Theory of melting of molecular crystals II: solid-solid and melting transitions

The modified form of the Pople-Karasz theory of melting of inolecualr crystatls in a pervious paper is applied to study the thermodynamics of solid-solid and melting trasitions. The results are in substantial agreement with the predictions of the theory in its original form

Theory of melting of molecular crystals: the liquid crystalline phase

The theory of melting of molecular crystals developed by Pople and Karasz, which takes into account order-disorder processes in both the positions and orientations of the molecules, is discussed in a slightly modified form. The theory is an extension of the two-lattice model of Lennard-Jones and Devonshire so as to allow the molecules to take up two orientations on any site. It is assumed in this paper that the energy required for a molecule to diffuse to an interstitial site varies as V−4, as in the original formulation, but that the orientational barrier varies as V−3, in conformity with recent calculations of the orientational potential energy in nematic liquid crystals. The thermodynamic properties of the disordered system are evaluated relative to those of the perfectly ordered one using the Bragg-Williams approximation. For small orientational barriers, the theory predicts two transitions, a solid state rotational transition followed by a melting transition. For larger orientational barriers, the two transitions coalesce and there is a corresponding increase in the entropy of fusion. For even larger orientational barriers, the positional melting precedes the rotational melting and there occurs an intermediate phase, similar to the nematic mesophase, that has orientational order but no positional order. The predicted entropies of transition from the liquid crystal to the isotropic phase for a certain range of orientational barriers are comparable to those observed in nematic compounds. Theoretical curves are drawn for the degree of orientational order, the anomalous specific heat and thermal expansion as functions of temperature in the liquid crystalline range, and for the variation of the transition temperatures with pressure. The curves reproduce the trends in the physical properties of nematic liquid crystals

Orientational order in anisaldazine in the nametic phase

The refractive indices of anisaldazine, CH3OC6H4CH:NN:CHC4H4OCH3, have been measured in the crystalline, nematic and isotropic phases and the orientational order parameter in the mesophase has been evaluated by the application of the Vuks formula. The curve for the order parameter versus the relative temperature (Te-T) is nearly parallel with those for p-azoxyanisole and p-azoxyphenetole and lies approximately midway between them

A new multicritical point in a single component liquid crystal: high pressure study of DOBBCA

We report here the results of our high pressure optical and DTA studies on the compound 4(4-n-decyloxybenzoyloxy)-benzylidene-4'-cyanoaniline. The P-T diagram shows a new kind of multicritical point, viz., a reentrant nematic-smectic C-smectic A point at 0.52 ± 0.02 kbar, 86.2 ± 0.2°C

The search for a Lifshitz point in a single-component liquid crystalline system: a high pressure study of 50.6

The pressure-temperature diagram of N-(4-n-pentyloxybenzylidene)-4'-n-hexylaniline has been investigated up to 8 kbar. The smectic C-smectic A and smectic A-nematic phase boundaries converge and nearly meet, indicating that a Lifshitz point is likely to occur at a higher pressure

The role of serum magnesium level in type 2 diabetes mellitus

Background: Diabetes mellitus is one of the most common metabolic disorder and leading cause of death and disability in the world. The incidence of diabetes is increasing globally and in India. Magnesium depletion has a negative impact on glucose homeostasis and insulin sensitivity in patients with type 2 diabetes. Hypomagnesaemia can lead to development of complications in diabetes. Hence there is need for the study to explore the status of magnesium in type 2 diabetes. Objectives: To estimate and compare the serum magnesium levels in type 2 diabetes patients with age/sex matched non diabetic controls.Methods: A case control study was done in randomly chosen 100 type 2 diabetic patients and 100 non diabetic age/sex matched controls. Estimation of serum magnesium was done by enzymatic end point method.Results: 37% of diabetic patients had low serum magnesium levels (Mg2+ level ≤1.5 mg/dL) and 9 % of controls had low serum magnesium levels. The mean serum magnesium levels were 1.96 ± 0.54 mg/dL and 2.375 ± 0.449 mg/dL in diabetics and controls respectively (P value <0.0001 highly significant). Hypomagnesaemia (Mg2+ level ≤1.5 mg/dL) was correlating with retinopathy (P = 0.041 significant).Conclusion: This study demonstrated that low serum Mg2+ status is common in type 2 diabetes mellitus patients when compared to non-diabetic controls. It may be prudent in clinical practice to periodically monitor plasma Mg2+ concentration in diabetic patients. If plasma Mg2+ is low, an intervention to increase dietary intake of magnesium may be beneficial to prevent the complications.

A review of the drug pregabalin

Pregabalin (PGB) is a well-established anticonvulsant and analgesic agent. The stydy reviewed the mechanism of action, pharmacokinetics, adverse drug reactions, contraindications, and various uses of PGB. Literature search was done to identify the relevant studies. PGB is an antagonist of voltage-gated calcium channels and specifically binds to α2-δ subunit to produce antiepileptic and analgesic activity. It has less protein binding activity and lacks hepatic metabolism. It is unlikely to cause pharmacokinetic drug-drug interactions. It has a wide safety margin and does not require serum drug monitoring. The above-mentioned favorable pharmacological benefits of PGB makes it a first-line or adjunctive therapy in various conditions like diabetic peripheral neuropathy, post-herpetic neuralgia, in partial seizures and generalized anxiety disorders

Experimental Study of Manjistha root (Rubia cordifolia Linn.) w.s.r. to Anti-Diabetic Activity

Manjistha is well known for its various activities, one of which is Pramehagna (Anti-Diabetic) activity. The Manjistha was collected from market and its authenticity was approved by its organoleptic characters and is used for present study. The sample was processed and it’s alcoholic and aqueous extracts were prepared. Then the drug was subjected to experimental study on albino rats. Study was carried out to assess the anti-diabetic activity. Results showed that there is significant reduction in sugar level which indicates that both aqueous and alcoholic extracts do possess significant antihyperglycemic activity as compared to Metformin (Standard drug), which could be due to antioxidants and flavonoids present in it. The variations in above said analysis make it very interesting and important to analyse the expected Anti-microbial and immune modulatory activity of Manjistha root

Progression of Gastric Acid Production in Preterm Neonates: Utilization of \u3cem\u3eIn-vitro\u3c/em\u3e Method

Background: Limited studies are done regarding ability to produce gastric acid in preterm infants and most studies used in vivo method of assessing gastric pH. Objectives: To assess the feasibility of using an in vitro method of measuring gastric pH in babies ≤ 28 weeks gestational age (GA) and determine whether changes in gastric pH differ with gestational age, mode of delivery, and use of antenatal steroids. Design/Methods: Prospective study that enrolled extremely low birth weight (ELBW) babies. Gastric aspirate collected before feeding. In vitro testing of gastric aspirates for pH were done on days of life 1, 3, 5, 7, 14, and 28 by using pH electrode. The pH was measured on each sample in triplicate, mean calculated and used for data analysis. Statistical methods included descriptive statistics, t-tests and repeated measures ANOVA. Results: 29 subjects ≤ 28 weeks or birth weight ≤ 1,000 g were enrolled. No significant change was noted in pH measurements over time. Antenatal steroids and mode of delivery did not affect gastric acid pH. Conclusion: The in vitro method for gastric pH measurements is non-invasive and affords more frequent testing. It would be useful in studying various conditions that may affect gastric pH