Frequently Asked Questions about LiqCryst
What is LiqCryst ?
LiqCryst 3.2 is a database for liquid crystalline compounds on personal computers, running with Windows 3.1 or Windows 95/98/NT. It contains the chemical structures and the physical data of all known thermotropic liquid crystals including metallomesogens, combined polymers, lipids, soaps etc. LiqCryst is an expert system, because all information can be used for calculations. It is developed by Volkmar Vill, University of Hamburg. LiqCryst is exclusively available directly from these publishers:
Fujitsu Kyushu System Engineering (FQS) for Asia
LCI Publisher for Europe and America
LiqCryst is not available in bookshops or any other places.
LiqCryst 3.2, the present version, needs about 60 MB memory on a hard disk.
What are the goals of LiqCryst ?
- documentation of all kinds of information on liquid crystals
- analysis and comparison of all properties of liquid crystals
- prediction of physical properties of liquid crystals
What are the sources of information ?
The data is extracted from
All data are carefully checked. The data of the experimental part are compared with the drawings and descriptions in the text and the common knowledge of liquid crystal behavior. Obvious mistakes have been corrected and less trustworthy data is marked.
- PhD theses
- Conference abstracts
The literature quoted is fully extracted. Modern PhD theses are only refered to if the data is not already published in patents or papers.
The references have been found by:
- Keyword search in CAS-Online
- Substructure search in Beilstein
- complete processing of leading journals
- complete processing of PhD theses belonging to LC research groups
- complete processing of international and national abstract books
- references obtained by own research in the field of liquid crystals
What is the difference between LiqCryst and other databases in chemistry and physics ?
- LiqCryst contains data, which is not published in any other system. About 5000 of the compounds included in LiqCryst have been only accessible through PhD theses and about 1000 compounds have been only reported in conference abstracts.
- LiqCryst allows the connection of physical properties (by value) to a chemical structure.
- LiqCryst offers statistical tools for the analysis of structure-properties-relationships, thus LiqCryst is an expert system.
Which compounds are compiled in the data selection ?
- classical calamitic liquid crystals e.g. MHPOBC
- non liquid crystalline compounds, which have been studied in vain for liquid crystal properties
- chiral dopants (for cholesteric and ferroelectric mixtures)
- colorants with mesogenic shape
- amphiphilic liquid crystals (soaps, surfactants, glycolipids)
- discotic liquid crystals
- side chain polymers
- combined polymers
- paraffins and lipids
Which data is collected for a given compound ?
a) chemical structure
- as a list of atoms and bonds
- as a list of fragments (rings, bridges, ...)
- as a line notation (e.g. NC-Ph-COO-Ph-C4H9)
b) phase behavior
c) further physical data
- transitions in the solid state (melting point, glass transition, solid-solid transitions)
- mesophase behavior
- general remarks (decomposition, extrapolated data, unsure data, ..)
- transition enthalpies
- viscoelastic constants
- information about spectroscopy
- dieelectric and optical data
- helical pitch, spontaneous polarization, tilt angles
- superviser (for PhD thesis)
- company (for patents)
- journals: title, volume, first page, publication year
- patent: patent number, application date, patent family information, priority date
- publication year
How is the data evaluated ?
LiqCryst gives a documentation of all published data, even if they are seemly wrong, but LiqCryst selects and evaluates the data used for search functions and statistical methods. Whenever possible, data has been checked for consistency. Where available, data of the same compound, but from different sources has been included. Evident descrepancies, or obvious misinterpretations of textures are commented on. Where more than one set of (divergent) data has been found for a compound, the data that gave the best fit for a homologous series has been included for a search by value, while the divergent data can be found in the further physical data (searchable by text). Where there is more than one reference for a given value in the data sheet, the oldest reference is used as main reference and the other can be found in the file for additional data.
Common proves for a correct set of data are:
a) Correspondence of a compound, concerning the chemical structure and the name, in all parts of a given article and the cited references.
b) Accuracy of values
The trend observed in homologous series, the deviation of the values between reported and predicted value and the occuracy of other data in the same paper are used to evaluate a reported information. (Some papers where discovered to have exclusively imaginary data.) Sometimes, the authors
themselves marked values as questionable.
c) Phase identification
Outdated names (nomenclature of Vorländer) have been replaced by modern termology. Misleading textures description or missing proves for the phase identification are marked in the data set.
What is contained in an update ?
Updates are released twice a year. They contain:
- new data (about 5000 new structures every update)
- new physical data for already registered compounds (about 10000 new entries per
- new types of data (complex physical data, mixtures)
- new functions of the program.
Which properties are searchable ?
a) chemical structures
b) phase transitions
- by structure drawing
- by chemical elements and functional groups
- by general classifications (crown ether, polymer, chiral, ..)
