Hydrated history

Sometimes it can be difficult to know if the system has come to a true equilibrium concerning water distribution. It has been noted that water adsorption isotherms sometimes show hysteresis effects, which means that the water content, for example, that bound to the enzyme, depends not only on the water activity, but also on the hydration history [6]. More water is thus bound if a specified water activity is approached from a higher value (dehydration direction) than if the enzyme is hydrated from a drier state. The hysteresis effects might be due to slow conformational changes in the enzyme. 

There has been a general consensus among hydrate researchers that hydrates retain a memory of their structure when melted at moderate temperatures. Consequently, hydrate forms more easily from gas and water obtained by melting hydrate, than from fresh water with no previous hydrate history. Conversely, if the hydrate system is heated sufficiently above the hydrate formation temperature at a given pressure, the memory effect will be destroyed. Some experimental observations of the memory effect phenomenon are summarized in Table 3.3. 

The definition above is a particularly restrictive description of a nanocrystal, and necessarily limits die focus of diis brief review to studies of nanocrystals which are of relevance to chemical physics. Many nanoparticles, particularly oxides, prepared dirough die sol-gel niediod are not included in diis discussion as dieir internal stmcture is amorjihous and hydrated. Neverdieless, diey are important nanoniaterials several textbooks deal widi dieir syndiesis and properties [4, 5]. The material science community has also contributed to die general area of nanocrystals however, for most of dieir applications it is not necessary to prepare fully isolated nanocrystals widi well defined surface chemistry. A good discussion of die goals and progress can be found in references [6, 7, 8 and 9]. Finally, diere is a rich history in gas-phase chemical physics of die study of clusters and size-dependent evaluations of dieir behaviour. This topic is not addressed here, but covered instead in chapter C1.1, Clusters and nanoscale stmctures, in diis same volume. 

The history of iaclusion compounds (1,2) dates back to 1823 when Michael Faraday reported the preparation of the clathrate hydrate of chlorine. Other early observations iaclude the preparation of graphite iatercalates ia 1841, the P-hydroquiaone H2S clathrate ia 1849, the choleic acids ia 1885, the cyclodexthn iaclusion compounds ia 1891, and the Hofmann s clathrate ia 1897. Later milestones of the development of iaclusion compounds refer to the tri-(9-thymotide benzene iaclusion compound ia 1914, pheaol clathrates ia 1935, and urea adducts ia 1940. 

Historical Introduction and Perchlorates in General History. The early history of perchlorates and the perchlorate mdustryhas been thoroughly discussed (Refs 12 14, p 2), so it will be only briefly reviewed here. Early exptl work on chlorates and perchlorates was closely tied to the discovery and identification of Cl. Several workers, notably Priestly, Lavoisier, and Scheele reported the isolation of volat liqs and gases which probably were oxides or oxyacids of Cl, but they failed to identify and characterize the compds isolated. Scheele, for example, treated muriatic ac (HCl) with Mn dioxide and obtained a volat liq which he called muriatic ac derived of its phlogiston (Ref 14, p3). The first perchlorate definitely identified was the K salt which was prepd by Stadion in 1816 by the thermal decompn of K chlorate (Ref 2). From this he prepd a hydrate of perchloric ac by heating the K salt with sulfuric ac (Ref 3). Pure (anhyd) perchloric ac was first prepd by Roscoe in 1862 by distn of the hydrated ac (Ref 4)... 

Nephrolithiasis/ urolithiasis/ crystalluria IDV Onset Any time after initiation of therapy, especially if 4- fluid intake Symptoms Flank pain and/or abdominal pain, dysuria, frequency pyuria, hematuria, crystallauria rarely, Tserum creatinine and acute renal failure 1. History of nephrolithiasis 2. Fhtients unable to maintain adequate fluid intake 3. High peak IDV concentration 4. tDuration of exposure Drink at least 1.5-2 L of non-caffeinated fluid per day Tfluid intake at first sign of darkened urine monitor urinalysis and serum creatinine every 3-6 months Increased hydration pain control may consider switching to alternative agent stent placement may be required... 

Nephrotoxicity IDV potentially TDF Onset IDV—months after therapy TDF—weeks to months after therapy Symptoms IDV—asymptomatic rarely develop end-stage renal disease TDF—asymptomatic to symptoms of nephrogenic diabetes insipidus, Fanconi syndrome 1. History of renal disease 2. Concomitant use of nephrotoxic drugs Avoid use of other nephrotoxic drugs adequate hydration if on IDV monitor creatinine, urinalysis, serum potassium and phosphorus in patients at risk D/C offending agent, generally reversible supportive care electrolyte replacement as indicated... 

