence that the transition from metal to insulator in K(x)C60 monolayers is caused by the Jahn-Teller effect.     

A Synchrotron X-ray Study of a Solid-Solid Phase Transition in a Two-Dimensional Crystal

A measurement and interpretation on a molecular level of a phase transition in an ordered Langmuir monolayer is reported. The diagram of surface pressure (pi) versus molecular area of a monolayer of chiral (S)-[CF(3)-(CF(2))(9)-(CH(2))(2)-OCO-CH(2)-CH (NH(3)(+))CO(2)(-)] over water shows a change in slope at about pi(s)= 25 millinewtons per meter. Grazing-incidence x-ray diffraction and specular reflectivity measurements indicate a solid-solid phase transition at pi(s). The diffraction pattren at low pressures reveals two diffraction peaks of equal intensities, with lattice spacings d of 5.11 and 5.00 angstroms; these coalesce for pi >/=pi(s). Structural models that fit the diffraction data show that at pi> pi(s) the molecules pack in a two-dimensional crystal with the molecules aligned vertically. At pi < pi(s) there is a molecular tilt of 16 degrees +/- 7 degrees . Independent x-ray reflectivity data yield a tilt of 26 degrees +/- 7 degrees . Concomitant with the tilt, the diffraction data indicate a transition from a hexagonal to a distorted-hexagonal lattice. The hexagonal arrangement is favored because the -(CF(2))(9)CF(3) moiety adopts a helical conformation. Compression to 70 millinewtons per meter yields a unit cell with increased crystallinity and a coherence length exceeding 1000 angstroms.     

铁离子掺杂TiO2基自洁净玻璃的制备及性能

用溶胶—凝胶法制备了表面镀有Fe—TiO2光催化薄膜的自洁净玻璃，并利用DTA—TG，XRD，SEM等手段研究了Fe—TiO2光催化薄膜的结构与特征。利用紫外—可见光分光光度计测量了不同镀膜层数的玻璃的透光率。通过光催化降解有机磷农药敌敌畏的水溶液，研究了不同铁含量以及不同镀膜层数对自洁净玻璃光催化活性的影响。研究结果表明：光催化薄膜主要由粒径为几十纳米的Fe3O4和TiO2颗粒构成；铁离子掺杂可以提高自洁净玻璃的光催化活性，在同样镀膜层数(2层)的情况下，[Fe]/[TiO2](摩尔比)＝0．005时的光催化性能最好；当用同样浓度的铁离子掺杂时，镀膜层数为9的光催化活性最高。     

不同免疫程序对MDV抗独特型抗体苗效果的影响

探讨不同免疫程序对MDV（Marek＇s DiseaseVirus,MDV）抗独特型抗体苗抗感染保护的影响.将MDV抗独特型抗体苗用胚内.皮下与单纯皮下相结合的方法免疫SPF鸡,以第二次免疫接种5 d攻毒后, 进行抗感染保护测定,比较各实验组淋巴细胞增生病变,病毒分离及大肠杆菌感染指标等的差异,确定MDV抗独特型抗体苗的免疫程序.结果表明,二种免疫效果相同,抗MD感染保护力达90%.     

Atmospheric lifetimes of long-lived halogenated species

The atmospheric lifetimes of the fluorinated gases CF(4), C(2)F(6), c-C(4)F(8), (CF(3))(2)c-C(4)F(6), C(5)F(12), C(6)F(14), C(2)F(5)Cl, C(2)F(4)C(12), CF(3)Cl, and SF(6) are of concern because of the effects that these long-lived compounds acting as greenhouse gases can have on global climate. The possible atmospheric loss processes of these gases were assessed by determining the rate coefficients for the reactions of these gases with O((1)D), H, and OH and the absorption cross sections at 121.6 nanometers in the laboratory and using these data as input to a two-dimensional atmospheric model. The lifetimes of all the studied perfluoro compounds are >2000 years, and those of CF(3)Cl, CF(3)CF(2)Cl, and CF(2)ClCF(2)Cl are >300 years. If released into the atmosphere, these molecules will accumulate and their effects will persist for centuries or millennia.     

Disorganization of cultured vascular endothelial cell monolayers by fibrinogen fragment D

Fibrinogen fragment D, which is heterogeneous, has several important biological functions. Human fibrinogen fragments D94 (molecular weight, 94,000), D78 (78,000), and E (52,000) were purified. Fragments D78 and D94 but not purified fibrinogen or fragment E specifically caused disorganization of bovine aortic endothelial cells cultured as monolayers. Within 2 hours of exposure to pathophysiological concentrations of fragment D, the confluent endothelial cells retracted from each other and projected pseudopodia. These disturbed cells subsequently became rounded and detached from the substrate. The actin present in stress fibers in stationary monolayer cells was diffusely redistributed in cells with fragment D-induced alterations in morphology. This effect was not observed in monolayers of kidney epithelial cells. The results demonstrate a specific effect of fibrinogen fragment D on the disorganization of cultured vascular endothelial cell monolayers and suggest that fragment D plays a role in the pathogenesis of syndromes with vascular endothelial damage.     

Seeing phenomena in flatland: studies of monolayers by fluorescence microscopy

Monolayers formed at the interface between air and water can be seen with fluorescence microscopy. This allows the phase behavior of these monolayers to be determined by direct observation and opens up the possibility of following the kinetics of phase transformations in two-dimensional systems. Some unexpected morphologies have been discovered that provide information about the nature of monolayer phases and have connections to pattern formation in other systems.     