- by similarity
- by trivial names and abbreviations (e.g.: MBBA, 5CB)
- by simple line notation (e.g.: -Ph-COS-Ph-O-CHMe-)
c) further physical data
- by sequence of phases ( e.g.: N -> SmA -> SmC sequence)
- by temperature ranges of mesophases ( e.g.: SmC* between 30°C and 50°C)
- by melting points
- by general classifications (ferroelectric, ..)
d) bibliographical information
- by type of data (enthalpy, elastic constants, ..)
- by text additives (extrapolated data, spectroscopy parameters, ..)
- by reference
- company (by patents)
- supervisor (by PhD theses)
- source (journal, patent number, etc.)
- publication year
- CAS registry numbers (only, if the data is known)
- LiqCryst registry numbers
In which ways are chemical structures described ?
LiqCryst contains two independent representation systems for chemical structures which allows supplementary funcionality:
a) connectivity as defined by atoms and bonds
LiqCryst allows classical substructure search as possible in all other chemistry databases. Furthermore, LiqCryst can interact with all other information systems.
b) linear list of fragments
Fragments are building blocks such as rings, terminal groups, linking groups.
The advantage of fragments is the possibily to compare substructures and to allow a prediction of functions. Besides, fragments are similar to the building blocks used in the synthesis of liquid crystals. Fragments are the origin of mesophase properties, thus the transition temperature of a compound is not a function of 6 carbons and 6 bonds, but a function of a phenyl ring.
Finally, the fragments give every molecule a clear defined sequence of priority in the tables. Fragments allow table display of mesogenic cores and the display of homologes as graphical sketch.
What is the ordering principle for the molecules and the templates(=fragments) ?
a) Order of compounds (as used in the arrangements of the compounds in tables):
- chemical classicication (e.g. classical calamitics < acids < discotics)
- number of rings (-Ph-Ph- < Ph-Ph-Ph- )
- number of bridges (-Ph-Ph- < -Ph-COO-Ph- )
- priority of rings and bridges (-Ph- < -PhCl-
- priority of terminal groups ( -CN < -OMe )
b) Order of rings (as used in the selection windows):
- frequently occuring rings (Ph, Py, Cy, Dio)
- simple rings
- 6 membered aromatic rings, subst. phenyl
- 6 membered heteroaromatic rings
- other aromatic rings
- cyclohexane rings
- other 6 membered aliphatic rings
- other aliphatic rings
- fused ringsystems
- naphthaline, substituted, hetero, aliphatic ..
- other systems with two cycles
- other systems with more than two cycles
- metallo rings
- ionic structures
- polymer crosspoints (-> combined polymers)
This sequence is based on the following order of precedence:
- aromatic > aliphatic ring systems
- 6 membered > 3 membered > 4 membered > 5 memberd > 7 membered ...rings
- unsubst. > deuterated > lateral subst. > hetero subst.
c) Order of the bridges:
- paraffines with ether functions
- paraffines with ester functions
- siloxanes, sulfons,...and metallorganics at the end of the sequence.
Which data is not given ?
- details about the synthesis of the materials (only the reference is given)
Which data can be compared in LiqCryst ?
The transition temperatures for two different chemical substructures can be compared. Future versions will expand this method to other physical data.
Substructures can be defined as:
- different fragments, e.g.: compare cyclohexane with dioxane
- different sequences of fragments e.g.: (any ring)-OOC-(any ring)-COO with (any ring)-SOC-(any ring)-COS
- different line notations, e.g.: Ph-COO-Ph-OOC-Ph with Ph-OOC-Ph-COO-Ph
One can compare the bridge CH=N with the COO fragment under the aspect of the transition temperatures for the nematic phase. LiqCryst creates this table:
The pair of data x,y can be used for statistical analysis by LiqCryst itself or by Excel or other programs.
|structure 1||structure 2||y (temp. of 1)||x (temp. of 2)
Which statistical methodes are used in LiqCryst ?
LiqCryst uses the classical formulas for mean value statistics and linear regressions as described in all statistic books.
This are the methods used by LiqCryst itself, but user is encouraged to develope new methodes.
|x,y ||pair of data (e.g. transition temperature of compound 1 and 2)
|n ||number of pair
|X ||mean value of x
|Y ||mean value of y
|sx ||standard deviation of the x data (scattering of the x values)
|sX ||standard deviation of the X mean value (error of X)
|r ||correlation coefficent for the linear regression function between y and x
|m,b ||parameters of the linear regression functiun (y = m*x + b)
|S ||symbol for the sum of all data sets
|sqr ||square root
|X = ||S x / n
|sx = ||sqr( (S x*x - S x * S x) / n * (n-1) )
|sy = ||sqr( (S y*y - S y * S y) / n * (n-1) )
|sX = ||sx / sqr(n-1) (sX is not used yet in the display)
|m = ||(S x*y - S x * S y / n) / (S x*x - S x * S x / n)
|b = ||(S y - m * S x ) / n
|r = ||m * sx / sy
What is the meaning of the term similarity as it is used within the
database LiqCryst ?
