Using Water as a Design Element in Crystal Engineering. Host-Guest Compounds of Hydrated 3,5-Dihydroxybenzoic Acid

Thirteen host guest compounds of 3,5-dihydroxybenzoic acid (DHBA) have been structurally characterized. Water molecules occupy the peripheries of a hexagonal void, created with DHBA molecules, and act as ``hooks'' to connect the guest molecules with the host-framework via hydrogen bonding. The ``water hook'' is an OH group acting as a donor. Consequently, the guest molecules were chosen so that they contain good hydrogen bond acceptor functionalities. A number of multicomponent hydrates were isolated with stoichiometries (DHBA)(x)(H2O). (guest),. Of these, compounds with the following as guests were obtained as crystals that were good enough for single crystal work: ethyl acetate (EtOAc), diethyl oxalate, dimethyl oxalate, di(n-propyl) oxalate, diethyl malonate, diethyl succinate, chloroacetonitrile, N,N-dimethyl formamide (DMF), acetone, dimethyl sulfoxide (DMSO), 1-propanol, and 2-butanol. From 2-butanol, a hemihydrate, (DHBA)(2)(H2O), was also obtained concomitantly. Further to guest stabilization, water acts as a good mediator of effective crystal packing and also determines the topology of the host framework. En the present series of compounds, the role of water is wide ranging, and it is not easy to classify it specifically as a host or as a guest.

Crystal engineering: A brief overview

Crystal structures of organic and metal-organic compounds have been determined in enormous numbers over the past century, and at the time of writing this review, the Cambridge Structural Database has just crossed the half million mark. The possibility of designing a particular crystal packing is, however, of more recent origin and the subject of crystal engineering has addressed this possibility, more or less systematically, during the past 30 years. Crystal engineering demands a detailed and thorough knowledge of intermolecular interactions, which act as the supramolecular glue that binds molecules into crystals. It also requires systematic strategies for the design of a crystal, the architectural blueprint as it were. Finally, this enterprise needs to be geared towards a useful property in that the crystal that is being designed is a functional one. All these features of the subject are directly or indirectly connected with the fact that there is a very large database of known crystal structures that is available to the crystal engineer. This review attempts to briefly survey the current scenario in this expanding subject.

Convergence feedback and unstable low frequency oscillations in a simple coupled ocean‐atmosphere model

The role of convergence feedback on the stability of a coupled ocean‐atmosphere system is studied using model III of Hirst (1986). It is shown that the unstable coupled mode found by Hirst is greatly modified by the convergence feedback. If the convergence feedback strength exceeds a critical value, several new unstable intraseasonal modes are also introduced. These modes have very weak dependence on the wave number. These results may explain the behaviour of some coupled models and to some extent provide a mechanism for the observed aperiodicity of the El‐Nino and Southern Oscillation (ENSO) events.

Studies in crystal engineering. Photochemical and crystallographic investigations of bromocoumarins and (±)-7-(p-bromobenzylidene)piperitone

Studies in crystal engineering. Photochemical and crystallographic investigations of bromocoumarins and (±)-7-(p-bromobenzylidene)piperitone

Atmospheric boundary-layer across Hadley and Ferrel cells over the Indian Ocean

A Southern Ocean Pilot cruise covering the latitudes from 10 degrees N to 56 degrees S in the open Indian Ocean was carried out during January February 2004. Surface and upper air data collected during this cruise are reported here. It is shown that the broad features of the atmosphere, in particular that of temperature, follow the tropical and mid-latitude weather expected during January February in this region. However, the atmospheric boundary-layer shows large variations, both in its height and structure between tropics and high latitudes. Strong influence of the surface heat flux on boundary layer structure is clearly seen. Humidity field reveals several local maxima and minima, suggesting a laminated atmosphere with air from different sources moving almost unmixed in adjacent layers.

