De Vries phase

There are numerous properties which make fluorinated LC attractive for applications. Short Rp-segments lead to de Vries phases and to 90° tilted anti-ferroelectric SmCA phases, useful for orthoconic switching in new display applications. Fluorination could also lead to enhanced polarization in ferroelectric and antiferroelectric LC phases. 

The structure of the so-caUed de Vries phase is shown in Fig. 4.8. It is a uniaxial smectic A phase (group Dooh) with very strong molecular tilt (about 20°) in any... 

Liquid crystal molecules usually tilt in the same direction over the smectic layers (synclinic [212]) in the smectic C (SmC) phase. However, in one of the smectic A (SmA) phases, called de-Vries phase [213,214], molecules tilt but the tile direction is random so that the overall molecular tilt cannot be recognized optically. Frustration can be produced between aligning and random orders [215]. There is another style of tilt, in which the tilting direction is aligning in one direction in each smectic layer however, tilting direction alternates between the adjacent layers (anticlinic [212]). It has been well known that the introduction of chirality into the synclinic and anticlinic stmctures produces the ferroelectric and antiferroelectric properties, respectively. Frustration between the ferroelectric and antiferroelectric properties produces the ferroelectric structure in which the spontaneous polarization is partially canceled by the different magnitude between plus and minus polarization directions [216, 217]. The anticlinic order, NOT the antiferroelectric order, has been reported to be created by achiral systems [218, 219], indicating that the frustration between synclinic and anticlinic structures occurs, without any polar effects. The clinicity is determined by the style of the molecular order between the adjacent smectic layers, and therefore, the molecular structures at the peripheral... 

An important aspect concerning catalytically active membrane reactors, is the distribution of the active phase within the membrane system. Modem modification techniques (van Praag et al. 1989, Lin, de Vries and Burggraaf 1989) allow control over the catalyst distribution and preferential deposition of the active phase at different places in the membrane (top layer/support) system. Studies on conventionally used plate-shaped and cylindrically-sha-ped catalytically active pellets (Vayenas and Pavlou 1987a, b, Dougherty and Verykios 1987) have shown that nonuniformly activated catalysts (catalysts with nonuniform distribution of active sites according to a certain profile)... 

Bos AM, de Vries EC( Dombemovsky P, Aamdal S, Uges DR, Schrijvers D, Wanders J, Roelvink MW, Hanauske AR, Bortini S, Capriati A, Crea AE, Vermorken JB. (2001) Pharmacokinetics of MEN-10755, a novel anthracycline disaccharide analogue, in two phase I studies in adults with advanced solid tumours. Cancer Chemother Pharmacol 48 361-369. 

LC phases usually corresponds to at least the number of attached chains [258]. Moreover, no SmA phases were observed for non-fluorinated polycatenar mesogens, whereas chain fluorination obviously enables the formation of SmA phases, which are most probably of the de Vries type. It seems that non-fluorinated polycatenars are mainly stabilized by core-core interactions, whereas the mesophase stabilization by the fluorophobic effect retains the layer structure even if core-core interactions are relatively weak. 

Goldberg, M. 1937 A class of multi-symmetric polyhedra. Tdhoku Math. J. 43, 104-108. Hedberg, K., Hedberg, L., Bethune, D. S., Brown, C. A., Dorn, H. C., Johnson, R. D. de Vries, M. 1991 Bond lengths in free molecules of buckminsterfullerene, Cso, from gas-phase electron diffraction. Science, Wash. 254, 410-412. 

C. A. T. Brinkman and G. de Vries, Thin-layer chromatography on chemically bonded phases a comparison of precoated plates, J. Chromatogr., 258 43 (1983). 

In all of this work, the samples were prepared by chemical reduction, under conditions where no liquid phase was present and the reaction mixture was completely transformed into a bronze of one or two phases. According to Ingold and de Vries (11), such preparations should lie on the pseudobinary join, W03-NaWOs, whereas bronzes prepared by methods such as electrolytic reduction may contain oxygen in excess of an oxygen-tungsten ratio of 3.0. Chemical analyses for sodium and tungsten at several compositions indicated that our samples have an O/W ratio of 3.0 0.15. Precision lattice constants of those samples which fell in the cubic range (x > 0.40), lay on the same lattice constant-nominal composition plot as reported by Brown and Banks (4). 

The involvement of a dark state in the decay of electronically excited states is not limited to methylated uracil and thymine. In fact, all five nucleic acid bases have demonstrated similar behaviors upon electronic excitation [27, 30]. The possibility of a low lying state that couples with the S2 state has been suggested by Levy and coworkers to explain the broad structureless spectra of uracil and thymine in jet-cooled gas phase experiments [31]. de Vries group has recorded vibrationally resolved... 

De Vries AH, Yefimov S, Mark AE, Marrinck SJ. Molecular structure of the lecithin ripple phase. Proc. Natl. Acad. Sci. U.S.A. 2005 102 5392-5396. 

Wachters FM, Groen HJ, Maring JG, Gietema JA, Porro M, Dumez H, de Vries EG, van Oosterom AT. A phase I study with MAG-camptothecin intravenously administered weekly for 3 weeks in a 4-week cycle in adult patients with solid tumours. Br J Cancer 2004 90(12) 2261-7. 

One such theory considers the statistical accumulation of molecular fracture events, in a plane perpendicular to the applied stress, for an assembly of chains under equal initial stress. Once a small number (say 3 or 4) adjacent chains have broken, the probability of further adjacent fractures increases rapidly and the process moves into a thermal propagation phase. Typical results as cited by Kausch and De Vries are shown in Fig. 3. 

De Vries and Roy (1954) attempted to summarize various data on high-temperature reduction of Ti02, expressing them in the usual form of a phase diagram for the system titanium —oxygen. When considering the section of the diagram adjacent to rutile, spontaneous reduction of TiO ... 

Dross, K., Rekker, R.F., de Vries, G. and Mannhold, R. (1998). The Lipophilic Behaviour of Organic Compounds 3. The Search for Interconnections Between Reversed/Phase Chromatographic Data and log Roct Values. Quant.Struct.-Act.Relat., 17,549-557. 

Fig. 2 The intensity of the (0,1,0.3) X-ray reflection from Ag(ll 1) during Sb deposition at a substrate temperature of 250°C. The sudden rise in intensity at a coverage of 1/3 ML is associated with the formation of the ordered (V3xV3)R30° faulted surface alloy phase as described in the text. From de Vries et al [8]...

Kema IP, Meijer WG, Meiborg G, Ooms B, Willemse PH, de Vries EG. Profihng of tryptophan-related plasma indoles in patients with carcinoid tumors by automated, on-line, solid-phase extraction and HPLC with fluorescence detection. Clin Chem 2001 47 1811-20. 

Figure 3.13. Experimental phase diagram of the Ca0-Xi02-Si02 system according to De Vries et al. (1955).

Reha D, Valdes H, Vondrasek J, Hobza P, Abu-Riziq A, Crews B, de Vries MS (2005) Stmc-ture and IR spectrum of phenylalanyl-glycyl-glycine tripetide in the gas-phase IR/UV experiments ab initio quantum chemical calculations and molecular dynamic simulations. Eur JChem 11 6803-6817... 

Some examples of pyrrolidinium-based ILCs have been reported in recent years, in all cases forming smectic phases, from low ordered SmA phases of de Vries type to highly ordered smectic phases of T type. These will be discussed in the following paragraphs. 

---