X-Message-Number: 7581 Date: 28 Jan 97 15:28:02 EST From: Michael Darwin <> Subject: Cryonics, cryoprotectants, conflict Jan Cotzee writes: >How toxic cryo protectants are is directly related to the quality and >purity of these chemicals. Apparently Visser's critics do their >experiments with 75c per liter chemicals. This is why she can >demonstrate that her heart and HIV methodes work and theirs fail! . Jan, where did you get such information? Who told you could buy DMF at $0.75 a liter from _any_ source? Which of "Visser's critics" are using DMF purchased at such a price? Since 21st Century Medicine (21CM) and BioPreservation (BPI) have worked with DMF and attempted to reduplicate Visser'swork to some extent (and your statement is without qualifications), I take these allegations _very_ seriously as they are both untrue and create a impression of unprofessionalism and incompetence about 21CM and BPI. This is unfortunate. THE FACTS: We do a lot of cryoprotective agent sceening. We have from the start known that purity and storage procedures used for evaluating putative cryoprotectants are critical to success. We generally use high pressure liquid chromotography (HPLC) grade materials when we can get them in that purity. Otherwise we use reagent grade at a minimum. I can think of only one putative cryoprotectant we have evaluated that was "technical grade" and that was triethylene glycol diacetate (TEGDA). We were constrained to do this because TEGDA is not available as a reagent grade or HPLC grade chemical (at least we could not find it). Incidentally, TEGDA failed as CPA for reasons we are reasonably confident were not related to purity. The dimethylformamide (DMF) we have used has come from several different sources and the _minimal_ purity has always been reagent grade. Our sources were: Sigma Chemical Company (reagent and HPLC) Spectrum Chemicals (reagent) BASF Wyandotte (reagent) We have found no significant differences between suppliers in how this agent behaves. We _have_ found very significant differences in the behavior of other cryoprotectants we have evaluated in terms of supplier and purity. Generally, freezing point depression, toxicity and glass forming ability are better in HPLC grade chemicals _if_ they are agents with the potential for containing toxic quantities of unreacted starting materials used to synthesize them. Technical grade TEGDA might, for instance, contain acetic acid. Water as an impurity is another critical consideration. Further, some years ago Greg Fahy had a costly experience with DMSO which bears repeating. The difference between survival and nonsurvival of kidney slices exposed to VS4 can hinge on as little as a difference of 1% in the concentration of the VS4. They had a successful run of experiments with a slightly modified version of VS4 which they were subsequently unable to reproduce. The one variable (other than the one they _knew_ about) was found to be the bottle of DMSO that was used to prepare the solution. Spectrophotometic analysis of this bottle subsequently demonstrated that it contained water (thus diluting it) from being stored with a loose cap in the refrigerator. At 21CM and BPI we are acutely sensitive to such complicating factors. We do not use technical grade or industrial grade chemicals for cryobiological research. Mike Darwin 21st Century Medicine, Inc. 10743 Civic Center Drive Rancho Cucamonga, CA 91730 (909)987-3883 Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=7581