Engineering behavior of uplifted Smectite-rich Cochin and Mangalore marine clays

The present study aims to assess whether the smectite-rich Cochin and Mangalore clays, which were deposited in a marine medium and subsequently uplifted, exhibit consistency limits response typical of expanding lattice or nonexpanding (fixed) lattice-type clays on artificially changing the chemical environment. The chemical and engineering behaviors of Cochin and Mangalore marine clays are also compared with those of the smectite-rich Ariake Bay marine clay from Japan. Although Cochin, Mangalore, and Ariake clays contain comparable amounts of smectite (32-45%), Ariake clay exhibits lower consistency limits and much higher ranges of liquidity indices than the Indian marine clays. The lower consistency limits of the Ariake clay are attributed to the absence of well-developed, long-range, interparticle forces associated with the clay. Also, Ariake clay exhibits a significantly large (48-714 times) decrease in undrained strength on remolding in comparison to Cochin and Mangalore clays (sensitivity ranges between 1 and 4). A preponderance of long-range, interparticle forces reflected in the high consistency limits of Cochin and Mangalore clays (wL range from 75 to 180%) combined with low natural water contents yield low liquidity indices (typically <1) and high, remolded, undrained strengths and are considered to be responsible for the low sensitivity of the Indian marine clays.

Indian Ocean Dipole: Processes and impacts

Equatorial Indian Ocean is warmer in the east, has a deeper thermocline and mixed layer, and supports a more convective atmosphere than in the west. During certain years, the eastern Indian Ocean becomes unusually cold, anomalous winds blow from east to west along the equator and southeastward off the coast of Sumatra, thermocline and mixed layer lift up and the atmospheric convection gets suppressed. At the same time, western Indian Ocean becomes warmer and enhances atmospheric convection. This coupled ocean-atmospheric phenomenon in which convection, winds, sea surface temperature (SST) and thermocline take part actively is known as the Indian Ocean Dipole (IOD). Propagation of baroclinic Kelvin and Rossby waves excited by anomalous winds, play an important role in the development of SST anomalies associated with the IOD. Since mean thermocline in the Indian Ocean is deep compared to the Pacific, it was believed for a long time that the Indian Ocean is passive and merely responds to the atmospheric forcing. Discovery of the IOD and studies that followed demonstrate that the Indian Ocean can sustain its own intrinsic coupled ocean-atmosphere processes. About 50% percent of the IOD events in the past 100 years have co-occurred with El Nino Southern Oscillation (ENSO) and the other half independently. Coupled models have been able to reproduce IOD events and process experiments by such models – switching ENSO on and off – support the hypothesis based on observations that IOD events develop either in the presence or absence of ENSO. There is a general consensus among different coupled models as well as analysis of data that IOD events co-occurring during the ENSO are forced by a zonal shift in the descending branch of Walker cell over to the eastern Indian Ocean. Processes that initiate the IOD in the absence of ENSO are not clear, although several studies suggest that anomalies of Hadley circulation are the most probable forcing function. Impact of the IOD is felt in the vicinity of Indian Ocean as well as in remote regions. During IOD events, biological productivity of the eastern Indian Ocean increases and this in turn leads to death of corals over a large area.Moreover, the IOD affects rainfall over the maritime continent, Indian subcontinent, Australia and eastern Africa. The maritime continent and Australia suffer from deficit rainfall whereas India and east Africa receive excess. Despite the successful hindcast of the 2006 IOD by a coupled model, forecasting IOD events and their implications to rainfall variability remains a major challenge as understanding reasons behind an increase in frequency of IOD events in recent decades.

Mechanisms of variability and predictability of the tropical coupled ocean-atmosphere system

A conceptual model is proposed to explain the observed aperiodicity in the short term climate fluctuations of the tropical coupled ocean-atmosphere system. This is based on the evidence presented here that the tropical coupled ocean-atmosphere system sustains a low frequency inter-annual mode and a host of higher frequency intra-seasonal unstable modes. At long wavelengths, the low frequency mode is dominant while at short wavelengths, the high frequency modes are dominant resulting in the co-existence of a long wave low frequency mode with some short wave intra-seasonal modes in the tropical coupled system. It is argued that due to its long wavelength, the low frequency mode would behave like a linear oscillator while the higher frequency short wave modes would be nonlinear. The conceptual model envisages that an interaction between the low frequency linear oscillator and the high frequency nonlinear oscillations results in the observed aperiodicity of the tropical coupled system. This is illustrated by representing the higher frequency intra-seasonal oscillations by a nonlinear low order model which is then coupled to a linear oscillator with a periodicity of four years. The physical mechanism resulting in the aperiodicity in the low frequency oscillations and implications of these results on the predictability of the coupled system are discussed.

