We have recently introduced a new family of materials - metal-organic composites - in which organic molecules, small or polymeric, are entrapped within metals. Besides the basic motivation, namely that these composites have been unknown, the practical motivation is based on the potential ability to tailor metals with any of the properties of the vast library of organic molecules, on the potential to affect the properties of the organic dopant by virtue of immersing it in a sea of electrons, on the potential of creating materials that are “in-between” metal and, say, plastics, and on the potential of the emergence of new properties which are not found in either of the components. Proof-of-concept for these expectations is now rapidly being accumulated. For instance, one can induce unorthodox properties such as having silver which acts as an acid; or having right-handed and left-handed enantiomers of chiral gold and silver; or forming superior catalysts; and more. Two principal methods were developed for the synthesis of these composites, both of which are based on the reduction of the metal-cation in the presence of the molecule to be entrapped. In one method, the process is homogeneous, in that all components, including the reducing agent, are soluble. In the second method, employed in this report, the metal cation is reduced by a heterogeneous dispersion of a sacrificial reducing metal. For instance, solutions of silver and copper salts were treated with metallic zinc powder and gold salt solution was treated with copper powder in the presence of the dopants, either the polymer Nafion or the dye thionin, thus creating various Nafion@metals and thionin@metals. An important property of these composites, is that they are porous; that the dopant is accessible for reaction by substrates diffusing into the composite; and that despite being accessible, the dopant d oes not leach out (even in solvents it is normally soluble in), or leaches out to a negligible extent [1,2].

In the past three years we have developed a new materials technology, which enables one to incorporate and entrap organic molecules and polymers within metals, thus creating a new family of composite materials, which, to the best of our knowledge, has been unknown so far. Various useful applications have been already demonstrated, including both the physical alteration of metal properties, the formation of new catalysts with superior performances, and the induction of new, unorthodox reactivities to the metals. The motivation is based on the fact that organic and bioorganic molecules represent a very rich library of properties that metals are devoid of. One can only imagine the huge potential which can be opened by the ability to tailor to metals with any of the properties of organic molecules. Metals will then have not only the traditional properties and applications, but also many new properties which will merge their classical virtues with the diverse properties of organic molecules. Likewise one expects that the incorporation of a molecule within the sea of electrons of a metal, will affect its physical and chemical properties. The entrapment methodology proved versatile for different types of molecules including hydrophilic and hydrophobic small molecules and polymers, as well as bioactive molecules. So far we have proven the feasibility of the entrapment on silver, copper, gold, palladium and more. Detailed studies employing SEM, XRD, adsorption/desorption measurement, density measurements, TGA and more, provide a tentative picture as of physical caging inside partially closed pores, the walls of which are the faces of nano crystallites.

In summary, molecular level metal-organic hybrid materials comprise the practical opening of a new field within materials science. This new type of materials, at the border between metals and organic molecules, is being created, apparently for the first time. These materials are expected to have an impact wherever metals are used: Catalysis, electrochemistry, magnetism, corrosion protection, and the classical uses of metals as materials.

In recent years we have developed the proposition that structural chemistry is too rich to be described with the coarse binary language of either being or not being symmetric or chiral. We have promoted the notion that it agrees with chemical, biochemical and physical intuition to ask questions such as: “What is the symmetry content of a molecule (the structure of which cannot be described in exact symmetry terms?)“; or, “given a set of chiral molecules, by how much do they differ from each other in their achirality content?”; and so on. Addressing the need to answer this type of structural questions, which are common to many domains of chemistry, we showed that the problem of how to quantify symmetry and achirality is solvable. Towards this goal we have developed the Continuous Symmetry Measure (CSM) and the resulting Continuous Chirality Measure (CCM) methodologies. In essence, the measure quantifies the distance of a given structure from the desired ideal symmetry or from achirality.

This approach already proved to be useful in a number of symmetry/chirality related issues all across chemistry. Examples include:
The application of the symmetry measure as an order parameter in small clusters;
the use of continuous symmetry and chirality in the elucidation of new enzymatic structure/activity correlations;
the quantitative approach to the chirality properties of the cyclic trimer of water and of its enantiomerization pathways;
the analysis of the correlation between the degree of centrosymmetricity and hyperpolarizability;
the quantitative and conceptual analyses of the chirality of large random objects;
the analysis of energy/chirality correlation in the enantiomerization chiral fullerenes;
the analysis of the chirality of crystals;
the elucidation of the relation between the degree of chirality of a catalyst and the enantiomeric excess of the product;
the correlation between pressure and the symmetry of the building blocks of materials;
the correlation between the degree of symmetry and the allowedness of spectral transitions;
the correlation between the degree of symmetry and the energy of tetracoordinated molecules;
and much more.

Three major findings emerged from these studies:

1. The symmetry measure describes the molecular world in a well behaved way: Its trends of change agree with intuition and reflect what is visible to the eye and what has been expected on a qualitative level, before measurement was possible.
2. Hitherto unknown quantitative correlations between symmetry and physical, chemical, biochemical properties have been revealed.
3. Far more than before, the importance of a global-shape descriptor - symmetry - for the quantitative observation and analysis of structural chemistry, in distinction from the classically specific geometry descriptors, has been revealed.