Porous, crystalline, covalent organic frameworks

Covalent organic frameworks (COFs) have been designed and successfully synthesized by condensation reactions of phenyl diboronic acid {C6H4[B(OH)2]2} and hexahydroxytriphenylene [C18H6(OH)6]. Powder x-ray diffraction studies of the highly crystalline products (C3H2BO)6.(C9H12)1 (COF-1) and C9H4BO2 (COF-5) revealed expanded porous graphitic layers that are either staggered (COF-1, P6(3)/mmc) or eclipsed (COF-5, P6/mmm). Their crystal structures are entirely held by strong bonds between B, C, and O atoms to form rigid porous architectures with pore sizes ranging from 7 to 27 angstroms. COF-1 and COF-5 exhibit high thermal stability (to temperatures up to 500 degrees to 600 degrees C), permanent porosity, and high surface areas (711 and 1590 square meters per gram, respectively).     

Monoclinic hydroxyapatite

The existence of a monoclinic phase of hydroxyapatite, Ca(2)(PO(4))(4)OH, has been confirmed, by single-crystal structure analysis (weighted "reliability" factor = 3.9 percent on |F|(2)). The structure has space group P21/b, a = 9.4214(8) angstroms, b = 2a, c = 6.8814(7) angstroms, and gamma = 120 degrees , and is analogous to that of chlorapatite. The distortions from the hexagonal structure with which the monoclinic structure is pseudosymmetric are similar to those in chlorapatite, including enlargement of that triangular array of oxygen atoms in which the chlorine ion or, in hydroxyapatite, the hydroxyl hydrogen ion is approximately centered. The hydroxyapatite specimen was prepared by the conversion of a single crystal of chlorapatite in steam at 1200 degrees C, was mimetically twinned, and was approximately 37 percent monoclinic.     

Parent volatiles in comet 9P/Tempel 1: before and after impact

We quantified eight parent volatiles (H2O, C2H6, HCN, CO, CH3OH, H2CO, C2H2, and CH4) in the Jupiter-family comet Tempel 1 using high-dispersion infrared spectroscopy in the wavelength range 2.8 to 5.0 micrometers. The abundance ratio for ethane was significantly higher after impact, whereas those for methanol and hydrogen cyanide were unchanged. The abundance ratios in the ejecta are similar to those for most Oort cloud comets, but methanol and acetylene are lower in Tempel 1 by a factor of about 2. These results suggest that the volatile ices in Tempel 1 and in most Oort cloud comets originated in a common region of the protoplanetary disk.     

蛇足石杉茎尖灭菌方法与组织培养的研究

[目的]研究蛇足石杉组织培养的灭菌方法和培养条件。[方法]以野生孢子体茎尖为外植体,先用不同灭菌液单独或配合使用对外植体进行表面灭菌,将表面无菌外植体转到添加多种抗生素和孔雀石绿的培养基上杀灭内生菌,然后将外植体分别接种到不同的培养基上,筛选茎尖培养的最佳灭菌方法和培养条件。[结果]最佳表面灭菌方法为70%乙醇灭菌40 s,0.1%升汞溶液灭菌8 min,70%双氧水溶液灭菌10 min,培养2周,表面无菌率为63%。适宜的杀灭内生菌方法为表面无菌的外植体在附加0.5 mg/L孔雀石绿和100 mg/L抗生素AAS的培养基上培养4~6周,无菌率达52%。适宜的培养基为1/4MS矿质元素+1/2MS有机元素+2%蔗糖+4.5 g/L琼脂,pH5.8。在此培养基上茎尖外植体可生长出新枝,并可再生根。[结论]建立了蛇足石杉茎尖组织培养的灭菌方法且筛选出适合其生长的适宜培养基,为蛇足石杉组织培养的深入研究提供实验基础。     

Synthesis of Graphite and Hydrocarbons by Reaction between Calcite and Hydrogen

The reaction of calcite with hydrogen was investigated over a range of pressure, temperature, and time. The reaction initiates at about 500 degrees C. Its primarily temperature-dependent rateproceeds in a crystallographically anisotropic manner, and reaction products are CaO, Ca(OH)(2), H(2)O, CO, CH(4), C2H(6), and C (graphite), plus a black solid residue that may be hydrocarbon.     

Antibody-mediated bacteriorhodopsin orientation for molecular device architectures

A rational method for constructing highly oriented films of purple membrane (PM) has been established by using two kinds of bispecific antibodies with different antigen-binding sites, one binding to a specific side of bacteriorhodopsin and the other to a phospholipid hapten. A hapten monolayer deposited on a metal electrode was treated with a bispecific antibody solution and incubated with a PM suspension to produce a highly oriented PM film, as confirmed by electron microscopy in which an immunogold labeling technique was used. This antibody-mediated PM monolayer was then used in the construction of a light-sensing photoelectric device. A comparison of the two incorporated PM monolayers showed that highly efficient photocurrents were produced by the PM monolayer whose unidirectionally oriented cytoplasmic surface faces the electrode.     

A Quantum State-Resolved Insertion Reaction: O((1)D) + H(2)(J = 0) --> OH((2) product operator product operator product operator, v, N) + H((2)S)

The O((1)D) + H(2) --> OH + H reaction, which proceeds mainly as an insertion reaction at a collisional energy of 1.3 kilocalories per mole, has been investigated with the high-resolution H atom Rydberg "tagging" time-of-flight technique and the quasiclassical trajectory (QCT) method. Quantum state-resolved differential cross sections were measured for this prototype reaction. Different rotationally-vibrationally excited OH products have markedly different angular distributions, whereas the total reaction products are roughly forward and backward symmetric. Theoretical results obtained from QCT calculations indicate that this reaction is dominated by the insertion mechanism, with a small contribution from the collinear abstraction mechanism through quantum tunneling.