Transferability of Multipole Charge Density Parameters for Supramolecular Synthons: A New Tool for Quantitative Crystal Engineering

The modularity of the supramolecular synthon is used to obtain transferability of charge density derived multipolar parameters for structural fragments, thus creating an opportunity to derive charge density maps for new compounds. On the basis of high resolution X-ray diffraction data obtained at 100 K for three compounds methoxybenzoic acid, acetanilide, and 4-methyl-benzoic acid, multipole parameters for O-H center dot center dot center dot O carboxylic acid dimer and N-H center dot center dot center dot O amide infinite chain synthon fragments have been derived. The robustness associated with these supramolecular synthons has been used to model charge density derived multipolar parameters for 4-(acetylamino)benzoic acid and 4-methylacetanilide. The study provides pointers to the design and fabrication of a synthon library of high resolution X-ray diffraction data sets. It has been demonstrated that the derived charge density features can be exploited in both intra- and intermolecular space for any organic compound based on transferability of multipole parameters. The supramolecular synthon based fragments approach (SBFA) has been compared with experimental charge density data to check the reliability of use of this methodology for transferring charge density derived multipole parameters.

Prediction of the Indian summer monsoon rainfall using a state-of-the-art coupled ocean-atmosphere model

A state-of-the-art model of the coupled ocean-atmosphere system, the climate forecast system (CFS), from the National Centres for Environmental Prediction (NCEP), USA, has been ported onto the PARAM Padma parallel computing system at the Centre for Development of Advanced Computing (CDAC), Bangalore and retrospective predictions for the summer monsoon (June-September) season of 2009 have been generated, using five initial conditions for the atmosphere and one initial condition for the ocean for May 2009. Whereas a large deficit in the Indian summer monsoon rainfall (ISMR; June-September) was experienced over the Indian region (with the all-India rainfall deficit by 22% of the average), the ensemble average prediction was for above-average rainfall during the summer monsoon. The retrospective predictions of ISMR with CFS from NCEP for 1981-2008 have been analysed. The retrospective predictions from NCEP for the summer monsoon of 1994 and that from CDAC for 2009 have been compared with the simulations for each of the seasons with the stand-alone atmospheric component of the model, the global forecast system (GFS), and observations. It has been shown that the simulation with GFS for 2009 showed deficit rainfall as observed. The large error in the prediction for the monsoon of 2009 can be attributed to a positive Indian Ocean Dipole event seen in the prediction from July onwards, which was not present in the observations. This suggests that the error could be reduced with improvement of the ocean model over the equatorial Indian Ocean.

Patent Price Dynamics in the Context of Patent Age and Patent Latent Variables

The decision to patent a technology is a difficult one to make for the top management of any organization. The expected value that the patent might deliver in the market is an important factor that impacts this judgement. Earlier researchers have suggested that patent prices are better indicators of value of a patent and that auction prices are the best way of determining value. However, the lack of public data on pricing has prevented research on understanding the dynamics of patent pricing. Our paper uses singleton patent auction price data of Ocean Tomo LLC to study the prices of patents. We describe price characteristics of these patents. The price of these patents was correlated with their age, and a significant correlation was found. A price - age matrix was developed and we describe the price characteristics of patents using four quadrants of the matrix, namely young and old patents with low and high prices. We also found that patents owned by small firms get transacted more often and inventor owned patents attracted a better price than assignee owned patents.

Role of organic fluorine in crystal engineering

The design of compounds with novel and improved physico-chemical properties as advanced functional materials with a specific application spectrum requires the knowledge about possible supramolecular packing motifs and their experimental control in crystalline lattice. Besides the structure of the individual molecule, non-covalent interactions play a significant role in the determination of molecular conformation, along with the formation of three-dimensional supramolecular architecture in a crystal as a requirement for molecular recognition processes, and the related bioactivity. Involvement of functional groups will contribute to the formation of a predefined packing motif due to their well-defined interactions. The strength and directionality of these interactions create characteristic packing motifs, which can be used for the design of supramolecular arrangements by the development of appropriate strategies for the precise control of their topology. Most relevant of these non-covalent interactions are stacking interactions and hydrogen bonds, which have been subjects of extensive study in the last two decades. In recent literature, substantial efforts have been put in by various researchers towards the understanding of interactions involving organic fluorine and the role they play in generating different packing motifs which guides assembling of molecules in the crystal lattice.