The history and physical examination should be obtained while initial therapy is being provided. A history of previous asthma exacerbations (e.g., hospitalizations, intubations) and complicating illnesses (e.g., cardiac disease, diabetes) should be obtained. The patient should be examined to assess hydration status use of accessory muscles of respiration and the presence of cyanosis, pneumonia, pneumothorax, pneumomediastinum, and upper airway obstruction. A complete blood count may be appropriate for patients with fever or purulent sputum. 

The name of zeolites, which originates from the Greek words zeo (to boil) and lithos (stone), was given some 250 years ago to a family of minerals (hydrated aluminosilicates) that exhibited intumescence when heated in a flame. However, the history of zeolites really began 60 years ago with the development of synthesis methods. Commercial applications in three main fields—ion exchange, adsorption, and catalysis—were rapidly developed, the corresponding processes being more environmentally friendly than their predecessors. 

If there is a suitable electron-withdrawing substituent, hydrate formation may be favoured. Such a situation exists with trichloroacetaldehyde (chloral). Three chlorine substituents set up a powerful negative inductive effect, thereby increasing the 8- - charge on the carbonyl carbon and favouring nucleophilic attack. Hydrate formation is favoured, to the extent that chloral hydrate is a stable solid, with a history of use as a sedative. 

Use sulindac with caution in patients with a history of renal lithiasis and keep patients well hydrated while receiving the drug. 

Sorbitol exhibits a number of different crystal forms and there is little agreement in the literature concerning the number of polymorphs, the existence of hydrated species, melting points of the various forms, and even nomenclature [7-14]. Much of the data in the literature was collected on commercial powders that were not fully described, or whose history is not fully known. Table 2 attempts to summarize the various forms based on reports by DuRoss [7] and Quinquenet et al. [8]. 

Using these assumptions the computer then calculates the sequential results of a large number of exposure increments on a chain 200 nucleotides long. The result is called a case history. Several hundred case histories are then averaged, and the cumulated number of hydrates and dimers and unreacted sites per chain are averaged as functions of exposure. Several comparisons of experimental results with expectations calculated by this method will be given below. 

The density of bulk milk (4% fat and 8.95% solids-not-fat) at 20°C is approximately 1030 kg m 3 and its specific gravity is 1.0321. Milk fat has a density of about 902 kg m " 3 at 40°C. The density of a given milk sample is influenced by its storage history since it is somewhat dependent on the liquid to solid fat ratio and the degree of hydration of proteins. To minimize effects of thermal history on its density, milk is usually prewarmed to 40-45°C to liquify the milk fat and then cooled to the assay temperature (often 20°C). 

The temperature-dependent irreversibility demonstrates that the ion-exchange behavior of NaX towards bivalent cations depends strongly upon the thermal history of the sample. The rather pronounced differences in behavior of transition-metal ions, also observed in synthetic zeolite 4 A (9) is in very sharp contrast with the nearly identical, either hydrated or crystallographic, dimensions of these ions (10). Obviously, this observation raises important questions as to the value of the current interpretation (nearly) exclusively in terms of physical dimensions of ions and pore width. In contrast, the similarity of behavior in mont-morillonite is remarkably close the AG0 value for the replacement of Na by either Ni, Co, Cu, or Zn is —175 cal ( ll)/equivalent, irrespective of the nature of the cation (11). Therefore, the understanding of their difference in behavior in zeolites must take other effects into consideration. 

The density of milk is the resultant of the densities of the various components. It is complicated by changes related to the liquid-solid fat ratio and to the degree of hydration of the proteins. Thus the density of a given specimen of milk is determined by its previous temperature history, as well as by its composition. 

The degree of hydration of the products from these preparations and the water content given by analytical procedures depends upon the heat treatment (method and history) of the product. A sample subjected to TGA (thermal gravimetric analysis) looses water almost continually from room temperature until it becomes the completely anhydrous heteropolytungstate salt at about 400°C. On the other hand, these crystals lose some lattice water rapidly upon removal from the mother liquor and exposure to air even at room temperature. 

The hydroxide is usually converted by acids and salts into chromium tetraphenyl salts,1 the fifth phenyl group being split off as phenol or diphenyl. The amount of phenol formed varies apparently with the previous history of the base, homogeneous chromium pentaphenyl hydroxide in its hydrated form giving a 100 per cent, yield of phenol and only traces of diphenyl when treated with a salt such as potassium bromide in the presence of chloroform. The hydrate in absolute alcohol in the complete absence of air affords one molecule of phenol from each molecule of base when acted upon by potassium iodide. The production of phenol probably occurs according to the scheme... 

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