The difference in one fragment is defined as similarity.
C2H5-O-Ph-COO-Ph-CN and C3H7-O-Ph-COO-Ph-CN are similar (difference in the terminal group)
C2H5-O-Ph-COO-Ph-CN and C2H5-O-Ph-CH=N-Ph-CN are similar (difference in the bridge)
C2H5-O-Ph-COO-Ph-CN and C3H7-O-Ph-CH=N-Ph-CN are not similar (two differences)
The search for similar compounds can be used to:
- find interesting compounds for a comparison with compounds that are currently interesting to a research group
- predict physical data
What is the prediction function ?
a) Prediction with classical statistical methods (as used in LiqCryst itself)
The user enters a complete description of the chemical structure, e.g. MeO-Ph-CH=N-Ph-Bu, and defines the requested property, e.g. transition from nematic to isotropic.
The program looks for all similar compounds, which already have this property, e.g.:
|similar compound ||measured value||extrapolation
|MeO-Ph-COO-Ph-Bu ||25 ||50 (by COO/CH=N statistics)
|EtO-Ph-CH=N-Ph-Bu ||80 ||58 (by EtO/MeO statistics)
|.. other molecules ..
All these single extrapolations are summarized and evaluated with the standard deviation of the single statistic to give the final prediction, e.g. 52 ± 6 °C .
b) Prediction using neural nets (as an example for the cooperation).
The data of LiqCryst can be exported to other systems. For example, we could use artifical neural nets to predict transition temperatures.
This is a field for future development.
How can data be exported from LiqCryst ?
- graphical image ("Copy Image" in the edit menu)
The drawing of molecules and diagrams (statistical analysis, homologous series) can be copied via clipboard to programs such as Winword and Excel (Microsoft Corp.).
- numerical data and text ("Copy text" in the edit menu)
The data of compounds, tables, statistics and homologous series can be copied via clipboard to calculation and word proccessing programs.
- chemical drawings ("Copy Image" in the edit menu, "Export MOL-file" in the file menu)
The chemical structure can be exported as MOL-file (MDL Corp.) or copied via clipboard to chemical drawing programs.
How can data be imported into LiqCryst
You can import MOL files as a search query. This MOL files can be created by LiqCryst itself or by programs such as ChemDraw, IsisDraw (MDL Corp.) or other chemistry programs, which allow the export of MOL files or which copies MOL files via clipboard.
Can the user add new data ?
So far this is not possible to add own data to the 3.1 version of LiqCryst. The possibility for the input of data is planed for the next version.
Can LiqCryst run in an local network ?
LiqCryst is a single CPU system. Multiuser licences are available.
What is the development history for LiqCryst and what are the plans for further extensions ?
LiqCryst 1.0: Development Period 1986 to 1992
- high speed
- low system requirements
- based on DOS
- all types of thermotropic liquid crystals
- all types of references
- only single components
- only single data entries
- 9 master files, complex internal structure
LiqCryst 2.0: Development Period 1993 to 1995
- compare functions based on fragments
- graphical interface
- based on Windows 3.1
- simple data structure, but still 9 main files
LiqCryst 2.1: Development Period 2nd Quarter of 1996
- predict function based on simple differences in fragments
- search by connectivity
- search by line notation
- new data fields
- more hard disk space needed (from 15 MB -> 40 MB)
- analysis tools for homologus series
- more details in statistical analysis
- complete new structure (object-oriented structure)
- all compounds in one file instead of nine main files
- huge update
- bio mesogens, carbonaceous mesophase, simple mixtures
- enhanced graphics of molecular structures
- further enhanced graphics of molecular structures
LiqCryst 4.0: Developing Period: future
- technical mixtures
- more details in references
- more CAS-RN numbers
- new program using SciDex database technology
Main Changes made during the development of different versions:
1.0 -> 2.0 graphical interface, DOS -> Windows
2.0 -> 2.1 search by connectivity
2.1 -> 3.0 all compounds in one file, object-oriented system
What are possible cooperations within the LiqCryst development ?
- create a unique decription of data
- exchange registry numbers, cross references to other databases
- create new sources of data
- create new methods for the evaluation of data
Please, contact the author for further questions
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last change 01/09/97, V. Vill