Those who would like to use our programs can find them at http://www.csm.huji.ac.il/.

A novel materials technology has been gradually developed since the early 80’s. It allows the incorporation within ceramic materials organic and bioorganic molecules. Traditionally, this has been impossible, because of the very high temperatures employed in glasses and ceramic technology. Now, the properties of ceramic materials can be altered to create a very wide range of previously unknown materials, by doping of glasses and ceramics with practically each of the millions of organic and bioorganic molecules known today. That development was made possible by the utilization of a room temperature procedure for the preparation of glasses and other ceramics known as the "sol-gel" process. It involves a polymerization reaction (rather then the classical melting technology) in the presence of the host molecule and results in a porous material which has the chemical composition of glass, looks like glass (it is transparent), and behaves like glass. As a consequence of the wide scope of the technology, it touches upon many domains of modern needs. Following are some of the demonstrated applications of the new technology accumulated at The Hebrew University, and by many research groups, worldwide, who followed in our footsteps. These applications can be divided into four major areas:

1. Optics, including filters, colored coatings, luminescent materials, light guides and light collectors, dye-laser components, photochromic materials, hole-burning materials and optical memory materials, non-linear optical materials and liquid crystal materials.
2. Reactive materials, including chemical sensors, catalysts for organic synthesis, reagents (redox, acid-base, etc.), photocatalysts and photoreagents, chemiluminescent materials, and materials for electrochemistry, photoelectrochemistry and electrocatalysis.
3. Bioactive materials, including enzymatic biosensors, bioactive materials for synthesis, bioelectrodes, catalysts based on antibodies and ceramic materials which contain whole cells and cell-extracts.
4. Active adsorbents, including chromatographic materials (special ion-exchangers, indicating materials and more), chemical sponges for medical and environmental uses, immunoadsorbents with entrapped antibodies; and, in opposite direction, materials for controlled release.

The main message is that the chemistry and physics of organic molecules are carryable within ceramic matrices, allowing a plethora of novel and classical applications, and providing new insight on properties of both the organic component and of the matrix itself. Three recent examples follow:

1. A central paradigm in chemistry has been, that a given compound provides a typical, narrowly defined performance (such as indicating a specific pH value). By employing a sophisticated combination of surfactant modified sol-gel materials, Avnir has shown that that a single compound can be viewed in broader terms as carrying a potential library of reactivities which can be realized by properly tailoring the heterogeneous microenvironment. A consequence of this broadening of view is the ability to tailor "dream" molecules from ordinary ones. A specific example concerns acidity constants, where it was shown that, by tailoring intra-cage properties of SiO2 sol-gel materials with surfactants, the acidity constant (Ki) of a given acid can be fine-tuned, pushed to extremes, and placed either at the basic or acidic range of the pH scale.
2. Another important example with far-reaching consequences is the ability to induce in enzyme properties that were not there inherently. An astonishing case here has been the ability to produce enzymatic activity from alkaline phosphatase at the extreme acidity of pH 1(!), whereas, as the name of the enzyme implies, a basic pH is needed for its operation (pH 9.5).
3. It is generally held that opposing reagents cannot be put in one-pot in order to carry out sequences of reactions. Avnir showed that entrapment of reagents in sol-gel matrices enables carrying out simultaneously reactions which otherwise must be carried out as consecutive steps. This methodology enables to put in one-pot acids with bases, oxidants with reductants, catalysts with the reagents that poison them and yet keep them active. Many useful organic synthesis reaction networks (up to four reactions in one pot) have been demonstrated.

Under this topic, various investigations of the role that complex geometry of surfaces and materials has in determining chemical reactivity have been undertaken. The studies, which have included computer simulations, experimental studies and theoretical formulations of these problems, dealt with accessibility analyses in surface derivatizations, dynamics of electronic energy transfer, reactivity of surfaces and particularly of catalysts, x-ray and neutron scattering from disordered systems, polymer structures and polymer adsorption of irregular surfaces, thermodynamics and adsorption isotherms on irregular surfaces, diffusion limited reactions on surfaces, the kinetics of dissolution of drug particles, adsorption kinetics and more.
Recently we are deeply involved in two related topics: The first is the problem of the very limited range of experimentally derived fractals and the very justification of using this term. The second is a search for global explanation for the abundance of these limited range fractals in all domains of the natural sciences. Here we came up with a surprising finding: Randomness in its most elementary and pure forms generates apparent fractal structures over 1-2 decades. We have revealed therefore, that bound randomness exhibits crossover behaviour with near symmetry of dilation.

Both experimental and theoretical work has been conducted to understand the origin of pattern formation at liquid interfaces due to reactions (photochemical, gas/liquid, membranes). The phenomenon we revealed in the early Eighties is perhaps the widest known in the area of spatial chemical patterning, from the point of view of the number of different reactions in which it was found. Detailed analysis of the dynamics of the evolution of the supramolecular patterns was conducted.